Efficiency and gain of slot antennas and arrays on thick dielectric substrates for millimeter-wave applications: a unified approach

A unified approach for representing the surface-wave fields and for computing the corresponding radiation efficiencies from arbitrarily shaped slot-type antennas on thick dielectric substrates at millimeter-wave (mm-wave) frequencies is presented. In this approach, two different representations of the surface-wave fields, i.e., the one based on the idea that the surface-wave power can be associated with a substrate radiation pattern and the other based on the cylindrical wave expansion, are linked together in a unified way. The developed theory is then applied for investigating the surface wave characteristics of printed twin offset slots and uniform linear slot arrays. Based on the developed theory, new insight into the mechanism with which surface-wave power is coupled by the slot pair is presented. Subsequently, the optimum number of elements and corresponding interelement spacing for linear, uniformly excited, slot dipole arrays is explored for achieving maximum radiation efficiency and gain. In order to provide guidance on practical mm-wave integrated slot antenna array design, supportive numerical results are presented for Substrates of dielectric constant /spl epsi//sub r/ = 4.0 and /spl epsi//sub r/ = 12.0.     

Full-wave spectral-domain computation of material, radiation, andguided wave losses in infinite multilayered printed transmission lines

A unified solution for full-wave computation of losses in a general multilayered planar transmission line is presented. It includes material losses (dielectric and conductor losses), losses due to radiation leakage, and losses caused by leakage of power to source-free characteristic modes (surface-wave or waveguide modes, for example) of the multilayered geometry. A spectral-domain moment method is used with the Galerkin testing procedure. Significant modification of the conventional spectral-domain analysis of planar transmission lines is necessary in enforcing proper boundary conditions in the Galerkin testing procedure and, more importantly, in accounting for poles and branch cuts in the complex Fourier transform domain in order to rigorously account for the different loss mechanisms discussed. Results for a few representative geometries, namely, strip and/or material loss in a microstrip line and a slotline, surface parallel plate mode leakage loss in a conductor-backed slotline and a two-layer stripline, and radiation loss in a single and a coupled stripline at the interface between two infinite mediums, are presented to demonstrate these various loss effects     

Computations for radiation and surface-wave losses in coplanarwaveguide bandpass filters

A new approach is developed to simulate both radiation and surface-wave losses in general coplanar waveguide (CPW) discontinuity structures. The newly derived formulas are concise, simple, and efficient for computation. Full-wave characterization of CPW filter structures are first accomplished by the mixed-potential integral equation and the method of moments. Given equivalent magnetic-current distributions on the apertures of a CPW, the matrix pencil approach is applied to extract the scattering parameters and the new formulas are employed to obtain the losses and far-field patterns of the space-wave radiation and surface wave. Simulation of the calculated radiation and surface-wave losses by field theory is found to be consistent to the total power loss determined from the scattering parameters by circuit theory, which verifies the correctness of our new expressions     

Design of a single-mode tapered waveguide for low-losschip-to-fiber coupling

The novel waveguide structures described in this paper have nonlinearly tapered shapes that result in low radiation losses despite their relatively short lengths. The core at the waveguide endface connected with the fiber has a very small cross section and an expanded mode field with a non-Gaussian shape. The taper structures are analyzed by using an improved step-transition method. This method is a based on the theory of enclosing a waveguide within electrical walls and that can therefore treat the radiation modes in a tapered waveguide as discrete mode spectra. Analyzing the relationships between the lengths and shapes of the tapers and the radiation loss due to the tapers show that appropriately tapered semiconductor waveguides operating at an optical wavelength of 1.55 μm and having a taper length of less than 0.7 mm can have a radiation loss of only 0.1 dB and a coupling loss with a conventional single-mode fiber of less than 0.5 dB     

Space wave radiation efficiency of a wraparound antenna and theeffect of surface wave radiation due to the dielectric substratetruncation

A theoretical study of the problem of excitation of surface waves in wraparound microstrip antennas is presented. The surface waves are obtained by using a contour integral in the complex plane. The surface-wave energy loss in the antenna truncation region is partially radiated and interfaces with the space wave. The radiation efficiency and the effect of the dielectric substrate truncation of the antenna radiation pattern are shown as functions of antenna dimensions and for two values of substrate dielectric constants     

A generalized method for distinguishing between radiation andsurface-wave losses in microstrip discontinuities

A generalized method for calculating both radiation and surface-wave losses is developed for microstrip discontinuities. The losses are determined by a rigorous Poynting vector analysis where the current distribution over the microstrip discontinuities is a result of a full-wave moment method solution. The power loss mechanism of such microstrip discontinuities as open-end, right-angle-bend, gap and stub lines, EMC lines, and rectangular patches are investigated. A self-consistency check of the result based on power conservation is performed to confirm the numerical results. It is found that, above a certain frequency, the surface-wave loss becomes more important than the radiation loss     

