A Compact Electrically Tunable VHF Antenna

An electrically small dipole antenna that can be tuned from 35 MHz to 90 MHz is reported. The proposed design is low profile and lightweight, and is integrated on the landing gear of a compact UAV. The antenna operates as an inductively loaded, folded dipole to efficiently utilize the available space. The antenna is tuned with both RF switches and varactor diodes. The RF switches short out different sections of the inductive coil enabling discrete frequency tuning. The varactor diodes in parallel with the coil allow for continuous frequency adjustments. Full wave simulation results show that the antenna can be tuned from 35 to 90 MHz. The instantaneous bandwidth and gain at 42 MHz are 1% and -8 dB, respectively. The gain and bandwidth increase when the antenna is tuned to the higher end of the frequency band of interest.