Frequency-selective reflection and transmission by a periodicdielectric layer

The feasibility of using a periodic dielectric layer, composed of alternating bars having dielectric constants ϵ₁ and ϵ₂, as a dichroic surface at millimeter-wave frequencies is examined. For oblique incidence, it is found that total transmission and total reflection can be obtained at different frequencies for proper choices of ϵ₁ and ϵ₂ and the geometric parameters. The frequencies of total reflection and transmission can be estimated from wave phenomena occurring in a layer of uniform dielectric constant equal to the average value in the periodic layers. For some of the frequencies of total transmission, the bandwidth for 90% transmission is found to be 40%. The bandwidth for 90% reflection is always found to be much narrower, the greatest value obtained being 2.5%     

Radiation from cylindrical leaky waves

Formulas are derived for the far-infrared radiation pattern of cylindrical leaky waves propagating on a planar surface. The formulas can be used to predict the radiation pattern of a general class of leaky-wave antennas, consisting of a finite-size source which excites a radially propagating leaky wave on some planar surface. Leaky-wave antennas consisting of antenna elements embedded in dielectric layers (microstrip elements) fall into this category. Using the equivalence principle, formulas are derived for both transverse electric (TE) and transverse magnetic (TM) leaky waves with arbitrary propagation constants. The formulas allow for radiation from cylindrical apertures of arbitrary size, so that the effect of truncating the supporting planar surface with an absorbing material can be determined. Particular attention is devoted to the case of a leaky wave for which the real and imaginary parts of the complex propagation constant are equal, since this type of wave has been shown to be responsible for broadside radiation in certain leaky-wave antennas comprised of dielectric layers     

The axisymmetric modes in a longitudinal inhomogeneous SELFOC fiber

The authors consider the propagation characteristics and mode conversion of axisymmetric modes in an imperfect SELFOC fiber with longitudinal gradually varying dielectric constant K=ϵ/ϵ₀=K₀-K ₂(z)r². An analytic solution which is expressed in terms of generalized Laguerre polynomials is found     

Deep field penetration into a conducting cylinder

In this paper we investigate the penetration of both E and H waves into a cylinder of arbitrary cross section (characteristic dimension L). The material of the cylinder is a nonmagnetic good conductor, and we examine the limits of deep penetration (small L/δ, where δ is the penetration depth) and small quality factor Q=(ωϵ₀/σ). These two asymptotic conditions imply a low-frequency situation, for which we derive formulas for the induced currents and associated Joule and radiation losses     

Bilayered dielectric measurement with an open-ended coaxial probe

An equivalent circuit of an open-ended coaxial line used as a probe for bilayered dielectric measurement which consists of three parallel capacitances C_f, C₀ϵ₁ and C₁(ϵ₂≫-ϵ₁) is presented. The measurement method, based on both the analytical expression of the probe's equivalent circuit and the bilinear transformation relationships between the equivalent admittance of the probe and the reflection coefficient and between the real reflection coefficient and the measured reflection coefficient, is described. With using this method, the measurements were made in 0.6-2.6 6Hz. The results show that the permittivity of either layer of bilayered dielectrics can be determined by using the measured reflection coefficients without knowledge of equivalent capacitances C_f, C₀ and C₁(t) or the thickness of the first layer medium     

Theoretical analysis of coupling and cross polarization ofperpendicular slot antennas on a dielectric half-space

In this paper, design curves are given for minimizing the coupling between two perpendicular slot antennas on a dielectric half space. Such antennas may be utilized in polarimetric receivers in which coupling must be minimized to ensure polarization purity and in polarization diplexed quasi-optical receivers in which the local oscillator (LO) is received in a polarization perpendicular to that of the RF signal. For this analysis, Galerkin's method in the spectral domain is applied along the length of the slots and point matching across their widths. At the second resonance, for equal length slots and for constant width/length (w/L) of the slots, there is a decrease of about 2-dB coupling for a factor of three increase in dielectric constant (ϵ₁=1.0→3.8 and ϵ₁=3.8→12.8). For fixed dielectric constant there is a 1-2-dB increase in coupling for a factor of two increase in w/L. For slots of unequal length (L₂=L₁/2), the changes are even smaller. Design curves are shown for various relative positions of the slots in two dimensions. A strong correlation between coupling levels and peak cross-polarization levels is found     

The inductance matrix of a multiconductor transmission line inmultiple magnetic media

