Class-E, Active Electrically-Small Antenna for High-Power Wideband Transmission at the High-Frequency (HF) Band

TL;DR

This work tackles the challenge of wideband, high-power HF transmission from electrically small antennas by integrating a switch-mode Class-E amplifier directly with an electrically small resonant load. By operating in sub-optimum mode (ZVS-only), the design achieves wide bandwidth without a heavy external matching network, delivering up to ~64 W radiated power at ~3 MHz and efficiencies around 60–78%, while boosting the bandwidth-efficiency product by 5.4–9.8 dB over passive ESAs. Demonstrated modulation schemes include ASK, PSK, and BFSK with favorable BER and manageable in-band nonlinearities, and a detailed passively-matched comparison shows substantial gains in both β×η and radiated power relative to conventional HF antennas. The results suggest practical high-power, wideband HF transmitters based on active ESAs, with the potential for higher power and more complex modulation in future work. The approach offers a pathway to robust, long-range HF communications where traditional passive ESAs struggle with bandwidth and efficiency constraints.

Abstract

Antennas operating at the high-frequency (HF) band (3-30 MHz) are frequently electrically small due to the large wavelength of electromagnetic waves (10-100 m). However, the bandwidth-efficiency products of passively matched electrically small antennas (ESAs) are fundamentally limited. Wideband HF waveforms using bandwidths of 24 kHz or more have recently received significant attention in military communications applications. Efficiently radiating such signals from conventional passive ESAs is very challenging due to fundamental physical limits on bandwidth-efficiency products of ESAs. However, active antennas are not subject to the same constraints. In this work, we present the design and experimental characterization of a high-power, active ESA with enhanced bandwidth-efficiency product compared to {that of} passively matched ESAs. Specifically, the proposed active ESA can radiate wideband HF signals with banwidths of 24 kHz or more, with total efficiencies up to 80$\%$, and radiated power levels approaching 100 W. Our approach uses a highly-efficient, integrated class-E switching circuit specifically designed to drive an electrically small, high-Q HF antenna over a bandwidth exceeding 24 kHz. Using a high-Q RLC antenna model, we have successfully demonstrated wideband binary ASK, PSK, and FSK modulations with the proposed class-E switching architecture. Experimental results indicate that the bandwidth-efficiency product of this class-E active antenna is 5.4-9.8 dB higher than that of an equivalent passive design with the same data rate, and bit-error-rate (BER).

Figures (12)

• Figure 1: (a) Class-E amplifier schematic and drain voltage. (b) Integrated class-E amplifier with a top-hat-loaded electrically-small dipole antenna. (c) Efficiency and radiated power for optimum and sub-optimum designs. Results show significant bandwidth improvement with sub-optimum design.
• Figure 2: Measured input impedance of the antenna model. The dashed lines show the location of the series resonance, at which point the imaginary part of the impedance is zero.
• Figure 3: Circuit schematic of the integrated sub-optimum class-E active antenna.
• Figure 4: Experimental setup for measuring the integrated sub-optimum class-E active antenna.
• Figure 5: Measured and simulated drain voltage and antenna current. $V_{DC}$ = 40 V, with a measured DC supply current of $I_{DC}$ = 1.96 A. The frequency of operation is at 3.045 MHz, and the total efficiency is 78$\%$, which includes DC driver power of 3.8 W.