Dual Polarized near Field Probe Based on OMJ in Waveguide Technology Achieving More Than Octave Bandwidth

In classic probe-corrected spherical NF measurements, one of the main concerns is the probe [1], [2], [3]. Standard NF-FF transformation software applies probe correction with the assumption that the probe pattern behaves with μ=±1 azimuthal dependence. In reality, any physically realizable probe is just an approximation to this ideal case. Probe excitation errors, finite manufacturing tolerances and probe interaction with the mounting interface and absorbers are examples of uncertainties that can lead to presence of higher-order spherical modes in the probe pattern [4], [5]. Although probe correction techniques for high-order probes are feasible [6], they are highly demanding in terms of implementation complexity as well as in terms of calibration and post-processing time. In this paper, a new OMJ designed entirely in waveguide and capable of covering more than an octave bandwidth is presented. The excitation purity of the balanced feeding is limited only by the manufacturing accuracy of the waveguide. The paper presents the waveguide based OMJ concept including probe design covering the bandwidth from 18 to 40 GHz using single and dual apertures. The experimental validation is completed with measurements on the dual aperture probe at the DTU-ESA Spherical Near-Field facility in Denmark.