Waveguide slot radiators

Hill, David Roy (1978). Waveguide slot radiators. MPhil thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f923


This dissertation presents part of the work done in the development of Aircraft Microwave Landing System Antennas, which use slotted wave-guides as radiating elements.

A theoretical analysis of the coupling of electromagnetic energy, from waveguides, through slot apertures, and into free-space is described. In particular the method is applied to "I" shaped slots in the narrow walls of rectangular waveguides. Such slots form elements of a series fed linear array antenna. Expressions are developed for the slot conductance in terms of physical dimensions, and the radiation resistance of an assumed equivalent wire dipole antenna.

Firstly the general theory of radiation patterns obtained from current elements, apertures and line source distributions is reviewed. Magnetic Vector Potential (MVP) is introduced, to simplify the procedure for determining the magnetic field radiated by a current carrying circuit.

Antenna pattern synthesis is a procedure for deriving an aperture distribution which will produce a prescribed antenna radiation pattern. Some synthesis methods having application to both uniformly and non-uniformly spaced arrays are introduced and discussed.

However good the synthesis procedure may be, the final practical result will depend very much upon how accurately the aperture distribution is realised. In any practical system errors are inevitable. Their effects on the radiation pattern are discussed in detail for continuous and discrete element array apertures.

Following a survey of slot analysis methods, field equations for an arbitrary slot in cylindrical waveguide are developed. The method is extended to I slots in the narrow wall of rectangular waveguide. Resonance is assumed, enabling the slots to be represented by shunt conductances on a transmission line. The theory is tested by application to shunt displaced broadwall slots, for which the results have already been published.

Finally the development of a practical array using I slots is described and its measured performance is discussed.

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