Algorithm and results of designing the circular pillbox-type vacuum windows in rectangular waveguides

Abstract

The considered components have the input and output rectangular waveguides and placed between them a circular waveguide segment with one or two dielectric plates that are firmly secured into annular grooves. The latter essentially improves the component manufacturing and air-tightness. The possibility of inserting the second plate rises the operate reliability of windows used as units for hermetic sealing the satellite antenna fairleads and vacuum electronic devices. The windows are related to the class of complicated structures, a direct high accuracy analysis of which by the mode-matching technique is difficult even with mainframes The matter is that such structures are three-dimensional ones, and electromagnetic fields in their partial domains must be expended in terms of the vector basis functions of TE mn and TM mn modes. The application of decomposition principle allows to divide the complicated structure into a set of key elements, the integration of which with the aid of the generalized S-matrix technique gives a possibility to create a more economical algorithm that does not lose the efficiency at PC realization. That is why we used this approach for creating the numerical algorithm for the design of vacuum windows. The following elements were separated as the key ones: 1) rectangular-to- square waveguide junction, 2) junction of a square waveguide and a circular one inscribed into the former, 3) junction of circular waveguides of different diameters and dielectric fillings. The algorithms of exact calculation of the key elements' generalized scattering matrices were built on the basis of mode-matching method. It should be noted that the connection of the first two elements by a zero length square waveguide results in the junction of circular and inscribed into it rectangular waveguides. The algorithm is realized for IBM PC 286-486 in MS DOS media as a C ++ software. The results of design are presented for some vacuum window constructions having one and two dielectric sealing plates One-plate windows have the value of SWR<1.15-1.2 within the waveguide operation range, For two-plate windows increasing of SWR is observed at the high-frequency part of the range. The physical explanation of broad-band matching effect is provided Real components were manufactured for waveguides with the cross-sections of 23x10 mm and 28.5x12.6 mm. The sapphire and ceramics with permittivity of e = 9.6 were chosen as material for sealing plates. The theoretical results are in good agreement with measured ones.