Anomalous mutual coupling between microstrip antennas

An asymptotic expansion of the microstrip Green's function is used to facilitate a study of mutual coupling between two printed antennas, and coupling versus element separation is presented for substrate parameters of practical interest. For certain substrate parameters, it is found that the magnitude of mutual coupling does not decay monotonically with increasing element separation. Instead, the magnitude exhibits a quasi-periodic oscillation which can be attributed to the interference of surface and space waves. The presentation and discussion of this anomalous behavior is the purpose of the paper. The asymptotic representation of the Green's function, which differentiates space wave terms from surface wave terms when source and observation points are largely separated, is used to characterize the behavior of mutual coupling in the principal planes     

Measured mutual coupling between microstrip antennas

Mutual coupling betweenL-band rectangular, nearly square, and circular microstrip antennas has been investigated experimentally by a series of measurements of theS-parameters. The mutual coupling level decreases monotonically with increasing separation between elements with theE-plane coupling down 20 dB and theH-plane coupling down 25 dB for typical adjacent element spacings. For 1/16 in and 1/8 in substrates atL-band the predominant coupling mechanism is via the space wave since the surface wave is shown experimentally to be small.     

Comparison of measured and calculated antenna sidelobe couplingloss in the near field using approximate far-field data

Computer programs presently exist to calculate the coupling loss between two antennas provided that the amplitude and phase of the far field are available. It is shown that when this far-field information is not available it is possible to specify approximate far fields from a knowledge of the sidelobe of each antenna along the axis of separation and the electrical size of each antenna. The ENVLP computer program developed by M.H. Francis and A.D. Yaghjian (ibid. vol.AP-34, p.952-5, July 1986) was modified for this purpose. Measurements of near-field coupling loss between two moderately sized microwave antennas were made to determine the effectiveness of using approximate sidelobe level data instead of the detailed far fields. Comparison of the measured and computed coupling indicates that the use of approximate far fields gives an estimate of the coupling loss with an uncertainty of about ±5 dB     

Focused aperture microwave antennas operating in the near field zone

Focusing a microwave antenna is often convenient in order to produce a Fraunhofer-type pattern at short distance from the aperture. The characteristics of the radiation patterns produced by some specimens were experimentally tested and compared with theoretical predictions. Basic criteria are given to design focused antennas, once their radiation pattern characteristics are specified.     

Measured mutual coupling between linearly tapered slot antennas

Mutual coupling between two linearly tapered slot antennas arranged in coplanar as well as stacked configurations has been measured. Results indicate that mutual coupling level generally decreases with antenna separations and varies with dielectric constant, and antenna lengths     

Lowest mutual coupling between closely spaced loop antennas

The conditions for zeroing the mutual flux between two closely spaced coil antennas are examined. The analysis is expanded to examine the case of multiple linear antenna coils. Array antennas are used in many areas including magnetic resonance imaging (MRI). Theoretical and experimental results are presented and compared. Good agreement between theory and measurements has been confirmed. A two-dimensional receiving array antenna is proposed     

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.     

互耦效应对波束赋形天线的影响分析

波束赋形天线技术可以通过基带调零等手段降低干扰信号影响,提升系统抗干扰性能,通过数字信号处理还可以在空间上形成多个波束,从而形成空分多址,大幅度提升系统的容量。但是波束赋形天线技术要求天线间隔尽可能小,一般约为工作频率的半波长,而较小的天线间隔在实际工程实现时会引起严重互相耦合。由于对互耦效应进行有效的数学描述非常困难,一般通过计算量极大的专业天线仿真软件进行仿真验证,严重制约了互耦效应解决方案的提出和论证。文中针对上述问题,提出了互耦效应的数学模型,并利用MATLAB和ANSYS-HFSS工具对相关模型进行了交叉验证。不同平台的对比仿真结果显示了相关模型的正确性和有效性。     

