Showing papers in "IEEE Transactions on Antennas and Propagation in 2008"

Dyadic Green's Functions for an Anisotropic, Non-Local Model of Biased Graphene

Abstract: Dyadic Green's functions are presented for an anisotropic surface conductivity model of biased graphene. The graphene surface can be biased using either a perpendicular static electric field, or by a static magnetic field via the Hall effect. The graphene is represented by an infinitesimally-thin, two-sided, non-local anisotropic conductivity surface, and the field is obtained in terms of Sommerfeld integrals. The role of spatial dispersion is accessed, and the effect of various static bias fields on electromagnetic field behavior is examined. It is shown that by varying the bias one can exert significant control over graphene's electromagnetic propagation characteristics, including guided surface wave phenomena, which may be useful for future electronic and photonic device applications.

Simple and Accurate Analytical Model of Planar Grids and High-Impedance Surfaces Comprising Metal Strips or Patches

Abstract: Simple analytical formulas are introduced for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied.

A Decoupling Technique for Increasing the Port Isolation Between Two Strongly Coupled Antennas

Abstract: A compact decoupling network for enhancing the port isolation between two closely spaced antennas is proposed in this paper. In the network, we first connect two transmission lines (TLs) individually to the input ports of two strongly coupled antennas. The length of the TLs is designed so that the trans-admittance between ports changes from a complex one at the antenna inputs to a pure imaginary one. A shunt reactive component is then attached in between the TL ends to cancel the resultant imaginary trans-admittance. Finally, a simple lumped-element circuit is added to each port for input impedance matching. The even-odd mode analysis is adopted to investigate the currents excited on the antennas for predicting the radiation pattern of the two-element antenna array. Two examples of printed antennas at 2.45 GHz are tackled by using the proposed decoupling structure. The measurement results agree quite well with the simulation ones. High antenna isolation and good input return loss are simultaneously achieved in both cases, which demonstrates the feasibility of the structure. The decoupled antenna array in each example radiates, as prediction, toward different but complementary directions when the input power is fed in turn to the two input ports. The array efficiency is estimated better than 75% in each example. This pattern diversity effect is helpful for reducing the channel correlation in a multiple-input multiple-output (MIMO) communication system.

A Compact Ultrawideband Antenna With 3.4/5.5 GHz Dual Band-Notched Characteristics

Abstract: We propose a compact planar ultrawideband (UWB) antenna with 3.4/5.5 GHz dual band-notched characteristics. The antenna consists of a beveled rectangular metal patch and a 50 Omega coplanar waveguide (CPW) transmission line. By etching two nested C-shaped slots in the patch, band-rejected filtering properties in the WiMAX/WLAN bands are achieved. The proposed antenna is successfully simulated, designed, and measured showing broadband matched impedance, stable radiation patterns and constant gain. An equivalent circuit model of the proposed antenna is presented to discuss the mechanism of the dual band-notched UWB antenna. A UWB antenna and a single band-notched one are also provided for references.

Metamaterial-Inspired Efficient Electrically Small Antennas

Abstract: Planar two-dimensional (2D) and volumetric three-dimensional (3D) metamaterial-inspired efficient electrically-small antennas that are easy to design; are easy and inexpensive to build; and are easy to test; are reported, i.e., the EZ antenna systems. The proposed 2D and 3D electrical- and magnetic-based EZ antennas are shown to be naturally matched to a 50 source, i.e., without the introduction of a matching network. It is demonstrated numerically that these EZ antennas have high radiation efficiencies with very good impedance matching between the source and the antenna and, hence, that they have high overall efficiencies. The reported 2D and 3D EZ antenna designs are linearly scalable to a wide range of frequencies and yet maintain their easy-to-build characteristics. Several versions of the 2D EZ antennas were fabricated and tested. The measurement results confirm the performance predictions. The EZ antennas systems may provide attractive alternatives to existing electrically-small antennas.

A Multiplicative Calderon Preconditioner for the Electric Field Integral Equation

Abstract: In this paper, a new technique for preconditioning electric field integral equations (EFIEs) by leveraging Calderon identities is presented. In contrast to all previous Calderon preconditioners, the proposed preconditioner is purely multiplicative in nature, applicable to open and closed structures, straightforward to implement, and easily interfaced with existing method of moments (MoM) code. Numerical results demonstrate that the MoM EFIE system obtained using the proposed preconditioning converges rapidly, independently of the discretization density.

