ALMA Memo #275 Analysis of Re ective Gratings as Infrared Filters
نویسنده
چکیده
Re ective di raction gratings are investigated for use as infrared lters in submillimeter-wave cryogenic receivers, to reduce radiative loading via the dewar window on the 4K stage. The grating di racts incident IR away from the signal path, back toward the window. Analysis using scalar approximations indicate a single grating lter blocks close to 98% of the incident IR at 300K along the RF signal path, assuming a =20 (15 m) RMS surface deviation and 45 degree incidence. With a blazed grating pro le, the lter rejection was found to depend only on the RMS surface deviation and incident angle.
منابع مشابه
ALMA MEMO NO. 412 68.5 to 118 GHz Measurements of Possible Infrared Filter Materials: Black Polyethylene, Zitex, and Grooved and Un-Grooved Fluorogold and HDPE
For the ALMA production test receivers at present being designed in the NRAO CDL, there is a need for infrared filters to reduce the thermal loading. One possibility is to use a plastic material which has reasonable absorption or scattering for the infrared wavelengths but low loss at the signal wavelengths. Black polyethylene (polyethylene with carbon filler) [1, 2], Zitex (expanded PTFE) [3],...
متن کاملALMA Memo No. 335 Phase Drift Measurements of YIG-Tuned Oscillator Sources for the ALMA LO
In this memo, we present measured phase drift data of a YIG-tuned oscillator (YTO) multiplied to mmwave frequencies, a prototype of the baseline ALMA LO source. The test setup and analysis algorithms are described. We also discuss phase drift added by mmwave multipliers and power amplifiers, with the conclusion that their contribution is insignificant. Various components and system concepts are...
متن کاملMma Memo No. 265 Cost-beneet Analysis of Alma Conngurations
A cost-beneet analysis for ALMA conngurations is conducted based on the previous analysis of the MMA conngurations by Holdaway (1998). In particular, the impacts of having a larger number of antennas and longer baselines on the overall array eeciency are addressed along with several practical concerns that may aaect the connguration plan.
متن کاملNormal incidence filters using symmetry-protected modes in dielectric subwavelength gratings
We investigate narrowband transmission filters based on subwavelength-grating reflectors at normal incidence. Computational results show that the filtering is realized through symmetry-protected mode coupling. The guided mode resonances introduced by the slab layer allow flexible control of the filter frequencies. The quality factor of the filters could exceed 106. Dielectric gratings can be us...
متن کاملThe Dual - Load Calibration device revisited
Following ALMA memo 371, I re-investigate the dual load calibration scheme which has been proposed for ALMA. This memo improves on the requirements derived in memo 371 by using a better prediction for the atmospheric fluctuations at short time scales. It is shown that because of atmospheric properties and of the antenna geometry, a dual-load system located in the ALMA antenna subreflectors need...
متن کامل