TeraSCREEN is an EU FP7 Security project aimed at developing a combined active, with frequency channel centered at 360 GHz, and passive, with frequency channels centered at 94, 220 and 360 GHz, imaging system for border controls in airport and commercial ferry ports. The system will include automatic threat detection and classification and has been designed with a strong focus on the ethical, legal and practical aspects of operating in these environments and with the potential threats in mind. Furthermore, both the passive and active systems are based on array receivers with the active system consisting of a 16 element MIMO FMCW radar centered at 360 GHz with a bandwidth of 30 GHz utilizing a custom made direct digital synthesizer. The 16 element passive receiver system at 360 GHz uses commercial Gunn diode oscillators at 90 GHz followed by custom made 90 to 180 GHz frequency doublers supplying the local oscillator for 360 GHz sub-harmonic mixers. This paper describes the development of the passive antenna module, local oscillator chain, frequency mixers and detectors used in the passive receiver array of this system. The complete passive receiver chain is characterized in this paper.
We describe the design and characterisation of a cryogenic millimetre/sub-millimetre wave calibration load, cooled by
use of a closed cycle refrigerator that is used to test the performance of the ALMA receiver front-end system. Use of the
refrigerator removes the need for liquid cryogen (nitrogen) cooling and allows for long duration, and unattended
operation independent of orientation angle. Key requirements of the load include provision of a well-characterised and
constant brightness temperature over a wide frequency range (from ~100 GHz to ~1 THz) polarisation insensitivity, high
emissivity and mechanical stability. Test and verification of the load performance characteristics is achieved by using
several measurement techniques; these are presented and compared with measurements made using a liquid cryogen load
Most parts of the electromagnetic spectrum are well understood and exploited, but the terahertz region between the microwave and infrared is still relatively under developed. Potential receiver applications are wide-ranging and cross-disciplinary, spanning the physical, biological, and medical sciences. In this spectral region, Schottky diode technology is uniquely important. InP MMIC amplifiers are generally limited to frequencies less than ~200 GHz, above which their noise performance rapidly deteriorates. Superconducting circuits, which require cooling, may not always be practical. Either as varistor diodes (heterodyne mixing), or varactor diodes (sub-millimetre power generation), Schottky technology underpins terahertz receiver development.
A compact, solid state, zenith looking 94 GHz meteorological radar is described. Samples of the reflectivity data obtained from representative samples of hydrometeors, including cirrus cloud and fog, are presented. This bistatic FMCW radar delivers continuous information on the distribution and thickness of cloud layers, permitting accurate determination of the cloud base altitude and upper limit. The maximum range is 16 km, with a corresponding resolution of 30 m: both range and averaging time are user selectable in ranges 2-16 km and 5-60 s respectively. A radiated millimetre wave power of below 200 mW yields a dynamic range of over 60 dB in the received signal.
MARSCHALS is the airborne simulator of a proposed future satellite instrument to measure millimetre-wave limb emission from O<sub>3</sub>, H<sub>2</sub>O, CO and other trace gases in the upper troposphere and lower stratosphere.
To achieve comparatively high vertical resolution and pointing stability, MARSCHALS scans the atmospheric limb in 1km vertical steps using a 235mm diameter antenna controlled by a dedicated inertial measurement unit. A quasi-optical network directs radiation from the antenna or an ambient (~300K) or cold (~90K) calibration target into three front-end receivers and suppresses each unwanted side-band by >30dB using multi-layer frequency selective surfaces. Each receiver comprises a waveguide mixer pumped subharmonically by a phase-locked LO and a wideband IF preamplifier. The IF outputs are directed to channeliser spectrometers of 200MHz resolution which instantaneously and contiguously cover 12GHz wide (RF) frequency bands centred near 300, 325 and 345GHz. To identify clouds, images of near-IR sunlight scattered into the limb direction are recorded concurrently by an 850nm wavelength camera.
MARSCHALS has been built under ESA contract by a consortium led by Rutherford Appleton Laboratory in the UK, and had its first flights on the Russian Geophysica (M55) aircraft during 2005, culminating in a deployment during the SCOUT-O3 campaign based in Darwin, Australia. This paper describes the MARSCHALS instrument and an initial assessment of its performance, determined on ground and during flight.
MARSCHALS (Millimeter-wave Airborne Receivers for Spectroscopic CHaracterization in Atmospheric Limb Sounding) is being developed with funding from the European Space Agency as a simulator of MASTER (Millimeter-wave Acquisitions for Stratosphere Troposphere Exchange Research), a limb sounding instrument in a proposed future ESA Earth Explorer Core Mission. The principal and most innovative objective of MARSCHALS is to simulate MASTER's capability for sounding O<SUB>3</SUB>, H<SUB>2</SUB>O and CO at high vertical resolution in the upper troposphere (UT) using millimeter wave receivers at 300, 325, and 345 GHz. Spectra are recorded in these bands with 200 MHz resolution. As such, MARSCHALs is the first limb-sounder to be explicitly designed and built for the purpose of sounding the composition of the UT, in addition to the Lower Stratosphere (LS) where HNO<SUB>3</SUB>, N<SUB>2</SUB>O and additional trace gases will also be measured. A particular attribute of millimeter-wave measurements is their comparative insensitivity to ice clouds. However, to assess the impact on the measurements of cirrus in the UT, MARSCHALs has a near-IR digital video camera aligned in azimuth with the 235 mm limb-scanning antenna. In addition to UT and LS aircraft measurements, MARSCHALs is capable of making mid-stratospheric measurements from a balloon platform when fitted with a 400 mm antenna. Provision has been made to add further receiver channels and a high resolution spectrometer.