Non-Foster Impedance Matching of Electrically-Small Antennas
TL;DR: In this paper, the authors present the non-Foster impedance matching, which employs active networks of negative inductors and capacitors to bypass the restrictions of gain-bandwidth theory.
Abstract: Electrically-small antennas present high-Q impedances characterized by large reactances and small radiation resistances. For such antennas, the effectiveness of passive matching is severely limited by gain-bandwidth theory, which predicts narrow bandwidths and/or poor gain. With receivers, the inability to resolve this impedance mismatch results in poor signal-to-noise (S/N) ratio, as compared to using a full-size antenna. With transmitters, the consequence is poor power efficiency. However, in many applications full-size antennas are impractical, and a means is required to effectively match their electrically-small counterparts. This paper presents the technique of non-Foster impedance matching, which employs active networks of negative inductors and capacitors to bypass the restrictions of gain-bandwidth theory. We first review the origins and development of non-Foster impedance matching, and then present experimental results for the non-Foster impedance matching of electrically-small dipoles and monopoles. For receivers, our best measurements on the antenna range demonstrate up to 20 dB improvement in S/N over 20-120 MHz; for transmitters, we show a power efficiency improvement which exceeds a factor of two over an 5% bandwidth about 20 MHz with an average signal power of 1 W to the radiation resistance.
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TL;DR: A survey of the development of reconfigurable and tunable metamaterial technology as well as of the applications where such capabilities are valuable is presented.
Abstract: Metamaterials are being applied to the development and construction of many new devices throughout the electromagnetic spectrum. Limitations posed by the metamaterial operational bandwidth and losses can be effectively mitigated through the incorporation of tunable elements into the metamaterial devices. There are a wide range of approaches that have been advanced in the literature for adding reconfiguration to metamaterial devices all the way from the RF through the optical regimes, but some techniques are useful only for certain wavelength bands. A range of tuning techniques span from active circuit elements introduced into the resonant conductive metamaterial geometries to constituent materials that change electromagnetic properties under specific environmental stimuli. This paper presents a survey of the development of reconfigurable and tunable metamaterial technology as well as of the applications where such capabilities are valuable.
193 citations
11 Jul 2010
TL;DR: In this paper, the authors proposed impedance matching networks (MNs) to maximize the transfer of power from a resistive source to the highly reactive antenna to reduce the radiation quality factor of small antennas.
Abstract: When the size of an antenna is electrically small, the antenna is neither efficient nor a good radiator because most of the input power is stored in the reactive near-field region and little power is radiated in the far-field region. As demonstrated in [1]- [2], the radiation quality factor of small antennas is definitely high. In other words, the input impedance of small antennas is considerably reactive. To reduce the radiation quality factor in the whole or partial frequency range of interest, it is important to increase the radiation resistance and/or reduce the reactance of the antenna. Hence, it is necessary to modify the antenna to reduce the reactance of the antenna and/or add impedance matching networks (MNs) to maximize the transfer of power from a resistive source to the highly reactive antenna.
145 citations
Cites background from "Non-Foster Impedance Matching of El..."
...Most Non-Foster impedance matching for electrically small antennas have been implemented with a series or a shunt negative capacitor [5]- [ 7 ]....
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TL;DR: The standard quantum limit for data capacity is introduced, and the quantum sensor based on thermal Rydberg atoms is used to receive data encoded in electromagnetic fields in the extreme electrically small regime.
Abstract: We use a quantum sensor based on thermal Rydberg atoms to receive data encoded in electromagnetic fields in the extreme electrically small regime, with a sensing volume over $1{0}^{7}$ times smaller than the cube of the electric field wavelength. We introduce the standard quantum limit for data capacity, and experimentally observe quantum-limited data reception for bandwidths from 10 kHz up to 30 MHz. In doing this, we provide a useful alternative to classical communication antennas, which become increasingly ineffective when the size of the antenna is significantly smaller than the wavelength of the electromagnetic field.
114 citations
TL;DR: In this paper, an experimental demonstration of the overcoming of basic dispersion energy constraints in metamaterials with the help of active non-Foster negative capacitors is reported.
Abstract: Experimental demonstration of the overcoming of basic dispersion-energy constraints in metamaterials with the help of active non-Foster negative capacitors is reported. The experimental metamaterial operates in RF regime, and it is based on air transmission line loaded with negative capacitors. Measurement results clearly show almost dispersionless Epsilon-Near-Zero behavior, accompanied with superluminal both phase and group velocities, over a bandwidth of more than four octaves (2 MHz-40 MHz). The principle of periodic loading of transmission line with negative capacitors may find applications in ultra-broadband active metamaterials for antennas and cloaking technology.
