A Large-Frequency Ratio RF Device With Dual-Circularly Polarized Antenna and Bandpass Filter Integration

This letter proposes an RF device that integrates dual-circularly polarized antenna (DCPA) and bandpass filter (BPF) functions. It is the first attempt to utilize the square slots for radiating energy of a DCPA at millimeter-wave (mm-W) band, and simultaneously serving as the feeding structure for a BPF operating at microwave band. The DCPA function involves exciting two square slots to generate dual-polarized (DP) radiations, which are then passed through two 3D-printed polarizers placed above the slots to generate directional circularly polarized (CP) beams. Also, two resonators are constructed above the square slots, forming a filtering circuit for the BPF function. In this way, the slots serve as both the radiation aperture for DCPA at mm-W band and the feeding structures for the BPF operating at microwave band. For measurement results, the DCPA function has a 18.7% overlapped bandwidth for 3-dB axial ratio (AR) and impedance matching from 36.2 to 43.7 GHz, with a high isolation level of 32 dB between two ports and an average realized gain of 13.7 dBic. The BPF function has a measured impedance matching bandwidth of 6.8% from 5.65 to 6.05 GHz, with an average insertion loss of 2.2 dB.