Wideband hybrid system

[57] ABSTRACT

An input diplexer separates wide frequency range signals by frequency to provide, at a plurality of outputs, signals within different narrow frequency bands. A plurality of quadrature hybrids are adapted so that each hybrid achieves equal power division and 90° relative phase shift with low distortion over one of the narrow frequency bands. A hybrid is coupled to each output of the input diplexer. Output diplexers are coupled to the two outputs of each of the hybrids to combine the power divided narrow frequency band signals into two wide frequency band signals of substantially equal power and of 90° differential phase.

Claims, 2 Drawing Figures

QUADRATURE

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Ila

PATENTED ACT 231973

3.768,043

QUADRATURE HYBRID·»

SHEET 1 CF 2

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PATENTE00CT23B73

3,768,043

SHEET 2 OF 2

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3,768,043

WIDEBAND HYBRID SYSTEM

BACKGROUND OF THE INVENTION

This invention relates to hybrids and more particularly to a polarizer using a system of hybrids for achieving 90° differential phase shift and power splitting over a wide band of frequencies with low amplitude and phase error.

It is desirable for achieving circular polarization that the signals fed to the orthogonally polarized antenna radiating element be at phase quadrature or 90° difference in relative phase and that the power be exactly divided. A practical way of achieving this with low loss is by means of a short slot hybrid. Although these short hybrid slot devices have had humps put at the center of the short slot region or the cross sectional width made smaller near the slotted region to achieve broadband operation, these hybrid structures remain relatively narrow band devices. When one of these devices is operated over a wide frequency band such as for example from 3,700 to 4,200 MHz (as in satellite communication systems), phase error of over 5° is produced at some frequencies in the band. Consequently, relatively high axial ratios occur when the outputs of one of these are applied to the elements of an antenna. Wideband polarizers capable of achieving axial ratios in the order of 0.25 to 0.5 db are required over these above frequencies in satellite communication systems. This has heretofore not been achieved over such widebands using hybrids.

Briefly, according to the present invention substantially lower amplitude and phase error is achieved for providing equal power division and 90° relative phase shift between the power divided outputs by the use of a first diplexer for subdividing the signals by frequency into subfrequency bands and by coupling the narrow frequency band signals to separate hybrids. The separate hybrids are each adapted to provide at their two separate outputs, power division and 90° relative phase shift between the power divided signals over the particular narrow frequency band coupled thereto with minimum amplitude and phase error. That one of the two outputs from each of the separate hybrids having substantially identical phase is coupled to a second diplexer for combining the narrow band signals to a first wideband output. The second output from each of the separate hybrids is coupled to a third diplexer for combining the 90° relative phase shifted narrow frequency band signals to a second wideband output.

A more complete description of the subject invention follows in conjunction with the following drawings wherein:

FIG. 1 is a schematic diagram of a wideband hybrid system and a polarizer system using the same according to the present invention.

FIG. 2 is a perspective view of a portion of a wideband hybrid system shown in FIG. 1 with a portion of the top walls removed.

Referring to the block diagram of FIG. 1, there is shown a wideband hybrid system 10 consisting of two diplexers 11 and Ila at the input and two output diplexers 41 and 43 with four short slot quadrature hybrids 21, 23, 25 and 27 coupled therebetween. The purpose of the circuit is to divide the input power fed to the input terminal Ij of diplexer 11 into two parts occurring at the output terminals Oj of diplexer 41 and O₂of diplexer 43 in such a way that the output powers are equal in amplitude, 90° different in relative phase and no output power is coupled at I₂ or reflected back to Ip Further, the purpose of the circuit is that the terminal Ii of diplexer 11 and the I₂ terminal of diplexer 11α be interchangable and simultaneously useful. All of the above functions are maintained in the fi through /₅frequency band. Circular polarization is achieved by coupling the output at terminal to one terminal 9α of an orthogonal coupler 9, for example, and the other output at terminal O₂ is coupled to an orthogonally oriented terminal 9b of coupler 9. If these outputs at Oi and O₂ are equal in power and at phase quadrature pure circular polarization is achieved. The coupling to the orthogonally oriented terminal 9b may require a rotation of the polarization attitude 90°. This rotation may be accomplished by a twisted waveguide section (rotator) 8 located in the coupling lead between terminal O₂ and terminal 9b.

The input signal I, at frequencies fi to/₅ is divided on the basis of frequency by diplexer 11 into four frequency bands fi to fi; fi to /₃; fi to fi and fi to fi. The diplexer 11 is made up of a power divider 13 followed by a plurality of band-pass filters 15,16,17 and 18. The power divider 13 splits the input signal power into, for example, four signals of equal power and couples these separate signals to separate filters 15, 16, 17 and 18. The band-pass filter 15 is selected to pass those frequencies within the fi to fi frequency band. Similarly, band-pass filters 16,17 and 18 are selected to pass the frequency bands fi tofi;fi tofi and/, tofi respectively.

