Seeing CRPA Spatial Nulling in Action

What does CRPA jammer suppression actually look like?

In this AJAS-2 demonstration, the spectrum display shows more than 30 dB of jammer suppression in portions of the affected band, while the highlighted GPS satellite remains tracked with a 5 dB decrease in C/N₀.

The test setup

Testing took place on the lower section porch of a 20-story building, with approximately one-third of the sky visible. The GPS jammer was switched on and off three times.

The screen compares:

• Upper left: a conventional GNSS receiver connected to an active antenna.

• Lower left: AJAS-2’s internal GNSS receiver.

• Right: the two antenna-input spectra and CRPA output, input-signal coherence, and suppression versus frequency.

Jammer down more than 30 dB; GPS PRN14 down 5 dB

With the jammer off, AJAS-2 reports 37 dB-Hz for GPS PRN14. In the highlighted jammer-on capture, it reports 32 dB-Hz.

Meanwhile, the conventional receiver’s displayed satellite signal levels collapse. AJAS-2 still shows multiple tracked satellite signals.

On the spectrum display, the CRPA output sits well below the antenna-input spectra across the interference bands. The suppression trace exceeds 30 dB in parts of the band—not uniformly across every frequency.

Why the jammer and satellites behave differently

A CRPA does not simply turn down everything equally. It combines signals from multiple antennas to reduce sensitivity toward the interference source: spatial nulling.

Satellite signals arriving from other directions can remain usable, although their levels may also change as the reception pattern changes.

The coherence plot provides another clue: with the jammer on, coherence between the two antenna inputs approaches one across the interference bands, indicating a strongly correlated component.

The important result is selective suppression: much greater reduction of the jammer than the observed reduction in the highlighted satellite’s C/N₀.

The 5 dB figure is a before/after C/N₀ change for one satellite—not a calibrated insertion-loss measurement or a guarantee for every satellite. These screenshots demonstrate interference suppression and retained tracking, not a position-accuracy specification.