N101-104 TITLE: Co-Site Interference Mitigation in Phased Arrays

TECHNOLOGY AREAS: Ground/Sea Vehicles, Sensors, Electronics

ACQUISITION PROGRAM: PEO C4I PMW770 - Advanced High Data Rate Antenna and NAVSEA PMS435 - BLQ-10

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted." The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: To develop method(s) to address the effects and impacts of co-site interference with respect to phased array technology at X-band where transmit and receive bands are close in frequency.

DESCRIPTION: The limited space in the submarine sail requires the co-location of phased array apertures in a single antenna housing structure to provide capabilities in the desired frequencies of interest. Phased array technology is currently being investigated to provide wideband receive X-K band capability in one aperture with various narrowband transmit phased array apertures for X, Ka and Q-band transmit capability. Of particular concern is the communications degradation resulting from in-band transmit signals impacting the wideband receive array performance. GFI will be provided for approximate physical area allocated for various apertures.

The expected performance degradation will be the result of the transmitting in-band signal being received by the wideband receive array. The following are particular concerns with respect to the transmit signal: 1) Create a large signal very close to the intended SHF downlink channel degrading the G/T in the downlink receive band if there�s transmitter noise at the downlink frequency - even if the LNA is not saturated. 2) Create significant harmonics that will eliminate utility at those frequencies for any other functions - even if the LNA is not saturated. 3) Saturate the LNA in most of the array elements - blinding the array for all downlink functions. 4) Damage the circuits in the receive elements.

Potential methods to investigate include, but are not limited to the following: 1) Component design such as high output power LNA stages to provide a larger spurious free dynamic range 2) Physical separation of the transmit array from the receive array as much as possible 3) Design techniques on the structure between the XMIT and RCV arrays that will reduce surface currents propagating between the two (RAM, resonant choke structures, frequency selective surfaces) 4) Separate radomes for XMIT and RCV arrays addressing reflected energy off adjacent radomes back into the receive array 5) Design rejection filters into the RCV elements before the LNA (will cause Noise Figure degradation) 6) Use Frequency Selective Surfaces (FSS) in front of the array to reduce incident energy at XMIT frequency 7) Attempt phase cancellation of interfering signal 8) Design all power and control signals to have significant rejection of the SHF uplink frequencies so that interference doesn�t enter the array chain from the power supply and control lines. 9) Physical gating (choke structures) between the arrays.

PHASE I: Conduct modeling and analysis to determine the ability of the method(s) proposed for mitigating co-site interference to address the problem. A full analytical and if possible initial prototype assessment should be summarized and presented by the completion of Phase I to assess the effectiveness and likelihood of the proposed methods to allow full duplex communications of Narrowband X-band transmit operating with Wideband X-K band receive given the physical/spatial constraints.

PHASE II: Fabricate a proto-type system and test in a relevant environment the effectiveness of the developed method(s) in mitigating co-site interference with full duplex communications. Provide all modeling and test data to the Navy in a final report.

PHASE III: Partner with phased array equipment manufacturer to seek commercialization of the developed method(s). Method(s) should be ruggedized and capable of suitable operations in environmental conditions including shock and vibration related to the submarine environment.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Other potential applications include other branches of DOD (Army and Air Force) phased array applications, and commercial communications applications that are space limited and require arrays to be deployed in proximity to each other.

REFERENCES:
1. "Tactical communication EMI/EMC co-site problems and solutions"; Bahu, M.B.; Taylor L.L.;Tactical Communications Conference, 1994, Vol.1 Digital Technology for the Tactical Communicator;10-12 May 1994.

2. "Wideband RF photonic pre-selector for dynamic co-site interference mitigation"; Borbath, Michael; Middleton, Charles; Wyatt, Jeffrey; DeSalvo, Richard; Avionics, Fiber-Optics and Photonics Technology Conference, 2008 IEEE.

3. SBIR Topic 101-104 Antenna Description, 8 pages

KEYWORDS: co-site interference; submarine communications; phased arrays; x-band transmit; x-band receive; high data rate

** TOPIC AUTHOR (TPOC) **

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