Abstract :
An account is given of the development at the National Physical Laboratory of rotating H-type Adcock systems suitable for use at metre and decimetre wavelengths. Instruments of high precision for the range 26¿600 Mc/s (0.5¿12 m wavelength) are described, and details of their performance are given. The direction-finders at the tower end of this frequency range are of high sensitivity and have seen considerable practical service. At the higher frequencies the instruments are of an experimental nature, constructed with a view to examining the problems to be encountered in exploiting this part of the band. Development has proceeded largely on empirical lines, but from this work a fair appreciation has now been obtained of the fundamental factors affecting performance and of the practical means for taking them into account. Some progress has been made, for example, in understanding the cause of polarization errors, which are of importance in some¿but not all¿d.f. applications at these frequencies. The first half of the paper is therefore devoted to a discussion of these factors and to a description of certain common design features which have emerged. It is probable that, at frequencies above about 300 Mc/s, the application of ground-based simple Adcock systems will be limited by their inherently low sensitivity. This disadvantage may be partly overcome by the use of passive reflecting elements, and a system is described in which a sheet reflector is used in conjunction with an H-type Adcock aerial.
