Study on a Multi-Point Differential Feeding Strategy for Design of Filtering Patch Antennas With Stopband Enhancement

In this article, a novel multi-point differential feeding technique is introduced and applied in the design of filtering patch antennas with a wide upper stopband. Different from the traditional differential feeding structure, the proposed method has four physical feeding points on the patch. Our analysis results indicate that the proposed feeding approach can not only effectively excite the desired fundamental TM<inline-formula> <tex-math notation="LaTeX">$_{\mathbf {01}}$ </tex-math></inline-formula> mode but also flexibly allow for the elimination of high-order modes by selecting suitable feeding positions. Just relying on this feeding method, unwanted harmonic radiations can be totally removed up to <inline-formula> <tex-math notation="LaTeX">$4{f} _{\mathbf {0}}$ </tex-math></inline-formula> without any additional elements. For demonstration, a prototype of a stacked patch antenna with filtering response has been then designed. With resorting to the proposed feeding scheme, both driven and stacked patches are indeed able to support good excitation of TM<inline-formula> <tex-math notation="LaTeX">$_{\mathbf {01}}$ </tex-math></inline-formula> mode with other harmonics to be suppressed, leading to a wide upper stopband performance. In addition, several radiation nulls are generated in the stopband to improve the filtering selectivity. Measured results agree well with the simulated ones, indicating that the designed differential antenna possesses enhanced fractional impedance bandwidths, high in-band gains, low cross polarization, as well as intrinsic wide stopband rejection, further verifying the proposed feeding concept.