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Pasternack BlogPulsed radar are used in a variety of applications for weather sensing, marine sensing, aerospace navigation, and defense. Critical to pulsed radar performance is the behavior of the radar’s RF front-end hardware. Though pulse radars have advanced significantly in the past several years, with deep digital integration, the RF front-end hardware of these radars is essentially the same as legacy pulse radar systems. The RF front-end consists of a power amplifier (PA), low noise amplifier (LNA), duplexer/switch, and antenna. Though some radar may use several stages of amplification, the basic principles and requirements apply to both multi-stage and single stage amplified pulse radar.
Pulse Radar Power Amplifier
The main criteria for a pulse radar PA is peak pulsed power handling, gain, frequency, bandwidth, efficiency, and linearity. These specifications are important as the goal of the pulse radar PA is to amplify the narrow radar pulse from the pulse modulator to very high-power levels without degrading the pulse signal. As radar pulses consist of a wideband and complex spectrum response, wideband linearity is essential in preventing degradation of the pulse signal quality.
Any degradation to the pulse signal quality can result in reduced radar resolution and other undesirable phenomena. Hence, pulse radar are designed with PAs specifically built for pulse application to prevent traces and easily identifiable characteristics. For instance, a radar with added pulse train traits like droop, overshoot, and ringing could result in an adversary identifying the radar by these pulse characteristics. A pulsed radar with minimized pulse distortion may remain undecipherable to adversarial receivers. This is also why optimal “tuning” of a pulsed radar PA is critical for some radar applications.
To meet the high peak power level requirements of pulsed radar traveling wave tube amplifiers (TWTAs) are still commonly used in high power pulse radar for defense applications. Other methods include large banks of solid-state power amplifiers (SSPAs). The latest in pulse radar PA technology consists of multiple gallium nitride (GaN) power amplifiers in a compact amplifier module.
Pulse Radar Low Noise Amplifier
LNAs for pulse radar are tasked with the job of amplifying very weak and distorted signals without adding additional distortion, noise, or phase noise. In the era of direct RF conversion, or “RF in, bits out” technology that is very sensitive to phase noise, this requirement is becoming increasingly important. Naturally, the gain of a LNA for pulse radar is also of significant concern, as inadequate gain of weak radar signals may require additional amplification that will cumulatively add noise and phase noise while potentially introducing unique nonlinearities and distortion.
Beyond amplifying weak radar signals, some applications also require pulse radar LNAs to be able to handle substantial input powers without being damaged, dubbed as high survivability. During radar jamming, a high-power transmitter is directing much higher power than typical radar receive signals, which may result in a desensitized receiver, in part by saturating the front-end LNA. Hence, pulse radar LNAs are often protected with limiters or other protection circuitry. The challenge with this is that the protection circuitry introduces its own signal degradation and attenuation. This is why there has been interest in using GaN LNAs over gallium arsenide (GaAs) LNAs for pulse radar applications, even though GaAs technology is more established for this application and lower noise GaAs LNAs are more widely available.
