Compact Bandpass Waveguide Filters with Inductive Couplings with E-plane Symmetry and without E-plane Symmetry

Introduction. Modern satellite communication systems continue to impose stricter requirements on the frequency response, weight, and size of filters. In this paper, several designs of bandpass filters with inductive couplings on corrugated waveguides are considered. Although such filters have been described previously, this paper considers their possible implementations based on narrow cross-section waveguides, as well as on structures with and without electric field symmetry.Aim. To study filters with inductive couplings with and without electric field symmetry, as well as to assess the filter stopband width and attenuation.Materials and methods. Numerical studies were carried out by the finite element method (FEM) and the method of final difference in the time domain (FDTD).Results. Modeling of filters with inductive couplings with and without electric field symmetry was carried out. Filters without electric field symmetry were found to exhibit higher characteristics in terms of weight and size, at the same time as having a narrower stopband. The conducted modeling also showed that filters with stubs of the same cross section allow stopband attenuation to be improved by almost 20 dB compared to filters with stubs of varied cross section. The frequency responses of filters with inductive couplings obtained by electrodynamic modeling were established to agree well with those obtained experimentally. A ten-order ultra-compact filter with inductive couplings without electric field symmetry was considered, with the bandwidth loss of not more than 0.7 dB, the attenuation of at least 80 dB in the frequency range from 7.9 to 8.4 GHz, and the filter length of 30 mm.Conclusion. The use of filters with inductive couplings allows their mass and dimension characteristics to be significantly improved without increasing losses in the bandwidth at the same time as maintaining a high level of attenuation in the stopband.