Modeling folded dipoles and feedlines for radiation and scattering

Dipole-like antennas, suited for use as radiating elements in large phased arrays, are modeled for efficient analysis by decomposing the antenna into a radiating mode part and a transmission line mode part. All the essential features of folded dipoles, integrated balun feedlines, and feedline scattering are contained in the models. Feedline scattering, in particular, is an important consideration in analyzing phased arrays. The models are suited for moment-method analysis of arrays of such antennas, because the models entail simplified radiation mode parts. Extensive results of exercising the models were obtained for assessing model accuracy. Agreement between full-moment-method analyses and combined-mode analyses was reasonably good     

Advanced design of phased-array beam-forming networks

Recent, very general and fundamental results in the theory of electrically large microwave networks lead to new, advanced designs of high-efficiency beam-forming networks, for high-directivity electronically-steered phased arrays. On the basis of the rigorous new results, the beam-forming networks of electronically-steered phased arrays can be simultaneously impedance matched to any given set of radiating elements on one side, and to any given set of mutually-coherent, phase- and amplitude-controlled microwave sources on the other. Further, the impedance match attained in transmission also holds in reception, as long as the set of mutually-coherent receivers used has the same internal impedances as the set of sources used. The impedance match attained accounts simultaneously for both the electromagnetic proximity coupling between all the radiating array elements, and for any given internal cross-coupling of the set of sources, in transmission, or of the set of receivers, in reception. The resulting impedance match is totally independent from the amplitude and phase settings of the sources, in transmission, and from the direction of the incoming beam, in reception, completely suppressing the notorious array-blindness effect for all beam directions. Further, beam-forming networks can also be designed with prescribed transmission responses-besides a prescribed impedance match-in both the transmission and reception modes, and with a number of beam-steering control components that is much smaller than the number of array elements     

矩形波导宽边偏置交叉缝研究

提出了一种新的矩形波导缝隙阵列的单元形式－宽边偏置交叉缝，并采用全域正弦基Ｇａｌｅｒｋｉｎ法对其散射特性和谐振特性进行了理论分析。数值结果表明，这种缝隙单元的散射作用与宽边偏置纵缝相似，二者均可以用等效传输线上的一个并联导纳来表示，但交叉缝的谐振长度比纵缝显著缩短，因而交叉缝阵列中单元间的互耦相对较弱，频带相对较宽。理论计算结果与实验测量数据的良好吻合验证了上述分析方法的准确性。     

Synthesis of linear arrays of series fed proximity-coupled microstrip antennas

This paper presents a synthesis of linear standingwave arrays of microstrip antennas such as transverse dipoles, series-fed by a proximity coupled microstrip line. Each radiating element is characterized by its self-admittance and mutual coupling admittance. The self-admittance depends on geometrical parameters and on the nature of the substrate, while the mutual coupling admittance is related to the presence of the other radiating elements. These values are computed exactly using an integral equation technique combined with a two-port model of the element. The synthesis procedure is validated with measurements of the radiation pattern and a return loss of a 20-dipole array. The importance of mutual coupling in the design process is clearly demonstrated.     

Infinite planar arrays of arbitrarily bent thin wire radiators

A plane wave expansion moment method is presented for computing active impedances and current distributions of infinite planar arrays of thin wire radiating elements. The array lattices can be rectangular or triangular. The excitations can be plane waves or progressively phased voltage sources. Each radiating element, including feedline, can be any collection of bent thin wires. Results are given for arrays of straight dipoles with straight feedlines, straight dipoles with bent feedlines, and swept back dipoles (arms inclined with respect to the array planes) with straight feedlines. The experimentally observed phenomenon of array blindness as a consequence of feedline scattering is verified theoretically. The absence of this effect when the dipole arms are inclined with respect to the array plane also is verified.     

