Waveguide Orthomode Transducer Research Articles

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

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

A 3-D Printed Lightweight Miniaturized Dual-Band Dual-Polarized Feed Module for Advanced Millimeter-Wave and Microwave Shared-Aperture Wireless Backhaul System Applications

A 3-D-printed lightweight miniaturized dual-band dual-polarized feed module of wireless backhaul systems consisting of a dual-band air-filled waveguide orthomode transducer (OMT) and a shared-aperture conical horn radiator is investigated. The OMT operating in both Ku- and E-bands with a large frequency ratio is realized by combining the turnstile-junction-type and Bøifot-junction-type OMTs sharing a common-mode-composite coaxial port. A design method of the dual-band OMT considering the requirement for a self-supporting geometry in metallic 3-D printing is presented, so that its compact configuration that is difficult to fabricate by traditional milling technology can be fulfilled conveniently in a whole piece with the use of commercial 3-D printing facilities. A millimeter-wave horn with a small radiation aperture is embedded into a larger aperture of a microwave horn. A proper longitudinal offset between them is introduced to guarantee promising radiation characteristics of the shared-aperture scheme in the two bands. By connecting the OMT with the radiator, the proposed dual-band dual-polarized feed module with a weight of only 100 g is manufactured and measured. Excellent performance, involving the wide bandwidths of 46.7% and 31.2% at microwave and millimeter-wave frequencies, a high isolation of almost larger than 40 dB, a high radiation efficiency of about 90%, and stable dual-polarized radiation patterns with low cross polarizations, is confirmed experimentally. Benefitted from the geometric and operating merits, the feed module would be attractive for applications in advanced millimeter-wave and microwave shared-aperture wireless backhaul systems.

Very Compact Waveguide Orthomode Transducer in the K-Band for Broadband Communication Satellite Array Antennas

A very compact waveguide orthomode transducer (OMT) is described in this paper. The design is characterized with a twofold rotationally symmetric cross-section in the probing area, adapted from a side-coupling OMT design, simultaneously enabling low port-to-port coupling and high cross-polarization discrimination (XPD) over a fractional bandwidth of about 15-20%. Compared to previously reported compact waveguide OMTs, the proposed design is simpler, thus facilitating its manufacture at millimeter-wave frequencies. The concept is demonstrated with a design in the K-band for a broadband communication satellite downlink over the frequency band of 17.3-20.2 GHz. For test purposes, transitions to standard waveguide WR42 are included, and the OMT is assembled with a conical horn antenna. The measured reflection and coupling coefficients are below -19.5 dB and -22.9 dB, respectively, over the nominal bandwidth, and they are in good agreement with the simulation's results. The on-axis XPD, measured in an anechoic chamber, is better than 30 dB over the nominal bandwidth, which is also in line with simulations. The proposed waveguide OMT may be designed to fit in a lattice below one wavelength at the highest operating frequency, which is desirable for dual-polarized closely spaced array antennas in low and medium Earth orbit communication satellite systems. The simple mechanical design of the proposed OMT makes it particularly appealing for additive manufacturing techniques, as demonstrated with a variant of the design having folded single-mode waveguides, which preserves the RF properties of the original design.

Square Waveguide Cavity for Complex Permittivity and Permeability Measurement by Perturbation Method Without Repositioning

This article presents a novel configuration for the simultaneous complex permittivity and permeability determination with only a single sample placement inside the resonant cavity. The proposed structure incorporates two waveguide orthomode transducers (OMTs) and a square cavity. The square cavity is designed to overcome the limitation of permeability measurement by the rectangular cavity perturbation method. These components allow the product of two orthogonal transverse electric (TE) resonant modes (TE10L and TE01L) with the same cutoff frequencies. Based on Maxwell equations and perturbation theory, new relations are developed to characterize the complex permeability of specimens at TE01L modes. The proposed structure eliminates the main drawbacks of previous studies such as depolarization effect of partial-height samples, radiation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> -plane sample hole, need to apply the sample holder and precision positioner, multistate positioning, iterative calculations, extra calibration process, and employing complicated mathematical equations. The proposed configuration was designed using CST Microwave Studio (MWS) and ANSYS high-frequency structural simulator (HFSS) and then manufactured and measured. The operating frequency has been selected from 7.5 to 12.5 GHz. Good agreement is achieved between measurement and simulation. The performance of the developed structure was verified by measuring the material characteristics of bar-shaped dielectric and magneto-dielectric specimens and compared with other studies.

