A note on the coupling efficiency between an antenna and a Gaussian beam

In this communication a note on the coupling efficiency between an antenna and a Gaussian beam is presented. The calculations of the coupling efficiency from both methods, a nomorlized inner product between the antenna radiation pattern and the Gaussian-beam pattern or alternatively, between the electric field at the antenna aperture and a two-dimensional field representation of a Gaussian beam, are compared for different aperture size in wavelength. How a correct solution can be gotten is stated.     

TEM coupling between orthogonal crossing wires: a closed-formapproximation

The equations describing the coupling mechanism between two crossing, orthogonal thin wires over a perfectly conducting ground plane are derived from first principles. Cast in the form of two cross-coupled Fredholm integral equations of the second kind, the equations are manipulated in such a way as to show the nature of the coupling between the TEM modes, the evanescent modes and the radiation terms. The assumption is made that the coupling between the evanescent and radiation terms to the TEM mode is weak after the first wave bounce. By neglecting such effects, we derive a closed-form approximation for the equivalent lumped junction capacitances. The resulting expressions are surprisingly simple and are amenable to desktop calculation. The final formulas are numerically compared with previously published data     

Mutual coupling reduction in an antenna array by using two parasitic microstrips

This paper presents a new method of reduction mutual coupling. The proposed antenna array operating at 2.4 GHz is comprised of two rectangular patches and two parasitic microstrips, the parasitic microstrips are printed on substrate top layer over two rectangular patches. The measured results indicate that the mutual coupling is greatly suppressed, which becomes to −32 dB from −13.4 dB, and the radiation patterns are practically unaffected, as demonstrated by the comparison of identical antenna arrays with and without parasitic microstrips.     

Study of the magnetic coupling between a SQUID and wires integratedon a chip

Magnetic coupling between a SQUID and wires in an integrated circuit has been studied. Using test integrated circuits, the coupling is measured by varying the distance from the SQUID to each wire. The coupling between the SQUID and the wires with and without a groundplane decreases with an increase in the distance. The coupling for the wires with the groundplane is smaller than that for the wires without the groundplane at distances less than 595 μm. However, the rate of the decrease in the coupling for the wires with the groundplane falls off for distances more than 595 μm and the coupling converges to around 2.9 pH. From two dimensional simulations for the magnetic flux coupling, the origin of the residual inductance is found to be the coupling between the SQUID, and shielding current in the groundplane. The value of the distance, 595 μm, does not depend on the size of the SQUID. To decrease the coupling, the use of wires with stripline structure or coplanar structure is desirable     

Longitudinal coupling between elements in a disc-on-rod antenna array

A general expression is proposed for the coupling of surface wave antennas based on the equivalence principle and on the reciprocity theorem. A particular application is presented for disc-on-rod antennas, and the coupling coefficient is evaluated as a function of frequency, the array parameters and the element parameters. A physical explanation of the results is suggested.     

Analysis of mutual coupling between an infinite phased array ofhorizontal dipoles and vertical wires

A theoretical method is presented to analyze the radiation characteristics of an infinite phased array of horizontal dipoles in the presence of adjacent vertical wires protruding out of the ground plane. Green's functions for vertical and horizontal δ-sources in a unit cell are derived in terms of Floquet modes. By superposition of the Green's functions, the E- and H-fields in a unit cell are obtained. The current distributions and the input radiation impedances of the dipole array are obtained by making use of the method of moments. Numerical examples are given to show the coupling effects. Measurements of the radiation impedances in a waveguide simulator with and without the coupling effects due to the vertical wires have been conducted to verify the theoretical model. The general trend of measured data has been predicted quite well by the theoretical computation     

Electromagnetic coupling between wires inside a rectangular cavityusing multiple-mode-analogous-transmission-line circuit theory

This paper examines the coupling between two arbitrarily positioned wire segments inside a rectangular enclosure. The enclosure is treated as a superposition of analogous transmission lines which have been short circuited at two positions on the propagation axis. Each analogous transmission line is associated with a particular waveguide mode in the cavity. Previous work has used this analogy to predict the coupling between two monopoles inside a small box using the dominant TE ₁₀ mode. This paper considers the general case of high-frequency coupling between two wire monopoles in a large rectangular cavity, where several higher order modes are active. By taking into account higher order modes, and the mutual coupling between the modes, a simple equivalent circuit is presented which can give a prediction for the coupling between the monopoles. Experimental results for various monopole pair positions are shown, which indicate the success of the multimode theory. The technique requires far less computer resources than traditional methods for solving such a problem (e.g., MoM, TLM or FDTD), with solution times of less than a second on an average PC. In addition, considerable insight into the coupling process can be gained by including or excluding particular waveguide modes. This is not possible with numerical methods     

