WO2004013930A2

WO2004013930A2 - Modular phased array with improved beam-to-beam isolation

Info

Publication number: WO2004013930A2
Application number: PCT/US2003/023172
Authority: WO
Inventors: Anthony W. Jacomb-Hood
Original assignee: Lockheed Martin Corporation
Priority date: 2002-08-06
Filing date: 2003-07-25
Publication date: 2004-02-12
Also published as: US20040027279A1; US6738017B2; WO2004013930A3

Abstract

A modular phased array antenna provides a reduction in the error signals that are introduced into beam signals by electromagnetic coupling that is inexpensive and does not cause an increase in weight in power consumption. A modular phased array antenna has irregular or random connections of beam signals to beam ports of each modular antenna assembly so as to provide improved beam-to-beam isolation. A modular phased array antenna comprises a plurality of modular antenna assemblies, each modular antenna assembly having a plurality of beam ports, each beam port of a modular antenna assembly connected to a different beam signal, wherein the beam signals are irregularly connected to the beam ports relative to the modular antenna assemblies. The beam signals may be randomly connected to the beam ports relative to the modular antenna assemblies.

Description

MODULAR PHASED ARRAY WITH IMPROVED BEAM-TO-BEAM

ISOLATION

Field of the Invention

The present invention relates to a modular phased array antenna having

irregular or random connections of beam signals to beam ports of each modular

antenna assembly so as to provide improved beam-to-beam isolation.

Background of the Invention

The costs of communications spacecraft are under downward pressures

due to competition among spacecraft manufacturers, and also due to

competition with other forms of communications. One way to reduce the cost

of a communications spacecraft is the use of modularized spacecraft

techniques. For example, United States Patent 5,666,128 to Murray, et al.,

describes the used of array antennas that are modular, so that a spacecraft may

have its antennas made up of standard subarrays mounted in a standardized

structure. Likewise, United States Patent 5,870,063 to Cherrette, et al.,

describes a spacecraft having antennas that are constructed with modular

elements, for ready interchangeability and configuring. A typical modular phased array antenna includes a number of antenna

array modules or building blocks radiating a number of signal beams. Each beam

signal is processed by beam specific electronics, then input to each antenna array

module. In a traditional design, each beam is input to the same input port of each

antenna array module. A problem arises with this design due to electromagnetic

coupling among the paths within the antenna array module. In particular,

electromagnetic coupling among the circuit paths of an antenna array module

cause coupling of the beam signal on each circuit path to the circuit paths of

every other beam signal in the antenna array module. This coupling effect is

typically dependent upon the geometry and layout of the circuit paths in the

antenna array module, with (in general) greater coupling occurring among circuit

paths that are physically closer to each other and that are parallel to each other. A

signal that is introduced due to electromagnetic coupling may be seen as an error

signal introduced into the intended signal.

Due to the regular geometry of antenna array modules, the coupling of

beam signals will tend to conelate from module to module. Since the antenna

anay modules are typically mass-produced, the coupling among signals in each

antenna anay module will be similar. Thus, the magnitude and phase of the

coupling is repeatable from module to module. These conelated, coupled signals

reinforce each other and produce a much greater error signal in each beam than would be produced by any one unconelated signal. The beam pattern for each

beam signal will be the vector sum of the intended beam pattern for the beam

signal and the intended beam pattern for each other beam signal path that

receives power from the first beam signal by unintended coupling, attenuated by

the isolation of the coupling path. Each coupled error signal will create a

sidelobe in the beam pattern of the beam associated with that signal in the

direction of the mainlobe of the intended beam pattern of the beam into which the

signal has coupled. This may cause unacceptable interference.

While the magnitude of the coupled enor signals may be reduced by

increasing the isolation of the coupling paths, this is an expensive and weight-

increasing solution. What is needed is a technique by which the enor signals that

are introduced into beam signals by electromagnetic coupling may be reduced

without resorting to expensive and weight-increasing solutions.

Summary of the Invention

The present invention is a modular phased array antenna that provides a

reduction in the enor signals that are introduced into beam signals by

electromagnetic coupling. The invention is inexpensive to implement and does

not cause an increase in weight or power consumption. The modular phased

array antenna has inegular or random connections of beam signals to beam ports of each modular antenna assembly so as to provide improved beam-to-beam

isolation.

In one embodiment of the present invention, a modular phased array

antenna comprises a plurality of modular antenna assemblies, each modular

antenna assembly having a plurality of beam ports, each beam port of a modular

antenna assembly connected to a different beam signal, wherein the beam signals

are nregularly connected to the beam ports relative to the modular antenna

assemblies. The beam signals may be randomly connected to the beam ports

relative to the modular antenna assemblies. The beam signals may be connected

to the beam ports relative to the modular antenna assemblies so that vector sums

of coupling coefficients of beam signal to beamformer paths is reduced compared

to a regular connection of the beam signals to the beam ports relative to the

modular antenna assemblies. The beam signals may be connected to the beam

ports relative to the modular antenna assemblies so that vector sums of coupling

coefficients of beam signal to beamformer paths is minimized.

In one embodiment of the present invention, the modular phased array

antenna is a receiving antenna, which may comprise a plurality of modular

antenna assemblies. Each modular antenna assembly may comprise a plurality of

power combiners, each power combiner having an output connected to a beam

port of the modular antenna assembly, and each power combiner having a plurality of inputs, a plurality of phase shift attenuators, each phase shift

attenuator having an output connected to an input of a power combiner, and each

phase shift attenuator having an input, a plurality of power dividers, each power

divider having a plurality of outputs, each output connected to an input of a phase

shift attenuator, and each power divider having an input, a plurality of amplifiers,

each amplifier having an output connected to an input of a power divider, and

each amplifier having an. input, and a plurality of antenna elements, each antenna

element having an output connected to an input of an amplifier.

