Turnstile OMT using magic-TS for higher tolerance to misalignment and layout asymmetry

Abstract

An orthomode transducer comprising: a waveguide input; a first branch pair comprising a first waveguide defining a first port and a second waveguide defining a second port, wherein the first branch pair is associated with a first polarization; a second branch pair comprising a third waveguide defining a third port and a fourth waveguide defining a fourth port, wherein the second branch pair is associated with a second polarization; a first magic-tee combiner configured to absorb trapped modes of the first branch pair through a first sum port; and a second magic-tee combiner configured to absorb trapped modes of the second branch pair through a second sum port.

Description

TURNSTILE OMT USING MAGIC-TS FOR HIGHER TOLERANCE TO MISALIGNMENT ANDLAYOUT ASYMMETRYFIELD

[0001] The present disclosure relates to waveguide devices. More particularly, it relates to millimetre-wave orthomode transducers (OMTs) using a waveguide and a turnstile junction as the polarisation discriminator.BACKGROUND

[0002] Within millimeter-wave receivers for radio astronomy, an orthomode transducer (OMT) is used with the receiver front-end to separate out the received signal into two linear polarizations. Four common implementations of OMTs for millimeterwave frequencies include: planar, Boifot, turnstile junction, and dual -junction (some recent examples are

[0001] - [7]). When using a turnstile junction, as shown in Figs, la-d (PRIOR ART), the input signal is split into two branch pairs where each pair is recombined into the respective polarization. Fig la shows a model of a turnstile junction for transducing an electromagnetic field from circular or square waveguide (annotated as port 1) and separate it out into 4 outputs (ports 2-5). Assuming that port 1 contains the linearly polarized fundamental mode, TE11, the circular tuning stubs will bisect the field producing outputs that are 180° out-of-phase, as shown in Fig. lb. T-junction or Y- junction combiners are typically used for recombination, and their effectiveness depends on phase and amplitude balance (180° difference with equal amplitudes). Under ideal symmetric conditions, each polarization is wholly contained within one branch pair of signals and is fully recombined, as shown in Figs. 1c and d. If the input field is partially rotated with respect to either polarization, then the input signal will appear in both branches according to how much it is rotated. Accordingly, depending on how the input field is rotated, the turnstile will direct the outputs accordingly: aligned with Polarization A (Fig. 1c) and aligned with Polarization B (Fig. Id).

[0003] In practice, however, measured performance of OMTs often shows sharp signal drops in the gain or “spikes” in the isolation response. There are several contributing factors for this degraded performance, as discussed in [8] and [9], and the most common factors include: branch path length imbalances and layer misalignment.The performance of an OMT is dependent on symmetry of the structure, and any deviation through misalignment or fabrication tolerance will degrade the signal throughput and isolation responses.

[0004] One conventional approach in designing an OMT is shown in Fig. 2a (PRIOR ART) where T- or Y-junctions are used

[0014] , A branch symmetry plane is highlighted to emphasize the importance of equal path length for each branch half. For illustration, one half of the branch has been extended by 25 pm intentionally breaking symmetry and changing the phase at point of recombination. As a result of the path length imbalance, the signals within each side of the branch are no longer exactly differential and, instead of combining at the Y-junction, some signal will be reflected back towards the turnstile junction and combined to form undesired higher-order modes within the circular sections of the turnstile and circular waveguide . Fig . 2b (PRIOR ART) shows this behavior clearly as narrow signal drops are shown in the transmitted gain response, signifying trapped modes. Within a receiver front-end, an OMT will be connected to a feed horn and these undesired field modal patterns may reflect out the feed horn and degrade the crosspolarized beam response.SUMMARY

[0005] In one of its aspects, an orthomode transducer comprising: a waveguide input; a first branch pair comprising a first waveguide defining a first port and a second waveguide defining a second port, wherein the first branch pair is associated with a first polarization; a second branch pair comprising a third waveguide defining a third port and a fourth waveguide defining a fourth port, wherein the second branch pair is associated with a second polarization; a first magic-tee combiner configured to absorb trapped modes of the first branch pair through a first sum port; and a second magic-tee combiner configured to absorb trapped modes of the second branch pair through a second sum port

[0006] In another of its aspects, a magic-tee combiner comprising: a first input waveguide comprising a first output port; a second input waveguide comprising a second output port; a sum port; and a termination absorber associated with the sum port.

