Communications: radio wave antennas – Antennas – Plural separate diverse type
Reexamination Certificate
2000-07-12
2002-08-20
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Plural separate diverse type
C343S793000
Reexamination Certificate
active
06437750
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, the present invention relates to techniques for determining electrical size, as well as the physical design/structure and other characteristics, of electromagnetic (EM) radiation sources (or simply referred to as, antennas) that operate in a frequency range up to about 5 GHz. The novel technique and associated “electrically small” radiator structures described herein allow radiation/waves to be ‘launched’ as a generally directed beam and radiate away from the radiator source rather than remaining in proximity to the structure (as “standing energy”) when operating. More particularly, the instant invention relates to electrically small, wideband radiator structures for radiating EM waves as well as a novel method of producing EM waves and associated novel techniques for producing novel electrically-small radiator/antenna designs, such that the source-associated standing energy, i.e. the energy that returns from the radiated field to the structure to affect operation, is minimal. According to the novel design technique of the invention, optimally the source-associated standing energy for a fully-optimized ‘perfect’ radiator structure of the invention (i.e., one that behaves identically as predicted by mathematical theory), would be zero. To produce designs having minimal source-associated standing energy, the technique of the invention incorporates the identification of a solution to generally satisfy a unique expression derived by the applicants hereof. This unique expression utilizes the time-dependent Poynting theorem (rather than the conventionally-used complex Poynting theorem, the frequency-domain solutions for which are missing important antenna phase information) and takes into account three numbers/expressions in specifying time-varying power of a radiating antenna structure rather than just two numbers/expressions, as has conventionally been done to create solutions using the complex Poynting theorem.
The application of the novel techniques of the invention leads to the design of novel radiator structures, each structure preferably having at least four dipole moments arranged as dipole pairs with an overall electrical size, k*a, with a value less than &pgr;/2. Each dipole pair is configured to have at least a magnetic dipole element, and preferably also an electric dipole moment, the dipole pairs oriented in such a way that: the divergence of the Poynting vector of the system of two pairs of dipole moments with respect to ‘retarded time’ is a small, or negligible value (and, in an optimal case, this divergence value is zero). Although considered electrically small, surprisingly these novel structures readily emit waves with longer wavelengths (such as are encountered in wireless communications, radar detection, microwave technology devices, and medical device technology) at lower frequencies (throughout the electromagnetic wave Radio Spectrum and below, generally targeting frequencies<5 GHz) as non-reciprocal, wideband devices.
The low frequency radiator structure designs of the invention, unlike any currently in use, can be sized with a relative electrical length smaller than ka≈&pgr;/2, where the physical dimension “a” used throughout is that identified by Chu (1948), and indeed sized as small as ka≈&pgr;/2000 (i.e., up to 1000 times smaller than any currently in operation); and such a structure may readily be configured up to 10,000 times smaller than any conventional antenna, or where ka≈&pgr;/20,000. For further background reference, see Chu, L. J. Physical limitations of omni-directional antennas,
J. Appl. Phys.,
19, 1163-1175, 1948, for an analysis of one-dimensional multipolar sources of only electric dipoles (TM) fields. In his research, Chu (1948) provided a physical interpretation of dimension a by constructing the smallest possible circumscribing sphere having a radius “a” that fully contained the radiating source to then calculate the integral of the complex Poynting vector over that surface. Traditional and current antenna design practices lead designers to build extremely long structures to emit electromagnetic waves at selected frequencies, for example, the dimension a of an electric dipole antenna that operates at a frequency of 1 MHz would be on the order of 150 meters, and a 1.0 GHz dipole antenna for wireless communications would be approximately 15 cm in length. Whereas, using the novel technique of the invention allows one to produce EM waves using novel radiator structures sized on the order of 0.150 m (at 1 MHz) and 0.015 cm (at 1 GHz) long, respectively.
The historical difficulty in directing scientific research toward the exploration of building low Q, electrically small antennae stems from the conventional use of frequency domain mathematics to describe operational performance. According to accepted definitions, reactive power in electrical circuits is in time quadrature with the real power and its magnitude is 2&ohgr; times the energy that oscillates twice each field cycle between the source and the circuit, where &ohgr; is the radian frequency of the field. It is widely believed that this statement applies to power in radiation fields, differing only in that energy oscillation is between the source and the fields. It is commonly accepted that, for a closed volume in space, the real part of the surface integral of the complex Poynting theorem is equal to the time-average output power and the imaginary part is proportional to the difference between the time-average values of electric and magnetic energy within the volume. By way of review: The Poynting vector was defined long ago in the late-1800's in connection with the flow of electromagnetic power through a closed surface as
≡E×H VA/m
2
, or W/m
2
; J. H. Poynting, “On the transfer of energy in the electromagnetic field,”
Phil. Trans. Royal Society,
175, 343, 1884. For further general background information and explanatory figures on the theorem of Poynting, particularly the simplification of the complex Poynting for the time-average Poynting theorem, see the reference C. T. A. Johnk,
Engineering Electromagnetic Fields and Waves,
John Wiley & Sons, Inc., New York, pp. 385-402 (chapter 7), 1988.
In their pursuit to more-closely study power in radiation fields in earlier work (see Grimes, D. M., and C. A. Grimes, “Power in modal radiation fields: Limitations of the complex Poynting theorem and the potential for electrically small antennas,”
Journal of Electromagnetic Waves Applications,
vol. 11, pp. 1721-1747, 1997), two of the applicants hereof rigorously analyzed power in sinusoidal steady state radiation fields and identified that for certain antenna designs the conventional practice to define reactive power as the imaginary part of the surface integral of the complex Poynting vector (which allows for a more straight-forward calculation thereof) causes a loss of very important information about the radiation source's properties. The authors, Grimes and Grimes (1997) instead found that in order to find solutions that correspond better with what is actually happening in the fields around an antenna, use of the time-dependent Poynting theorem (TDPT) characterizes power in a sinusoidal field with three important values. In an effort to simplify notation within their mathematical expressions, Grimes and Grimes (1997) introduced the variable t
r
=t−&sgr;/&ohgr; (which they refer to simply as “retarded time” where: &ohgr;=radian frequency, &sgr;=kr, k=wave vector, and r=radial distance from source).
In their 1997 publication, applicants Grimes and Grimes point out a fatal flaw in the premises (particularly, the concept applied regarding power in a radiation field) on which commonly accepted proofs concerning the behavior of the radiative Q of a radiation source (antenna) have been conventionally based. More particularly, these commonly accepted proofs lead to the conclusion that, in the limit as the product k*a goes to zero, the radiative Q of a radiation source (e.g., an a
Grimes Craig A.
Grimes Dale M.
Lui Gang
Tefiku Faton
Dinh Trinh Vo
Le Hoang-anh
Macheledt Bates LLP
University of Kentucky Research Foundation
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