Calculation of radiated electromagnetic fields from cables usingtime-domain simulation

Radiated electromagnetic fields are produced by currents in cables or transmission lines interconnecting various circuits. An elegant method of computing the resultant electromagnetic field, produced by several radiating current elements, is given. The current in each radiating cable is first found from a time-domain simulation algorithm and this may be a steady-state or transient current. The radiated field is then calculated by assuming that a radiating transmission line can be treated as a chain of short radiating dipoles. The problems associated with the calculation of the near-zone term at low frequencies and the overall response near the radiator are clarified. The proposed technique is fully evaluated and compared with other methods     

Multifunction wide-band array design

High-performance active arrays operating over C, X, and Ku-band have been demonstrated using newly developed designs of wide-band radiating elements and wide-band monolithic microwave integrated circuits (MMICs). The advanced shared aperture program (ASAP) explored the development of wide-band multifunction arrays capable of simultaneous and time interleaved radar, electronic warfare, and communications functions. Two iterations of radiating element and transmit/receive (T/R) module design were completed during this program. The radiating aperture design approach, overall array concepts, and current design technology and performance are summarized     

Multiport scattering analysis of general multilayered printedantennas fed by multiple feed ports. I. Theory

A general solution is given for a class of printed antenna geometries composed of multiple dielectric layers or ground planes, radiating patches, dipoles, or slots, and an arbitrary configuration of multiple transmission lines proximity-coupled or aperture-coupled to the radiating elements. The solution uses a full-wave spectral-domain moment method approach, and a new generalized multiport scattering formulation to model the excitation from the multiple feed lines. This method treats infinite phased arrays as well as isolated elements. The general theory using the new multiport scattering formulation is elaborated, with details of the key analytical and numerical aspects. Considering the unified nature of the multiport scattering analysis, and its simplicity, this analysis is appropriate for computer simulation of a large variety of multilayered microstrip antennas involving radome layers, dual polarized feeds, proximity-coupled or aperture-coupled elements, multifeed stacked or parasitic patches, and several related configurations for integrated phased array applications     

A Method of Cross-Polarization Reduction

A method for the reduction of cross-polarized radiation is described. The method can be used for various antenna array systems made up of radiating elements with higher cross-polarized radiation. This solution enables numerous possibilities for selecting the position, the spacing, and the excitation coefficient of any array element. It is even possible to use two different linearly polarized arrays that use the same or different polarizations. Two examples are given: a quarter-wave microstrip antenna system operating in two frequency bands, and a suspended patch array     

A self-matching wideband feed network for microstrip arrays

A novel technique for feeding microstrip antenna arrays is proposed. It consists of a microstrip feed network designed to operate in dual standing and traveling-wave modes and provide uniform excitation to its elements with either mode. It, therefore, produces a uniform aperture distribution, regardless of the array element input impedances. The traveling wave propagates when radiating elements are matched, but resonant standing wave prevails if loads become mismatched. Since the feed network resonance does not alter the array excitation, it can be used in combination with the radiating patch resonance to broaden the impedance bandwidth. The physical reasons for such behaviors are explained and experimental verification are provided. The generalization of the concept to large arrays is also discussed     

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     

Impedance of an antenna-array element

A number of expressions for calculating the active impedances of the radiating elements of large linear and planar antenna arrays with allowance for the interaction of the entire set of the elements are presented. The expressions are applicable not only to the radiating elements distant from the edge of the array but also to the edge and corner elements. The expressions are based on the formulas for certain sums of elementary and higher transcendental functions that give simple closed-form expressions for the sums of mutual impedances. As an illustration, the resistances of weakly directional radiating elements in dense arrays, where the mutual coupling of the elements is extremely strong and results in important effects, are calculated.     

Statistically designed density-tapered arrays

The design of "thinned" planar array antennas is considered in which the density of elements located within the aperture is made proportional to the amplitude of the aperture illumination of a conventional "filled" array. Density tapering permits good sidelobe performance from arrays of equally radiating elements. The selection of the element locations is performed statistically by utilizing the amplitude taper as the probability density function for specifying the location of elements. The statistical design procedures and the theoretical prediction of performance are given. Application to a 50 wavelength diameter planar aperture is discussed and the results compared to conventional amplitude-taper designs. Examples of computed patterns are shown for density tapers modeled after 25, 30, 35, and 40 db circular Taylor distributions. The properties of a planar array of 10,000 elements are examined for "natural" thinning and for 70 per cent and 90 per cent of the elements removed. The sidelobes are determined more by the number of remaining elements than by the model amplitude taper. Statistically designed density-tapered arrays are useful when the number of elements is large and when it is not practical to employ an amplitude taper to achieve low sidelobes.     