Radiation Fields of a Tapered Film and a Novel Film-to-Fiber Coupler

Light in a tapered thin-film optical waveguide radiates into the substrate because the waveguide mode in the taper becomes cut off. Our measurement of the radiation pattern shows that the light emerges from the taper as a narrow beam with an angular width of only 2/spl deg/-4/spl deg/. We have studied the problem based on ray optics and based on a wave theory of radiation modes. We also have demonstrated a film-to-fiber coupler in which an optical fiber collects all the light emerging from the taper.     

Metal wave-guide to dielectric image guide transition using exponential taper

A unique metal wave guide to dielectric image guide transition has been developed using exponential taper in dielectric wave guide. The propagation characteristics have been computed theoretically and taper impedance for the different cross-sections have been evaluated, so as to match it with the metal wave guide for efficient mode conversion. Transmission loss and return loss for triangular and exponentail taper with frequency for same dimensional parameters have been measured.     

Microstrip patch designs that do not excite surface waves

Two variations of a circular microstrip patch design are presented which excite very little surface wave power. Both of the designs are based on the principle that a ring of magnetic current in a substrate (which models the patches) will not excite the dominant TM₀ surface wave if the radius of the ring is a particular critical value. Numerical results for radiation efficiency and radiated field strength from a ring of magnetic current are shown to verify this basic design principle. The proposed patch designs are chosen to have a radius equal to this critical value, while maintaining resonance at the design frequency. The designs excite very little surface-wave power, and thus have smoother radiation patterns when mounted on finite-size ground planes, due to reduced surface-wave diffraction. They also have reduced mutual coupling, due to the reduced surface-wave excitation. Measured results for radiation patterns and field strength within the substrate are presented to verify the theoretical concepts     

用于空间功率合成的新型22渐变鳍线阵分析与设计

渐变鳍线阵在空间功率合成放大器中具有重要的应用价值。该文简化渐变鳍线阵的模型,将渐变鳍线阵设计等效为TE模式波阻抗的渐变阻抗变换,采用谱域导纳法计算渐变鳍线阵的传播常数,依据小反射理论,提出一种新型基于Hecken形式的紧凑、宽带渐变鳍线阵。利用高频仿真软件HFSS进行优化仿真设计,通过引入槽线微带过渡电路,实际加工了X波段22鳍线阵,背靠背测试结果表明:在X波段(8~12 GHz)内,反射系数小于-12 dB,插入损耗小于1 dB,实测结果与理论计算吻合。该文系统地给出渐变鳍线阵设计优化的理论计算和仿真方法,对基于波导内空间功率合成模块设计具有指导意义,具有良好的工程应用前景。     

Radiation losses of tapered dielectric waveguides: a finitedifference analysis with ridge waveguide applications

The finite-difference third-order simplified wave equation method is used to study the radiation losses of optical waveguides with step (abrupt) and parabolic tapers, including the radiation losses of the tapered ridge waveguides used as electro-optic phase modulators for tuning the frequencies of infrared lasers. The radiation losses of the parabolic taper given by Burns et al. is found to be under 5%. The results of a step taper are compared with Marcuse's; and found to be in good agreement. The numerical results are also compared with those from the coupled wave equations used by Sporloder and Unger     

A Method for Accurate Design of a Broad-Band Multibranch Waveguide Coupler

A new approach is made to the problem of tapering the branch impedances for broad-band performance. A taper is proposed, which, for a 3-db branch coupler, is shown to give much better results in theory and practice than the currently used binomial taper. Also, simple expressions are developed which enable the effects of waveguide junction discontinuities to be adequately corrected, thus allowing a greater accuracy in design to be achieved than was hitherto possible.     

High-gain meanderless slot arrays on electrically thick substratesat millimeter-wave frequencies

Introduces new techniques and architectures for the implementation of linear slot arrays on electrically thick dielectric substrates at millimeter-wave frequencies. The slot arrays are fed by a coplanar waveguide series line and lead to high gain by utilizing the phase cancellation technique to reduce coupling to the dominant surface-wave mode. Unlike traditional designs, no meander lines are used in the proposed structures, easing their fabrication by eliminating the need for air bridges and leading to patterns with low cross-polarization and high gain. In addition, the option of including a backing ground reflector to render the patterns unidirectional is explored and implemented. In this latter case, it is shown that simultaneous reduction of the dominant surface-wave and TEM modes through phase cancellation can be achieved. The design of the proposed arrays is based on an intuitive transmission-line model, which enables the implementation of arrays with a gradual current taper and, thus, maximum gain. This study is verified experimentally around a nominal frequency of 27.8 GHz     

Mode conversion in planar-dielectric separating waveguides

The mode-conversion behavior of branching or separating planar-dielectric waveguides is studied theoretically as a function of branch asymmetry and taper slope. When the taper slope is large in a near-symmetric structure, considerable mode conversion will occur and the structure will act as a power divider. In an asymmetric structure with small taper slope, mode conversion is negligible and the structure will act as a mode splitter. A quantitative formula is presented which can be used to determine the behavior of a given separating structure.     

