A low-profile dual-polarized multilayer parasitic patch array antenna with narrow air gap

This article proposes a low-profile dual-linear polarized multilayer parasitic patch array antenna, which is composed of 3-layer printed substrates and 1 air gap layer inserted between the lower and middle substrate. There is 1 slotted square patch printed on the lower substrate with 2 excited probes acting as feeding element, and 1 and 4 slotted square patches are on the middle and upper substrate respectively as parasitic elements. The stacked patches introduce additional dual-polarized resonances for bandwidth enhancement. Specifically, the T- and rectangular slots and T-stubs are employed near/on the orthogonal axis of the patches in order to achieve impedance matching and to improve 2 orthogonal polarizations. Furthermore, 6 stacked complementary split-ring resonators (CSRRs) are loaded in the middle and upper substrate mainly for both impedance matching and port isolation adjustment. Simulated and measured results comply with each other, which shows that the fabricated antenna has an operational fractional bandwidth of 6.6% (2.34-2.5 GHz), a maximum gain of 7.9 and 6.9 dB at port 1 and 2 (while 10.2 and 9.3 dBi for the simulated ones), respectively, and port isolation better than 19 dB. In addition, the air-gap thickness can be maintained at an extremely narrow level of 0.02(0) ((0) is the free-space wavelength at the central frequency).