Bandwidth enhancement by optimizing the cross-sectional shape of the coupling region in a waveguide 2-plane hybrid

Fig. 1 shows the waveguide 2-plane hybrid [1] . The bandwidth of the conventional hybrid was 6.5% [2] . The main modes to be considered in the coupled region are the TE10-like, the TE20-like, the TE/TM11-like and the TE/TM21-like modes. These modes have two-dimensional polarity in the cross section and different propagating constants. These propagation constants should satisfy β 11 =β 20 = (β 10 + β 21 )/2. The length of the coupled region for the hybrid should be π / (β 10 – β 21 ). The waveguide 2-plane coupler has four ports in the input and the output sides. These ports are rectangular and have two-dimensional symmetry. The sizes and the positions of the ports are determined so that the four main modes should have equal coupling with the coupled region. Then the ideal operation of the 2-plane hybrid is achieved, where for incidence from Port 1 as an example, all the input power is divided equally to the four output ports 5-8, and the phase difference of 90 degrees at Ports 6 and 7 and that of 180 degrees at Port 8 are obtained in comparison with Port 5. The 1/8 model is introduced by placing PEC/PMC properly at Plane A, B and C considering the three-dimensional symmetry as shown in Fig. 1 . This model is analyzed by a hybrid of the mode matching method and the finite element method [2] .