Illustrative beam patterns of a CRPA antenna in the presence of jamming (Figure: Michael Jones)
Controlled Reception Pattern Antennas (CRPAs, pronounced “serpers”) are still the single most effective counter to the threat to GNSS from jamming and spoofing — a growing problem in and near conflict areas, such as Ukraine and the Middle East. CRPAs, which make use of the fact that the desired satellite signals and the unwanted jamming signals generally arrive from different directions, reduce the effective range of jammers by up to five orders of magnitude. They are attractive because they replace existing antennas on GNSS receivers without requiring any other changes — though they are generally larger than typical GPS antennas because they contain several antenna elements and some associated electronics.
Beginning on Sept. 15, 2025, CRPAs will no longer be covered by the International Traffic in Arms Regulations (ITAR), which prohibit the sale outside of the United States of defense articles, services and technical data and impose very large penalties for violators. ITAR is managed by the Directorate of Defense Trade Controls (DDTC) in the Bureau of Political-Military Affairs at the U.S. Department of State, which announced the rule change in mid-January. It removes items that “no longer warrant inclusion” from the U.S. Munitions List (USML), which defines the “defense articles” that fall under ITAR jurisdiction. CRPAs for PNT will instead be classified as dual-use commercial items and fall under the Export Administration Regulations list managed by the Department of Commerce. The Directorate removed CRPAs for PNT from the USML because they “no longer provide a critical military advantage, with increasing commercial utilization applicable to civil GPS resiliency” and because the department “intends to facilitate civil global navigation system resiliency.”
This is a seismic shift that many in the GNSS/PNT community — including the National Space-Based Positioning, Navigation and Timing Advisory Board (PNTAB) — have been advocating for years. While U.S. manufacturers have been prohibited from exporting CRPAs, TUALCOM, a Turkish company based in Ankara, has been selling 4- and 8-element CRPAs for GNSS applications, as have some Canadian companies.
Airlines and manufacturers of autonomous vehicles will be among the early beneficiaries of this policy change, as will many safety-of-life applications. Presumably, the vast expansion in the market for CRPAs also will quickly lead to a sharp drop in their cost.
In a November 2022 presentation to the PNTAB, Brad Parkinson listed the use of CRPAs among the major techniques that can make GPS receivers “virtually immune” to jamming and spoofing, recalling that they were first tested in 1978. However, he pointed out, they had been neglected because they were perceived as too expensive and large for many applications, because of delays in implementing the L5 signal, and because ITAR prohibited beam-steering antennas with more than three elements. He argued that restrictions on GNSS CRPAs were no longer effective at preventing potential enemies of the United States from using them.
Barring a reversal from the new administration, U.S. CRPA manufacturers can now help protect GNSS worldwide from jamming and spoofing.
<p>The post First Fix: Freeing CRPAs first appeared on GPS World.</p>
