Compact Low-Profile Differential Filtering Microstrip Patch Antenna With High Selectivity and Deep Rejection Using Single-Layer Substrate

A compact low-profile differential filtering microstrip patch antenna with high selectivity and deep rejection using single-layer substrate is proposed. The presented antenna mainly consists of the quasi-H-shaped patch (QHSP) and the meandering quasi-T-shaped resonator (QTSR) which is composed of two open-end meandering arms in opposite direction and an inset coupling structure. To the best of our knowledge, a novel differential feeding structure is adopted for the first time that a pair of differential inset coupling feeding structures are placed in opposite direction to drive the QHSP with insetting-capacitive-coupling, simultaneously. Its equivalent lumped circuit is further analyzed to study the characteristics. In the point of views of filter and antenna design, the meandering QTSR not only acts as the first stage of resonator, but also a feed structure, and the QHSP can be treated as the last order of resonator as well as the radiator. A prototype of the proposed antenna is designed, analyzed, simulated and measured. Two controllable radiation nulls (RNs) locate at the both sides of the passband, a sharp skirt selectivity with the sideband roll-off rates of 667/182 dB/GHz and out-of-band suppressions of −40.1/−39 dB in lower and upper stopbands are achieved, respectively. The measured flat realized gain can be obtained in the passband with the average gain more than 6 dBi and the low cross-polarization level can be achieved. The dimension of the proposed antenna is only
$0.361\lambda _{0} \times 0.426\lambda _{0} \times 0.013\lambda _{0}$
. Good agreement between the simulated and measured results is obtained, which verifies the proposed antenna with the differential feeding structure has excellent performance only using single layer low profile substrate. The proposed antenna is a good candidate for WLAN and power harvest application.