Wideband HF Van Atta Retrodirective Array: Study and Design

An active ultra-wideband Van Atta retrodirective array for HF operation is investigated. The array is enabled by an ultra-wideband element, consisting of a TEM horn combined with a loop, allowing for instantaneous coverage of the entire 2–30 MHz HF band. The antenna fits within a 3-meter radius sphere which corresponds to ka of 0.5 and 1 at 7.95 and 15.9 MHz, respectively. For instantaneous un-tuned operation, the total efficiencies are 10% and 79% at the two frequencies, respectively. The retrodirective behavior of the array is characterized using the monostatic and bistatic radar cross section responses. Simulated validation of the RCS synthesis method applied to this array is presented giving confidence to use of the method for the further analyses presented. The quality of the retrodirective behavior of the array with different element counts as well as active enhancement of the retrodirective scattering using amplification in the Van Atta beamforming network is discussed demonstrating good potential across the entire HF band.