Computer‐aided development and experimental investigation of a double‐ridged orthomode transducer for modern satellite and space communication systems

This article presents results of development, optimization, and experimental measurements of electromagnetic characteristics of a wideband orthomode transducer for satellite and space communications. Analyzed design of the transducer is based on a double-ridged waveguide junction, which allows to obtain high level of discrimination of fundamental electromagnetic modes with perpendicular linear polarizations. Numerical modeling of the designed microwave waveguide orthomode transducer was performed by an effective finite elements method in the frequency domain. Optimization of the structure elements allowed to obtain high quality of matching and to improve the isolation between orthogonal polarizations simultaneously. To optimize the electromagnetic performance of the developed orthomode transducer a trust region method, which previously demonstrated its effectiveness for the improvement of electromagnetic characteristics of waveguide polarization converters, was applied. Experimental measurements of all scattering parameters of an antenna feed system, which included a designed orthomode transducer and a corrugated horn, were performed for the verification of simulated results. Results of computer-aided modeling and of measurements are in agreement. Measured good matching and high level of isolation between orthogonal polarizations confirm effective electromagnetic performance of the developed orthomode transducer. Designed wideband waveguide device can be applied in modern microwave antenna systems operating simultaneously at two linear or circular polarizations of electromagnetic waves.

Feasibility Study of a W-Band Multibeam Heterodyne Receiver for the Gregorian Focus of the Sardinia Radio Telescope

We report on the feasibility study of a W-band multibeam heterodyne receiver for the Sardinia Radio Telescope (SRT), a general purpose fully steerable 64-m diameter antenna located on the Sardinia island, Italy, managed by INAF (“Istituto Nazionale di Astrofisica,” Italy). The W-band front-end is designed for the telescope Gregorian focal plane and will detect both continuum and molecular spectral lines from astronomical sources and radio emission from the Sun in the 3 mm atmospheric window. The goal specification of the receiver is a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> focal plane array operating in dual-linear polarization with a front-end consisting of feed-horns placed in cascade with waveguide Orthomode Transducers (OMTs) and LNAs (Low Noise Amplifiers) cryogenically cooled at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx $ </tex-math></inline-formula> 20 K. The instantaneous FoV (Field of View) of the telescope is limited by the shaping of the 64-m primary and 7.9-m secondary mirrors. The cryogenic modules are designed to fit in the usable area of the focal plane and provide high-quality beam patterns with high antenna efficiency across the 70 – 116 GHz Radio Frequency (RF) band. The FoV covered by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> array is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.15\times 2.15$ </tex-math></inline-formula> arcmin <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , unfilled, with separation between contiguous elements of 43 arcsec. Dual-sideband separation (2SB) down-conversion mixers are designed to be placed at the cryostat output and arranged in four four-pixel down-conversion modules with 4 – 12 GHz Intermediate Frequency (IF) bands (both Upper Side Band and Lower Side Band selectable for any pixel and polarization). The receiver utilizes a mechanical derotator to track the parallactic angle.

Novel Double-Ridged Waveguide Orthomode Transducer for mm-Wave Application

This letter presents our study on a millimeter wave (mm-wave) orthomode transducer (OMT) based on novel double-ridged waveguide junction. By reducing the length of ridges in the square waveguide, the ridge width of proposed junction is about three times wider than that of conventional junction. This benefits the fabrication and mechanical performance of double-ridged waveguide OMT in the higher mm-waveband or terahertz band. The simulated reflection coefficients for both orthogonal modes are less than −20 dB over 37% bandwidth. As practical application, an E-band OMT based on the novel junction is fabricated. A smooth-horn is integrated with the OMT as a dual-polarized antenna. The measured results show that reflection coefficients less than −15 dB, isolation better than 39 dB, and cross-polarization discrimination (XPD) higher than 23 dB are achieved from 71 to 86 GHz.