凸表面上天线间互耦的射线分析法

本文给出了在电尺寸很大的理想导体光滑凸表面上,无限小磁矩或电矩在空间产生的电磁场的近似渐近解,利用该解可以准确有效地计算凸表面上天线间的互耦。此解中,表面塌沿Keller的表面射线路经传播,且在阴影边界过渡区域,包括对于源的邻城,它们仍然一致适用。除此之外,在给出的解中,通过一个系数T/K给出了关于表面场的表面射线绕曲的影响,其中,T表示表面射线的绕曲,K表示射线方向上的表面曲率。该解是由简单的典型问题的近似解导出的。给出了圆柱面和圆锥面上裂缝间互耦的数字结果,它与实验结果相吻合。     

Theory of mutual coupling among minimum-scattering antennas

A novel and rigorou formulation for mutual impedance among a class of idealized but realizable antennas is presented. Unlike past treatments of mutual coupling, which have proceeded from structurally specified antennas, the present treatment deals with a class of antennas, all the electromagnetic properties of which are rigorously expressed explicitly in terms of their radiation patterns alone. Employing a network formulation based on a scattering representation of electromagnetic fields in terms of spherical (or cylindrical) modes, the mutual impedances between such antennas are computed exactly. Several alternate representations for the mutual impedance are derived, one of which is an integral representation involving the power pattern function for both real and complex angles. In special cases, these exact results agree with published results obtained by applying well-known approximate techniques to structurally specified antennas. An important and illuminating example is provided by an infinite planar array of antennas radiating into a half-space for which the present formulation yields the well-known grating-lobe series representation of the active impedance without an explicit reference to structural properties of the radiating elements.     

High mutual coupling reduction between microstrip patch antennas using novel structure

In this paper, a novel parasitic configuration to reduce the mutual coupling between two adjacent microstrip patch antennas is presented. It is shown that mutual coupling between the antenna elements can be reduced significantly by two simple slots structure on the ground plane and several shorted simple conducting strips between patch antennas. The structure has been constructed and tested. Both simulated and measured results are presented. The results are shown that more than 7 dB reduction within operational frequency bandwidth with the maximum 41 dB mutual coupling at center frequency can be achieved. The measurement results prove the high efficiency of this configuration in multi antenna systems.     

Comparative study on the mutual coupling between different sized cylindrical dielectric resonators antennas and circular microstrip patch antennas

A systematic comparative study on the mutual coupling (S/sub 21/) between dielectric resonator antennas (DRAs) and microstrip patch antennas is presented. The mutual coupling between two cylindrical probe-fed DRAs is studied for different radius to height (a/L) ratios. It is found that the mutual coupling decreases with the radius to height ratio. Comparison between mutual coupling of probe-fed cylindrical DRAs and circular microstrip patch antennas with different dielectric substrates are also studied. The mutual coupling between DRAs is 2 dB stronger than between microstrip patch antennas when the patch is etched on a dielectric substrate of a dielectric constant close to the permittivity of the DRA. The mutual coupling of the circular patch antennas reduces with the dielectric constant of the substrate.     

Curvature effects on the mutual coupling of cylindrical-rectangularmicrostrip antennas

The mutual coupling between two cylindrical-rectangular microstrip antennas is studied from the application of the generalised transmission line model (GTLM). Theoretical solutions and measured results of both E-plane and H-plane coupling coefficients are presented. The curvature effects on the mutual coupling are discussed     

Comparison of mutual coupling of blade antennas with predictionsbased on minimum-scattering antenna theory

The utility of the minimum-scattering antenna model in describing the mutual coupling between two L-band aircraft blade antennas is examined. The communication and sensor requirements of many aircraft, particularly those used by the military, frequently necessitate antennas being placed in close proximity to one another. For such cases, the relatively simple minimum-scattering antenna model provides a very good approximation of the measured mutual coupling of blade antennas and eliminates the need for solving coupled integral equations     

Input impedance and mutual coupling of rectangular microstrip antennas

A moment method solution to the problem of input impedance and mutual coupling of rectangular microstrip antenna elements is presented. The formulation uses the grounded dielectric slab Green's function to account rigorously for the presence of the substrate and surface waves. Both entire basis (EB) and piecewise sinosoidal (PWS) expansion modes are used, and their relative advantages are noted. Calculations of input impedance and mutual coupling are compared with measured data and other calculatious.     

