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Antennas and Propagation, 2001. Eleventh International Conference on (IEE Conf. Publ. No. 480)

Date 2001

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Displaying Results 1 - 25 of 110
  • Interference effects induced by an adjacent terrestrial microwave system on the performance of a triple-site dual polarized Earth-space system

    Page(s): 637 - 640 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    Frequencies above 10 GHz are of high importance in current satellite systems. In this band of frequencies attenuation and depolarization caused by rain are the basic limiting factors affecting the performance of these systems in heavy rain climatic regions. Site diversity protection is a mitigation technique for reducing the link fade margins. In some severe cases such as operation in the Ka band (20/30 GHz), the double-site diversity can be proved to be inadequate leading to the employment of triple diversity. In addition, the reliable design of these systems requires the consideration of interference effects. Because of the inevitably necessity for establishment of operating satellite Earth stations and terrestrial microwave systems at the same location, the following interference problem: “a triple-site dual-polarized system interfered by an adjacent terrestrial microwave operating at the same frequency ”, addressed by Hosoya et al. (1980) will be usual in the near future. In this case, the degradation of the carrier-to-interference ratio (CIR) is due to differential rain attenuation along with cross polarization. In this paper, an analytical propagation model for the prediction of the (CIR) statistics is presented View full abstract»

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  • Broadband analysis of finite microstrip patch antenna structure using FDTD

    Page(s): 403 - 407 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    Broadband analysis of a microstrip patch antenna on a finite substrate is investigated using the finite difference time domain (FDTD) method. The effects of varying the ground and dielectric size against the return loss at the input port and the far fields are discussed. Two different ways of feeding the antenna are addressed. The problem space size requirements of the FDTD method are presented. A thin wire code that includes the wire radius of the coaxial feed cable is used. The frequency response of several microstrip patch antennas is analysed over wide bandwidths, using Gaussian pulses with a total bandwidth of 20 GHz. The results are in good agreement with measurements View full abstract»

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  • Electromagnetic scanning 3 element array with integral phase shifters

    Page(s): 664 - 667 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    A compact linear array is presented featuring beam scanning with simple ferrite microstrip phase shifters. The advantage of this system over other ferrite devices is the small variable bias field necessary. Permanent magnets are combined with electromagnets to achieve beam steering of 30° for drive currents of about 2 A. An alternative implementation in a stripline is also considered View full abstract»

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  • FDTD simulation for small antenna geometries by using non-uniform mesh algorithm

    Page(s): 408 - 411 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    Numerical modeling of realistic engineering problems using the FDTD technique often requires smaller cell size, higher simulation accuracy and less computation resources. But in the simulation of small antennas, an obvious limitation of FDTD simulation is the trade-off between accuracy and computation resource. To reduce the computation resource for FDTD calculation, a high performance solution, the non-uniform mesh FDTD was proposed in a previous paper (see IEICE Trans. Commun., vol.E83-B, no.7, p.1544-53, 2000). The proposed algorithm allows flexible cell size, which can improve the accuracy of modeling and reduce the computation resource. In this paper, we calculated several small antenna geometries by using the non-uniform mesh FDTD algorithm. The computer simulation results are compared with the uniform mesh FDTD method and measurement results View full abstract»

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  • Antenna design and optimization with CLASP

    Page(s): 470 - 474 vol.2
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    The CLASP suite of computer programs is some of the most advanced software in the UK for electromagnetic analysis using the method of moments in the frequency domain. This paper describes a variety of practical design calculations of antenna directivity using the software View full abstract»

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  • Wideband channel dynamics (measurement and simulation)

    Page(s): 428 - 431 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    The increasing demands on the limited frequency spectrum combined with the higher data rate requirements imposed by the convergence of data and voice services mean that increasingly, mobile operators are turning to spectrally efficient wideband systems such as code division multiple access (CDMA). However, in order to successfully implement capacity enhancement techniques, or to design a reliable wireless data link, a detailed knowledge of the radio channel is required. Ideally, accurate spatial channel models and wideband non-stationary channel models are required to evaluate the proposed technologies. It is the aim of this paper to present and discuss selected results derived from power delay profiles (PDPs) which were obtained during a set of propagation trials conducted at 1.9 GHz in central London by Nortel Networks Radio Technology Group in 1999. It also presents results from an enhanced version of the Turin et al. (1972)/Hashemi (1977) wideband, non-stationary simulation of the urban radio propagation (SURP) model which uses statistics derived from the wideband London measurements View full abstract»

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  • Cylindrical dielectric resonator antenna arrays