In one aspect of the present invention, the modular phased anay antenna

may further comprise a plurality of driver amplifiers, each driver amplifier

connected between a beam port of the modular antenna assembly and a power

combiner output, each driver amplifier having an input connected to a power

combiner output and having an output connected to a beam port.

In one aspect of the present invention, the modular phased array antenna

may further comprise a plurality of power combiners, each power combiner

having an output connected to a beam signal and having a plurality of inputs

inputting the beam signal, each of the plurality of inputs connected to a beam port

of a modular antenna assembly. The connections of the beam signals to the beam

ports of the modular antenna assemblies may be randomly assigned. The

connections of the beam signals to the beam ports of the modular antenna assemblies may be assigned so that vector sums of coupling coefficients of beam

signal to beamformer paths is reduced compared to a regular connection of the

beam signals to the beam ports relative to the modular antenna assemblies. The

connections of the beam signals to the beam ports of the modular antenna

assemblies may be assigned so that vector sums of coupling coefficients of beam

signal to beamformer paths is minimized. The connections of the beam signals to

the beam ports of the modular antenna assemblies may be hard-wired. The

connections of the beam signals to the beam ports of the modular antenna

assemblies may be provided by at least one of fiber optic cable, coaxial cable, or

printed circuit board traces. The connections of the beam signals to the beam

ports of the modular antenna assemblies may be configurable in software. The

connections of the beam signals to the beam ports of the modular antenna

assemblies may be provided by a switching matrix or other programrriable

connection device.

In one embodiment of the present invention, the modular phased anay

antenna is a transmitting antenna, which may comprise a plurality of modular

antenna assemblies. Each modular antenna assembly may comprise a plurality of

power dividers, each power divider having an input connected to a beam port of

the modular antenna assembly, and each power divider having a plurality of

outputs, a plurality of phase shift attenuators, each phase shift attenuator having an input connected to an output of a power divider, and each phase shift

attenuator having an output, a plurality of power combiners, each power

combiner having a plurality of inputs, each input connected to an output of a

phase shift attenuator, and each power combiner having an output, a plurality of

amplifiers, each amplifier having an input connected to an output of a power

combiner, and each amplifier having an output, and a plurality of antenna

elements, each antenna element having an input connected to an output of an

amplifier.

In one aspect of the present invention, the modular phased array antenna

may further comprise a plurality of driver amplifiers, each driver amplifier

connected between a beam port of the modular antenna assembly and a power

divider input, each driver amplifier having an input connected to a beam port and

having an output connected to a power divider input.

In one aspect of the present invention, the modular phased anay antenna

may further comprise a plurality of power dividers, each power divider having an

input connected to a beam signal and having a plurality of outputs outputting the

beam signal, each of the plurality of outputs connected to a beam port of a

modular antenna assembly. The connections of the beam signals to the beam

ports of the modular antenna assemblies may be randomly assigned. The

signal to beamformer paths is reduced compared to a regular connection of the

beam signals to the beam ports relative to the modular antenna assemblies. The

connections of the beam signals to the beam ports of the modular antenna

assemblies may be assigned so that vector sums of coupling coefficients of beam

signal to beamformer paths is n inimized. The connections of the beam signals to

I the beam ports of the modular antenna assemblies may be hard-wired. The

connections of the beam signals to the beam ports of the modular antenna

printed circuit board traces. The connections of the beam signals to the beam

ports of the modular antenna assemblies may be configurable in software. The

connections of the beam signals to the beam ports of the modular antenna

assemblies may be provided by a switching matrix or other programmable

connection device.

In one embodiment of the present invention, the modular phased array

antenna is a transmitting and receiving antenna, which may comprise a plurality

of modular antenna assemblies. Each modular antenna assembly may comprise a

plurality of first power dividers/combiners, each first power divider/combiner

having a first input/output connected to a beam port of the modular antenna

assembly, and each first power divider/combiner having a plurality of second outputs/inputs, a plurality of phase shift attenuators, each phase shift attenuator

having a first input/output connected to a second output/input of a first power

divider/combiner, and each phase shift attenuator having a second output/input, a

plurality of second power combiners/dividers, each second power

combiner/divider having a plurality of first inputs/outputs, each first input/output

connected to a second output/input of a phase shift attenuator, and each second

power combiner/divider having a second output/input, a plurality of duplexed

amplifier pairs, each duplexed amplifier pair comprising a first amplifier and a

second amplifier connected between a pair of duplexers, each duplexed amplifier

pair having a first input/output connected to second output input of a second

power combiner/divider, and each amplifier having second output/input, and a

plurality of antenna elements, each antenna element having an input/output

connected to a second output/input of a duplexed amplifier pair.

In one aspect of the present invention, the modular phased anay antenna

may further comprise a plurality of duplexed driver amplifier pairs, each

duplexed driver amplifier pair connected between a beam port of the modular

antenna assembly and a power divider/combiner input/output, each duplexed

amplifier pair comprising a first driver amplifier and a second driver amplifier

connected between a pair of duplexers, each duplexed driver amplifier pair

having a first input/output connected to a beam port of the modular antenna assembly, and having a second output input connected to a power

divider/combiner input/output.

