H. D. Hristov

Measurement and modeling of propagation losses in brick and concrete walls for the 900-MHz band

The prediction of wall losses is a fundamental aspect in the planning of cellular systems. The broad variety of building materials and construction codes makes accurate attenuation prediction very difficult without the support of specific construction data or measurements. In this paper, the attenuation and equivalent electric parameters /spl epsiv/ and /spl sigma/ of brick and doubly reinforced concrete walls are estimated for the 900-MHz band by fitting simple ray tracing models to empirical transmission data. The measurement setup is described, and extensive experimental results justifying the quasioptical modeling are presented.

Focusing characteristics of curvilinear half-open Fresnel zone plate lenses: plane wave illumination

A diffraction field-focusing equation based on a specific conical-segment linearization procedure is derived for the Fresnel zone plate (FZP) lens of arbitrary curved profile and is applied for contrasting plane, spherical, parabolic and conical zone plate lenses, convex-side illuminated by a paraxial plane wave front. Two sets of 100-GHz curvilinear and plane FZP lenses are studied numerically with regards to their dimensions, axial focusing intensity and footprint, and frequency bandwidth. For the first set , where the curvilinear and plane lenses share a common lens base aperture and have equal focal lengths, the following new finding has resulted: regardless of their different in shape profiles the FZP lenses have equal zone numbers and produce similar axial focusing. The second set also consists of plane, spherical, parabolic and conical lenses. They share a common apex, and have equal in diameter base apertures and focal lengths but different thicknesses. For such disposition and proportions, the FZP lenses possess different zone numbers and focusing parameters (gain, efficiency, footprint and bandwidth). The belief that the curvilinear FZP have superior (or inferior) electromagnetic characteristics, compared to those of the plane FZP lens with equal number of zones is not in general true. Their relative focusing qualities can vary significantly depending on the lens positioning and dimensions.

Design Equation for Multidielectric Fresnel Zone Plate Lens

A structural design equation for multidielectric Fresnel zone plate (ZP) lens is outlined in this letter. Based on this equation, multidielectric ZP lenses/lens antennas are studied numerically in the 30-50 GHz microwave band and contrasted to an ordinary plano-convex lens/lens antenna. Usually, the ZP lens is made half-wavelength thick but we discovered that a similar wavelength thick lens can be built with lower-permittivity dielectrics, and that this lens can focus more efficiently. In a confined frequency band, the thin and light-weight multidielectric ZP lens of four or more dielectric rings per full-wavelength zone is comparable in focusing to the ordinary bulky lens.

Improving indoor signal coverage by use of through-wall passive repeaters

Improving indoor coverage of wireless networks is an important issue for service providers and users alike. Standard procedures include the deployment of active in-building repeaters and the careful selection of transmission power levels for base stations. Various manufacturers also offer passive repeaters for enhancement of cellular signals in automobiles. In this paper we study the improvement in coverage attainable by use of low-cost through-wall passive repeaters. The analysis considers various situations of signal propagation.

Compound Diffractive Lens Consisting of Fresnel Zone Plate and Frequency Selective Screen

We describe a new Fresnel zone plate (FZP) and frequency selective screen (FSS) compound lens consisting of a binary FZP and FSS. The FZP has eight circular zones totally, four open and four closed, and the FSS is a square array of 40 × 40 four-leg loaded elements cut in a thin metal sheet. The FZP-FSS lens is designed for a paraxial plane-wave illumination at the frequency of 12 GHz, with a focal length of 15 cm. The compound lens is simulated and analyzed numerically by means of a specially developed hybrid PSTD-FDTD algorithm and software. The PSTD-FDTD results are contrasted with those obtained by lens prototype measurements. As a result, some attractive focusing and spectral properties of the FZP-FSS lens compared to the same-size FZP lens have been found: a frequency filtering property enhancement, about 2 dB increase in the peak focusing intensity, and more than 4 dB reduction of the first off-axis maximum. Both lenses have roughly the same transverse angular resolution.

