In this article, we investigate the radiation and impedance properties of arrays of tilted dipoles. A spectral periodic method of moments (MoM) is developed for the analysis of infinite arrays with arbitrarily tilted dipole elements, in free space or with a backing reflector. With the aid of this analysis method, the radiation characteristics of arrays of stacked dipoles over a ground plane are studied, explaining the variation of the patterns as a function of the interelement distance and the angle of inclination of the elements. Finite linear arrays of tilted dipoles are also investigated, to assess the dependence of the array characteristics on the number of elements. The developed method can be used to design arrays with nonsymmetric radiation patterns for angular filtering or pattern shaping.

In this work we present a 340 GHz volumetric radar imager with 1 cm ³ voxel resolution and multi-hertz frame rate. The radar uses a sparse focal plane array of 16 transceivers and mechanical scanning to achieve real beam imaging of people for future aviation security applications.

In this work, we present a study on the radiation and impedance properties of antenna arrays with tilted elements. We developed a spectral method of moments (MoM) for the analysis of doubly-periodic arrays with arbitrarily tilted dipole or stacked dipole elements, in free space or in the presence of a backing reflector. By using this analysis method, we study the radiation characteristics of arrays of stacked dipoles over a ground plane, highlighting the variation of the patterns as a function of the inter-element distance and the angle of inclination of the elements. The guidelines derived from the MoM analysis have been applied to the design of a linear array of tilted stacked dipoles.

Kinetic inductance bolometer (KIB) technology is a candidate for scalable submillimeter wave imaging systems, particularly suitable for person security screening applications. We have previously shown that the basic figures of merit are compatible with room-temperature radiometric imaging applications, and demonstrated the functionality of kilo-pixel detector arrays. In this article, we report on our imaging system based on 8208 KIBs organized on a 2D focal plane. We provide an overview on the basic components, including the detectors, optics, and cryogenics, and describe aspects relevant in system integration. Moreover, we demonstrate the capacity in actual concealed object detection by presenting datasets revealing metallic and dielectric objects hidden under the clothes of a test person.

A wide field of view (FOV) inversely magnified dual-lens system for submillimeter wavelength imagers is presented in this paper. The antenna is designed for near-field focusing, at a range of 2.1 m from the primary aperture and to work in the frequency range from 200 to 600 GHz. The half-power beamwidth (HPBW) is 0.27° (1 cm in the image plane) at 500 GHz, corresponding to a focused antenna directivity of approximately 55 dBi. The FOV is as large as ±25.4° (±1 m at the nominal range), corresponding to a scan range of ±100 HPBWs. The shapes of the lens surfaces are optimized to minimize the phase aberration loss over the entire scanning range. Moreover, the lenses are designed to be as thin as possible to limit the dielectric absorption loss. The directivity reduction of the edge pattern with respect to broadside is approximately 1 dB with efficiency of 56%, making this lens an excellent candidate for imaging applications. The dual-lens system can be refocused by displacing the secondary lens and shows an essentially unchanged angular HPBW over a refocusing range of ±50% with respect to the nominal imaging distance. A demonstrator was fabricated and the experimental results at 500 GHz confirm the predicted performance.

The need for improved security at airports with high detection performance, high throughput rates and an improved passenger experience is motivating research into new sensing technologies. The European Union funded CONSORTIS project is addressing these aims by demonstrating a system which combines a submillimeter wave radar, a dual-band passive submillimeter wave camera and automatic anomaly detection software for reliable detection while ensuring passenger privacy. In this paper we describe the 340 GHz 16-channel FMCW radar which produces 3D maps of the subject with ∼1 cm³ voxel resolution over a 1 m³ sense volume at multi-hertz frame rates. The radar combines advanced transceiver electronics with high speed mechanical beam steering and parallelized processing to achieve this level of performance.

Passive imaging cameras at sub-millimeter wavelengths with large format focal plane arrays are being developed as the next generation of security screening systems. In this contribution, a dual-band focal plane array (FPA) for security imagers at submillimeter wave frequencies is presented. The detectors are based on bolometric superconducting kinetic inductance resonators, which allows the development of large FPAs at medium cooled temperatures. Two frequency selective absorber (FSA) sets coupled to superconductive resonator lines are designed to implement a dual color security imager. The performance of the dual band imager is evaluated using spectral analysis approach that combines Fourier optics with a Floquet mode field representation. The geometry of the unit cells is based on a Jerusalem cross configuration and the designed FSAs show a stable angular response and a rejection 1 to 3 of the undesired bandwidth. The detectors in the dual band FPA are distributed over a hexagonal grid to maximize their physical size and then improve their sensitivity. The effective point spread function of the imager coupled to a black body point source over a wide frequency band (1:6) was demonstrated experimentally with excellent agreement to the one estimated by using the proposed spectral technique.

In this paper, the practical tradeoffs for designing submillimeter wavelength imagers based on optomechanical systems combined with focal plane arrays (FPAs) are presented. The architecture of these systems differs for operation at short and long ranges. General formulas to derive the effective field of view of diffraction limited quasi-optical systems in these two scenarios are shown. These formulas can be used to evaluate the performance of a specific optical system implementation. As an application example, we present the design of an optomechanical system that can operate at both ranges in a modular approach. The presented implementation achieves an effective field of view, which is 70% of the canonical one. The proposed solution consists of a linear FPA of eight active transceivers combined with a raster scan technique. The system for short-range scenario is a side-fed dual-reflector Dragonian architecture because of its good scanning performance when illuminated by an FPA. Thanks to the system's small aperture, the scanner is arranged after the primary mirror, without causing additional scan loss. The Dragonian system is then used to illuminate a confocal dual-reflector architecture to magnify its aperture, and can be used in the long-range scenario. The scanner in this case is before the main aperture and it has to be considered in the performance optimization of the optical system since it adds phase aberration loss.

We present the design of a frequency selective surface (FSS) with large harmonic rejection bandwidth. The FSS comprises five metal layers, each consisting of a periodic array of subwavelength elements. The design is based on an equivalent transmission line model that includes only the fundamental Floquet mode. This model is valid under the condition that the unit cell size is smaller than the distance between layers. The multi-layer FSS has an overall height of one sixth of the free-space wavelength at the central frequency of operation. The simulated frequency response exhibits good stability over a wide conical incidence range, up to 45 degrees. A prototype of the designed FSS is fabricated and combined with a wide-scanning connected array of dipoles to implement an antenna element for phased array applications, with integrated filtering properties.

The EU FP7 project CONSORTIS (Concealed Object Stand-Off Real-Time Imaging for Security) is developing a demonstrator system for next generation airport security screening which will combine passive and active submillimeter wave imaging sensors. We report on the development of the 340 GHz 3D imaging radar which achieves high volumetric resolution over a wide field of view with high dynamic range and a high frame rate. A sparse array of 16 radar transceivers is coupled with high speed mechanical beam scanning to achieve a field of view of ∼ 1 x 1 x 1 m³ and a 10 Hz frame rate.

A combination 95 GHz radar and 270/560 GHz spectrometer is being built as a space instrument prototype for probing plumes and jet phenomena in the solar system. Dubbed GAISR (Gas And Ice Spectrometer/Radar), the instrument's radar will make simultaneous range/Doppler measurements of 0.1-10 mm sized ice and dust particles out to a few km in range, while its tunable spectrometer will detect the abundance and velocities of gaseous water and other volatiles. Here we describe how the radar and spectrometer share a back-end architecture, and present some innovative elements of GAISR's frequency-modulated continuous-wave (FMCW) radar, including high-isolation and low-loss transmit/receive duplexing and a phase-noise-canceling RF architecture.