Dual-polarized Probe Research Articles

Digital Twin-Enabled Characterization of GNSS Multipath in Challenging Reference Stations Using a Dual-Polarized Probe

Digital Twin-Enabled Characterization of GNSS Multipath in Challenging Reference Stations Using a Dual-Polarized Probe

Dual-Polarized Probe for Planar Near-Field Measurement

A dual-polarized probe enables the simultaneous sampling of two orthogonal polarizations, which decreases the time for the characterization of co- and cross-polar properties of the antenna under test in transmission mode by 50%. In this work, a dual-polarized probe comprising of a square waveguide and grating polarizer-based orthomode transducer is presented. The Ku-band dual-polarized probe is manufactured in-house using additive manufacturing and coated with conductive paint. The simulated and measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 10 dB impedance bandwidth is between 10.7 and 14.5 GHz. The peak simulated and measured coupling between the orthogonal polarizations is less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 60 dB and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 40 dB, respectively.

A Cost-Effective Tethered-UAV-Based Coherent Near-Field Antenna Measurement System

For antenna measurements, the device under test (DUT) is usually transported to an anechoic chamber equipped with a scanner system. To measure on-site, unmanned aerial vehicles (UAVs) are a flexible solution as they can precisely maneuver a probe antenna over a surface in the DUT&#x2019;s near-field region. In this work, the designed multi-rotor UAV enables electromagnetically optimal placement of the probe antenna and effective gravity center re-balacing by payload position adjustment. The on-board software-defined radio (SDR) serves as a dual-channel receiver for the dual-polarized probe and as a signal source. For phase-coherent measurements, the source signal is transmitted to the DUT via an optical fiber tethering the UAV to the ground control station. Power supply cables allow unlimited flight times. A laser-based tracking system originating from virtual reality (VR) applications measures the probe position and orientation. The developed operator software guides the UAV along a trajectory and records the irregularly distributed near-field samples. An inverse equivalent sources solver (IESS) with full probe correction computes equivalent sources for antenna diagnostics and the DUT far field. The deployed components make the system very cost-effective. Still, verification measurements demonstrate its usability and the accuracy of the results for frequencies up to several GHz.

Calibration of a Dual-Polarized Probe Using the 16-Term Calibration Model

A calibration method for square or circular waveguide-based dual-polarized probes is proposed based on the 16-term network analyzer calibration model, allowing systematic errors, such as polarization impurity and mismatches to be corrected. The unique issues associated with such a dual-polarized probe are discussed, namely, the difficulty in creating thru or delay calibration standards and known asymmetric reflect standards. A novel calibration procedure solving the 16-term calibration model is developed and proposed, which overcomes these issues by utilizing three known symmetric reflect standards, one unknown asymmetric reflect standard, and an optional unknown but reciprocal standard. Subsequently, two Ka -band (26.5–40 GHz), square-waveguide-based dual-circularly polarized probes are fabricated along with the required calibration standards, and the proposed calibration method is then applied and its efficacy verified. In addition, the ability of the calibration algorithm to correct for polarization impurity is demonstrated through synthetic aperture radar (SAR) measurements in conjunction with a sample containing a plurality of identical targets with different relative orientations.

Spherical Near-Field Scanning With Higher-Order Probes

A general method for higher-order probe correction in spherical scanning is obtained from a renormalized least-squares approach. The renormalization causes the normal matrix of the least-squares problem to closely resemble the identity matrix when most of the energy of the probe pattern resides in the first-order modes. The normal equation can be solved either with a linear iterative solver (leading to an iterative scheme), or with a Neumann series (leading to a direct scheme). The computation scheme can handle non-symmetric probes, requires only the output of two independent ports of a dual-polarized probe, and works for both φ and θ scans. The probe can be characterized either by a complex dipole model or by a standard spherical-wave representation. The theory is validated with experimental data.