The Jet Propulsion Laboratory has developed a 170 GHz airborne radar for cloud and humidity remote sensing. Called VIPR (Vapor Inside-cloud Profiling Radar), the system uses differential absorption at closely spaced frequencies near the 183 GHz water vapor resonance to obtain range-profiling measurements of absolute humidity inside clouds, and partial-water- column measurements in clear skies. VIPR transmits around 300 mW over 167-174.8 GHz, has a system noise figure of 8 dB, and uses a 60-cm diameter aperture. The radar has been deployed both on the ground pointing toward zenith, and from an aircraft with nadir pointing. Based on architectures originally developed for submillimeter-wave security imaging, VIPR uses ultra-high-isolation transmit/receive duplexing with a single primary antenna. This approach achieves thermal noise limited sensitivity even while using frequency-modulated continuous-wave ranging methods, and even when the radar is mounted in an aircraft with its beam emerging from an open-air viewport. Here we present a validation measurement of VIPR’s ability to sense humidity in clear skies using ground reflection magnitudes at different altitudes and frequencies. These results have also motivated a new investigation of using a higher-frequency 557 GHz differential absorption radar for water vapor sensing in the low pressure, cold, and dry conditions on Mars. We have developed a 552-558 GHz RF source with several mW of output power that could be used for making local humidity measurements on Mars out to several kilometer ranges.
APEX, the Atacama Pathfinder Experiment, is collaboration between Max Planck Institut fur Radioastronomie (MPIfR) with Astronomisches Institut Ruhr Universitat Bochum, Onsala Space Observatory and the European Southern Observatory (ESO). The telescope was supplied by VERTEX Antennentechnik in Duisburg, Germany, and is a 12 m antenna with 15 μm rms surface accuracy operating at the Atacama Desert Llano Chajnantor, in the Chilean Andes at 5100 m altitude. APEX heterodyne single pixel facility receiver are placed in the telescope Nasmyth cabin A. The receivers are coupled to the antenna via relay optics providing possibility to operate either one of the two different PI-type instruments or a multi-channel facility heterodyne receiver to cover 211 - 1500 GHz frequency range. In this report, we present the optical design for APEX single-pixel facility heterodyne receiver providing frequency independent illumination of the secondary for all the receiver channels. We present design of the two-channel facility receiver APEX A, installed and operating since June 2005, and of the coming 6-channel APEX facility receiver. The report includes a brief review of the mixer technology development status for APEX Band 1, 211 - 270 GHz, using sideband separation technology (2SB), Band 2, 270 - 370 GHz, 2SB, Band 3, 385 - 500 GHz, 2SB, and Band T2, 1250 - 1390 GHz, HEB waveguide balanced mixer, those on the development at Onsala Space Observatory. We present description of the receiver control system and example observation of APEX 2a receiver.
The Atacama Pathfinder EXperiment (APEX) is a 12 m antenna operating at the Atacama Desert on the Chilean Andes at about 5000
m altitude. APEX would be equipped with a suit of single-pixel heterodyne receivers covering 211 - 1500 GHz frequency range. We
present here a design of a sideband-separating superconductor-insulator-superconductor (SIS) mixer for the APEX, receiver Band 3,
operating in 385 - 500 GHz band. The receiver uses quadrature scheme with the RF signal passing via a 90-degree waveguide 3 dB
hybrid and the LO is divided by a waveguide E-plane Y-junction. The outputs of the waveguide hybrid are coupled to the mixer SIS
junctions through an E-probe with integrated bias-T. For the LO coupler, conventional branch waveguide couplers are difficult to
manufacture at this high frequency with required accuracy as the branch waveguides become extremely narrow. In order to solve this
problem, we propose an on-chip LO injection, where the LO coupler is integrated onto the mixer chip and fabricated together with the
SIS junction and the tuning circuitry. The on-chip LO coupler is made of superconducting lines, which gives almost a lossless
solution and provides fabrication accuracy better than 0.5 μm by using optical lithography only. Furthermore, the mixer design
includes a novel component, an ellipse termination for the idle LO port, made of thin-film resistive material with sheet resistance
equal to the transmission line characteristic impedance, which gives very broadband performance using extremely compact area.
The Atacama Pathfinder EXperiment (APEX) is a 12 m antenna now operating at the Llano Chajnantor on the Atacama
Desert in Northern Chile at 5100 m altitude. APEX will be equipped with single-pixel heterodyne receivers covering
211 - 1500 GHz frequency range. We present a sideband separation (2SB) mixer using superconducting-insulator-superconductor
(SIS) junction for the APEX band 2, 275-370 GHz. The 2SB mixer is based on a previous development
of a double sideband (DSB) mixer, which is currently installed at the APEX telescope. This DSB receiver has a noise
temperature of about 40-50 K across the band, and, as installed on one of the best site on the Earth, yields total DSB
system noise temperatures of about 100 K for excellent weather.
The 2SB mixer layout uses a modular approach with two identical DSB mixers, independently tested, having similar
characteristics, and combined with an intermediate waveguide block, containing a 3 dB-90° branch-line coupler for the
RF signal and a 3 dB-180° divider for the LO signal. The LO signals are injected into the mixer using a novel
waveguide directional coupler based on 2 quartz chips containing E- probes, allowing to couple -15 dB of the LO to the
RF path. At the conference, we will present the first measurements of this 2SB mixer, together with the current
performance the DSB receiver at the APEX telescope.