Design of a Horizontal and Vertical Polarized Slotted Waveguide Antenna Array for an Airborne Ka-Band Polarimetric Interferometric SAR System

This paper presents the design of a fully polarimetric low-profile antenna array intended for use in a side-looking airborne synthetic aperture radar (SAR) sensor operating at Ka-band. The proposed antenna provides maximum gain of up to 23 dB, a low side lobe level and high cross-polarization suppression values exceeding 38 dB. Furthermore, the proposed antenna demonstrates robust behavior and stable electrical performance in a variety of environmental conditions encountered during the measurement campaigns. The antenna system was designed using slotted waveguide technology, comprising separate antenna arrays for each polarization, which were mounted side by side on the aircraft platform. An appropriate design was developed based on theoretical analysis, considering the specifications of the electrical and mechanical systems. The horizontally polarized antenna consists of four subarrays, each comprising 22 transverse slots cut into the narrow waveguide wall. The alternately placed iris pairs enable radiation. The antenna with vertically polarized radiation is realized through the implementation of four subarrays, comprising 18 longitudinal slots, situated within the broad waveguide wall. Appropriate feeding networks with unbalanced amplitude distributions were designed to feed both arrays. For the horizontally polarized antenna, a conventional H-plane T-junction power divider and a Bethe-hole directional waveguide coupler were used. In contrast, a two-stage H-plane T-junction with a non-uniform amplitude taper was applied for vertical polarization. The proposed design was validated by compact test range measurements, which demonstrated a very good agreement with the simulation results.