A Dual-Polarization Scattering Probe for Modulated Scatterer Technique Measurements

A scattering probe for use in the modulated scatterer technique (MST) measurements was proposed. The proposed probe has dual-polarization capability and a high modulation depth (MD) for both polarizations. The high MD values are made possible by loading shorted transmission lines (STLs) at the center of dipoles, such that the integration of the dipole currents vanishes, resulting in an electrically invisible state for broadside observations. For the actual implementation of the dual-polarization MST probes, the scattering geometry on an FR-4 substrate was considered and the effects of the substrates, particularly in the invisible states, were studied. The dual-polarization scattering probes (DPSPs) were implemented on FR-4 substrates using 4 PIN diode switches, low-frequency blocking capacitors, and biasing structures to provide bias voltages to the PIN diode switches. The biasing structures were implemented using inductors and resistive wires. The locations of the blocking capacitors were offset from the ends of the dipoles to compensate for the nonideal characteristics of the PIN diodes and other parts. The performance of the implemented DPSPs was measured and demonstrated to have high MDs for both polarizations over a wide bandwidth indicating that the proposed probe may increase the sensitivity of the MST system.