Kubilay Sertel

Frequency-selective surfaces to enhance performance of broad-band reconfigurable arrays

We present a novel frequency-selective surface (FSS) design aimed at enhancing the performance of broad-band reconfigurable antenna apertures. In particular, reconfigurable printed dipole arrays are examined in the presence of a multilayer FSS. Of particular interest is the design of FSS structures whose reflection coefficient has prespecified phase response over a broad set of frequencies. Previous FSSs primarily considered designs on the basis of the reflection coefficient amplitude and were intended for radome applications rather than substrates. Designing FSSs subject to phase requirements is seen to require some compromise in the magnitude. Broad-band requirements also present us with a need for noncommensurate FSS designs.

Array decomposition method for the accurate analysis of finite arrays

Presented in this paper is a fast method to accurately model finite arrays of arbitrary three-dimensional elements. The proposed technique, referred to as the array decomposition method (ADM), exploits the repeating features of finite arrays and the free-space Greens function to assemble a nonsymmetric block-Toeplitz matrix system. The Toeplitz property is used to significantly reduce storage requirements and allows the fast Fourier transform (FFT) to be applied in accelerating the matrix-vector product operations of the iterative solution process. Each element of the array is modeled using the finite element-boundary integral (FE-BI) technique for rigorous analysis. Consequently, we demonstrate that the complete LU decomposition of the matrix system from a single array element can be used as a highly effective block-diagonal preconditioner on the larger array matrix system. This rigorous method is compared to the standard FE-BI technique for several tapered-slot antenna (TSA) arrays and is demonstrated to generate the same accuracy with a fraction of the storage and solution time.

Coupling studies and shielding techniques for electromagnetic penetration through apertures on complex cavities and vehicular platforms

The multilevel fast multipole moment method is employed to compute the electromagnetic coupling and shielding of various aperture-coupled metallic enclosures. A phenomenological study of electromagnetic coupling, due to various slot shapes and sizes, with or without the presence of wire penetration is conducted. These slots are situated on over-moded cavities and two methods are proposed to mitigate slot coupling into the cavitys interior. As part of this work, we also investigate the coupling through similar slots and apertures within a complex platform such as an automobile. The proposed methods have shown to increase shielding by as much as 5-35 dB within the frequency range of interest.

A Wideband, Wide Scanning Tightly Coupled Dipole Array With Integrated Balun (TCDA-IB)

A key challenge in the design of wideband dipole phased arrays is the design of equally wideband baluns which are sufficiently compact to fit within the unit cell (typically in the linear dimension at low frequencies). In this paper, we exploit the reactance of a compact Marchand balun as an impedance matching network for each array element. The elimination of bulky external baluns results in a significant reduction of size, weight and cost, while the bandwidth is simultaneously improved by over 30%, compared to standard feeding techniques. In this manner, a tightly coupled dipole array with an integrated balun (TCDA-IB) is developed which achieves 7.35:1 bandwidth (0.68 - 5.0 GHz) while scanning to ±45° in all directions, subject to . In a dual-polarization configuration, the TCDA-IB has low cross polarization of over the majority of the band. Measured results are presented for a prototype 8 × 8 element TCDA-IB, showing good agreement with simulation.

A Broadband Focal Plane Array Camera for Real-time THz Imaging Applications

We present a large-format, sub-millimeter-resolution, focal plane array sensor for THz imaging. Each pixel in the sensor array consists of broadband THz antennas monolithically integrated with ultra-fast heterostructure backward diodes for THz sensing. With the aid of in-house hybrid electromagnetic modeling tools, the focal plane array is optimized for diffraction limited image resolution and conjugate impedance matching for highest THz sensitivity. The camera is designed to operate in the 0.6–1.2 THz band with 5 frames-per-second image acquisition speeds, making it ideal for THz imaging applications, such as security screening, non-destructive evaluation and chemical, pharmaceutical, and medical imaging. The simulation results are validated by measurements to demonstrate sub-millimeter resolution with a pixel optical responsivity of 600 V/W at 0.7 THz.

