A 12:1 Ultra-Wideband High-Gain Probe for Future Direct Circular Polarization Antenna Measurements

This paper presents a 12:1 high-gain ultra-wideband (UWB) circular polarized (CP) probe for use in anechoic chamber measurements. The solution is based on a log spiral antenna printed in a conical shape and, to the best of the authors' knowledge, has the widest band reported of direct CP solution with high gain and stable performance. It covers simultaneously several interesting frequency bands, including L-band (1.518-1.675 GHz), S-band (1.97-2.69 GHz), C-band (3.4GHz-7.025 GHz), X-band (7.25-8.44 GHz) and part of Ku-band (10.7-12 GHz) which makes it the preferred probe for testing CP antennas for the various applications that exist in these bands. The direct CP probe will be preferable to avoid the inclusion of extra bulky components for linear to circular polarization converters or the requirements of accurate phase measurements for software conversion. Besides decreasing the required measurements to half as the CP patterns will be directly estimated instead of the dual linear polarizations used for CP generation. With the comparison to the performance of the state-of-the-art UWB solutions (both in literature and commercial), this probe has six main attractive characteristics: stable radiation patterns, negligible sidelobe levels, high and stable gain of about 9 dBi, pure CP with an axial ratio below 2 dBi, easy scalability for different frequency bands, and low weight (compared to standard metallic horn probes). Additionally, studies for four fabrication techniques are investigated.