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Journal ArticleDOI

Fundamental Limitations of Small Antennas

01 Dec 1947-Vol. 35, Iss: 12, pp 1479-1484
TL;DR: In this paper, a simple formula for the more fundamental properties of small antennas and their behavior in a simple circuit is given for 1-Mc operation in typical circuits, which indicates a loss of about 35 db for the I.R.E. standard capacitive antenna, 43 db for a large loop occupying a volume of 1 meter square by 0.5 meter axial length, and 64 db for an antenna loop of 1/5 these dimensions.
Abstract: A capacitor or inductor operating as a small antenna is theoretically capable of intercepting a certain amount of power, independent of its size, on the assumption of tuning without circuit loss. The practical efficiency relative to this ideal is limited by the "radiation power factor" of the antenna as compared with the power factor and bandwidth of the antenna tuning. The radiation power factor of either kind of antenna is somewhat greater than (1/6π) (Ab/l2) in which Ab is the cylindrical volume occupied by the antenna, and l is the radianlength (defined as 1/2π wavelength) at the operating frequency. The efficiency is further limited by the closeness of coupling of the antenna with its tuner. Other simple formulas are given for the more fundamental properties of small antennas and their behavior in a simple circuit. Examples for 1-Mc. operation in typical circuits indicate a loss of about 35 db for the I.R.E. standard capacitive antenna, 43 db for a large loop occupying a volume of 1 meter square by 0.5 meter axial length, and 64 db for a loop of 1/5 these dimensions.
Citations
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Journal ArticleDOI
TL;DR: In this paper, an exact method for the calculation of the minimum radiation Q of a general antenna was derived, which is more straightforward than those previously published, and has implications on both the bandwidth and efficiency of antennas which fall into this category.
Abstract: An exact method, which is more straightforward than those previously published, is derived for the calculation of the minimum radiation Q of a general antenna. This expression agrees with the previously published and widely cited approximate expression in the extreme lower limit of electrical size. However, for the upper end of the range of electrical size which is considered electrically small, the exact expression given here is significantly different from the approximate expression. This result has implications on both the bandwidth and efficiency limitations of antennas which fall into this category.

978 citations

Journal ArticleDOI
TL;DR: In this article, a periodic surface texture is used to alter the electromagnetic properties of a metal ground plane by covering the surface with varactor diodes, and a tunable impedance surface is built, in which an applied bias voltage controls the resonance frequency and the reflection phase.
Abstract: By covering a metal ground plane with a periodic surface texture, we can alter its electromagnetic properties. The impedance of this metasurface can be modeled as a parallel resonant circuit, with sheet inductance L, and sheet capacitance C. The reflection phase varies with frequency from +/spl pi/ to -/spl pi/, and crosses through 0 at the LC resonance frequency, where the surface behaves as an artificial magnetic conductor. By incorporating varactor diodes into the texture, we have built a tunable impedance surface, in which an applied bias voltage controls the resonance frequency, and the reflection phase. We can program the surface to create a tunable phase gradient, which can electronically steer a reflected beam over +/- 40/spl deg/ in two dimensions, for both polarizations. We have also found that this type of resonant surface texture can provide greater bandwidth than conventional reflectarray structures. This new electronically steerable reflector offers a low-cost alternative to a conventional phased array.

702 citations


Cites background from "Fundamental Limitations of Small An..."

  • ...[25] L. Chu, “Physical limitations of Omni-directional antennas,”J. Appl....

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  • ...We recognize as the radian length in (7) [24]....

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  • ...The field distribution within a resonant textured surface affects its bandwidth in much the same way as for a small resonant antenna, as first described by Wheeler and Chu [24]–[26]....

    [...]

