A design for dual‐band circularly polarized microstrip antennas with different radiation patterns is described. The design is based on a stacked patch antenna composed of an upper circular patch and a lower ring patch. For the higher operation band, the two patches are simultaneously resonant at the TM21 mode and the stacked patch antenna can produce a conical radiation pattern. As for the lower operation band, only the upper patch is resonant at its fundamental mode and a broadside radiation pattern is obtained. To allow the two radiation patterns to be with circular polarization, 90° hybrid couplers are used to excite the patch antennas at the two operation bands. A prototype designed at the GPS and WLAN bands is constructed. The experimental results demonstrate that the prototype operated at each frequency band has a 3dB‐axial‐ratio bandwidth of more than 15%. Simulation performed with HFSS also validates the measured results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:404–408, 2017

A design of the antenna with dual diagonal polarizations for 2G/3G/LTE base station applications is first described in this paper. The antenna has a compact size, and its structure is mainly composed of two orthogonally situated dipoles fed with coaxial baluns, a cross strip mounted on the dipoles, and a planar reflector. The cross strip can be regarded as dual orthogonal loop antennas. By embedding thin slots into the loop‐dipole composite antenna, the impedance bandwidth for return loss less than 15 dB can cover the frequency band from 1.7 to 2.7 GHz. Because the adopted balun also serves as an impedance transformer, the cross polarization level at the broadside is lower than −30 dB for all operation frequencies. Then, we found that by varying the dimensions of the slot, the loop‐dipole composite antenna can also deliver a 70% impedance bandwidth for return loss less than 10 dB, and the cross polarization level is lower than −25 dB in whole E‐plane and H‐plane. Antenna prototypes are constructed, and experimental and simulated results have good agreements.

A design for polarization reconfigurable patch antennas is presented. The antenna has a suspended radiating patch embedded with a cross slot. Two feed mechanisms are used to excite the patch antenna, including top-loaded coaxial cable and microstrip-to-slotline balun. To realize polarization reconfigurability, the lengths of the two linear slots of the cross slot are controlled with PIN diodes. When the slot lengths are the same, the antenna fed with the balun can generate a linearly polarized unidirectional radiation. On the other hand, as the slot lengths are different, the antenna fed with the top-loaded coaxial cable produces a circularly polarized broadside radiation, and the polarization sense can be switched between right-handed circular polarization and left-handed circular polarization. A prototype is constructed. Experimental results show that the operating bandwidth of the reconfigurable antenna is about 7%; in addition, good impedance matching as well as low cross polarization are obtained within the bandwidth.