A Compact Asymmetric Waveguide Orthomode Transducer for Millimeter-Wave Applications

A compact asymmetric waveguide orthomode transducer (OMT) with broad bandwidth and high isolation is presented in this letter. A novel combined transition-bending structure is proposed within the common arm in the design of the OMT branching T-junction. It implements the E-/H-plane 90° waveguide bends and the square-to-rectangular waveguide transition for both polarization sidearms. Its multiple roles help to reduce the geometry discontinuities and improve the matching bandwidth. The measurements demonstrate that the OMT achieves higher than 50 dB isolation level between the two modes and better than 18 dB return loss from 30.3 to 36.3 GHz (18%). Furthermore, the isolation level is typically 60 dB over 50% of the operation bandwidth. The insertion loss of each polarization is below 0.23 dB for a single OMT. The overall size of the OMT functional section is reduced to 1.55 λ₀x 1.45 λ₀x 0.78 λ₀.

Two-Probe Waveguide Orthomode Transducer With Twofold Rotational Symmetry

A novel (patent pending) waveguide orthomode transducer (OMT) design is presented. The use of a common waveguide cross section with twofold rotational symmetry is proposed to mitigate the typical drawbacks of a two-probe OMT geometry. In particular, the cross-polarized electric field component may be reduced by introducing a twofold rotationally symmetric cross-sectional design with slant axes in the reference frame defined by the directions of the two coupling probes. Interestingly, it is also demonstrated that this solution may be used directly in the probing area to either reduce the cross-polarized field component or to reduce the probe-to-probe coupling. The aspect ratio of the required asymmetric section is close to 1, and the design has limited impact on other signals when used as an orthomode junction (OMJ) in multifrequency feed systems. Two designs, one with dual-linear operation and one with dual-circular operation, are optimized in K-band (17.7–20.2 GHz). Good agreement is found between simulated and measured data, validating the concept. This solution is of interest for the design of future multifrequency feed systems onboard broadband communication satellites.

High-Performance Wideband Double-Ridged Waveguide OMT for the 275–500 GHz Band

In this article, a high-performance wideband double-ridged waveguide orthomode transducer (OMT) for the 275-500 GHz band has been designed, fabricated, and tested. Such wideband performance would allow to cover two full RF bands in radio astronomy, 275-373 GHz and 385-500 GHz, with a single receiver, allowing for additional science cases and simplified operations. Successful fabrication of prototypes by direct machining in two split blocks and successful testing prove the readiness for complex fabrication of OMT components in this frequency range. The reported performance of our prototype OMT is to our knowledge the best at sub-mm wavelengths over such as wide bandwidth.

Fixed and Steerable Beam Dual-Polarized Lens Antenna With High Tx to Rx Isolation

A co-polarized, co-channel simultaneous transmit and receive (STAR) antenna system utilizing a two-layer spherically stratified lens with nominal directivity of 24.3 dBic is demonstrated in the 27–29 GHz frequency band. The STAR operation is achieved with a WR28 waveguide-implemented balanced circulator beam forming network (BC-BFN), which relies on two 90° hybrids and two circulators along with antenna symmetry to cancel the circulator leakages and achieves theoretically infinite isolation between the transmit and the receive ports. The sensitivity of the BC-BFN to alignment imperfections is studied and it is found to be robust to this kind of error. To comply with the BC-BFN’s symmetry requirements, a highly symmetric WR28 waveguide orthomode transducer (OMT) is developed. Transmitted (Tx)/receiver (Rx) isolation of 30 and 34 dB is measured with and without the lens, respectively; indicating acceptable impact of the lens on the system isolation. To demonstrate the STAR with the beam steering, the proposed configuration is modified into a mechanically rotated half spherical lens over a ground plane. The experiments show that the isolation of the rotating half-lens system degrades when compared to the full-lens counterpart due to the break of the geometrical symmetry. However, respectable isolation greater than 27 dB and high-quality circularly polarized radiation patterns are still maintained over the operational bandwidth.

