On the Development of Wideband Direct Detection Focal Plane Arrays for THz Passive Imaging Applications

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In the design of millimeter and sub-millimeter wave radiometric imaging systems a persistent goal is the increase in the speed of acquisition of the image while maintaining a high sensitivity. Typically, the highest sensitivity is achieved by cryogenically cooling the detectors, specifically in astronomical applications. However, for the purpose of low-cost imaging applications it is desirable to operate at room temperature. Without cryogenically cooling, the electronic noise introduced by the detectors becomes dominant, making the detectors less sensitive. Resorting to detection architectures containing amplification circuitry might be impractical for implementation in large focal plane arrays (FPAs) fabricated in integrated technologies. This work derives the focal plane architecture that maximizes the imaging speed of radiometers operating at room temperature without using any amplification circuitry. It is shown that in such scenario a practical image acquisition speed can still be achieved when a very broad portion of the THz-band is exploited. Ultimately the imaging speed is maximized when the FPA is undersampled, implying a trade-off in the size of the optics. The analysis is substantiated by a case study using wideband leaky lens antenna feeds operating over a 3:1 relative frequency band. ..