The microwave frequency discriminators (MFD) are important part of instantaneous frequency measurement (IFM) receivers. There are known, so-called, single function discriminators (SFMFD) and quadrature discriminators (QMFD). The QMFDs have a more complicated structure but enable achieve, in comparable conditions, a higher frequency measurement resolution. Directional couplers, among other elements, are used for MFD construction. The couplers based on coupled lines provide wide operation frequency band but their fabrication requires more complicated technology. The new structure of quadrature microwave frequency discriminator based on two single-step power dividers and two rat-race 3 dB couplers is proposed in the paper. The correlator of the QMFD was designed and fabricated onto single printed circuit board (PCB). The input port connector and connectors for output microwave detectors were mounted in such way to avoid crossings of the transmission lines on PCB. The middle part of the made discriminator’s operation frequency range includes WiFi frequency band. Structure and measured parameters of the developed and fabricated quadrature microwave frequency discriminator were presented in the paper.
Direction finding that is establishing an angle position of microwave sources is an important element of reconnaissance of electromagnetic space and threat warning tasks. For these purposes, direction finding of sources, which are operating transiently and irregularly is especially significant, as well as difficult to accomplish. In these cases, the direction of the emission source is established on the basis of a single pulse, using the phase method or the amplitude method. The precision of direction finding for a single microwave emitter is relatively good. It may not exceed a tenth of a degree over the wide frequency range. In operating conditions, where strong disturbances exist, for instance with several sources operating simultaneously, results of direction finding may have a significant error. Ideas of monopulse direction finding using amplitude methods and phase methods were described in the work. Results of simulation for a single microwave emitter, as well as multiple emitters operating simultaneously were presented. It was shown that when multiple sources operate at the same time, the direction finding process becomes interrupted, but an intra-pulse analysis of received signals enables reduction of the error of angle position measurement of each observed emitters.
Research work related to the design and use of anti-radiation missiles (ARM), and any systems intended to protect radar and other radiation-emitting installations against ARMs, requires access to theoretical and physical models of direction finding devices, which are used in guidance systems installed in the aforementioned missiles. In this work, the authors present the concept of an electromagnetic source seeker working in the microwave band. In the solution presented herein, the direction finding is accomplished using the phase method. Phase analysis of signals emitted by the observed microwave source is relatively fast due to the quadrature configuration of the microwave phase discriminator used for this purpose. During an attack, an anti-radiation missile moves at great speed, which exceeds 1000 m/s. Due to this fact, the missile needs to be equipped with systems, which are capable of estimating the direction of the targeted source, and which can update the relevant information as quickly as possible. Such properties in the presented concept were achieved by using comparators with analogue inputs and logical digital (0/1) outputs. As a result, the information from the direction finding channel is obtained in a digital format, with the number of bits (the resolution) being dependent on the number of applied comparators. The authors therefore assume that a coarse direction finding will be used when the deviation between missile trajectory and the direction of target source is relatively large, whereas the more precise target location estimation algorithm will be used when the trajectory of the missile is matched (within established limits) to the direction of the emission source.
Single-function microwave frequency detectors are used in the structures of multichannel frequency discriminators. They allow determining the frequency of an unknown signal in a very short time of the order of hundreds of nanoseconds. The shape of the output voltage of the single-function detector versus frequency is described with a cosine or a sine function. In the systems, where a great accuracy of frequency determination is not required, and a time measurement is vital, it is possible to apply only one single-function frequency detector. A single-function frequency detector is composed of two blocks: a system of developing of proportional phase difference and a phase sensitive detector. The function of the first block is to generate two output microwave signals with a phase difference between them proportional to the frequency of the input signal. A phase sensitive detector converts the difference of phases of input signals into voltage. The output voltage is subject to further processing and, based on it, the frequency of the input signal is determined.