WO2014035274A1

WO2014035274A1 - Odd harmonic radial rf filter

Info

Publication number: WO2014035274A1
Application number: PCT/RU2012/000702
Authority: WO
Inventors: Oliver Heid; Timothy Hughes; Stepan Alexanrovich POLIKHOV; Alexander Yourievich SMIRNOV
Original assignee: Siemens, Research Center Limited Liability Company
Priority date: 2012-08-27
Filing date: 2012-08-27
Publication date: 2014-03-06

Abstract

A radial filter, comprises a plurality filter radial segments connected in series, wherein three segments are based on radial transmission lines with constant line impedances, wherein the line impedance value of each segment is defined by the value of opening angle seen at its longitudinal section; one segment is based on a plurality of filter radial segments (horn antennae) with constant line impedances, which are defined by antenna profile.

Description

ODD HARMONIC RADIAL RF FILTER

FIELD OF THE INVENTION

The present invention relates to higher-order harmonic filter design, particularly, to an odd harmonic radial RF filter.

BACKGROUND OF THE INVENTION

The higher-order harmonic filters are needed for creation of class-F RF power amplifiers. These filters are required both to increase the efficiency of the amplifiers by reflecting the power carried by odd harmonics and to combine the power from several amplifiers (RF modules) and deliver it the load. The demand for such device is especially high for designing compact high-efficient RF generators/amplifiers.

Currently, there exist several patents concerning this problem: US4562409, US4926145, US6242984B 1 , US4238747 etc. All mentioned patents describe devices that solve the problem of parallel power combining with suppression of unwanted higher-order modes, propagating at frequencies higher than the operating one. The radial transmission line, to which the plurality of RF modules is connected, and output coaxial line are used in all patents.

US 4,238,747 discloses a mode filter apparatus for preventing unwanted modes in a multi-moded structure utilizing a radial plurality of resonant slots on the bottom of the filter cavity. The top of the filter cavity includes a variable height center section to provide mode selectivity in cooperation with the resonant slots. The cylindrical resonant cavity has a radial pattern of resonant slots in the bottom plate and a variable height center portion in the top plate of the apparatus. The mode selectivity of the mode filter apparatus may be controlled by varying the height of the center portion of the top plate, as well as by changing the length, width and depth of the radial slots. The mode selectivity may also be varied by filling the radial slots with absorbing material to various depths.

US 4,926, 145 discloses a radial power combiner/divider in which energy corresponding to undesired higher order modes in the radial transmission line, including the m=l and m=2 modes, is effectively absorbed. In said radial power combiner/divider radial slots are provided for suppression of undesired modes, certain undesired modes which are not adequately suppressed by the radial slots are allowed to be propagated in a central coaxial transmission line and suppressed therein by means of longitudinal slots in the outer conductor. In an alternative embodiment, the central transmission line of the combiner/divider is in the form of a circular waveguide, and the suppression means comprises thin, spaced coaxial cylinders of dissipative material. US 4,562,409 discloses a cavity resonator coupling-type power distributor/power combiner which can distribute or combine microwave electric power over a wide bandwidth with a small insertion loss. A cavity resonator coupling-type power distributor/power combiner includes a first cavity resonator operatively resonating with a cylindrical ΤΟ,η,Ο mode, and a plurality of second cavity resonators arranged on the periphery of the first cavity resonator and extending radially and symmetrically with respect to the first cavity resonator. The second cavity resonators each have the same shape and size so that magnetic-field coupling is established between the first cavity resonator and each of the second cavity resonators, for distributing or combining microwave power in a microwave amplifier.

In the cavity resonator the higher harmonics are suppressed with radial slits in conductors of the radial line and longitudinal slits in the outer conductor of the output coaxial line; all slits are filled with absorbing dissipative material. These patents solve the problem of power combining and signal filtration. In mentioned patents, the power of the higher harmonics either dissipates in combiner walls or in dielectric material, but is not reflected back to the RF modules as it is claimed in present invention disclosure.

US 6,242,984 relates to solid state power amplifier (SSPA) modules that splits a signal into multiple parts, uses distributed amplifiers to amplify the parts, and recombines the amplified parts into a single output.

