Wideband Orthomode Transducer Research Articles

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.

Wideband Dual-Circular-Polarization Antenna With High Isolation for Millimeter-Wave Wireless Communications

This article presents a wideband dual-circular-polarization (dual-CP) antenna with high port isolation based on a grooved-wall CP horn combined with an orthomode transducer (OMT) in the W-band. A pair of grooves on the inner wall of the horn serves as an inbuilt polarizer within the horn antenna, which is capable of generating both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) without any septum. The continuous linearly tapered groove design also allows this multisection grooved-wall CP horn to achieve low reflection coefficients over a wide bandwidth, thereby realizing wideband dual-CP with high port isolation when it is used together with a wideband OMT. A prototype of the proposed dual-CP antenna is designed in simulation and measured in an experiment. The simulated and measured results agree very well, showing that port isolation >32.5 dB over 31.6% bandwidth from 80 to 110 GHz is achieved with axial ratio (AR) < 2.8 dB and reflection coefficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; -20$ </tex-math></inline-formula> dB for both LHCP and RHCP. Rotationally symmetric radiation patterns over the entire operating bandwidth are also observed with a measured gain of 19.6 ± 2 dBic.

Development of wideband orthomode transducers for FAST cryogenic receiver system

This paper describes the design, construction, and performance of the wideband orthomode transducers (OMTs) for the L- (1.2–1.8 GHz), the S- (2–3 GHz) and the P- (0.56–1.12 GHz) band receiver systems of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These OMTs operate at the cryogenic temperature of 70K to reduce their thermal noise contribution to the receiver chains. The development on the FAST L- and S-band quad-ridged waveguide (QRWG) OMTs is carried out based on the theoretical mode analysis. In view of the miniaturization of FAST cryogenic receiver system at P-band, a novel wideband compact bowtie dipole OMT is designed with an octave bandwidth as well as a length of only quarter wavelength. The proposed L-, S- and P-band OMTs are designed and optimized by using Ansys High Frequency Structure Simulator (HFSS), and then manufactured, tested at room temperature. Measurement of FAST cryogenic receiver system noise is also performed with the L-, S- and P-band OMTs installed. The measured results fully comply with the design specifications.

Wideband orthomode transducer for the Square Kilometre Array band4 single pixel feed

The design of a compact wideband orthomode transducer (OMT) for band4 single pixel feed of the Square Kilometre Array (SKA) dish is presented. The geometry of the proposed OMT is based on circular quad-ridged waveguide to obtain wideband characteristics, which consists of a coaxial to quad-ridged waveguide transition and a circular to quad-ridged waveguide tapered transition. By adopting circular quad-ridged waveguide and high-order cosine taper for the ridges, the length of OMT is compact and the levels of higher-order modes generated at the circular waveguide aperture are lower. To verify the OMT performance, a prototype is manufactured and tested using a vector network analyzer. The measured results agree very well with the calculated ones across the frequency range 2.8-5.18 GHz. The tested reflection coefficients are less than –19 dB, the insertion losses are less than 0.25 dB for both polarization channels, and the isolation between two output ports is better than 37.7 dB. It is confirmed that the designed OMT can be satisfied with the requirement of the SKA band4 feed system.

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.

Theory of Polarization-Selective Coupling and Its Application to Design of Planar Orthomode Transducers

With the rapid and continuous development of new generations of wireless technologies and networks, exploring the underutilized millimeter-wave (mm-wave) band becomes inescapable. Polarization diversity has been an essential factor in the performance and capacity enhancement of various wireless systems including cellular networks. Accordingly, the design and development of dual-polarized antenna feeding structures in the mm-wave band is a must. In this paper, a compact wideband orthomode transducer design in the Ka-band is proposed and explored. The proposed architecture and design are based on a forward mode polarization-selective coupling strategy between two unconventional waveguides. These special waveguides are a combination between two types of guiding structure, namely, nonradiative dielectric waveguide and substrate-integrated waveguide. Polarization-selective coupling can be achieved in these structures due to different mechanisms by which orthogonally oriented modes are guided. Theoretical coupling levels of 0 dB are possible in the designed structure. Analytical analysis and design steps are given in detail. This analysis facilitates a complete control on the single-mode operation for each polarization. This control, besides the structure being planar, represents the main advantages of the proposed structure. Finally, a prototype is implemented and measured where an excellent agreement is achieved with the simulation results.

Wide-band orthomode transducers

A summary of the results of a mainly experimental investigation into the development of wideband orthomode transducers (OMTs) is presented. It is shown that satisfactory performance for many applications is possible over bandwidths in excess of 2:1. The wideband return loss and cross-polarization behavior are given where the OMT used is measured in conjunction with a wideband corrugated horn. Two types of OMT are considered: one based on a finline technique and the other on a quad-ridged waveguide geometry. Overall, the latter design gives superior performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>