A Q‐band compact high‐performance double‐ridged orthomode transducer

In this article, a Q-band compact waveguide orthomode transducer (OMT) based on a stepped double-ridged waveguide is presented. By using a symmetrical structure, good output return losses of above 20 dB are obtained from 35 to 50 GHz. In particular, the measured insertion losses are as low as 0.15 to 0.4 dB over the entire band for both polarization channels with an improved assembly configuration. The measured cross-polarization levels are well below −37 dB, while the circular-polarized output port isolation is less than −20 dB combined with a feed horn and a differential phase shifter. The developed OMTs have been used in a Q-band two-beam cryogenic receiver on the Tianma Radio Telescope, contributing only 1 to 2 K noise at an operating temperature around 20 K.

An x‐band waveguide orthomode transducer with integrated filters

AbstractThis letter presents a novel waveguide orthomode transducer (OMT) with integrated filters. Resonator‐based bandpass filters are used for the two channels forming a duplexing OMT. As an example, a two‐channel duplexing OMT is designed with channels at 9.9‐10.1 GHz and 10.9‐11.1 GHz. A good filter response with 20 dB return loss is achieved for both the channels. The upper and lower bands are isolated to −80 dB due to the filtering elements and a transmission zero. This new multifunction compact filter‐OMT design leads to the size reduction and improved inter‐band isolation. A CNC machined waveguide OMT is demonstrated and its performance is verified with excellent agreement between the electromagnetic wave (EM) simulation and measured results.

Compact wideband bowtie dipole orthomode transducer

AbstractA compact wideband orthomode transducer (OMT) with an octave bandwidth is proposed for a 0.56‐1.12 GHz receiver system in the five hundred meter aperture spherical radio telescope. The OMT operates in a cryostat at a temperature of 70 K and therefore it is critical to minimize its dimension while insuring good electrical properties. The complete OMT comprises 2 bowtie dipoles orthogonally arranged in a circular waveguide. Because of the innovative structure, competing modes, TM01 TE21, and TE01, have been effectively suppressed, and the bandwidth of the dominate mode TE11 has achieved to 2.08:1. The final optimized OMT has a length of 300 mm, shorter than a half of the popular quardruple‐ridged waveguide OMT. Measurements at room temperature agree well with simulation results, with a reflection coefficient below −10 dB for both polarizations and cross‐coupling levels of −30.5 dB over the whole required frequency range.

The first measurement of plasma density by means of an interfero-polarimetric setup in a compact ECR-plasma trap

This paper presents the first measurement of plasma density by a K-band microwave polarimetric setup able to measure the magnetoplasma-induced Faraday rotation in a compact size plasma trap. The polarimeter, based on rotating waveguide OMTs (OrthoModeTransducers), has been proven to provide reliable measurements of the plasma density even in the unfavorable conditions λp≈ Lp≈ Lc (being λp, Lp and Lc the probing signal wavelength, the plasma dimension and the plasma chamber length respectively) that complicates the measurements due to multi-patterns caused by reflections of the probing wave on the metallic walls of the plasma chamber. An analysis method has been developed on purpose in order to discriminate the polarization plane rotation due to magnetoplasma Faraday rotation only, excluding the effects of the cavity resonator. The measured density is consistent with the previous plasma density interferometric estimations. The developed method is a powerful tool for probing plasmas in very compact magnetic traps such as Electron Cyclotron Resonance Ion Sources and for in-plasma β-radionuclides' decay studies.

Design of a Compact Wideband Feed Cluster With Dual-Polarized Sum- and Difference-Patterns Implemented via 3-D Metal Printing

A compact wideband feed cluster with dual-polarized sum- and difference-patterns is proposed in this paper. By utilizing dual-ridged waveguide orthomode transducers (OMTs) and wideband Magic-Tees, a highly integrated feed cluster with wide operational bandwidth, dual-polarization, and good isolation is developed. The feed cluster consists of five horns with square apertures arranged in a cross. A total of five OMTs and four Magic-Tees are used to construct the necessary comparator network to achieve sum- and difference-patterns in both polarizations. All components and the interface between them are designed with the three-dimensional metal printing in mind. A prototype is fabricated and the measured results show that the isolation between the orthogonal polarizations is better than 50 dB throughout the operational bandwidth of 10.5 to 14.5 GHz. The null-depths of the difference-patterns are better than –30 dB. The proposed feed cluster is practically useful in a variety of satellite-based applications.

