COMFIL - COMpact C-/Ku-band broadband waveguide FILters

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The design of innovative on-board compact broadband bandpass filters at C- and Ku-band with wide spurious-free range are the scope of the project. Such filters are based on both TMmode cavities and ridged/combline waveguide resonators.

RF Microtech (Perugia, Italy) is the prime contractor and electro-magnetic designer. Pasquali Microwave Systems (Florence, Italy) is the partner involved in the mechanical design and fabrication of prototypes.


Main challenge of the project is to find out filter concepts able to provide minimization of volume and mass while keeping unchanged insertion loss and wide spurious-free out-of-band range (up 2xf0) with respect to standard waveguide technology based on the cascade of a high-Q cavity bandpass filter and a waveguide low-pass filter. 


The main benefit of the new product will be the significant mass and volume reduction with respect to standard technology (30% reduction is the target). This will lead to a significant mass and volume reduction of the satellite payloads, thus to a significant reduction of the satellite launch cost.


The proposed filters are based on two types of waveguide resonators that are used in two different sections of the filter. The first section is composed by compact TM waveguide cavities (single-mode for C-band and dual-mode for Ku-band) able to minimize the filter length. The second section is composed by ridge/combline resonators in an evanescent mode waveguide. TM cavities allow for minimization of the filter length, while maintaining high the resonator Q. They also allow for an easy introduction of transmission zeros close to the passband. Ridge resonators, instead, have a very wide spurious-free out-of-band response.

System Architecture

The first section based on TM cavities fulfils the bandpass and near out-of-band requirements, while the second section based on ridge resonators allows for the fulfilment of the out-of-band requirements.


The activity to carry out within the project is divided into 2  technical parts, each consisting of several work packages (WP) The total duration is 24 months from Kick-Off Meeting (KO).

Part 1 is dedicated to the review of the current state of the art of broadband waveguide filters at C- and Ku- band for satellite applications and identification of detailed filter concepts based also on the preliminary ideas presented in this proposal. Several filter concepts are analysed to select the best concepts and identify, prevent, mitigate and solve possible problems. At least one breadboard type per each frequency band is built and tested.

Part 2 is dedicated to the design, manufacturing and test in laboratory under environment condition of EM filters based on BBs results of Part 1 employing the developed techniques and technologies in Part 1. Starting from a TRL of 3, the final TRL is 5-6. 

Current status

Part 2 of the project is finalized (FR July 2018). Both  EMs are very close to the objective of the project. All objectives of the project have been reached. Insertion Loss and Rejection performances are excellent and filter mass and volume are both less than 50% compared to standard technology for both EMs (Ku- and C- band filters) with a wideband spurious-free frequency range of operation (more than 2 times central frequency in the passband). Results of thermal and mechanical test are compliant with specifications. The same design concepts used for C-band and Ku-band bandpass filters can be adopted for similar specifications with wider and narrower passband from C- to Ka-band. 

Prime Contractor