Broadband dual-polarized MICROSTRIP antenna fed with horizontal coaxial baluns

摘要

A novel feed mechanism for dual-polarized microstrip patch antennas with broadband operation and high isolation is presented. The feed structure is a coaxial balun composed of coaxial cables and copper tubes, and it is placed parallel to the ground plane. With the horizontal coaxial baluns, the radiating patch can be symmetrically excited through proximity coupling. For the proposed feed mechanism, the parametric analyses are performed, and the critical dimension affecting the impedance bandwidth of the microstrip antenna is also addressed. An antenna prototype is constructed, and its measured results indicate that the microstrip antenna can give an impedance bandwidth of more than 20%, and within the bandwidth, the isolation between the two orthogonal ports is higher than 40 dB; moreover, symmetrical broadside radiation with low cross polarization is obtained. Simulated results for the cases of microstrip antennas with various substrate thicknesses are also provided.