[0007] In one example, an orthomode transducer (OMT) assembly comprising a turnstile junction that provides balanced signal outputs, and suitable for either linear or circular polarization. The OMT uses magic -tees for recombination which has the advantage of terminating higher-order modes that could arise from fabrication and assembly uncertainties. Trapped higher order modes can become even more troublesome when greater waveguide integration is used, such as in focal plane array layouts. Generally, integrating magic-tees within a waveguide network for differential or in-phase power division is advantageous because of their improved isolation, compared to simple T- or Y-j unctions. As such, the turnstile junction OMT can be improved using magic -tee hybrid couplers that absorb the trapped modes through the sum port.

[0008] In one example, an OMT assembly is fabricated using magic-tees with waveguide integration using hole couplers for receiver calibration using noise-injection. In one example, the OMT assembly is suitable for the Q band frequency range spanning the Band 5 receiver specifications for the Next Generation Very Large Array (ngVLA) radio telescope (30.5-5ng0.5 GHz). Such greater levels of waveguide integration are desirable in dual -linear sideband-separating focal plane arrays

[0010] , In focal plane arrays, unwanted leakage from reflections and shared coupling paths, e.g. local oscillator distribution, may be improved by incorporating magic -tees due to their isolation. The impact of reflections on sideband-separating waveguide layouts is described in

[0011] , BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figs, la-d (PRIOR ART) show an operation of a conventional turnstile OMT for the fundamental linearly-polarized modes, TE11c and TE1 Is;

[0010] Fig. la (PRIOR ART) shows a model of a turnstile junction for transducing an electromagnetic field from circular or square waveguide and separate it out into 4 outputs;

[0011] Fig. lb (PRIOR ART) shows field producing outputs that are 180° out-of- phase;

[0012] Fig. 1c (PRIOR ART) shows a turnstile output when input field is aligned with Polarization A;

[0013] Fig. Id (PRIOR ART) shows a turnstile output when input field is aligned with Polarization B;

[0014] Fig. 2a (PRIOR ART) shows a conventional OMT using Y -combiners in each branch, in which a branch symmetry plane is highlighted to emphasize the importance of equal path length for each branch half (i.e., the solid and dashed paths);

[0015] Fig. 2b (PRIOR ART) shows a simulated transmission of an ideal symmetric response (red trace) compared with the effect when one side of the branch is extended by 25 pm (green trace);

[0016] Fig. 2c shows an OMT assembly with magic-tee combiners, in one example;

[0017] Fig. 2d shows a simulated transmission when path length differences are 0 and 25 pm, and showing an absence of trapped modes;

[0018] Fig. 3a shows a CAD model of a conventional OMT assembly with a 3 mm offset from the mid plane;

[0019] Fig. 3b shows an effect on insertion gain when the position of the output tee waveguide is shifted, while still keeping equal path length for the conventional OMT assembly of Fig. 3a, displaying some trapped energy and signal drops within the transmission gain;

[0020] Fig. 3c shows a CAD model a magic-tee OMT assembly with a 3 mm offset from the mid plane;

[0021] Fig. 3d shows the effect on insertion gain when the position of the output tee waveguide is shifted, while still keeping equal path length for the magic-tee OMT assembly of Fig. 3c, where simulation indicates no degradation in the transmission gain;

[0022] Fig. 4a shows a conventional OMT assembly, with the bottom layer (highlighted) misaligned by 25 gm along the x- and y-axes;

[0023] Fig. 4b shows a corresponding transmission gain response illustrating the effect of misaligning the crucial layer, containing the turnstile, within a 3 -layer OMT assembly;

[0024] Fig. 4c shows a magic-tee OMT assembly, with the bottom layer (highlighted) misaligned by 25 gm along the x- and y-axes;

[0025] Fig. 4d shows a corresponding transmission gain response illustrating the effect of misaligning the crucial layer, containing the turnstile, within a 3 -layer OMT assembly;

[0026] Fig. 5a shows a CAD model of an OMT assembly using integrated noise injection hole couplers and magic-tees to recombine turnstile outputs within each branch;

[0027] Fig. 5b shows a view of the four machined layers of the OMT assembly;

[0028] Fig. 5c shows a close-up of the top layer showing the features of the magic- tees;

