Irregularities and irregular motions in the upper atmosphere have been detected and studied by a variety of techniques during recent years, but their proper interpretation has yet to be established...

Internal atmospheric gravity waves at ionospheric heights

the of the magnitude, i.e., intensity, of the field.) It is shown that Rayleigh statistics govern the fist-order behavior of the magnitude; and the autocorrelation of the resulting image speckle is obtained by the methodof Middleton. The corresponding power spectrum follows immediately by Fourier transformation. Theoretical and experimentally determined autocorrelation functions and power spectra derived from B-scans of a scattering phantom containing many scatterers per resolution cell are presented. These functions lead naturally to the definition of the average speckle spot or cell sue, and this inturn is comparable to the resolution cell. Each independent speckle servesas a degreeof freedom that determines the number of samples of tissue available over a target.As the speckle cell size decreases this number increases in a manner predictable from the physical parameters of the cell size. However, it is found that the speckle cellis broadened, the degrees of freedom diminished, when the object structureis correlated. This yields the possibilityof deducing information about the object structure from the second-order statistics of the speckle texture, in addition to that obtainable from the fiistorder statistics.

Statistics of Speckle in Ultrasound B-Scans

This paper calls attention to some of the most important and easily recognizable forms of surface wave, pointing out that their essential common characteristic is the evanescent field structure over the wave front, as represented by equiphase planes. The problems of launching and supporting surface waves must, in general, be distinguished from one another and it does not necessarily follow that because a particular surface is capable of supporting a surface wave that a given aperture distribution of radiation, e.g. a vertical dipole, can excite such a wave. The paper concludes with a discussion of the behavior of surface waves and their applications.

http://ieeexplore.ieee.org/iel5/10933/4065481/04065500.pdf

Surface Waves

This paper presents a patterned ground shield inserted between an on-chip spiral inductor and silicon substrate. The patterned ground shield can be realized in standard silicon technologies without additional processing steps. The impacts of shield resistance and pattern on inductance, parasitic resistances and capacitances, and quality factor are studied extensively. Experimental results show that a polysilicon patterned ground shield achieves the most improvement. At 1-2 GHz, the addition of the shield increases the inductor quality factor up to 33% and reduces the substrate coupling between two adjacent inductors by as much as 25 dB. We also demonstrate that the quality factor of a 2-GHz LC tank can be nearly doubled with a shielded inductor.

/pdf/on-chip-spiral-inductors-with-patterned-ground-shields-for-264z6iiemk.pdf

On-chip spiral inductors with patterned ground shields for Si-based RF ICs

Whistlers and Related Ionospheric Phenomena

The theory of scattering by a turbulent medium is applied to scattering of radio waves in the troposphere. In the region below the horizon of the transmitter, energy is received (1) by diffraction round the curved surface of the earth (modified as appropriate by atmospheric refraction), and (2) by scattering from turbulence in the region of high field strength above the horizon. At distances beyond the horizon that are not too great, we may think of (1) as giving the mean signal received, and (2) as giving the fading. However, contribution (2) usually decreases with distance more slowly than contribution (1). Beyond a certain distance, therefore, contribution (2) becomes predominant and the mean signal is no longer given by (1). (See Fig. 3.) Values of the scale of turbulence and of the departure of refractive index from mean expected on meteorological grounds are fully adequate to explain the scattered field strengths observed experimentally.