    Page(s): 668 - 671 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    In this paper, the study of dielectric resonator antenna arrays is reported. The results of two- and four-element linear arrays in two configurations and a four-element planar array are presented. It is shown that different configurations can be used to form cylindrical dielectric resonator antenna broadside arrays. A gain of the order of 10 dB can be achieved using two or four elements. The simulated and measured results also show that the arrays have a usual bandwidth for applications in radar or wireless communication systems View full abstract»

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  • First results of a long-term propagation experiment at 19 GHz

    Page(s): 542 - 545 vol.2
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    A long term propagation experiment at 19 GHz and V polarisation on a 27.3 km long path was started in April 1995. The investigation was focused on attenuation due to hydrometeors (rain, hail, snow). The measured data from the 5-year period of observation were statistically processed and the cumulative time distributions of attenuation due to hydrometeors were obtained. The experiment was finished in March 2000. Rain intensities were measured by means of a siphon raingauge located near the path. Cumulative time distributions of rain intensities were obtained. The distributions obtained were compared with the 50-year distributions of rain intensities measured in the Czech Republic. The obtained cumulative time distributions of attenuation due to hydrometeors as well as the cumulative time distributions of rain intensities were also compared with the cumulative distributions calculated in accordance with the corresponding ITU-R Recommendations. The best methods for the calculation of cumulative time distributions of attenuation due to hydrometeors from the cumulative time distribution of rain intensities were determined for the 19 GHz frequency band in accordance with the ITU-R criterion View full abstract»

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  • Degradation in neural network prediction models of f0F2 with time

    Page(s): 787 - 791 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    Ionospheric forecasting services fall short of the precision required for many practical applications. In-service models of ionospheric parameters often fail to offer much of an increase in performance over simple persistence or recurrence. In particular, predictions of storm events and disturbances are very poor. This performance shortfall can be attributed to several causes one of which is an inability to adequately model solar-magnetospheric-ionospheric physics. To circumvent this knowledge gap some authors have adopted knowledge independent (time-series) modelling techniques that can utilise typical ionospheric data sets. A number of experimental and theoretical studies have demonstrated the importance of non-linear behaviour within the solar-terrestrial environment. Attention has also turned to time series predictive methods derived from studies into artificial intelligence (AI) and the application of neural network (NN) based techniques to geophysical prediction problems. Francis et al. (2000) undertook a study of neural networks for the prediction of the ionospheric parameter f0F2 based on the use of historical data from the 1970s. The resultant model for the one hour ahead prediction of this parameter had an RMS error of only ~0.4 MHz. A version of this model, but re-optimised, was incorporated in the Ionospheric Forecasting Demonstrator (IFD). However, it soon became clear that the predictive capability of the IFD was degrading with time. This paper reports on our studies to understand the reasons for this degradation and to improve the model View full abstract»

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  • Dielectric feed for dual band operation of parabolic reflector antennas

    Page(s): 701 - 704 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    A dielectric feed for dual band operation of non-offset parabolic reflectors is presented. It works in the bands 3.6-4.2 GHz and 6.425-7.125 GHz. Simulations show a VSWR<1.15 and an efficiency of more than 60% in a 3 m parabolic reflector with a subtended half angle of 90 degrees. Measurement data are not yet available as the corresponding feed network is still under development View full abstract»

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  • Broadband probe-fed patch antenna with reduced cross-polarisation radiation

    Page(s): 525 - 528 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    This article presents novel designs of broadband patch antennas with reduced cross-polarisation radiation. The design for a 1×2 probe-fed E-patch subarray antenna fed by using two feeds of a 180°-phase shift is first demonstrated. Results for the same technique applied to a broadband single-patch microstrip antenna fed by dual L-strip coupled feeds are also presented. Finally, a new design of a broadband probe-fed E-shaped patch antenna with a U-shaped ground plane is proposed. These broadband designs all show reduced cross-polarisation for operating frequencies within a wide impedance bandwidth View full abstract»

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  • The characteristics of rainfall and melting layer in Singapore: experimental results from radar and ground instruments

    Page(s): 852 - 856 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    The radio frequencies used by current and future satellite communications systems have been gradually shifted towards higher bands due to a rapidly increasing demand for bandwidth. At higher frequencies, such as Ku-band systems, which have been deployed widely in most of the Asian countries, rain-induced attenuation can severely affect the availability of the Earth-satellite communications service. In particular, tropical regions have posed extra difficulties in predicting attenuation due to the lack of understanding of tropical precipitation and climate, e.g., rainfall intensity and rainfall heights. Moreover, millimetre wave specific attenuation is very dependent on raindrop size distributions. In addition, total path integrated attenuation on satellite paths depends on the maximum height of rainfall. To explore these uncertainties, the Radio Communications Research Unit (RCRU) at Rutherford Appleton Laboratory (RAL) installed a tropical rain radar in 1998. We aim to study the characteristics of tropical rainfall and predict attenuation by utilising data gathered by rain radar, distrometer and a ground-based beacon receiver. Moreover, this radar has been involved with the ongoing Tropical Rainfall Measurement Mission (TRMM) and EuroTRMM projects to improve our understanding of the characteristics of tropical rainfall View full abstract»