[0029] Fig. 6a shows a fixture to characterize the MF-117 waveguide terminations;

[0030] Fig. 6a shows reflected power measurements of two different samples;

[0031] Figs. 7a-i show measurements of a fabricated OMT assembly using 5000 points without trace smoothing;

[0032] Figs. 8a-e show five example propagating modes within a circular waveguide;

[0033] Fig. 9a shows fundamental TE11c and TE1 Is modes propagating through the OMT between ports 1-2;

[0034] Fig. 9b shows fundamental TE11c and TE1 Is modes propagating through the OMT between ports 1-3;

[0035] Fig. 9c shows a TE21c coupled through sum ports of each magic-T branch, then combined by a third magic-tee to show overall propagation between ports 1-4; and

[0036] Fig. 9d shows relevant S-parameters when TE21c excites the OMT structure indicating — 10 dB reflected power and ~1 dB transmitted signal loss.DETAILED DESCRIPTION

[0037] The following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar elements. While embodiments of the disclosure may be described, modifications, adaptations, and other implementations are possible. For example, substitutions, additions, or modifications may be made to the elements illustrated in the drawings, and the methods described herein may be modified by substituting, reordering, or adding stages to the disclosed methods. Accordingly, the following detailed description does not limit the disclosure. Instead, the proper scope of the disclosure is defined by the appended claims.

[0038] Moreover, it should be appreciated that the particular implementations shown and described herein are illustrative of the disclosure and are not intended to otherwise limit the scope of the disclosure in any way. Indeed, for the sake of brevity, certain subcomponents of the individual operating components, and other functional aspects of the systems may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and / or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system.

[0039] Looking at Fig. 2c, there is shown an orthomode transducer (OMT) assembly 10 comprising an OMT, or turnstile junction, 12 with magic-tee combiners 14, 16, in one example. The OMT 12 comprises a waveguide input 18, a first branch pair 20 comprising a first waveguide 22 and a second waveguide 24, a second branch pair 26 comprising a third waveguide 28 and a fourth waveguide 30. The first waveguide 22 comprises a first port 32 and the second waveguide 24 comprises a second port 34, while the third waveguide 28 comprises a third port 36 and the fourth waveguide 30 comprises a fourth port 38.

[0040] A first magic -tee combiner 14 is coupled to the OMT 12 via the first port 32 of the first waveguide 22 and the second port 34 of the second waveguide 24, while asecond magic-tee combiner 16 is coupled to the OMT 12 via the third port 36 of the third waveguide 28 and the fourth port 38 of the fourth waveguide 30.

[0041] An additional 4th port (i.e., the sum port) 50a, 50b of the hybrid coupler 14, 16, respectively, allows the hybrid coupler 14, 16, to recover signals 0° phase difference so that each of the first branch pair 20 and the second branch pair 26 imbalances can be captured and terminated, instead of being reflected back within the structure 12. As such, trapped modes and signal drops due to branch imbalances are suppressed, and overall isolation is improved.

[0042] Fig. 2d shows a simulated plot of the transmitted signal gain, illustrating that Importantly, even with an asymmetric path length, there are no longer any sharp signal drops because unbalanced power has been terminated within the magic-tee combiner 14 or 16. In fact, simulation shows that much greater path length imbalances can be tolerated. The OMT assemblies in Figs. 2a and 2c have slightly different group delay, port reflection, and bandwidth design goals which accounts for the small mean difference in insert ion loss between the two models.

[0043] In many turnstile OMT assemblies, pure branch symmetry is not maintained in order to make the design more compact or to shift the outputs off-center for layout convenience (see examples in [8],

[0015] —

[0020] ). In these designs, the electrical path length is kept the same for branch halves, but since discontinuities occur along different points, locally-generated evanescent fields will decay differently and the higher-order mode content cannot be guaranteed equal at the point of recombination.

[0044] Fig. 3a shows a CAD model of a conventional OMT assembly 10, with OMT 12 and Y-junction combiners 60a, 60b, with the output is shifted by 3 mm from a mid plane 62. Fig. 3b shows the effect on insertion gain when the position of an output tee waveguide is shifted, while still keeping equal path length for the conventional OMT assembly of Fig. 3a, displaying some trapped energy and signal drops within the transmission gain.

