Low-Profile Planar Ultrawideband Modular Antenna Array Loaded With Parasitic Metal Strips

A low-profile dual-polarized planar ultrawideband modular antenna (PUMA) array is proposed in this article. The overall profile is as small as 11.4 mm (0.228 lambda(high), where lambda(high) is the free-space wavelength at the highest operating frequency) based on element sizes 25 x 25 mm(2) (0.5 x 0.5 lambda(2)(high)) and a large operating frequency bandwidth achieved by loading lossless parasitic metal strips between the dipole patches and the ground plane. The loop-mode resonance that causes deterioration of the port isolation around the lowest operating frequency is comprehensively analyzed and suppression methods are proposed. To further reduce the overall profile, a metasurface-based wideangle impedance matching (MS-WAIM) layer is introduced. The surface waves guided by the MS-WAIM layer during wideangle scanning in H-plane are suppressed by cutting properlysized square holes at critical positions. The calculated results show that the proposed infinite array can scan up to +/- 60 degrees in E-/H-planes with active voltage standing wave ratios (VSWRs) below 2.9 within 2-6 GHz and orthogonal port isolations beyond 20 dB. A 12 x 11 array prototype is fabricated and reasonable agreement is achieved between the calculated and measured results.