A Single-Layer Broadband Ka-Band Reflectarray Using Novel Windmill Elements

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.