Cagatay Tokgoz

Closed-form Green's functions for cylindrically stratified media

A numerically efficient technique is developed to obtain the spatial-domain closed-form Greens functions of the electric and magnetic fields due to z- and /spl phi/-oriented electric and magnetic sources embedded in an arbitrary layer of a cylindrical stratified medium. First, the electric- and magnetic-field components representing the coupled TM and TE modes are derived in the spectral domain for an arbitrary observation layer. The spectral-domain Greens functions are then obtained and approximated in terms of complex exponentials in two consecutive steps by using the generalized pencil of function method. For the Greens functions approximated in the first step, the large argument behavior of the zeroth-order Hankel functions is used for the transformation into the spatial domain with the use of the Sommerfeld identity. In the second step, the remaining part of the Greens functions are approximated on two complementary parts of a proposed deformed path and transformed into the spatial domain, analytically. The results obtained in the two consecutive steps are combined to yield the spatial-domain Greens functions in closed forms.

A UTD based asymptotic solution for the surface magnetic field on a source excited circular cylinder with an impedance boundary condition

An asymptotic solution based on the uniform geometrical theory of diffraction (UTD) is proposed for the canonical problem of surface field excitation on a circular cylinder with an impedance boundary condition (IBC). The radius of the cylinder and the length of the geodesic path between source and field points, both of which are located on the surface of the cylinder, are assumed to be large compared to a wavelength. Unlike the UTD based solution pertaining to a perfect electrically conducting (PEC) circular cylinder, some higher order terms and derivatives of Fock type integrals are found to be significantly important and included in the proposed solution. The solution is of practical interest in the prediction of electromagnetic compatibility (EMC) and electromagnetic interference (EMI) between conformal slot antennas on a PEC cylindrical structure with a thin material coating on which boundary conditions can be approximated by an IBC. The cylindrical structure could locally model a portion of the fuselage of an aircraft or a spacecraft, or a missile. Validity and accuracy of the numerical results obtained by this solution are demonstrated in comparison with those of an exact eigenfunction solution.

An asymptotic solution for the surface magnetic field within the paraxial region of a circular cylinder with an impedance boundary condition

It is well-known that the high-frequency asymptotic evaluation of surface fields by the conventional geometrical theory of diffraction (GTD) usually becomes less accurate within the paraxial (close to axial) region of a source excited electrically large circular cylinder. Uniform versions of the GTD based solution for the surface field on a source excited perfect electrically conducting (PEC) circular cylinder were published earlier to yield better accuracy within the paraxial region of the cylinder. However, efficient and sufficiently accurate solutions are needed for the surface field within the paraxial region of a source excited circular cylinder with an impedance boundary condition (IBC). In this work, an alternative approximate asymptotic closed form solution is proposed for the accurate representation of the tangential surface magnetic field within the paraxial region of a tangential magnetic current excited circular cylinder with an IBC. Similar to the treatment for the PEC case, Hankel functions are asymptotically approximated by a two-term Debye expansion within the spectral integral representation of the relevant Greens function pertaining to the IBC case. Although one of the two integrals within the spectral representation is evaluated in an exact fashion, the other integral for which an exact analytical evaluation does not appear to be possible is evaluated asymptotically, unlike the PEC case in which both integrals were evaluated analytically in an exact fashion. Validity of the proposed asymptotic solution is investigated by comparison with the exact eigenfunction solution for the surface magnetic field.

Iterative physical optics: its not just for cavities anymore [EM wave propagation]

Iterative physical optics (IPO) is the iterative refinement of first-order PO surface currents to incorporate higher-order multi-bounce and multiple diffraction effects on electrically large geometries. The advantages of IPO are that it is a high-frequency asymptotic solution that does not require ray tracing, and can be applied to a general CAD surface mesh. This talk is an overview of the development of IPO and presents some new antenna and scattering applications.

Modeling and characterization of partially inserted electrical connector faults

Faults within electrical connectors are prominent in avionics systems due to improper installation, corrosion, aging, and strained harnesses. These faults usually start off as undetectable with existing inspection techniques and increase in magnitude during the component lifetime. Detection and modeling of these faults are significantly more challenging than hard failures such as open and short circuits. Hence, enabling the capability to locate and characterize the precursors of these faults is critical for timely preventive maintenance and mitigation well before hard failures occur. In this paper, an electrical connector model based on a two-level nonlinear least squares approach is proposed. The connector is first characterized as a transmission line, broken into key components such as the pin, socket, and connector halves. Then, the fact that the resonance frequencies of the connector shift as insertion depth changes from a fully inserted to a barely touching contact is exploited. The model precisely c...

Application of UTD for prediction of radiation pattern and mutual coupling associated with antennas on faceted airborne platforms

In this paper, development of a new generation UTD code has been discussed. What makes the proposed UTD code unique is the application of UTD directly to faceted airborne platforms without going through the complicated task of approximating the electrically large platform in terms of canonical shapes. Numerical results show that the proposed UTD code produces promising results in the prediction of radiation pattern of antennas on faceted airborne platforms. This code will be very useful for the placement of antennas on electrically large platforms, and their EM interference/EM compatibility (EMI/EMC) analysis.

Surface field excitation by a magnetic point source on an impedance cylinder

An approximate uniform geometrical theory of diffraction (UTD) solution has been developed for the analysis of surface magnetic fields excited by a magnetic point source on an impedance cylinder. This solution is useful not only for the analysis of mutual coupling on an impedance cylinder with a uniform surface impedance or with a surface impedance patch, but also for the modeling of a thin material coating on a PEC circular cylinder. Analytically, the proposed UTD solution reduces to that of a PEC circular cylinder when the surface impedance goes to zero. This approximate solution compares well also with the eigenfunction solution, numerically. These comparisons confirm the validity of the solution.

GPU accelerated iterative physical optics to predict RF propagation in urban environments

Multi-objective path planning during autonomous navigation of rotorcraft is very important to accomplish critical missions in dangerous territories. Besides other objectives, it is desired to know in advance if two-way communications between rotorcraft, and downlink and uplink communications with ground control stations will be maintained during a critical mission. In addition, it is required to predict how communication links change if the scene of the autonomous flight is constantly varying. Hence, it is critical to instantly compute the coverage of antennas on rotorcraft or at ground stations in an urban environment. However, fast computation of antenna coverage becomes very challenging as the scene gets larger compared to a wavelength. In this paper, a technique based on iterative physical optics (IPO) accelerated using graphical processing units (GPU) is presented to predict radio frequency (RF) propagation in urban environments. Results of physical optics (PO) and IPO for RF propagation in an urban environment will be presented along with the speedup achieved using GPUs compared to central processing unit (CPU) based implementations.

Physics based modeling of connectors faults

In this paper, a physics based connector model that consists of coaxial lines with different characteristic impedances and lengths is proposed. Method of Moments (MoM) analysis was performed using commercial electromagnetic simulation software, FEKO, for transverse electric and magnetic (TEM) wave propagation through the connector to optimize its physical parameters to fit its measured S parameters.

Modeling of partially inserted connector faults

A partially inserted electrical connector model based on a two-level nonlinear least squares (NLS) approach is proposed. The connector is characterized as a transmission line, broken into sections. The model precisely captures resonant frequency shifts as insertion depth changes from a fully inserted to a barely touching contact by varying only two length parameters.