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A compact circularly polarized (CP) vertical patch antenna is presented that employs a microstrip to slot-line transition for a wideband operation. The antenna is composed of two vertical patches, which are shaped as helix to obtain a broadband CP performance. The loop structure and the vertical overlap configuration lead to significant size reduction as much as 48% when compared to that of the printed dual-loop antenna. Simulated results agree well with the measurement, showing that the antenna possesses a wide axial ratio (AR < 3 dB) bandwidth of 28.5%, and a broad return loss ([S.sub.11] < -10 dB) bandwidth of 37.8%. Also, it has symmetric radiation patterns and low cross-polarization levels in the broadside direction over the operating bandwidth. Moreover, the antenna gain is around 8 dBi, and it is very stable across the operating bandwidth. Index Terms--Broadband antennas, circularly polarized antennas, vertical patch antennas.

New broadband impedance matching circuits used to increase the impedance bandwidth of the microstrip antennas for transmit applications are proposed and analyzed. A microstrip patch operating at 10.5 GHz having 12.2% bandwidth has been utilized as a reference antenna. The impedance bandwidth of the antenna has been enhanced by using negative capacitance and inductance compensation networks from 12.22% to 16.96% and 24.50%, respectively. In addition, it has been shown that the active compensation significantly improves the radiation pattern. Index Terms--Active matching, bandwidth improvement, negative capacitance, negative inductance.

Genetic algorithm (GA) optimization is applied to the design of planar monopole antennas, which exhibit both ultrawideband (UWB) operation and a narrow-hand frequency notch. Such an antenna is useful in applications involving wideband communications where it is desired to mitigate interference with other radio systems colocated with the operating hand. It is demonstrated in this paper that traditional band-notched planar monopole antennas exhibit asymmetry in radiation patterns within the notch band such that the attenuation provided by the antenna varies as a function of azimuth angle, which lowers the effective bandwidth of the notch. A GA optimizer, which uses of a weighted sum cost function related to impedance matching and radiation patterns at frequencies within both the wide operating band and narrow notch band, is used to improve the performance of the band-notch planar monopole antenna. A two-dimensional (2-D) matrix chromosome is used in the GA to represent a wide-range on planar element shapes. It is shown that the GA generates antenna designs that exhibit equal wideband performance as traditional band-notched designs, but have improved azimuth plane radiation pattern symmetry, which widens the effective notch bandwidth. The GA-generated antenna design is measured and compared with simulation. Index Terms--Band-notched antenna, genetic algorithm (GA) optimization, planar monopole antenna, ultrawideband (UWB) antenna.

A triple-frequency antenna combining a dual-band and a monoband antenna with broadside radiation patterns is presented. The dual-band antenna is inspired in the Sierpinski fractal. Such a dual-band antenna is stacked over a monoband antenna. The antenna presents a broadband behavior at each band thanks to parasitic patches. The antenna has been designed using a MoM commercial code and has been experimentally tested, obtaining three bands with a broad bandwidth, high efficiency, and similar radiation patterns. Index Terms--Fractal-shaped antennas, microstrip antennas, stacked patches, triple-frequency operation.

Narrow band space-fed (lens) scanning arrays have played a major role in many military and commercial applications. However, wider bandwidth space-fed arrays with phase shifters in the objective aperture, and subarrayed time delay have not found many ready applications because of network losses, complexity, and more recently because of a perceived incompatibility with active solid state module technology. This paper demonstrates that a feed array with transmit/receive (T/R) modules and digitally reconfigured control, can accommodate both narrow band and radiation with relatively efficient use of the active sources.

We analyze the impact of the matching network on compact multiple-input multiple-output systems. Existing studies have found that the matching network has a significant influence on the performance of multiple antenna systems when the antennas are in close proximity. However, none has examined the wide-band case. In this paper, we investigate the wide-band performance of four different matching networks for multiple dipole antennas. The performance of the matching networks is given in terms of the bandwidths of correlation and matching efficiency, which are extensions of the single-antenna concept of bandwidth to multiple antenna systems. We also investigate the impact of the propagation conditions on the matching and bandwidth. For a uniform two-dimensional (2-D) angular power spectrum, we find that while individual-port matching can achieve in excess of 3% fractional correlation bandwidth for envelope correlation of 0.5 at an antenna separation of 0.01[lambda], multiport matching is required for efficiency bandwidth to exist for a return loss of -6 dB. Moreover, even with multiport matching, both correlation and efficiency bandwidths decrease drastically at small antenna separations. At 0.01[lambda], the correlation and efficiency bandwidths are 0.4% and 0.2%, respectively. Similar evaluations were performed for measured outdoor-to-indoor channels with moderate to small 2-D angular spreads. We find that the efficiency advantage of multiport matching over individual-port matching diminishes with decreasing angular spread. Index Terms--Antenna arrays, antenna efficiency, correlation, impedance matching, mutual coupling.

