Compact and High-Selectivity Wideband Filtering Patch Antennas on Stacked Multimode Radiators

Abstract

In this article, we conduct an in-depth investigation into a 3-D stacked configuration for filtering patch antennas to achieve wide bandwidth, high selectivity, and compact size simultaneously. In contrast to conventional methods that employ multiple stacked single-mode radiators (SMRs), we, for the first time, propose a generalized 3-D coupling architecture of multiple stacked multimode radiators (MMRs) and hybrid MMRs-SMRs configurations, enabling the design of new filtering patch antennas with low profile and high performance. Leveraging this configuration, we first propose and design a triple-mode filtering patch antenna. Specifically, its bottom MMR is implemented by integrating shorting pins and slots to excite dual resonant modes, while the top SMR operates in the fundamental resonant mode. This design enables a third-order filtering response with two radiation nulls on both sides of the passband, thereby realizing a sharp roll-off rate at the lower and upper band edges. The experimental results show that it achieves a wide fractional bandwidth of 16% and the selectivity values of 0.13 and 0.10, respectively. To further improve the bandwidth and selectivity, we propose a quadruple-mode filtering patch antenna consisting of two stacked MMRs. These two MMRs are realized via combined pin-loaded, slot-loaded, and stub-loaded techniques, which independently support dual resonant modes each. It achieves a fourth-order filtering response and two radiation nulls on both sides of the passband. The bandwidth is enhanced to 19.2%, and the selectivity values are boosted to 0.10 and 0.09, respectively. Besides the high performance, the proposed antennas also have the compact size of only $0.58~\lambda _{0}~\times 0.58~\lambda _{0}~\times 0.067~\lambda _{0}$ and $0.58~\lambda _{0}~\times 0.58~\lambda _{0}~\times 0.058~\lambda _{0}$ , respectively ( $\lambda _{0}$ is the free-space wavelength at the center frequency $f_{0} = 3.5$ GHz).