In one aspect of the present invention, the modular phased anay antenna

may further comprise a plurality of third power dividers/combiners, each third

power divider/combiner having a first input output connected to a beam signal

and having a plurality of second outputs/inputs connected to a beam port of a

modular antenna assembly. The connections of the beam signals to the beam

ports of the modular antenna assemblies may be randomly assigned. The

connections of the beam signals to the beam ports of the modular antenna

assemblies may be assigned so that vector sums of coupling coefficients of beam

signal to beamformer paths is reduced compared to a regular connection of the

beam signals to the beam ports relative to the modular antenna assemblies. The

connections of the beam signals to the beam ports of the modular antenna

assemblies may be assigned so that vector sums of coupling coefficients of beam

signal to beamformer paths is minimized. The connections of the beam signals to

the beam ports of the modular antenna assemblies may be hard-wired. The

connections of the beam signals to the beam ports of the modular antenna

printed circuit board traces. The connections of the beam signals to the beam

ports of the modular antenna assemblies may be configurable in software. The connections of the beam signals to the beam ports of the modular antenna

assemblies may be provided by a switching matrix or other programmable

connection device.

Brief Description of the Drawings

The details of the present invention, both as to its structure and

operation, can best be understood by referring to the accompanying drawings,

in which like reference numbers and designations refer to like elements.

Fig. 1 is an exemplary block diagram of a typical prior art modular phased

anay antenna.

Fig. 2 is an exemplary block diagram of a modular antenna assembly,

shown in Fig. 1.

Fig. 3 is an exemplary block diagram of modular phased anay antenna,

according to the present invention.

Fig. 4 illustrates an example of a predicted beam pattern for a modular

antenna assembly shown in Fig 7.

Fig. 5 illustrates an example of a predicted beam pattern for a modular

antenna assembly shown in Fig 7.

Fig. 6 illustrates an example of a composite beam pattern for a modular

anay antenna shown in Fig 7. Fig. 7 is an exemplary block diagram of a modular anay antenna.

Detailed Description of the Invention

The present invention is a modular phased array antenna that provides a

reduction in the enor signals that are introduced into beam signals by

electromagnetic coupling. The invention is inexpensive to implement and does

not cause an increase in weight or power consumption. The modular phased

anay antenna has inegular or random connections of beam signals to beam ports

of each modular antenna assembly so as to provide improved beam-to-beam

isolation.

An exemplary block diagram of a typical prior art modular phased anay

antenna 100 is shown in Figure 1. Modular phased anay antenna 100 creates a

plurality of beams. Each beam is associated with a signal such as beam signals

102A-N. Typically different signals are connected to each of the beam ports.

Each of these signals are intended to be directed in a particular direction by

modular phased anay antenna 100. In an embodiment in which modular phased

array antenna 100 is a transmitting antenna, each beam is radiated in a particular

direction. In an embodiment in which modular phased anay antenna 100 is a

receiving antenna, each beam is received from a particular direction. Each beam signal is processed by beam specific electronics. For example,

beam signal 102A is processed by beam specific electronics 104A, beam signal

102B is processed by beam specific electronics 104B, etc. In an embodiment in

which modular phased anay antenna 100 is a transmitting antenna, each beam

signal is input to beam specific electronics. In an embodiment in which modular

phased anay antenna 100 is a receiving antenna, each beam signal is output from

beam specific electronics. Beam specific electronics includes functions such as

amplification/attenuation, frequency conversion and filtering.

The beam specific electronics 104A-N is connected to power

dividers/combiners 106A-N, which are connected to modular antenna assemblies

110A-Z via beam ports 108AA-NZ. In an embodiment in which modular phased

anay antenna 100 is a transmitting antenna, each beam signal that is output from

the beam specific electronics is divided by a power divider having one output

connected to one beam port of each modular antenna assembly. Each power

divider output is connected to the same input beam port of each modular antenna

assembly. Thus, in the example shown in Fig. 1, each output from power divider

106A is connected to the first input beam port 108AA-AZ of each, modular

antenna assembly 110A-Z, each output from power divider 106B is connected to

the second input beam port 108BA-BZ of each modular antenna assembly, etc. In an embodiment in which modular phased anay antenna 100 is a

receiving antenna, each beam signal that is input to the beam specific electronics

is output from a power combiner having one input connected to one beam port of

each modular antenna assembly. Each power combiner input is connected to the

same output beam port of each modular antenna assembly. Thus, in the example

shown in Fig. 1, each input to power combiner 106A is connected to the first

output beam port 108AA-AZ of each modular antenna assembly 110A-Z, each

input to power combiner 106B is connected to the second output beam port

108BA-BZ of each modular antenna assembly, etc.

An exemplary block diagram of a modular antenna assembly 110, such as

is shown in Fig. 1, is shown in Fig. 2. In the example shown in Fig. 2, modular

antenna assembly 110 is a transmitting embodiment. Modular antenna assembly

includes a plurality of input beam ports 202A-N, a plurality of driver amplifiers

214A-N, a plurality of power dividers 204A-N, a plurality of phase shift

attenuators 206A-A to 206N-X, a plurality of power combiners 208 A-X, a

plurality of power amplifiers 210A-X, and a plurality of antenna elements 212A-

X.