Combining the concepts of pulse fidelity, time-domain correlation patterns, and frequency-domain pattern stability, we propose the concept of frequency-domain correlation patterns and a figure of merit, called pattern stability factor (PSF), to characterize pattern stability of wideband antennas. The frequency-domain correlation pattern represents the relationship between radiation in a reference direction to radiation in all other directions of interest, over a specified bandwidth. With practical examples, we demonstrate that this tool is very useful when selecting a single transfer function (and a reference direction) for the antenna when designing or optimizing an ultrawideband (UWB) system. Careful selection of the reference direction is crucial for antennas with relatively less stable patterns, but even antennas with relatively stable patterns can perform poorly overall if an inappropriate reference direction is chosen. The PSF represents the overall pattern stability of an antenna for a specific bandwidth and a range of directions. It is useful as a quantitative measure: a) to compare the suitability of different antennas for a given wideband or multiband application; b) to assess pattern stability improvement methods; and c) to quantify the effect of packaging, etc., on stability. We also propose the concept of PSF bandwidth and show how it can be used to identify stable frequency bands of a given antenna within its impedance bandwidth, and how it compares with the impedance bandwidth of some UWB antennas. Index Terms--Antenna bandwidth, broadband, characterization, correlation, fidelity, multiband, optimization, pattern stability factor (PSF), radiation pattern, stability, transfer function, ultrawideband (UWB), wideband.

A new class of miniature printed embedded inverted-F antennas are proposed for operation in the 2.4-2.485 GHz wireless local-area network band. One of the proposed antennas on FR4 substrate (dielectric constant = 4.4) measures 9.2 mm by 4.1 mm and has a bandwidth of 3.5%. The peak gain of this antenna is 1.4 dBi. An overall size reduction of 70% is achieved compared to a conventional inverted-F antenna. Effects of dielectric loss tangent and material conductivity on the bandwidth and efficiency of these antennas are also investigated. Finally, two embedded antenna elements are analyzed to demonstrate the feasibility for a decoupled antenna pair consisting of switched and combining diversity schemes. Index Terms--Antenna, diversity, Hilbert, wireless.

A novel technique for enhancing the impedance bandwidth of wireless terminal antennas is presented. By introducing resonant short circuit transmission lines to the long sides of the chassis edges, an effective electrical shortening of the terminal ground plane is achieved. This effect has been used to realize terminal ground planes with resonant lengths at high frequencies, such as GSM 1800/1900 MHz or UMTS 2 GHz, thereby extending the impedance bandwidth. The proposed technique has been validated by simulations and measurements. Three typical applications are presented where the introduction of wavetraps improves the bandwidth and/or in-band performance. Index Terms--Bandwidth, broadband communication, microstrip antennas, mobile antennas.

A metamaterial paradigm for achieving an efficient, electrically small antenna is introduced. Spherical shells of homogenous, isotropic negative permittivity (ENG) material are designed to create electrically small resonant systems for several antennas: an infinitesimal electric dipole, a very short center-fed cylindrical electric dipole, and a very short coaxially-fed electric monopole over an infinite ground plane. Analytical and numerical models demonstrate that a properly designed ENG shell provides a distributed inductive element resonantly matched to these highly capacitive electrically small antennas, i.e., an ENG shell can be designed to produce an electrically small system with a zero input reactance and an input resistance that is matched to a specified source resistance leading to overall efficiencies approaching unity. Losses and dispersion characteristics of the ENG materials are also included in the analytical models. Finite element numerical models of the various antenna-ENG shell systems are developed and used to predict their input impedances. These electrically small antenna-ENG shell systems with idealized dispersionless ENG material properties are shown to be very efficient and to have fractional bandwidths above the values associated with the Chu limit for the quality factor without any degradation in the radiation patterns of the antennas. Introducing dispersion and losses into the analytical models, the resulting bandwidths are shown to be reduced significantly, but remain slightly above (below) the corresponding Chu-based value for an energy-based limiting (Drude) dispersion model of the permittivity of the ENG shell. Index Terms--antenna theory, Chu limit, complex media, electrically small antennas, electromagnetic theory, metamaterials.

