Ozan Yurduseven

Wideband Dielectric Lens Antenna With Stable Radiation Patterns Fed by Coherent Array of Connected Leaky Slots

A broadband reflector feed is presented, which consists of a dielectric extended hemispherical lens fed by a connected array of leaky-wave slots. The slot elements are coherently combined to generate directive radiation patterns that mostly illuminate the central part of the lens, the most efficient one. The array is capable of producing secondary patterns with almost constant -10 dB beamwitdh over a 3:1 bandwidth. This allows efficient illumination of the reflector over a wide frequency range. Performance is estimated in terms of amplitude taper and phase error losses at the reflector, yielding efficiency of about 80% over the entire 3:1 bandwidth. Although the envisaged applications are in the terahertz (THz) and mm-wave frequency bands, a low-frequency prototype demonstrator has been tested in the 4 to 12 GHz band, for experimental validation of the concept.

Full characterisation of a background limited antenna coupled KID over an octave of bandwidth for THz radiation

We present the design, fabrication, and full characterisation (sensitivity, beam pattern, and frequency response) of a background limited broadband antenna coupled kinetic inductance detector covering the frequency range from 1.4 to 2.8 THz. This device shows photon noise limited performance with a noise equivalent power of 2.5 × 10−19 W/Hz1∕2 at 1.55 THz and can be easily scaled to a kilo-pixel array. The measured optical efficiency, beam pattern, and antenna frequency response match very well the simulations.

A Dual-Polarized Leaky Lens Antenna for Wideband Focal Plane Arrays

This paper presents the design and measurements of a wideband dual polarized leaky lens antenna suitable for tightly spaced focal plane arrays. The antenna is composed of two crossed leaky slots fed by two orthogonal microstrips to realize the dual-polarization operation. The crossed microstrips are fed differentially in order to couple the radiation into the slots. The slots are then coupled to a dielectric lens to achieve directive patterns suited for feeding large Focal distance to Diameter ratio reflectors. In this paper, the proposed leaky lens antenna is optimized to achieve high aperture efficiency with clean symmetric patterns in both polarizations exceeding an octave bandwidth. The concept is validated by the measurements of the primary fields inside the lens and with GRASP simulations of the focal plane array.

Performance verification of a double-slot antenna with an elliptical lens for large format KID arrays

Microwave Kinetic Inductance Detectors (MKIDs) are becoming a very promising candidate for next generation imaging instruments for the far infrared. A MKID consists of a superconducting resonator coupled to a feed-line used for the readout. In the devices presented here radiation coupling is achieved by coupling the MKID directly to planar antenna. The antenna is placed in the focus of an elliptical lens to increase the filling factor and to match efficiently to fore-optics. In this paper we present the design and the optical performance of MKIDs optimized for operation at 350 GHz. We have measured a device consisting of 14 pixels, characterized the coupling efficiency, antenna-lens frequency response and beam pattern and compared these to theoretical simulations. The optical efficiency has been measured by means of a black body radiator mounted in an ADR cryostat, through the variation of the black body temperature a variable illumination of each pixel (from 0.1 fW to 2 pW) is achieved. The frequency response and beam pattern have been directly measured in a He3 cryostat directly via the cryostat window and without the use of intermediate optics.

A dual polarized antenna for THz space applications: Antenna design and lens optimization

This contribution presents the design of a dual polarized leaky lens antenna. This antenna is fed by a CPW, which will make part of a Kinetic Inductance Detector (KID) in order to enable a broadband THz detector for future space applications. A parametric study on the lens geometry has also been performed by means of varying the extension length and it is optimized to achieve optimum aperture efficiency. The designed leaky lens antenna presents high efficiency and clean symmetric patterns in both polarizations.

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.

Asymptotic evaluation of the radiation from small dielectric lenses fed by a single leaky-wave slot

When the dimensions of a dielectric lens are large in terms of the wavelength, a leaky wave type of feed radiates a space wave emerging from the feeding point of the slot, and thus appropriately excites the lens with a spherical wave. However, when the lens antenna is operating at low frequencies, this simplified ray picture is not accurate. In this paper, we present a method to evaluate analytically the near field on the lens surface, to be used as an input for a physical optics (PO) tool. The method allows to analyze dielectric lens antenna in these critical configurations, without added computational efforts. A conclusion of this paper is that the lens can in fact be used also when it is only a few wavelength in diameter, if one accounts for higher order physical mechanisms in the design phase.

Extended hemispherical lens fed by wideband arrays of connected leaky-wave slots

We propose an array of connected leaky-wave slots as feed of an extended hemispherical dielectric lens, for broadband imaging applications. Simulations of the entire structure, including array and lens, are performed by combining a spectral Greens function approach and an accelerated physical optics method. The antenna characteristics are investigated over a 4:1 bandwidth parametrically varying the feed off-axis distance (x/R, y/R) and the lens extension length (L). Measurements from prototype demonstrator are also presented to validate the method of analysis.

On the use of antenna engineering tools for the optimization of the focal plane sampling in direct detection of distributed sources

The design of focal planes of direct detectors for the characterization of radiometric distributed sources in the sub-mm wave regime is a problem of renewed interest for the scientific community. The important question is how to optimize the focal plane sampling or the focal plane feed elements for maximizing the acquisition speed. The key speed limitations for some popular feed solutions have been qualitatively discussed in the optical scientific literature. The presented solutions were dominated only by the photon and detector noise. However, the actual realistic estimation of the acquisition speeds is complicated when rigorous electromagnetic calculations have to be performed. While, the basic estimations are supposedly well understood in the scientific astronomical communities, the realistic estimation requires the tools typical of antenna engineers. This is particularly important when the bandwidth of the desired systems is large. This paper tries to address some key difficulties, from a rigorous electromagnetic point of view, which seem to be clouding the discussions on optimal sampling.