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  • Size reduction of printed quadrifilar helical antenna using simulated annealing

    Page(s): 565 - 568 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    We have presented a method to reduce the size of a printed quadrifilar helical antenna (PQHA) by the modification of the antenna pitch angle on each segment of the wires. A global optimisation method (simulated annealing) has been used in order to obtain the optimum pitch angles according to the desired radiation pattern. A size reduction of 14% has been obtained in comparison to the conventional PQHA while maintaining the same features (half power beamwidth, axial ratio, impedance) View full abstract»

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  • FD-TD modelling of microstrip patch antennas

    Page(s): 412 - 414 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    This paper describes FD-TD (finite difference-time domain) modelling of a dual band multi-layered microstrip patch antenna operating at 35 GHz on an in-house fabricated semi-insulated GaAs substrate. The simulated and measured resonant frequencies at both lower and upper resonant frequencies are compared to check the accuracy of the different EM modelling techniques View full abstract»

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  • Active integrated antennas using the direct-conversion detection

    Page(s): 475 - 478 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    Two active integrated antennas are implemented to act as direct-conversion receivers. These active antennas can be applied for Doppler frequency detection, I&Q demodulation and direction finding View full abstract»

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  • Planar antenna arrays on LTCC-multilayer technology

    Page(s): 710 - 714 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    This paper present the design and prototyping of different 24.125 GHz low temperature co-fired ceramic (LTCC) aperture-coupled patch antenna arrays for ISM-band applications. Thorough analysis of material loss, gain and bandwidth shows the LTCC material to be well suited for realising antenna arrays up to the typical ceramic wafer size of about 15×15 cm2 (6×6 in2). Some aspects of the prototyping process like the implementation of meshed ground planes and the realisation of integrated thick film resistors are discussed. Various measurements of far field patterns and gain are presented and found to be in good agreement with the simulation results. Finally, the measurement results of different antenna prototypes show very good reproducibility View full abstract»

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  • Measuring wide angle antenna performance using small planar scanners

    Page(s): 451 - 455 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    A technique for the prediction far field antenna patterns from data obtained from non-coplanar partial scans is presented. The applicability of this technique in the measurement of antenna assemblies in planar facilities that would normally be considered too small to acquire suitable near field data, sufficiently free from truncation, is illustrated. The accuracy of the transformation technique is assessed via the application of a novel statistical measure of association. The derivation of this metric of association is accomplished through an unconventional analysis of the ordinal aspects of the predicted far field interval data. The limitations of the technique are explored and the directions to be followed in subsequent research are discussed View full abstract»

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  • High temporal-resolution channel characteristics at 40 GHz from a 30 km slant path radiowave propagation experiment

    Page(s): 839 - 843 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    Propagation at millimetric frequencies (30-300 GHz) is highly dependent on tropospheric phenomena such as rain, clouds, fog, water vapour and atmospheric gases, all of which combine to cause signal absorption, dispersion and scattering. The need to accurately characterise the signal propagation channel in both time and frequency is essential not only for cost effective system design, but also to minimise interference and optimise globally deployable mobile links. Although models exist to predict (e,g, MAPEL, ITU) the long term attenuating characteristics of the tropospheric channel due to clouds, rain, water vapour and atmospheric there is limited information regarding characteristics of the channel. For example, MAPEL may predict a 1% (~7 hours) monthly signal-outage in June at a signal to noise threshold of 15 dB. To optimise and evaluate key system elements such as AGC loops, mobile antenna tracking loops, adaptive data-rate schemes, etc., it is important to know if the predicted 7 hour outage is distributed. For example, does it occur in a few long (e.g. 1 hour) periods, or in small (<1 min) segments; how long before such an event occurs again ? To obtain high (<l s) temporal-resolution channel data, a slant path experiment was designed to represent a short range air-ground link. Although the complete trial data-set comprises 28 days of data, this paper only presents an analysis of a small sub-set in order to provide illustrative channel characteristics View full abstract»

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  • Delay profile in quasi-millimeter band for fixed wireless access in urban area

