Short Electric Dipole Research Articles

Zero Thickness Surface Susceptibilities and Extended GSTCs—Part I: Spatially Dispersive Metasurfaces

A simple method to describe spatially dispersive metasurfaces is proposed where the angle-dependent surface susceptibilities are explicitly used to formulate the zero thickness sheet model of practical metasurface structures. It is shown that if the surface susceptibilities of a given metasurface are expressed as a ratio of two polynomials of tangential spatial frequencies, k|| with complex coefficients, they can be conveniently expressed as spatial derivatives of the difference and average fields around the metasurface in the space domain, leading to extended forms of the standard generalized sheet transition conditions (GSTCs) accounting for the spatial dispersion. Using two simple examples of a short electric dipole and an all-dielectric cylindrical puck unit cells, which exhibit purely tangential surface susceptibilities and reciprocal/symmetric transmission and reflection characteristics, the proposed concept is numerically confirmed in 2D. A Lorentzian representation with angle-dependent parameters is further proposed and found to accurately model the complex temporal-spatial frequency response via their electric and magnetic susceptibilities of two unit cell examples - a metallic dipole and a dielectric puck resonator. For both cases, the appropriate spatial boundary conditions are derived.

Design of an Electrically Small 3-D Antenna With Quasi-Isotropic Radiation Pattern

An electrically small three-dimensional (3-D) antenna is proposed to generate a quasi-isotropic radiation pattern. The proposed antenna consists of a single layer conductor with bilateral symmetrical structure before being wrapped in a cylindrical foam. An H-shaped inductive coupling element is used to feed the antenna to obtain a magnetic dipole and a pair of short electric dipoles after the antenna is wrapped in a cylindrical foam. Therefore, by combining orthogonal complementary dipoles with the same radiation intensity and quadrature phase difference, a quasi-isotropic radiation pattern can be obtained. As a proof of this design, a 3-D antenna structure operating at 2.45 GHz is designed, fabricated and measured. It has been shown that the gain variation of the proposed electrically small antenna (ka = 0.48) in total space is 2.72 dB in simulation and 3.53 dB in measurement.

ESPRIT-Based DOA Estimation with Spatially Spread Long Dipoles and/or Large Loops

The radiation efficiency of short electric dipole and small magnetic loop is low. Therefore, the long electric dipole and large magnetic loop for direction of arrival (DOA) estimation are investigated in this study. A novel array composed of long electric dipole, large magnetic loop, or a hybrid long electric dipole and large magnetic loop is proposed. Then a corresponding algorithm based on ESPRIT is proposed to estimate the two-dimensional (2D) DOA. The proposed array has eight elements. The first four elements and other four elements construct the rotational invariant property. Then, the 2D direction cosine can be estimated accurately but with ambiguity. After that, the ambiguous value is instituted into the spatially spread vector sensor for spatial phase compensation. Then, the steering vector of the collocated orthogonal vector sensor is obtained to calculate a fake coarse DOA estimation. By comparing the above ambiguous fine estimation with the fake coarse estimation, the closest estimation is taken as the finally 2D DOA estimation. The computation of the proposed algorithm is small due to a lack of angle searching. Moreover, the long dipole has high radiation efficiency, and the spatially spread vector sensor has low mutual coupling. Simulation results demonstrate the effectiveness of the proposed algorithm.

Dual-Wideband Magnetoelectric Dipole Antenna With Director Loaded

In this letter, a dual-band magnetoelectric (ME) dipole antenna with wide operation bands is proposed for WiMAX and WLAN applications. A full-metal rectangular director is loaded right above the ME dipole antenna and it resonates at around 3.6 GHz due to the excitation of the long electric dipole (LE-dipole). Then, the lower operation bandwidth is extended significantly. This added director also allows our antenna to work as a quasi-Yagi antenna at specific frequencies, and thus, the proposed antenna is capable to achieve better unidirectional radiation performance and higher gain. In order to satisfy WLAN communication, a short trapezoid electric dipole is designed beneath the LE-dipole, which maintains the overall antenna dimensions as unchanged. Besides, such design strategy avoids the distortion of the radiation pattern at 5 GHz as well. As for the ground, a hornlike reflector is adopted instead of traditional planar structures. The measured results show that our proposed antenna achieves two wide bandwidths, 2.3–3.7 GHz (46.7%) and 5–6.25 GHz (22.2%), and high stable gain (8.5 ± 0.9 and 9 ± 1 dB) within these two operation bands.