Each input beam port 202A-N is connected to the input to a driver

amplifier 214A-N, which amplifies the signal and outputs the a plified signal to

the input to a power divider 204A-N. Each power divider 204A-N divides the input signal into a plurality of signals of nominally equal power, which are output

from the plurality of outputs of power dividers 204A-N. Each output of each

power divider 204A-N is connected to the input of a conesponding phase snifter

attenuator 206A-A to 206N-X. Each phase shifter attenuator shifts its input

signal by a predetermined phase angle and attenuates the input signal by a

predetermined amount. The phase angles and attenuation amounts may be

different for each phase shifter attenuator 206A-A to 206N-X. Phase shifter

attenuators 206A-A to 206N-X are used to electronically steer and shape the

beams created by the antenna anay. A beam may be pointed in different

directions by resetting the phase shifts of all of the phase shifters associated with

that beam.

The output of each phase shifter attenuator 206A-A to 206N-X is

connected to an input of a power combiner 208A-X. Each power combiner

combines the input signals to form a single output signal. The output of each

power combiner is input to a power amplifier 210A-X, which amplifies the signal

and outputs the amplified signal to an antenna element 212A-X.

Modular antenna assemblies for receiving antennas and for

transmit/receive antennas are also known. For example, in a receiving antenna,

signals are received by antenna elements and input to amplifiers, such as low

noise amplifiers. The output signals from the amplifiers are input to power dividers. Each power divider divides the input signal into a plurality of signals of

nominally equal power, which are output from the plurality of outputs of power

dividers to the input of a conesponding phase shifter attenuator. Each phase

shifter attenuator shifts its input signal by a predetermined phase angle and

attenuates the input signal by a predetermined amount. The phase angles and

attenuation amounts may be different for each phase shifter attenuator. The

output of each phase shifter attenuator is connected to an input of a power

combiner. Each power combiner combines the input signals to form a single

output signal which is input to an amplifier, which amplifies the signal and

outputs the amplified signal.

As another example, in a transmit/receive antenna, the Low Noise

Amplifiers (LNAs) of the receive example and the power amplifiers of the

transmit example are replaced by duplexed amplifier pairs. Each duplexed

amplifier pair includes a power amplifier and an LNA connected between a pair

of duplexers. By controlling the operation of the duplexers, the system may be

operated in either transmit or receive mode as desired, as is well known to those

of skill in the art. The duplexers may be implemented as switches or circulators

Electromagnetic coupling among the circuit paths of an antenna anay

module cause coupling of the beam signal on each circuit path to the circuit paths

of every other beam signal in the antenna array module. This coupling effect is typically dependent upon the geometry and layout of the circuit paths in the

antenna anay module, with (in general) greater coupling occurring among circuit

signal that is introduced due to electromagnetic coupling may be seen as an enor

signal introduced into the intended signal.

Due to the regular geometry of antenna anay modules, the coupling of

beam signals will tend to conelate from module to module. Since the antenna

anay modules are typically mass-produced, the coupling among signals in each

antenna anay module will be similar. Thus, the magnitude and phase of the

coupling is repeatable from module to module. These conelated, coupled signals

reinforce each other and produce a much greater enor signal in each beam than

would be produced by any one unconelated signal. The beam pattern for each

beam signal will be the vector sum of the intended beam pattern for the beam

signal and the intended beam pattern for each other beam signal path that

receives power from the first beam signal by unintended coupling , attenuated by

the isolation of the coupling path. Each coupled enor signal will create a

sidelobe in the beam pattern of the beam associated with that signal in the

signal has coupled. This may cause unacceptable interference. An exemplary block diagram of modular phased array antenna 300,

according to the present invention, is shown in Fig 3. Modular phased anay

antenna 300 creates a plurality of beams. Each beam is associated with a signal

such as beam signals 302A-N. Each of these beam signals are intended to be

directed in a particular direction by modular phased anay antenna 300. In an

embodiment in which modular phased anay antenna 300 is a transmitting

antenna, each beam is radiated in a particular direction. In an embodiment in

which modular phased array antenna 300 is a receiving antenna, each beam is

received from a particular direction.

Each beam signal is processed by beam specific electronics. For example,

beam signal 302A is processed by beam specific electronics 304A, beam signal

302B is processed by beam specific electronics 304B, etc. In an embodiment in

which modular phased array antenna 300 is a transmitting antenna, each beam

signal is input to beam specific electronics. In an embodiment in which modular

phased anay antenna 300 is a receiving antenna, each beam signal is output from

beam specific electronics. Beam specific electronics includes such functions as

amplification/attenuation, frequency conversion and filtering.

The beam specific electronics 304A-N is connected to power

dividers/combiners 306A-N, which are connected to beam ports 3 8AA-NZ of

modular antenna assemblies 310A-Z. In the present invention, the connections 312 between the power dividers/combiners 306A-N and the modular antenna

assemblies 310A-Z are not regular. That is, each power divider/combiner is not

connected to the same beam port of each modular antenna assembly. Preferably,

the connections 312 between the power dividers/combiners 30 A-N and the

beam ports 308A-Z of modular antenna assemblies 310A-Z are connected so that

the sum of coupling coefficients of beam signal to beamformer paths are reduced

or minimized, or the connections are randomized. The non-regular connections

between the power dividers/combiners 306A-N and the beam ports 308 -Z of

modular antenna assemblies 310 A-Z breaks up the anay level conelation of the

electromagnetic coupling paths among modular antenna assemblies 31OA-Z.

Since the electromagnetic coupling paths are not conelated at the anay level, the

coupled signals do not reinforce each other and thus produce a much s aller

degradation in each beam than would be produced by the prior art.