Double-Ridged Waveguide Orthomode Transducer (OMT) for the 67–116-GHz Band

A high-performance low-loss high-reflection-loss compact double-ridged waveguide orthomode transducer (OMT) for the 67–116 GHz band has been designed, fabricated, and tested. The focus in the design has been to achieve the best possible performance while keeping the design compact and fabrication as simple as possible. The designed OMT is based on a double-ridged waveguide Boifot junction followed by a main arm with an E-plane bend, and two side arms which are combined into a Y-junction. Wideband performance has been achieved by careful control of the waveguide width at the waveguide junction, and by the use of a variable width septum. The design is very compact and can be fabricated by conventional computer numerical control (CNC) milling techniques in two split blocks. The output waveguides are standard WR-10 rectangular waveguides. Prototype OMTs have been fabricated and tested with good agreement with simulations. The measured insertion loss is around 0.15 dB, the reflection loss is better than 23 dB, and isolation and cross-polarization are lower than – 45 dB at all frequencies. This OMT is intended to be used in cryogenic low-noise receivers for radio astronomy. To the extent of our knowledge, this is the best reported performance for an OMT over a 55% fractional bandwidth at W-band frequencies.

A Simple Coaxial to Circular Waveguide OMT for Low-Power Dual-Polarized Antenna Applications

A simple design for an orthomode transducer (OMT) is proposed for low-power antenna applications, such as receiver antennas as well as laboratory testing antennas. The design exploits detuning pins to enable enlarging the higher order mode-free bandwidth in an asymmetric configuration without compromising the port isolation. The design guidelines are presented for a scalable design. Moreover, the design is optimized to utilize all the single-mode operation bandwidth of the circular waveguide, covering the satellite communications band in North America (i.e., from 11.7 to 14.2 GHz). The presented OMT features a port coupling level below −34 dB. The measurement results are in a very good agreement with the full-wave analysis simulations.

A new interferometric/polarimetric setup for plasma density measurements in compact microwave-based Ion Sources

A K-band (18.5÷26.5 GHz) microwave interferometry/polarimetry setup, based on the Frequency-Modulated Continuous-Wave (FMCW) method, has been developed at INFN-LNS under the VESPRI project. The interferometer has been proven to provide reliable measurements of the plasma density even in the extreme unfavorable conditions λp≃ Lp≃ Lc, being λp, Lp and Lc the probing signal wavelength, the plasma dimension and the plasma chamber length respectively. The VESPRI setup has been therefore upgraded with a rotating polarimetric system based on waveguide OMTs (OrthoModeTransducers) for the measurement of the magnetoplasma-induced Faraday rotation. An analysis method has been developed on purpose in order to discriminate the polarization plane rotation due to the plasma only, excluding the effects of the cavity resonator which represents the primary error source on phase angle measurement. Results about the first collected data, showing a significative agreement of the plasma-induced polarization plane rotation with the well-known λ2 law, are hereby presented. The developed method will be a powerful tool for probing plasmas in very compact magnetic traps such as Electron Cyclotron Resonance Ion Sources.

Wideband Decoupling Techniques for Dual-Polarized Bi-Static Simultaneous Transmit and Receive Antenna Subsystem

A wideband, bistatic, and dual-polarized simultaneous transmit and receive antenna subsystem with isolation >60 dB over 6–19 GHz band is demonstrated. The proposed configuration employs two quad-ridge horns fed by a ridge waveguide ortho-mode transducer (OMT) as transmitting (TX) and receiving (RX) antennas. The OMT enables dual-polarized high-power operation for the TX antenna over the entire bandwidth. The TX/RX antennas are flush mounted in a flat ground plane and oriented in D-plane to achieve similar isolation for both polarizations. Different decoupling techniques for increasing isolation between TX/RX antennas are investigated. Specifically, a high capacitive reactance bed of nails is designed to suppress TM polarized surface waves on the metallic ground plane. Moreover, a wideband planar and low-profile high-impedance surface is developed and performance thereof is compared to that of the other considered surfaces. Effect of recessing the RX antenna in an absorber is also discussed. Computational and experimental studies are conducted to demonstrate and validate the performance of the proposed antenna subsystem. Good impedance match, excellent radiation characteristics, and high isolation are achieved.