SPDR is almost identical in use to other resonator cavity perturbation techniques. A metal cavity has two dielectric posts that load the cavity and impose a specific mode structure (Figure 1 below). A sample (purple rectangle) in the cavity perturbs the mode structure, shifting the resonance frequency and decreasing the quality factor.

Figure 1: Schematic diagram of a split-post dielectric resonator


  • Ease of use

  • Reliability

  • Resilience to user error


  • No commercial instruments above 15 GHz

While this technique does not extend to the mmWave bands, it is relevant because industry often relies on it for cross validation, using permittivity models to extrapolate results to mmWaves.

As part of the 5G/6G MAESTRO project, work on this page is supported by the Office of Advanced Manufacturing in the National Institute of Standards and Technology (NIST), under the Federal Award ID Number 70NANB22H050.

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