Continuous Adaptive Interference Nulling for Defeat of Wideband GNSS Interference

R. Vosburgh, V. Haridasan, C. Wilson

Abstract:	Test and modeling results are presented on the defeat of severe wideband interference at GNSS frequencies using low size, weight, power and cost (SWAP-C) antenna electronics providing Continuous Adaptive Interference Nulling (CAIN). We also report on modeling of a passive linear phase bandpass filtering (LBF) derived from CAIN, which being free of group delay distortion will enhance timing and navigation in any GNSS receiver. CAIN comprises signal-agnostic, linear-phase RF technology that in over-air tests has demonstrated >> 30 dB of jammer mitigation by blocking jamming at the face of the antenna or by cancelling it after the fact, which capabilities can be used together to defeat one jammer by >60 dB or used to simultaneously defeat two independent jammers by >30 dB each. LBF modeling at L1 has demonstrated >>30 out of band rejection for topologies for C/A and M-code reception. The low SWAP-C aspect of both CAIN and LBF enable their use on tier-1 unmanned air vehicles; integrated circuits now in development will enable their integration in Smartphones, and personal GNSS receivers. Field blocking tests were conducted using two (primary and secondary) closely spaced passive GPS L1 patch antennas connected to a simple RF circuit consisting of COTS vector modulator, delay and combiner components. In these tests using synthetic signals, the CAIN circuit was connected to a spectrum analyzer and, via an ADAC, to a notebook PC running the deterministic, single-pass CAIN algorithm. A prototype now in development will replace the external instruments with power detectors, ADAC and a microcontroller. Blocking employs an emitter (here another patch antenna) immediately below the primary antenna and a signal derived from the second antenna signal to generate an anti-jamming field around the primary antenna to offset the field created there by the jammer, thereby blocking excitation of the antenna. Field blocking was modeled using AWR to validate test results with respect to primary-secondary antenna separation and primary-emitter spacing. LBF modeling was conducted with SONNET for various configurations with respect to bandwidth, out of band rejection and insertion loss. CAIN tests were conducted over-air in an open lab without anechoic suppression to assess performance in a multipath environment. Results will be presented on the effect of separation between the primary and secondary antennas, the separation between the primary antenna and the closely underlying inductive emitter and on severity of jamming. Over-air tests also show CAIN provides >>30 dB of signal agnostic cosite mitigation, which can be utilized to support reception of wideband signals while transmitting high power narrowband signals at the same center frequency. As ultra-wideband tunable technology, CAIN can tune on the fly to defeat interference at any UHF frequency, including GNSS. And, the linear phase characteristic of CAIN and LBF will enhance timing of receivers using either or both. The combination of superior performance and low cost enabling use of CAIN and LBF in applications where space, weight and power are critical constraints, e.g. tier-1 unmanned systems, as well as on larger platforms.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	3417 - 3423
Cite this article:	Vosburgh, R., Haridasan, V., Wilson, C., "Continuous Adaptive Interference Nulling for Defeat of Wideband GNSS Interference," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 3417-3423.
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