Phased array antennas are made of multiple modules that can transmit and receive RF or microwave signals. Those modules are arranged in groups forming a usual flat surface that replaces a traditional mechanically steered antenna. The main advantages in this approach include the capability to aim at different directions simultaneously, easier integration and better reliability (as the assembly need not be moved), module failure tolerance and individual plug-in replacement.
The principle of operation comes from the wave combination of those multiple modules output. Arranging the phase of the various outputs, a "wave-front" is generated creating similar behavior as if a traditional antenna was steered in this direction.
The modules can be passive or active. The active modules include a power amplifier in the transmit section on top of the phase shifter and variable attenuator. This is where the active module becomes interesting. The amplifier component in the module has to be tested.
Testing traveling wave tubes (TWT) can be done with commonly available test and measurement equipment, as the power is high and dynamic range request limited. Spectrum analyzers, power analyzers and pulsed vector analyzers can be used to perform most of the required test but can present limits that are not compatible with the latest generation of such amplifiers.
Pulse stability, residual noise, moving target indication, carrier and pulse cancellation residual and inter-pulse noise power are different measurements or specifications that are linked altogether and are based on the same test equipment core. They all express limitations of radar to detect a given cross-section.
Measuring pulse-to-pulse stability
The pulse-to-pulse stability determines the threshold of detection for targets with a weak echo, thus the instability of radar introduces a main detection limit. In particular, it causes problems to the fixed echoes processing. These can be identified by a Doppler process, but a big phase and amplitude instability can generate false data on the Doppler signature of the targets, generating a risk of triggering wrong alarms.
On the other side of the radar, the pulse-to-pulse stability impacts the dynamic of several components of the receiver like the analog-to-digital converters (a higher dynamic of these components would be limited by this signal instability).