[0045] Fig. 3c shows a CAD model a magic-tee OMT assembly 10, with OMT 12 and magic -tee junction combiners 70a, 70b, with a 3 mm offset from the mid plane. Fig.3d shows the effect on insertion gain when a position of the output magic-tee waveguide 72 is shifted, while still keeping an equal path length for the magic-tee OMT assembly of Fig. 3c, where simulation indicates no degradation in the transmission gain, despite the offset, which provides greater layout flexibility and facilitates integration.

[0046] Another common reason for sharp signal drops and isolation spikes in an OMT is due to layer misalignment. If the assembled layers are misaligned, or if the machining itself is off-centered with respect to the turnstile axis, then branch asymmetry will be introduced. Layer misalignment is particularly troublesome because, in addition to causing path length differences (which the magic -tees can mitigate), it may also create waveguide channel discontinuities that can trap energy or excite higher order modes locally within the circular waveguide (which are independent and not mitigated by magic- tees). For example, layer misalignment has the largest effect on the layer containing the turnstile junction. If the turnstile junction becomes offset from the entrance circular waveguide, the field will not be bisected at the midpoint and transmitted power will be divided unequally within each branch half.

[0047] Magic -tees may mitigate the unequal power recombination through the branches. However, the offset layer will shift all waveguide interfaces and the scenario is most severe along the circular waveguide sections that support higher modes that can result in cross-polarization leakage. Within the rectangular waveguide sections of the network, offset layers may create resonant sections — this cannot be helped by using magic -tees.

[0048] Figs. 4a-c show the effect of a scenario when a layer containing the turnstile 10, within a 3-layer OMT assembly 80a, 80b, is purposely misaligned along the x- and y- axes. Fig. 4a shows a conventional OMT assembly 80a, with the bottom layer (highlighted) misaligned by 25 pm along the x- and y-axes. Fig. 4b shows a corresponding transmission gain responses illustrating the effect of misaligning the crucial layer, containing the turnstile, within a 3-layer OMT assembly 80b. The transmitted gain is plotted with the circular port terminated with 1 or 5 modes.

[0049] Fig. 4c shows a magic -tee OMT assembly, with the bottom layer (highlighted) misaligned by 25 gm along the x- and y-axes. Fig. 4d shows corresponding transmission gain responses illustrating the effect of misaligning the crucial layer, containing the turnstile, within a 3 -layer OMT assembly, in which the transmitted gain is plotted with the circular port terminated with 1 or 5 modes.

[0050] Using a “1-mode” port boundary represents the scenario when measuring in the lab using a rectangular-to-circular waveguide transition that only allows the fundamental mode to be measured even though the circular waveguide can support up to 5 modes within the band, modes 2-5 are shorted out when a transition is used during measurement. A “5 -mode” port boundary corresponds to a scenario when the OMT is connected to a feed horn whereby all 5 possible modes within the circular waveguide are allowed to escape. By comparing Fig. 4b and c, and looking at the 1-mode plot, it is clear that the misalignment excites severe local higher modes in both OMT assemblies. However, comparing the 5 -mode curves, one can see residual trapped energy spikes in Fig. 4b, whereas the magic-tee OMT assembly 10 shows a smooth response in Fig. 4d. Greater waveguide integration will help to facilitate new receiver layouts that support focal plane arrays

[0010] , but with increasing complexity in the waveguide networks the importance of using components with inherent isolation becomes more critical.

[0051] Fig. 5a shows a CAD model of an OMT assembly 90 comprising orthomode transducer (OMT) 12 using integrated noise injection hole couplers 92 and magic -tees 94 to recombine turnstile outputs within each branch. OMT 12 comprises circular waveguide input port 96; ports 97a and 97b signal outputs; and port 98 noise-injection. The magic- T sum ports and hole couplers each have an internal load that is epoxied within the channel. In Figs. 5a-c, an additional, shared noise-injection path (through hole couplers

[0021] ) has been added to the OMT to demonstrate increased waveguide integration within the block and to apply the design to show suitability for receivers of the upcoming Next Generation Very Large Array (ngVLA). In one example, a prototype OMT 10 is machined at Q-band to correspond with ngVLA band 5 receiver specifications (30.5-50.5 GHz, a fractional bandwidth of 49.3%). Features of this particular design include:balanced amplitude and phase to support linear or circular polarization; integrated magic- T couplers to reduce signal drops from higher-order modes; integrated noise-injection couplers (—35 dB) for receiver calibration; input circular waveguide (direct connection to feed horn with no transition needed); and downward-facing waveguide outputs for symmetric assembly of each downstream receiver chain.

