What is AESA and PESA Radar and difference between a PESA and an AESA radar?

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• published: 30 Mar 2017
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What is AESA and PESA Radar and difference between a PESA and an AESA radar? Both AESA and PESA radars are (generally) pulsed radars. AESA as well as modern PESA both are frequency agile and can frequency hop over different frequencies at different times. Both can have narrowband or wideband mode, and both can be used for ECM, passive scanning, beam-forming, etc. The primary difference is in the source of the high-power RF signal. How is a radar pulse formed? A digital pulse command is created by the radar computers which tell it to send a pulse out in some direction. The receiver/exciter (REX) creates the baseband pulse, which is really just a square wave, which is used to modulate the Intermediate Frequency (IF). Signal processing is applied to the IF pulse to compress it, shape it into efficient Gaussian forms, etc. Then the IF pulse is used to modulate an oscillator that is operating at the final RF frequency. This refers to the final up-converted frequency that will be used for transmission over the air. This modulated RF signal goes through high power amplification and is sent to the antenna for transmission. It is only this last step, the high-power RF generation/amplification that differs between AESA and PESA. In PESA, there is a single high-power transmitter source, often an older device like a Klystron or a Traveling-wave tube. These devices can amplify RF signals at microwave frequencies up to very high powers and then there is a single antenna horn radiating the signal out. After the signal is radiated there is an RF “lens”. An RF “lens” is an array of thousands elements that can selectively delay a portion of the RF signal. So by delaying the radiated RF signal in a particular shape, beam shapes can be formed that allow the beam to be steered or spoiled to serve specific purposes. In AESA, the thousands of phase-shifting elements are also themselves transmitters and antennas. The IF signal from the REX is fed to each of the AESA elements, along with a digital “command” which tells the element how to delay the signal to form a particular beam. The individual element does the RF up-conversion and power amplification, along with phase shifting in order to form and steer a beam. Each radiating module is much less powerful than the Klystron or the TWT, but the sum of all of the AESA elements allows for high total power levels. Contrary to other answers posted here, the difference in capability between AESA and PESA is less than you might think. Both AESA and PESA can be low probability of intercept (LPI). Being LPI isn’t determined by anything special the modules are doing. It’s just due to the fact that you can change your frequency with every dwell, so that over time the average power level on any particular frequency channel is kept very low. Both AESA and PESA can do this. It’s more typical to do this on AESA because the oscillators and tuned amplifiers are more modern solid-state devices, but you can do the same thing with modern PESA as well. Also, the suggestion that you can change the frequency with every single pulse is true, but not very practical. Few radars do that. Unless the radar is looking up at the sky, a radar signal will be contaminated with clutter (energy returns from other objects in the scene). Typically this clutter is not moving, so Doppler processing is used to separate out the clutter from the moving signals. This is particularly important with ships doing horizon search or with airplanes that are looking downwards (strong ground return). In order to do Doppler processing, you must send out a series of pulses all at the same RF carrier frequency. This “dwell” may last up to several milliseconds until the required number of pulses is received, and then the radar can switch to a new frequency for the next dwell. Different methods and waveforms can be used if an airplane is trying to be stealthy, but radar situational awareness is also minimized in those circumstances.