Wide-Band High-Frequency Antennas for Military Vehicles: Design and testing low-profile half-loop, inverted-L, and umbrella NVIS antennas

The design of low-profile, wide-band (WB), high-frequency (HF), vehicular, on-the-move (OTM) antennas is associated with a number of challenges, including their small electrical size, mounting constraints, and the diverse environment in the near field, to name a few. This article considers antennas for near vertical incidence skywave (NVIS) operation from 2 to 15 MHz with a wide tunable bandwidth of at least 24 kHz. The minimum gain at the zenith of -25 dBi is comparable to that of state-of-the-art 3-kHz channel OTM NVIS antennas. The baseline configuration is a two-arm half loop operating in NVIS mode, designed such that it can be easily reconfigured into either an inverted-L or an umbrella-loaded monopole. Each arrangement has its own advantages in terms of radiation patterns, impedance, and practicality. Two arms are used to satisfy the performance requirements and keep the overall profile under 1 m. A full-scale prototype is fabricated and integrated with a specific military vehicle. The stand-alone measurements confirm the expected impedance behavior, whereas the tests with an experimental WB HF radio prove the validity of the design approach. Because of the diverse operation modes, the antenna is flexible and can readily adapt to various communication conditions.