Backfire Microstrip Leaky-Wave Antenna With Reduced Sidelobe and Low Cross Polarization

In this letter, a microstrip-based periodic leaky-wave antenna is designed for backfire radiation. Top-plane periodic open-stubs along with periodic rectangular slots in the ground plane are used to align radiating E-field in the top and bottom sides of the antenna in the same phase. This helps to achieve perfect backfire radiation from the n = -1th space harmonic, which is a fast wave. A transmission line model is presented to explain different radiation modes. A prototype of the antenna is fabricated and measured. Backfire radiation is obtained at 11.95 GHz with a measured peak gain of 12.7 dBi and cross-polarization level below -27 dB. Next, Taylor tapered aperture illumination is introduced for low sidelobe levels. The measured gain, sidelobe, and cross-polarization levels of the tapered antenna are 13.8 dBi, -18.5 dB, and -33 dB, respectively, at 12 GHz.

I. Introduction

Endfire antennas are widely used in long-distance communication systems and in radar applications. Due to their low aerodynamic drag, they are also popular in airborne electronic equipment [1]. Surface-wave-based antennas have been used since long for obtaining endfire beams [2], [3]. The antennas like Vivaldi antenna [4], helical antenna [5], and Yagi–Uda antenna [6] are also reported for endfire radiation. Recent works [7], [8] show stable endfire radiation with wide gain bandwidth. However, it is not easy to control the amplitude distribution to reduce the sidelobe levels (SLLs) for surface-wave-based antennas. Yagi–Uda [9] and surface-wave antennas [10] have been tapered for low SLL, however the design and fabrication still pose complexity.