The horn plays an elemental role in the make up of a radio-telescope. The focus of this research is on one particular type of horn – the diagonal horn. An analysis of the diagonal horn is made using the Fourier method. The analysis begins from Maxwell’s equations, as the basic building block, and describes the steps involved in developing the radiation pattern. Based on the theory, a program was written that produces the theoretical graphs referred to throughout the thesis. A diagonal horn was manufactured and the radiation patterns were measured. A comparison of these measured patterns is made against the theoretically generated patterns. Further research was carried out to demonstrate the effects on the radiation patterns when the horn is fitted with a dielectric plug. This practice may enhance the directivity of the horn at the cost of introducing new losses / Master of Engineering (Hons)