Fabry-Perot Open Resonator (FPOR)
QWED offers a novel type of a Fabry-Perot open resonator (FPOR) with Gaussian mirrors for automated broadband and precise resonant measurements of electromagnetic properties of low-loss dielectric sheets in the 20-110 GHz frequency range.
The FPOR system is equipped with a specialized software controlling the measurement process and extracting complex permittivity of the material under test from the measured frequency and quality factor.
Fabry-Perot Open Resonator
Measurement setup
The whole measurement setup consists of a computer, where the aforementioned control software is installed, connected to the FPOR and to measurement equipment (either VNA or scalar Q-Meter). The FPOR operates at consecutive TEM0,0,q Gaussian odd modes spaced every 1.5 GHz.
Due to a sophisticated adaptive algorithm implemented in the control software dedicated to precise and robust tracking of the modes during the measurement, total measurement time for 21 frequency points (e.g. in the 20 - 50 GHz frequency range) usually does not exceed 10 minutes.
Exemplary measurement results
Table1: Parameters of a Fabry-Perot Open Resonator (FPOR)
Application FPOR is intended for the measurements of the complex permittivity of low-loss laminar dielectric materials.
Accuracy of measurements of a sample of thickness h Δε/ε = ±0.5% for ε = 1...15

Δtanδ/tanδ = ±2% for tanδ ≤ 2%
Operational frequency range 20 - 110 GHz
The upper frequency depends on the network analyzer, so it is usually one of the following: 50 GHz, 67 GHz or 110 GHz.
Operational temperature range Room temperature.
Additional equipment needed to perform measurement Vector Network Analyser (e.g. Keysight, Rohde&Schwarz, Anritsu, Ceyear) and National Instruments 488.2 GPIB controller or LAN, scalar Q-Meter.
Measurement procedure The whole measurement is automated and controlled via dedicated software installed on a PC computer. At first, resonant frequencies and Q-factors of TEM0,0,q odd modes of the empty resonator are measured. Afterwards, sample is inserted onto the holder and all the modes of interest are adaptively sought for and the changed resonant frequencies and Q-factors are measured in order to extract dielectric constant and loss tangent by comparing the results with a look-up table computed with a dedicated FPOR electromagnetic model.
Additional information The thickness of the sample should be in the 1 µm - 3 mm range, while the diameter should exceed 75 mm.
Dielectric measurements with a Fabry-Perot open resonator (up to 130 GHz):