The beam pattern for each beam is the vector sum of the beam pattern of

that beam created by each modular antenna assembly. The beam pattern of each

modular antenna assembly is the vector sum of the intended beam pattern for the

beam and the intended beam pattern for each other beam attenuated/phase shifted

by the (vector) coupling factor between the two beam paths within the modular

antenna assembly. Because the signal to beam port connections are irregular

across the modular antenna assemblies, the direction of the beam mainlobes associated with each modular antenna assembly beam port are also inegular. So

the resulting beam patterns associated with a specific signal (including the effects

of finite isolation) of the modular antenna assemblies are all different. In

particular the sidelobes created by finite isolation are in different directions.

When the beam pattern of the whole anay is formed, for a particular signal, by

summing the beam patterns of the modular antenna assemblies, the sidelobes

created by the finite isolation effect are substantially lower than would be the

case for a prior art antenna.

The mechanism for achieving improved sidelobes is described above for

the general case. Referring to Fig. 7, an exemplary modular anay antenna 700 is

illustrated. The example shown in Fig. 7 is a three beam modular anay antenna

including two modular antenna assemblies 702 A and 702B. In this example it is

arbitrarily assumed that the three beams are intended to point 0, +0.2 and -0.3

radians from the antenna boresight. These directions apply to beam signals

704 A, 704B, and 704C respectively. It is assumed that the coupling factor from

beam port 706A- 1 to beamformer 708 A-2 of modular antenna assembly 702A

and beam port 7O6B-1 to beamformer 708B-2 of modular antenna assembly

702B within the modular antenna assembly is -10 dB and that the coupling factor

from beam port 706A-1 to beamformer 708A-3 of modular antenna assembly

702A and beam port 706B-1 to beamformer 708B-3 of modular antenna assembly 702B within the modular antenna assembly is -20 dB. It is also

assumed that beam signal 704A is applied to beam port 706 A- 1 of modular

antenna assembly 702A and beam port 706B-1 of modular antenna assembly

702B. It is further assumed that beam signal 704B is applied to beam port 706 A-

2 of modular antenna assembly 702A and beam port 706B-3 of modular antenna

assembly 702B. It is assumed that beam signal 704C is applied to beam port

706A-3 of modular antenna assembly 702A and beam port 706B-2 of modular

antenna assembly 702B.

Referring now to Fig. 4 in conjunction with Fig. 7, an example of a

predicted beam pattern for modular antenna assembly 702 A is shown. All four

curves contained in this Figure apply to beam signal 704A, which is applied to

beam ports 706 A- 1 and 706B-1. The curve 402 (shown with a dashed line with

diamond symbols) is the intended beam pattern for beam signal 704A. This

signal flows through beam port 706 A- 1 and the beamformer 708 A- 1 path within

modular antenna assembly 702A. It can be seen from Fig. 4 that this beam is

pointed in the direction of the antenna boresight. The beam plots in Fig. 4 have

been normalized so that the peak gain of beam 402 is 0 dB.

Curve 404 in Fig. 4 (shown with a dashed/dot line with triangle symbols)

is the beam pattern for the portion of bea signal 704Athat flows through beam

port 706A1 and then electromagnetically couples into the beamformer 708A-2 path within modular antenna assembly 702A. This beam signal passes through

the phase shifters in the beamformer 708A-2 path, which steers the beam to 0.2

radians from boresight. (This is the intended direction for beam signal 704B,

which is steered by the beamformer 708A-2 path in modular antenna assembly

702 ). The peak antenna gain for this beam is 10 dB lower than the first beam

due to the 10 dB coupling factor.

Curve 406 in Fig..4 (shown with a dashed line with square symbols) is the

beam pattern for the portion of beam signal 704A that flows through beam port

706A- 1 and then electromagnetically couples into the beamformer 708A-3 path

within modular antenna assembly 702A. This beam signal passes through the

phase shifters in the beamformer 708A-3 path, which steers the beam to -0.3

radians from boresight. (This is the intended direction for beam signal 704C,

which is steered by the beamformer 708A-3 path in modular antenna assembly

702A) . The peak antenna gain for this beam is 2O dB lower than the first beam

due to the 20 dB coupling factor.

Curve 408 in Fig. 4 (shown with a solid line with circle symbols) is the

composite beam pattern associated with beam signal 704A created by modular

antenna assembly 702A. It is formed by vector summing curves 402, 404, and

406. It can be seen that this beam pattern has a primary lobe at boresight and a

large sidelobe at ~ 0.2 radians. Referring now to Fig. 5 in conjunction with Fig. 7, an example of a

predicted beam pattern for modular antenna assembly 702B is shown. All four

curves 502-508 shown in Fig. 5 apply to beam signal 704A, which is applied to

beam ports 706 A- 1 and 706B-1. Curve 502 (shown with a dashed line with

diamond symbols) is the intended beam pattern for beam signal 704A. This

signal flows through beam port 7O6B-1 and the beamformer 708B-1 path within

modular antenna assembly 702B. It can be seen from Fig. 5 that this beam is

pointed in the direction of the antenna boresight. The beam plots in Fig. 5 have

been normalized so that the peak gain of this beam is 0 dB.

Curve 504 in Fig. 5 (shown with a dashed/dot line with triangle symbols)

is the beam pattern for the portion of beam signal 704A that flows through beam

port 706B-1 and then electromagnetically couples into the beamformer 708B-2

path within modular antenna assembly 702B. This beam signal passes through

the phase shifters in the beamformer 708B-2 path, which steers the beam to - 0.3

radians from boresight. (This is the intended direction for beam signal 704 ,

which is steered by the beamformer 708B-2 path in modular antenna assembly

702B). The peak antenna gain for this beam is 10 dB lower than the first beam

due to the 10 dB coupling factor.