A Universal Condition Satisfied by the Action of Electromagnetic Radiation Fields

The action (the product of radiated energy and the time of emission) of the radiation fields generated by four types of radiators, namely, short electric dipole, small magnetic dipole, travelling wave antenna and bi-conical antenna is investigated with special reference to the charge associated with the current waveform which is responsible for the radiation. The results obtained can be summarized by the order of magnitude inequality where A is the action (product of the radiated energy and the time of emission), h is the Planck constant, q is the charge associated with the current that gave rise to the radiation and e is the electronic charge. The condition is obtained when the length of the antenna and its radius are pushed to its extreme natural limits. Based on the results obtained here and elsewhere, it is suggested that this inequality is valid in general for electromagnetic radiation fields as predicted by classical electrodynamics.

Planar Yagi–Uda Antenna Array Based on Split-Ring Resonators (SRRs)

A novel planar Yagi–Uda antenna is presented in this letter. The proposed antenna uses electrically small resonators as radiating elements that behave as short electric dipoles. Its radiation pattern, gain, front-to-back ratio, and efficiency are maintained close to that of a Yagi–Uda antenna of stacked half-wavelength dipoles. However, its physical dimensions are considerably reduced. The choice of the resonant particle and its radiation properties, along with the antenna structure, are discussed. Simulated results show a good impedance matching (–29 dB) at the working frequency of 5.5 GHz for a 15-elements antenna, as well as a high gain (11.5 dBi). These characteristics are experimentally validated and compared to that of other Yagi–Uda designs from the literature.

Compact Internal Antenna for Handheld Devices With Comprehensive DTV Band Coverage

A compact internal antenna design applicable to handheld digital TV receivers is proposed. Its operation bandwidth extends from 470 MHz to 860 MHz, which covers most terrestrial digital TV broadcasting bands. The antenna sizes protruding from the ground plane are 80 mm×15 mm×10 mm only and can fit in most palm-sized terminals. Major geometric features include a 3D folding structure that reduces the antenna footprint, a parasitic element that induces additional modes, and a folded microstrip line near the feed that improves the matching condition. The proposed design employs various methods to create multiple resonances in a confined antenna volume. Yet, a consistent radiation pattern is achieved over the operation band with decent efficiency performance. This is done by exciting several resonant modes within and adjacent to the desired band. Though the resonances take places at different antenna parts, most radiation comes from the current near the feed. The resulting antenna acts as a short electric dipole at all frequencies. Also, an abrupt efficiency roll-off is setup at the upper band limit to reduce interference from the nearby mobile service band. Rigorous studies were conducted to associate its superior performance features with implemented techniques.

Radiation from a short vertical dipole in a metal-backed rod array

Based on an effective medium approach, we investigate the problem of radiation of a short vertical electric dipole embedded in a metal-backed dielectric rod array. We obtain the radiated electromagnetic field in the form of a Sommerfeld integral, and calculate the near and far electric fields for both lossless and lossy rod arrays. The characteristic equation for the guided modes is derived and solved. The guided modes are found to be slow waves and their propagation constants and modal distributions are extracted. All theoretical results are compared with full-wave simulations.

Electric Dipole Antenna in Presence of a Double Wire-Mesh Planar Interference Filter

In this letter, we derive a new full-wave analytical field solution for the problem of two separated planar thin-wire meshes excited by a short horizontal electric dipole (HED). Both meshes are constructed from identical perfectly conducting parallel wires with small period (interwire spacing) compared to wavelength. A fast-converging solution is obtained employing averaged boundary conditions and image theory approach. A set of computed near- and far-field patterns is presented.

Radiation From a Hertzian Dipole Embedded in a Wire-Medium Slab

The radiated field expression for a short vertical electric dipole embedded in a wire-medium slab is derived using an effective medium approach. The dispersion characteristic equation of wave modes is presented, and the propagation and attenuation constants of each propagating mode are determined. Both a surface wave and a leaky wave are shown to propagate in the wire-medium slab. Near- and far-field distributions of the wave modes are computed and compared to full-wave simulation results.

