Horizontally Polarized Antenna for Calibration of a Multiple Probe Antennas Measurement System

The accurate calibration of a multiple probe antennas measurement system (MPAMS) is an essential requirement for ensuring reliable wireless terminals over the air measurement. Dipole and horizontally polarized (HP) dipole arrays are commonly used as calibration antennas for the MPAMS. In order to improve the calibration accuracy of the MPAMS, a horizontally polarized omnidirectional calibration antenna with a highly symmetric pattern is presented in this paper. The proposed antenna consists of four identical arc-shaped printed dipoles, rotationally placed on the front and back of the substrate. A tapered balun integrates with parallel strip lines transforming impedance matching from unbalance to balance. Dimension of the feeding network is reduced by introducing the Archimedes spiral tapered balun. As a result, the proposed antenna has a reduced size of 52.4 mm × 52.4 mm × 1 mm. The measurement results show that the proposed antenna has -10 dB return loss operating bandwidth of 2.4-2.53 GHz (about 5% bandwidth), a good omnidirectional performance with gain variation in azimuth being less than 0.2 dB, and the cross-polarization ratio in azimuth is larger than 20 dB for each frequency; meanwhile, the farthest apparent phase center point is about 0.3 mm from the geometric center, which is almost coincident with the geometric center.