An analysis of antenna coupling between arrays on a polyhedronstructure

Antenna coupling between arrays on a polyhedron structure is investigated. First of all, a high-frequency asymptotic closed-form formula is derived for the mutual admittance between two linearly polarized circular microstrip antennas located on the different faces of a perfectly conducting wedge. The microstrip antennas are modeled by the cavity model, and the mutual coupling caused by the wedge-diffracted field is analyzed by the EMF method using Keller's GTD diffraction coefficients for the diffracted field. Next, the antenna coupling between arrays is calculated and compared with an experimental result. Good agreement between them supports the theory. Finally, the properties of the antenna coupling are described by some numerical simulations     

基于液态金属的频率可重构天线新设计

提出一种新型的液态金属频率可重构天线设计方法。以对称振子天线为原型,采用镓铟液态合金(EGaIn)为辐射元,将其包裹在微流体通道内。在天线适当位置开口添加绝缘片,呈断路状态;撤掉绝缘片,利用液态金属自我修复性能,加热挤压切口使其愈合,呈通路状态;通过调节绝缘片的位置实现1.6~3.0 GHz频率范围内的重构,并通过曲线拟合提出了适合该天线的工作频率估算公式。仿真结果表明天线具有良好的带宽、阻抗特性,并保持较高增益,辐射性能良好。     

Analysis of an antenna composed of arbitrarily located slots and wires

A technique of analyzing an antenna composed of arbitrarily oriented thin wires and slots in a planar conducting screen is presented. The analysis is based on the generalized Hallen's type integral equation with closed form kernel. A parametric evaluation is done for a configuration of slot and two bending wires (Clavin element). The results obtained are shown to be in close agreement with the experimental ones obtained by Clavin et al.     

The radiation efficiency of a dipole antenna located above an imperfectly conducting ground

The dyadic Green's function technique is used to develop integral expressions for the radiation efficiency of three types of dipole antennas located above an imperfectly conducting, infinite ground plane. The three antennas treated are: 1) vertical Hertzian dipole, 2) horizontal Hertzian dipole, and 3) a vertical half-wave dipole with sinusoidal current distribution. The results of numerical evaluation of the integral expressions for several values of ground constants are presented in graphical form. The radiation efficiency of a vertical Hertzian dipole is found to exhibit a distinct peak when located at a height of one-eighth wavelength.     

A curved spiral antenna above a conducting cylinder

A curved spiral antenna above a finite hollow conducting cylinder is analyzed using the method of moments. The effects of cylinder length 2H and cylinder radius r_cy on the radiation characteristics of the spiral are evaluated. As 2H increases, the cross-polarization component of the radiation field in the broadside direction decreases to a constant value (approximately -18 dB). When 2H is greater than one wavelength (λ₀), the input impedance of the spiral above a cylinder of radius r_cy=0.25 λ₀ is almost constant (250-j20 Ω) with a gain of approximately 7 dB. The spiral above a cylinder of (2H, r_cy)=(2.7 λ₀, 0.25 λ₀) shows a 3-dB axial ratio bandwidth of approximately 23%, which is wider than a flat spiral antenna above a flat ground plane of infinite extent     

Wide-band microstrip antenna with an H-shaped coupling aperture

Theoretical and experimental results of a wide-band planar antenna are presented. This antenna can achieve a wide bandwidth, low cross-polarization levels, and low backward radiation levels. For wide bandwidth and easy integration with active circuits, it uses aperture-coupled stacked square patches. The coupling aperture is an H-shaped aperture. Based on the finite-difference time-domain method, a parametric study of the input impedance of the antenna is presented, and effects of each parameter on the antenna impedance are illustrated. One antenna is also designed, fabricated, and measured. The measured return loss exhibits an impedance bandwidth of 21.7%. The cross-polarization levels in both E and H planes are better than 23 dB. The front-to-back ratio of the antenna radiation pattern is better than 22 dB. Both theoretical and experimental results of S parameters and radiation patterns are presented and discussed     

Efficient upconversion by a frequency factor between two and threeusing an optical parametric oscillator

