A Low-Profile, Top-Loaded, Multielement, Monopole Antenna for Compact UGV Systems

Abstract

This communication presents a low-profile and efficient low-very high-frequency (VHF) antenna designed for compact unmanned ground vehicles (UGVs). An effective miniaturization strategy for a top-loaded multielement monopole antenna is proposed to improve its gain while maintaining a low profile. The approach introduces multiple closely spaced short vertical radiating elements and a structurally constructed 180° phase shifter connecting the elements on a small ground plane. The phase shifter enables electric currents flowing through the vertical elements to be in phase, resulting in enhanced radiation without increasing the antenna profile. In order to improve the antenna bandwidth, a monopole configuration with a sleeve feed and capacitive top loading is adapted. The proposed antenna optimized for a compact UGV via parametric analysis has a height of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.028\lambda $ </tex-math></inline-formula> at 42 MHz (the corresponding electrical size <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ka=0.24$ </tex-math></inline-formula> ). The measured performance of an antenna prototype shows the 3 dB bandwidth of 0.67 MHz and the peak gain of −2.5 dBi. The proposed design can achieve more than 16% reduction in lateral dimensions and 1 dB improvement in gain compared to the state-of-the-art design with similar topology. The performance of the antenna integrated on an actual UGV system is also evaluated by experiments.