A circular waveguide antenna using high-impedance ground plane

A high-impedance ground plane (HIGP) is used for a circular waveguide antenna. The benefits of using such a HIGP are related to the suppression of surface waves excited by the circular waveguide mouth, because the HIGP has a very obvious surface wave bandgap. Suppression or reduction of surface waves is expected to improve antenna efficiency and to bring a reduction of sidelobe level due to diffraction of the surface waves. In agreement with the expected result, the measured radiation patterns show that a 2 dB addition in the antenna gain and a 10 dB reduction in the back lobes, if the circular waveguide antenna working frequency is in the HIGP surface wave bandgap.

I. Introduction

Photonic bandgap (PBG) structures are periodic structures, which offer the property to forbid the propagation of electromagnetic waves whose frequencies are within some certain bands. The idea of employing PBG structures was first used in the optical frequency domain [1]. However, PBG structures not only can mimic the properties of the semiconductors in the optical range, but are also scalable to a wide range of frequencies, including those of microwaves. In the microwave region, PBG structures have been used to increase the output power and efficiency of power amplifiers [2] and improve radiation pattern of antennas [3] as well as with the design of reflectors [4].