We present the theory of a scheme for frequency up-conversion from pump frequency ω_p to a desired frequency ω_d between 2ω_p and 3ω_p. The proposed device consists of three nonlinear crystals in series inside a cavity resonating light at a signal frequency ωs. Sum-frequency generation (SFG) in the first crystal produces the desired radiation, ω_s+ω_p=ω_d. Second-harmonic generation (SHG) in the second crystal doubles the frequency of the residual pump, 2ω_p=ω_h, while the signal passes through unaffected. Optical parametric oscillation (OPO) in the third crystal generates the signal and idler frequencies, ω_h=ω_s+ω. A plane-wave analysis predicts a quantum efficiency close to 30% over an extended range of pump intensity. Iteration of the plane-wave solutions over many passes yields dynamics very similar to that recently calculated for the SFG-OPO device. As in that device, a small detuning of the SFG interaction enlarges the dynamic range yielding stable operation. Highest efficiency occurs when ω_i is at the low-frequency end of the OPO crystal transmission window. As an example, we consider a device using a noncritically phase-matched KTP SFG crystal, a quartz crystal polarization rotator, an angle-tuned KTP SHG crystal, and a noncritically phase-matched LiNbO₃ OPO crystal. This device is designed to convert λ_p=1.064 μm to λ_d=0.455 μm. We calculate a power conversion efficiency as great as 73%     

外场作用双导线的电磁耦合时域分析方法

基于时域有限差分（finite-difference time-domain，FDTD）法和传输线方程，并结合插值技术，研究了一种高效的时域混合算法，能够快速模拟电磁波照射自由空间和屏蔽腔内双导体传输线的电磁耦合，并实现空间电磁场与双导线瞬态响应的同步计算.该算法先采用FDTD方法模拟双导线周围空间的电磁场分布，结合插值技术构建适用于双导线电磁耦合的传输线方程，再采用FDTD的中心差分格式进行离散，从而求解得到传输线和端接负载上的瞬态响应.同时，分析双导线间距对其电磁耦合的影响，掌握其耦合规律.通过相应数值算例的模拟，并与FDTD方法进行对比，验证了该时域混合算法的正确性和高效性.     

Technique for improving coupling between microstripline anddielectric resonator antenna

A cylindrical dielectric resonator antenna fed by a microstripline is studied. By connecting a vertical strip at the end of the microstripline, the input matching of a dielectric resonator antenna can be improved substantially. Moreover, it offers an impedance bandwidth as wide as 19% and a stable radiation pattern across the operating frequency range     

Network modeling of an aperture coupling between microstrip lineand patch antenna for active array applications

An analytical method based on the aperture coupling theory and the derivation of the S-parameter matrix has been developed for modeling a microstrip line coupled to a microstrip patch antenna using a circular coupling aperture. Closed-form solutions were derived for scattering parameters of the coupling circuit. Input impedance and matching condition can be calculated from the equivalent six-port network. The theoretical results agree well with the measurements. The analysis should have many applications in active array and spatial power combining systems     

Stop-band characterization of an isolated DGS for reducing mutual coupling between adjacent antenna elements and experimental verification for dielectric resonator antenna array

A new technique to characterize an isolated defected ground structure (DGS) is explored. The technique is used to optimize the dimensions of a compact partial-ring DGS to suppress mutual coupling between two E-plane coupled cylindrical dielectric resonator antennas. The optimized design is verified experimentally using a set of fabricated prototypes operating in S-band. A suppression up to 6–7 dB, showing good agreement with the predicted values, is experimentally demonstrated.     

Input impedance of a dipole antenna above a conducting half space

The derivation of an expression for the change in free space input impedance of a finite horizontal dipole, due to the proximity of a conducting half space, is outlined. The impedance change is expressed in a conveniently computable form in terms of the Fourier transform of the antenna current distribution. Using available transforms some typical results are shown over a 50:1 frequency range.     

Mutual coupling between two circular waveguides

The problem of coupling between two circular waveguides is solved using the Wiener-Hopf technique. Expressions for the radiated, reflected, and the transmitted fields are obtained and are expressed by three terms. The first term in these expressions represents the solution for an open ended circular waveguide, while the other two are due to the interaction between the two waveguides. It is shown that, the radiated, reflected, and the transmitted fields can also be found from the reflection coefficient of an open ended circular waveguide and an evaluation of a semi-infinite integral involving the fourier transformed Green's function of the Weiner-Hopf equation. Exact solutions are used to generate the approximate solution of the ray theory of diffraction. This is achieved by expanding the exact solution and using the modified diffraction coefficient of Lee in conjunction with a spherical wave-factor.