A Broadband VHF Probe Antenna Based on Common-mode Current Suppression

The low-frequency part of Square kilometer array(SKA-Low) antennas helps the radio astronomy community to explore the universe’s origin further. However, due to the large volume, the radiation characteristics of SKA-Low antennas in the working environment cannot be measured by microwave anechoic chambers, which limits the further application of SKA-low antennas. To solve this problem, some scholars have successfully performed far-field calibration of radio telescopes through unmanned aerial vehicles (UAV). However, limited by the performance of existing drones and probe antennas, it is difficult to obtain the large amount of data required for near-field measurement at one time. In order to make measurements conveniently and efficiently, this article proposes a broadband probe antenna based on common-mode current suppression. By introducing a self-balancing balun structure, the common-mode current on the coaxial feed line is suppressed ensuring the probe pattern’s stability and reducing cross-polarization. Then through the impedance loading theory, the working bandwidth of the probe is further expanded. The VSWR bandwidth of the probe antenna is 158MHz-225MHz (35%), the cross-polarization is greater than 25dB, and the dimensions are 80cm × 1.8cm × 1cm ($0.431 \lambda_0 \times 0.09 \lambda_0 \times 0.01 \lambda_0, \lambda_0$ is the maximum operating wavelength). In addition, the antenna has the advantage of a stable pattern and is nearly omnidirectional, especially in the front half space, which is positive for antenna measurement.