Browsing by Subject "Coated cylinders"

Now showing 1 - 6 of 6

Open Access
Analysis of finite arrays of axially directed printed dipoles on electrically large circular cylinders
(IEEE, 2004) Ertürk, V. B.; Rojas, R. G.; Lee, K. W.
Various arrays consisting of finite number of printed dipoles on electrically large dielectric coated circular cylinders are investigated using a hybrid method of moments/Green's function technique in the spatial domain. This is basically an "element by element" approach in which the mutual coupling between dipoles through space as well as surface waves is incorporated. The efficiency of the method comes from the computation of the Green's function, where three types of spatial domain Green's function representations are used interchangeably, based on their computational efficiency and regions where they remain accurate. Numerical results are presented in the form of array current distributions, active reflection coefficient and far-field pattern to indicate the efficiency and accuracy of the method. Furthermore, these results are compared with similar results obtained from finite arrays of printed dipoles on grounded planar dielectric slabs. It is shown that planar approximations, except for small separations, can not be used due to the mutual coupling between the array elements. Consequently, basic performance metrics of printed dipole arrays on coated cylinders show significant discrepancies when compared to their planar counterparts. © 2004 IEEE.
Open Access
Analysis of finite arrays of circumferentially oriented printed dipoles on electrically large cylinders
(Wiley, 2004) Ertürk, V. B.; Güner, B.
An efficient and accurate hybrid method of moments (MoM)/Green's function technique in the spatial domain is developed for the rigorous analysis of large, finite phased arrays of circumferentially oriented printed dipoles on electrically large, dielectric-coated, circular cylinders. Basic performance metrics (in the form of array current distribution, active reflection coefficient, far-field patterns, and so forth) of several arrays have been obtained and compared with similar printed arrays on grounded planar substrates. Certain discrepancies have been observed and discussed. © 2004 Wiley Periodicals, Inc.
Open Access
An asymptotic closed-form paraxial formulation for surface fields on electrically large dielectric coated circular cylinders
(2005) Erdöl, Tuncay
Investigation of surface fields excited on material coated perfectly conducting (PEC) circular cylinders is a problem of interest (i) due to its application in the design and analysis of conformal microstrip antennas and arrays, and (ii) it acts as a canonical problem useful toward the development of asymptotic solutions valid for arbitrarily convex material coated smooth surfaces. Nevertheless, integral equation based solutions that use the eigenfunction representation of the appropriate dyadic Green’s function, as well as pure numerical solutions become intractable when the geometry of interest is electrically large. A few asymptotic solutions have been suggested in the literature to overcome this problem. However, these solutions are not accurate within the paraxial (nearly axial) region of the cylinder. This is a well known problem that has been observed for PEC and impedance cylinders in the past as well. Recently, a novel paraxial space-domain representation for the surface fields has been presented by Ert¨urk et. al. (IEEE Trans. Antennas and Propagat., 11, 1577-1587, 2002), which is much faster than the well-known eigenfunction solution. However, in this representation the fi- nal expressions for the surface fields have some special functions which involve Sommerfeld type integrals to be evaluated numerically. In this thesis, using the final results of this paraxial space-domain formulation as a starting point, a relatively simple closed-form asymptotic representation for the surface fields of a dielectric coated, electrically large circular cylinder is developed. The large parameter in this asymptotic development is the separation between the source and observation points. The solution uses the fact that existing special functions in the previously developed paraxial formulation are in similar forms when compared to the special functions used in the Sommerfeld integral representation for the single layer microstrip dyadic Green’s function for the planar case. Furthermore, when the radius of the cylinder goes to infinity, using the leading terms of Debye representations for the Hankel and Bessel functions (as well as their derivatives), cylindrical special functions recover their planar counterparts. Therefore, first a steepest descent path representation of these special functions is obtained. Then, using the method suggested by Barkeshli et. al. (IEEE Trans. Antennas and Propagat., 9, 1374-1383, 1990) closed-form expressions are achieved. Numerical results in the form of mutual coupling between two tangential electric current modes have been obtained using these closed-form expressions and compared with the previously developed paraxial formulation as well as eigenfunction solution to assess the accuracy and efficiency of these closed-form solutions. Details of the formulation is presented.
