Low-Sidelobe-Level Circularly Polarized Short Leaky-Wave Antenna With A-Shaped Element Based on Substrate Integrated Image Guide

In this letter, a low-sidelobe-level (SLL) circularly polarized (CP) leaky-wave antenna with A-shaped elements is proposed based on substrate integrated image guide (SIIG). The A-shaped CP radiating element consists of a horizontal linearly polarized (LP) structure and a vertical LP structure. The horizontal LP wave and the vertical LP wave can be excited by a pair of inclined transversal metal strip patches and a longitudinal metal strip patch, respectively. Their phases are orthogonal and amplitudes can be controlled to be equal by adjusting the tilted angle of the horizontal LP structure and the length of the vertical LP structure. Moreover, the longitudinal metal strip patch is modified to the V-shaped strip patch, which can realize the field cancellation, thereby achieving the boresight radiation for such a leaky-wave antenna. Furthermore, a low SLL is realized by controlling the aperture-field distribution to obtain the desired amplitude distribution and the relatively small axial ratio. In addition, because of the short waveguide wavelength of the SIIG, this feedline can be used to achieve the small interelement spacing and element size, thereby realizing the short length of the array. The measured peak gain of this antenna is 12.3 dBic, the SLL is –19.1 dB and the efficiency is 92.3% at the center frequency of 14 GHz.