A SIW-Based Polarization Rotator With an Application to Linear-to-Circular Dual-Band Polarizers at $K-/Ka$ -Band

A polarization rotator based on substrate integrated waveguide (SIW) is proposed in this article. The rotator is designed as a dual-band, single-layer, frequency-selective surface (FSS) that transmits a wave rotated of 90° with respect to the incident one in one of the two bands maintaining unchanged the polarization in the other one. Other than the design and characterization of the rotator, its application to a linear-to-circular dual-band polarizer is also investigated. To this purpose, the rotator is coupled to a conventional meander line polarizer generating orthogonal circular polarizations (CP) in the two bands. This configuration is useful in SatCom applications where the required high isolation between TX and RX channels is obtained assigning orthogonal polarizations to the two bands. As a design example, a prototype is designed and experimentally validated in the SatCom K-/Ka-bands. Measured performance shows an isolation between the TX and RX channels of more than 35 dB and insertion losses which do not exceed 1.5 dB in the two operating bands.

I. Introduction

Polarization properties of the electromagnetic fields are used in both telecommunications and remote sensing to increase the quality and the capacity of communication links and to extract information from the interaction of electromagnetic waves with the matter. For this reason, it is of a fundamental importance to create techniques and devices capable to manipulate the polarization of electromagnetic waves. Planar polarizers or, more in general, polarization filters, act as frequency-selective surfaces (FSSs) that change the polarization states of an impinging electromagnetic wave re-radiating in output a wave with polarization characteristics different from the one of the incoming waves. Rotators are a class of polarizing surfaces designed to rotate the polarization plane of a linearly polarized wave of a well-defined angle (normally 90°). In the past, many designs of rotators were presented in the literature as reported in [1]. To mention a few of them: wire gratings [2], cascaded meander lines [3], and split-ring resonators [4], [5] were used to realize polarization rotators in different frequency bands. Recently, substrate integrated waveguide (SIW) cavities have been adopted to design FSS and a number of rotators with different performances have been proposed [6]–[10]. In particular, it has been shown that square SIW cavities are suited to design 90° rotators as the same cavity mode can be excited with a different polarization, like the TM₁₂₀ and TM₂₁₀ modes in [6]. In this article, we exploit this concept to design a dual-band SIW rotator that selectively rotates the polarization of the incoming wave in one of the two bands leaving the polarization of the other one unchanged. In particular, we consider the K-/Ka-bands assigned to Satellite Communications (SatCom) for downlink (RX-band), ranging from 19.7 to 20.2 GHz, and for uplink (TX-band), spanning from 29.5 to 30 GHz. The polarization rotator described in this article rotates of 90° the polarization of the input wave in the RX-band only.