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    Project Abstract

    Tunable Preselect Filters for Reconfigurable Radios

    Widely tunable base station quality filtering in mobile form factors

    ASP Logo

    Isolating different waveforms on a battlefield requires adaptable communication systems.  With the backend of a wireless system becoming highly flexible due to advances in digital processes there is a need for a non-static front end.  This project addresses the remaining bottleneck for fully tunable wireless systems by developing low loss reconfigurable preselect filters for radio communication. The Purdue team on this DARPA funded project was recognized by DARPA for "Outstanding Technical Contribution to Phase 1 of the Analog Spectral Processors Program".

    Insertion loss of a filter is inversely proportional to bandwidth and in order to create low loss, yet narrow preselect filters, high quality factors (Q) are needed.  Providing high Q and simultaneously tuning over a wide range is another challenge.  Highly loaded cavities offer up to 100% reduction in size compared to an unloaded cavity with only a small reduction in Q.  Package-scale cavity resonators enable Q >1000 in the 3-6 GHz range in a compact form factor.

    Fig1

    Fig. 1. Comparison between potential Q values and size for different technologies.

    By utilizing a capacitive post to load the evanescent-mode cavity, the E-field can be concentrated at the top of the post creating a capacitive gap between the top of the post and the cavity.  On changing the gap by applying a force to bend the top substrate, the frequency changes according to equation 1.  

    Eqn1 (1)
    where Cp is the capacitance between the post and the roof of the cavity [1].
    Fig2
    Fig. 2. Evanescent-mode cavity filter showing a top view of the E-field distribution in the cavities, along with a cross-sectional view of the post area.

    The goal is to create six low loss bandpass filters in parallel that can be from 3 GHz to 6 GHz and have a constant bandwidth of 25 MHz across the entire band.

     

    Video 1. This movie shows an overview of some of the basic capabilities of the filter. Filter performance and tuning has been improved and refined as described in the papers at the bottom of this page.
    Published Papers:
    [8] H. H. Sigmarsson, A. Christianson, H. Joshi, S. Moon, D. Peroulis, and W. J. Chappell, "In-Situ Control of Tunable Evanescent-Mode Cavity Filters Using Differential Mode Monitoring," IEEE MTT-S International Microwave Symposium Digest, June 2009, pp. 633-636.
    [7] H. Joshi, H. H. Sigmarsson, S. Moon, D. Peroulis, and W. J. Chappell, "Tunable High Q Narrow-Band Triplexer," IEEE MTT-S International Microwave Symposium Digest, June 2009, pp. 1477-1480.
    [6] H. Joshi, H. H. Sigmarsson, S. Moon, D. Peroulis, and W. J. Chappell, "High Q Narrowband Tunable Filters With Controllable Bandwidth," IEEE MTT-S International Microwave Symposium Digest, June 2009, pp. 629-632.
    [5] H. Joshi, H. H. Sigmarsson, and W. J. Chappell, "Analytical Modeling of Highly Loaded Evanescent-Mode Cavity Resonators for Widely Tunable High-Q Filter Applications," Proceedings of Union Radio Scientifique Internationale (URSI), Chicago, USA, no. D09.6, Aug. 2008.
    [4] H. H. Sigmarsson, H. Joshi, D. Peroulis, and W. J.Chappell, "3-6 GHz Tunable Bandpass Filter using Heavily Loaded Evanescent-mode Cavity Resonators and Piezoelectric Actuators" Proceedings of International Symposium on Microelectronics, International Microelectronics and Packaging Society (IMAPS), Providence, USA, 2008, pp. 360-366.
    [3] A. Mahmood, H. H. Sigmarsson, H. Joshi, W. J. Chappell, and D. Peroulis, "An Evanescent-mode Cavity Resonator Based Thermal Sensor," Sensors, 2007 IEEE , vol., no., pp.950-953, 28-31 Oct. 2007.
    [2] H. Joshi, H. H. Sigmarsson, D. Peroulis, and W. J. Chappell, "Highly Loaded Evanescent Cavities for Widely Tunable High-Q Filters" IEEE MTT-S International Microwave Symposium Digest, June 2007, pp. 2133-2136.
    [1] X. Gong, A. Margomenos, B. Liu, S. Hajela, L. P. B. Katehi and W. J. Chappell, “Precision Fabrication Techniques and analysis on High-Q Evanescent-Mode Resonators and Filters of Different Geometries,” IEEE Trans. on microwave theory and techniques, Vol. 52, No. 11, November 2004.[1] X. Gong, A. Margomenos, B. Liu, S. Hajela, L. P. B. Katehi and W. J. Chappell, “Precision Fabrication Techniques and analysis on High-Q Evanescent-Mode Resonators and Filters of Different Geometries,” IEEE Trans. on microwave theory and techniques, Vol. 52, No. 11, November 2004.

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