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|Analysis of the Fabrication Issues Relating to Multilayer Microwave Components|
|Keywords: multilayer, filters, fabrication|
|Multilayer fabrication techniques offer the microwave designer the opportunity to develop very high performance planar components. However, there is a lack of information in the literature on the optimum design procedures, and no authors have so far addressed the key issue of how fabrication errors can affect the RF performance. In this paper we present a design strategy for multilayer, edge-coupled, bandpass filters (ECBPFs). The design methodology is complemented with new data from a sensitivity analysis that shows how electrical performance is affected by errors in the fabrication process. Wide bandwidth from symmetrical ECBPFs in single-layer configuration is only achievable with tight conductor coupling, and hence very high line and space resolution. These resolution requirements lead to fabrication difficulties that can be overcome with a multilayer process, where the coupling is between conductors on different layers. This approach also leads to very compact devices with increased design flexibility. However, in order to maintain the correct impedances for the conductors on different layers, the structure become asymmetric. Modal analysis has been employed for the asymmetric coupled lines, and this has led to a new, efficient design procedure. A full-wave analysis was used for the realization of the physical dimensions of the filter. Following from this an analysis of the effect of registration errors between the top and embedded conductor layers was performed, and included the effects of frequency and materials parameters. This offers a useful guideline for manufacturers as to the degree of alignment accuracy needed in particular situations. The use of the dielectric materials with higher relative permittivity was shown to be more tolerant to registration errors. Measurement data are presented for filters at 2.5GHz, 5GHz, and 7.5GHz, with 4 and 6 sections, to validate the design procedure, and for comparison with the analytical results.|
|Chunwei Min, Student
University of Surrey
Guildford, Surrey GU2 7XH,