We report on low noise terahertz mixers (1.4–1.9THz) developed for the heterodyne spectrometer onboard the Herschel Space Observatory. The mixers employ double slot antenna integrated superconducting hot-electron bolometers (HEBs) made of thin NbN films. The mixer performance was characterized in terms of detection sensitivity across the entire rf band by using a Fourier transform spectrometer (from 0.5to2.5THz, with 30GHz resolution) and also by measuring the mixer noise temperature at a limited number of discrete frequencies. The lowest mixer noise temperature recorded was 750K [double sideband (DSB)] at 1.6THz and 950K DSB at 1.9THz local oscillator (LO) frequencies. Averaged across the intermediate frequency band of 2.4–4.8GHz, the mixer noise temperature was 1100K DSB at 1.6THz and 1450K DSB at 1.9THz LO frequencies. The HEB heterodyne receiver stability has been analyzed and compared to the HEB stability in the direct detection mode. The optimal local oscillator power was determined and found to be ...

Hot-electron bolometer terahertz mixers for the Herschel Space Observatory.

We report on a 275-425-GHz tunerless waveguide receiver with a 3.5-8-GHz IF. As the mixing element, we employ a high-current-density Nb-AlN-Nb superconducting-insulating-superconducting (SIS) tunnel junction. Thanks to the combined use of AlN-barrier SIS technology and a broad bandwidth waveguide to thin-film microstrip transition, we are able to achieve an unprecedented 43% instantaneous bandwidth, limited by the receiver's corrugated feedhorn. The measured double-sideband (DSB) receiver noise temperature, uncorrected for optics loss, ranges from 55 K at 275 GHz, 48 K at 345 GHz, to 72 K at 425 GHz. In this frequency range, the mixer has a DSB conversion loss of 2.3 plusmn1 dB. The intrinsic mixer noise is found to vary between 17-19 K, of which 9 K is attributed to shot noise associated with leakage current below the gap. To improve reliability, the IF circuit and bias injection are entirely planar by design. The instrument was successfully installed at the Caltech Submillimeter Observatory (CSO), Mauna Kea, HI, in October 2006.

/pdf/a-275-425-ghz-tunerless-waveguide-receiver-based-on-aln-2r9qcf5inv.pdf

A 275–425-GHz Tunerless Waveguide Receiver Based on AlN-Barrier SIS Technology

This paper describes a type of waveguide-to-microstrip transition incorporated with a "built-in" DC/IF return and an offset probe which is proposed for the applications of submillimeter-wave superconductor-insulator-superconductor (SIS) mixers. The effects of the DC/IF return and the probe location and orientation are understood by simulating a 100-GHz transition using the finite element method (FEM). The simulation results are compared to the experimental results of a Ka-band scale model for the simulated transition. The performance of a 100-GHz SIS mixer employing such a transition is finally presented.

A Waveguide-to-Microstrip Transition with a DC/IF Return Path and an Offset Probe

In this paper, we present our studies on a technology demonstrator for a balanced waveguide hot-electron bolometer (HEB) mixer operating in the 1.6–2.0 THz band. The design employs a novel layout for the HEB mixer combining several key technologies: all-metal THz waveguide micromachining, ultra-thin NbN film deposition and a micromachining of a silicon-on-insulator (SOI) substrate to manufacture the HEB mixer. In this paper, we present a novel mixer layout that greatly facilitates handling and mounting of the mixer chip via self-aligning as well as provides easy electrical interfacing. In our opinion, this opens up a real prospective for building multi-pixel waveguide THz receivers. Such receivers could be of interest for SOFIA, possible follow up of the Herschel HIFI, and even for ground based telescopes yet over limited periods of time with extremely dry weather (PWV less than 0.1 mm).

http://publications.lib.chalmers.se/records/fulltext/local_138880.pdf

A Technology Demonstrator for 1.6–2.0 THz Waveguide HEB Receiver with a Novel Mixer Layout

We present a novel compact wideband waveguide T-junction power divider, especially suited for millimeter-wave and THz frequencies. It incorporates substrate-based elements into a waveguide structure to provide the output port's isolation and matching. The internal port is introduced at the apex of the T-junction formed as an E-probe on a substrate. This facilitates efficient coupling of the reflected energy from the output port to a novel thin-film-based resistive termination integrated with the E-probe onto the same substrate and fabricated by means of thin-film technology. A power divider was designed, simulated, and fabricated for the frequency band 150–220 GHz to experimentally verify the theoretical and simulated performance. The results showed excellent agreement between the simulations and measurements with the devices demonstrating a remarkable return loss of 20 dB for both the input and output ports for a three-port device with equal split and isolation better than 17 dB between the output ports. Furthermore, the measured insertion loss is less than 0.3 dB and the amplitude and phase imbalance are 0.15 dB and 0°, respectively. Moreover, the divider's remarkable tolerance to the dimensions and sheet resistance of the resistive material of the built-in absorbing load makes the device a very practical component for millimeter-wave and THz systems, in particular radio-astronomy receivers.

/pdf/millimeter-wave-wideband-waveguide-power-divider-with-1091czdo1s.pdf

Millimeter-Wave Wideband Waveguide Power Divider With Improved Isolation Between Output Ports

We present the results of the development of a 275–370 GHz, fixed-tuned double sideband (DSB) receiver based on superconductor-insulator-superconductor (SIS) junction mixer. The mixer block uses a full height rectangular waveguide and employs a novel radial-like probe structure with integrated bias-T. The measured uncorrected receiver noise temperature is 30–50 K corresponding to about 2–3 quantum noise across the full frequency band with an IF from 3.8 to 7.6 GHz. The mixer is to be used on the Atacama Pathfinder EXperiment (APEX) submillimeter telescope in Chile.

I. Lapkin

Papers

A 275–370 GHz Receiver Employing Novel Probe Structure