A Septum Polarizer with Integrated Square to Circular Tapered Waveguide Transition

A compact septum polarizer has been designed, manufactured and tested with an integrated square to circular tapered waveguide transition yielding two linearly polarized rectangular waveguide ports and one circularly polarized circular waveguide port. The measured S-parameters and axial ratio (AR) are compared with simulated values from CST Microwave Studio. From 18.5-21.5GHz, the AR is less than 0.6dB, insertion loss is less than 0.25dB, and return loss is greater than 25dB.

I. Introduction

Circularly polarized (CP) antennas are frequently used to increase robustness against fading and polarization misalignment that can affect linearly polarized (LP) antennas. Waveguide polarizers are most suited for use with aperture antennas, and can be separated into two-port and three-port varieties. Two-port waveguide polarizers using irises [1] or dielectric septa [2] have the advantage of single input and output ports, however the polarizer performance is highly dependent on the load of the circularly polarized port and the two should be optimized together. Three-port devices such as waveguide septum polarizers [3]–[6] have the advantages of: generating both senses of CP; and less susceptibility to the load that is placed on the CP port compared to two-port devices.