11,073 research outputs found
Structural Antennas for 3cm Radar Onboard Multi-Rotor UAV
A series of 3cm amateur band radar antennas suitable for installation on a cinematic grade multi-rotor UAV were considered. A wideband open waveguide mouth antenna was developed that can be made from the existing arms of a multi-rotor UAV without any increase in weight for side-looking wall detection ranging radar. For downward looking radio altimeter, cutting slots in the arms to form slotted waveguide antennas was shown in simulation to be possible both in terms of covering the entire 3cm band from 10 to 10.5GHz and without overly weakening the arms as structural members
Wideband and UWB antennas for wireless applications. A comprehensive review
A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems
Using a Conformal Water Bolus to Adjust Heating Patterns of Microwave Waveguide Applicators
Background: Hyperthermia, i.e., raising tissue temperature to 40-45°C for 60 min, has been demonstrated to increase the effectiveness of radiation and chemotherapy for cancer. Although multi-element conformal heat applicators are under development to provide more adjustable heating of contoured anatomy, to date the most often used applicator to heat superficial disease is the simple microwave waveguide. With only a single power input, the operator must be resourceful to adjust heat treatment to accommodate variable size and shape tumors spreading across contoured anatomy. Methods: We used multiphysics simulation software that couples electromagnetic, thermal and fluid dynamics physics to simulate heating patterns in superficial tumors from commercially available microwave waveguide applicators. Temperature distributions were calculated inside homogenous muscle and layered skin-fat-muscle-tumor-bone tissue loads for a typical range of applicator coupling configurations and size of waterbolus. Variable thickness waterbolus was simulated as necessary to accommodate contoured anatomy. Physical models of several treatment configurations were constructed for comparison of simulation results with experimental specific absorption rate (SAR) measurements in homogenous muscle phantom. Results: Accuracy of the simulation model was confirmed with experimental SAR measurements of three unique applicator setups. Simulations demonstrated the ability to generate a wide range of power deposition patterns with commercially available waveguide antennas by controllably varying size and thickness of the waterbolus layer. Conclusion: Heating characteristics of 915 MHz waveguide antennas can be varied over a wide range by controlled adjustment of microwave power, coupling configuration, and waterbolus lateral size and thickness. The uniformity of thermal dose delivered to superficial tumors can be improved by cyclic switching of waterbolus thickness during treatment to proactively shift heat peaks and nulls around under the aperture, thereby reducing patient pain while increasing minimum thermal dose by end of treatment. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE)
Nanoantennas for visible and infrared radiation
Nanoantennas for visible and infrared radiation can strongly enhance the
interaction of light with nanoscale matter by their ability to efficiently link
propagating and spatially localized optical fields. This ability unlocks an
enormous potential for applications ranging from nanoscale optical microscopy
and spectroscopy over solar energy conversion, integrated optical
nanocircuitry, opto-electronics and density-ofstates engineering to
ultra-sensing as well as enhancement of optical nonlinearities. Here we review
the current understanding of optical antennas based on the background of both
well-developed radiowave antenna engineering and the emerging field of
plasmonics. In particular, we address the plasmonic behavior that emerges due
to the very high optical frequencies involved and the limitations in the choice
of antenna materials and geometrical parameters imposed by nanofabrication.
Finally, we give a brief account of the current status of the field and the
major established and emerging lines of investigation in this vivid area of
research.Comment: Review article with 76 pages, 21 figure
Reflector antennas with low sidelobes, low cross polarization, and high aperture efficiency
Techniques are presented for computing the horn near field patterns on the subreflectors and for correcting the phase center errors of the horn pattern by shaping the subreflector surface. The diffraction pattern computations for scanned beams are described. The effects of dish aperture diffraction on pattern bandwidth are investigated. A model antenna consisting of a reflector, shaped subreflector, and corrugated feed horn is described
SARAS 2: A Spectral Radiometer for probing Cosmic Dawn and the Epoch of Reionization through detection of the global 21 cm signal
The global 21 cm signal from Cosmic Dawn (CD) and the Epoch of Reionization
(EoR), at redshifts , probes the nature of first sources of
radiation as well as physics of the Inter-Galactic Medium (IGM). Given that the
signal is predicted to be extremely weak, of wide fractional bandwidth, and
lies in a frequency range that is dominated by Galactic and Extragalactic
foregrounds as well as Radio Frequency Interference, detection of the signal is
a daunting task. Critical to the experiment is the manner in which the sky
signal is represented through the instrument. It is of utmost importance to
design a system whose spectral bandpass and additive spurious can be well
calibrated and any calibration residual does not mimic the signal. SARAS is an
ongoing experiment that aims to detect the global 21 cm signal. Here we present
the design philosophy of the SARAS 2 system and discuss its performance and
limitations based on laboratory and field measurements. Laboratory tests with
the antenna replaced with a variety of terminations, including a network model
for the antenna impedance, show that the gain calibration and modeling of
internal additives leave no residuals with Fourier amplitudes exceeding 2~mK,
or residual Gaussians of 25 MHz width with amplitudes exceeding 2~mK. Thus,
even accounting for reflection and radiation efficiency losses in the antenna,
the SARAS~2 system is capable of detection of complex 21-cm profiles at the
level predicted by currently favoured models for thermal baryon evolution.Comment: 44 pages, 17 figures; comments and suggestions are welcom
Compact, Efficient, and Wideband Near-Field Resonant Parasitic Filtennas
As a hybrid component in RF front-end systems, filtennas possess the distinctive advantages of simultaneously combining filtering and radiating performance characteristics. Consequently, filtennas not only save space and costs but also reduce transmission losses. In this chapter, three sorts of filtennas have been proposed: the first sort is band-pass/band-stop filtennas, which are mainly realized by assembling band-pass/band-stop filters and antennas to achieve the combined functions; the second sort is multi-resonator-cascaded filtennas, which are obtained by altering the coupled-resonators in the last stage of the filters to act as the radiating elements; and the third sort is near-field resonant parasitic, bandwidth-enhanced filtennas, which are accomplished through organically combining radiator and filtering structures. For the second and third sorts, it is worth noting that the design methods witness significant electrical size reduction without degrading the radiation performance of the filtennas in general
The Optical Design and Characterization of the Microwave Anisotropy Probe
The primary goal of the MAP satellite, now in orbit, is to make high fidelity
polarization sensitive maps of the full sky in five frequency bands between 20
and 100 GHz. From these maps we will characterize the properties of the cosmic
microwave background (CMB) anisotropy and Galactic and extragalactic emission
on angular scales ranging from the effective beam size, <0.23 degree, to the
full sky. MAP is a differential microwave radiometer. Two back-to-back shaped
offset Gregorian telescopes feed two mirror symmetric arrays of ten corrugated
feeds. We describe the prelaunch design and characterization of the optical
system, compare the optical models to the measurements, and consider multiple
possible sources of systematic error.Comment: ApJ in press; 22 pages with 11 low resolution figures; paper is
available with higher quality figures at
http://map.gsfc.nasa.gov/m_mm/tp_links.htm
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