Defected ground structure to reduce mutual coupling between cylindrical dielectric resonator antennas

Use of a simple ring-shaped defected ground structure is experimentally demonstrated to suppress considerable mutual coupling between two cylindrical dielectric resonators. About 5 dB suppression has been obtained near the operating frequency around 3.3 GHz. The radiation characteristics with and without defect in the ground plane are also reported.     

The near field of annular antennas

The circular loop antenna has been investigated by many authors beginning as early as 1897 with Pocklington's study of the thin wire loop excited by a plane wave. Later, both Hallen and Storer considered the case of driven antennas. All of these authors used a Fourier series expansion for the loop current, and the latter two found numerical difficulties with the approach. These difficulties, as pointed out by Wu, can be avoided by integration of the free-space Green's function over the toroidal surface of the wire. The theory developed here is an improvement on previous works because it specifically takes into account the finite dimension of the wire. Consequently, the range of validity for our solution extends to fatter wires than previously considered. Furthermore, some detail of the loop current around the cross section of the wire is revealed. The theory, if applied to thin wire loops, gives radiation admittances in excellent agreement with results obtained by previous investigators. The computations of the electromagnetic fields near resonant loops show that the electric field strength is larger by a factor of ten than previously published values. Experimental results validate the theory presented in the following sections.     

Scattering properties and mutual coupling of antennas with prescribed radiation pattern

An analysis is presented of the interrelations among the radiative, scattering, and coupling properties of arbitrary lossless antennas. The analysis is based on a well-known scattering representation of antennas in terms of spherical modes in free space. This scattering representation is given a network interpretation which brings into focus the degree of interdependence between scattering and radiation characteristics. The scattering matrix of a reciprocal antenna with one port and a prescribed radiation pattern is represented in a canonical form which exhibits explicitly the permissible range of adjustments in the antenna scattering characteristics. The significance of the canonical form is examined from several points of view, noting in particular its connection with the concept of resonant modes of a scatterer. The network interpretation also facilitates the evaluation of mutual coupling, and the mutual impedance between two antennas is expressed explicitly in terms of the radiative and scattering parameters of each antenna. It is shown that, generally, the mutual impedance may be expressed as a sum of two terms: a zeroth-order term, dependent exclusively on the radiation pattern, and a second term involving the scattering properties as well as the radiation patterns. Under certain conditions the mutual impedance may be approximated by the zeroth-order term alone. It is also shown that a similar zeroth-order approximation of the active impedance in an infinite planar phased array leads to a grating lobe series type of representation.     

Relationships between squinted, sum and difference radiation patterns of amplitude monopulse antennas with mutual coupling between feeds

The relationships between the squinted beams and sum and difference beams of amplitude monopulse antennas are usually given on the basis that mutual coupling between feeds is negligible. These relationships can lead to gross conceptual errors regarding the basic capabilities of amplitude monopulse antennas. This paper develops similar relationships which include the effects of mutual coupling. It is found that the sum and difference beams are still proportional to the sum and to the difference of the squinted beams but the constants of proportionality, which are related to the VSWR's at the sum and difference ports before matching, are generally different. These constants of proportionality, or VSWR's, can be evaluated in terms of the squinted beams in the case of lossless antennas by applying the principle of conservation of energy. The matched sum pattern gain on boresight and the matched difference pattern slope on boresight are computed for a lossless antenna with squinted beams of the formsin ktheta/kthetaversus squint angle. The results obtained are drastically different from previously published results. Both of these antenna parameters are maximum in the limit of zero squint angle. However, for these squinted beam shapes, a small squint angle implies that a very high VSWR is to be matched at the difference port. It is noted that a given pair of matched sum and difference patterns can be produced by different pairs of squinted beams. These pairs of squinted beams can differ in their amplitudes and shapes. However, a single pair of squinted beams corresponds to inherently matched sum and difference ports.