Isolation Enhancement Between Two Closely Packed Antennas

Abstract: This paper introduces a coupling element to enhance the isolation between two closely packed antennas operating at the same frequency band. The proposed structure consists of two antenna elements and a coupling element which is located in between the two antenna elements. The idea is to use field cancellation to enhance isolation by putting a coupling element which artificially creates an additional coupling path between the antenna elements. To validate the idea, a design for a USB dongle MIMO antenna for the 2.4 GHz WLAN band is presented. In this design, the antenna elements are etched on a compact low-cost FR4 PCB board with dimensions of 20times40times1.6 mm3. According to our measurement results, we can achieve more than 30 dB isolation between the antenna elements even though the two parallel individual planar inverted F antenna (PIFA) in the design share a solid ground plane with inter-antenna spacing (Center to Center) of less than 0.095 lambdao or edge to edge separations of just 3.6 mm (0.0294 lambdao). Both simulation and measurement results are used to confirm the antenna isolation and performance. The method can also be applied to different types of antennas such as non-planar antennas. Parametric studies and current distribution for the design are also included to show how to tune the structure and control the isolation.

Elevation Dependent Shadowing Model for Mobile Communications via High Altitude Platforms in Built-Up Areas

Abstract: An empirical propagation prediction model is described for mobile communications from high altitude platforms (HAPs) in different types of built-up areas. The model introduced here is defined as a function of the angle of elevation. The target frequencies are selected from the 2 to 6 GHz frequency band prospective for 3G and 4G mobile systems, namely at 2.0,3.5, and 5.5 GHz. This new HAP model recognizes two cases - line of sight (LOS) and non-line of sight (NLOS) between a HAP and a user at street level. The simulation of the urban environment is based on a statistical approach. Additional shadowing path loss is calculated using the uniform theory of diffraction for NLOS conditions. Normal distribution of the additional shadowing path loss was distinguishable from the simulation results. The shadowing path loss is defined as a function of the elevation angle. The results of the empirical model developed for idealized conditions are verified by measurements taken from a remote-controlled airship in different types of urban environment. Close correlation was achieved between the theoretical model and the experimental data. The HAP elevation dependent shadowing model is easy to implement and can be used for realistic planning and simulations of mobile networks provided via HAPs in built-up areas.

Planar Ultrawideband Antennas With Multiple Notched Bands Based on Etched Slots on the Patch and/or Split Ring Resonators on the Feed Line

Abstract: Three types of ultrawideband (UWB) antennas with triple notched bands are proposed and investigated for UWB communication applications. The proposed antennas consist of a planar circular patch monopole UWB antenna and multiple etched slots on the patch and/or split ring resonators (SRRs) coupled to the feed line. Good agreement is achieved between the simulated and measured results. These techniques are significant for designing UWB antennas with multiple narrow frequency notched bands or for designing multiband antennas.

Mutual Coupling Reduction in Patch Antenna Arrays by Using a Planar EBG Structure and a Multilayer Dielectric Substrate

Abstract: Periodic structures can help in the reduction of mutual coupling by using their capability of suppressing surface waves propagation in a given frequency range. The purpose of this work is to show the viability of using a planar electromagnetic band gap (EBG) structure based on a truncated frequency selective surface (FSS) grounded slab to this aim. The goal is to use it in patch antenna arrays, keeping both the element separation smaller than for grating lobes avoidance (assuming broadside case) and the patch antenna size large enough to have a good antenna directivity. To this aim, a multilayer dielectric substrate composed of high and low permittivity layers is convenient. This allows the use of a planar EBG structure made of small elements printed on the high permittivity material and, at the same time, the low permittivity layer helps the bandwidth and the directivity of the antenna to be increased. The EBG structure was designed under these premises and optimized for the particular application via an external optimization algorithm based on evolutionary computation: ant colony optimization (ACO). The mutual coupling reduction has been measured and it is larger than 10 dB with a completely planar structure.

