The current baseline channel filter design consist in the cascading of 2 asymmetric response BPFs (BPF-1 + BPF-2, pseudo LPF + pseudo HPF configuration), with centre frequency fc tuning screws. With this configuration no direct BW tuning is required, since BW selection is achieved by shifting fc1 and fc2.

Each individual BPF is based in waveguide 3D cavity resonators, to benefit from the high Q and relatively low modelling and realization complexity. The cavities accommodation is such as to present compact profile. Tuning will be implemented by means of tuning screws penetrating inside the resonators. Screws movement is achieved by means of a single motor for each type of tuning, e.g., one motor moves all BPF-1 fc tuning screws and another motor moves all BPF-2 fc tuning screws.

The main features of the proposed solution are:

1. Use of very high Q rectangular waveguide resonators (in excess of 11.000).
2. All the cavities are coupled sidewall, resulting in a more compact solution. This is an essential feature in view of including the filter in a multiplexer.
3. Zig zag topology allows to insert cross-couplings between cavities in such a way as to create transmission zeroes which improve the attenuation close to the pass-band, without requiring the filter to be folded.
4. Mechanical tuning of each cavity is achieved by means of a metallic cylinder penetrating parallel to the waveguide axis. This allows:
   a) to reduce sensitivity with respect to the case where tuning cylinders penetrate parallel to the Electric Field in the centre of the wide wall of the cavity;
   b) There is no necessity for the fc tuning screws to present contact with the side walls: even when a small gap is left between the cylinder and its housing, external to resonator, since the resonator mode and the mode of the resulting coaxial do not couple to each other, there are no spills which could reduce the high Q of the cavities.