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The operating principle and design of compact, non-standard, reduced height waveguide planar magic tee junctions are described. The. distinguishing feature of these components is the placement of the difference port on a layer separated from other three ports by a common waveguide broadwall. The two parts of the component are coupled through a slot located in the common broadwall of two. A design methodology making use of extensive electromagnetic modelling based on method of moment (MoM) analysis and finite element method (FEM)-based commercial software has been developed. The use of such planar magic tee junctions in developing planar monopulse comparators for airborne slotted array applications has been demonstrated.
The workhorse of most tactical aircraft and missile systems deployed in the field today, as well as a number of non-military applications, is the mechanically scanned monopulse slotted waveguide array antenna because of its rugged and compact structure, high radiation efficiency, precise control over amplitude and phase, and high power handling capacity.1-4 These arrays use a multilayer feeding structure with two plane monopulse comparator networks to get the required monopulse capability. The weight, size and profile (compactness) of the slotted array antenna depends on the individual modules of the array like radiating and coupling waveguides, feeder networks and monopulse comparator networks. The monopulse comparator network forms a critical part of an antenna system. This network extracts power from the four quadrants of the antenna to give a sum pattern and two orthogonal difference patterns. Any error in the network can severely affect the performance of the complete antenna. A magic tee, being the basic building block of a monopulse comparator, plays a very important role in making such arrays lightweight and compact. The performance of a monopulse comparator depends on the accuracy with which individual magic tees are designed. Due to the compact nature of the slotted waveguide structure it is required to design compact folded magic tees. Also, care should be taken in the design to see the viability of mass producing these comparators as an integral part of the antenna.
In this article, the designs of two different types of compact planar magic tee junctions - a planar magic tee junction (PMTJ1) using a collinear transverse waveguide slot coupler and...