Active, Ultra-Wideband, Electrically Small Antennas for High-Power Transmission in the HF Band

Antennas operating at the high-frequency (HF) band (3-30 MHz) are often electrically small due to the large wavelength of electromagnetic waves (10-100 m). Passive electrically small antennas (ESAs) have low bandwidth and poor efficiency values, which makes them challenging to radiate instantaneously broadband, high-power signals for applications such as electronic warfare. To address these challenges, we present the design and experimental demonstration of an active ESA capable of transmission over the entire HF band. The proposed antenna consists of a 2-m long dipole integrated with a class-AB push-pull amplifier. The amplifier circuit that drives the antenna is specifically designed to behave as a high-voltage current buffer to the antenna, resulting in ultra-wideband operation. The amplifier uses high-power vertically diffused MOSFET transistors capable of sustaining the high voltage and current swings that occur at the terminals of the highly reactive dipole during transmission. A prototype of the antenna is fabricated and characterized in field tests. Experiments demonstrate stable, ultra-wideband operation over the entire HF band. Measurement results show that the proposed active antenna can offer total efficiency improvements of over 15 dB compared to a passive matching scenario. The advantages of this approach over non-Foster impedance matching techniques are also highlighted.