Low-Profile Broadband Plasma Antenna for Naval Communications in VHF and UHF Bands

This article presents a broadband reconfigurable very-high-frequency/ultrahigh-frequency (VHF/UHF) plasma antenna with omnidirectional features for naval communications. A copper element, engineered as an inverted-discone antenna, operates at a high frequency of 100-512 MHz. We loaded eight similar plasma tubes above the discone as metal bars, which enable radiations at 30-100 MHz frequency. The antenna height over a ground plane is λ/10 at the lowest band. By applying the electrically tuned plasma, we achieved reconfiguration and obtained an average of 9.5 dB radar cross section (RCS) reduction. We fabricated Butterworth low-pass filter (LPF) and high-pass filter (HPF) to isolate 13.56 MHz radio frequency (RF) signal which is used to activate plasma. Moreover, we designed a lumped-distributed impedance matching network at the feeding position to improve transmission. The measurement results show that the VSWR of the antenna is less than 3 over a 17:1 bandwidth, and the azimuth gain of the antenna is greater than -5 dB. Besides, an unmanned aerial vehicle (UAV) system is proposed to measure the radiation patterns. The results confirm that the proposed antenna is a viable candidate for naval communications with ships and ground base stations.