A Wideband and Low-Profile Circularly Polarized Filtering Stacked Back-Cavity Antenna Using Magnetodielectric Materials

A circularly polarized (CP) filtering stacked back-cavity antenna with wideband and low-profile characteristics using magnetodielectric materials is presented in this letter. The proposed antenna consists of a top metal plate, a middle layer with a dual square loop slotted patch, a bottom layer ground plate, a Wilkinson power divider, a metal cavity, and magnetodielectric materials. The aforementioned structures are embedded in a metal cavity that can form a conformal antenna with the communication systems. Most importantly, magnetodielectric materials are utilized to improve impedance bandwidth matching and realize the low-profile characteristic. In addition, the dual square loop slots are etched on the patch, which can generate two radiation nulls and obtain the filtering performance without adding an external filter. Furthermore, the Wilkinson power divider is used to achieve the CP radiation characteristic and operate an excellent axial ratio bandwidth. For verification, a prototype is fabricated and tested with the dimensions of 0.30λ₀ × 0.30λ₀ × 0.08λ₀, where λ₀ is the free-space wavelength at the lowest frequency of operation. The simulated and measured results match well that an impedance bandwidth of 37.6% (0.80 GHz to 1.17 GHz), an axial ratio bandwidth of 34.2% (0.80 GHz to 1.13 GHz), and a realized gain of 3.25 dBi are achieved. The stopbands have a good out-of-band suppression level of more than 22 dB.