Curve 506 in Fig. 5 (shown with a dashed line with square symbols) is the

beam pattern for the portion of beam signal 704A that flows through beam port 706B-1 and then electromagnetically couples into the beamformer 708B-3 path

within modular antenna assembly 702B. This beam signal passes through the

phase shifters in the beamformer 708B-3 path, which steers the beam to 0.2

radians from boresight. (This is the intended direction for beam signal 704B,

which is steered by the beamformer 708B-3 path in modular antenna assembly

7O2B). The peak antenna gain for this beam is 20 dB lower than the first beam

due to the 20 dB coupling factor.

Curve 508 (shown with a solid line with circle symbols) is the composite

beam pattern associated with beam signal 704A created by modular antenna

assembly 702B. It is formed by vector summing curves 502, 504 and 506. It can

be seen that this beam pattern has primary lobe at boresight and a large sidelobe

at ~ -0.3 radians.

Referring now to Fig. 6 in conjunction with Fig. 7, an example of a

composite beam pattern for beam signal 704A for an antenna including modular

antenna assembly 702 A and modular antenna assembly 702B is shown. Curve

602 (dashed line with circular symbols) shows the beam pattern with a

conventional anay architecture (for example with beam signal 704A connected to

beam ports 706 A- 1 and 706B-1, beam signal 704B connected to beam ports

7O6A-2 and 706B-2, and beam signal 704C connected to beam ports 706A-3 and 706B-3. It can be seen that this configuration results in a worst case sidelobe of

—10 dB.

Curve 604 (heavy solid line) shows the beam pattern with the antenna

array architecture of the present invention. In this case, the beam signal to beam

port assignments are shown in Fig 7. It can be seen that the worst case sidelobe

is ~ -13.5 dB. This is 3.5 dB better than for the conventional architecture. In

general, the achievable improvement in the worst case sidelobe level is roughly

equal to the number of modular antenna assemblies in the antenna anay. So a

practical antenna anay with many more than two modular antenna assemblies

will have a significantly larger improvement in the worst case sidelobe level.

For an antenna anay containing many modular antenna assemblies it is

desired to select the signal to beam port assignments so that the sum of the

coupling factors is reduced or minimized. If there are N beams, each beam will

have N-1 sidelobes created by finite isolation effects. These sidelobes are

pointed in the direction of the other N-1 beams. So there are a total of N*(N-1)

sidelobes created by finite isolation effects. The magnitude of each of these

sidelobes will be determined by the vector sum of Z coupling coefficients, where

Z is the number of modular antenna assemblies in the complete antenna.

To minimize the magnitude of the sidelobes created by finite isolation, it

is necessary to optimize the signal to beam port assignments across the anay so that all of the vector sums of the N*(N-1) sets of Z coupling coefficients are

minimized. For a large anay, a random assignment of signal/beam port

assignments is likely to be a good approximation to the optimum solution. In

general it is important to minimize repetition/patterns of signal to beam port

assignments from modular antenna assembly to modular antenna assembly. For

example if Signals 1, 2 and 3 are assigned to beam ports 1, 2 and 3 of a modular

antenna assembly respectively, it is not good to also assign the same signals to

the same beam ports of any other modular antenna assembly. Repeating or

regular patterns result in the same coupling coefficient appearing more than once

in a set Z coefficients which are added to determine the magnitude of a particular

sidelobe. This is likely to increase the magnitude of the sidelobe. Statistically it

is more likely that the sum of Z vectors will be smaller if the vectors are all

different. If, for example, all the vectors have the same magnitude but random

phases, the expected value of the magnitude of the sum of Z randomly selected

vectors will be *J^~Z times larger than the magnitude of one vector. In the extreme

case where all the vectors are the same (which is analogous to the prior art) the

magnitude is Z times larger than the magnitude of one vector.

In a practical application it is likely that a small number of the coupling

coefficients will be much larger than the rest. In this case it is important to

carefully select the signal to beam port assignments to minimize sidelobes resulting from these stronger coupling paths, (i.e. minimize repeating patterns

for these port combinations). The signal to beam port assignments for beam port

pairs with good isolation/low coupling is much less important.

Since the worst case sidelobes resulting from finite isolation are much

smaller than in the prior art, the requirements for the isolation of the coupling

path may be relaxed. In particular, the isolation requirement may be relaxed by a

factor roughly equal to the number of modular antenna assemblies. For example,

a typical antenna anay may have approximately 20 to 30 modular antenna

assemblies. Thus, according to the present invention, the isolation requirement

for such an anay may be relaxed by approximately 13 to 15 dB. Alternatively,

for the same isolation of the coupling path, the coupled enor signals will be

reduced by approximately 13 to 15 dB. Likewise, one of skill in the art would

recognize that any combination of relaxation of the isolation requirement and/or

reduction in coupled enor signals within the range of approximately 13 to 15 dB

may be achieved.

In an embodiment in which modular phased anay antenna 300 is a

transmitting antenna, each signal that is output from the beam specific electronics

is divided by a power divider having one output connected to one beam port of

each modular antenna assembly. Thus, in the example shown in Fig. 3, each

output from power divider 306A is connected to an input beam port of each modular antenna assembly, each output from power divider 306B is connected to

an input beam port of each modular antenna assembly, etc. The connections

from the power dividers to the inputs of the modular antenna assemblies are not

regular, and preferably are connected so that the sum of coupling coefficients of

beam signal to beamformer paths are reduced or minimized, or the connections

are randomized.