In this paper, the far-field phase shift properties of microstrip patch antennas are investigated. It is shown that, similar to reflectarrays, the resonant nature of microstrip patches can be used to change the phase of the radiated field. This phase change can be caused by the dimensional change of the microstrip patch, or by a reactive loading of its cavity such as an aperture on its ground plane. However, the available phase shift is limited by the antenna impedance bandwidth. The problem is initially investigated for conventional patch antennas, determining the available phase shift range. It is then studied for a wideband E-slot microstrip antenna, showing a considerably larger phase shift range. Then, a micro-electro-mechanical (MEM) based ground plane membrane, activated by an electrode from below, is proposed to adaptively generate and control the required phase shifts. It provides a low loss, continuously variable phase shifter that can be used at high frequencies for beam scanning in small arrays. Index Terms--Far-field phase shift, frequency tuning, microstrip antenna, microstrip array, phased array.

This paper describes a design strategy to achieve the maximum bandwidth and efficiency for a printed slot antenna surrounded by EBGs. First the dielectric constant and the thickness of the dielectric slab that guarantees an acceptable front to back radiation ratio is identified. Then electromagnetic bandgap (EBG) structures are designed to achieve the optimal bandwidth (BW) while obtaining high surface wave efficiency in the radiating half space. To achieve this goal the wave interaction between the slot and the EBG structures is investigated in depth and clearly described. For the case of Planar circularly symmetric (PCS) EBGs the maximum of radiation BW is shown to occur when the distance between the central antenna and the EBG is approximately half wavelength of the first surface wave, [[lambda].sub.sw]/2. Index Terms--Electromagnetic bandgap (EBG), planar circularly symmetric electromagnetic bandgap (EBG), planar printed antennas, slot antennas, surface waves, wideband antennas.

A wide-band probe fed patch antenna with low cross polarization and symmetrical broadside radiation pattern is proposed and studied. By employing a novel meandering probe feed and locating a patch about 0.1[[lambda].sub.0] above a ground plane, a patch antenna with 30% impedance bandwidth (SWR < 2) and 9 dBi gain is designed. The far field radiation pattern of the antenna is stable across the operating bandwidth. Parametric studies and design guidelines of the proposed feeding structure are provided. Index Terms--Low cross polarization level, probe feed, wide-band patch antenna.

By supporting an L-probe coupled circular patch antenna with four metallic posts at appropriate locations, it is demonstrated that the conical and the broadside modes which are excited separately by two different sets of L-shaped probes, can be operated at the same frequency range. For a tested antenna operated at 1.85 GHz, the bandwidth (SWR < 2) achieved is 24%, and the isolation between the two input ports is 28 dB. The gains of the conical and broadside modes are 4 and 8.5 dBi, respectively. With suitable switching feed networks, the antenna can be reconfigurable in radiation pattern. The antenna can also be used as a pattern diversity antenna for modern mobile communications. Index Terms--Antenna radiation patterns, microstrip antenna, wide-band antenna.

Dielectrics are used in antenna design to support the printed structure and to also reduce antenna resonance and size. However, to our knowledge, dielectric volumes have not been used in the design process (by modifying or texturizing the dielectric) to possibly alter the overall performance and behavior of the antenna. In this paper, we begin with a given metallic geometry and show how changes in dielectric loading (position and permittivity values) can be used to produce a variety of antenna configurations having broadband and multi-band characteristics while still pursuing size reduction. More specifically, using a 15 cm x 15 cm x 6 cm antenna geometry, we show various designs giving resonant frequencies down to 350 MHz (0.175[[lambda].sub.0] linear dimension) and having bandwidths that can reach as high as 23.5% at 520 MHz (0.261[[lambda].sub.0] linear dimension). Also shown are designs with dual band characteristics. An example broadband design is fabricated and measured. Index Terms--Ceramics, dielectric loaded antennas, electrically small antennas, UHF antennas.

A novel internal dual-band patch antenna with a small thickness of 3 mm for application in Global System for Mobile Communication/Digital Communication System (GSM/DCS) mobile terminals such as the mobile phone or Personal Digital Assistant (PDA) phone is presented. The patch antenna occupies an area of 15 x 60 m[m.sup.2], with its top patch embedded with a simple T-shaped slit, which separates the top patch into two resonant paths to generate two resonant modes for 900/1800 MHz operation. Then, by extending a small portion of the top patch beyond the top edge of the system ground plane of the mobile terminal, the antenna can provide two wide bandwidths covering the GSM/DCS bands. The proposed antenna is experimentally studied, and effects of the extended top-patch portion and the ground-plane length on the obtained bandwidths are discussed. Index Terms--Antennas, dual-band antennas, Global System for Mobile Communication/Digital Communication System (GSM/DCS) mobile antennas, mobile antennas, mobile phone antennas, Personal Digital Assistant (PDA) phone antennas.