[0052] Fig. 5b shows example four machined layers lOOa-d of the OMT 12. Waveguide channels are machined into both sides of each platelet and careful attention was given to flatness. In one example, to consider scaling to higher frequencies aspect ratios are specified to stay within 5 : 1 and an end mill cutter no smaller than 0.8 mm radius (approximately 0. 13 x free-space wavelength of the highest frequency).

[0053] A close-up of a layer 102 containing the two magic-tee couplers 14, 16 is shown in Fig. 5c. The sum ports of each magic-tee coupler 14, 16, and each isolated port of the hole couplers, are internally terminated with an absorber 106 machined from Eccosorb® MF-117. Since the available space was limited around the magic-tee, a shortened compact waveguide termination 104 was designed and measured using the fixture shown in Fig. 6a. To facilitate machining, the shape of the absorber 106 was chosen to have a thickened rectangular base so that it could be held in a vise. The thick base has the benefit of avoiding any fine-tipped features (e.g., as in a pointed wedge- shaped absorber) on the termination, but required recessing the waveguide channel. Excellent consistency between the machined samples is shown in Fig. 6b. From the simulation, the reflected power was expected to be less than -25 dB, and better material parameter matching was therefore required (here, material parameters were extrapolated from out-of-band values given in the data sheet). Even still, for a compact, wideband, and machinable load, performance is good. Room temperature measurements of the OMT are given in Figs. 7a-i and measurements are shown spanning 30-51 GHz that provide some margin for the already challenging ngVLA band 5 frequency specification of 30.5-50.5 GHz. All measurements include the effects of a WR-22 to circular waveguide transition (i.e., its effects have not been de-embedded), which is 63.5 mm long and adds some extra insertion loss, as shown in Fig. 7d. From Figs. 7a-c, the reflected power, cross-polarization leakage, and isolation all indicate smooth responses without the appearance of trapped modes. Since the noise-injection path is shared between each polarized path, it can easily degrade the cross-polarization and isolation as the additional couplers can provide an additional leakage path. The hole couplers used, however, have excellent isolation and a low coupling value of — 35 dB, as shown in Fig. 7g including another 3 dB from the T-divider. Plots shown in Figs. 7d-f show that the RF signal paths are evenly balanced and maintain a phase and amplitude balance with 2° and 0.2 dB, indicating suitability for circularly polarized signals if paired with a 90° hybrid. Finally, the noiseinjection path was also designed with symmetry and the measurements shown in Figs. 7h and i indicate a phase and amplitude balance of 4° and 0.4 dB (the additional noise in the difference measurements is because these coupled paths have much lower power and are closer to the network analyzer noise floor). Note that these results may also serve as a step towards demonstrating local oscillator distribution in focal plane arrays

[0010] ,

[0054] One example application within satellite communications is to use the functionality of the sum ports to receive a TE21 tracking mode. An OMT is commonly used to receive a dual-linear polarized signal within a circular waveguide; the field patterns of these two fundamental modes are shown in Fig. 8a and b. Each mode within a waveguide has corresponding “cut-off frequency,” above which it may propagate. Within circular waveguide, the TM01 and TE21 higher order modes, as in Figs. 8c -e, have cut-offs corresponding to ~1.3 and -1.7 of TE11, implying that in the upper part of the signal band will support these additional modes. The field patterns of the TM01 and TE21 modes contain a null in the centre which, in turn, result in a radiated feed horn pattern with a null at the boresight that may be used for positional tracking.

[0055] Various types of special mode couplers may be used to extract out the tracking mode. According to the art, an 8-arm TE21 coupler is used to recover both the TE21c and TE21s modes. These couplers are somewhat bulky and require a waveguide recombination network. The 8-arm coupler recovers both TE21 modes, using 4 arms for each mode. To recover the full power, three magic-tees are used for each 4-arm output (this is similar to the implementation of the turnstile junction shown here). Given thatthe proposed OMT already has 2 integrated magic-tees, and is amplitude and phase balanced, only one extra magic-T is required-saving complexity and weight. Considering a turnstile junction, and comparing the possible tracking modes of Figs. 8 c-e, the TM01 mode does not couple well, but the TE21c mode may be transduced (TE21s will be completely shorted out).