A simple relationship between the inductance matrix and the auxiliary capacitance matrix is given. For a multiconductor transmission line consisting of N_c conducting cylinders in inhomogeneous media consisting of N_d homogeneous regions with permeabilities μ_i and permittivities ϵ _i, the inductance matrix [L] for the line is obtained by solving the magnetostatic problem of N_c conductors in N_d regions with permeabilities μ _i. The capacitance matrix [C] for the line is obtained by solving the electrostatic problem of N_c conductors in N_d regions with permittivities ϵ _i. It is shown that [L]=μ₀ϵ₀[C^'] ^-1, where [C^'] is the capacitance matrix of an auxiliary electrostatic problem of N_c conductors in N_d regions with relative permittivities set equal to the reciprocals of the relative permeabilities of the magnetostatic problem, i.e. ϵ^' _i/ϵ₀=μ₀/μ_i     

Slot excitation of the dielectric disk radiator

Dielectric disk radiators which are excited by a narrow slot in the ground plane of a microstrip line are investigated. The resonance frequencies of the dielectric disk for the HEM₁₁ mode are computed numerically in the complex frequency plane. From the later results, the actual resonance frequency and the Q-factor are obtained. The dielectric disk is made of a high dielectric constant ceramic material with ϵ_r=22. The radiation patterns and reflection coefficients are measured and presented for several slot lengths and dielectric disk dimensions. The radiation patterns are also computed assuming a magnetic current element, which models the slot and excites the HEM₁₁ mode. Good agreement is obtained between the computed and measured results. The results presented here also demonstrate the viability of this type of antenna, which has high dielectric constants an efficient radiator provided the proper mode is excited     

Radiation from one-dimensional dielectric leaky-wave antennas

Dielectric leaky-wave antennas consist of multiple dielectric layers above a ground plane, along with a simple source such as an infinite line current in the one-dimensional case. The layers act as a guiding structure for one or more leaky waves, which are responsible for producing a narrow-beam radiation pattern. Depending on the beam angle, the leaky waves may extend for a considerable distance from the source, and thus experience truncation effects due to a finite-size substrate. One of the purposes of the present investigation is to study efficient methods for calculating the patterns under such conditions. The chirp z-transform (CZT) is shown to be very efficient for this. Simple approximate formulas for calculating the radiation pattern are also investigated. In addition, a study is also made of the different contributions to the total aperture field, including the leaky-wave field, the space-wave field, and the surface-wave field     

A dispersion formula satisfying recent requirements in microstripCAD

A dispersion formula ϵ^*_eff(f)=ϵ^* -{ϵ^*-ϵ^*_eff(0)}/{1+( f/f₅₀)^m}, for the effective relative permittivity ϵ^*_eff(f) of an open microstrip line is derived for computer-aided design (CAD) use. The 50% dispersion point (the frequency f₅₀ at which ϵ^*_eff(f₅₀)={ϵ ^*+ϵ^*_eff(0)}/2}) is used a normalizing frequency in the proposed formula, and an expression for f₅₀ is derived. To obtain the best fit of ϵ ^*_eff(f) to the theoretical numerical model, the power m of the normalized frequency in the proposed formula is expressed as a function of width-to-height ratio w/ h for w/h⩾0.7 and as a function of w /h, f₅₀, and f for w/h⩽0.7. The present formula has a high degree of accuracy, better than 0.6% in the range 0.1<w/h⩽10, 1<ϵ^*⩽128, and any height-to-wavelength ratio h/λ₀     

Bayesian estimation of soil parameters from radar backscatter data

Given measurements m₁,m₂,...,m_J representing radar cross-sections of a given resolution element at different polarizations and/or different frequency bands, the authors consider the problem of making an “optimal” estimate of the actual dielectric constant ϵ and the rms surface height h that gave rise to the particular {m_j} observed. To obtain such an algorithm, the authors start with a data catalog consisting of careful measurements of the soil parameters ϵ and h, and the corresponding remote sensing data {m_j}. They also assume that they have used these data to write down, for each j, an average formula which associates an approximate value of m_j to a given pair (ϵ;h). Instead of deterministically inverting these average formulas, they propose to use the data catalog more fully and quantify the spread of the measurements about the average formula, then incorporate this information into the inversion algorithm. This paper describes how they accomplish this using a Bayesian approach. In fact, their method allows them to (1) make an estimate of ϵ and h that is optimal according to the authors' criteria; (2) place a quantitatively honest error bar on each estimate, as a function of the actual values of the remote sensing measurements; (3) fine-tune the initial formulas expressing the dependence of the remote sensing data on the soil parameters; (4) take into account as many (or as few) remote sensing measurements as they like in making their estimates of ϵ and h, in each case producing error bars to quantify the benefits of using a particular combination of measurements     

