Circularly polarized microstrip antennas for frequency control with a variable reactance

This paper presents circularly polarized microstrip antennas (CP MSA) for frequency control with a variable reactance. Operating frequency of circular polarization of the proposed antennas can be controlled by the variable reactance. 8% bandwidth with axial ratio less than 3 dB and over 3 dBi gain is obtained by the proposed CP MSA. In order to enhance the CP bandwidth, a stacked CP MSA for frequency control with the variable reactance is also designed. 23% bandwidth with axial ratio less than 3 dB and over 7 dBi gain is achieved by the stacked CP MSA. Stable LHCP radiation patterns with low cross polarization are observed in the CP bandwidth for the both CP MSAs. The variable reactance is realized by one varactor diode, therefore, it is demonstrated that frequency control of the proposed CP MSAs is accomplished by one varactor diode.