Browsing by Author "Rojas, R. G."

Now showing 1 - 7 of 7

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
Efficient analysis of input impedance and mutual coupling of microstrip antennas mounted on large coated cylinders
(IEEE, 2003-04) Ertürk, V. B.; Rojas, R. G.
An efficient and accurate hybrid method, based on the combination of the method of moments (MoM) with a special Green’s function in the space domain is presented to analyze antennas and array elements conformal to electrically large material coated circular cylinders. The efficiency and accuracy of the method depend strongly on the computation of the Green’s function, which is the kernel of the integral equation that is solved via MoM for the unknown equivalent currents representing only the antenna elements. Three types of space-domain Green’s function representations are used, each accurate and computationally efficient in a given region of space. Consequently, a computationally optimized analysis tool for conformal microstrip antennas is obtained. Input impedance of various microstrip antennas and mutual coupling between two identical antennas are calculated and compared with published results to assess the accuracy of this hybrid method.
Open Access
Efficient computation of surface fields excited on a dielectric-coated circular cylinder
(IEEE, 2000-10) Erturk, V. B.; Rojas, R. G.
An efficient method to evaluate the surface fields excited on an electrically large dielectric-coated circular cylinder is presented. The efficiency of the method results from the circumferentially propagating representation of the Green’s function as well as its efficient numerical evaluation along a steepest descent path. The circumferentially propagating series representation of the appropriate Green’s function is obtained from its radially propagating counterpart via Watson’s transformation and then the path of integration is deformed to the steepest descent path on which the integrand decays most rapidly. Numerical results are presented that indicate that the representations obtained here are very efficient and valid even for arbitrary small separations of the source and field points. This work is especially useful in the moment-method analysis of conformal microstrip antennas where the mutual coupling effects are important.
Open Access
Frequency‐selective loading for a transmitting active integrated antenna
(Wiley, 2001-10-05) Ertürk, V. B.; Rojas, R. G.; Roblin, P.
A simple frequency‐selective load in the form of a compensating network is attached to an oscillator‐type transmitting active integrated antenna (AIA) to suppress undesired low‐frequency oscillations and to improve the robustness of the oscillator. Although the input impedance of the active device (transistor) remains unchanged at the upper frequencies, it changes drastically at the lower frequencies.
Open Access
Paraxial space - domain formulation for surface fields on large dielectric coated circular cylinders
(IEEE, 2001-07) Ertürk Vakur B.; Rojas, R. G.
A space-domain represention for the surface fields excited by an elementary current source was discussed. Green's function was used and an approximation was made using Fourier series (FS), where FS coefficients were calculated using numerical integration. The integrals were evaluated numerically along the real axis using a Gausian quadrature algorithm. However, the developed scheme yielded field expressions that remain valid along the paraxial region for arbitraily small and large separation between observation and source points.
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.