Analysis of infinite arrays of microstrip-fed dipoles printed onprotruding dielectric substrates and covered with a dielectric radome

A method for analyzing infinite arrays of antennas printed on both sides of substrates protruding from a ground plane and covered with a dielectric radome is described. Using the equivalence principle, the array unit cell is decomposed into homogeneous regions where the fields are expressed as Floquet summations, and an inhomogeneous cavity region where the fields can be found by a combination of the method of moments and modal analysis. The approach is rigorous in the sense that the combined effects of the radiating element and feed geometry printed on opposite sides of a protruding substrate are taken into account. The method is quite general, capable of modeling any antenna elements with substrate currents that are perpendicular and/or parallel to the ground plane. In addition, both the radiating and scattering/receiving modes of operation are treated in the analysis. The method is used to calculate the active element impedance of an infinite array of dipoles transmission line-coupled to microstrip feeds. Examples of numerical results are presented for various scan conditions and the effects of a near-field dielectric radome are demonstrated     

The radiation pattern of an array of dipoles in a dielectric slab

By using the reciprocity theorem, simple expressions are derived for the far-field patterns of normal and parallel dipoles in a plane dielectric slab. The dielectric slab may have a conducting ground plane on one surface. Numerical results are presented in a graphical form to show the effects of the dielectric on the antenna pattern. A dipole array embedded in a radome occupies less space than a conventional parabolic antenna, and the ground plane offers structural support for the radome.     

Beam reconfiguration of linear array of parallel dipole antennas through switching with real excitation voltage distribution

In this paper, authors propose a method based on the modified particle swarm optimization (PSO) for beam reconfiguration of linear array of mutually coupled parallel half-wavelength dipole antennas with real excitation voltage amplitude distribution. Two different beam pairs are generated, one pencil/pencil beam pair and another pencil/flat-top beam pair in the horizontal plane. One beam is changed to another through switching while sharing a common amplitude distribution. Two examples are presented, one without ground plane and another in presence of ground plane. Dipoles are connected to its feed network through a switch, so that it can be turned on or off, depending on the switch position. Beam reconfiguration is achieved by suitably turning the array elements on or off using same voltage excitation distribution. Modified PSO is used to compute the excitation voltages as well as the switching configuration for each pattern having a prefixed side lobe level. The current in the driven and parasitic elements is determined via induced EMF method considering the current distribution on each dipole to be sinusoidal. Proposed method efficiently synthesizes dual-beam switching the power pattern from pencil to pencil and pencil to flat-top having same or different side lobe levels using common excitation voltages. It calculates the maximum variation of the active impedance of driven elements and the power losses when the radiation patterns switch from one beam to another. The paper calculates the array directivity as the distances between antenna array and the ground pane varies. Three other state-of-the-art metaheuristics like differential evolution, gravitational search algorithm, artificial bee colony algorithm are also employed for achieving a comparative evaluation.     

Integral equation analysis of a sheet impedance coated window slotantenna

Presents an integral equation and method of moments analysis of a window slot antenna. The antenna is modeled by a sheet admittance coated rectangular aperture in an infinite ground plane. It is shown that the sheet admittance coated aperture is complementary to a sheet impedance plate, which permits the window slot antenna to be analyzed with existing computer programs. Numerical results are compared with measurements for input impedance and radiation efficiency     

Scattered and absorbed powers in receiving antennas

This paper discusses the amount of power, which is scattered and absorbed by a receiving antenna and in particular, whether an antenna can absorb the entire power incident upon it. The absorbed and scattered power from dipole arrays in either free space, or over ground plane is considered. By defining a suitable "aperture efficiency" for the receiving case, a dipole array without a ground plane can best absorb half of the incident power (scattering the rest), while an array over a ground plane can absorb all of the incident power. It is shown how aperture efficiency varies with load impedance, which is of practical interest for array designers.     