Superstrate-Enhanced Ultrawideband Tightly Coupled Array With Resistive FSS

An efficient low-profile ultrawideband tightly coupled array employing a resistive frequency selective surface (FSS) and a superstrate is introduced. The FSS suppresses destructive ground plane interference, resulting in an increase in the array bandwidth by a factor greater than two. A superstrate is used to alleviate losses due to the resistive FSS. It is shown that a properly designed superstrate reduces losses by about 2.5 dB. The proposed array, which employs tightly coupled bowtie elements, achieves very low profile (0.055λlow) , 21:1 bandwidth, and radiation efficiency greater than 73% across the band. This paper presents the analysis and design of the array, particularly the FSS and superstrate. To validate the design, measurements of a prototype array are presented as well.

Miniature Antenna Using Printed Coupled Lines Emulating Degenerate Band Edge Crystals

A miniature printed antenna design that exploits higher-order dispersion behavior in degenerate band edge (DBE) crystals is proposed. First, the unit cell of a DBE crystal is emulated using a simple combination of uncoupled and coupled microstrip (MS) line sections printed on a low loss dielectric substrate. Subsequently, a resonant antenna is formed by cascading two such MS-DBE unit cells in a circularly periodic fashion. The first part of the paper is devoted to the antenna/array design and characterization using a low contrast dielectric substrate (Rogers Duroid, isinr = 2.2). Next, fabrication and design verification using a high dielectric constant substrate (alumina: Al2O3, isinr = 9.6) is given. The manufactured antenna was measured to have a broadside gain of 4.5 dB at 1.48 GHz with 3.0% bandwidth. For this gain and bandwidth, we demonstrate that the proposed MS-DBE antenna has a lambda0/9 times lambda0/9 footprint and is among the smallest in the literature.

Miniature Antennas and Arrays Embedded Within Magnetic Photonic Crystals

This letter presents the performance of small antennas embedded within a new class of magnetic photonic crystals (MPCs) constructed from periodic arrangements of homogenous and anisotropic material layers. Earlier studies of these crystals demonstrated that they exhibit slow modes within their propagation bands associated with minimal reflection at the air-crystal interface, drastic slow down of the group velocity and concurrent increase in the amplitude of the field within the crystal. In this letter, we take advantage of the latter to demonstrate the extraordinary high gain that small antennas exhibit when placed within the MPC. We also examine array configuration inside the MPC to enhance power reception and to further narrow the radiation pattern beam. An initial investigation on the effect of crystal thickness and material loss due to the MPC is also considered.

RF propagation in finite thickness unidirectional magnetic photonic crystals

This paper presents an analysis of a new class of magnetic photonic crystals (MPCs) constructed from periodic arrangements of available (possibly anisotropic) homogeneous material layers. Earlier, analytical studies of semi-infinite versions of these crystals demonstrated that they exhibit the phenomena of minimal reflection at their interface, large amplitude growth of the harmonic wave within the crystal, and concurrent group velocity slow-down. These characteristics are associated with the so called frozen mode and occur at a specific frequency associated with a stationary inflection point within the Bloch diagram. In this paper, we present a characterization of these phenomena for a practical, finite thickness crystal slab and propose a realizable combination of materials consisting of available ferrite and dielectric media. The existence of significant wave amplitude growth and slow down are verified for materials with realistic losses. In addition, we identify and characterize the bandwidth of the magnetic photonic crystals and examine its relationship to the amplitude growth.

Emulation of Propagation in Layered Anisotropic Media With Equivalent Coupled Microstrip Lines

A microstrip transmission line model is proposed for a new class of photonic crystals which exhibit a degenerate band edge (DBE). The microstrip line model is formed from a pair of coupled and uncoupled lines (one per field component, Ex and Ey) and is the first (to our knowledge) representing propagation within an anisotropic layered medium. Using the standard scattering matrix representation for the three consecutive layer sections forming the DBE unit cell, we calculate the band diagram and show that the periodic microstrip structure supports a DBE mode for a specific fabricatable design