Design and Evaluation of a Reconfigurable Antenna Array for MIMO Systems

Abstract: New reconfigurable antenna array is demonstrated for multiple input multiple output (MIMO) communication systems that improves link capacity in closely spaced antenna arrays. The antenna system consists of an array of two printed dipoles separated by a distance of a quarter wavelength. Each of the dipoles can be reconfigured in length using PIN diode switches. The switch configuration can be modified in a manner adaptive to changes in the environment. The configuration of switches effects the mutual coupling between the array elements, and subsequently, the radiation pattern of each antenna, leading to different degrees of pattern diversity which can be used to improve link capacity. The PIN diode-based reconfigurable antenna solution is first motivated through a capacity analysis of the antenna in a clustered MIMO channel model. A new definition of spatial correlation coefficient is introduced to include the effects of antenna mismatch and radiation efficiency when quantifying the benefit of pattern diversity. Next, the widespread applicability of the proposed technique is demonstrated, relative to conventional half wavelength printed dipoles, using computational electromagnetic simulation in an outdoor and indoor environment and field measurements in an indoor laboratory environment. It is shown for the 2 times 2 system considered in this paper, that an average improvement of 10% and 8% is achieved in link capacity for a signal to noise ratio (SNR) respectively of 10 dB and 20 dB in an indoor environment compared to a system employing non reconfigurable antenna arrays.

60-GHz Patch Antennas and Arrays on LTCC With Embedded-Cavity Substrates

Abstract: The design is presented of aperture-coupled microstrip line-fed patch antennas (ACMPAs) and 4times4 planar arrays on Ferro A6-S low-temperature cofired ceramic (LTCC) substrate operating in the 60-GHz frequency band. In addition to the traditional ACMPA design, air cavities processed inside the LTCC substrate are used to improve the bandwidth and gain of the antennas. The arrays are excited through the microstrip-line feed networks using quarter-wave matched T-junctions and using Wilkinson power dividers. The results show that ACMPAs and arrays can be fabricated with a standard LTCC process even for the millimeter-wave region. Good agreement is achieved between simulations and measurements. The measured S-parameters indicate impedance bandwidths of 9.5% and 5.8% for the array elements with and without an embedded cavity. The measured maximum gains for the 16-element patch arrays (with and without cavity) are 18.2 and 15.7 dBi, respectively.

High Frequency Properties of Electro-Textiles for Wearable Antenna Applications

Abstract: A systematic study of the high frequency electrical properties of electro-textiles is presented in this paper. First, conductive thread characterization is completed with a waveguide cavity method. The effect of conductive thread density and comparison of several different types of conductive threads are included. Second, comparisons of knitted patterns and weave patterns are made in terms of effective electrical conductivity through a microstrip resonator method. The effect of various weave patterns on conductive and dielectric loss is detailed. Finally, the relevance of the high frequency characterization of the electro-textile materials is shown through electro-textile patch antenna fabrication and measurements. The efficiency of the fully fabric patch antenna is as high as 78% due to the use of low loss electrotextiles characterized in this paper.

Gains For RF Tags Using Multiple Antennas

Abstract: Backscatter radio systems, including high frequency radio frequency identification (RFID), operate in the dyadic backscatter channel - a two-way pinhole channel that has deeper small-scale fades than that of a conventional one-way channel. This paper shows that pinhole diversity is available in a rich scattering environment caused by modulating backscatter with multiple RF tag antennas - no diversity combining at the reader, channel knowledge, or signaling scheme change is required. Pinhole diversity, along with increased RF tag scattering aperture, can cause up to a 10 dB reduction in the power required to maintain a constant bit-error-rate for an RF tag with two antennas. Through examples, it is shown that this gain results in increased backscatter radio system communication reliability and up to a 78% increase in RF tag operating range.

Optimized Element Spacing for Low Sidelobe Concentric Ring Arrays

Abstract: It is described how to optimize the element placement in a concentric ring array to obtain the lowest maximum sidelobe level at boresight.

