Wideband Circularly Polarized Horn Antenna With Twisted Ridges of Gielis Super-Formula Contour

This communication presents a wideband singly fed circularly polarized (CP) twisted-ridge horn antenna. This horn antenna has a record-high CP operating bandwidth of 86.3%. The Gielis super formula is used to design the twisted ridges, enhancing the axial ratio (AR) bandwidth. A new waveguide-coax launcher with a ridged back cover is incorporated to boost the impedance bandwidth. Using these new design techniques, the overlapped bandwidth of the CP horn antenna can be increased. For demonstration, a K-band CP twisted-ridge horn antenna is designed, fabricated, and experimentally evaluated. The measured 10-dB impedance bandwidth and 3-dB AR bandwidth are 90.6% (14.6–38.8 GHz) and 88.2% (15.4–39.7 GHz), respectively, giving a very wide overlapped bandwidth of 86.3% (15.4–38.8 GHz). It is found that the measured antenna gain generally increases with frequency in the operating passband.

I. Introduction

The circularly polarized (CP) horn antenna has been widely used in radars, satellite communications, cellular communications, and many other applications. When compared with the linearly polarized (LP) horn antenna, the CP horn antenna is less sensitive to orientation mismatch between the transmitting and receiving devices. It is straightforward to generate CP fields using a pair of orthogonal quadrature feeding sources. However, a singly fed scheme is generally preferred because of its simplicity. Various CP design techniques have been investigated for a singly fed horn, such as septum loading [1], iris loading [2], waveguide/horn deformation [3], and polarizer loading [4]. In general, the bandwidths of the existing singly fed CP horn antennas are limited to 50% [5]. In contrast, an LP horn antenna is capable of achieving a 10:1 bandwidth [6]. In addition, it is challenging to maintain a stable CP radiation pattern across a wide operating bandwidth in singly fed design.