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Bandpass Filter with In Orbit Reconfigurable Bandwidth

Objectives

This project aims at the development of a on-board tunable channel filter in Ku-Band, which is the first step for the development of such reconfigurable IMUX devices.

Reconfigurable hardware platforms for modern communication systems are highly desired since by allowing for real-time system adaptation to different parameters (users varying demands and distribution, environmental conditions etc.) tends to maximize the return of investment.

One of the major bottlenecks in the development of reconfigurable payloads is the input and output filtering section, where for the moment filters of fixed centre frequency and bandwidth are employed. The utilization of reconfigurable IMUX and OMUX would allow substantial reduction of both mass and costs wrt today's switched multiplexer solution. Ideally one reconfigurable IMUX and OMUX design could apply to all payloads operating in a certain band. Thus, the necessity to design a new filtering section everytime a new payload is developed would be eliminated, while the reconfigurability would also eliminate many risks regarding last-minute changes in the development of a payload/system.

Challenges

The key issues for the in-orbit reconfigurable channel filter are:

  • Reliability: Reliability is a key requirement of this project, emerging from the application of the reconfigurable filter in satellite communications. Certain reconfiguration concepts that do not allow for simple redundancy concepts or involve the utilization of materials and mechanisms of high design risk will need to be excluded. Reconfiguration needs to be proven safe. Proven technologies with heritage in space applications will be preferred;
  • RF sensitivity to tuning mechanism inaccuracies;
  • Compactness of the design.

To handle these issues, a RF and mechanical (tuning mechanism) co-design approach will be implemented.

Benefits

The main benefit of this project will be the demonstration of a possible attractive design for space qualified reconfigurable channel filters in Ku-Band. Such a demonstration will enable the design of reliable channel filters for future reconfigurable IMUX devices in Ku-Band.

Features

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.

Plan

The study is divided in two phases of overall duration equal to 24 months. The first phase (10 months) is dedicated to:

  • An extended review of the available in literature and patens solutions;
  • Trade-off studies between the available solutions (also by experimentally obtained results) taking into account the requirements set forth in the statement of work;
  • Identification of two most suitable solutions;
  • Preliminary electrical and mechanical analyses of the two selected solutions and selection of the most suitable one;
  • Preparation of an evaluation plan in order to validate by test the proposed reconfiguration concept.

The second phase (14 months), which will take place only upon positive decision of the Agency, foresees:

  • The evaluation of the selected reconfiguration concept by means of tests on simplified models (implementing the evaluation plan prepared in phase 1);
  • The development and manufacturing of an elegant breadboard model of the proposed channel filter.

The filter will be tested according to the agreed plan. The obtained results will be evaluated with respect to the expected performances and will also be used as a basis for proposing further improvements and applications for IMUX.

Current status

In the first stage of the project the following activities have been performed:

  • Literature and patents review to identify existing solutions, the state-of-the-art and the trend in reconfigurable filters;
  • Trade-offs that will lead to the identification and the selection of the most adequate engineering approaches, both from the RF and mechanical point of view.

Once the preferred solutions are identified with ESA, the refinement of the trade-offs and preliminary analyses will be performed. The trade-offs will be supported by experimental results obtained by means of bread-boarding activities on selected test-items.

 

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Status date

Thursday, February 27, 2014 - 09:06

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