C. T. Tai

Bio: C. T. Tai is an academic researcher. The author has contributed to research in topics: Square (algebra) & Characteristic impedance. The author has an hindex of 1, co-authored 1 publications receiving 18 citations.

A Study of the e.m.f. Method

Abstract: The present work contains an investigation of the e.m.f. method to determine the input impedance of a thin biconical antenna as first suggested by Schelkunoff. By considering the various components of the currents flowing on the antenna, it has been shown that the sinusoidal part is, indeed, the dominating component among all these currents. An investigation of the total current at the end of the antenna, where the lateral surface of the cone and the spherical cap meet, shows that the current is not identically zero at that point, but vanishes as the reciprocal of the square of the characteristic impedance of the cone. The two approximate expressions of the complex conjugate power used in the e.m.f. method are derived, as well as the exact expression. Computation of some integrals occurring in the formulation is also treated in detail to show the various approximations involved.

Biconical antennas with unequal cone angles

Abstract: The problem of radiation and reception of electromagnetic waves associated with a spherically capped biconical antenna having unequal cone angles /spl psi//sub 1/ and /spl psi//sub 2/ 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 /spl psi//sub 1/=/spl psi//sub 2/ or /spl psi//sub 2/=/spl pi//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 /spl theta/, which is similar to that of a short dipole; whereas the pattern behaves like 1/sin /spl theta/ for electrically large cones. The parameter /spl theta/ 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.

Electromagnetic Back-Scattering from Cylindrical Wires

Abstract: The problem of electromagnetic back‐scattering or radar response from cylindrical wires has been investigated using a variational method. The relation between this method and the induced emf method is discussed. To demonstrate the flexibility of the variational calculation different trial functions have been used to determine the numerical values of the back‐scattering cross section for the case of broadside incidence. The boundary condition regarding the currents at the ends of the wire is also carefully examined.

Application of a Variational Principle to Biconical Antennas

Abstract: A theoretical examination is made of the impedance of a biconical antenna, based upon a method devised by Schwinger in studying the discontinuity problems of a wave guide. In the present analysis, an integral equation to determine the aperture field is obtained by matching the tangential electric and magnetic fields along the boundary sphere. Using this integral equation, the effective terminating admittance of the antenna can be expressed in a form that is stationary with respect to small variations in the aperture field. It is shown that the zeroth‐order solution of the admittance function thus obtained is the same as the one that Smith derived by neglecting all the high order waves in the interior region except the principal mode. For small‐angle cones, the present formulation yields the same exact solution obtained previously, based upon several different methods. The paper also contains a discussion of the first‐order approximate solution which is applicable to both small‐ and wide‐angle cones. The analysis includes a detailed treatment of a method by which the characteristic values and characteristic functions for a given cone may be found approximately, but very accurately; as well as certain integrals involving the product of Legendre functions.

Monopole and conic antennas on spherical vehicles

Abstract: The radiation and impedance characteristics of a spherically capped conic antenna protruding from a spherical vehicle are studied as a function of cone height, cone angle, and diameter of the vehicle. The conic antenna is excited by a gap at the cone base. The excitation is assumed rotationally symmetric. Considered in detail is the thin conical monopole extending from a sphere. The radiation patterns and antenna impedance referred to the base are calculated and compared with that of a cylindrical monopole over an infinite conducting plane.

A circuit model for mutual coupling analysis of a finite antenna array

Abstract: Mutual coupling effects within an antenna array play a very important role in the areas of EMC (electromagnetic compatibility) and antenna array design. A circuit model is developed to represent the input admittance of an antenna array with a finite number of elements. This model consists of a component to represent the input admittance of an isolated antenna element and infinite shunt components with each to represent different degrees of antenna mutual coupling effects. Twersky's (1952) algorithm of multiple scattering analysis is used to illustrate the physical meaning of each circuit component. Numerical results show that good accuracy for the antenna input admittance calculation can be obtained by using this model to the second order approximation. As the array is large and sparse, a very small amount of computation can yield good accuracy. This model is shown not only to be numerically efficient compared to the full wave analysis using the moment method, but also to give a physical insight into the antenna array mutual coupling mechanism. Furthermore, this model has no limitation on antenna array geometry and excitation.