Advances in microwave direction finding

The purpose of the paper is to describe three new microwave direction-finding (d.f.) systems employing the principle of amplitude comparison. Though designed, in this case, for use with pulse signals, application of the systems could also be extended to continuous-wave signals. Theoretical predictions of performance and considerations of design requirements are supported by experimental confirmation from complete laboratory models of two of the systems, and from measurements on certain component parts of the third system. The systems are individually suitable for different types of application, and collectively they represent advances in increasing bearing accuracy and system sensitivity, and in reducing equipment bulk and cost, without degrading broadband frequency coverage. The first system employs a switching and storage technique which enables a single, preferably a tunable narrowband, receiver to be used with four (or more) fixed aerials, thereby saving three (or more) receivers, which would otherwise need to be used for amplitude-comparison d.f. The switch rate is relatively slow, so that a few cycles are accomplished within the time that the transmitting aerial illuminates the d.f. site. The second system employs a modulation-marking technique to achieve the same objects as the first system. Its operation is continuous in time, as opposed to that of the first system, which is cyclic, and so it is capable of employment with signals of duration short compared with the cycle period of the first system. The third system employs very fast (intrapulse) switching of a pair of receivers around a fixed circular array of sixteen aerials. Theoretically, it is capable of high-accuracy d.f. on a pulse-by-pulse basis, since the larger number of aerials in the array reduces the aerial contribution to d.f. errors, which is usually dominant. Its d.f. performance is also dependent on the amplitude balance (tracking) of either radio-frequency switches or frequency changers, whi- ch, at present, may be the factor limiting d.f. accuracy.