Analysis And Design Of Frequency Domain Reflectometer In Transmitters

RF signal is transmitted and received with antenna feeder, whose installation and operation directly affect the quality and coverage of signal and the situation of transmitter. If antenna feeder fails, RF signal loss and the coverage is reduced. If the fault is more serious, the front-end equipments are likely to be damaged. Therefore, the routine maintenance of antenna feeder is very necessary.For the maintenance test of antenna feeder in transmitters, the traditional method, computing VS WR with PF and Pr is mostly used. Its shortages are:1. directivity of the coupler is poor. As a result, echo signal contains strong forward signal, so that the accuracy cannot be guaranteed. Ideally, forward signal leaked is far less than echo signal, and the traditional method is accurate. However, in practice, transmitting signal leaked is often close to echo signal, and this method is not inaccurate.2. when using the traditional method, only the range of fault point, but not the distance, can be computed.For long distance fault detection of antenna feeder, phase detecting method is generally used. The main idea is to divide the measuring signal, whose frequency is already known, into two way. One way is consulted for phase detecting, and the other way is transmitted, while the signal reflected is obtained. The delay of reflection signal and reference signal are different, and there is a certain lag. In the electronic measurement technology, the measuring target is usually quantified via the range of signal. Therefore, the phase should be converted to amplitude.This thesis researches the transmitter frequency domain reflectometry, namely high-precision standing wave detection:1. the PDFDR technology is complemented, with which the standing wave ratio of feed system, cable loss and fault point distance of antenna feeder in transmitter, can be measured.2. high precision standing wave measurement solves the inaccuracy of traditional standing wave detection.3. online standing wave detection can be done, without interrupting the communication of transmitters.