MICROWAVE CIRCUIT ANALYZERS ON A MULTI-PROBE MEASURING LINE. REVIEW OF SIGNAL PROCESSING METHODS, PROBLEMS AND PROSPECTS (REVIEW)

Abstract

Further progress in microwave technology is inextricably linked with the creation of new precision automatic measuring systems. In our country, microwave circuit vector analyzers that can measure the amplitude and phase relationships of the S-parameters of the microwave networks under test are not mass-produced. The use of multi-port reflectometers (MPR) as measuring devices in automatic microwave circuit analyzers allows creating relatively cheap and high-precision devices for studying load parameters. The paper provides an overview of the works in which the MPR method is developed, when the latter can be represented by a multi-probe transmission line reflectometer (MTLR). The history of the development of measurement methods using traditional MPR is briefly described and it is shown that the main problem of their use is reflectometer calibration, which can be carried out accurately only using a set of precision calibration standards. MTLR, which is a special case of MPR, is studied in detail. It is shown that random measurement errors by the MTLR method are higher than those of a precisely calibrated MR. However, the MTLR has important advantages that are discussed in the paper. A strategy for increasing the measurement accuracy using the MTLR is described: 1) optimal methods for processing output signals from the MTLR probes using the maximum likelihood method are proposed; 2) methods for calibrating the MTLR sensors are studied in detail and it is shown that it can be calibrated using a set of inaccurately known loads with their parallel certification, therefore, systematic calibration errors are significantly reduced; 3) methods for optimizing the MTLR design by arranging the probes inside the microwave path for measuring with maximum accuracy in narrow and wide frequency ranges are studied, and it is also shown how it is possible to measure with potentially achievable accuracy due to the proper choice of weighting coefficients in the MTLR probes. Random and systematic errors in measuring the complex reflection index of microwave loads, as well as uncertainties in measuring types A and B by the MTLR method are investigated, and references to relevant works are given. In conclusion, the possibilities of joint use of the MTLR and MPR methods are considered, a combined MPR is briefly described, which measures with an accuracy characteristic of a traditional MPR, but can be calibrated using a set of unknown loads, which is inherent in the MTLR method. Automatic network analyzer, multi-pole reflectometer, multi-probe measuring line, maximum likelihood method, error dispersion matrix, meter calibration.