A DERIVED PHYSICALLY EXPRESSIVE CIRCUIT MODEL FOR ELECTRICALLY SMALL RADIATING STRUCTURES

Recently, a new radiation model for the partial element equivalent circuit (PEEC) technique has been proposed. This model makes use of the concept of generalized complex inductance to account for the radiation efiect and preserve the (quasi-)static condition for the capacitance. Therefore, PEEC models with the radiation efiect included consists of real-valued capacitors but complex-valued inductors. In this paper, a method for deriving a concise and physically intuitive equivalent circuit from such a radiating PEEC model is presented. The method is based on the Y -to-¢ transformation to eliminate all \unimportant internal circuit nodes and results in an equivalent circuit with only a few nodes left. The equivalent circuit for a short electric dipole is flrst derived analytically to ofier a simple explanation to the basic principles. The proposed method is then applied to several practical and electrically small antennas for more detailed demonstrations. Numerical results obtained from these examples suggest that a physically intuitive circuit model can potentially be derived for arbitrary radiating multi-conductor structures, showing the method is useful for analysis and design of modern integrated and electrically small antennas.

Scattering analysis of planar electric and magnetic dipoles in multilayered chiral structures

This paper describes a model for the analysis of multilay-ered chiral structures containing planar electric and magnetic scattering elements of arbitrary shape, illuminated by an elliptically polarized plane wave. The particular case of a single chiral layer is analyzed and the scattering matrices for single and dual electric and/or magnetic dipole distributions are derived in an original way. As an application, the polarimetric response of a short electric or magnetic dipole is directly obtained from their scattering matrix.

Compensation of electric cross-field response in shielded loop probe

The singly-loaded shielded loop probe is investigated with respect to its sensitivity to electric fields. A standing-wave open microstrip transmission line cell is used to measure the response of a loop probe of 1% wavelength diameter to the magnetic field normal to the loop plane and to the electric field along its symmetry axis and along its cross direction. The response to the electric cross-field is shown to exhibit the characteristic of a short electric dipole, which has inspired a compensation technique using an additional wire dipole cross-connected over the shield gap. Experimental results of the compensation technique are presented, which show effective reduction of the E-field pick-up by 10–15 dB while maintaining the useful properties of the H-field probe.

Mode-Based Computation Method of Channel Characteristics for a Near-Field MIMO

This letter proposes a new mode-based method for estimating the channel characteristics of a near-field multiple-input-multiple-output (MIMO). When an antenna array composed of a short electric dipole and a small solenoidal loop is used, a 2×2 near-field MIMO can be effectively constructed according to the orthogonality of the TM10 and TE10 modes. By using the proposed method, the transmission characteristics of the MIMO and the mutual coupling effect at the antenna array can be easily calculated. In addition, the capacity of the MIMO can also be calculated by using the analysis results.

Metamaterial-based efficient electrically small antennas

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, i.e., 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.

Evaluation of inductance for various distributions of windings on straight ferromagnetic cores: an unusual approach

The detailed electromagnetic duality that relates small magnetic structures and small electric structures at ultralow and extremely low frequencies has recently been treated. The strict duality relationship holds provided that the structures possess similar geometry. For example, a short electric dipole antenna gapped in the middle is strongly related to the magnetic structure consisting of a short coil mounted in the middle of a rod of highly permeable material. In particular, the inductance of the latter magnetic structure can be derived directly from the capacitance between the electric dipole arms. The relationship has been thought to hold only for situations where the coil in the center of the core is very short. Here, however, we show that inductance can be evaluated even in cases where the windings are distributed beyond the center and cover relatively long portions of the ferromagnetic core. The extension of the theory described here relies on the fact that the distribution of the flux along the core is triangular-a fact derived from the similarity of the magnetic structure to a short electric dipole antenna, in which the current has a triangular profile. The triangular distribution provides a basis for evaluating the inductance of extended coils by relying on integration of the flux profile through the windings along the core. The results of the evaluation are in good agreement with laboratory measurements. The evaluation method, despite its simplicity, is based on analytical approach, unlike the many empirical methods of inductance evaluation described in the literature.

Unusual method for impedance evaluation of short dipole with arbitrarily mutual arms location and the implications for dc field sensors

