VNA calibration suitable for free-space one-port measurements of large targets

This report is an evolution of [1] (which implemented the calibration technique described in [2], [3]). A different technique is described here, best suited for a large or heavy Device Under Test (DUT) that cannot be moved easily. It implements the variable short, variable load, fixed short calibration as described in [4], and the calibration coefficients are used to remove systematic errors from individual DUT measurements. The process also computes the phase of the reflection coefficient, which is however not usually interesting for this type of measurements. The main advantage of this method is that calibration can be made using calibration standards made with easily movable low-weight targets, using only one (frequency) sweep on the (static) DUT. The disadvantages are the lower signal-to-noise ratio, since only one sweep is made on the DUT, and the sensitivity (i.e. maximum measureable return loss), which is better than the return loss of the variable load standard by one or two orders of magnitude only. Nonetheless, this calibration technique is suitable for large heavy DUTs, normally with moderate return loss, which allows using lightweight commercial absorbers as calibration loads. [1] A. Simonetto, E. Sassolini Free-space measurement of low-reflectivity targets IFP Internal Report FP16/04 [2] A. Murk, A. Duric and F. Patt Characterization of ALMA Calibration Targets, 19th International Symposium on Space Terahertz Technology, Groningen, 28-30 April 2008. [Online] http://www.nrao.edu/meetings/isstt/papers/2008/2008530533.pdf [3] A. Murk, A. Duric ALMA Calibration Device Prototype Calibration Load Test Report FEND-40.06.04.00-005-A-REP [Online] https://safe.nrao.edu/wiki/pub/ALMA/CalAmp/FEND-40.06.04.00-005-A-REP.pdf [4] G. F. Engen Microwave circuit theory an foundations of microwave metrology Peter Peregrinus Ltd on behalf of IEE, ISBN 0 86341 287 4, Chapter 9