Calibration Loop Antenna for Multiple Probe Antenna Measurement System

In order to achieve high accuracy in measurements of the multiple probe antenna measurement system (MPAMS), an omnidirectional calibration antenna with a small gain variation in the horizontal polarization (named calibration loop antenna, in convention) is required. This article presents such an antenna design. The proposed calibration loop antenna consists of four arc-folded dipoles with dimensions of 52 mm \times52 mm \times 1 mm, balun structures for suppressing common mode current, and four parasitic strips for impedance matching on each of the top and bottom planes. The experimental results show that the proposed calibration loop antenna has a small gain variation in the horizontal polarization less than 0.16 dB in a bandwidth of 20% (2.25-2.75 GHz), and its 10-dB return loss bandwidth is 18.2%. Also, the cross-polarization ratio in the operating bandwidth is greater than 24 dB. Along with the desired omnidirectional radiation pattern, the low profile and compact design further make the proposed calibration loop antenna a suitable selection for calibration in MPAMS.