Communications: radio wave antennas – Antennas – Measuring signal energy
Reexamination Certificate
2002-01-30
2003-12-02
Nguyen, Hoang (Department: 2821)
Communications: radio wave antennas
Antennas
Measuring signal energy
C343S753000, C343S755000
Reexamination Certificate
active
06657596
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to wireless communications, and more particularly to a method and system for measuring an electromagnetic radiation pattern of an antenna.
II. Description of the Related Art
With the proliferation of wireless communications, the coverage area of antennas has become an increasing area of interest. For example, knowledge of the coverage area of an antenna aides in the field installation of a wireless base station by providing valuable information regarding dead-spots as well as high gain regions of the system. The coverage area of an antenna is more commonly referred to as the far-field electromagnetic radiation pattern or Fraunhofer pattern. A Fraunhofer pattern may be defined as the three-dimensional volumetric pattern surrounding an antenna from which electromagnetic radiation appears at a distance to be coming from a single point.
The Fraunhofer pattern of an antenna may be determined by various techniques. To accurately determine an antenna's Fraunhofer pattern, the measurements should be made at a sufficiently large distance away from the antenna to insure the relevant field of the antenna approximates a uniform plane wave. A relatively arbitrary boundary may be established between the aperture field distribution (e.g., the near-field or Fresnel) of the antenna and the far-field using the following mathematical expression:
R
=2*(
D
2
/&lgr;)
where R is the radius of the electromagnetic radiation pattern, D is the aperture or diameter of the antenna, and &lgr; is the wavelength of the electromagnetic radiation. For more information, see J. D. Kraus,
Antennas,
2
nd
ed., McGraw-Hill, 1988, p. 60. It has been established that a tolerable phase difference between the actual, spherical wave front and the ideal plane wave may be, for example, about 22.5°, corresponding with the relatively arbitrary boundary. Referring to
FIG. 1
, the far-field and the near field patterns, as well as relatively arbitrary boundary are illustrated. From the above, it may be deduced that if the radius, R, is relatively large, direct measurement of the antenna's far-field pattern may be impractical. In such circumstances, the far-field pattern may be indirectly determined by measuring the aperture field distribution (e.g., the near-field) of the antenna. Upon determining the aperture field distribution, the far-field pattern may be mathematically deduced by performing a Fourier transform on the determined distribution.
It should be apparent that direct measurement of an antenna to determine the Fraunhofer pattern involves recording measurements in a number of directions. Given its volumetric properties, the accuracy of a Fraunhofer pattern directly corresponds with the number of measurements recorded over the total solid angle of a sphere—e.g., 4&pgr; steradians. Consequently, an accurate Fraunhofer antenna pattern requires numerous measurements, which is tedious, time consuming, labor intensive, and thusly, expensive.
Alternatively, theoretical analysis may be performed to determine the Fraunhofer pattern of an antenna. Theoretical analysis of a three-dimensional electromagnetic pattern commonly involves applying a model or models of an actual antenna implementation. Here, a model employs a series of numerical solutions based on a number of idealizations and/or assumptions. This approach effectively produces the antenna's Fraunhofer pattern by computational electromagnetics.
In the field of operation—when implementing cellular, PCS, or fixed wireless systems, for example—various additional factors are needed to determine the actual antenna pattern. These factors include the topography of the terrain, atmospheric conditions, as well as man-made structures, for example. Presently, a number of commercially available software packages may be used to the model an antenna's Fraunhofer pattern. While useful, these commercially available software packages may not be sufficiently accurate for certain applications. Though the aforementioned additional factors may be taken into consideration to some degree, these software packages do not rely on actual measurements, but rather model and predict the antenna pattern. For certain applications, the coverage predicted by these software packages may have to be verified—thereby requiring numerous measurements much like experimental examination.
Consequently, a need exists for a method for measuring the pattern of electromagnetic radiation that is more accurate, simpler, faster, less labor intensive, and relatively less expensive than the methods presently known.
SUMMARY OF THE INVENTION
The present invention provides a more accurate, simpler, faster, less labor intensive, and relatively less expensive method for measuring pattern of electromagnetic radiation from an antenna than the methods presently known. The method relies on the principle of scattering to ascertain the far-field measurements needed to determine the pattern of electromagnetic radiation. The antenna first transmits a signal from which a number of scattered electromagnetic radiation samples are sensed. Each scattered sample comprises two-dimensional information corresponding with the power detected at a specific coordinate. Depending on the required accuracy of the antenna pattern, a greater number of samples are accumulated. Once a sufficient number of samples are sensed, a three-dimensional antenna pattern or beamshape may be developed.
The sensing of the present method may be realized using various means. In one embodiment, the sensing is performed by at least one detecting antenna. Here, the one or more detecting antennas scan the scattering region to develop the requisite number of samples. In another embodiment, a number of detecting antennas each sense at least one scattered electromagnetic radiation sample.
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Lucent Technologies - Inc.
Nguyen Hoang
Teitelbaum Ozer M. N.
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