An Improved Two-Port Transmission Line Permittivity and Permeability Determination Method With Shorted Sample

Area of Science:

• Electromagnetics
• Materials Science
• Microwave Engineering

Background:

• Traditional methods for determining complex permittivity and permeability can suffer from resonance effects, leading to significant uncertainties, especially for low-loss materials.
• These uncertainties arise when sample thickness is an integer multiple of the guided half-wavelength, complicating material property fitting.
• Existing techniques like the Nicolson-Ross-Weir (NRW) solution and the National Institute of Standards and Technology (NIST) iterative method have limitations in handling these resonance issues.

Purpose of the Study:

• To introduce a modified measurement technique and nonlinear least-squares solution for accurate complex permittivity and permeability determination.
• To mitigate the uncertainties caused by resonance effects in low-loss samples encountered in traditional methods.
• To enhance the reliability and reduce the uncertainty in material property measurements.

Main Methods:

• Employs a combination of a two-port S-parameter measurement and a novel one-port measurement of a shorted sample.
• Utilizes a nonlinear least-squares solution method for fitting material properties.
• Introduces a shorted reflectivity measurement (S11) to improve accuracy and reduce uncertainty compared to standard two-port measurements.

Main Results:

• The proposed technique significantly reduces uncertainties associated with resonance effects.
• Obtained complex permeability and permittivity values exhibit smoother profiles and lower uncertainty.
• Validation performed on cast epoxy and ferrite-loaded microwave absorber samples in WR42 waveguide, alongside finite element simulations.

Conclusions:

• The modified measurement technique, incorporating a shorted sample reflectivity measurement, provides improved accuracy and reduced uncertainty for complex material property determination.
• This method effectively overcomes the limitations of traditional techniques when dealing with low-loss materials and resonance phenomena.
• The enhanced accuracy is demonstrated through experimental results and simulations, offering a more reliable approach for material characterization.