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Tunable Bandstop Filters for Suppression of Co-site Interference and Jamming Sources


OBJECTIVE: To design and develop tunable bandstop filters capable of dynamically changing bandwidth, center frequency, and stop band attenuation in the 2 GHz to 18 GHz band for ship board co-site interference and jamming source mitigation. DESCRIPTION: The radio spectrum has become extremely crowded in the past decade due to the exponential growth of wireless systems. With multiple wireless system technologies allocated close to one another in the radio spectrum, optimum performance of one system cannot be achieved due to interference caused by another system that is located physically and/or spectrally close to the desired communication system. This problem is further compounded aboard naval vessels where multiple high power systems are co-located on the same mast or submarine sail thus eliminating the possibility of interference mitigation through spatial separation of the wireless systems and even jamming sources. In order to mitigate the effects of co-locating multiple high power systems on the top side of naval vessels, it is desirable to have a low-loss filter on the input of the receiver for a given system. While bandpass filters are an acceptable solution for this purpose, in order to achieve low insertion loss performance, relatively high quality factors are required, leading to large, bulky front end filters. Therefore, it is desirable to have a bandstop filter on the front end that is capable of extremely low loss out of band characteristics while simultaneously providing a high rejection of an interferer in a compact form factor. Compounding the problem is an ever changing radio environment and potential jamming sources. Therefore, in order for the front end filter to provide flexible, dynamic mitigation of co-site interference and other undesirable RF signals it is necessary for the bandpass filter to posses the ability to change its center frequency, rejection bandwidth, and notch depth to optimize the interference mitigation and maximize system performance. The tunable bandstop filter proposed for this topic should cover the band from 2 GHz to 18 GHz and should be capable of adjusting both stop band bandwidth as well as the notch depth. PHASE I: Demonstrate feasibility and provide initial design/simulation of the developed tunable notch filters and establish a fabrication and testing plan for the prototype devices in Phase II. Key technology features shall be demonstrated empirically and an initial assessment of risks and reliability in a fielded EW/Radar system shall be conducted. PHASE II: Fabricate and characterize prototype tunable notch filters for co-site interference mitigation. By the end of this phase, the tunable bandstop filters should be demonstrated as a stand-alone component. As part of the demonstration a user should be able to enter the desired stopband bandwidth and notch depth via a graphical user interface (GUI). The filter should have the ability to automatically tune the stop band to the frequency, bandwidth and depth specified by the user without any further input from the user. It is anticipated the tunable notch filter should also be capable of handling higher power levels of>30 dBm input power in the stop band. Initial assessment of the technologies reliability, manufacturing and cost factors shall be studied and application limitations identified. PHASE III: Produce production tunable notch filters and integrate the notch filters into actual ship-board EW/Radar system demonstrations working with prime contractor and Navy Program personnel. Establish reliability, manufacturing and cost data to support transition. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Successful development of the tunable bandstop filters should provide the commercial sector the ability to mitigate co-site and other radio frequency and microwave interference in current and future commercial wireless systems. REFERENCES: [1] E.J.Naglich, Juseop Lee, D. Peroulis, and W.J. Chappell,"Tunable, substrate integrated, high Q filter cascade for high isolation,"IEEE MTT-S Int. Microwave Symposium Digest, Anaheim, CA, May 2010 pp.1468-1471. [2] D.R. Jachowski and C. Rauscher,"Frequency-agile bandstop filter with tunable attenuation,"IEEE MTT-S Int. Microwave Symposium Digest , Boston, MA June 2009 pp.649-652. [3] A. I. Abunjaileh and I.C. Hunter,"Tunable combline bandstop filter with constant bandwidth,"IEEE MTT-S Int. Microwave Symposium Digest, Boston, MA June 2009 pp.1349-1352. [4] R.V. Snyder; Sanghoon Shin and K. Keck,"Bandstop filter design using evanescent mode resonators,"IEEE MTT-S Int. Microwave Symposium Digest, Philadelphia, PA June 2003 pp. 1073- 1076 vol.2, 8-13. [5] I. Reines, S.-J. Park, G.M. Rebeiz,"Compact Low-Loss Tunable X -Band Bandstop Filter With Miniature RF-MEMS Switches,"IEEE Trans. Microwave Theory and Techniques, vol.58, no.7, pp.1887-1895, July 2010.
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