Pulsed radar measurements and related equipment

Abstract

The purpose of this thesis has been to develop novel methods for pulsed radar measurements, creating practical tools for verifying the operation of a modern pulsed radar, and to build working prototypes suitable for field use. Very little information has been published in the radar field perhaps due to the military nature of many research projects. Methods and equipment are typically researched by different armed forces. In this thesis, some tools for frequency, power and waveform measurements are presented. Even the most modern commercial measuring instruments, however, are not capable of measuring a pulsed radar signal, mostly due to the short (even tens of nanoseconds) pulse length. The limitations of conventional measuring devices are discussed in the overview part of the thesis and also in Publications II and IV. The first publication demonstrates a radar calibration system, based on a fiber-optic delay line. The idea to use an optical delay line for such a purpose is not new, but an operational setup has not been published previously. The calibrator provides a convenient method to use the radar's own signal for calibration. The optical link makes it possible to use long delays, even tens of microseconds, without significant signal attenuation. Furthermore, two frequency measurement methods for short-term stability evaluation are presented. Both are based on a phase detector. The first setup has better frequency uncertainty, even 1.6 Hz, with a sampling speed of 10 000 s-1. The other setup is used to detect frequency differences: A deviation of 200 kHz in the carrier frequency could be detected when the pulse length was 200 ns. This system outperforms the first one when short pulses are evaluated. The phase detector based setup itself is old and familiar technology, but the idea to use it in this application is one thing new. Finally, two new instrumentation radars are also presented. They are used to measure the effects that terrain, weather, vegetation and seasonal changes have on radar clutter or signal propagation. A significant effort has been made by other scientists in developing mathematical models to be able to simulate the effects mentioned, but so far the only reliable method for creating clutter models is to collect data with a real radar. Such instrumentation radars have probably been developed earlier, but until now they have not been published.