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Novel Timing Antennas for Improved GNSS
Resilience
Erik Lundberg and Ian McMichael
The Homeland Security Systems Engineering and Development Institute (HSSEDI)™
Operated by The MITRE Corporation on behalf of the Department of Homeland Security
BIOGRAPHIES
Dr. Erik Lundberg is a senior signal processing engineer at The MITRE Corporation’s National Security Engineering Center.
He received a B.S. in physics and a B.A. in mathematics from Augsburg College in 2006, and master’s and Ph.D. degrees from
Cornell University in electrical and computer engineering in 2011 and 2012. At MITRE, he has worked in the areas of GPS
spoofing detection and mitigation; GPS antenna technology; systems engineering; timing; and navigation sensor fusion.
Dr. Ian McMichael received a B.S.E.E. degree from George Mason University in 2001, a M.S.E.E. degree from the George
Washington University in 2008, and a Ph.D. degree in electrical and computer engineering from the University of Delaware
in 2013. From 2002 to 2013, he was with the U.S. Army Research, Development, and Engineering Command
Communications-Electronics Research, Development and Engineering Center (RDECOM CERDEC) Night Vision and
Electronic Sensors Directorate, Ft. Belvoir, researching and developing electromagnetic sensors for landmine detection,
computational electromagnetics, antenna design, and high impedance ground planes. From 2013 to 2014, he was with
Raytheon Integration Defense Systems in Sudbury, Mass., contributing antenna and microwave structure designs. Since
2014, he has been with The MITRE Corporation in Bedford, Mass., contributing to antenna design, radome analysis, and
computational electromagnetics.
ABSTRACT
Global Navigation Satellite System (GNSS) antennas installed at fixed site infrastructure are susceptible to interference,
jamming, and spoofing signals incident along the direction of the horizon. In this paper, a set of requirements are derived for
GNSS antennas that ensure critical infrastructure timing receivers have access to sufficient satellites to derive resilient time
and frequency while placing a null in all polarizations at and below the horizon. Multiple quadrifilar helix antennas that meet
these requirements are also presented. The efficacy of the designs is demonstrated with field test results. The salient feature
of these antennas is a null in the gain pattern in the direction of the horizon and around all azimuth angles to suppress ground-
based interference. Other types of antennas have been developed to minimize interference, such as controlled reception
pattern antennas. However, none of these antennas simultaneously have sufficient performance, size, weight, power, and cost
for widespread applications in commercial and military installations. The proposed high-performance antennas provide
GNSS resilience in a small form factor at a low-cost due to the simple architecture.
The first antenna operates at L1 (1.575 GHz) and employs a novel method of reactive loading along the length of the multi-
turn helix. The phase distribution along the helix creates a deep null in the gain pattern at the horizon while maintaining
sufficient beamwidth in the zenith direction. The prototype antenna is 7.5 inches tall, 1 inch in diameter, and is mounted on a
7-inch diameter ground plane. Gain pattern measurements exhibit a 4.0 dBiC zenith gain and a zenith-to-horizon gain ratio
(i.e. null depth) of 29 dB for right hand circular polarization (RHCP) and 34 dB for left hand circular polarization (LHCP).
This horizon null minimizes ground based interference. The half power beamwidth (HPBW) of this antenna is approximately
100°, which is sufficient to have access to the required number of satellites for timing applications at least 99 percent of the
time.
The second antenna operates at L1 and achieves a horizon null by varying the pitch of the helix arms along the length of the
antenna. The variable pitch antenna prototype is 7.8 inches tall, 1.4 inches in diameter, and is mounted on a 7-inch diameter
ground plane. Gain pattern measurements exhibit a zenith gain of 7.5 dBiC and a 30-dB zenith-to-horizon ratio for both
