Approach to realize wide-scan-angle phased array with enhanced bandwidth and filtering function by using integrated filter/patch

For microstrip patch phased arrays, larger fractional bandwidth (FBW) and wider scan angle are challenging to achieve at the same time. Phased arrays on thin substrates typically can scan to large angles due to the reduction of mutual coupling caused by surface waves. However, thin substrates limit the achievable FBW of the phased array antenna. In this paper, an integrated filter/patch technology is proposed to realize phased arrays with large scan angle capabilities and enhanced bandwidth. In addition, this integrated filter/patch is able to provide filtering function which is desirable for RF front ends. To prove the concept, a 2^nd-order filter/antenna comprised of one cavity resonator and one patch antenna is designed, fabricated and measured. The center frequency and FBW of the filter/antenna are 5.89 GHz and 5.5%, respectively, with the thickness of the antenna layer being 50 mil. As a comparison, the FBW of a regular coax-fed patch antenna on 50-, 75-, and 100-mil-thick substrates is 2.5%, 4.3%, and 6.3%, respectively. Full-wave Floquet analysis is performed to investigate the active impedance behavior of phased arrays using filter/antenna or patch antennas on substrates with different thickness. It is shown that the filter/antenna phased array exhibits the best performance in terms of active reflection coefficient when the array scans to large angles among all cases. Though the patch antenna phased array on 50-mil-thick substrate has the similar active impedance performance, its FBW (2.5%) is much narrower than that (5.5%) of the filter/antenna phased array.