In the early 1970s, Electronically Scanned Antennas (ESAs) emerged as a new and impactful technology for ISR missions. Replacing Mechanically Scanned Antennas (MSAs), ESAs were much faster for beam switching from a mission timeline perspective, and eliminated the size weight and power associated with a gimbal. As ESAs became better understood, passive EW modes were added as part of their capability offering. This highlights the revolutionary impact of ESAs on the warfighter battlespace.
Early ESAs were “passive” antennas. The front end of the antenna was composed of array elements with phase shifters. A passive manifold was employed for RF combining to form a single beam. At the output of the manifold was a switch with an LNA (Receive) and large tube amplifier (Transmit). Solid state electronic device capability was not developed enough to include active amplifiers at the front end of the array for each array element. With the LNA and amplifier behind the manifold the amount of RF loss was quite large causing inefficiency on transmit (Power Aperture) and limitations on sensitivity (G/T) on receive.
With the emergence of GaAs, solid state devices could be miniaturized at the size of the array elements enabling distributed ESA architectures. High power amplifiers and LNAs could be placed close to the front end and included for each element. This resulted in drastic power efficiency improvement and much higher receive sensitivity, since the only loss before the first LNA was the radome and array element. The amplifiers were packaged in Transmit/Receive (T/R) modules with phase shifter and attenuator. This new style of architecture was called an “active” ESA. This eliminated the need for a large tube transmit amplifier and led to the distributed “active” ESAs that are commonplace today.
This talk will show the genesis from MSA to passive ESA to active ESA and provide a conceptual understanding of the advantages of an active ESA. Additionally, the talk will show how the next ESA transformation that is currently taking place is from analog active ESAs to digital active ESAs.
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