Design of Miniaturized Metamaterial Patch Antennas With $\mu$ -Negative Loading

Abstract: Recent theoretical studies have shown that circular patch antennas loaded by an inhomogeneous substrate partially filled with a mu-negative (MNG) metamaterial may in principle support a resonant radiating mode, even if the total size of the radiator is significantly smaller than the wavelength of operation. In those theoretical analyses, MNG metamaterials have been assumed as continuous, isotropic and readily available materials, characterized by a proper dispersion in frequency and by inherent ohmic losses. The fabrication of such compact antennas, however, would require the major effort of designing proper subwavelength inclusions that realize the MNG behavior of the substrate, and consequently a careful design of their geometry, location and orientation. The fabrication of a fully isotropic MNG sample to reside underneath the sub-wavelength patch, moreover, may be challenging with the current technological limitations. In this paper, we first show that the proposed sub-wavelength radiator may operate even when the fabricated MNG sample is not isotropic, due to the specific polarization of the magnetic field in the MNG region. Then, we propose a complete design of the magnetic inclusions, presenting full-wave numerical simulations of the structure, which effectively supports the expected resonant mode, despite the small size of the antenna. The comparisons among analytical results of the patch loaded by: (a) the ideal MNG sample applying a simple cavity model; (b) full-wave numerical simulations of the same antenna considering the presence of the feed; and (c) full-wave numerical simulations of the antenna loaded by the proposed magnetic inclusions, show how our design effectively simulate the presence of an MNG sample, allowing the realistic design of a sub-wavelength metamaterial patch antenna with satisfactory matching and radiating features. This may open up new venues in the realization of efficient metamaterial radiating components for practical purposes.

Reducing the Number of Elements in a Linear Antenna Array by the Matrix Pencil Method

Abstract: The synthesis of a nonuniform antenna array with as few elements as possible has considerable practical applications. This paper introduces a new non-iterative method for linear array synthesis based on the matrix pencil method (MPM). The method can synthesize a nonuniform linear array with a reduced number of elements, and can be also used to reduce the number of elements for linear arrays designed by other synthesis techniques. In the proposed method, the desired radiation pattern is first sampled to form a discrete pattern data set. Then we organize the discrete data set in a form of Hankel matrix and perform the singular value decomposition (SVD) of the matrix. By discarding the non-principal singular values, we obtain an optimal lower-rank approximation of the Hankel matrix. The lower-rank matrix actually corresponds to fewer antenna elements. The matrix pencil method is then utilized to reconstruct the excitation and location distributions from the approximated matrix. Numerical examples show the effectiveness and advantages of the proposed synthesis method.

Design of Ultrawideband Planar Monopole Antennas of Circular and Elliptical Shape

Abstract: An efficient approach is described for designing ultrawideband (UWB) antennas in the form of planar monopoles of elliptical and circular shape. To avoid the time consuming trial-and-error approach presented in other works, simple design formulas for this type of radiators are described and their validity is tested via electromagnetic analysis and measurements. Full electromagnetic wave investigations are performed assuming three types of substrates with wide range of dielectric constant and thickness. The presented results show that the proposed method can be applied directly to design planar antennas that cover the ultrawide frequency band from 3.1 GHz to more than 10.6 GHz. Four types of monopole antennas were manufactured using RT6010LM substrate and their operation was tested in terms of return loss, radiation pattern characteristics, gain, and time domain response. The developed antennas feature UWB behavior with near omnidirectional characteristics and good radiation efficiency. The time domain transmission tests between two identical elements show that the manufactured circular monopoles offer better performance in terms of distortionless pulse transmission than their elliptically shaped counter parts. These antennas are also assessed in terms of fidelity factor. The manufactured antennas show a high fidelity factor which is more than 90% for the face-to-face orientation.

A Novel Single-Feed Circular Microstrip Antenna With Reconfigurable Polarization Capability

Abstract: A single-feed circular microstrip antenna with reconfigurable polarization capability is proposed. This antenna has a simple structure, which consists of a radiating circular patch, five switches (PIN diode), three matching stubs, and a 50 microstrip feed line. It can be switched between 4 different states: two states (low-frequency and high-frequency) for linear polarization (LP), one state for left hand circular polarization (LHCP) and one for right hand circular polarization (RHCP) by controlling the bias voltage of two PIN diodes. At the same time, three switchable matching stubs are used for matching every polarization state. Simulation results and experimental results show that the proposed antenna demonstrates a low cross polarization level, good impedance bandwidth, and a very good axial ratio in the circularly polarized states.

