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Synthesis of microwave lossy filters

The project goals at large are to investigate novel lossy filter synthesis techniques to obtain filters whose insertion loss flatness can be made equal to that of an (ideal) lossless filter, despite the limited Q of the resonators within the filter.

The classical synthesis procedure consists on obtaining a purely reactive (no dissipation effect) network that defines the resonant frequency of the resonators forming the filter and the way they are coupled. However, in practice, some dissipation always exist in the final filter implementation which can be evaluated afterwards by introducing the material losses (finite Q of the resonators) into the synthesized lossless network.

Among other effects, this approach leads to filters with minimum insertion loss in the passband at one frequency at the expense of additional passband rounding towards the band-edges, being the use of high Q resonators the only way to achieve filters with flat pass-band response by means of classical synthesis techniques. This may result in heavy and large filters which might be impractical in space systems, or in wireless and handset components with strong demand for low-cost and small size.

This can be overcome by the use of non standard filter synthesis techniques such as:

- Pre-distortion synthesis: synthesizes a lossless network whose pole placement is such that, after introducing the losses, produces the desired (improved) in-band flatness. However, this is at the expense of increased in-band signal reflections.
    R. J. Cameron, C. M. Kudsia, R.R. Mansour, Microwave Filters for Communication systems. Fundamentals, Design, and applications, John Wiley & Sons, 2007. Dissipation I movement de sigma
    Ming Yu et al., "Predistortion Technique for Cross-Coupled Filters and its application to satellite communication systems", IEEE MTT-51, pp. 2505-2515, Nov. 2003
- Prescribed insertion loss synthesis: In order to obtain both good insertion loss flatness and good return loss, the insertion loss flatness is obtained at the expense of an increase of the overall insertion loss, therefore the resulting filters are of use in those applications where the filters are placed after the low noise amplifier without affecting the noise figure, as it occurs in input multiplexers (IMUX) for satellite transponders.
    V. Miraftab, Ming Yu, "Advanced Coupling Matrix and Admittance Function Synthesis Techniques for Dissipative Microwave Filters," Microwave Theory and Techniques, IEEE Transactions on , vol.57, no.10, pp.2429-2438, Oct. 2009.
    I. C. Hunter, A. Guyette, and R. D. Pollard, "Passive Microwave Receive Filter Network Using Low-Q Resonators", IEEE microwave Magazine, September 2005.
    A.C. Guyette, I. C. Hunter, R. Pollard, "The design of microwave bandpass filters using resonators with nonuniform Q", IEEE MTT-54 (11), November 2006, pp.3914-3922.
  Using these lossy filters synthesis techniques, very low resonator Q that can be employed and, therefore, low cost and compact filters (such as microstrip filters) can be realized.

# References:

The main references to the work in this project are:

  J.Mateu, C. Collado, J.M. O'Callaghan,
  "Lossy Filter Synthesis and Study of Topology Solution Space",
  ESA working paper 2366. TEC-ETM/2009.142/CE. First issued: September 2008.

  J. Mateu, A. Padilla, C. Collado, M. Martinez-Mendoza, E. Rocas, C. Ernst, J M. O’Callaghan,
  "Synthesis of 4th order Lossy Filters with uniform Q distribution",
  Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International, pp.568-571, 23-28 May 2010.
  doi: 10.1109/MWSYM.2010.5517741
  URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5517741&isnumber=5514662
  URL: http://upcommons.upc.edu/e-prints/bitstream/2117/10412/1/Synthesis%20of%204th%20order%20Lossy%20Filters%20with%20uniform%20Q%20distribution.pdf

  A. Padilla, J. Mateu, C. Collado,, C. Ernst, J.M. Rius,, J.M. Tamayo, J.M. O'Callaghan,
  "Comparison of lossy filters and predistorted filters using novel software",
  Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International, pp.1720-1723, 23-28 May 2010
  doi: 10.1109/MWSYM.2010.5517713
  URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5517713&isnumber=5514662
  URL: http://upcommons.upc.edu/e-prints/bitstream/2117/10413/1/Comparison%20of%20lossy%20filters%20and%20predistorted%20filters%20using%20novel%20software.pdf