[Show abstract][Hide abstract] ABSTRACT: An analytical model is presented for the analysis of multilayer wire media loaded with 2-D arrays of thin material terminations, characterized in general by a complex surface conductivity. This includes the cases of resistive, thin metal, or graphene patches and impedance ground planes. The model is based on the nonlocal homogenization of the wire media with additional boundary conditions (ABCs) at the connection of thin (resistive) material. Based on charge conservation, new ABCs are derived for the interface of two uniaxial wire mediums with thin imperfect conductors at the junction. To illustrate the application of the analytical model and to validate the new ABCs, we characterize the reflection properties of multilayer absorbing structures. It is shown that in such configurations the presence of vias results in the enhancement of the absorption bandwidth and an improvement in the absorptivity performance for increasing angles of an obliquely incident TM-polarized plane wave. The results obtained using the analytical model are validated against full-wave numerical simulations.
Full-text · Article · Dec 2012 · IEEE Transactions on Antennas and Propagation
[Show abstract][Hide abstract] ABSTRACT: We present an analytical model to study the reflection properties of a multilayered wire media loaded with 2-D arrays of thin imperfect conductors. Based on charge conservation, generalized additional boundary conditions (ABCs) for the interface of two uniaxial wire mediums loaded with thin arbitrary imperfect conductors at the junction are derived. It is observed that by proper selection of the structural parameters, the mushroom structure acts as a wideband absorber for an obliquely incident TM-polarized plane wave. The presented model along with the new ABCs are validated using the full-wave numerical simulations.
[Show abstract][Hide abstract] ABSTRACT: Antenna effects on a monostatic multiple-input-multiple-output (MIMO) Radar for direction estimation are studied by analyzing the Cramer-Rao lower bound (CRLB). The CRLB is derived for a multi-band MIMO Radar system, and is in a form that incorporates the characteristics of a practical antenna array. Two different uniform linear antenna arrays, one narrowband and the another wideband, are investigated by exploring the CRLB. The estimation performance for the real antenna array is compared to that for an ideal array composed of isotropic antenna elements. It is found out that the mutual coupling between antenna elements alters the radiation patterns a lot, and therefore tremendously affects the estimation performance. Furthermore, the study demonstrates that by distributing the transmitted power over several frequency bands, more accurate estimation can be achieved due to frequency diversity, and the negative effects of radiation pattern deviation can be alleviated.
No preview · Article · Jun 2011 · IEEE Transactions on Antennas and Propagation
[Show abstract][Hide abstract] ABSTRACT: Design of a linear array of rectangular dielectric resonator antennas (DRAs) fed by dielectric image guide (DIG) is presented. Coupling between the DIG and the DRAs is predicted using the effective dielectric constant method. In order to achieve a specific power distribution, the power coupled to each DRA is controlled by changing the spacing between the DRAs and the DIG. Cross polarization reduction is achieved by wrapping a conducting strip around the middle of the DRA without affecting the co-polarized radiation pattern. The antenna is fabricated and tested. Good agreement between the measured and computed results is obtained.
No preview · Article · Apr 2010 · IEEE Transactions on Antennas and Propagation
[Show abstract][Hide abstract] ABSTRACT: Multiple-input-multiple-output (MIMO) radar makes use of orthogonal signals to obtain the phase delay for each transmitting/receiving antenna pair, and thus increasing the accuracy of direction estimation. The previously proposed MIMO radar assumes narrowband signals that guarantee the waveform orthogonality during the signals- transmission, propagation and reception. However, a narrowband system is unstable in target localisation because of the fluctuation of the target-s radar cross section. An MIMO-OFDM radar is proposed for target localisation. It adopts the OFDM technique to simultaneously transmit and receive a set of multiple narrowband orthogonal signals at orthogonal frequencies. A practical model accommodating a physical target is presented to simulate the MIMO-OFDM radar. As an example, a composite target composed of five infinite dielectric cylinders is localised by a four-element uniform linear array. The performance of the MIMO-OFDM radar is investigated by examining the estimation error for different numbers of sub-bands, different signal-to-noise ratios and different target directions. It is demonstrated by simulation that the MIMO-OFDM radar gives more statistically stable estimation by spreading the signal power over a wider spectrum.