In an embodiment in which modular phased anay antenna 300 is a

receiving antenna, each signal that is input to the beam specific electronics is

output from a power combiner having one input connected to one beam port of

each modular antenna assembly. Thus, in the example shown in Fig. 3, each

input to power combiner 306A is connected to an output beam port of each

modular antenna assembly, each input to power combiner 306B is connected to

an output beam port of each modular antenna assembly, etc. The connections

from the power combiners to the outputs of the modular antenna assemblies are

not regular, and preferably are connected so that the sum of coupling coefficients

of beam signal to beamformer paths are reduced or minimized, or the connections

are randomized.

The connections from the power dividers/combiners to the inputs/outputs

of the modular antenna assemblies may be accomplished in a number of ways.

For example, the connections may be "hard-wired" using fiber optic cable, coaxial cable, printed circuit board traces, or other suitable connection

technology. Likewise, the phase shifts and attenuations provided by the phase

shift attenuators may be provided by installation of appropriately valued fixed

components or by appropriate adjustment of variable components. As another

example, the connections may be configured in software, which controls a

switching matrix or other programmable connection device. Likewise, the phase

shifts and attenuations provided by the phase shift attenuators may be provided

by appropriate configuration of programmable components. Regardless of the

connection technology, the system that controls the operation of the antenna anay

must be aware of the particular connections from the power dividers/combiners

to the inputs/outputs of the modular antenna assemblies that are present and must

configure and control the associated circuitry as necessary.

One of skill in the art would recognize that the present invention may also

be advantageously applied to a transmit/receive embodiment. This

implementation is of interest for radar and half-duplex communications

applications. This embodiment is similar to that shown in Fig. 3. However the

Low Noise Amplifiers (LNAs) of the receive embodiment and the power

amplifiers of the transmit embodiment are replaced by duplexed amplifier pairs.

Each duplexed amplifier pair includes a power amplifier and an LNA connected

between a pair of duplexers. By controlling the operation of the duplexers, the system may be operated in either transmit or receive mode as desired, as is well

known to those of skill in the art. The duplexers may be implemented as

switches or circulators. According to the present invention, the connections from

the power dividers/combiners to the inputs/outputs of the modular antenna

assemblies are not regular, and preferably are connected so that the sum of

coupling coefficients of beam signal to beamformer paths are reduced or

minimized, or the connections are randomized.

Although specific embodiments of the present invention have been

described, it will be understood by those of skill in the art that there are other

embodiments that are equivalent to the described embodiments. Accordingly,

it is to be understood that the invention is not to be limited by the specific

illustrated embodiments, but only by the scope of the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A modular phased anay antenna comprising:

a plurality of modular antenna assemblies, each modular antenna

assembly having a plurality of beam ports, each beam port of a modular antenna

assembly connected to a different beam signal, wherein the beam signals are

inegularly connected to the beam ports relative to the modular antenna

assemblies.

2. The modular phased anay antenna of claim 1, wherein the beam signals

are randomly connected to the beam ports relative to the modular antenna

assemblies.

3. The modular phased anay antenna of claim 1, wherein the beam signals

are connected to the beam ports relative to the modular antenna assemblies so

that vector sums of coupling coefficients of beam signal to beamformer paths is

reduced compared to a regular connection of the beam signals to the beam ports

relative to the modular antenna assemblies.

4. The modular phased anay antenna of claim 1, wherein the beam signals

are connected to the beam ports relative to the modular antenna assemblies so

that vector sums of coupling coefficients of beam signal to beamformer paths is

minimized.

5. The modular phased anay antenna of claim 1 , wherein the modular

phased anay antenna is a receiving antenna.

6. The modular phased anay antenna of claim 5, wherein each modular

antenna assembly comprises:

a plurality of power combiners, each power combiner having an output

connected to a beam port of the modular antenna assembly, and each power

combiner having a plurality of inputs;

a plurality of phase shift attenuators, each phase shift attenuator having an

output connected to an input of a power combiner, and each phase shift attenuator

having an input;

a plurality of power dividers, each power divider having a plurality of

outputs, each output connected to an input of a phase shift attenuator, and each

power divider having an input; a plurality of amplifiers, each amplifier having an output connected to an

input of a power divider, and each amplifier having an input; and

a plurality of antenna elements, each antenna element having an output

connected to an input of an amplifier.

7. The modular phased anay antenna of claim 6, further comprising:

a plurality of driver amplifiers, each driver amplifier connected between a

beam port of the modular antenna assembly and a power combiner output, each

driver amplifier having an input connected to a power combiner output and

having an output connected to a beam port.

8. The modular phased anay antenna of claim 6, further comprising:

a plurality of power combiners, each power combiner having an output

connected to a beam signal and having a plurality of inputs receiving the beam

signal, each of the plurality of inputs connected to a beam port of a modular

antenna assembly.

9. The modular phased anay antenna of claim 8, wherein the connections of

the beam signals to the beam ports of the modular antenna assemblies are

randomly assigned.

10. The modular phased anay antenna of claim 8, wherein the connections of

the beam signals to the beam ports of the modular antenna assemblies are

assigned so that vector sums of coupling coefficients of beam signal to

beamformer paths is reduced compared to a regular connection of the beam

signals to the beam ports relative to the modular antenna assemblies.

11. The modular phased anay antenna of claim 8, wherein the connections of

the beam signals to the beam ports of the modular antenna assemblies are

assigned so that vector sums of coupling coefficients of beam signal to

beamformer paths is minimized.