Plane-wave expansion for arrays of arbitrarily oriented piecewise linear elements and its application in determining the impedance of a single linear antenna in a lossy half-space

An infinite array of arbitrarily oriented identical elements with arbitrary identical currents is considered. The field from this array is expanded into plane inhomogeneous waves, and the mutual impedance between the array elements and an exterior arbitrarily oriented element is derived. The formulation is particularly useful when the array is located adjacent to a dielectric interface. Numerical examples are given and the relationship to earlier formulations pointed out. It is further shown that the impedance of a single element can be obtained as the average of the scan impedance taken over the entire hemisphere (called the array scanning method (ASM)). This technique has a clear physical interpretation which greatly facilitates its uses, which include the moment method solutions of wire antennas as applied to the Sommerfeld integral. Numerical evaluation is straightforward when the dipole is in the lossy half-space, and the utility of the method is demonstrated by the presentation of results for the input impedance of dipoles in a variety of half-space environments. Solution is by Galerkin's method with a piecewise sinusoidal expansion for the current. Computer time is proportional tod^{-1}, wheredis the distance of the dipole to the interface. For conducting media and low frequencies an approximation is made to reduce computation time. The moment method solution of a dipole buried at a depth as small as 1/150000 wavelength in the earth is presented.     

Radiation of an aperture antenna covered by a spherical-shellchiral radome and fed by a circular waveguide

This paper presents a full-wave analysis of the radiation characteristics of an aperture antenna that is flush-mounted on a ground plane and fed by a circular waveguide supporting the dominant TE₁₁ mode. The antenna is covered by a dielectric hemispherical chiral radome. Huygen's equivalence principle and the image theory are utilized to simplify the problem. The magnetic dyadic Green's function for the three-layered geometry is formulated and applied to analyze the radiated electromagnetic fields outside the chiral radome. Both the exact and approximate expressions of electric fields valid for the Fresnel and Fraunhofer zones are obtained using the spherical vector wave functions and their approximations in the far zone. Various chiral materials are assumed and computations of antenna parameters are carried out. The effects of the dielectric chiral radome on the radiation power patterns, sidelobe levels, and 3-dB beamwidths are also discussed numerically     

Radiation and scattering analysis of infinite arrays of endfireslot antennas with a ground plane

A Green's function moment-method analysis of infinite arrays of endfire slot antennas is described that includes the constant width slot antenna (CWSA) and the linearly tapered slot antenna (LTSA), with a ground plane. The method utilizes an application of equivalence at a plane in front of the array which facilitates the extension of this analysis to antennas printed on protruding dielectric sheets and/or the addition of a radome. Numerical calculations are compared with waveguide simulator experiments for CWSA and LTSA arrays as well as several less complex problem. Relevant numerical considerations and convergence issues are also discussed     

A network model of a feedthrough phased array lens of printed dipole elements

An easy-to-use simplified network representation for the internal multiple reflection model of feedthrough phased array lens antenna elements is presented. This model makes use of the readily known active radiation impedances of an infinite array rather than the self and mutual impedances between array elements. In particular, this model is applied to a printed dipole lens array case, for which the computation of the radiation impedance is described. Numerical results for this lens array are given to show the aperture distribution variations due to the lens internal multiple reflection, and the gain falloff as a function of scan angle.     

Plane wave scattering from an infinite planar dipole array buried in a lossy half-space

The plane wave scattering from an infinite planar impedance-loaded dipole array buried in a lossy half-space is investigated theoretically and experimentally. Formulations for the scattering field and the input impedance of the dipole are derived by using Floquet's theorem and the induced electromotive force (EMF) method. In order to demonstrate the validity of these formulations, the numerical examples for a concrete as the lossy medium at frequency 9.32 (GHz) are compared with the experimental data. The results show that this array, even when loaded by zero impedance, can greatly suppress the radio wave reflection from the concrete surface by choosing the array dimensions properly and the depth of the array surface.     