No preview · Article · Mar 2010 · IET Radar Sonar ? Navigation
[Show abstract][Hide abstract] ABSTRACT: This paper presents the design of a rectangular dielectric resonator antenna array coupled to narrow slot apertures that are fed by dielectric image guide (DIG). The DIG is excited by an X-band rectangular waveguide through a waveguide transition, and DIG tapering is used to match between the waveguide and the DIG. Reflection cancelling slots are added near the original slots to improve impedance matching. Since the slots radiate in both directions, a reflecting conducting plate is inserted above the DIG to decrease the back radiation of the antenna. The antenna is fabricated and the measured results are compared to the simulated results.
No preview · Article · Sep 2009 · IEEE Transactions on Antennas and Propagation
[Show abstract][Hide abstract] ABSTRACT: This book gives a step-by-step presentation of a generalized transmission line method to study the far-zone radiation of antennas under a multilayer structure. Normally, a radiation problem requires a full wave analysis which may be time consuming. The beauty of the generalized transmission line method is that it transforms the radiation problem for a specific type of structure, say the multilayer structure excited by an antenna, into a circuit problem that can be efficiently analyzed. Using the Reciprocity Theorem and far-field approximation, the method computes the far-zone radiation due to a Hertzian dipole within a multilayer structure by solving an equivalent transmission line circuit. Since an antenna can be modeled as a set of Hertzian dipoles, the method could be used to predict the far-zone radiation of an antenna under a multilayer structure. The analytical expression for the far-zone field is derived for a structure with or without a polarizer. The procedure of obtaining the Hertzian dipole model that is required by the generalized transmission line method is also described. Several examples are given to demonstrate the capabilities, accuracy, and efficiency of this method.
No preview · Article · Oct 2008 · Synthesis Lectures on Antennas
[Show abstract][Hide abstract] ABSTRACT: It has been found that a set of Hertzian dipoles can be optimized to model the radiation characteristics of an antenna. However, the existing models are normally for narrowband antennas and invalid for a wideband antenna. In addition, it is difficult to combine several such models at different frequencies into a wideband model because the interpolation of dipole parameters is not applicable. This paper presents a procedure to optimize a Hertzian dipole model for a wideband antenna, where each dipole parameter is a polynomial in the phase constant. The tangential electric field on a surface enclosing the antenna is first obtained by full wave analysis at multiple frequencies. An optimization method is then applied to determine the polynomial coefficients for each dipole parameter, by minimizing the error between the exact field and the field due to the dipoles. As an example, a wideband stacked dielectric resonator antenna (DRA) is modeled by four electric and three magnetic Hertzian dipoles. The dipole model is used to efficiently study the radiation characteristics of the DRA mounted on a circular ground plane. Moreover, it is pointed out that the dipole model is resistant to Gaussian noise added to the near-field data, and is frequency scalable.
No preview · Article · Sep 2008 · IEEE Transactions on Antennas and Propagation
[Show abstract][Hide abstract] ABSTRACT: A linear array of longitudinal shunt slots etched on top of a substrate integrated waveguide was presented. This array was fed using the grounded co-planar waveguide mechanism to take advantage of the planar structure. A linear slot-array antenna was designed, fabricated and tested. We showed the concept of extending the linear array to a planar array using the appropriate microstrip feeding network.
[Show abstract][Hide abstract] ABSTRACT: The aperture coupled dielectric resonator antenna array fed by dielectric image line backed with a reflector was simulated using HFSS. A good return loss was obtained for an array of 7 DRA elements by adding cancelling slots with the radiating slots. Adding a reflector in the DIL side decreases the back radiation and increases the gain for the array.
[Show abstract][Hide abstract] ABSTRACT: A linear dielectric resonator antenna array fed by dielectric image line is presented. The effective dielectric constant method is used to approximate the coupling between the DIL and the DRAs. A Dolph-Chebyshev amplitude distribution was used to control the sidelobe level of the array radiation pattern. The cross polarization is suppressed by inserting a metal sheet at the center of the DRA or by inserting a microstrip line around the DRA at the center.
