A Single-Layer Single-Fed Shorted-Patch Antenna With Broadside Circular Polarization by Using Nondegenerate TM0,1/2 and TM1,1/2 Modes

A novel design concept to excite and produce the broadside circularly polarized (CP) radiation is presented in a shorted-patch antenna (SPA). First, the far-zone radiated fields of the SPA under radiation of TM0,1/2 and TM1,1/2 modes are theoretically studied. It demonstrates that the broadside |E-theta| component of its TM0,1/2 mode is generated in yoz plane. In contrast, the orthogonal |E-phi| component of its TM1,1/2 mode is produced in this plane. Then, the resonant frequency of the TM0,1/2 mode is gradually pushed up to around that of TM1,1/2 mode, aiming to generate the normal CP radiation between these dual modes. After that, a linear slot is etched out on the core radiator so as to counteract the equivalent inductance caused by the loaded pins and feeding probe. Finally, the proposed antenna is fabricated and tested. The measured results reveal that it's operating bandwidth (|S-11|<-10 dB and AR<3 dB) is kept at about 1.2% or at a range of 2.720-2.752 GHz. Most importantly, the CP radiation (AR<3 dB) of the antenna at the broadside direction is indeed resonated at around 2.738 GHz, while keeping the reduced length, single-layer, and single-fed properties.