A plurality of hybrids 21, 23, 25 and 27 equal to the number of band-pass filters is provided. The hybrid 21 is adapted to provide equal power division of the input signal with 90° differential phase shift between the power divided signals. The hybrid 21 is designed to accomplish this with minimum phase and amplitude error between its two output ports over the frequencies of from/! to/₂. The output of band-pass filter 15 is coupled via lead 29 to input terminal 21α of hybrid 21. The hybrid 23 is similarly adapted to operate as a 90° differential phase shifting power dividing coupler but with minimum phase and amplitude error over the frequencies from fi tofi. The output of band-pass filter 16 is coupled via lead 30 to terminal 23α of hybrid 23. The hybrid 25 is similarly a 90° differential phase shifting power dividing coupler which is adapted to operate with minimum phase and amplitude error over the frequencies fromfi tofi. The output of band-pass filter 17 is coupled via lead 31 to terminal 25α of hybrid 25. The hybrid 27 is a 90° differential phase shifting power dividing coupler which is adapted to operate with minimum phase and amplitude error over the frequencies from fi to /₅. The output of band-pass filter 18 is coupled via lead 32 to terminal 27α of hybrid 27. The hybrids 21, 23, 25 and 27 may each be short slot hybrids as described, for example, by Riblett in U.S. Pat. Nos. 2,739,287 and 2,739,288. Basically, each of these short slot hybrids consists of two rectangular waveguide sections having a common wall with an aperture in the common wall. Signals coupled to one of the waveguides are power divided at the aperture with one half of the power coupled through the aperture and phase shifted 90° relative to the other one half of the signal which is coupled to the other end of the input waveguide without such additional phase shift.

The output from the quadrature hybrids 21, 23, 25 and 27 are coupled to diplexers 41 and 43. The di3,768,043 plexer 41 includes band-pass filters 45, 46, 47 and 48. Band-pass filter 45 is adapted to couple only those signals with low attenuation between the frequencies of/, to /₂. Similarly, band-pass filter 46 is adapted to pass the frequencies of/₂ to/₃. Band-pass filter 47 is adapted to pass the frequencies between/, to/, with low attenuation and band-pass filter 48 is adapted to pass frequencies between /, to /, with low attenuation. In the diplexer 41 the outputs of band-pass filters 45, 46,47 and 48 are each coupled to a power combiner 49 wherein the signals at frequencies from /, to/₅ are combined to provide an output at terminal O,. Diplexer 43 is similarly arranged comprising band-pass filter 55 covering the frequency range from /, to /₂, band-pass filter 56 covering the frequency range from /₂ to/₃, band-pass filter 57 covering the frequency range from/, to f_t and band-pass filter 58 covering the frequency range from /, to/₅. All the output power at the band-pass filters 55 through 58 are combined at power combiner 59 to provide a single output at output terminal O₂ of diplexer 43.

The power divided signal at terminal 21b of hybrid 21 is coupled via lead 33 to band-pass filter 45 in diplexer 41. The equal power 90° phase shifted signal at terminal 21c of hybrid 21 is coupled via lead 35 to band-pass filter 55 of diplexer 43. The one half power output signal at terminal 23b of hybrid 23 is coupled via lead 37 to band-pass filter 46 of diplexer 41. The equal power 90° relative phase shifted signal from hybrid 23 at terminal 23c is coupled via lead 38 to band-pass filter 56 of diplexer 43. The half power output signal from hybrid 25 at terminal 25b is coupled via lead 39 to bandpass filter 47 of diplexer 41. The equal power and 90° relative phase shifted signal at terminal 25c of hybrid 25 is coupled via lead 40 to band-pass filter 57 of diplexer 43. The half power output signal at terminal 27b of hybrid 27 is coupled to band-pass filter 48 of diplexer 41 via lead 36. The equal power 90° differential phase shifted signal at terminal 27c is coupled via lead 34 to band-pass filter 58 of diplexer 43.

