K. S. Yngvesson

The tapered slot antenna-a new integrated element for millimeter-wave applications

Tapered slot antennas (TSAs) with a number of potential applications as single elements and focal plane arrays are discussed. TSAs are fabricated with photolithographic techniques and integrated in either hybrid or MMIC circuits with receiver or transmitter components. They offer considerably narrower beams than other integrated antenna elements and have high aperture efficiency and packing density as array elements. Both the circuit and radiation properties of TSAs are reviewed. Topics covered include: antenna beamwidth, directivity, and gain of single-element TSAs; their beam shape and the effect of different taper shapes; and the input impedance and the effects of using thick dielectrics. These characteristics are also given for TSA arrays as are the circuit properties of the array elements. Different array structures and their applications are also described. >

Quantum noise in a terahertz hot electron bolometer mixer

We have measured the noise temperature of a single, sensitive superconducting NbN hot electron bolometer (HEB) mixer in a frequency range from 1.6 to 5.3 THz, using a setup with all the key components in vacuum. By analyzing the measured receiver noise temperature using a quantum noise (QN) model for HEB mixers, we confirm the effect of QN. The QN is found to be responsible for about half of the receiver noise at the highest frequency in our measurements. The β-factor (the quantum efficiency of the HEB) obtained experimentally agrees reasonably well with the calculated value.

Terahertz detection in single wall carbon nanotubes

It is reported that terahertz radiation from 0.69to2.54THz has been sensitively detected in a device consisting of bundles of carbon nanotubes containing single wall metallic carbon nanotubes, quasioptically coupled through a lithographically fabricated antenna, and a silicon lens. The measured data are consistent with a bolometric detection process in the metallic tubes and the devices show promise for operation well above 4.2K.

Wide-bandwidth electron bolometric mixers: a 2DEG prototype and potential for low-noise THz receivers

A new type of electron bolometric (hot electron) mixer is presented. The authors have demonstrated a three-order-of-magnitude improvement in the bandwidth compared with previously known types of electron bolometric mixers, by using the two-dimensional electron gas (2DEG) medium at the hetero-interface between AlGaAs and GaAs. Both in-house, MOCVD-grown material and MBE material were tested with similar results. The conversion loss (L/sub c/) at 94 GHz is presently 18 dB for a mixer operating at 20 K, and calculations indicate that L/sub c/ can be decreased to about 10 dB in future devices. Calculated and measured curves of L/sub c/ versus P/sub Lo/ and I/sub DC/, respectively, agree well. It is argued that there the several different known configurations of electron bolometric mixers will all show wide bandwidth, and that these devices are likely to become important as low-noise terahertz receivers in the future. >

NbN hot electron bolometric mixers-a new technology for low-noise THz receivers

New advances in Hot Electron Bolometer (HEB) mixers have resulted in record low receiver noise temperatures at THz frequencies recently. We have developed quasi-optically coupled NbN HEB mixers and measured noise temperatures up to 1.56 THz, as described in this paper. We project the anticipated future performance of such receivers to have even lower noise temperature and LO power requirement as well as wider gain and noise bandwidths. We introduce a proposal for integrated focal plane arrays of HEB mixers which will further increase the detection speed of THz systems.

Ultrafast two-dimensional electron gas detector and mixer for terahertz radiation

A hot-electron bolometric detector and mixer (heterodyne detector), which uses the nonlinearities of the heated two-dimensional electron gas medium, is proposed and analyzed. The cooling process of the detector is through diffusion of the electrons into the contacts; a time constant of 1 ps and responsivity of 3000 V/W are calculated for a device which is 0.8 μm long. The predicted double-sideband receiver noise temperature for the mixer version is in the range 1000–2000 K at 1 THz, with a 100 GHz intermediate frequency bandwidth. The operating temperature would be 77 K and the local oscillator power 1 μW.

A terahertz focal plane array using HEB superconducting mixers and MMIC IF amplifiers

We present a focal plane array (FPA) designed for operation at terahertz frequencies. The FPA is based on NbN phonon-cooled hot electron bolometer mixers directly coupled to wide-band microwave monolithic integrated circuit IF amplifiers. The array incorporates all the required dc-bias and IF circuitry in a compact split-block design. We present new experimental results describing the optical coupling efficiency to the array, as well as receiver noise temperature measurements. The measurements were performed at 1.6 THz, showing good agreement with theoretical predictions. This is the first low-noise heterodyne focal plane array to be reported for any frequency above 1 THz.

Development of integrated HEB/MMIC receivers for near-range terahertz imaging

We present measurement results for a new type of integrated terahertz receiver, as an extension to previous work by the authors. The receiver we developed integrates quasi-optically coupled phonon-cooled NbN hot electron bolometric (HEB) mixers in close proximity with InP monolithic microwave integrated circuit (MMIC) intermediate-frequency (IF) amplifiers. We have measured antenna radiation pattern, receiver noise temperature, and bandwidth, as well as short-term stability of the integrated receivers. The measurements were performed at 1.6 and 2.5 THz over a very broadband IF frequency range. We have been able to extend the effective bandwidth of these receivers up to 5 GHz, the widest reported for any integrated configuration operating above 1 THz. The suitability of the HEB/MMIC approach for imaging applications has been confirmed through the development of a prototype system for near-range scanning. The results presented here are very promising for the future development of heterodyne focal plane arrays for space-based receivers, medical applications, and surveillance

Direct and heterodyne detection of microwaves in a metallic single wall carbon nanotube

This letter reports measurements of microwave (up to 4.5GHz) detection in metallic single walled carbon nanotubes. The measured voltage responsivity was found to be 114V∕W at 77K. The authors also demonstrated heterodyne detection at 1GHz. The detection mechanism can be explained based on standard microwave detector theory and the nonlinearity of the dc IV curve. The authors discuss the possible causes of this nonlinearity. While the frequency response is limited by circuit parasitics in this measurement, the authors discuss evidence that indicates that the effect is much faster and that applications of carbon nanotubes as terahertz detectors are feasible.

Very wide bandwidth hot electron bolometer heterodyne detectors based on single-walled carbon nanotubes

A hot electron bolometer heterodyne detector is proposed that has the potential for achieving intermediate frequency bandwidths of several hundred GHz. The concept relies on experimentally measured ballistic∕quasiballistic transport properties of single-wall carbon nanotubes and the measured temperature dependence of the resistance of such tubes. Receiver noise temperatures of a few thousand Kelvin, and local oscillator powers of 1μW or less are estimated.