[Show abstract][Hide abstract] ABSTRACT: A transmission line (TL) method was proposed to compute the far-field radiation of Hertzian dipoles in a multilayer dielectric structure previously. This method is generalized here to deal with a structure embedded with perfectly electric conducting (PEC) strip interfaces. The problem is solved by analyzing an equivalent network, where each PEC strip interface is mapped into a four-port network, and each dielectric layer is mapped into two two-port networks for transverse electric (TE) and transverse magnetic (TM) modes. The S matrix of a four-port network is obtained analytically by applying the asymptotic boundary conditions. As an application, the PEC strip interfaces are used to reduce the cross polarization or rotate the polarization of a dielectric resonator antenna (DRA). In addition, the TL method is valid for a structure with any type of homogeneous and reciprocal layers whose S matrices are known. It is also able to solve two kinds of problems which cannot be done by a full-wave analysis equipped with a periodic boundary condition. Furthermore, the investigation of the system matrix singularity helps us to avoid the cavity mode in designing a radiating structure.
No preview · Article · Dec 2007 · IEEE Transactions on Antennas and Propagation
[Show abstract][Hide abstract] ABSTRACT: Analysis of dielectric resonator probe (DRP) arrays operating in an oversized hard waveguide with sectoral hard horn excitation is presented. A single DRP excited by a coaxial probe is first investigated inside a hollow rectangular waveguide and a waveguide loaded with hard walls, respectively. Simulation results are compared with measurement results and show a good agreement. Then, a one-dimensional DRP array is analysed inside a dielectric-loaded, oversized waveguide with sectoral hard horn excitation. A full-wave analysis based on the region-by-region finite-difference time-domain technique is applied for the optimisation of array parameters such as inter-element coupling, active reflection coefficients and uniform excitation. Numerical results are compared with those generated by using commercial software and exhibit a very good agreement.
[Show abstract][Hide abstract] ABSTRACT: Wideband probe-fed dielectric resonator antenna (DRA) arrays in an oversized dielectric loaded waveguide with hard horn excitation and radiating in free space are investigated for their use in waveguide-based spatial power-combining systems. A single embedded DRA element excited by a coaxial probe is analyzed first inside a hollow rectangular waveguide and a TEM waveguide. 1-D embedded DRA arrays are then studied inside the H- and E-plane sectoral hard horns. Finally, an entire spatial power-combining system with a 2-D embedded DRA array radiating in free space is analyzed. The analysis of the entire system is based on the finite-difference time-domain method with region-by-region discretization and subgridding schemes. The system's prototype of 2-D 3 times 3 embedded DRA array inside a pyramidal hard horn was fabricated and simulation results were compared with measurement results, showing a good agreement. Numerical results for radiation patterns are demonstrated for the examples of 2-D embedded dielectric resonator arrays excited by a pyramidal hard horn and radiating in free space.
Full-text · Article · Jul 2007 · IEEE Transactions on Microwave Theory and Techniques
[Show abstract][Hide abstract] ABSTRACT: Wideband coaxial probe-fed dielectric resonator antenna (DRA) arrays with hard horn excitation are investigated, In waveguide-based spatial power combining systems. The pyramidal horn is first studied by the Finite-Difference Time-Domain (FDTD) approach with region-by-region discretization and a uniform field distribution is obtained at the horn aperture. Then, a one dimensional 4 × 1 embedded DRA array is investigated inside E-plane sectoral hard horn. Finally, a two dimensional 3 × 3 embedded DRA array is studied inside a pyramidal hard horn. The systems' prototypes were fabricated and simulation results were compared with measurement results, showing a good agreement.
[Show abstract][Hide abstract] ABSTRACT: Vectorial modal analysis of a 2-D magneto-dielectric grating structure is presented. The modal analysis is combined with the generalized scattering matrix to obtain the transmission and reflection coefficients of multilayered 2-D magneto-dielectric grating slabs. The results are verified with available commercial codes. Physical interpretation of the grating slab behavior is introduced. An equivalent homogeneous magneto-dielectric slab is found using a simple approach for extracting the equivalent permittivity and permeability. Several examples are presented to find the relation between the physical parameters of magneto-dielectric grating slabs and their equivalent parameters. Emphasis on the possibility of designing a metamaterial with equivalent negative permittivity and/or negative permeability by using these grating structures is considered.
Full-text · Article · Jan 2007 · Progress In Electromagnetics Research