Characteristics of the skeletal biconical antenna as used for EMCapplications

The Numerical Electromagnetics Code (NEC) is used to simulate the radiators of a skeletal biconical antenna and the model is optimized to return a drive point impedance as close as possible to measured values. The horizontally polarized model is then illuminated in free space and above a ground plane to deduce its plane-wave antenna factors and their variations as functions of height. It is shown that changes in effective length have to be considered in addition to changes in impedance mismatch when calculating antenna factor variations with the biconical antenna, although only the latter are necessary with a resonant dipole. The measured scattering parameters of the balun of the biconical antenna are then incorporated with the NEC simulation to give a complete model of the real antenna     

Radiation impedance of a dipole printed on periodic dielectric slabs protruding over a ground plane in an infinite phased array

The radiation impedance of a dipole printed on periodic dielectric slabs standing over a ground plane in an infinite phased array is calculated. The calculation is made by means of modal expansions in terms of longitudinal section electric (LSE) and longitudinal section magnetic (LSM) modes. Derivations of these hybrid space modes and development of the modal expansions are presented first. The impedance of the dipole element is then calculated by a method based on the complex power relations with the aid of Poynting's theorem. The results calculated by the present theory in the limiting case of no dielectric slab loading have been compared with the results calculated by the method of ordinary plane wave expansions. A comparison is also made between results calculated by the theory and the experimental data obtained from waveguide simulators or test array. These results are shown to be in good agreement. An outline of steps to formulate the solution of the current distribution on dipole is also given.     

Scattering from a cavity-backed slit in a ground plane-TM case

Two-dimensional transverse-magnetic wave scattering from a cavity-backed slit in a ground plane is analyzed by the Harrington-Mautz generalized network formulation (1976). The admittance matrix of the cavity of arbitrary shape and medium is obtained by the finite-element method. The computed admittance matrix, added to the radiation admittance matrix of the equivalent magnetic current on a ground plane, is used to find a solution for the equivalent magnetic current on the slit. Numerical results for coated staggered cavities are included. Accurate results for the magnetic surface currents and radiation patterns have been obtained     

Millimeter-wave integrated-horn antenna. II. Experiment

For pt.I see ibid., vol.39, no.11, p.1575-81 (1991). The impedance and radiation patterns of a dipole-fed horn antenna in a ground plane are experimentally investigated at microwave and millimeter-wave frequencies. The agreement with the full-wave analysis technique presented in part I is good. The results indicate that for a 70° flare-angle horn, horn apertures from 1.0 λ-square to 1.5 λ-square with dipole positions between 0.36 and 0.55 λ yield good radiation patterns with a gain of 10-13 dB a cross-polarization level lower than -20 dB, and resonant dipole impedances between 40 Ω and 120 Ω. It is also found that the impedance measurements can be safely used for 2-D horn arrays, but the radiation patterns differ because of the Floquet modes associated with the array environment. The integrated horn antenna is a high-efficiency antenna suitable for applications in millimeter-wave imaging systems, remote-sensing, and radioastronomy     

Hemispherical coverage using a double-folded monopole

A traveling-wave current distribution can be produced on a monopole over a ground plane by inserting a resistance of suitable magnitude one-quarter wave length from its end. It has been shown that the resistor can be replaced with a modified folded dipole which has a radiation resistance approximately equal to that of the resistor. Furthermore, it was found that when the folded element was about 0.1λ above the ground plane, near hemispherical coverage was obtained in the plane of the element. In this paper, the resistor is replaced with orthogonal folded elements. The main objective is to obtain an antenna which is circularly polarized and which has near hemispherical coverage. The input impedance, current distribution, and radiation patterns of this antenna were computed using the numerical electromagnetics code (NEC); the radiation patterns and input impedance were also measured. To produce a circularly polarized wave it is necessary to tilt the folded elements. After experimenting with a number of different configurations an antenna design having directional and polarization properties approaching those that were desired was obtained. All computations and measurements were conducted near 1.6 GHz, a frequency close to that of the proposed IRIDIUM communications system and the L1 band of the Global Positioning System (GPS). The double-folded monopole may prove to be a very low cost option as a ground antenna for these systems     