12. The modular phased array antenna of claim 8, wherein the connections of

the beam signals to the beam ports of the modular antenna assemblies are hard-

wired.

13. The modular phased array antenna of claim 8, wherein the connections of

the beam signals to the beam ports of the modular antenna assemblies is provided

by at least one of fiber optic cable, coaxial cable, or printed circuit board traces.

14. The modular phased anay antenna of claim 8, wherein the connections of

the beam signals to the beam ports of the modular antenna assemblies is

configurable in software.

15. The modular phased anay antenna of claim 8, wherein the connections of

by a switching matrix or other programmable connection device.

16. The modular phased anay antenna of claim 1, wherein the modular

phased anay antenna is a transmitting antenna.

17. The modular phased anay antenna of claim 16, wherein each modular

antenna assembly comprises:

a plurality of power dividers, each power dividers having an input

connected to a beam port of the modular antenna assembly, and each power

divider having a plurality of outputs;

a plurality of phase shift attenuators, each phase shift attenuator having an

input connected to an output of a power divider, and each phase shift attenuator

having an output; a plurality of power combiners, each power combiner having a plurality of

inputs, each input connected to an output of a phase shift attenuator, and each

power combiner having an output;

a plurality of amplifiers, each amplifier having an input connected to an

output of a power combiner, and each amplifier having an output; and

a plurality of antenna elements, each antenna element having an input

connected to an output of an amplifier.

18. The modular phased anay antenna of claim 17, further comprising:

a plurality of driver amplifiers, each driver amplifier connected between a

beam port of the modular antenna assembly and a power divider input, each

driver amplifier having an input connected to a beam port and having an output

connected to a power divider input.

19. The modular phased anay antenna of claim 17, further comprising:

a plurality of power dividers, each power divider having an input

connected to a beam signal and having a plurality of outputs outputting the beam

signal, each of the plurality of outputs connected to a beam port of a modular

antenna assembly.

20. The modular phased anay antenna of claim 19, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies are

randomly assigned.

21. The modular phased anay antenna of claim 19, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies are

assigned so that vector sums of coupling coefficients of beam signal to

beamformer paths is reduced compared to a regular connection of the beam

signals to the beam ports relative to the modular antenna assemblies.

22. The modular phased anay antenna of claim 19, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies are

assigned so that vector sums of coupling coefficients of beam signal to

beamformer paths is minimized.

23. The modular phased anay antenna of claim 19, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies are

hard-wired.

24. The modular phased anay antenna of claim 19, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies is

provided by at least one of fiber optic cable, coaxial cable, or printed circuit

board traces.

25. The modular phased anay antenna of claim 19, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies is

configurable in software.

26. The modular phased anay antenna of claim 19, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies is

provided by a switching matrix or other programmable connection device.

27. The modular phased anay antenna of claim 1, wherein the modular

phased anay antenna is a transmitting and receiving antenna.

28. The modular phased anay antenna of claim 27, wherein each modular

antenna assembly comprises:

a plurality of first power dividers/combiners, each first power

divider/combiner having a first input/output connected to a beam port of the modular antenna assembly, and each first power divider/combiner having a

plurality of second outputs/inputs;

a plurality of phase shift attenuators, each phase shift attenuator having a

first input/output connected to a second output/input of a first power

divider/combiner, and each phase shift attenuator having a second output/input;

a plurality of second power combiners/dividers, each second power

connected to a second output/input of a phase shift attenuator, and each second

power combiner/divider having a second output/input;

a plurality of duplexed amplifier pairs, each duplexed amplifier pair

comprising a first amplifier and a second amplifier connected between a pair of

duplexers, each duplexed amplifier pair having a first input/output connected to

second output/input of a second power combiner/divider, and each amplifier

having a second output/input; and

a plurality of antenna elements, each antenna element having an

input output connected to a second output/input of a duplexed amplifier pair.

29. The modular phased anay antenna of claim 28, further comprising:

a plurality of duplexed driver amplifier pairs, each duplexed driver

amplifier pair connected between a beam port of the modular antenna assembly and a power divider/combiner input/output, each duplexed amplifier pair

comprising a first driver amplifier and a second driver amplifier connected

between a pair of duplexers, each duplexed driver amplifier pair having a first

input/output connected to a beam port of the modular antenna assembly, and

having a second output/input connected to a power divider/combiner

input/output.

30. The modular phased anay antenna of claim 28, further comprising:

a plurality of third power dividers/combiners, each third power

divider/combiner having a first input/output connected to a beam signal and

having a plurality of second outputs/inputs connected to a beam port of a modular

antenna assembly.

31. The modular phased anay antenna of claim 30, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies are

randomly assigned.

32. The modular phased anay antenna of claim 30, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies are

assigned so that vector sums of coupling coefficients of beam signal to bearnformer paths is reduced compared to a regular connection of the beam

signals to the beam ports relative to the modular antenna assemblies.

33. The modular phased anay antenna of claim 30, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies are

assigned so that vector sums of coupling coefficients of beam signal to

beamformer paths is minimized.

34. The modular phased anay antenna of claim 30, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies are

hard-wired.

35. The modular phased anay antenna of claim 30, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies is

board traces.

36. The modular phased anay antenna of claim 30, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies is

configurable in software.

37. The modular phased anay antenna of claim 30, wherein the connections

of the beam signals to the beam ports of the modular antenna assemblies is

provided by a switching matrix or other programmable connection device.