Circularly Polarized Patch Antenna With Filtering Performance Using Polarization Isolation and Dispersive Delay Line

A circularly polarized (CP) filtering patch antenna implemented via dispersive delay line (DDL) is proposed in this letter by adopting a new strategy of polarization isolation. Different from a linearly polarized antenna, the effective radiation gain of a CP antenna, i.e., CP gain, is not only determined by the magnitude of electric field but also its phase. For a CP antenna, left-hand circular polarization (LHCP) has perfect isolation with the right-hand one, which has nothing with the orientation between transmitters and receivers. As such, the aforementioned concept is especially used in the proposed design of CP filtering antenna and achieved by DDL, which works as a key technique in the proposed antenna. By controlling the parameters of DDL, the in-band and out-of-band phases of two orthogonal electric components are effectively changed, thus affecting the axial ratio, and finally leading to opposite CP radiations of in-band and out-of-band, which means that the filtering performance has been realized. For demonstration, an antenna prototype operating in the 2.4 GHz ISM band is fabricated and measured. The simulated and measured results match well with each other. More importantly, the feasibility of the proposed CP filtering strategy is verified by the good filtering performance of CP radiation gain.