Broadband substrate-integrated-waveguide six-port applied to the development of polarimetric imaging radiometer

In this paper, a Ka-band broadband substrate integrated waveguide (SIW) six-port technique proposed for polarimetric imaging radiometer is reported. Conventional polarimetric radiometer systems generally consist of a phase discriminator composed of couplers, crossovers and external loads. A six-port is proposed for the first time to replace this discriminator. This approach presents advantages such as lower cost and smaller size. Furthermore, the use of SIW technology allows integrability, compactness and low interference susceptibility. Simulation and measurement results show that the proposed six-port can operate over 20% of bandwidth centered at 34 GHz. To the knowledge of the authors, the achieved bandwidth is higher than other SIW six-ports reported in the literature. To validate the proposed application, the six-port is integrated in a front-end receiver. Measurements show achieved polarimetric channel symmetry of 1 dB and isolation of 29 dB which presents excellent performances. This six-port architecture presents advantages for implementation in passive millimeter-wave remote sensing systems.