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.