An SSPA module in accordance with the present invention comprises a signal input, and a radial splitter connected to the signal input comprising a plurality of radially extending splitter waveguides. The SSPA module also includes a signal output, and a radial combiner connected to the signal output comprising a plurality of radially extending combiner waveguides. Connections between the splitter and combiner are provided by a plurality of vertically extending waveguides. The SSPA module also includes a plurality of processing circuits for example MM1C amplifiers, connected to the combiner waveguides. A waveguide to microstrip transition may also be used to connect signals propagating in the waveguides to and from microstrip lines connected to the processing circuitry. Generally, the transition includes a waveguide section with a top conducting layer that defines a first slit and a second slit bounding a transition area abutting a microstrip section to form a waveguide to microstrip transition.

In patent US4562409 as in US6242984B 1 the signal from each RF module is first injected to a cavity resonator based on rectangular waveguide, which is coupled via magnetic field to a radial line segment with coaxial output. That design implies two resonators in series, which is possible to use for the reflection of the third harmonic. SUMMARY OF THE INVENTION

Thus, filters are required both to increase the efficiency of the amplifiers, by reflecting the power carried by odd harmonics and to combine the power from several amplifiers (RF modules) and deliver it the load.

The object of the present invention is to provide an odd harmonic radial RF filter that serve the problem of increasing the efficiency of the amplifiers by reflecting the power carried by odd harmonics and to combine the power from several amplifiers (RF modules) and deliver it the load.

According to one aspect of the invention, an odd harmonic radial RF filter comprises a plurality filter radial segments connected in series,

three segments are based on radial transmission lines with constant line impedances, wherein the line impedance value of each segment is defined by the value of opening angle seen at its longitudinal section;

one segment is based on a plurality of horn antennae with constant line impedances, which are defined by antenna profile.

Preferably the radial filter, further comprises outer shield, representing shunt inductance, high enough for avoidance of useful power leakage.

The advantage obtained or the contribution to the claimed solution is unification of non-resonant power combiner and stepped-line filter based on radial transmission lines. The main advantages of the proposed invention are following:

a. Multiple devices based on the present invention can be easily integrated to a single power combiner design;

b. The odd harmonics are reflected back to the RF modules in order to achieve high efficient operation of solid state microwave amlifier;

c. The geometry of conducting walls of the radial filter with absence of resonating cavities yields low useful power dissipation.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the embodiments of the invention will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings that are not considered to be limiting of its scope. The aspects of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

Fig. l depicts a redial filter (longitudinal section), according to the invention; Fig.2 depicts a perspective view of the radial filter (outer shield and load are not shown), according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device according to the invention disclosure unites the features of power combiner and 3^rd harmonic filter. It compensates the reactance of the output impedance of plurality of RF modules at fundamental frequency (allowing power delivery from the RF modules to the load) and transforms the load impedance into high real value at the 3rd harmonic (three times the fundamental frequency), which leads to reflection of the 3rd harmonic power back to each RF module output with a zero phase shift.

Such reflection serves both for reducing unwanted harmonics from output signal and recharging parasitic capacitance of transistors in RF modules. This allows reaching class-F operation with high theoretical efficiency (>85%).

The radial filter consists of four segments connected in series with different line impedances:

- a plurality filter radial segments are based on radial transmission lines with constant line impedances, wherein the line impedance value of each filter radial segment is defined by the value of opening angle seen at its longitudinal section;

- one filter radial segment is based on a plurality of horn antennae with constant line impedances, which are defined by antenna profile.

The preferable embodiment is shown on Fig. l and fig. 2. Three radial filter segments 2 serves to a number of RF modules connected in parallel to horn antennae 1 , combining their power simultaneously and delivering it to the load, i.e. coaxial cable 3 in this case. One filter radial segment 6 is based on a plurality of filter radial segments (horn antennae) with constant line impedances, which are defined by antenna profile. The outer shield 4 represent shunt inductance, which is high enough for avoidance of useful power leakage.

Output slit 5 is shown in fig. 2.

Claims

1 . A radial filter, comprising:

a plurality filter radial segments connected in series,

2. The radial filter, further comprising:

outer shield, representing shunt inductance, high enough for avoidance of useful power leakage.