In the operation of the device described in FIG. 1, the input signals I, of frequencies from /, to/₅ which cover the operating frequency band of the system are coupled to the input power divider 13 wherein these signals are divided into four equal power sections and coupled to the respective filters 15, 16, 17 and 18. The filter 15 passes frequencies from/, to/₂ to short slot hybrid 21. At the hybrid 21 the /, to /₂ frequency signals are equally power divided and with one portion undergoing zero or reference phase shift to terminal 21b and the other portion undergoing 90° differential phase through the short slot 22 in hybrid 21 to terminal 21c. The output at terminal 21b is coupled to band-pass filter 45 in diplexer 41 via lead 33. The 90° differential phase shifted signal at terminal 21c is coupled via lead 35 to band-pass filter 55 of diplexer 43. Similarly, those signals at frequencies from /₂ to/₃ are coupled to short slot hybrid 23 and power divided such that those signals at the reference phase at hybrid terminal 23b are coupled to band-pass filter 46 of diplexer 41 and the 90° differential phase shifted signals at terminal 23c are coupled to band-pass filter 56 of diplexer 43. Those signals between frequencies /₃ to /, are coupled to short slot hybrid 25 with the one half power output at terminal 25b at reference phase coupled to band-pass filter 47 of diplexer 41 and those half power signals undergoing 90° differential phase shift being coupled out of ter4 minal 25c to band-pass filter 57 of diplexer 43. The signals at frequencies between f_t and/, are coupled out of band-pass filter 18 to short slot hybrid 27. The output signals at reference phase at terminal 27b of hybrid 27 are coupled to band-pass filter 48 of diplexer 41 and the 90° differential phase shifted signals at terminal 27c are coupled to band-pass filter 58 of diplexer 43. As can be seen by reviewing the above, those signals which undergo the 90° additional phase shift are coupled to the diplexer 43 and the other signals of equal power but of reference phase are coupled to diplexer 41. The signals at the band-pass filters 45 through 48 are combined at power combiner 49 to provide one half the total output power at the reference phase at terminal O,. The band-pass filters 55 through 58 are coupled to power combiner 59 wherein the other half of the total power at the frequencies from/, to/₅ are combined and applied to the output terminal O₂. The power at terminal O₂ should approximately equal the power at terminal O, and be at 90° relative phase to the phase of the signal at terminal O,.

A nearly circular polarized wave with a relatively low axial ratio of powers at the two terminals is achieved for example by coupling the output at terminal O, to one terminal 9α of orthogonal coupler 9 and by coupling the other output at terminal O₂ to terminal 9b of the orthogonal coupler 9 via attitude rotator 8. The orthogonal coupler 9 may be coupled at terminal 9c to a radiating horn antenna, not shown, whereby the circular polarized waves are radiated or received. The orthogonal coupler 9 may be a square section of waveguide (not shown) with the terminals 9α and 9b oriented to excite the output signal at terminal O, in for example a TE₁₀ mode and to excite the output signal at terminal O₂ in the orthogonal TE₀, mode. Metal irises (not shown) can be placed across the input of terminal 9α orthogonal to the electric field in the TE,₀ to provide isolation of the two terminals 9α and 9b. A typical waveguide orthogonal coupler may be like that shown in FIG. 8 and described in connection therewith in (J. S. Pat. No. 3,569,870 issued to Peter Foldes.

Input signals applied to terminal I₂ in FIG. 1 undergo similar operation to that described above for input signals applied to diplexer 11. Input signals applied to terminal I₂ of diplexer 11α are power divided at divider 13α with those signals from frequency/, to/₂ being coupled through filter 15α and lead 29α to terminal 21d of hybrid 21. Similarly, those signals at frequencies /₂ to /₃ at divider 13α are coupled through filter 16α and lead 30α to terminal 23d of hybrid 23. Signals at frequencies /₃ to /, at divider 13α are passed through filter 17α and lead 31α to terminal 25d of hybrid 25. Signals at frequencies/, to/₅ at divider 13α are passed through filter 18α and lead 32 to terminal 27d of hybrid 27. The operation of the hybrids 21, 23, 25 and 27 and diplexers 41 and 43 is similar to that described above with the output at terminals O₂ and O, being of equal power at 90° relative phase but in this case the output at terminal O, undergoes the additional 90° phase shift and the output at terminal O₂ is at reference phase. This is due to the fact that the signals which are ultimately coupled to diplexer 41 are coupled through the slots in each of the hybrids 21, 23, 25 and 27.

As mentioned previously, it is desirable that the device be reciprocal. It can be seen that by making the power dividers and power combiners identical by having them both with the filters at the input and output

3,768,043 at these apertures. At the hybrids 92, 93, 94 and 95 the signals are power divided with the outputs from the two output terminals of each hybrid being substantially 90° out of phase and of substantially equal power. The 5 outputs from the hybrids 92, 93, 94 and 95 are coupled to a structure (partly shown) which is a continuation of waveguide sections 63 and?64. The remaining structure is similar to that shown at the input but is symmetrically arranged so that the outputs of the hybrids are coupled 10 to the band-pass filter sections including the plates and irises and the output of the filter sections is coupled to the undivided waveguide section to form a combiner. The fdter section coupled to each terminal of each hybrid is made substantially the same.

¹⁵ Numerous and varied other arrangements within the sphere and scope of the principle of the invention will have occurred to those skilled in the art. The general principles of the invention are, for example, readily applicable to systems employing two or more hybrids and ²⁰ corresponding band-pass filters and power dividers.

Power division can be up to any n number of sections with n band-pass filters and n hybrids to achieve the desired minimum phase and amplitude error through such hybrids. In the configuration using only two such hy²⁵ brids, four diplexers and an orthogonal coupler, an axial ratio on the order of 0.35 db is achieved in the 3,700 to 4,200 MHz frequency band.