It is desirable to measure the electromagnetic properties of devices and materials in the millimeter part of the spectrum. For guided wave-based devices and materials (waveguides, coaxial devices), a vector network analyzer (VNA) is an excellent tool for this purpose since it provides full reflection and transmission characterization at high precision.
Calibration techniques such as SOLT (Short-Open-Load-Thru) and TRL (Thru-Reflect-Line) have been developed specifically for this purpose and involve the measurement of several standards that can be placed in the line to explicitly solve for the response of the system. When measuring a device of interest, the system correction can be applied, leaving a well-calibrated data set. VNAs can be coupled to free space (via a beam waveguide); however, it has historically been much more difficult to perform vector calibration in this configuration. Separation of the instrument and test device response has been previously demonstrated, but a complete solution applicable in the more general cases is extremely useful and is the motivation of this work.
A technique has been developed for VNAs that allows for complete calibration of coupled quasi-optical systems. The technique involves the translation of one or more standards in the beam path to infer the form of the error matrices of the system. The prime advantage of this technique is the potential for characterizing quasi-optical devices and to test material samples that are not easily accommodated in waveguide. This technique and associated hardware can enhance the utility of existing VNAs and reflectometers by adding the capability of using such devices to measure quasi-optical devices.
This work was done by David Chuss and Edward Wollack of Goddard Space Flight Center. GSC-16996-1