B. Blazquez

A Rigorous Equivalent Network for Linearly Polarized THz Absorbers

Linearly polarized electromagnetic absorbers are often used in THz space science as means of power detection. In this paper, we present a rigorous and analytical equivalent network suitable for the analysis of these structures. The model includes, on one hand, the vectorial representation of the general propagation and scattering of the dominant electromagnetic waves and, on the other hand, details of the absorber geometry. Unlike existing models for frequency selective surfaces (FSS), the present network highlights the full interaction between TE and TM modes and the current in the strips that couples them. The network is elegant, simple and accurate, providing the explicit description of the dominant physical mechanism involved. The tool derived from the network is used for designing several THz absorber based detectors showing broadband absorption efficiencies. The network is validated with full wave simulations.

Time-Delay Multiplexing With Linear Arrays of THz Radar Transceivers

The acquisition time of a terahertz imaging radar system with a single transceiver can be halved by using time-delay multiplexing of its beam. This is achieved by splitting a transmitted beam into two beams pointing towards different positions in the target plane. For near-video imaging frame rates, arrays of transceivers would be needed. Both techniques, time-delay multiplexing and the use of transceiver arrays, can be combined to achieve the fastest possible imaging speeds. In this contribution, the feasibility of using the multiplexing technique applied to linear arrays of transceivers is studied. A completely optical multiplexing system, that can work for relatively large arrays, is presented. The technique is demonstrated with measurements in a two-element array.

Refocusing a THz Imaging Radar: Implementation and Measurements

In this contribution we present the upgrade of an existing reflector antenna system to provide a THz imaging Radar with refocusing capabilities. The method used to perform this refocusing is based on a mechanical translation of the transceiver, and it allows a 50% change of the focusing distance with respect to the normal position (25 m) maintaining well focused beams and high efficiency. The refocusing system has been validated with measurements and a resolution under 1.5 cm is obtained for the whole focusing range with spillover losses lower than 0.75 dB.

Fourier Optics for the Analysis of Distributed Absorbers Under THz Focusing Systems

An analytical spectral model able to accurately and efficiently characterize absorbers distributed in the focal plane of focusing THz systems is presented. The model is obtained by using a Fourier optics representation of the electromagnetic field in the focal plane in conjunction with a recently developed equivalent network representation for the interaction of plane waves with distributed absorbers. The model is validated by comparisons with numerical full-wave simulations. Finally, the model is used to design a few architectures based on lens-coupled Kinetic Inductance Detectors (KIDs), which show high absorption efficiency over a large bandwidth.

Impact of the antenna bandwidth in the imaging speed of kinetic inductance detectors focal plane arrays

In this paper we present the comparison in terms of acquisition speed between octave bandwidth radiometric imagers that are based either on antenna coupled or bolometer coupled direct detection instruments. The considered configurations are all characterized by dielectric lenses which can be coupled to bolometric focal planes, double slot feeds or leaky wave enhanced feeds. The acquisition speeds that can be obtained via these architectures are compared in the SAFARI/SPICA imaging scenario. The comparison shows that the leaky lens structures are significantly outperforming the double slot configurations. The leaky lens antenna also outperforms the bolometric architectures, unless noise coming from the spill over is of no concern (i.e. cold box scenarios).

Analytical model for distributed power absorbers under a focusing system

An analytical spectral model to efficiently characterize direct power detectors located on the focal plane of focusing THz systems is presented. The model is obtained by extending a Fourier Optics like representation of the electromagnetic field in the focal plane to the THz domain and combining it with a recently developed equivalent network representation. This analytical model is then use to efficiently design the whole system (focusing system and detector).

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.