A tunable electrically small antenna for ground wave transmission

A tunable, electrically small, wire antenna is developed for HF/VHF ground wave transmission. A variable capacitor is serially connected to tune the resonant frequency of the antenna. The optimal position for the placement of the capacitor is evaluated by numerical simulation. The tuning range and sensitivity are also investigated. A prototype antenna is built and tested, and the measured tuning performance is compared to the simulation results. Transmission loss tests are carried out in several nonline-of-sight environments. The measured transmission loss of the tunable small antenna is found to be within 1 to 2 dB of that of a commercial whip across the tested frequency range.