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SHF Bandpass Filter Based on the LTCC Technology

Keywords:

A.V. Shorokhova, A.I. Tyumentsev


Electrical filters intended for the desired signal selection and noise suppression are widely used in communication, location, navigation, and telecommunication radio systems. Conventionally within a range of comparatively low frequencies (up to several hundreds of MHz) LC filters based on lumped elements are used whereas for higher frequencies filters based on distributed elements are used. However these filters have a number of disadvantages. Thus LC filters have large dimensions and limited frequency range and transmission line filters have spurious passbands on frequencies multiple to the fundamental frequency and comparatively large dimensions within the lower part of SHF range. LC filters using LTCC technology do not have disadvantages. These filters have wider practical applications as they fully meet state-of-the-art radio equipment requirements. Filters using lumped elements and LTCC technology can be realized based on the well-known LC filter circuits consisting of inductors and capacitors. Although a great number of LC filter circuits are known, only a few of them are suitable for practical applications using LTCC technology. First of all this is due to the problems of filter elements physical implementations. Therefore developing SHF filters based on lumped elements is necessary to select such circuit variants that can be realized practically. The paper analyzes different ways for LC filter elements realization and circuit variants that provide high technical parameters and are manufacturable and realizable practically. As a result a circuit is synthesized and filter design is determined that meet the abovementioned requirements. Based on the results of the electromagnetic analysis of the obtained solution, SHF LC filter prototypes are manufactured using low temperature ceramics and experimentally tested. The following conclusions result from this paper: 1. Although conventional bandpass LC filters can potentially provide somewhat lower losses within the passband as compared with LTCC multilayer printed filters, the latter have much better weight and dimension parameters and manufacturability with relatively similar other electrical parameters. 2. Using LTCC ceramics allows high repeatability of filter characteristics, operation within a wider, relative to the printed circuit boards, temperature range and is perspective for developing devices providing frequency selection of signals for multi purpose communication, navigation and location equipment particularly that must satisfy higher requirements on weight and dimensions. The circuit proposed in this paper is low cost as regards from the viewpoint of the quantity of used elements and allows high electrical parameters and small dimensions to be provided.
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