A Theory of Radio Scattering in the Troposphere

A half-wave slot in a metal sheet may be used as a resonant aerial in a manner similar to a half-wave dipole. The polar diagrams are the same, but the directions of vibration of the electric and magnetic fields are interchanged. If the slot is driven by means of a transmission line connected between opposite edges at the centre, the input impedance at resonance is about 485 ohms. The relation between resonant dipoles and resonant slots is an example of what in optics is known as Babinet's principle. This principle is established in the form required for electromagnetism and quantitative relations are deduced from it. Arrays of slots may be fed by transmission lines or wave guides to form linear or broadside aerials. Resonant gratings of slots may be used to polarize incident waves or act as band-pass filters. Single resonant slots may be used in wave guides in the same way as paralleltuned circuits are shunted across transmission lines. All devices adopted in connection with wire aerials have complements for slot aerials. Slots and dipoles may be combined to produce aerials with special polarization properties. Slots (with dielectric plugs) may be used in the skin of aircraft to provide dragless aerials. In addition, Babinet's principle may be used to reduce new problems to old ones whose solution is already known. These include problems connected with discontinuities in transmission lines, wave guides with corrugated sides, magnetron cavities, and the leakage of electromagnetic radiation through holes in metal walls. There is a wide variety of problems, both practical and theoretical for which it is always wise to consider the possibility of applying Bubinet's principle.

Slot aerials and their relation to complementary wire aerials (Babinet's principle)

An analysis is made of the diffraction effects produced when a plane wave is incident upon an irregular diffracting screen, and the results are applied to the problem of the reflexion of radio waves from an ionosphere which is irregular in the horizontal plane. The nature of the irregular screen is assumed to be given in terms of the variation of electric wave-field in a plane just beyond the screen, and it is assumed that variations occur over the plane in one direction only. It is further assumed that the screen is 9random’ in the sense that it is one of an assembly all of which differ from each other, but have statistical properties in common, and deductions are made about the diffraction patterns averaged over the assembly. It is shown that many aspects of the problem can be investigated by use of the theory of ‘random’ electrical noise as developed by Rice and Uhlenbeck. The angular spectrum (Fraunhofer diffraction pattern) and the Fresnel diffraction pattern are described in terms of their spatial auto-correlation functions, and there is some discussion of a related method of dealing with Fresnel diffraction problems from completely determined screens. In part II of the paper the irregular ‘fading’ exhibited by a radio wave returned from the ionosphere is discussed in terms of two models in which the fading is assumed to be produced by movements of the diffracting centres in the ionosphere. The temporal auto-correlation function of the amplitude of the irregularly fading signal is related to the velocity of the ionospheric diffracting centres.

Diffraction from an irregular screen with applications to ionospheric problems

A theory of scattering by nonisotropic irregularities with application to radar reflections from the aurora

A critical examination is made of the somewhat loose and incomplete statement that a polar diagram is the Fourier transform of an aperture distribution. By aperture distribution it is necessary to understand, in the two-dimensional case, distribution across the aperture of the component along the aperture plane of the electromagnetic field in the plane of propagation. Furthermore, the concept of the polar diagram has to be replaced by that of an angular spectrum, except in the common case when the aperture may be considered more or less limited in width, and the field is being evaluated at a point whose distance from the aperture is large compared with the width of the aperture (and the wavelength). For example, it is convenient for some purposes to regard the problem of diffraction of a plane wave by a semi-infinite plane screen, with a straight edge, as a problem about an aperture distribution in the plane of the screen. This is a case for which the concept of a polar diagram is not in general applicable, and has to be replaced by that of an angular spectrum. The field at all points in front of a plane aperture of any distribution may be regarded as arising from an aggregate of plane waves travelling in various directions. The amplitude and phase of the waves, as a function of their direction of travel, constitutes an angular spectrum, and this angular spectrum, appropriately expressed, is, without approximation, the Fourier transform of the aperture distribution. If the aperture distribution is of such a nature that the concept of the polar diagram is applicable at sufficiently great distances, then the polar diagram is equal to the angular spectrum. But the angular spectrum is a concept that is always applicable, whereas the polar diagram is one that is liable to be invalid (for example, in the Sommerfeld theory of propagation over a plane, imperfectly reflecting earth).

Henry G. Booker

Papers

A Theory of Radio Scattering in the Troposphere

Slot aerials and their relation to complementary wire aerials (Babinet's principle)

Diffraction from an irregular screen with applications to ionospheric problems

A theory of scattering by nonisotropic irregularities with application to radar reflections from the aurora

The concept of an angular spectrum of plane waves and its relation to that of polar diagram and aperture distribution