基于EBG结构吸波材料在螺旋天线阵中的应用

研究了基于EBG结构的超薄吸波材料在螺旋天线阵RCS缩减中的应用。通过采取在EBG贴片之间加载集总电阻的方式实现吸波材料,并将螺旋天线阵金属底面用EBG吸波材料代替,以期实现了天线阵工作频带内RCS减缩的目标。实验结果表明,在EBGRAM的吸收频段内该吸波材料能有效缩减螺旋天线阵的RCS,同时保持天线单元辐射性能,仅前向增益有所下降。     

Scan performance of infinite arrays of microstrip-fed dipoles withbent arms printed on protruding substrates

E-plane scan results are presented for infinite arrays of microstrip-fed dipoles printed on protruding dielectric substrates. Active impedance values are calculated for dipoles with bent arms and for the array with a near-field dielectric radome cover. It is found that bending the dipole's arms produces a small improvement in the scan range, as compared to the element with the arms straight, and that a dielectric radome with a low permittivity causes a small shift in the impedance curves. The scan limitation of the array is dictated, however, by the presence of the coplanar feedlines with improvement achievable by varying the substrate's thickness and permittivity as well as the dipole/feed geometry. A dipole element with a modified coplanar feed design is introduced for wider scan coverage     

A monopole antenna loaded with a modified folded dipole

A traveling-wave distribution of current can be produced on a linear antenna by inserting a resistance of suitable magnitude one-quarter wavelength from its end. In this study the resistor is replaced with a modified folded dipole which has a radiation resistance approximately equal to that of the matching resistor. Thus the input section has a traveling wave distribution up to the inserted antenna, as before, but now the power that was previously dissipated in the resistor is also radiated. Input impedance, current distribution, and radiation patterns of this antenna are computed, and input impedance and radiation patterns are also measured. Horizontally polarized patterns are similar to those of a horizontal dipole over a ground plane, and vertically polarized patterns in a plane orthogonal to the folded element are similar to those of a monopole over a ground plane. Coverage is also obtained in the zenith direction in the plane of the folded element, as long as it is not an integral number of half wavelengths above the ground plane. The peaks and nulls can be controlled by adjusting the monopole height accordingly and it is possible to achieve near hemispherical coverage     

Microwave modeling of 2-D active grid antenna arrays

A new measurement technique for determining the broadband driving point impedance of large two-dimensional active grid arrays is presented. The active array radiates a plane wave in the broadside direction when all elements are locked in phase. For analysis, the array is reduced to a single unit cell by exploiting the array symmetries. The driving point impedance of the unit cell is determined by using the dielectric waveguide measurement method (DWM). The approximations of the method are discussed, and the method is compared with other measurement techniques. Results are presented for four square arrays: dipole, bow-tie, double-vee and slot array. The measurement method is verified by comparing it to the full-wave theory in the whole range. It is shown that all four antenna arrays can be represented by very simple circuits that use only transmission lines as circuit elements. The bow-tie array is found to represent the best choice for broadband operation     

Impedance of a monopole antenna over a ground plane and immersed in a magnetoplasma

A treatment of the input impedance of a monopole antenna over a ground plane covered with a magnetoplasma with any arbitrary direction of the static magnetic field is presented. The analysis is restricted to a cold plasma with uniaxial and quasi-static approximations. It has been found that for parallel and perpendicular directions of the static magnetic field with respect to the ground plane perfect mirror reflections can be obtained. For other directions of the static magnetic field, the reflection is birefringent so that the monopole impedance becomes modified over a dipole impedance. These modifications can be significant under hyperbolic plasma conditions. A short and a long monopole were considered. From laboratory measurements of a long monopole impedance, the resonance cone and the resonances corresponding to the antenna length have been observed.