[0056] Now turning to Figs. 9a-d, when magic-tees are used within the OMT branches, the sum ports of each magic -tee will contain half of the power within the TE21c mode. The branches may be combined (since they are phase and amplitude balanced), to fully recover all three orthogonal modes: TE11c shown in Fig. 9a; TE1 Is shown in Fig. 9b and TE21c shown in Fig. 9c. Fig. 9d shows the simulated response of the OMT when the TE21c mode excites the circular waveguide input and indicates satisfactory performance for positional tracking, with better than 10 dB return loss and 1 dB of signal loss from conductive metal loss. Of the two TE21 modes, only TE21c will be transduced but the TE21s mode will be shunted by the turnstile.

[0057] For tracking purposes, it is important that the tracking maintains correct polarisation alignment (with respect to TE21c) or that a circularly-polarised TE21 tracking signal be used. If a circularly polarized TE21 signal is used, the arrangement indicated in Figs. 9a-d will transduce both the right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP), but will not be able to distinguish between the two. Using an 8 -slot TE21 coupler, the TE21s and TE21c may be separately summed and compared to derive the pointing error in elevation and azimuth. Again, according to the art, it is mentioned that if circular polarisation is used, then only one of the TE21 modes is necessary, in combination with TE 11. Note that the turnstile OMT proposed within this document maintains phase and amplitude balance for TE11c and TE1 Is, and circular polarisation may be used for TE11 and RHCP and LHCP can be distinguished for TE11. Only one TE21 mode is necessary fortracking when circular polarization is used. That said, many existing systems appear to use couplers that recover both TE21c and TE21s. In the art, there are single-mode TE21 couplers in use for satellite tracking purposes. This would be the built-in functionality offered by theembodiment of Figs. 9a-d. As a result, a separate TE21 mode coupler can be eliminated from the waveguide network, along with any adverse effects of the coupling slots in conventional designs, provided that coupling slots may be carefully design so as to not affect the TE11 signal.

[0058] According to an embodiment, the performance of the OMT maintains full rectangular waveguide bandwidth for the fundamental TE11 signals, and the tracking beacon frequency can be set accordingly in the upper quarter of the band where the TE21 is no longer cut-off, as illustrated for W-band in Fig. 9d. Note that the desired TE11 signal modes remain unaffected since they are each orthogonal to the TE21 by definition. Finally, the design can be scaled to other waveguide bands, but shown here for W-band. Conveniently, all three output waveguide ports are downward facing for integration.

[0059] The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical fiinction(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustration, and combinations of blocks in the block diagrams and / or flowchart illustration, can be implemented by special purpose hardware -based systems that perform the specified functions or acts or carry out combinations of special purpose hard-ware and computer instructions.

[0060] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as critical, required, or essential features or elements of any or all the claims. As used herein, the terms "comprises," "comprising," or any other variations thereof, are intended to cover a nonexclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, no element described herein is required for the practice of the disclosure unless expressly described as "essential" or "critical."

[0061] The preceding detailed description of exemplary embodiments of the disclosure makes reference to the accompanying drawings, which show the exemplary embodiment by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that logical and mechanical changes may be made without departing from the spirit and scope of the disclosure. For example, the steps recited in any of the method or process claims may be executed in any order and are not limited to the order presented. Thus, the preceding detailed description is presented for purposes of illustration only and not of limitation, and the scope of the disclosure is defined by the preceding description, and with respect to the attached claims.

