Broadband Printed-Circuit-Board Characterization Using Multimode Substrate-Integrated- Waveguide Resonator

Broadband printed-circuit-board characterization using a multimode substrate-integrated-waveguide (SIW) resonator is proposed and investigated in this paper. The resonator sample is fed by two closed rectangular waveguides through two coupling slots positioned at two ends of the cavity. A series of TE
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resonant modes with large mode index can be excited sequentially in the cavity. This design is able to perform an effective control of the frequency interval (Δf ) between two neighboring modes. Besides, Δf approaches to be a constant with a large mode index k. This feature is important to test dielectric materials at small and approximately uniform frequency intervals. The detailed design process is introduced to synthesize the dimensions of the resonator sample and the feeding structure for a given operation frequency band. As an example, the Taconic TLY-5 substrate is measured at Ka-band firstly to validate the accuracy of this method. Two types of samples with different thicknesses are fabricated and tested to calibrate the conductor loss. After that, this SIW multimode measurement is employed to accurately test the same substrates over the whole W-band with approximately uniform frequency intervals. This task cannot be implemented by conventional resonance methods based on microstrip lines because of the selection of resonant modes and the radiation leakage.