In this paper, the performance of the mobile phone handset antenna-chassis combination is analyzed based on an approximate decomposition of the waves on the structure into two resonant wavemodes: the antenna-element wavemode and the chassis wavemode. A double resonator equivalent circuit model is presented and used to estimate the impedance bandwidth and the respective distribution of radiation losses with typical parameter values at 900 and 1800 MHz. It is noticed that at 900 MHz, the radiation losses by the antenna element wavemode represent typically less than 10% of the total power. Thus, the antenna element works mainly as a matching element, which couples to the low-Q resonant wavemode of the chassis. At 1800 MHz, the contribution of the antenna element wavemode is larger. By enhancing the coupling and by tuning the chassis resonance, it is possible to obtain an impedance bandwidth of over 50% (6-dB return loss) at both at 900 and 1800 MHz. The results given by the equivalent circuit study are fully supported by those of three-dimensional phone-model simulations, including calculation of the SAR and efficiency values. In prototyping, the 6-dB bandwidth of 5.5 % was obtained at 980 MHz with a nonradiating coupling element with a volume of 1.6 [cm.sup.3] on a 120-mm-long chassis. Index Terms--Bandwidth, handset antennas, mobile communications, quality factor, resonators, small antennas.

A sleeve-cage monopole has parasitic wire elements that form a sleeve around the driven cage antenna. Appropriate placement and dimensions of the wire parasites lead to bandwidth enhancement. Genetic algorithms and an integral equation solver are employed to determine the position and lengths of the parasitic wires in order to minimize voltage standing wave ratio (VSWR) over a band. The cage is replaced by a normal-mode quadrifilar helix for height reduction and the resulting structure is referred to as a sleeve helix. Measured VSWR and input impedance data are in good agreement with computed data. A fabricated sleeve-cage monopole has a bandwidth ratio of 4.4:1 and a sleeve helix has a bandwidth ratio of 3.5:1 for measured VSWR less than 3.5. Index Terms--Genetic algorithms, helical antennas, monopole antennas.

A wideband and dual-frequency quarter-wave U-shaped patch antenna with two unequal arms on FR4 substrate is presented. The U-shaped patch antenna is fed electromagnetically by another coaxially-fed patch on the same layer, which operates at a higher frequency band. In this paper, we first proposed a new technique to obtain two closely staggered resonant modes to achieve a wide impedance bandwidth using two unequal arms of the U-shaped patch for the lower band. For the substrate thickness = 5, 7.5 and 11 mm, the measured bandwidths of the antennas operating around at 900 MHz are 7%, 10%, and 18%, respectively. Then, we modify the coaxially-fed patch so that both bands are wide in bandwidth. The resulting antenna operating at 900 and 1800-MHz bands with the substrate thickness = 11 mm has a measured impedance bandwidth of 13.3% and 20%, respectively. This thickness corresponds to 0.033 free-space wavelength at 900 MHz. The far-field radiation patterns are stable in the two operating bands. The proposed antenna is simple in structure compared with the regular stacked or coplanar parasitic patch antennas. It is highly suitable for indoor mobile communications. Index Terms--Bandwidth widening, electrically small antennas, multiple band antennas, microscript antennas.

We present a thin, uni-planar printed antenna that is electrically small and has a near omnidirectional radiation pattern. The antenna is based on a folded meander line slot radiator and uses a short circuit near the feed location to provide a good impedance match at the frequency of operation. The low cost antenna has a 10 dB return loss bandwidth of approximately 5% and a gain of near 0 dBi.

This paper presents a novel single-patch wide-band microstrip antenna: the E-shaped patch antenna. Two parallel slots are incorporated into the patch of a microstrip antenna to expand it bandwidth. The wide-band mechanism is explored by investigating the behavior of the currents on the patch. The slot length, width, and position are optimized to achieve a wide bandwidth. The validity of the design concept is demonstrated by two examples with 21.2% and 32.3% bandwidths. Finally, a 30.3% E-shaped patch antenna, resonating at wireless communication frequencies of 1.9 and 2.4 GHz, is designed, fabricated, and measured. The radiation pattern and directivity are also presented. Index Terms--Dual parallel slots, E-shaped, patch antenna, wide band, wireless communications.