Dual Polarized Wideband Directional Coupled Sectorial Loop Antennas for Radar and Mobile Base-Station Applications

This paper presents a new dual polarized antenna structure with matching and radiation characteristics suitable for radar and base-station applications. Two slightly different designs based on a dual polarized radiating element are presented. For radar applications, the radiating element is used to excite the two degenerate modes of a cavity with square cross-section. The resulting overall antenna size is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.5{\lambda _m} \times 0.5{\lambda _m} \times 0.2{\lambda _m}$</tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\lambda _m}$</tex-math></inline-formula> is the free space wavelength at the minimum operating frequency. The measured results showed isolation better than 30 dB and voltage standing wave ratio (VSWR) less than 2.5 over 1–1.95 GHz as well as good radiation pattern performance. For base-station applications, the exciting element was placed in front of a metallic ground plane to increase the beamwidth. This results in a smaller antenna size ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.38{\lambda _m} \times 0.38{\lambda _m} \times 0.25{\lambda _m}$</tex-math></inline-formula> ) at the expense of reduced directivity. The antenna is designed to work over 1710–2170 MHz which covers three common frequency bands of mobile radio application. The measured results showed return loss better than 14 dB over the operating band and more than 30 dB polarization isolation.