Ahmet C. Durgun

Design, Simulation, Fabrication and Testing of Flexible Bow-Tie Antennas

Design, simulation, fabrication and measurement of two different novel flexible bow-tie antennas, a conventional and a modified bow-tie antenna with reduced metallization, are reported in this paper. The antennas are mounted on a flexible substrate fabricated at the Flexible Display Center (FDC) of Arizona State University (ASU). The substrate is heat stabilized polyethylene naphthalate (PEN) which allows the antennas to be flexible. The antennas are fed by a microstrip-to-coplanar feed network balun. The reduction of the metallization is based on the observation that the majority of the current density is confined towards the edges of the regular bow-tie antenna. Hence, the centers of the triangular parts of the conventional bow-tie antenna are removed without compromising significantly its performance. The return losses and radiation patterns of the antennas are simulated with HFSS and the results are compared with measurements, for bow-tie elements mounted on flat and curved surfaces. The comparisons show that there is an excellent agreement between the simulations and measurements for both cases. Furthermore, the radiation performance of the modified bow-tie antenna is verified, by simulations and measurements, to be very close to the conventional bow-tie.

Flexible bow-tie antennas

The Flexible Display Center (FDC) at Arizona State University (ASU) was founded in 2004 as a partnership between academia, industry, and government to collaborate on the development of a new generation of innovative displays and electronic circuits that are flexible, lightweight, low power, and rugged [1]. Due to the increasing need for flexible and lightweight electronic systems, FDC aims to develop materials and structural platforms that allow flexible backplane electronics to be integrated with display components that are economical for mass-production [2]. Currently, FDC is focusing on the incorporation of antenna structures, which can function cooperatively with the other flexible circuit elements. Design of flexible antennas, as a part of flexible electronic circuits, may have a very wide spectrum of applications in military and civilian wireless communication, which can allow people to wear antenna structures instead of carry them. Hence, flexible and fluidic antennas have a great potential [3]. In this paper, the design, fabrication, simulation and measurements of a bow-tie antenna with a flexible substrate is discussed. The antenna is modeled and simulated with Ansoft HFSS, and the simulations are compared with measurements performed in the Electromagnetic Anechoic Chamber (EMAC) at ASU.

High-Impedance Surfaces With Periodically Perforated Ground Planes

Because of the design limitations of conventional high-impedance surfaces (HIS), it is not possible to miniaturize the HIS and increase the bandwidth, simultaneously. To overcome this, a novel HIS is proposed with a periodically perforated ground plane. The magnetic flux flowing through the perforations results in an extra inductance which increases the fractional bandwidth and decreases the center frequency. Since the perforated HIS can also be considered as a defected ground structure (DGS), surface wave suppression can also be achieved by properly determining the geometry of the perforations. Therefore, a bandgap can be obtained without the need of vias, which considerably increase fabrication costs. It is also possible to tune and overlap the reflection phase and surface wave suppression bands. However, due to the rotational asymmetry of the structure, surface wave suppression is achieved in only one direction.

Reflection Phase Characterization of Curved High Impedance Surfaces

Reflection phase characteristics of cylindrically curved high impedance surfaces (HISs) are examined. Due to the non-periodicity of the problem, full wave solutions can be time consuming. To overcome this problem, an approximate semi-analytical method, which assumes a homogenized model for the curved HIS, is developed. The model parameters can be extracted from the reflection properties of the flat HIS. For the cases where only Floquet currents are excited, the reflection phase diagram of a curved HIS is independent of the curvature. However, the surface waves generated on HISs, due to their periodic geometry, distorts their reflection phase characteristics within specific frequency intervals. In those intervals, the reflection phase changes as a function of radius of curvature and size of the HIS. These effects are not observed for the flat cases because of the lower radiation resistance of the surface waves. In this paper, the normal incidence case is considered for TEz and TMz polarizations.

COMPUTATION OF PHYSICAL OPTICS INTEGRAL BY LEVIN'S INTEGRATION ALGORITHM

In this paper, a novel algorithm for computing Physical Optics (PO) integrals is introduced. In this method, the integration problem is converted to an inverse problem by Levins integration algorithm. Furthermore, the singularities, that are possible to occur in the applications of Levins method, are handled by employing trapezoidal rule together with Levins method. Finally, the computational accuracy of this new method is checked for some radar cross section (RCS) estimation problems performed on flat, singly- curved and doubly-curved PEC plates which are modeled by 8-noded isoparametric quadrilaterals. The results are compared with those obtained by analytical and brute force integration.

Flexible bow-tie antennas with reduced metallization

This paper presents design, simulation, fabrication and measurement of a modified bow-tie antenna with reduced metallization. The antenna is mounted on a flexible substrate which is fabricated at the Flexible Display Center (FDC) of Arizona State University (ASU). The substrate is heat stabilized polyethylene naphthalate (PEN) which allows the antenna to be flexible. The antenna is fed by the aid of a microstrip-to-coplanar feed network balun. The reduction of the metallization is based on the observation that the majority of the current density is confined towards the edges of the regular bow-tie antenna. Hence, the centers of the triangular parts of the bow-tie antenna are removed. The radiation performance of the modified bow-tie is verified to be very close to the conventional bow-tie by simulations and measurements.

Physical realization and reflection phase characteristics of a flexible high impedance surface

This paper presents the fabrication and reflection phase measurements of a flexible high impedance surface (FHIS). The surface is fabricated by using DuPont pyralux polyimide as the substrate. Cyanoacrylate is used to adhere the samples of polyimide. The reflection phase response of the FHIS, which is curved in the form of a cylinder, is measured in the anechoic chamber and compared with that of the flat FHIS. As expected, reflection phase characteristics of the curved FHIS are polarization dependent and slightly different than those of the flat one. The measured reflection phase characteristics of the curved FHIS will be compared with simulations which presently are under consideration.

A novel HIS with a perforated ground plane for miniaturization and bandwidth enhancement

Because of the design limitations of conventional high impedance surfaces (HIS), it is not possible to miniaturize the HIS and increase the bandwidth, simultaneously. To overcome this, a novel HIS is proposed with a periodically perforated ground plane. The magnetic flux flowing through the perforations results in an extra inductance which increases the fractional bandwidth and decreases the center frequency.

Surface wave suppression properties of Perforated Artificial Impedance Surfaces

Surface wave suppression properties of Perforated Artificial Impedance Surfaces (PAIS) are investigated. It is shown that, by a proper choice of perforation geometry, surface wave propagation can be suppressed without the need of vias. This significantly decreases fabrication costs. It is also possible to overlap the surface wave suppression and reflection phase bands of the PAIS. Due to the rotational asymmetry of the structure, surface wave suppression is achieved in only one direction.

Plane wave scattering from a curved HIS: Normal incidence

An approximate analytical method is developed to characterize the reflection properties of a cylindrically curved high impedance surface (HIS). This method assumes a homogenized model for the curved HIS which can be extracted from the reflection properties of the flat HIS. In this work, only the normal incidence case is considered for TEz and TMz polarizations.