Fast Analysis of Large Antenna Arrays Using the Characteristic Basis Function Method and the Adaptive Cross Approximation Algorithm

Abstract: The characteristic basis function method (CBFM) has been hybridized with the adaptive cross approximation (ACA) algorithm to construct a reduced matrix equation in a time-efficient manner and to solve electrically large antenna array problems in-core, with a solve time orders of magnitude less than those in the conventional methods. Various numerical examples are presented that demonstrate that the proposed method has a very good accuracy, computational efficiency and reduced memory storage requirement. Specifically, we analyze large 1-D and 2-D arrays of electrically interconnected tapered slot antennas (TSAs). The entire computational domain is subdivided into many smaller subdomains, each of which supports a set of characteristic basis functions (CBFs). We also present a novel scheme for generating the CBFs that do not conform to the edge condition at the truncated edge of each subdomain, and provide a minor overlap between the CBFs in adjacent subdomains. As a result, the CBFs preserve the continuity of the surface current across the subdomain interfaces, thereby circumventing the need to use separate ldquoconnectionrdquo basis functions.

Electromagnetic Characterization of Textured Surfaces Formed by Metallic Pins

Abstract: We develop a homogenization model to characterize textured surfaces formed by a periodic arrangement of thin metallic pins attached to a conducting ground plane: the ldquoFakir's bed of nailsrdquo substrate. It is demonstrated that the textured surface can be accurately modeled using a dielectric function, provided spatial dispersion effects are considered as well as additional boundary conditions. We derive closed analytical formulas for the reflection coefficient, and for the dispersion characteristic of the surfaces waves. In addition, it is demonstrated that the artificial substrate may mimic almost exactly the behavior of an ideal impedance surface boundary, and that the only physical factor that may limit this remarkable property is the skin depth of the metal. The reported results are supported by full wave simulations as well as by experimental data.

Integrating Compact Printed Antennas Onto Small Diversity/MIMO Terminals

Abstract: The integration of compact printed multielement antenna (MEA) systems on small diversity and multiple input multiple output (MIMO) terminal devices operating in the 5.2 GHz industrial, scientific and medical (ISM) band is presented. The investigated MEA systems comprise up to six printed elements (inverted F and Minkowski monopole antennas) and their performance is evaluated by means of the effective diversity gain (EDG) and the 1% outage MIMO capacity. The role of the propagation environment (both outdoor and indoor) on EDG is examined, proving that the uniform scenario is a good approximation to many real environments. The tradeoff study between system's performance and number of integrated antenna elements indicates that both diversity and MIMO performance saturate when placing more than five closely spaced elements. Even the least efficient 6-element system however, can be advantageously used as a reconfigurable 2-element array under the concept of receive antenna selection, since it provides significantly improved MIMO performance over a conventional 2-element fixed one. The paper concludes with a summary of useful guidelines for the MEA design optimization procedure that emanated from this study.

Bandwidth Improvement in Large Reflectarrays by Using True-Time Delay

Abstract: A significant improvement in the bandwidth of large reflectarrays is demonstrated using elements which allow true-time delay. Two identical, large reflectarrays have been designed using different phase distributions to generate a collimated beam. In the former, the phase distribution is truncated to 360deg as is usual in reflectarray antennas, while in the second, the true phase delay is maintained (three cycles of 360deg). The chosen phase-shifter elements are based on previously measured and validated patches aperture-coupled to delay lines. The radiation patterns for both reflectarrays have been computed at several frequencies and the gain is represented as a function of frequency for both cases. Bandwidth curves are presented as a function of the reflectarray size.

An Eigen-Analysis of Compact Antenna Arrays and Its Application to Port Decoupling

Abstract: Placing the radiators of antenna arrays closer than aggravates the problem of power mismatch. Based on efficiency considerations, a general analysis of this effect is presented, putting forward a simple tool to quantify, compare, and optimize the performance of antenna arrays. This analysis is not restricted with respect to the number of radiators or the degree of compactness. In order to improve power matching, a systematic approach for the design of lossless decoupling and matching networks based on 180 directional couplers is suggested for up to eight radiators. Implications of network losses, which have not yet received appropriate attention by researchers in the past, will be analyzed and discussed by means of a manufactured three-element prototype array.

