A Novel Filter in Antenna (FiA) With Compact Size and High Performance

In this article, a novel and effective integrated design method for filtering antennas is proposed for the first time, with the name Filter in Antenna (FiA). This method takes a holistic perspective, utilizing the antenna structure to build a shielding cavity and implanting the smaller-sized filter into the larger-sized antenna. To demonstrate the superiority of this method, an FiA prototype is designed by integrating a magneto-electric (ME) dipole and a compact filter. Initially, a metal shielding cavity is built with the M-dipole structure of the low-profile ME dipole. Second, a miniaturized filter is built using multilayer coupling structures. Subsequently, the filter is inserted in the feeding line inside the shielding cavity of the ME dipole. Accordingly, the ME dipole and the multilayer filter are integrated into an FiA. The design preserves the antenna’s size while achieving full filter and antenna functionality integration. As a validation, a fully functional prototype is manufactured and tested. The FiA prototype has compact dimensions of
$0.47\lambda _{0} \times 0.48\lambda _{0} \times 0.076\lambda _{0}$
(
$\lambda _{0}$
is the free-space wavelength at the center frequency) and measured results coincide well with the simulation. Excellent filtering performance (return loss of 21 dB, insertion loss of 0.6 dB, six transmission zeros to achieve 15 dB out-of-band suppression bandwidth of
$1.6f_{0}$
, etc.) and nice antenna performance (stable gain of 7.8 dBi, low cross-polarization, low back radiation, etc.) are obtained, verifying the feasibility of the proposed method.