Investigation of SIW Cavity-Backed Slot and Patch Antennas With Conical Radiation Patterns

Abstract

Substrate integrated waveguide (SIW) cavity-backed slot and patch antennas with conical radiation patterns are investigated. In a center-fed SIW circular cavity with the top wall removed, a series of cavity modes with conical radiation patterns can be excited, wherein the lowest two modes are the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> modes. The cavity-backed slot antenna with either of the two modes can work independently, but the bandwidth is narrow. In order to improve the bandwidth, an SIW cavity-backed gap-coupled patch antenna is proposed. The antenna has a wide triple-resonance bandwidth, which includes the patch TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode, and the cavity TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> modes. The working principle and the mode characteristics are investigated. The antenna is designed, fabricated, and measured. Measurement results show that the antenna has a wide bandwidth of 64.6%. In the operation band, the antenna has a low reflection coefficient below -10 dB and provides a conical radiation pattern.