112 citations
TL;DR: In this paper, the authors review recent theoretical and experimental activities on optical Yagi-Uda nanoantennas, including their design, fabrication, and applications, and discuss several extensions of the conventional YagiUda antenna design for broadband and tunable operation for applications in nanophotonic circuits and photovoltaic devices.
Abstract: Conventional antennas, which are widely employed to transmit radio and TV signals, can be used at optical frequencies as long as they are shrunk to nanometer-size dimensions. Optical nanoantennas made of metallic or high-permittivity dielectric nanoparticles allow for enhancing and manipulating light on the scale much smaller than wavelength of light. Based on this ability, optical nanoantennas offer unique opportunities regarding key applications such as optical communications, photovoltaics, nonclassical light emission, and sensing. From a multitude of suggested nanoantenna concepts the Yagi-Uda nanoantenna, an optical analogue of the well-established radio-frequency Yagi-Uda antenna, stands out by its effi cient unidirectional light emission and enhancement. Following a brief introduction to the emerging fi eld of optical nanoantennas, here we review recent theoretical and experimental activities on optical Yagi-Uda nanoantennas, including their design, fabrication, and applications. We also discuss several extensions of the conventional Yagi-Uda antenna design for broadband and tunable operation, for applications in nanophotonic circuits and photovoltaic devices.
111 citations
References
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Book•
01 Jan 1945
2,469 citations
"Non-Foster Impedance Matching of El..." refers methods in this paper
...With a high-Q antenna impedance, such matching is difficult to perform because of the realizability constraints imposed by the gain-bandwidth theory of Bode, Fano, and Youla [9]–[11]....
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TL;DR: In this paper, the physical limitations of omni-directional antennas are considered and the potentiality of a broad band width of an antenna with the maximum dimension of 2a has been shown.
Abstract: The physical limitations of omni‐directional antennas are considered. With the use of the spherical wave functions to describe the field, the directivity gain G and the Q of an unspecified antenna are calculated under idealized conditions. To obtain the optimum performance, three criteria are used, (1) maximum gain for a given complexity of the antenna structure, (2) minimum Q, (3) maximum ratio of G/Q. It is found that an antenna of which the maximum dimension is 2a has the potentiality of a broad band width provided that the gain is equal to or less than 4a/λ. To obtain a gain higher than this value, the Q of the antenna increases at an astronomical rate. The antenna which has potentially the broadest band width of all omni‐directional antennas is one which has a radiation pattern corresponding to that of an infinitesimally small dipole.
1,954 citations
"Non-Foster Impedance Matching of El..." refers methods in this paper
...Chu [2] and Harrington [3], using spherical mode theory, defined electrical length as the radius of a circumscribing sphere....
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01 Dec 1947
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.
1,249 citations
"Non-Foster Impedance Matching of El..." refers background in this paper
...In 1947, Wheeler [1], looking at an antenna in terms...
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...Wheeler used power factor rather than its reciprocal—the quality factor or Q—because one can simply add the power factors associated with radiation, antenna loss and matching network loss to obtain an overall power factor....
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...From this, Wheeler concluded that the antenna radiation power factor decreases with the third power of electrical length....
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...Wheeler defined electrical length as the axial length of a cylinder that circumscribes the antenna....
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...In 1947, Wheeler [1], looking at an antenna in terms Manuscript received October 13, 2008; revised March 09, 2009....
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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
TL;DR: In this article, the authors considered the problem of matching an arbitrary load impedance to a pure resistance by means of a reactive network and derived necessary and sufficient conditions for the physical realizability of a function of frequency representing the input reflection coefficient of a matching network terminated in a prescribed load impedance.
Abstract: This paper deals with the general problem of matching an arbitrary load impedance to a pure resistance by means of a reactive network. It consists primarily of a systematic study of the origin and nature of the theoretical limitations on the tolerance and bandwidth of match and of their dependence on the characteristics of the given load impedance. Necessary and sufficient conditions are derived for the physical realizability of a function of frequency representing the input reflection coefficient of a matching network terminated in a prescribed load impedance. These conditions of physical realizability are then transformed into a set of integral relations involving the logarithm of the magnitude of the reflection coefficient. Such relations are particularly suitable for the study of the limitations on the bandwidth and tolerance of match. Definite expressions for these quantities are obtained in special cases. The practical problem of approaching the optimum theoretical tolerance by means of a network with a finite number of elements is also considered. Design curves are provided for a particularly simple but very important type of load impedance. In addition, a very convenient method is presented for computing the values of the elements of the resulting matching network.
852 citations