Surface wave excitation on a microstrip ring antenna

A theoretical analysis of the excitation of surface waves on a microstrip ring antenna is presented. The problem is formulated using dyadic Green's functions in a layered medium with magnetic-type equivalent current sources. The integral equation for the fields is solved in the wave number complex plane so that the fields from space and surface waves are obtained separately. The space wave radiation efficiency is calculated for the TM₁₁, TM₁₂, and TM₁₃ modes for various values of the normalized dielectric substrate thickness, d/λ₀. It is noted that the TM₁₃ mode radiates more efficiently than the TM₁₁ and TM₁₂ modes. The results are of importance in the design of these antennas     

Dielectric constant measurements of finite-size sheet at microwavefrequencies by pseudo-Brewster's angle method

Dielectric constant (ϵ_r) measurements for finite-size dielectric sheets (DS's) at centimeter wavelengths are presented using the method-of-measuring pseudo-Brewster's angle. This method is applied to measure ϵ_r of sheets of Plexiglas and window glass. In the experiment, two horn antennas are used to transmit and receive p-polarized waves. A dielectric sheet is located between the two antennas and rotated 180°, which produces two peaks in the transmittance curves. For a more accurate measurement of Brewster's angle, an optical spectrometer with 1-min accuracy is also used. By this method, ϵ_r of Plexiglas and window glass are obtained to be 2.55±0.13 and 5.35±0.1, respectively. This method measures |ϵ_r|, but the measurement is easy and nondestructive for DS's. Finally, an accurate method of error calculation is used to calculate the error in the measured values of ϵ_r     

Possibility ofNd1.9Ba1.1Cu3O7+δ andPr1.14Ba1.86Cu3O7-δsingle crystals for insulator in high-speed superconductingcircuits

Dielectric properties of both Nd_1.9Ba_1.1Cu ₃O_7+δ (NBCO-213) and Pr_1.14Ba_1.86Cu₃O_7-δ (Pr-rich PBCO) single crystals have been examined at low temperature. These materials have good lattice matching to high-T_c superconductors (HTS), but they are conductive at room temperature. Below 80 K, they are insulators with low dielectric constants, ε _τ below 25, and low dielectric loss tan δ below 0.1 at 100 kHz. The value of ε_τ is suitable for insulators in integrated circuits using strip line widths of 10 μm order, providing short delay time, no excitation of surface wave, and low radiation loss. The value of tan δ is comparable to loss of superconducting surface resistance above 100 GHz. These results indicate the applicability for the insulator layers in multilayer superconducting electronic devices such as Single Flux Quantum (SFQ) circuits operated at high speed     

Biconical antennas with unequal cone angles

The problem of radiation and reception of electromagnetic waves associated with a spherically capped biconical antenna having unequal cone angles ψ₁ and ψ₂ is investigated. Both cones that comprise a bicone are excited symmetrically at the apices by a voltage source so that the only higher order modes are TM. A variational expression for the terminal admittance is derived. Under the wide-angle approximation, expressions for the radiated field, the effective height, and the terminal admittance are obtained. In addition, limiting values of these quantities are derived for electrically small and electrically large wide-angle bicones. The results for arbitrary cone angles are new and subsume results that appear in the existing literature as special cases such as where ψ₁=ψ₂ or ψ₂=π/2. Moreover, the approximations of this paper are more accurate than many in the literature. It is argued that the radiation pattern of an electrically small cone is proportional to sin &thetas;, which is similar to that of a short dipole; whereas the pattern behaves like 1/sin &thetas; for electrically large cones. The parameter &thetas; is the angle from the bicone's axis of symmetry to the observation direction. Consequently, the direction of maximum radiation changes with exciting frequency for a bicone of fixed length. Although most of the analyses are presented in the frequency-domain, time-domain responses of bicones are discussed for some special cases that are similar to situations considered by Harrison and Williams. In particular, the time-domain radiated field and the received voltage are shown to depend on the input's passband and on the match between the source and the bicone     

Tilted- and axial-beam formation by a single-arm rectangular spiralantenna with compact dielectric substrate and conducting plane

