A Multi-Frequency-Excited MIMO Radar Array Architecture Enabling Exponential-Order Improvement in Angular Resolution

Improving angular resolution in millimeter-wave radars requires a large number of transceivers to fulfill a large array aperture. However, integrating tens or hundreds of transceivers is costly and power hungry. This motivates us to develop an alternative array architecture that supports high angular resolution but with many fewer transceivers. In this work, we propose a multi-frequency-excited radar array architecture by introducing a frequency dimension in multiple-input and multiple-output (MIMO) radars. By changing the excitation frequencies of the antenna array, we can diversify the electrical spacings across the antenna elements as the wavelength changes. Therefore, we can generate multiple equivalent sub-arrays with different electrical apertures and use them to synthesize an extremely large array. As a result, withkdifferent frequencies, our proposed radar architecture can generate$\mathbf { N^{2k}}$equivalent array elements in the synthesized array withNphysical transmitters (TX) andNreceivers (RX). For a fixed aperture area, this method can reduce the total number of physical elements exponentially without introducing grating lobes. As a proof of concept, we designed a single-channel TX chip and a dual-channel RX chip that operate at 15, 30, and 60 GHz in a 65-nm CMOS process. The TX has an output power of 11.8, 10.1, and 12.0 dBm, while the RX has a noise figure of 9.8, 12.6, and 12.4 dB, and an out-of-band (OOB) input 1-dB compression point (IP$\mathbf {_{\text {1{dB}}}}$) of −0.7, 1.5, and −0.2 dBm, measured at 15, 30, and 60 GHz, respectively. In the system demonstration, we use one TX chip and two RX chips to form a one-TX and four-RX radar system. The over-the-air (OTA) demonstration shows a 6° angular resolution, which is$4{\mathbf {\times }}$improved compared to the conventional one-TX and four-RX radar systems.