Design of Notch Cut Circularly Polarized Circular Microstrip Antenna

Abstract

The notch cut circular microstrip antenna to realize circular polarization on thinner substrate is proposed. The notch degenerates fundamental TM11 mode into two orthogonal modes, to yield circular polarization. To improve upon the gain and bandwidth, its three layer suspended configuration is proposed. It yields VSWR and axial ratio BW of 60 and 15 MHz, respectively with gain of more than 5 dBi over axial ratio bandwidth. Further formulation in resonant length at two orthogonal modes for notch cut circular patch on non-suspended and suspended configurations is proposed. The frequencies calculated using them closely agrees with the simulated results. Using proposed formulations, the design procedure for notch cut circularly polarized antennas in 1000 to 4000 MHz frequency band, is presented. It gives circularly polarized response with formation of small loop (kink) inside VSWR = 2 circle in the smith chart. Thus the proposed formulation can be used to design circular polarized antenna at any given frequency.