Dielectric characterization using the microstrip resonator method

Microstrip ring resonators and end coupled resonators with different substrate width, feed line length and gap width are fabricated and the ε_eff is measured. It is shown that these parameters can critically affect measurement results. A substrate width of twice the resonator diameter for the sample is recommended for correct measurement of ε_r. The effect of the coupling gap between the feed line and the resonator is investigated where too small a gap can induce a change of resonant frequency resulting in a measurement error for ε_eff extraction. A suitable gap is recommended for each type of substrate under examination.