A relatively unknown analytical method is developed further in order to evaluate the capacitance between two long cylinders of equal length and diameter. The main approximation associated with the relatively unknown method was in assuming that the cylinders are uniformly charged no matter what is their length and diameter and no matter what is their mutual location and orientation. The cylinders in our treatment are long in terms of length to diameter ratio, but they are much shorter than a wavelength. One of the presently treated cases is due to two gapped collinear cylinders of equal diameters and lengths. Such a structure (when the gap between the cylinders is small) is similar to that of a short dipole antenna. There have been several analytical methods mentioned in the literature for estimating the short dipole impedance. It is interesting that the present method of evaluation, which is completely independent, compliments some of the previous methods. It is also known relatively well that evaluating the inductance of iron cored coils bears direct relationship (through EM duality theory) to the short electric dipole capacitance evaluation. It means that the present work is helpful for inductors design and also for evaluating cored search coil magnetometers. The work contributes to better understanding of fieldmills and fluxgates that are employed for sensing electric and magnetic dc fields, respectively. Furthermore, a new type of an electric dc field sensor has been developed by us recently. Its structure is that of a short dipole, where the length of the gap between the dipole cylindrical arms is modulated periodically. Its operation is somewhat similar to that of a fieldmill, and is also due to the periodic variation of the structure antenna-capacitance. The presently developed analytical method serves also for evaluating the variable capacitance of the new sensor, and is in particular helpful for the interpretation of its operation. Generally speaking, the work is helpful in demonstrating that dc field sensors should be regarded as being related to antennas and should not be treated as if they were separate entities.

Applying wire antenna theory to cored search coils

It seems conceivable that the magnetic field pattern around ferromagnetic objects of high permeability is similar to the electric field pattern around conductive objects, provided that the shapes of the magnetic and electric objects are identical. As a result, we expect the mmf behavior in the gap between two ferromagnetic limbs immersed in a magnetic field to be similar to the open‐circuit voltage of a short electric dipole antenna immersed in a related electric field. Experimental setups have been developed in order to demonstrate the affinity between the electric and magnetic cases exists both in uniform and nonuniform surrounding field (electric and magnetic). The experimental results conform closely with the results obtained by the theoretical evaluation. We have thus discovered that the true counterpart of a short electric dipole is a geometrically similar magnetic structure, where ferromagnetic limbs of high permeability replace the conductive limbs of the short dipole. This is contrary to the majority of the literature on the subject, which regards a small wire loop as consisting of the entity dual to a short electric dipole. The present results enable us to treat practical magnetic sensors for ELF and ULF in terms of electric antenna theory. It is also shown that the present developments are of value in interpreting the results of measurements performed by employing ELF and ULF cored search coils in probing nonuniform magnetic fields.

Treatment of extremely low frequency magnetic and electric field sensors via the rules of electromagnetic duality

This work deals with extremely low frequency (ELF) electric and magnetic sensors. The discussion emphasizes the similarity existing between the two families and attempts to exploit this similarity in studying the performance of such devices. The new approach is not based merely on similarity. We show that the two families of devices are in fact mutually related by the strict rules of electromagnetic duality. It is known that a small loop antenna serves as a magnetic dual for the short electric dipole. This duality is usually demonstrated by the far fields behaviors and the radiation resistances. By introducing an appropriate ferromagnetic core into the loop, the detailed duality relationship can be extended to the immediate vicinity of the sensors as well. The latter means that sensors of both families process the near vicinity fields in a similar way in converting them to the measured signals. The existence of duality is assessed by showing that for geometrically similar structures, the reactances of the two entitles are correctly related. It is also shown that the electromagnetic duality manifested by the fields conforms also with the rules of duality in circuit theory. The latter is demonstrated by dealing in both cases with circuit models of the sensors, which are derived by considering similar circuit models that are common in antenna theory. The presently investigated sensors possess practical implications. It is well established that short electric dipoles are employed as sensors in the field of electromagnetic interference (EMI) and also as ELF electric field sensors aboard spacecrafts. Cored search coils are employed as ELF and even as ultra low frequency (ULF) magnetometers in geophysical and space research. They were even considered as possible antennas for ELF communications. The paper is concluded by showing that the present duality considerations of ac sensors can be even extended to deal with dc field sensors magnetic and electric.

A new algorithm for ground wave propagation based on a hybrid ray-mode approach

An efficient novel algorithm is introduced for ground wave propagation problems. First, ground wave propagation characteristics for a vertically polarized short electric dipole over a smooth spherical earth are reviewed, reducing the vector electromagnetic problem for the three-dimensional spherical geometry to an equivalent two-dimensional rectilinear scalar potential problem which is solved by spectral analysis and synthesis. Alternative evaluations of the spectral integral yield ray optical and normal mode solutions, which are conventionally referred to as the Norton and Wait formulations, respectively. Combining these formulations in an efficient manner yields a hybrid algorithm which is constructed so as to account adaptively for the characteristics of ground wave propagation in interference, intermediate and diffraction regions (including mixed paths) for various source and/or receiver heights. Numerical comparisons are made with reference results obtained via the parabolic equation (PE) method, in parametric ranges where PE is reliable; this permits assessment of the effectiveness of the hybrid approach. © 1998 John Wiley & Sons, Ltd.