Reception Power Pattern of Distributed Absorbers in Focal Plane Arrays: A Fourier Optics Analysis

Abstract

Passive imaging cameras at millimeter and submillimeter wavelengths are currently entering a new era with the development of large format arrays of direct detectors. Several of these arrays are being developed with bare absorbing meshes without any antenna coupling (lens or horn) structures. The design of such arrays is typically done resorting to geometrical considerations or basic broadside plane wave incidence analysis. This paper presents a spectral technique for the analysis of such focal plane arrays in reception using Fourier Optics, which is valid also for moderately skewed incident angles. The analysis constitutes a step improvement with respect to previously used methods by providing an accurate and efficient way to estimate the point-source angular response and the throughput from a distributed incoherent source of an absorbing mesh in the focal plane of a quasi-optical component (e.g. a parabolic reflector or lens). The proposed technique is validated with full-wave simulations. After presenting the analysis, the paper compares the performance of arrays of bare absorber in the focal plane of a quasi-optical component to those of corresponding antenna based arrays. It is found that absorbers lead to a comparable trade-off, in terms of spill-over and focusing efficiency, only for very tight samplings. For larger samplings, the focusing efficiency of absorbers is significantly lower than the one for antennas.

A Dual-Band Focal Plane Array of Kinetic Inductance Bolometers Based on Frequency-Selective Absorbers

“…The physical dimensions of the two detector sets are fixed to 1 = 0.625 1 # and 2 = 0.75 2 # , respectively. These values lead to a comparable utilization of the optical aperture to the one of an antenna based FPA [15].…”

“…In order to analyze the performance of an imager based on a FPA made of bare absorbers, the spectral Fourier optics (FO) technique described in [15] is used. This technique couples the spectrum of the optical system with a Floquet mode representation in the surrounding of the periodic absorber.…”

“…5 are difficult to model using lumped elements because of the coupling between the layers via higher order Floquet modes. Therefore, an equivalent circuit model based on an admittance matrix, ̅ ( ⃗ ⃗ ), representing the scattering of the FSA unit cells [15] will be used in the next sections to evaluate the coupling of the FSA KIBs to the optical system. Such matrix was evaluated using CST MWS simulations with periodic boundary conditions.…”

“…For non-fully sampled FPAs, the optimum configuration in terms of sensitivity typically leads to a distribution of the detectors over a hexagonal grid combined with a twodimensional jiggling mechanism, [24], [25], since this allows for the largest physical dimensions of the detectors. However, a FPA based on bare absorbers suffers from a significant penalty in angular resolution for large dimensions as described in [15]. Moreover, a two-dimensional jiggling mechanism requires a scanner operating at much higher speed than the frame rate [24].…”

One‐Pot Synthesis of Highly Fluorescent Poly(methacrylic acid)‐Capped Silver Nanoclusters for the Specific Detection of Iron(II)

“…Some methods have been come up with by researchers for iron quantitative analysis including chemiluminescence, high‐performance of liquid chromatography, radiometry, ion‐selective electrode, spectrophotometry, voltammetry, digital‐image‐based colorimetry, fluorescence detection method, and flow injection analysis method . Generally speaking, atomic absorption and high‐resolution inductively coupled plasma mass spectrometry are adopted to evaluate and determine the content of iron in samples .…”