Design and Feasibility Study of an Orthomode Transducer for the FAST Experiment

Abstract

An Orthomode Transducer (OMT) is a waveguide structure capable of discriminating two independent signals of an orthogonal dominant mode incident upon its common port and to the output port in its fundamental single mode form, therefore enabling the wave to be separated in a passive manner. It is essential that this function is achieved whilst maintaining excellent matching between all electrical ports and a high cross polarisation discrimination and isolation to maintain the required independent signals.The purpose of this thesis is to produce a feasibility study into the production of an Orthomode Transducer for the FAST experiment; china's contribution to the SKA, a global cosmological collaboration which will operate with approximately a 34 percent bandwidth across the L-band (0.95-1.45Ghz). With this in mind, a class three planar turnstile based OMT was investigated, designed and then simulated using Ansofts HFSS 13, a commercially available package.The method presented in the final design was formed through the use of a H-plane bend with an integrated reduced height transition, a compact ninety degree twist, turnstile junction and a Y junction recombining section all individually simulated during the course of this project. This resulted in a highly, compact of total volume of 212mm^3 uniquely planar low loss component; average return losses -28dB, isolation of -49dB and cross polarization of -55dB. All having been recorded across the chosen scaled W-band of 75-115GHz, with a view for this simulated design to be manufactured and analysed using the University of Manchester's VNA operating at this frequency. These measurements represent a sufficient improvement on both the specified thresholds stated in the FAST literature as well as other waveguide designs of similar size.

Date of Award	1 Aug 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Giampaolo Pisano (Supervisor)