Double Square Waveguide Directional Coupler for Polarimeter Calibration

Abstract

A novel full-band square waveguide coupler design based on directional couplers which couple the TE10 and TE01 orthogonal modes in a square waveguide is presented. This waveguide coupler is aimed at calibration of polarization receivers. This is composed of a pair of rectangular waveguide directional couplers, which are rotated 90º between them and both are coupled to a main square waveguide through each one of the square section walls. The coupler covers the full frequency band from 10 GHz to 18.9 GHz. It has inherent low cross-polarization, which allows to obtain any known elliptically polarized wave at a square waveguide when a signal is applied to the couplers. The fabricated prototype of this coupler exhibits 31 dB of coupling, with flatness of ±3.8 dB and excellent cross polarization better than 50 dB over the whole band.

Calibration of a Polarimetric Microwave Radiometer Using a Double Directional Coupler

“…For calibration purposes, a broadband double directional coupler (DDC) [35,36] based on a pair of rectangular waveguide directional couplers is mounted in the FEM of the receiver, just behind the antenna. Its insertion loss can be considered constant since it is thermally stabilized.…”

“…This paper presents a built-in calibrator system based on the injection of signals through a broadband double directional coupler (DDC) [35,36] for a polarimetric radiometer working in 10 to 14 GHz and 16 to 20 GHz bands. Any arbitrary polarized wave can be synthesized by an adequate combination of the amplitude and the phase of the injected signals in two separated input ports of the DDC.…”