Millimeter-Wave Conical Fresnel Zone Lens of Flat Dielectric Rings

Conical in shape Fresnel zone (CFZ) lens of flat dielectric rings is introduced and studied in this research. It is contrasted to a plane Fresnel zone (PFZ) lens, a CFZ lens of conical rings and a refractive plane-hyperbolic (PH) lens. For the same aperture diameter of about 25 mm and focal length of 30 mm, a 229-GHz CFZ lens of flat rings with a 30-degree opening semi-angle significantly surpasses the PFZ and PH lenses in focusing gain and efficiency. Also, it exhibits a subwavelength transverse resolution and much higher axial resolution. The cited 30-degree flat-ring CFZ lens has 4.5 times smaller weight than the PH lens, and is easy to manufacture as a plane multilayer package by means of precise machining or modern photolithographic and other microelectronic technologies. Nevertheless, the CFZ lens benefits over the corresponding PH refractive lens are attained on account of smaller frequency bandwidth and bigger lens thickness. The new flat-ring CFZ lens design can be applied in accurate imaging systems or for a creation of light and efficient microwave, terahertz and optical lens antennas.

Indoor signal focusing by means of Fresnel zone plate lens attached to building wall

A simple inexpensive on-wall Fresnel zone plate (FZP) lens for indoor focusing of microwave signals is studied. It consists of concentric metal rings mounted on the outside of an exterior building wall. In our theoretical and empirical work the on-wall FZP lens is illuminated normally by a plane or spherical wave, of vertical or horizontal polarization, but other, more general incidence situations can be treated by similar means. The scalar quasi-optical focusing theory of the free-space zone plate has been modified and used for design and analysis of one-, two-, and three-ring on-wall FZP lenses. It is found that the presence of the wall does not change the FZP lens focusing efficiency significantly, but it has a strong axial defocusing effect. A 2-GHz FZP lens assembly consisting of three metal rings made out of thin antimosquito mesh has a focusing efficiency of about 15 dB (measured) and 14 dB (calculated), and axial defocusing of about 0.22 m. Some variations of on-wall/on-roof FZP lenses and their feasible applications in the microwave/millimeter-wave communication links are also discussed.

Conical Double-Dielectric Fresnel Zone Lens and Antenna

A conical double-dielectric phase-reversal Fresnel-zone plate (FZP) lens is introduced. We present the lens design equations as functions of cone opening angle. As an example, the phase-reversal lens has been applied to four millimeter-wave antennas with different lens opening semi-angles: 45deg, 60deg, and 75deg (conical lenses) and 90deg (plane lens). The radiation characteristics of these antennas have been calculated and contrasted one-to-another, and to those with the same semi-angles and linear dimensions binary (half-open) FZP lens antennas. The double-dielectric FZP conical arrangement can serve as a conical antenna lens and a radome simultaneously

Cone-shape Fresnel zone lens of flat dielectric rings

Cone-shape Fresnel zone (FZ) lens of flat metal or dielectric rings is introduced. It is found that such a 229-GHz lens of three dielectric rings, focal length of 30mm, aperture diameter of 25mm and cone half-opening angle of 450 surpasses in focusing gain and space resolution the same in diameter and focal length plane-hyperbolic refraction lens. The new cone lens is by 2.2dB superior in gain and 45% in efficiency to the corresponding plane phase-reversal FZ lens. The lens can be easy manufactured at microwave and terahertz frequencies as a multilayer assembly of dielectric rings embedded in air or low-permittivity solid dielectric. It can be applied in microwave and terahertz focusing and imaging systems, and for a construction of light and effective FZ lens antennas.

Some experiences with resonant cavity antennas-oscillators

The authors describe some designs of X-band one- and two-cavity antenna-oscillators with semitransparent radiation apertures. The antennas are excited by Gunn-diode sources plus half-loop feeds. The power and radiation characteristics of one-, two-, and three-diode antenna-oscillators are described and compared. The experiments show that by using the field combining phenomenon in a single resonant cavity, a very high power efficiency is achieved.<<ETX>>