Design of compact-sizehigh isolation branching OMT by themode-matching technique

Thispaperpresents thedesign andperformance ofa compact-size branching orthomode transducer (OM1)with high isolation characteristics. Thedesign isperformed using themode-matching applied tothecircular-to-rectangular waveguide Tjunctions. Thedesign example demonstrates thehighefficiency ofthis design method forX-band branching OMT without septa, andrealizes excellent performance. Thetheory isverified byagoodagreement withmeasurements. Introduction Inorthogonal dual-polarized antenna feed systems, the orthomode transducer (OMT)isoneofthemostimportant components. Ingeneral, theOMTseparates twoindependent signals oftheorthogonal dominant modesexcited atthe commonport, andsupplies themtothefundamental mode oftheallocated single polarization signal interface ports. TheOMT typesofthestandard class aimathigh performance within theoperating narrowfrequency band andlowfabrication cost(l). TheOMT typeissuitable to meetthese requirements which isbased onashort circuited circular commonwaveguide without septa, andtwo rectangular branching waveguides. This OMTtypehasthe advantage ofreducing thecomponent size inthedirection ofthelongitudinal axis ofthecommonwaveguide andlow fabrication costbecause fabrication costforsepta isnot required. Since thelocation oftherespective branchings withrespect totheshort circuit ofthecommonwaveguide aregenerally determined byaquarter andthree quarters wavelength (k),thedistance between branchings becomes