This paper presents a multi-input multi-output (MIMO) radar with simultaneously transmitted orthogonal waveforms. The radar operates in W-band, 93.5-94.5 GHz, with frequency-modulated continuous wave (FMCW) signals. The radar is designed to be capable of simultaneous transmission rather than switching transmit channels. A suitable orthogonal waveform transmission method for the FMCW radar is selected and reflected in the transceiver design. The radar consists of a transceiver, antennas, and a signal processor. The design and specifications of each module are described in detail. The transceiver consists of two transmitting channels and two receiving channels. The transmitter is designed to have high transmit power aiming at the detection and imaging of objects with small radar cross section, up to 100-150-m range. A compact horn antenna and two-channel analog-to-digital converter with a high sampling rate are designed and fabricated. The performance of each module is measured and evaluated. The performance of the radar is tested through experiments. The MIMO capability of the radar was verified through the acquisition of the range profiles with respect to four distinct signal paths by distinguishing the simultaneously transmitted orthogonal signals. The experimental results verified that the specification of the radar system is feasible for high-resolution imaging applications.

A new method of sidelobe level (SLL) reduction for a substrate integrated waveguide (SIW) slot array antenna is presented. In this method, amplitude distribution is assigned to the slots by tapering the SIW width. SIWs with tapered width can be efficiently manufactured by varying the position of the side-wall vias. In this paper, the new method is validated on a 12-element SIW slot array antenna operating at 94 GHz, to achieve an SLL of approximately -30 dB. The antenna design procedure as well as the simulation and measurement results are presented.

In this article, the design of a small and light‐weight antenna and transceiving experiments for W‐band UAV‐mounted synthetic aperture radar (SAR) is presented. The antenna requirements i.e. gain, beam width, and antenna dimension are determined from the parameters of the radar system under implementation in our lab. To meet the requirements, 24‐by‐4 SIW slot array antennas have been designed. The antenna design includes a waveguide‐to‐microstrip transition for connection to circuits and metal flares for gain enhancement. Transceiving experiments are carried out by integrating the designed antennas with a SAR system prototype. Corner reflectors having various radar cross sections (RCS) are used as radar targets. Additionally, experiments with standard horn antennas are also carried out for a comparison. From the results, the designed SIW slot array antennas gives acceptable performance while maintaining small and light‐weight characteristics which are crucial for compact SAR.