A Low-Profile and Wide-Angle Scanning Planar Ultrawideband Modular Antenna with Ultra-Thin Loading Window

Ultrawideband phased antenna array has been widely used in communications, radars and detection. However, the high profile and poor wide-angle scanning characteristics have always been the critical limitation for many available ultrawideband antenna applications. In this paper, an ultra-thin loading window (UTLW) is proposed to replace the wide-angle impedance matching (WAIM) superstrate in the planar ultrawideband modular antenna arrays (PUMA), and reduces the profile height greatly. The UTLW consists of two strips in parallel, and each strip is loaded with one resistor and two capacitors. Following the equivalent circuit model (ECM) of the PUMA, the resistance and capacitance are specially designed to make the complex impedance of the UTLW equal to the impedance introduced by the WAIM. A dual-polarized PUMA with an UTLW achieves 6-18 GHz impedance bandwidth with active VSWR <= 2.6 for scanning up to 60 degrees and active VSWR <= 3 for scanning up to 70 degrees in E/D/H plane. The profile height of the proposed PUMA is only less than 0.07 lambda(l), or, 0.24 lambda(h) with reference to the typical Nyquist half-wavelength spacing frequency. A 20 x 20 prototype PUMA with the UTLW was fabricated and its measured results were found consistent with the simulation results.