Surface wave control for large arrays of microwave kinetic inductance detectors

Large ultra-sensitive detector arrays are needed for present and future observatories for far infra-red, submillimeter wave (THz), and millimeter wave astronomy. With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves, the surface wave. We demonstrate this effect with focal plane arrays of 880 lens-antenna coupled Microwave Kinetic Inductance Detectors (MKIDs). Presented here are near field measurements of the MKID optical response versus the position on the array of a reimaged optical source. We demonstrate that the optical response of a detector in these arrays saturates off-pixel at the $\sim-30$ dB level compared to the peak pixel response. The result is that the power detected from a point source at the pixel position is almost identical to the stray response integrated over the chip area. With such a contribution, it would be impossible to measure extended sources, while the point source sensitivity is degraded due to an increase of the stray loading. However, we show that by incorporating an on-chip stray light absorber, the surface wave contribution is reduced by a factor $>$10. With the on-chip stray light absorber the point source response is close to simulations down to the $\sim-35$ dB level, the simulation based on an ideal Gaussian illumination of the optics. In addition, as a crosscheck we show that the extended source response of a single pixel in the array with the absorbing grid is in agreement with the integral of the point source measurements.Comment: accepted for publication in IEEE Transactions on Terahertz Science and Technolog

Eliminating stray radiation inside large area imaging arrays

With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves. We demonstrate this effect with focal plane arrays of absorber coupled Lumped Element microwave Kinetic Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the response from a point source at the pixel position is at a similar level to the stray response integrated over the entire chip area. For the antenna coupled arrays, we show that this effect can be suppressed by incorporating an on-chip stray light absorber. A similar method should be possible with the LEKID array, especially when they are lens coupled.Comment: arXiv admin note: substantial text overlap with arXiv:1707.0214

An Ultra-Wideband Leaky Lens Antenna for Broadband Spectroscopic Imaging Applications

We present the design, fabrication and characterisation of a broadband leaky lens antenna for broadband, spectroscopic imaging applications. The antenna is designed for operation in the 300-900 GHz band. We integrate the antenna directly into an Al-NbTiN hybrid MKID to measure the beam pattern and absolute coupling efficiency at three frequency bands centred around 350, 650 and 850 GHz, covering the full antenna band. We find an aperture efficiency $\eta_{ap} \approx 0.4$ over the whole frequency band, limited by lens reflections. We find a good match with simulations for both the patterns and efficiency, demonstrating a 1:3 bandwidth in the sub-mm wavelength range for future on-chip spectrometers.Comment: Accepted for Publication at IEEE Transactions on Antennas and Propagatio

First light demonstration of the integrated superconducting spectrometer

Ultra-wideband 3D imaging spectrometry in the millimeter-submillimeter (mm-submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution. However, it is challenging to scale up conventional coherent heterodyne receivers or free-space diffraction techniques to sufficient bandwidths ($\geq$1 octave) and numbers of spatial pixels (>$10^2$). Here we present the design and first astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer, which covers 332-377 GHz with a spectral resolution of $F/\Delta F \sim 380$. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs) with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine, and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to $\sim$1.1 THz. The miniature chip footprint of a few $\mathrm{cm^2}$ allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible.Comment: Published in Nature Astronomy. SharedIt Link to the full published paper: https://rdcu.be/bM2F

Compact parabolic reflector antenna design with cosecant-squared radiation pattern

This paper deals with the parametric analysis and proper design of parabolic reflector antennas to obtain pencil-beam, cosecant-squared and inverse cosecant-squared radiation patterns for air and coastal surveillance radars. A novel design is introduced to obtain both pencil-beam and cosecant-squared radiation patterns by using the same modified parabolic reflector antenna structure fed by an H-plane horn feeder which can be adjusted as symmetric or asymmetric feeder by changing the bottom flare angle. The analytical regularization method (ARM) is used as a fast and accurate way to solve the problem of E-polarized wave diffraction by parabolic shaped perfectly electrical conductive (PEC) cylindrical reflector with finite thickness. The numerical procedure is initially verified by the analytical and numerical methods, and the calculated radiation characteristics are presented for the proposed antenna configurations

Triangular-Shaped Single-Loop Resonator: A Triple-Band Metamaterial With MNG and ENG Regions in S/C Bands

A new metamaterial topology, called triangular-shaped single-loop resonator (SLR), is introduced with two distinct mu-negative (MNG) regions and one epsilon-negative (ENG) region over the S/C frequency bands. Transmission and reflection characteristics of the suggested subwavelength resonator are analyzed using full-wave electromagnetic solvers, Ansoft HFSS and CST Microwave Studio (MWS), to demonstrate the presence of four closely located resonance frequencies within the 3.3-5.1 GHz range. Effective permittivity and permeability parameters of the resulting composite medium are retrieved from simulated complex scattering parameters to verify the existence of fully developed MENG and ENG regions. Dependence of the resonance frequencies on the design parameters of the triangular SLR unit cell and on the presence of its gaps are also investigated in detail

An outline of indirect holographic methods for antenna measurements and microwave imaging

Indirect microwave holographic techniques offer a simple, low cost technique for a range of microwave measurements including the determination of antenna characteristics and the ability to provide good quality images of passive objects. This work provides a brief outline of the basic theory of indirect microwave holography and how it can be used for the reconstruction of scattered complex fields at the measurement plane and how these results can be back propagated to provide the scattered fields at any preselected observation plane. It provides an outline of the different techniques required for antenna measurement and the imaging of passive objects. It demonstrates how indirect holography can be used to determine the far field radiation pattern of a high gain antenna and reconstruct the complex antenna aperture fields. This work also demonstrates the use of indirect holography for the imaging of passive objects. The techniques described have been validated by experimental results on a range of objects including buried objects

A compact five-band SLR type metamaterial

In this paper, a novel single-loop resonator (SLR) type metamaterial topology is proposed with five distinct resonance frequencies placed within the frequency band from 2.8 GHz to 5.1 GHz displaying two -negative (ENG) and three -negative (MNG) bands. This new SLR unit cell is obtained by slightly modifying the geometrical structure of the square-shaped SLR that is recently reported in literature with only three resonances. Transmission and reflection characteristics of both standard square-shaped SLR and its newly modified version are simulated by two different full wave electromagnetic solvers, Ansoft's HFSS and CST Microwave Studio, to verify the accuracy of numerical results. Effective permittivity and permeability parameters of these metamaterial structures are retrieved from simulated complex scattering parameters to verify the presence of distinct ENG and MNG regions. E-field distributions are computed over the conductive strips to investigate the mechanism of resonances. Finally, effects of substrate permittivity and substrate thickness on the values of resonance frequencies are inspected parametrically for the novel SLR topology. © 2012 IEEE