A Single-Layer Low-Profile Circularly Polarized Filtering Patch Antenna

A single-layer low-profile circularly polarized (CP) filtering patch antenna is investigated for wireless local area network (WLAN) applications. The CP antenna mainly consists of a feeding loop, four L-shaped radiating patches, and a square ground plane. To integrate the filtering function, four thin microstrip stubs and four shorting pins are introduced to the patches, and two U-shaped slots are etched in the feeding loop. These parasitic elements can realize the bandpass filtering function without requiring an external filter. In addition, these elements are skillfully added into the CP antenna, without increasing either the antenna footprint or profile. To verify the design, a prototype operating at 2.4 GHz WLAN band is fabricated and tested. The measured results show that the prototype has a low profile of 0.02 lambda(0), a passband bandwidth (|S-11| < -10 dB and axial ratio (AR) < 3 dB) of 4.1%, and a peak gain of 8.3 dBic. Moreover, the prototype also shows a sharp roll-off rate near the passband edge and a good out-of-band suppression level of more than 20 dB in the stopbands.

Automated summary

The single-layer low-profile circularly polarized filtering patch antenna, designed for WLAN applications, integrates filtering function without the need for an external filter using thin microstrip stubs, shorting pins, and U-shaped slots. The prototype operates at 2.4 GHz WLAN band with a low profile, passband bandwidth, and peak gain, demonstrating sharp roll-off rate and good out-of-band suppression levels.