New CRPA concept antenna designed

December 10, 2019 - By Tony Murfin

By Tony Murfin
GPS World Professional OEM Contributing Editor

In today’s world where local conflicts can spill over into many other places, it’s become common to encounter GPS signal jamming. Even in locations that defense forces might have considered “backwater” in terms of technology, enemies can apparently launch attack drones, jam adjacent countries, and generally render GPS, if not GNSS, useless for navigation.

The U.S. military came up with anti-jam technology to counter foreseen jamming scenarios several decades ago, but the initial seven-element controlled radiation pattern antenna (CRPA) designs were bulky and required multiple RF antenna cable connections to large, remote receiver processor units. These units not only processed the signals to derive position, but also eliminated jammer and satellite signals in the direction from which the jamming signal was received (null processing). Most of these early units were large and power hungry, so their application was limited to larger aircraft and ships.

Anti-jam technology has gradually evolved over time. Component integration and miniaturization has enabled CRPA performance to be self-contained within the antenna enclosure. At least one design has now migrated the null-processing into the same enclosure as the CRPA antenna, and is sold on a commercial basis to several military forces around the world. The device outputs a single composite RF signal that has been cleaned of any detected jamming signals for use by both commercial and military remote receivers alike.

Now Quantum Reversal (QR) — a new company based in Calgary, Alberta, Canada — has come up with a novel design that processes the CRPA signal in the RF domain, eliminating the need for extensive null-processing electronics. Without these signal-processing electronics, power requirements are reduced from about 15–30 watts to around 1 watt, the size is smaller (4 inches in diameter versus the nominal 6–8 inches in diameter), and cost is significantly lower. These reductions might allow this new anti-jam technology to move into small unmanned aerial vehicle (UAV) applications, timing networks, and reference monitoring networks where continuous uninterrupted GPS/GNSS service is mandatory.

This antenna is designed to enable continuous navigation using GPS or GNSS signals in the presence of unintentional low- to medium-power interference signals. It should be able to reduce the power of an unintentional interference or jamming signal by 35–45 dB, depending on whether it contains three or four CRPA antenna elements.

Increasing the number of antenna elements of the QR design improves the null depth (on average 8–10 dB per antenna element) at the expense of increased circuit complexity, power consumption and antenna size. An average null depth of –70 dB may be possible with a seven-element CRPA antenna. (Image: Quantum Reversal)