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The problem of calculation of tees in rectangular waveguides has been discussed a lot of times. Except of the main geometry of conventional H(E)-tee [1] the tees with inserts of different kinds have been studied [2]. At that the dominant goal of real calculations was to investigate the possibility of ideal matching at the excitation of tee side arm. However there is another problem of tee tuning that arises at the frequency selective systems design. For example one of different schemes of dilplexer design is based on using so called Y-type three-ports. Such a three-port has to characterize by the S-matrix that is similar to S-matrix of symmetrical 120° Y-junction. To use an E- or H-tee as a common junction of diplexer we have firstly to design a special load in tee that equalizes the reflectivities in common port and in channel ports. It may be achieved for example by introducing the capacitive iris in the side tee arm [3]. However this way is not the best one, as such a unit usually has relatively high dispersion and is not available for broadband diplexers.