S.A. Khodenkov – Ph.D. (Eng.), Associate Professor, Reshetnev Siberian State University of Science and Technology (Krasnoyarsk)
Frequency-selective devices of microwave frequencies are the most important elements of modern radio-engineering systems. Among a wide variety of such devices, bandpass filters, highpass and lowpass filters, amplitude and phase modulators are the most popular ones. In addition to the above-mentioned structures, dual-channel frequency dividers – diplexers, are also in great demand. Currently, when developing these devices, special attention is paid to microstrip structures, including multimode resonators, which reduce the size of diplexers in its turn.
In the microstrip diplexer developed by means of electrodynamic numerical analysis of 3D model, on the substrate with relative dielectric penetrability ε = 80, there are regular and irregular strip conductors grounded on the base with seven identical round holes with copper filling (diameter d ~ 0,45 mm) and the depth equal to the thickness of the substrate h = 1 mm. Therefore, central irregular strip conductor applied to the substrate, having the input port of the microwave structure is double grounded to the base, in this regard, so it is a 3-mode resonator, consisting of two quarter-wave resonators and one half-wave resonator. There are output ports on the extreme regular strip conductors of the structure.
The diplexer dimensions were chosen in such a way, that the lowest resonance from each quarter-wave resonator with a regular strip-shaped conductor formed a passband of either low-frequency channel or high-frequency one.
Therefore, the dimensions of the irregular strip conductor of half-wave resonator can be chosen in such a way, that its lowest resonance gets to the frequencies of low-frequency passband or high-frequency one. The additional strip conductor, applied to the substrate, allows to form additional coupling in a 3-mode resonator, so its dimensions and location were chosen in such a way, that attenuation pole in both channels at frequencies between the bandwidths existed in amplitude-frequency characteristics of the diplexer.
Diplexer dimensions are 26,7×21,9×1,0 mm.
Consequently, the presented new miniature microstrip diplexer based on 3-mode resonator with additional electromagnetic coupling has high electrical properties: sharp slopes of bandpass and the extended high-frequency stop band.
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