This letter presents a novel approach to build a compact lightweight unmanned aerial vehicle (UAV) radar for remote sensing applications. The proposed radar exploits the recent advancement of an automotive radar chip for broadband chirp generation and rapid data processing. To compensate for the path losses and improve penetration at the millimeter wave (mm-wave) frequency range, an up-and down-converters are developed to generate an UWB (3.25-5.15 GHz) chirp signal. The total payload of the radar is 2.5 kg. The proposed radar is installed on a UAV and tested in the field at 100 m altitude above the ground surface. The results show that the compact low-power UWB radar can be used to map vegetation and soil moisture with fine resolution.

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This paper details the development of a low-loss, PIN diode single-pole double-throw (SPDT) absorptive switch for an ultra-wideband radar. The fabricated switch operates with a peak power of 200 watts at a 10% duty cycle. It has an insertion loss of less than 0.8 dB, a return loss greater than 19 dB, and isolates the transmitter and receiver beyond 37 dB over the frequency band (170 MHz-470 MHz) for sensitive radar measurements. An external RF limiter and a low-power CMOS switch at the receiving end are used to reduce video leakage from the PIN diode switch and enhance the isolation up to 80 dB. In addition, a fast-switching MOSFET-based PIN diode driver circuit is designed with a dead-time control circuit to minimize the cross-conduction currents for the PIN diode switch. The rise and fall times for the PIN diode switch are less than 200 ns. The switch-driver includes integrated low-noise power supplies that generate −50 V, 15 V, and 5 V from a common rail 50 V input source.

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This paper details a new approach for enhancing the radiation characteristics of a coplanar Vivaldi antenna (CVA) array. First, the inter-element mutual coupling is reduced by introducing slots in the conventional CVA array. Then, a low-profile dielectric patch antenna (DPA) is situated between the CVA flares when it acts as a travelling wave radiator at the higher frequency band. The DPA is excited by the loop current at the radiation part of the CVA and a set of TE modes with omnidirectional radiation patterns are excited. This combination enhances the directivity in the broadside direction of the CVA by suppressing the grating lobes by as much as 10 dB. The 4×1 linear array covers the frequency range of 2.77-13.6 GHz, with 132% fractional bandwidth. Then, four of the proposed linear arrays are connected to constitute an 8×2 planar array to achieve a gain of 15.2-24.6 dBi. The proposed arrays are fabricated, tested and mounted on a small (Unmanned Aerial System) sUAS for radar measurements. The real-life field radar results with the proposed arrays are presented in this paper including the echogram of the scanned area.INDEX TERMS-High gain antennas, radar applications, radiation pattern enhancement.