Méthodes d’analyse et de synthèse de quelques “ microantennes” à large bande en mode quasi transversal électromagnétique

The transmission line model has been utilized to determine the input impedance, the bandwidth, the radiation patterns and the mutual impedance of several microstrip antennas such as the arbitrary shape patch antennas and the wideband flat dipole which is an hybrid radiating source. We suppose that the dominant mode of propagation is the quasiTem one having negligible variation of fields in the transverse direction. Nevertheless a general scattering problem of an arbitrary shaped tridimensional antenna solved by moments method and the finite difference approach applied to integral equations has explained the very large bandwidth microstrip antenna behaviour. The wideband flat dipole has been used in flat arrays, with more than several hundred of such elements, and in microstrip phased arrays with beam steering in a large angular sector.     

Planar 64 element millimetre wave antenna

A simple 64 element planar array antenna, with H-plane sidelobes below -35 dB at larger angles than 19° from boresight and a gain above 30.4 dBi, is presented for the band 37.0-39.5 GHz. The radiating elements are fed in parallel by a waveguide feed network. The H-plane sidelobe level is reduced by using a combination of arrays, the zero in the element radiation pattern, and amplitude tapering     

The cylindrical omnidirectional patch antenna

The need for omnidirectional (in the azimuth plane) antennas with narrow beams in the elevation plane, for wireless applications has increased considerably. The antennas are used in many frequency bands anywhere from 0.8 to 6 GHz, in a variety of configurations. The different collinear-array configurations are designed using back-to-back wide-beam elements or by simply using radiating elements with an intrinsic omnidirectional pattern. The motivation for this work was to devise a radiation element which has an omnidirectional pattern in the azimuth plane and allows for the design and fabrication of arrays that can be easily integrated with other collinear arrays to generate a multitasking omnidirectional antenna. The element proposed in this paper is a patch, which was built in a cylindrical geometry rather than a planar one, and which generates an omnidirectional pattern in the azimuthal plane     

Analysis of Traveling-Wave-Fed Patch Arrays

The design and analysis of traveling-wave-fed, circularly polarized, concentric ring arrays are presented. Linearly polarized microstrip radiating elements were used in the arrays, and fed in series by non-radiating apertures. High quality circular polarization (CP) was achieved by arranging the radiating patches in a concentric ring, with the patches fed with currents of the same magnitude and the appropriate phase delays. For the first time in the literature, a full-wave based model of the power distribution to each element is presented. This model formed the basis of a rigorous analysis of the antenna, not addressed by previous authors. Such analysis is essential to ensure that all the elements radiate identical amount of power, and thus maintain pattern symmetry and optimum CP characteristics. The proposed designs were validated through practical measurements, which showed good CP quality and well-defined radiation patterns.     

An array technique for reducing ground losses in the HF range

Ground losses of HF antennas situated near the earth's surface are reduced if single antennas are replaced by small arrays of, for example, two or four closely spaced radiating elements. It is shown both theoretically and experimentally that an array spacing ofsim 0.1 lambdais sufficient to achieve significant improvement in ground-to-ground transmission efficiency. In particular in the lower HF range and for poorly conducting ground, the improvement approaches a theoretical limit equal to the number of elements in the array.     

Transmission line model for mutual coupling between microstrip antennas

Although more rigorous treatments have been developed for mutual coupling between microstrip antennas, the purpose of this transmission line model is to provide a numerically efficient substitute for them. Therefore, two approximations have been introduced: first, the surface waves have been neglected and second, each rectangular resonator is replaced by two equivalent radiating slots. In most practical cases the approximations are acceptable; this has been proved while comparing the transmission line model with other published results. It is obvious that the efficieney of the transmission model and can be used to include mutual coupling in practical analysis or synthesis routines for arrays of rectangular microstrip antennas.