Near millimeter wave imaging/multi-beam integrated antennas

This report describes the most recent work on the theory of single element Linearly Tapered Slot Antennas (LTSAs) and Constant Width Slot Antennas (CWSAs). The radiation mechanism for these is presently well understood and allows quantitative calculation of beamwidths and sidelobe levels, provided that the antennas have a sufficiently wide conducting region on either side of the tapered slot. Appendices 4 to 7 represent earlier work on the grant. This work further elucidates the properties of arrays of CWSA elements, and the effects of coupling on the beam-shape. It should be noted that typical beam-efficiencies of 65% have been estimated, and that element spacings of about one Rayleigh unit are possible. Further, two-point resolution at the Rayleigh spacing has been demonstrated for a CWSA array in a 30.4 cm paraboloid at 31 GHz. These results underscore that interest in further studies of the radiation mechanism of tapered slot arrays. Appendix 7 constitutes a final, detailed report on the work leading to a 94 GHz seven element LTSA array imaging system, which has been reported previously in less detail. Experimental results are presented

Near millimeter wave imaging/multi-beam integrated antennas

Theoretical models of single element Linearly Tapered Slot Antennas (LTSA) and coupling effects of LTSA arrays are discussed. A list of publications is given

Direct and Heterodyne Detection of Microwaves in a Metallic Single Wall Carbon Nanotube

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

Terahertz detection in single wall carbon nanotubes

It is reported that terahertz radiation from 0.69 THz to 2.54 THz has been sensitively detected in a device consisting of bundles of metallic carbon nanotubes, quasi-optically coupled through a lithographically fabricated antenna, and a silicon lens. The measured data are consistent with a bolometric process and show promise for operation above 4.2 K.Comment: 9 page

Anomalous suppression of the transition temperature of superconducting nanostructured honeycomb films: Electrical transport measurements and Maekawa-Fukuyama model

We report electrical transport measurements made on thin superconducting niobium films perforated by an etched array of nanoscopic holes. The hole diameter in these “honeycomb” network films is comparable to the coherence length of the parent superconducting material. A series of 12 films, with varying hole depths, were measured. As the film thickness is decreased, an unusually large reduction of transition temperature is observed for the honeycomb films as compared to plain etched films of similar thicknesses. We report on a Tc reduction in superconducting network films that is not due to an applied magnetic field. These observations are in contrast to previous reports based on Ginzburg-Landau theory analysis, which does not allow for any change in the transition temperature for perforated films in comparison to plain films. The Maekawa-Fukuyama (MF) model for two-dimensional (2D) superconductors is used to fit the sheet resistance data. The MF-2D model fits very well to the lightly etched samples, but an anomaly in Tc reduction is observed for heavily etched samples. These deviations are analyzed on the basis of change in dimensionality using the Aslamozov-Larkin model

Antenna-coupled terahertz radiation from joule-heated single-wall carbon nanotubes

In this letter an experimental method is introduced that allows detection of terahertz (THz) radiation from arrays of joule-heated Single-Walled Carbon Nanotubes (SWCNTs), by coupling this radiation through integrated antennas and a silicon lens. The radiation forms a diffraction-limited beam with a total maximum radiated power of 450 nW, significantly greater than the power estimated from Nyquist thermal noise (8 nW). The physical radiation process is unknown at this stage, but possible explanations for the high radiated power are discussed briefly. The emission has a typical bandwidth of 1.2 THz and can be tuned to different frequencies by changing the dimensions of the antennas. Arrays of the devices could be integrated in CMOS integrated circuits, and find application in THz systems, such as in near-range medical imaging