A 345GHz SIS receiver for radio astronomy

A 345GHz superconductor insulator superconductor (SIS) tunnel junction receiver utilizing a full height rectangular waveguide mixer with two tuning elements, i.e. an E-plane and backshort tuner, has been constructed and installed on the Caltech Submillimeter Observatory 10m antenna on Mauna Kea, Hawaii. The receiver exhibits a best double side-band noise temperature response of 150K±20K (averaged over a 500 MHz IF bandwidth centered at 1.5GHz) at a design center frequency of 345GHz and at an ambient temperature of approximately 3.8K. Additional measurements show that the receiver has an excellent response at selected points within an RF input range of 280 to 363GHz.     

Simulated performance of SIS and SIN junctions as heterodyne receivers in waveguide and open antenna mixer mounts

Tucker's quantum theory of mixing (in the 3-port approximation) is employed to calculate the gain over a wide range of frequencies of model mixers employing SIS and SIN junctions with both real and idealI–V characteristics. A comparison is made between the performance of junctions in waveguide and open antenna mounts. It is concluded that ideal junctions give gain 1.5 to 2 times higher than real ones, SIS junctions have gain approximately three times greater than otherwise similar SIN junctions, and that junction areas need to be typically three times smaller in open antenna structures to provide comparable gain to those in waveguide mounts.     

The effect of mixer mount loss on the performance of SIS receivers

Tucker's quantum theory of mixing (in the 3-port approximation) is employed with Eisenhart and Khan's equivalent circuit for a junction mounted in waveguide to predict the gain of an SIS mixer as a function of guide impedance, series inductance, junction capacitance, IF load impedance and backshort loos. The improvements which will result from optimisation of these parameters are quantified. It is shown that for optimum performance a backshort VSWR>100 is required, which is hard to realise at high frequencies     

Characteristics of InSb mixers and backward wave oscillators in a submm heterodyne receiver

In this paper some aspects of two of the most important components of a previously described submm heterodyne are discussed: the InSb mexer and the backward wave oscillator. The (known) properties of the InSb mixer and our method of fabrication will be briefly discussed. The aspect of matching this mixer to the waveguide is treated more extensively both in theory and practice. Finally the performance of InSb as a mixer at higher frequencies is briefly considered. Some properties of the backward wave oscillator which are of special relevance when using it in combination with an InSb mixer, have been measured and they are discussed in the last section.     

Simple FTS Measurement System for Submillimeter SIS Mixer

We have constructed a simple Fourier Transform Spectroscopy system, and carried out performance measurement of our 640-GHz band SIS mixer devices. This system uses the identical quasi-optics to the one for heterodyne measurement, which allows a direct and quick comparison between FTS and heterodyne responses. With a room-temperature absorber for submillimeter source, instead of a high-temperature source such as Hg lamp, we successfully obtained interferogram with good signal-to-noise ratios. The frequency resolution is moderately coarse ( 17 GHz( due to a limitation on the travel length of scanning mirror for the interferometer, but we found it is useful to investigate broad-band characteristics of SIS mixers.     

SEMICONDUCTOR-SUPERLATTICE FREQUENCY MIXER FOR DETECTION OF SUBMILLIMETER WAVES

We report on a GaAs/AlAs superlattice frequency mixer for detection of submillimeter waves. The mixer is based on the nonlinear miniband transport giving rise to domains excited under the action of a microwave field. We designed the mixer for broadband operation (300–600 GHz). For studying basic properties, we investigated the mixer as a harmonic mixer in 15^th order to detect radiation at a radio frequency (RF) near 300 GHz using local oscillator (LO) radiation of a frequency near 20 GHz. We reached a noise equivalent power (NEP) of about 10 fW/Hz. We also show that the use of the superlattice mixer together with a superlattice frequency multiplier allows to realize a superlattice-based free-space transmission line for submillimeter waves.     

A low noise heterodyne receiver for astronomical observations operating around 0.63 mm wavelength

A heterodyne receiver is described in which an InSb hot electron bolometer is used as a mixer. The local oscillator power is obtained by doubling the frequency of a backward wave oscillator. The receiver operates between 460 and 500 GHz (0.65–0.6 mm). Noise temperatures amount typically to 1000 K.     

Variable-temperature loads for use in accurate noise measurements of cryogenically-cooled microwave amplifiers and mixers

We have demostrated the use of cryogenically-cooled variable-temperature loads for accurate noise measurements of low-noise cooled amplifiers and mixers in the microwave and millimeter wave range. The input noise temperature of the amplifier or mixer can be measured with an accuracy of ±1 K or better.     

Wavelengths for new CH3OH laser lines

Using a grating-tuned CO₂-TEA laser to pump CH₃OH in a metallic-wave-guide resonator, submillimeter laser emissions have been produced by pumping with 36 lines in the 9.4m CO₂ band and with 23 lines in the 10.6m band. Several dozen new SMM laser lines were observed. Wavelengths accurate to within 0.1% are given for 12 previously unmeasured lines between 34m and 225m.     

Antenna patterns of an open structure mixer at a submillimeter wavelength and of its scaled model

To verify the enhancement in sensitivity of a Schottky barrier diode using a 90° corner reflector at submillimeter wavelength a 651 scaled model of the open structure mixer was constructed and investigated at 2.8 cm wavelength.The results show clearly the advantage of a 90° corner reflector, the reality of the deviations for 45° and 60° corner reflectors found for submillimeter wavelengths, and the equality of the antenna patterns for a 90° corner reflector and a cat-eye (corner cube) reflector.