[0062] REFERENCES[1] J. Hubmayr, J. Austermann, J. Beall, J. Connors, S. Duff, J. McMahon, “Tolerance analysis of octave bandwidth millimeter-wave planar orthomode transducer,” in Proc. SPIE 12190, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI, 121901K (31 August 2022)[2] Shohei Ezaki and Wenlei Shan, “Development of Through-Substrate via Process for Silicon-Based Monolithic Microwave Integrated Circuits SIS Mixer”, IEEE Trans. Appl. Superconductivity, vol.33, no.5, pp.1-5, 2023.[3] J Wenninger, F. Boussaha, C. Chaumont, B.-K. Tan and G. Yassin, “Design of a 240 GHz on-chip dual-polarization receiver for SIS mixer arrays,” Supercond. Sci. Technol., vol. 36, Apr. 13, 2023.[4] A. Gonzalez and K. Kaneko, “Practical Aspects of the Design and Fabrication of High-Performance (sub)mm-Wave Dual-Ridged Waveguide Orthomode Transducers, and Application to a 205-280 GHz Design,” IEEE Trans. Terahertz Sci. Technol., vol.13, no. 6, pp. 587-593, Nov. 2023, doi: 10.1109 / TTHZ.2023.3308057.[5] C. Stoumpos, J. Duran-Venegas, T. Pierre and M. Garcia-Vigueras, “Orthomode Transducers in Additive Manufacturing for Broadband and High-Power Applications,” in 17th European Conference on Antennas and Propagation (EuCAP), Florence, Italy, Mar. 23-26, 2023, pp. 1-5, doi: 10.23919 / EuCAP57121.2023. 10132846.[6] D. Henke, N. Kelly, K. Marshall, I. Wevers and L. B. G. Knee, “A Turnstile Quad- Ridge Orthomode Transducer (OMT) for Octave-Bandwidth Receiver Front-Ends (24- 51 GHz),” IEEE Trans. Microw. Theory Tech., vol. 71, no. 11, pp. 4906-4921, Nov. 2023, doi: 10.1109 / TMTT.2023.3267544.[7] N. Fonseca, “Very Compact Waveguide Orthomode Transducer in the KBand for Broadband Communication Satellite Array Antennas” Sensors, vol. 23, no. 2, Jan. 9, 2023. https: / / doi.org / 10.3390 / s23020735[8] A. Navarrini and R. Plambeck, “A Turnstile Junction Waveguide Orthomode Transducer,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 1, pp. 272-277, Jan. 2006.[9] D. Henke and S. Claude, “Minimizing RF Performance Spikes in a Cryogenic Orthomode Transducer (OMT),” IEEE Trans. Microw. Theory Tech., vol. 62, no. 4, pp. 840-850, Apr. 2014.

[0010] D. Henke and C. Groppi, “Focal Plane Array Concept for ALMA 2030,” ALMA- FED 2021: ALMA Front End Development, Zenodo, Oct. 1, 2021. https: / / doi.org / 10.5281 / zenodo.5548445

[0011] R. Hesper, A. Khudchenko, A. M. Baryshev, J. Barkhof and F. P. Mena, “A High- Performance 650-GHz Sideband-Separating Mixer-Design and Results,” IEEE Trans. Terahertz Sci. Technol., vol. 7, no. 6, pp. 686-693, Nov. 2017.

[0012] N. J. G. Fonseca, “Compact waveguide orthomode transducer without crossings,” in 13th Int. Symp. Antenna Technol. Appl. Electromagn., Banff, AB, Canada, 2009, pp. 1-4.

[0013] B. Hozouri, “Orthomode transducer,” Worldwide patent W02008008702A2, Jan. 17, 2008.

[0014] D. Henke and S. Claude, “Design of a 70-116 GHz W-band turnstile OMT,” in 44th European Microw. Conf., Rome, Italy, 2014, pp. 456-459.

[0015] S. -G. Park, H. Lee and Y. -H. Kim, “A turnstile junction waveguide orthomode transducer for the simultaneous dual polarization radar,” in Asia Pacific Microw. Conf., Singapore, pp. 135-138, Dec. 7-10, 2009.

[0016] A. Tribak, J. L. Cano, A. Mediavilla and M. Boussouis, “Octave Bandwidth Compact Turnstile-Based Orthomode Transducer,” IEEE Microw. Wireless Compon. Lett., vol. 20, no. 10, pp. 539-541, Oct. 2010.

[0017] J. L. Cano, A. Tribak, R. Hoyland, A. Mediavilla, and E. Artal, “Full band waveguide turnstile junction orthomode transducer with phase matched outputs,” Int. J. RF Microw. Comput.-Aided Eng., vol. 20, no. 3, pp. 333-341, May 2010.

[0018] P. V. Prasannakumar, M. A. Elmansouri and D. S. Filipovic, “Wideband Decoupling Techniques for Dual-Polarized Bi-Static Simultaneous Transmit and Receive Antenna Subsystem,” IEEE Trans. Antennas Propag., vol. 65, no. 10, pp. 4991- 5001, Oct. 2017.

