A now concept of PTP vector network analyzer

Abstract

A new concept for vector network analyzers design based on a perturbation two-port (PTP) is presented. The approach uses redundant states of the PTP. The best states of the PTP for a certain place in Smith chart and frequency are chosen to determine a reflection coefficient with minimum uncertainty. Four criteria for the selection are designed. The criteria were tested on measured parameters of different states of the PTP. Significant improvements in PTP bandwidth and uncertainty of measured data were achieved. Summary Six-port vector network analyzers (VNA) are well known for decades, [1]. Similar concept using only a scalar network analyzer and a PTP was designed in [2], where only a basic principle was designed and experimentally verified using a PTP with properties far from optimum. No recommendations for the structure of the PTP were given. Some suggestions for an optimum three state PTP can be found in [3], yet the states of the PTP are unpractical for a realization and are suitable only in a narrow frequency bandwidth. The main demand in the PTP design is to realize optimum states valid on the whole Smith chart in wide frequency band. These demands can be hardly satisfied with any minimum 3-states PTP. The solution is a new concept of the PTP vector network analyzer based on redundant multi-state PTP. It releases the demands on PTP so that they must be satisfied only in a part of Smith chart. The concept can be summarized into three key steps. • over-determination of measured data using more than three minimum states of the PTP • approximate determination of measured reflection coefficient in Smith chart using proper three PTP states • state the measured reflection coefficient more precisely applying the best PTP states determined in given frequency in corresponding part of Smith chart by proper test criteria The purpose of this paper is to present proper criteria for the PTP state selection and a new circuit solution for individual states of the 7-state PTP. Theory A typical arrangement of the new PTP vector network analyzer with seven switched PTP states is presented in Fig.1. P m 1 PTP 7 PTP 2 PTP 1