A single-arm rectangular spiral antenna is analyzed using the finite-difference time-domain method. The spiral is printed on a finite-size dielectric substrate backed by a finite-size conducting plane. Both the substrate and conducting planes are square with a side length L of less than 0.6λ₀ (λ₀: wavelength in free space). The radiation pattern is dependent on the outermost arm peripheral length C. The spiral whose peripheral length is within 2λ_gg (λ_g: the guided wavelength of the current) radiates a tilted beam of circular polarization. When the peripheral length is decreased to λ_gg, the spiral radiates an axial beam. The axial beam has a wide half-power beam width of approximately 102° (for L≈0.369λ₀) with a gain of approximately 6.7 dB. The axial beam shows a 15% frequency bandwidth for a 3 dB axial ratio criterion. Over this bandwidth, the voltage standing-wave ratio (VSWR) is less than two, as desired. The experimental results for the radiation pattern, gain, axial ratio, and VSWR are also presented     

Finite-element solution of planar arbitrarily anisotropic diffused optical waveguides

The finite-element method for propagation in planar anisotropic diffused optical waveguides with arbitrary permittivity tensor is presented. A Galerkin procedure has been introduced to the finite-element formulation, to study both the nonleaky and leaky surface waves. The complex propagation constants are determined as a function of frequency for possible modes of propagation. The accuracy of the method has been checked by calculating the nonleaky and leaky surface waves of Ti-diffused LiNbO3waveguides with Gaussian index profiles. The numerical results of Ti-diffused LiNbO3waveguides with dielectric overlays are also presented and the effects of dielectric overlays on the propagation characteristics for the nonleaky and leaky surface waves are examined.     

Sensitivity limitation of a superconducting quantum interferometersensor-based gravity gradiometer

Differential displacement due to a gravitational force gradient, acting on two superconducting test masses which are elastically suspended from the instrument frame, is sensed by a superconducting quantum interference device (SQUID), coupled to the masses by a current flowing in the sensing circuits. The SQUID transducer absorbs energy from the masses, and, hence, it reacts with a random force (fluctuation-dissipation principle). This force increases if the coupling current grows. Additionally, the transducer outputs an amplification noise that is independent of the coupling. This output noise is equivalent to a force, applied to the masses, which decreases with stronger coupling, Hence, the strength of the total equivalent gravity gradient noise has a minimum with respect to the coupling. The minimum is found to be about 1.5ϵ_Aω₀ ²/(ml²), where ϵ_A means the equivalent energy sensitivity, in the white noise limit, of the SQUID junctions; ω₀ is the natural frequency of the mass suspension; m is the test mass, and l is the base length,     

Compositional design of Pb(Zr, Ti)O3 for highly reliableferroelectric memories

We have investigated Pb(Zr,Ti)O₃ (PZT) film composition suitable for highly reliable ferroelectric RAM (FeRAM) application. To obtain a wide operational margin for 2T/2C (two transistors and two capacitors) FeRAMs, the PZT film capacitor is needed to have a low coercive voltage (V_c) and a high dielectric constant on the polarization switching (ϵ_S) and a low dielectric constant on the nonswitching (ϵ_N), or essentially a large ϵ_S/ϵ_N ratio. Concerning the B-site composition in the perovskite structure, it is found that lowering the Zr/Ti ratio from 47/53 to Ti-richer ones increases the ratio of ϵ_S/ϵ_N as a positive effect on the wide operational margin, but increased V_c as a negative effect. Taking the balance of these factors into consideration, it is concluded that an optimum composition, such as Zr/Ti=30/70, provides the maximum operational margin. The A-site composition, on the other hand, affects the long-term reliability of a PZT capacitor. The endurance to the fatigue and imprint are enhanced by reduction of the Pb-excess and dope of La in the A-site. A La-doped PZT (Zr/Ti =30/70) capacitor is successfully integrated to the 8 kbit FeRAM macro with double-layer Al wiring to confirm the feasibility of this capacitor     

Design of lightweight, broad-band microwave absorbers using geneticalgorithms

A procedure for synthesizing multilayered radar absorbing coatings is presented. Given a predefined set of N_m available materials with frequency-dependent permittivities ∈_i(f) and permeabilities μ_i(f ) (i=1,. . ., N_m), the technique determines simultaneously the optimal material choice for each layer and its thickness. This optimal choice results in a screen which maximally absorbs TM and TE incident plane waves for a prescribed range of frequencies {f₁,f₂,. . ., f _Nf} and incident angles {&thetas;₁, &thetas;₂,. . .,&thetas;_N&thetas;}. The synthesis technique is based on a genetic algorithm. The technique automatically places an upper bound on the total thickness of the coating, as well as the number of layers contained in it, which greatly simplifies manufacturing. In addition, the thickness or surface mass of the coating can be minimized simultaneously with the reflection coefficient. The algorithm was successfully applied to the synthesis of wideband absorbing coatings in the frequency ranges of 0.2-2 GHz and 2-8 GHz