Time-Domain Finite-Difference and Finite-Element Methods for Maxwell Equations in Complex Media

Abstract: Extensions of finite-difference time-domain (FDTD) and finite-element time-domain (FETD) algorithms are reviewed for solving transient Maxwell equations in complex media. Also provided are a few representative examples to illustrate the modeling capabilities of FDTD and FETD for complex media. The term complex media refers here to media with dispersive, (bi)anisotropic, inhomogeneous, and/or nonlinear properties present in the constitutive tensors.

An Iteration-Free MoM Approach Based on Excitation Independent Characteristic Basis Functions for Solving Large Multiscale Electromagnetic Scattering Problems

Abstract: We describe a numerically efficient strategy for solving a linear system of equations arising in the Method of Moments for solving electromagnetic scattering problems. This novel approach, termed as the characteristic basis function method (CBFM), is based on utilizing characteristic basis functions (CBFs)-special functions defined on macro domains (blocks)-that include a relatively large number of conventional sub-domains discretized by using triangular or rectangular patches. Use of these basis functions leads to a significant reduction in the number of unknowns, and results in a substantial size reduction of the MoM matrix; this, in turn, enables us to handle the reduced matrix by using a direct solver, without the need to iterate. In addition, the paper shows that the CBFs can be generated by using a sparse representation of the impedance matrix-resulting in lower computational cost-and that, in contrast to the iterative techniques, multiple excitations can be handled with only a small overhead. Another important attribute of the CBFM is that it is readily parallelized. Numerical results that demonstrate the accuracy and time efficiency of the CBFM for several representative scattering problems are included in the paper.

Substrate Integrated Waveguide (SIW) Rotman Lens and Its Ka-Band Multibeam Array Antenna Applications

Abstract: A new type of substrate integrated waveguide (SIW) multibeam antenna is proposed for mobile satellite communications using beam switching and diversity techniques. It employs an SIW Rotman lens as the beamforming network. The prototype of a single multibeam antenna is implemented at 28.5 GHz with seven input ports and an antenna array constructed by nine SIW linear slot arrays, which can generate a corresponding number of beams along one dimension. Several such antennas are grouped in two different ways to cover a 2-D solid angle with multiple beams. Experiment results show that the 2-D solid angle around (-40deg, 40deg) X (-35deg, 35deg) or (-25deg, 25deg) x (-35deg, 35deg) are covered with 20 or 25 beams with 5 -dB beamwidth, respectively. It is demonstrated that this type of printed multibeam antenna is a good choice for communication applications where mobility and high gain are simultaneously required.

Signal Radiation and Power Losses of Time-Modulated Arrays

Abstract: We review and formalize the mathematical background of time-modulated linear arrays (TMLAs); then, a number of issues are examined. First, for signal transmission applications, restrictions to the frequencies involved in the procedure are highlighted. Second, the sideband power losses associated to the technique are thoroughly examined, introducing a coefficient appropriate to evaluate the efficiency of the procedure. Finally, a closed form expression for the total power associated to sideband radiation is obtained, very convenient for the implementation of real-time optimization of the system. Relevance of additional research on the subject is highlighted.

Transmission-Line Networks Cloaking Objects From Electromagnetic Fields

Abstract: We consider a novel method of cloaking objects from the surrounding electromagnetic fields in the microwave region. The method is based on transmission-line networks that simulate the wave propagation in the medium surrounding the cloaked object. The electromagnetic fields from the surrounding medium are coupled into the transmission-line network that guides the waves through the cloak thus leaving the cloaked object undetected. The cloaked object can be an array or interconnected mesh of small inclusions that fit inside the transmission-line network.

A Reconfigurable High-Gain Partially Reflecting Surface Antenna

Abstract: A high-gain partially reflective surface (PRS) antenna with a reconfigurable operating frequency is presented. The operating frequency is electronically tuned by incorporating an array of phase agile reflection cells on a thin substrate above the ground plane of the resonator antenna, where the reflection phase of each cell is controlled by the bias voltage applied to a pair of varactor diodes. The new configuration enables continuous tuning of the antenna from 5.2 GHz to 5.95 GHz using commercially available varactor diodes, thus covering frequencies typically used for WLAN applications. Both the PRS and phase agile cell are analyzed, and theoretical and measured results for gain, tuning range, and radiation patterns of the reconfigurable antenna are described. The effect of the varactor diode series resistance on the performance of the antenna is also reported.