Near and far field

About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.

Spatial correlations in the near field of random media.

Abstract: The conventional coherence theory suggests that the fields radiated by statistically homogeneous sources correlate over spatial regions of the order of the wavelength irrespective of the distance from the surface of the source. Contrary to these predictions, we show that the spatial correlations of optical fields in close proximity of highly scattering, randomly inhomogeneous media depend on this distance and, moreover, their extent can be significantly smaller than the wavelength. The contribution of evanescent fields is experimentally demonstrated and the coherence length in the near field is shown to relate to the coherence properties at the surface which are, in turn, determined by the structural characteristics of the random media.

Upper-Bound Errors in Far-Field Antenna Parameters

Abstract: General expressions are derived for estimating the errors in the sum or difference far-field pattern of electrically large aperture antennas which measured by planar near-field scanning technique. Upper bounds are determined for the far-field errors produced by 1) the nonzero fields outside the finite scan area, 2) the inaccuracies in the positioning of the probe, 3) the distortion and non-linearities of the instrumentation which measures the amplitude and phase of the probe output, and 4) the multiple refractions. Computational errors, uncertainties in the receiving characteristics of the probe, and errors involved with measuring the input power to the test antenna are briefly discussed.

Method and apparatus for production and use of nanometer scale light beams

Abstract: An optical system for determining and reproducing spatial separation of features in the range of 80Å to 2500Å for optical microscopy and lithography using visible light, the system being independent of the wavelength of the incident light. An aperture mask is provided having at least one aperture of between about 80Å and 2500Å diameter. The mask may be used in optical microscopy to view objects with a high degree of resolution by placing the mask within the near field of light emanating from a sample to be viewed. The mask may also be used for high resolution optical lithography by placing a resist material within the near field of light passing through the mask.

The inverse source problem of electromagnetics: linear inversion formulation and minimum energy solution

Abstract: We address the inverse source problem of finding the time-harmonic current distribution (source) with minimum L/sup 2/ norm (minimum energy) that generates a prescribed electromagnetic field outside the source's region of support. Using the well-known multipole expansion of the electromagnetic field we compute (via a linear operator formalism) the sought-after minimum L/sup 2/ norm-current distribution consistent with the data.

Design and analysis of a hexa-band frequency reconfigurable antenna for wireless communication

Abstract: A compact (33 × 16 × 1.6 mm3) and novel shaped hexa-band frequency-reconfigurable antenna with a very wide tuning band is proposed. The proposed antenna operates at two single band modes (i.e., 3.5 GHz and 4.8 GHz) and two dual band modes (i.e., 2.10 GHz, 4.15 GHz and 2.4 GHz, 5.2 GHz) depending upon the switching states. The lumped elements are used in the simulation environment to achieve tunable capacitance, which is responsible for frequency reconfigurability. The measured tuning capability of the fabricated antenna ranges from 2.1 to 5.2 GHz. The proposed antenna has a VSWR 1.3 for all the resonant bands. The radiation efficiency of the proposed structure ranges from 80.41% to 96% at the corresponding frequencies. The far field and the scattering parameters of the proposed antenna are analyzed using Computer Simulation Technology (CST) Microwave Studio 2014. The designed antenna, due to its compact and affordable geometry, can be easily integrated in the modern communication devices such as smart phones, laptops and other portable electronic devices. A prototype of the designed antenna is fabricated and measured using PIN diode switches to validate the simulation results. The proposed reconfigurable antenna demonstrates a reasonable agreement between the measured and simulated results.