The results of numerical investigation of coaxial quad-ridged waveguides’ eigenmodes of two configurations (with ridges on inner or on outer perfectly conducting circular cylinder) for different cross-section dimensions are presented. In particular, dependences of cutoff wave numbers on geometrical dimensions ratios for the first three TE modes and for the first TM mode have been investigated and transversal electric field components distributions for these eigenmodes and for theTEM mode have been obtained. Besides, the optimization of coaxial quad-ridged waveguides has been carried out at antiphase excitation in order to provide maximal single-mode operation frequency band for the first TE mode. As a result two optimal configurations of coaxial quad-ridged waveguides with single-mode operation bandwidth ratios 4.6:1 have been designed. It has been defined that the waveguide with the ridges at the inner conducting circular cylinder has smaller cross-section dimensions at the fixed single-mode operation frequency band. Calculations are conducted utilizing the mathematical models obtained in [1] by the integral equations technique taking correctly into account of singular behavior of the field at ridges’ edges. Reliability of the results obtained is confirmed by the calculations based on finite difference time domain technique, which is implemented in the software package CST Microwave Studio at mesh size λ/100.

Eigenmodes of coaxial quad-ridged waveguides. Numerical results

In this paper we present the design and simulated characteristics of a novel high performance coherent orthomode transducer to be used in dual-wideband coaxial horn feeds of reflector antennas with polarization diversity or polarization processing of radio signals. The main stages of the development process are described. For both polarizations the simulated VSWR is less than 1.06 within both operating frequency bands (3.4–4.2 GHz and 10.7–12.8 GHz). Calculated crosspolar isolation is higher than 70 dB. Simulated differential phase shift between the output signals with orthogonal linear polarizations is less than 1° in both operating frequency bands.

Novel high performance coherent dual-wideband orthomode transducer for coaxial horn feeds

The electrodynamics eigenmodes boundary problems’ solutions for the eigenmodes of coaxial quad-ridged waveguides are presented. These solutions have been obtained by integral equations technique utilizing the proposed system of orthogonal basis functions, which take correctly into account singular behavior of the field at the ridges’ edges. The formulas obtained provide possibilities to calculate cutoff wave numbers and electric and magnetic fields distributions for TEM, TE and TM modes in the presence of the ridges either on the inner or on the outer conducting cylinder. Analysis of the dependence of numerical solutions convergence for cutoff wave numbers on the number of basis functions and partial modes has been carried out. It has been shown that for calculation of cutoff wave numbers with residual error less than 0.1% it is enough to utilize the 7 proposed orthogonal basis functions and the 21 partial modes.

Eigenmodes of coaxial quad-ridged waveguides. Theory

This research presents the design and main electromagnetic characteristics of the novel compact microwave waveguide polarizer. The developed device's structure is based on a circular waveguide and anti-phase conducting posts located in it. The application of a circular waveguide instead of a square one allowed simple integration of a polarizer with corrugated horn antennas. The obtaining of required phase difference using a posts-based design provides the possibility of fine tuning of the developed circular waveguide polarizer after its manufacturing process. In addition, simultaneous adaptive operation at orthogonal circular and linear polarizations is available in the antenna system including a polarizer with posts. An automatic control of posts height must be applied in a waveguide in order to provide this option. Numerical simulation, optimization, manufacture and measurements of the polarizer's characteristics were carried out in the operating band 7.4-8.5 GHz. Measured characteristics proved that the suggested circular waveguide polarizer provides good matching and polarization performance. Developed circular waveguide polarizer can be integrated in corrugated horn antenna systems and applied in modern weather radars and satellite information systems.

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Circular Waveguide Polarizer for Weather Radars and Satellite Information Systems

The increase of information volumes, which are transmitted in modern satellite telecommunication systems, requires the development of new signal processing technologies, microwave devices, antenna systems and methods of their analysis. In particular, polarization-adaptive antennas are widely used for this purpose. Such antennas provide the possibility to transmit and receive radio signals with polarization of any type. Polarization processing devices of antenna systems must provide low levels of voltage standing wave ratio of waves with horizontal and vertical linear polarizations and high crosspolar discrimination simultaneously. Therefore, there is the need to improve designs and methods of analysis of modern polarization processing devices.
Polarizers based on a square waveguides with irises are widely used due to the simplicity of their design and manufacturing by milling technology. The article considers a new mathematical model of waveguide polarizers with reactive irises. For the example of model application we have simulated and optimized a polarizer based on a square waveguide with four irises. A mathematical model of this waveguide polarizer was developed based on the description of microwave devices and their elements by wave scattering and transmission matrices. The general scattering matrix of the polarizer has been obtained analytically. The main electromagnetic characteristics of the polarizer were determined based on the elements of this matrix. As a result, we have analyzed main characteristics of the model, including differential phase shift, voltage standing wave ratio for vertical and horizontal polarizations, axial ratio and crosspolar discrimination. The optimization of the characteristics of a polarizer has been performed using the developed mathematical model and a software based on the finite integration technique. The optimal characteristics and geometrical sizes of the structure are in good agreement, which proves the correctness of the developed mathematical model of square waveguide iris polarizers.

Equivalent Microwave Circuit Technique for Waveguide Iris Polarizers Development

This paper covers results of full wave analysis and optimization of electrical performance of key components of the multimode circularly polarised X-band monopulse feed, namely, the wideband circular corrugated horn supporting propagation of hybrid modes HE11 and HE21, the wideband multiholes directional coupler of orthogonal modes H21 and the wideband compact septum polariser. Also, results of design and laboratory testing in anechoic chamber of the whole manufactured monopulse feed prototype in the frequency range 7.7-8.5 GHz are presented. The simulated and measured results show that the developed feed has excellent sum and difference channels radiation patterns, high isolation between these channels and high crosspolar discrimination. Therefore the proposed feed can be considered as a promising candidate for application in ground station reflector antennas to provide capability of high accuracy autotracking and reception of high data rate information in both right hand circular polarisation (RHCP) and left hand circular polarisation (LHCP) from low Earth orbit (LEO) satellites.

Circularly Polarised X-Band H11- and H21-Modes Antenna Feed for Monopulse Autotracking Ground Station : Invited Paper

Copolar and crosspolar radiation as well as matching characteristics of a novel dual-band coaxial hybrid-mode feed horn with partial dielectric loading [1] for reflector antennas have been numerically and experimentally investigated. In comparison with dual-band corrugated horns this horn has higher crosspolar level, but provides larger band separation and rather good electrical performances over a wide frequency range (20% and more) within each operational frequency band. Furthermore, the main concept of the coaxial feed system can be easily extended for multi-band cost-effective applications in reflector antennas with polarization diversity.

Yuriy A. Ovsianyk

Papers

Circularly Polarised X-Band H11- and H21-Modes Antenna Feed for Monopulse Autotracking Ground Station : Invited Paper

Radiation and matching characteristics of a novel dual-band dielectric loaded coaxial horn