We are developing multi-chroic antenna-coupled TES detectors for CMB polarimetry. Multi-chroic detectors in- crease the mapping speed per focal plane area and provide greater discrimination of polarized galactic foregrounds with no increase in weight or cryogenic cost. In each pixel, a silicon lens-coupled dual polarized sinuous antenna collects light over a two-octave frequency band. The antenna couples the broadband millimeter wave signal into microstrip transmission lines, and on-chip filter banks split the broadband signal into several frequency bands. Separate TES bolometers detect the power in each frequency band and linear polarization. We will describe the design and performance of these devices and present optical data taken with prototype pixels. Our measurements show beams with percent level ellipticity, percent level cross-polarization leakage, and partitioned bands using banks of 2, 3, and 7 filters. We will also describe the development of broadband anti-reflection coatings for the high dielectric constant lens. The broadband anti-reflection coating has approximately 100% bandwidth and no detectable loss at cryogenic temperature. Finally, we will describe an upgrade for the Polarbear CMB experiment and installation for the LiteBIRD CMB satellite experiment both of which have focal planes with kilo-pixel of these detectors to achieve unprecedented mapping speed.
We are developing dual-polarized multi-channel antenna-coupled Transition Edge Sensor (TES) Bolometers for
Cosmic Microwave Background (CMB) Polarimetry in terrestrial experiments. Each pixel of the array couples
incident power into the lithographed microstrip circuits with a dual-polarized broadband planar sinuous antenna
who's gain is increased with a contacting extended hemispherical lens. Microstrip filter manifolds partition the
two-octave bandwidth into narrow channels before terminating at separate TES bolometers. We describe the
design methodology and fabrication methods used, and also the results of optical tests that show high optical
throughput in properly located bands, as well as high cross-polarization rejection. We have explored two antenna
feeding schemes that result in different quality beams and we comment on the relative merits of each. Finally,
we quantify the increases in mapping speed that an array of our multichroic pixels might realize over traditional
We are developing antenna-coupled Transition Edge Sensor (TES) bolometers to be used in the focal planes of
telescopes mapping Cosmic Microwave Background (CMB) polarization anisotropies. These detectors will be
both dual-polarized and ultra-wide band, each containing several frequency channels. Arrays of such detectors
could realize mapping speeds nearly an order of magnitude higher than previously deployed technology while
naturally facilitating foreground removal. For such detectors to be useful, the antennas must have a high gain
and a low cross-polarization. We have designed a novel modification of DuHamel's Sinuous antenna that couples
to a contacting lens and is driven by integrated microstrip feed-lines. The integrated feed lines allow the antenna
to interface with microstrip circuits and bolometers in a way that is planar and scalable to kilo-pixel arrays. We
have demonstrated the polarization and beam properties with scale model antennas that operate at 1-12 GHz.
We report on attempts to broaden the IF bandwidth of the BIMA 1mm SIS receivers by cascading fixed tuned double-sideband (DSB) SIS mixers and wideband MMIC IF amplifiers. To obtain the flattest receiver gain across the IF band we tested three schemes for keeping the mixer and amplifier as electrically close as possible. In Receiver I, we connected separate mixer and MMIC modules by a 1" stainless steel SMA elbow. In Receiver II, we integrated mixer and MMIC into a modified BIMA mixer module. In Receiver III, we devised a thermally split block where mixer and MMIC can be maintained at different temperatures in the same module. The best average receiver noise we achieved by combining SIS mixer and MMIC amplifier is 45 -50 K DSB for νLO = 215 - 240 GHz and below 80 K DSB for νLO = 205 - 270 GHz. The receiver noise can be made reasonably flat over the CARMA IF band (νIF = 1 - 5 GHz). Noise temperatures for all three receivers are comparable to or better than those obtained with the BIMA receiver.
We describe the development of an antenna-coupled bolometer array for use in a Cosmic Microwave Background polarization experiment. Prototype single pixels using double-slot dipole antennas and integrated microstrip band defining filters have been built and tested. Preliminary results of optical testing and simulations are presented. A bolometer array design based on this pixel will also be shown and future plans for application of the technology will be discussed.
The Allen Telescope Array, originally called the One Hectare Telescope (1hT)  will be a large array radio telescope whose novel characteristics will be a wide field of view (3.5 deg-GHz HPBW), continuous frequency coverage of 0.5 - 11 GHz, four dual-linear polarization output bands of 100 MHz each, four beams in each band, two 100 MHz spectral correlators for two of the bands, and hardware for RFI mitigation built in. Its scientific motivation is for deep SETI searches and, at the same time, a variety of other radio astronomy projects, including transient (e.g. pulsar) studies, HI mapping of the Milky Way and nearby galaxies, Zeeman studies of the galactic magnetic field in a number of transitions, mapping of long chain molecules in molecular clouds, mapping of the decrement in the cosmic background radiation toward galaxy clusters, and observation of HI absorption toward quasars at redshifts up to z=2. The array is planned for 350 6.1-meter dishes giving a physical collecting area of about 10,000 square meters. The large number of components reduces the price with economies of scale. The front end receiver is a single cryogenically cooled MIMIC Low Noise Amplifier covering the whole band. The feed is a wide-band log periodic feed of novel design, and the reflector system is an offset Gregorian for minimum sidelobes and spillover. All preliminary and critical design reviews have been completed. Three complete antennas with feeds and receivers are under test, and an array of 33 antennas is under construction at the Hat Creek Radio Observatory for the end of 2004. The present plan is to have a total of about 200 antennas completed by the summer of 2006 and the balance of the array finished before the end of the decade.
We built fixed-tuned SIS mixers for use between 70 and 115 GHz on the Berkeley-Illinois-Maryland Association (BIMA) array. The mixers are similar to 215 GHz SIS devices designed by R. Blundell et al. Our 1.4 X 1.4 micrometer Nb/Al-Al2O3/Nb junctions have extremely sharp I-V characteristics, with Rsg/Rn approximately 40, and (omega) RC approximately 2. Heterodyne tests were made with a temperature-regulated vane mounted in the input waveguide to the mixer block. With vane temperatures of 20 and 35 K, we measure double sideband receiver temperatures Trcvr of 17 K from 80 to 115 GHz. Some gain compression occurs for input load temperatures greater than 50 K. Hence, with vane temperatures of 85 and 280 K we measure Trcvr approximately 35 K. Similar noise temperatures are measured with 77 and 295 K loads mounted outside the dewar. Because the mixers are partially saturated, we bias the junctions approximately 0.1 mV above or below the gain maximum, where the receiver response is a nearly linear function of the input signal level. This yields Trcvr of 35 - 40 K and makes it possible to calibrate the receivers on the telescopes using the standard chopper wheel method. With no LO power applied to the mixer, we observe a small IF signal which is proportional to the square of the input load temperature; we believe this is due to self-mixing of blackbody photons in the junction.