REVIEW OF ANTENNAS DESIGNED FOR INFRARED DETECTION A BRIEF LITERATURE STUDY

摘要

THz sub mm region uwave & IR electronic communication researches offer numerous technical merits in terms of wider bandwidth, improved spatial resolution & compactness.Solid electronics THz capability is very minutely limited from basic signal source & systems perspective (in mW) due to two factors: extremely challenging component size in λ order & restricted applications of shorter λ μwave region Electronic devices suffer from transient times & parasitic RC time constants while photonic devices like laser diodes can only be used at approx. 10 THz. Sophisticated researches for FIRD, specifically based on resonant tunneling in quantum well hetero-structure, had been conducted for civilian & military applications. THz electronics mechanism provides promising tools for identification & interrogation of CBA. Recent developments have been done on μwave remote sensing techniques & sub mm wave heterodyne radiometric systems. Local oscillators & detectors for radiometers at 2.5 THz in new satellites are utilized for very accurate monitoring of ozone depletion & tropospheric chemistry. Low noise receivers from 30 GHz to more than 1THz are widely used in plasma diagnostics, atmospheric studies, space communication & radio astronomy. An optical antenna is an antenna coupled with optical detectors is an alternate detection device for mm, IR and visible spectra. Optical and IR antennas couple EMR in visible and IR wavelengths in same way as radio electric antennas do. Size of optical antennas lies in range of detected λ. They involve fabrication techniques with nano scale spatial resolution with proved potential advantages in detection of light showing polarization dependence, tune-ability and rapid time response. These point detectors are directionally sensitive elements. Successful use of niobium μbolometer coupled to μstrip dipole antennas for the detection of IR EMR is also possible. Measurement and characterization requires accurate use of experimental set-up with nano-metric resolution. Computation simulation of the interaction between the material structures and incoming EMR needs alternative designs of practical devices. Frequency coverage of NASA Sub mm Moderate Mission is 400 GHz - 1.2 THz & min. O/P power requirement of local oscillator at 1 THz is 50μw but a small, light weight, reliable device using low voltage power but capable in generating enough O/P power is the basic challenge. Imaging arrays offer much faster scanning of a scene than a scanned single element system and does not suffer from mechanical scanning problems. It allows a large integration time in radio astronomy remote sensing applications. IR antennas are essentially scaled-down versions of their counterparts found in uwave portion of EM spectrum. As freq of operation increases, so does the energy dissipation within the materials involved in antenna fabrication. Typical thickness of layers that make up an antenna coupled IRD is about 100 nm. Physical parameters of such thin layers depend on deposition conditions. Therefore, the material data available in literatures can only provide a starting point for the design of IR antennas. Here has been discussed how an antenna can be integrated with a detector for efficiently & effectively collecting THz radiations and some results have been reproduced.