Open Access
Design and analysis of finite arrays of circumferentially oriented printed dipoles on electrically large coated cylinders
(2004) Güner, Barış
Conformal antennas and arrays are used in a wide range of applications including mobile communication systems, missiles, aircrafts and spacecrafts. In these applications, the conformality is required for aesthetic and aerodynamic constraints and reducing the radar cross-section. Antennas and arrays conformal to the cylindrical host bodies are particularly important since cylindrical geometry can be used to approximate most of the practical problems and it is a canonical geometry. However, the available design and analysis tools for antennas/arrays conformal to cylindrical host bodies are either approximate methods or restricted to small arrays. Recently, a hybrid method based on Method of Moments (MoM) combined with a Green’s function in space domain is proposed to solve the aforementioned problem. In this work this method is used to analyze finite, phased arrays of circumferentially oriented printed dipoles conformal to the dielectric coated electrically large circular cylinders. The accuracy and efficiency of the method comes from the computation of the appropriate Green’s function which is the kernel of the electric field integral equation to be solved via MoM. There are three different high-frequency based representations for the Green’s function in the spatial domain which are valid in different but overlapping regions: Planar representation, steepest descent path (SDP) representation and the Fourier Series (FS) representation. These different representations are used interchangeably to obtain the most accurate solution that requires the least amount of computational time. Several modifications on the method are made in this work to increase the efficiency and accuracy of the solution. The effects of the array and host body parameters on the performance of the array are presented. The results are compared with a previously published spectral domain solution to show the accuracy of the method. Also, performance comparisons with those of the cylindrical arrays of axially oriented dipoles and planar arrays are made to observe the effects of curvature and the dipole orientation on the performance of the array.
Open Access
Paraxial space-domain formulation for surface fields on dielectric coated circular cylinder
(IEEE, 2002-11) Ertürk, V. B.; Rojas, R. G.
A new method to evaluate the surface fields excited within the paraxial (nearly axial) region of an electrically large dielectric coated circular cylinder is presented. This representation is obtained by performing the Watson’s transformation in the standard eigenfunction solution and using the fact that the circumferentially propagating series representation of the appropriate Green’s function is periodic in one of its two variables. Therefore, it can be approximated by a Fourier series where the two leading terms of the expansion yield engineering accuracy in most cases. This work can be used in conjunction with a method of moments solution for the design/analysis of conformal microstrip antennas and arrays. Numerical results are presented and compared with a standard eigenfunction expansion.
Open Access
Scan blindness phenomenon in conformal finite phased arrays of printed dipoles
(Institute of Electrical and Electronics Engineers, 2006) Ertürk, V. B.; Bakir, O.; Rojas, R. G.; Güner, B.
Scan blindness phenomenon for finite phased arrays of printed dipoles on material coated, electrically large circular cylinders is investigated. Effects on the scan blindness mechanism of several array and supporting structure parameters, including curvature effects, are observed and discussed. A full-wave solution, based on a hybrid method of moments/ Green's function technique in the spatial domain, is used to achieve the aforementioned goals. Numerical results show that the curvature affects the surface waves and hence the mutual coupling between array elements. As a result, the array current distribution of arrays mounted on coated cylinders are considerably different compared to similar arrays on planar platforms. Therefore, finite phased arrays of printed dipoles on coated cylinders show different behavior in terms of scan blindness phenomenon compared to their planar counterparts. Furthermore, this phenomenon is completely different for axially and circumferentially oriented printed dipoles on coated cylinders suggesting that particular element types might be important for cylindrical arrays.