Cheuk-Yu Edward Tong

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. >

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. >

Design and characterization of a 250-350-GHz fixed-tuned superconductor-insulator-superconductor receiver

A fixed-tuned superconductor-insulator-superconductor (SIS) receiver has been designed to operate in the 250-350-GHz frequency band. This receiver has a double-side-band noise temperature of between 35 and 45 K, or about 3h/spl nu//k/sub B/, over its entire operating band. Extensive characterization of the receiver has been carried out using techniques developed for submillimeter waves. The input noise, side-band ratio, 1 dB compression point, optimum LO drive level, and vector near-field beam profile have all been measured experimentally. The measurement techniques and results are presented and discussed.

A photomixer local oscillator for a 630-GHz heterodyne receiver

A photomixer local oscillator (LO) operating at the 630-GHz difference frequency of two laser diodes was successfully demonstrated with a heterodyne detector based on a niobium superconducting tunnel junction. The low-temperature-grown GaAs photomixer generated 0.20 μW in the input spatial mode of the receiver. Using the photomixer LO, the double-sideband noise temperature of the receiver was 331 K-in good agreement with the 323 K noise temperature obtained when a multiplied Gunn oscillator generating 0.25 μW was substituted for the photomixer.

Low noise NbN lattice-cooled superconducting hot-electron bolometric mixers at submillimeter wavelengths

Lattice-cooled superconducting hot-electron bolometric mixers are used in a submillimeter-wave waveguide heterodyne receiver. The mixer elements are niobium nitride film with 3.5 nm thickness and ∼10 μm2 area. The local oscillator power for optimal performance is estimated to be 0.5 μW, and the instantaneous bandwidth is 2.2 GHz. At an intermediate frequency centered at 1.4 GHz with 200 MHz bandwidth, the double sideband receiver noise temperature is 410 K at 430 GHz. The receiver has been used to detect molecular line emission in a laboratory gas cell.

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.

An integrated SIS mixer and HEMT IF amplifier

Design details are given for a 205-270 GHz fixed-tuned SIS receiver in which the SIS mixer and HEMT IF amplifier are integrated into a single compact unit. The mixer and IF amplifier are connected with an inductor which provides the reactive part of the optimum input impedance for the HEMT. This simple coupling circuit gives an IF bandwidth of /spl sim/4 GHz. The receiver has a DSB noise temperature in the range 35-80 K over the 205-270 GHz local oscillator band and 0.5-4.5 GHz IF band.

A 1-THz superconducting hot-electron-bolometer receiver for astronomical observations

In this paper, we describe a superconducting hot-electron-bolometer mixer receiver developed to operate in atmospheric windows between 800-1300 GHz. The receiver uses a waveguide mixer element made of 3-4-nm-thick NbN film deposited over crystalline quartz. This mixer yields double-sideband receiver noise temperatures of 1000 K at around 1.0 THz, and 1600 K at 1.26 THz, at an IF of 3.0 GHz. The receiver was successfully tested in the laboratory using a gas cell as a spectral line test source. It is now in use on the Smithsonian Astrophysical Observatory terahertz test telescope in northern Chile.

An efficient algorithm for transmission line matrix analysis of electromagnetic problems using the symmetrical condensed node

A study of the symmetrical condensed TLM (transmission line matrix) node is presented. The study reveals not only that the characteristic scattering matrix satisfies the law of conservation of energy but also that electromagnetic fields are conserved even for finite node spacing. Using the results of this study, the authors develop an efficient algorithm for TLM analysis using the symmetrical condensed node. This algorithm significantly reduces the number of floating point operations so that the speed of computation is comparable to that of other expanded node analysis schemes. The case of a lossy medium is also discussed. With a better understanding of this symmetrical node and equipped with a fast algorithm, TLM analysis of three-dimensional electromagnetic problems can improve the computer-aided design of microwave and millimeter-wave circuits. >

Superconductive hot-electron-bolometer mixer receiver for 800-GHz operation

In this paper, we describe a superconductive hot-electron-bolometer mixer receiver designed to operate in the partially transmissive 350-/spl mu/m atmospheric window. The receiver employs an NbN thin-film microbridge as the mixer element, in which the main cooling mechanism of the hot electrons is through electron-phonon interaction. At a local-oscillator frequency of 808 GHz, the measured double-sideband receiver noise temperature is T/sub RX/=970 K, across a 1-GHz intermediate-frequency bandwidth centered at 1.8 GHz. We have measured the linearity of the receiver and the amount of local-oscillator power incident on the mixer for optimal operation, which is P/sub LO//spl ap/1 /spl mu/W. This receiver was used in making observations as a facility instrument at the Heinrich Hertz Telescope, Mt. Graham, AZ, during the 1998-1999 winter observing season.