Journal ArticleDOI
01 Aug 1959
TL;DR: In this paper, the radiansphere is defined as the boundary between the near field and the far field of a small antenna, and the power that can be intercepted by a hypothetical isotropic antenna is that which flows through the radianphere or its cross section, the "radiancircle."
Abstract: The "radiansphere" is the boundary between the near field and the far field of a small antenna. Its radius is one radianlength (?/2?), at which distance the three terms of the field are equal in magnitude. A "small" antenna is one somewhat smaller than the radiansphere, but it has a "sphere of influence" occupying the radiansphere. The power that theoretically can be intercepted by a hypothetical isotropic antenna is that which flows through the radiansphere or its cross section, the "radiancircle." From a small electric dipole, the far field of radiation is identified as a retarded magnetic field. Between two such dipoles, the far mutual impedance is that of mutual inductance, expressed in terms of space properties and the radiansphere. A small coil wound on a perfect spherical magnetic core is conceived as an ideal small antenna. Its radiation power factor is equal to the ratio of its volume over that of the radiansphere. A fraction of this ratio is obtainable in various forms of small antennas (C or L) occupying a comparable amount of space. A radiation shield, in the form of a conducting shell the size of the radiansphere, enables separate measurement of radiation resistance and loss resistance.

593 citations

Journal ArticleDOI
TL;DR: In this paper, a metamaterial paradigm for achieving an efficient, electrically small antenna is introduced Spherical shells of homogenous, isotropic negative permittivity (ENG) material are designed to create a resonant system for several antennas: an infinitesimal electric dipole, a very short center-fed cylindrical electric dipoles, and a coaxially-fed electric monopole over an infinite ground plane.
Abstract: A metamaterial paradigm for achieving an efficient, electrically small antenna is introduced Spherical shells of homogenous, isotropic negative permittivity (ENG) material are designed to create electrically small resonant systems for several antennas: an infinitesimal electric dipole, a very short center-fed cylindrical electric dipole, and a very short coaxially-fed electric monopole over an infinite ground plane Analytical and numerical models demonstrate that a properly designed ENG shell provides a distributed inductive element resonantly matched to these highly capacitive electrically small antennas, ie, an ENG shell can be designed to produce an electrically small system with a zero input reactance and an input resistance that is matched to a specified source resistance leading to overall efficiencies approaching unity Losses and dispersion characteristics of the ENG materials are also included in the analytical models Finite element numerical models of the various antenna-ENG shell systems are developed and used to predict their input impedances These electrically small antenna-ENG shell systems with idealized dispersionless ENG material properties are shown to be very efficient and to have fractional bandwidths above the values associated with the Chu limit for the quality factor without any degradation in the radiation patterns of the antennas Introducing dispersion and losses into the analytical models, the resulting bandwidths are shown to be reduced significantly, but remain slightly above (below) the corresponding Chu-based value for an energy-based limiting (Drude) dispersion model of the permittivity of the ENG shell

519 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present some basic rules about electrically small antennas, give clues and guidelines about efficient antenna miniaturization, and, finally, show some examples of miniature antennas developed in their laboratory for practical applications.
Abstract: PCS (personal communication system) devices have become an important part of everyday life. The pressure to design small, lightweight, and user-friendly mobile-communication devices has increased accordingly, creating the need for optimal antennas for mobile applications. In this paper, we present some basic rules about electrically small antennas, give clues and guidelines about efficient antenna miniaturization, and, finally, show some examples of miniature antennas developed in our laboratory for practical applications.

459 citations

References
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Journal ArticleDOI
H.T. Friis1
01 May 1946
TL;DR: In this paper, a simple transmission formula for a radio circuit is derived, and the utility of the formula is emphasized and its limitations are discussed, as well as its utility and limitations.
Abstract: A simple transmission formula for a radio circuit is derived. The utility of the formula is emphasized and its limitations are discussed.

1,956 citations

Journal ArticleDOI
01 Oct 1928

488 citations

Journal ArticleDOI
C.R. Burrows1
01 Feb 1937
TL;DR: In this article, the results of Weyl for radio propagation over plane earth are found to differ from those of Sommerfeld by exactly Sommersfeld's surface wave, and experiments conducted under conditions for which these two theories differ greatly are entirely consistent with Weyl's results.
Abstract: The results of Weyl for radio propagation over plane earth are found to differ from those of Sommerfeld by exactly Sommerfeld's surface wave. Experiments conducted under conditions for which these two theories differ greatly are entirely consistent with Weyl's results and show that Sommerfeld's surface wave is not set up by simple antennas. Accordingly the Sommerfeld-Rolf curves are in error for all conditions for which the dielectric constant cannot be neglected.

102 citations