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A single-layer novel windmill element is designed to broaden the bandwidth of reflectarray antenna (RA) in this communication. To obtain the enough phase range, a windmill ring patch and a circular ring patch are utilized to realize the multiresonant state. As a result, a linear phase shift curve which covers 473.6° phase range is achieved by optimizing the parameters. Based on that, a large proportion of phase shift curve keeps parallel from 27.5 to 42.5 GHz, it indicates the proposed element features broadband property. To this end, a single-layer offset-fed prototype with a square aperture of 80 mm $\times80$ mm which is composed of 400 elements is designed, measured, and tested at Ka-band. Through detailed measurements, a peak gain of main beam is 27.86 dBi with an aperture efficiency of 51.7% has achieved at 37 GHz. The sidelobe level and cross-polarization are also lower than −17 and −25 dB, respectively. More importantly, the degradation of the peak gain from 27.5 to 40 GHz (35.71%) is less than 3 dB. The proposed antenna which features wide bandwidth with good radiation performance and simple structure will be suitable for 5G millimeter-wave communication. [ABSTRACT FROM AUTHOR]

The collocated time-division multiplexing (TDM) multiple-input multiple-output (MIMO) technique and frequency-modulated continuous-wave (FMCW) chirp sequence are widely used in automotive radar because of the low hardware complexity and the high-accurate range and velocity measurements. In conventional TDM chirp sequences, the transmitters are switched according to their natural spatial order (referred to as a fixed sequential order), thereby inducing space-Doppler frequency coupling and a relatively low unambiguous Doppler interval. In this paper, a new FMCW chirp sequence and corresponding signal processing method for TDM MIMO automotive radar are proposed. The novel waveform adopts the concept of random transmission to distort the linear phase relationship between space and Doppler, therefore, overcoming the coupling problem. Then, via compressed sensing processing, the scheme can suppress the sidelobe pedestal arisen in the conventional matched filter for targets detection. Besides, based on multiple-frequency observations of the same targets, the velocity ambiguity can be adequately resolved. Compared with conventional chirp sequence, the proposed scheme simultaneously overcomes the typical TDM MIMO chirp sequence problems, thereby avoiding a reduction in the data rate. Also, the scheme significantly reduces the mutual interference between adjacent systems. The simulations and experimental results demonstrate the effectiveness of the proposed chirp sequence scheme. [ABSTRACT FROM AUTHOR]