Raymond Blundell

Submillimeter receivers for radio astronomy

The state of development of receivers for submillimeter-wave radio astronomy is reviewed. Bolometers for continuum observation, hot-electron mixer receivers for narrowband spectral line observation, and heterodyne receivers, both Schottky diode and superconducting tunnel junction, are presented. At the lower frequency end of the submillimeter band, standard waveguide techniques, scaled from millimeter wavelengths, prevail. At wavelengths shorter than about 0.5 mm, quasioptical designs are preferred. In the case of Schottky diode receivers, corner cube designs are used almost exclusively, whereas integrated mixer designs are the focal point of research for superconductor-insulator-superconductor (SIS) receivers at these wavelengths. Although such designs are extensively reviewed, it is nevertheless the Schottky diode mixer remains the element of choice at the shortest submillimeter wavelengths. >

A wideband fixed-tuned SIS receiver for 200-GHz operation

We report on the design and development of a heterodyne receiver, designed to cover the frequency range 176-256 GHz. This receiver incorporates a niobium superconductor-insulator-superconductor (SIS) tunnel junction mixer, which, chiefly for reasons of reliability and ease of operation, is a fixed-tuned waveguide design. On-chip tuning is provided to resonate out the junctions geometric capacitance and produce a good match to the waveguide circuit. Laboratory measurements on the first test receiver indicate that the required input bandwidth (about 40%) is achieved with an average receiver noise temperature of below 50 K. Mixer conversion gain is observed at some frequencies, and the lowest measured receiver noise is less than 30 K. Furthermore, the SIS mixer used in this receiver is of simple construction, is easy to assemble and is therefore a good candidate for duplication. >

An annular slot antenna on a dielectric half-space

The radiation properties of both singly and multiply fed annular slot antennas on a dielectric/air interface have been analyzed using Galerkins method applied in the Hankel transform domain. The validity of our method has been confirmed through comparison with both theoretical and experimental results. The magic slot configuration has also been studied. The polarization diversity of this radiator makes it suitable for implementing a quasioptical balanced mixer. >

Understanding noise in SIS receivers

A simple laboratory test receiver has been built and used to examine some interesting aspects of heterodyne mixing with superconductor-insulator-superconductor tunnel junctions. Experiments made over the frequency range 220 GHz–490 GHz using junctions of both the Pb/Bi/In-type and the Pb/In/Au-type indicate that, in the majority of cases, a receiver may be characterized through a few simple measurements made external to its dewar. We also show that, at high local oscillator drive levels, excess mixer noise may be generated which may be removed by the application of a magnetic field. This is of particular relevance to high frequency mixing where Josephson interference may be strong. Finally, it is observed that even in the presence of severe interference a stable bias point, free from excess mixer noise, is often possible.

Quantum limited heterodyne detection in superconducting non‐linear transmission lines at sub‐millimeter wavelengths

A non‐linear superconducting transmission line has been successfully employed in heterodyne detection of sub‐millimeter waves. In our experiments an Nb/Al/AlOx/Nb tunnel junction, measuring 0.15×40 μm, with a critical current density of about 2500 A/cm2 is used as a distributed mixer element. We have demonstrated that quantum limited sensitivity can be achieved with this type of device. At 460 GHz, a Y‐factor of 2.5 has been recorded, corresponding to a double‐side‐band receiver noise temperature of 80 K. The double‐side‐band conversion loss is about 1 dB and the mixer noise temperature is estimated to be 18(±10) K.

A self-diplexing quasi-optical magic slot balanced mixer

Drawing on the principles of operation of the magic tee balanced mixer, a quasi-optical magic slot balanced mixer is proposed. The mixer exploits a diametrically fed annular slot radiator which radiates two orthogonal polarizations which are used as signal and local oscillator input ports. The idea has been tested at microwave frequencies. The measured radiation impedances, radiation patterns and conversion efficiency show that reasonable performance is readily obtained over a 30% bandwidth and that this quasi-optical balanced mixer is suitable for submillimeter wave applications. >

A quasi-optical image separation scheme for millimeter and submillimeter waves

We propose a compact quasi-optical scheme to achieve image separation using two mixers. With this scheme, an image rejection ratio of better than 12 dB has been obtained over 25 GHz in W-band without any mechanical tuning. This diplexing scheme should find applications in remote sensing and radioastronomy. >