Bilevel mode converter between a silicon nanowire waveguide and a larger waveguide

A bilevel mode converter is analyzed for providing low-loss coupling between the small fundamental mode of a silicon nanowire waveguide and the larger mode of a conventional silicon-on-insulator (SOI) rib waveguide. The bilevel converter can also be used to improve the coupling efficiency between a lensed fiber and a silicon nanowire waveguide. The mode converter consists of two tapers formed at different levels. The top taper comprises a parabolic and sine taper, which is optimized to improve the mode conversion efficiency. Numerical analyses are given by using a three-dimensional semivectorial beam propagation method. The design has good tolerance against misalignment of the two masks needed for the double etch.     

短波天波反射/地波绕射组合新传播模式及其可能应用

把电离层反射传播模式和地波绕射传播模式组合成新的传播模式.对这一新传播模式的构建形式、新模式的路径损耗因子、频域多普勒谱特性、工作频率特性等传播特性以及它的可能应用进行了研究.以天波/地波集成体制超视距雷达系统作为一种应用,导出了其雷达方程、定位方程和信息处理过程模型.具体的算例表明,该雷达体制有好的可行性.     

TM surface-wave power combining by a planar active-lens amplifier

Power combining of TM surface waves by a planar active-lens amplifier is the subject of this paper. An amplifier gain of 11 dB at 8.25 GHz with a 3-dB bandwidth of 0.65 GHz has been demonstrated. Gain is measured from input to output connector to facilitate comparisons with more conventional amplifiers. Measurements of output power versus input power are also presented. The amplifier behaved in a linear manner and no problems with spurious oscillations were encountered. Construction of the amplifier is compatible with planar fabrication technologies. A key component of the combiner is a microstrip-fed Yagi-Uda slot-array antenna for TM surface-wave excitation of a thick dielectric slab. Design and optimization guidelines for the antenna are presented as well as detailed spectral-domain and finite-difference time-domain (FDTD) analysis results. Measured and simulation results show an input return loss and front-to-back ratio better than 10 dB over a 5% bandwidth. Calculated and measured results for the fields radiated by the antenna confirm forward radiation of the dominant TM mode in the thick dielectric slab. Integration of the computed radiated fields shows the antenna has a surface-wave launching efficiency of 85%     

Coupled mode analysis of dielectric planar branching waveguides

The mode conversion behavior of planar dielectric branching waveguides is studied as a function of branching angle, propagation direction of modes, and thickness ratio of branches. The multimode coupled equation and new step approximation method of branch taper are introduced, which give the accurate analysis of mode behavior in the branching waveguide of a large taper angle.     

Surface waves on a lossy planar ferrite slab

The parallel-polarized surface waves which propagate on a planar ferrite slab are considered. The ferrite material is isotropic and homogeneous, the slab rests on a perfectly conducting ground plane, and the ambient medium is free space. Only one mode can propagate on a thin lossless slab, but more and more of the higher order modes begin to propagate when one increases the thickness or the loss tangent of the slab. As the thickness and the loss are increased, the lowest order mode takes on the properties of the Zenneck wave. At the same time, the higher order modes take on the properties of a homogeneous plane wave propagating in the grazing direction in the slab. Among the most interesting properties of a surface wave are the attenuation constant and the phase velocity. Contour maps are included to show how these quantities depend on the thickness, permittivity, permeability and loss tangents of the ferrite slab. Additional insight is provided by graphs showing the root trajectories, cutoff boundaries and field distributions of the four lowest order surface-wave modes.     

0.22 THz回旋管渐变输出结构的设计和分析

从渐变波导耦合波方程出发,设计了0.22 THz回旋管两种渐变输出结构,上升余弦和Dolph-Chebychev渐变波导过渡器;三维电磁仿真软件HFSS对这两种波导数值模拟验证的结果表明:两种渐变波导都符合设计要求,但是改进的Dol—ph-Chebychev渐变波导要比上升余弦渐变波导短,从而得到作为传输TE_(03)模回旋管输出段的最优波导过度器。