A single-feed dual-frequency dual-sense circularly-polarized (CP) printed slot antenna etched on a single substrate is proposed. This antenna is composed of an annular slot and a cross slot, which produce two different frequency bands. The lower band and the upper band are controlled by the annular slot and the cross slot respectively. By introducing asymmetry on both annular slot and cross slot, CP radiation at the two frequencies can be obtained. The method of impedance matching has been discussed in detail. The key parameters of the design are investigated to show how to obtain dual-frequency and dual circular polarization. Two antenna prototypes are fabricated and measured, experimental results show that good CP radiation performances are obtained at both frequencies.

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A millimeter-wave (MMW) windmill-shaped magnetoelectric-dipole antenna with broadband circular polarization and wide axial-ratio (AR) beamwidth is presented. Good circular polarization performances of the proposed antenna are contributed to excellent performances of the magnetoelectric-dipole, the benefit of windmill shape and the sequential feed scheme by a circular microstrip line. Simulation results show that the antenna obtains a wide impedance bandwidth of 58.8% over the band 30～55 GHz, a stable 3-dB AR bandwidth of 30% across the band 34～46 GHz. And the gain is higher than 6 dBic within the AR bandwidth, with the highest gain of 9.2 dBic at 45 GHz. In addition, a unidirectional and stable pattern has also been achieved.