Extremely electrically small MF/HF antenna

This study presents an extremely small frequency-tunable monopole antenna operating at medium frequency/high frequency (MF/HF) band with an omnidirectional radiation pattern. Most of the existing miniaturisation techniques operate at low bandwidth as well as low efficiency. The design is based on a capacitive top, allowing the antenna to resonate at much lower frequencies, and a tunable inductive centre loaded. Utilising the capacitive top, the radiation resistance of the antenna is significantly increased. The resonant frequency can be tuned over a wide range of frequency (0.974-30 MHz) without changing the antenna total size by virtue of the tunable loading coil. The tuning system contains arms, motors, contactor, microcontroller and remote control. The experimental results are 0.0032 lambda, ka = 0.01, |S-11| = - 15.8 dB, gain = -13.9 dBi and n = 2.2% at its lowest resonant frequency.