A novel broadband low-profile circularly polarized (CP) magneto-electric (ME) dipole antenna is proposed in the paper. Sharing the same aperture, a pair of electric dipoles (E-dipoles) and a pair of magnetic dipoles (M-dipoles) are combined through four bulges in the corners of the ring. The arms of the ring work as dipole antennas, i.e., E-dipoles, while the slots formed by the ring with bulges and the central patch work as slot antennas, i.e., M-dipoles. To realize CP radiation, a pair of vacant-quarter printed rings with short-end microstrip lines are utilized to excite the dipole and slot antennas simultaneously. The measurement results indicate that a wide overlapped impedance bandwidth (IMBW) and axial ratio bandwidth (ARBW) of 2.15-3.35 GHz (1.2 GHz, 43.6%) and a low height of 0.18 λ ₀ at the center frequency of 2.7 GHz are achieved. Moreover, a high gain of 8.5-10.3 dBic and stable radiation patterns with no side lobes and low back lobes of less than -20 dB are realized for wireless communication.

A circularly polarized (CP) broadside antenna array with a continuously adjustable beam is proposed and implemented. First, a reflection phase shifter with varactor diodes loaded on two output terminals of a branch directional coupler is realized. By controlling the voltage across both ends of the varactor diodes in the terminal load circuit, the reactance of the load is changed, allowing control of port phase shift. Following that, the microstrip patch antenna array is combined with the reflection phase shifter to achieve the pattern reconstruction for the array. For verification, a prototype of the designed pattern reconfigurable antenna (PRA) is fabricated and measured. The measurement results indicate that the beam direction of the antenna can be continuously adjusted with a change in the voltage across the varactor diodes. The maximum beam direction of the antenna reaches ±21° when the biggest DC bias voltage across the varactor diode is chosen as 15 V. Besides, the antenna shows good CP performance in different beam directions.

A circularly polarized (CP) and frequency reconfigurable microstrip antenna with loading inductive is presented in this paper. The designed antenna is comprised of a radiating patch, four short-circuited grounded metal posts, and four coupling branches. Each coupling branch has an end that is coupled to the shorted ground post and is also connected to the parasitic branches by means of a group of PIN diodes. By controlling the state of the PIN diodes connected to each parasitic branch, the working resonant frequency of the antenna can be changed. In order to further understand the mechanisms of operation of the antenna, the equivalent circuit model was built, and the circuit model of the antenna was analyzed, and this analysis was used for the development of the frequency reconfigurable microstrip patch antenna. Furthermore, the parameters of specific equivalent circuits can be solved by the three lengths of branch. Meanwhile, the calculated results derived from the given resonant frequency formula for the antenna are in good agreement with the simulation results of the antenna. Simulated results for the input impedance of the antenna are also in good agreement with the calculated values for the equivalent circuit. Finally, the antenna is fabricated and measured, and the measured results show that the antenna can not only achieve frequency reconfiguration at 1.14 GHz, 1.21 GHz, and 1.39 GHz but also accord well with the simulation value, while maintaining a compact size.