[0019] B. Du, J. Wang, Z. Meng and L. Xie, “High sensitivity feed systems for the Square Kilometer Array Dish,” in Cross Strait Quad-Regional Radio Science and Wireless Technology Conference (CSQRWC), Taiyuan, China, pp. 1-3, Jul. 18-21, 2019.

[0020] X. Jun, T. Geer ,L. Hongmei, D. Tongyu, and Y. Qiubo, “A Dual -Polarized Hom Antenna Covering Full Ka-Band Using Turnstile OMT,” Front. Phys., vol. 10, pp. 1-6, Apr. 4, 2022.

[0021] G. Moorey, R. Bolton, A. Dunning, R. Gough, H. Kanoniuk and L. Reilly, “A 77-117 GHz cryogenically cooled receiver system for radioastronomy,” in Proc. Workshop Appl. Radio Sci., February 15-17, 2006.

Claims

CLAIMS:

1. An orthomode transducer comprising: a waveguide input; a first branch pair comprising a first waveguide defining a first port and a second waveguide defining a second port, wherein the first branch pair is associated with a first polarization; a second branch pair comprising a third waveguide defining a third port and a fourth waveguide defining a fourth port, wherein the second branch pair is associated with a second polarization; a first magic-tee combiner configured to absorb trapped modes of the first branch pair through a first sum port; and a second magic-tee combiner configured to absorb trapped modes of the second branch pair through a second sum port.

2. The orthomode transducer of claim 1 , wherein the first branch pair and the second branch pair have an identical electrical path length.

3. The orthomode transducer of claim 1 , wherein the first branch pair and the second branch pair have differing electrical path lengths.

4. The orthomode transducer of claim 1 , wherein the first branch pair and the second branch pair are asymmetric.

5. The orthomode transducer of claim 1, wherein the first magic -tee combiner and the second magic-tee combiner mitigate layer misalignment by absorbing the trapped modes.

6. The orthomode transducer of claim 1, wherein the first magic -tee combiner comprises a first input waveguide comprising a first input signal port and first signal output port, whereby the first input signal port is coupled to the first port of the orthomode transducer.

7. The orthomode transducer of claim 6, wherein the second magic-tee combiner comprises a second input waveguide comprising a second input signal port and second signal output port, whereby the second input signal port is coupled to the second port of the orthomode transducer.

8. The orthomode transducer of claim 7, wherein the first sum port comprises a first termination absorber.

9. The orthomode transducer of claim 8, wherein the first sum port and the first termination absorber recover signals 0° phase difference thereby capturing and terminating the first branch length imbalances.

10. The orthomode transducer of claim 7, wherein the second sum port comprises a second termination absorber.

11. The orthomode transducer of claim 10, wherein the second sum port and the second termination absorber recover signals 0° phase difference thereby capturing and terminating the second branch length imbalances.

12. The orthomode transducer of any one of claims 1 to 11, wherein the first magic- tee combiner and the second magic-tee combiner mitigate unequal power recombination through the first branch pair and the second branch pair.

13. The orthomode transducer of any one of claims 1 to 12, further comprising a first noise injection hole coupler coupled to the first magic-tee combiner.

14. The orthomode transducer of any one of claims 1 to 12, further comprising a second noise injection hole coupler coupled to the second magic-tee combiner.

15. The orthomode transducer of any one of claims 1 to 14, wherein the orthomode transducer is operational in a Q-band frequency range.

16. A magic-tee combiner comprising: a first input waveguide comprising a first output port; a second input waveguide comprising a second output port; a sum port; a termination absorber associated with the sum port.

17. The magic-tee combiner of claim 16, wherein the first input waveguide comprises a first input signal port and first signal output port.

18. The magic-tee combiner of claim 16, wherein the second input waveguide comprises a second input signal port and second signal output port.

19. The magic-tee combiner of any one of claims 16 to 18, wherein the sum port and the termination absorber recover signals 0° phase difference thereby capturing and terminating the first branch length imbalances.

20. The magic-tee combiner of any one of claims 16 to 18, wherein whereby the sum port and the termination absorber suppress trapped modes and signal drops.

Images