What Is a CRPA Antenna? How Anti-Jam GNSS Arrays Work

A CRPA — controlled reception pattern antenna — is a GNSS antenna made of several antenna elements arranged in an array. Instead of receiving equally from every direction, the array works with an adaptive processor that changes the reception pattern in real time: it places deep “nulls” toward interference sources and keeps gain toward the satellites. That is why CRPA antennas are the core of military anti-jam GNSS systems.

Why a standard GNSS antenna is easy to jam

Satellite navigation signals reach the ground at around −130 dBm, below the thermal noise floor of the receiver. A conventional antenna — often called a FRPA, fixed reception pattern antenna — accepts energy from the whole sky with almost the same gain. A low-power jammer on the ground or on another platform therefore only has to raise the noise level a little to make the receiver lose lock.

How a CRPA antenna works

Each element of the array receives the same satellite and the same jammer, but with slightly different phase because the elements sit at different positions. The anti-jam electronics digitise all channels and combine them with complex weights. By solving for the weights that minimise total interference power, the processor steers nulls toward the jammers automatically — without needing to know where they are in advance.

• Spatial nulling: interference is suppressed by direction, not by frequency, so it works even when the jammer sits exactly on the GNSS band
• Adaptive: the pattern updates continuously as the platform manoeuvres or new jammers appear
• Satellites stay usable because they arrive from other directions than the nulls

How many elements do you need?

As a rule of thumb, an array with N elements can null up to N − 1 independent interference sources. More elements also give deeper suppression and more freedom when several jammers are close together, at the cost of size, weight and power. Sağlamtek’s BORAJ family shows the trade-off clearly:

• BORAJ-MINI4 and BORAJ-V4 — 4-element arrays for small UAVs, with anti-jam and anti-spoofing; BORAJ-V4 reaches 83 dB against one jammer
• BORAJ-V8 — 8-element dual-band array, 90 dB against one jammer and 80 dB with seven
• BORAJ-V16 — 16 elements on GPS L1, Galileo E1, BeiDou B1 and GLONASS G1, suppressing up to 15 jamming sources at once

Single-band or dual-band?

Many jammers target L1 only, but modern threats cover several bands. A dual-band CRPA that tracks L1/E1/B1 together with L2 or L5 keeps a usable signal on one band when the other is heavily attacked, and multi-constellation tracking gives the receiver more satellites to choose from.

Combining a CRPA with a passive shield

Most ground-based jammers arrive from low elevation angles. The SAJ GNSS Shield is a passive ring fitted around a standard or CRPA antenna that attenuates signals arriving from 90° and below by 20–30 dB. Added to a CRPA, it takes the BORAJ-V8 system above 100 dB of suppression without any change to the receiver chain.

What to check when choosing a CRPA system

• Number of jammers you expect and the suppression required per jammer
• Frequency bands and constellations your mission needs
• Size, weight and power available on the platform
• Output interface — for example NMEA 0183 or Pixhawk compatibility for UAV autopilots
• Environmental rating, connectors and mounting

If you are not sure which array fits your platform, our engineers can review your threat scenario and installation constraints and recommend a configuration.