Waveguide filters and diplexers constitute an essential part of modern communication systems. Despite impressive progress in the last few decades in the microwave technology, the important role of waveguide components remains undisputed. This is due to their low loss and high power capability performance.
In order to secure commercial success, the waveguide filters and diplexers need to be not only optimally designed in terms of performance, but also in terms of cost. E-plane filter technology with an electrically conductive foil is one of the most suitable technologies for mass production due to low cost involved.
A waveguide E-plane filter component normally comprises two main parts, a first main part comprising a first waveguide section part and a second main part comprising a second waveguide section part. Each waveguide section part comprises three walls; a bottom and corresponding sides.
The first main part and the second main part are arranged to be mounted together such that the first waveguide section part and the second waveguide section part face each other, and together constitute a resulting waveguide section part. This means that each main part comprises a half-width waveguide section part where, when mounted together, the resulting waveguide section part constitutes a full-width waveguide section part.
The electromagnetic field propagates parallel to the intersection. Since the waveguide section parts normally have equal sizes, and thus the same width of the corresponding sides, the dominant TE10 mode of the electromagnetic field has its maximum magnitude at said intersection.
Between the main parts, at the intersection, an electrically conducting foil is placed, having a filter part comprising full height or partial-height apertures. The filter part runs between the waveguide section parts.
The main advantage using E-plane filters is that in many cases the same main parts can be used for filters working at different center frequencies and/or covering different bandwidths. Then, since a filter function is determined by a topology of the electrically conducting foil, it is only the foil which needs to be replaced whenever a change in the filter characteristic is required
However, using E-plane technology results in filters/diplexers which are of a relatively large size. The size of an E-plane filer/diplexer, especially the longitudinal length of the electrically conducting foil, is defined by a desired filter performance; center frequency and bandwidth. This means that, to a large extent, the size of the main parts is determined by the longitudinal length of the electrically conducting foil.
This poses a problem since it brings inflexibility where instead flexibility may be required. For example, when a diplexer design is concerned, the distance between a so-called band-stop resonator in the form of a T-junction and a common port of the diplexer needs to be fixed. If the required longitudinal length of the electrically conducting foil which is placed between the band-stop resonator and the common port exceeds said fixed length some functionality may have to be degraded.
This can limit the possibility of having the same housing and different electrically conductive foils inserted between the main parts in order to realize different filter/diplexer characteristics.
There is thus a need for being able to vary the length of the electrically conductive foil in a controlled manner while keeping the same filter response, such that both flexibility and control are achieved for designing E-plane filters.