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- Ludvig-Osipov, Andrei, et al.
(author)
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Fundamental bounds on extraordinary transmission with experimental validation
- 2018
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Reports (other academic/artistic)abstract
- This paper presents a study of extraordinary transmission (EoT) through arrays of sub-wavelength apertures. Fundamental limitations for this phenomenon are formulated as a sum rule, relating the transmission coefficient over a bandwidth to the static polarizability. The sum rule is rigorously derived for arbitrary periodic apertures in thin screens. By this sum rule we establish a physical bound on the bandwidth of EoT which is verified numerically for a number of aperture array designs. We utilize the sum rule to design and optimize sub-wavelength frequency selective surfaces with a bandwidth close to the physically attainable. Finally, we verify the sum rule and simulations by measurements of an array of horseshoe-shaped slots milled in aluminum foil.
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- Lundgren, Johan, et al.
(author)
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Design and Optimization of Dual Band Circular Polarization Selective Structures
- 2017
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Reports (other academic/artistic)abstract
- We present a non-resonant, dual band circular polarization selective structure (CPSS) for satellite communication applications in the K- and Ka-band. The structure consists of multiple layers of cascaded anisotropic sheets, with printed meander lines, separated by low permittivity spacers. It reflects right hand circular polarization and transmits left hand circular polarization in the lower frequency band. In the upper frequency band the opposite polarization selectivity is achieved. The theory of dual band circular polarization selectivity from cascaded anisotropic sheets is presented, and it is concluded that the separation between the frequency bands of operation is governed by the relative rotation between subsequent layers. An optimization routine for synthesizing dual band CPSSs from predefined design requirements is introduced, where a number of different optimization algorithms are utilized. A simulated design is presented which fulfills the strict design requirements of insertion loss and return loss less than 0.5dB, and axial ratio less than 0.78dB, in the frequency bands 17.7–20.2GHz and 27.5–30.0GHz. A prototype of the optimized design has been fabricated and characterized experimentally, both in transmissionandreflection,andgoodagreementisobservedbetweensimulated and experimental results. This type of structure is a potential candidate for implementation in dual band multiple spot beam systems utilizing frequency and polarization reuse schemes.
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- Lundgren, Johan, et al.
(author)
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Near-Field Measurement and Calibration Technique for RF EMF Exposure Assessment of mm-wave 5G Devices
- 2019
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Reports (other academic/artistic)abstract
- Accurate and efficient measurement techniques are needed for exposure assessment of 5G portable devices---which are expected to utilize frequencies beyond 6 GHz---with respect to the radio frequency electromagnetic field exposure limits. Above 6 GHz, these limits are expressed in terms of the incident power density, thus requiring that the electromagnetic fields need to be evaluated with high precision in close vicinity to the device under test (DUT), i.e., in the near-field region of the radiating antenna. This work presents a cutting-edge near-field measurement technique suited for these needs. The technique---based on source reconstruction on a predefined surface representing the radiating aperture of the antenna---requires two sets of measurements; one of the DUT, and one of a small aperture. This second measurement functions as a calibration of both the measurement probe impact on the received signal, and the experimental setup in terms of the relative distance between the probe and the DUT. Results are presented for a 28 GHz and a 60 GHz antenna array; both developed for 5G applications. The computed power density agrees well with simulations at evaluation planes residing as close as one fifth of a wavelength away from the DUT.
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