Methods for shaping vertical radiation patterns of v.h.f. and u.h.f. transmitting aerials

An important problem in the design of v.h.f. and u.h.f. transmitting aerials is the provision of a vertical radiation pattern, which gives an approximately uniform field strength over the prescribed service area. A good solution is provided by a beam-tilted cosecant-shaped radiation pattern. Several methods are described for synthetising radiation patterns of this type by varying either the amplitudes or the phases (or both) of the radiating currents in a linear column of equispaced elements. Some examples are given of the application of these techniques to the types of multitiered aerials employed at v.h.f. and u.h.f. broadcasting stations. Consideration is also given to the problems of realising the required current distributions, and important design factors such as aerial-impedance matching and pattern bandwidth are discussed. Recommendations are made for selecting v.r.p.-shaping techniques to satisfy a range of design requirements.