    Page(s): 682 - 685 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    This paper describes the estimated delay profile in the quasi-millimeter band for a fixed wireless access system considering a statistical model of buildings in an urban area. The signal scattered by the buildings is estimated by the GTD method. Assuming random location of the buildings makes the estimation extremely complex: numerical integration corresponding to the Huygens-Fresnel principle is improved to reduce computation time. The shadowing effect of the buildings is considered for both of two paths between the reflection point, and the antennas of the base-station and subscriber. This effect is estimated as the possibility to receive the scattered signal under the condition that there is a line-of-sight path between the two antennas. The calculated delay profile has a bump in the region with short delay in addition to a Rayleigh distribution. Similar delay profiles are obtained for various business regions in Tokyo. The reflected signal is lower than the line-of-sight signal by about 50 dB when the distance between the base-station and subscriber is about 1 km. The results suggest that good channel conditions are obtained for a short distance line-of-sight communication system View full abstract»

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  • UMTS spatio-temporal propagation trial results

    Page(s): 497 - 501 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    The demand for novel signal processing architectures in mobile communication systems has never been greater. This is driven by the increasing demand for multimedia services and the inevitable rollout of 3G cellular systems such as Universal Mobile Telecommunications System (UMTS). Two techniques that are currently being considered to meet this demand are: multi-user detectors (MUDs) and smart antennas. In order to assess the performance of these techniques, the characteristics of the environments is of prime importance. This paper reports on a spatio-temporal measurement system that has been used to measure the multi-dimensional channel characteristics. The trials data can be used to assess the performance of MUDs and smart antennas for UMTS. The system has been used to characterise a number of representative environments, namely: urban, rural, indoor and outdoor-indoor. The channel data allows an appraisal of UMTS Terrestrial Radio Access (UTRA) Frequency Division Duplex (FDD) and Time Division Duplex (TDD) wireless communications systems incorporating novel signal processing techniques. Thus, the relative merits of each can be determined View full abstract»

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  • Model for the analysis of microstrip cylindrical antennas: efficient calculation of the necessary Green's functions

    Page(s): 615 - 618 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    Conformal antennas are of great interest, because there are lots of applications which require non-planar surfaces and therefore non-planar substrates, for example circular ones. To analyse such structures corresponding rigorous theoretical approaches should be developed. Because of the more complex geometry conformal antennas are less investigated than planar ones. However in general the lines of reasoning may be very similar. Here we follow an approach that was proposed and successfully realised for planar multilayer antennas. The main idea of this approach is to solve the problem in the spatial domain. This line of strategy is realised for circular microstrip patch antennas. In this paper the problem of a patch microstrip antenna printed on a circular metal-dielectric substrate (circular metal rod coated by a dielectric layer) is discussed. Mixed-potential integral equations for the electric field are constructed. These equations contain spatial Green's functions for sheet electric currents and they can be solved using the moment method. In order to realise the proposed scheme we should be able to calculate spatial Green's functions very efficiently. This is really a key point of the problem, which is successfully solved in this paper View full abstract»

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  • Hybrid method for time-domain analysis of wire antennas embedded in a scattering dielectric medium

    Page(s): 861 - 865 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    A hybrid time domain method for the analysis of embedded wire antennas is presented. The radiation from wire antennas placed within a heterogeneous dielectric medium is strongly dependent on near-field coupling effects and backscatter from material discontinuities. A time-domain MoM solution for the embedded wire antenna is combined with an FDTD model of the surrounding dielectric structure. The induction theorem is used to interface the sub-domains and establish equivalent current sources while also allowing scattered fields to re-enter the MoM (source antenna) domain. The technique is validated by comparing the hybrid model with a standard MoM solution for an 8-mm loop antenna with wire radius of 0.2 mm. The loop antenna was centred within a 30×30×30 cell FDTD domain composed of 5-mm voxels View full abstract»

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  • A waveguide array for an unmanned airborne vehicle (UAV)

    Page(s): 810 - 813 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    As part of the CORE radar developments taking place at Astrium UK (formally MMS(UK)) there is a desire to accommodate future synthetic aperture radar (SAR) users who are looking away from space applications towards more airborne based operations. Here the user is looking for very low ownership and operating costs and is naturally attracted to the UAV concept. UAV has by its very nature a more localized theatre of operation, and is ideally suited to policing and disaster monitoring for example. In SAR terms, the advantages of night time, all weather and through smoke/cloud cover operation is very attractive. The UAV that Astrium has under consideration will operate at X-band frequencies using an X-band narrow wall slotted waveguide array composed of individual subarray modules View full abstract»

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  • A new formulation for rain scatter interference

    Page(s): 627 - 631 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    Fundamental to frequency management and spectrum efficiency is the need to share the available radio spectrum among a number of services in such a way that maximum exploitation and minimum interference are achieved simultaneously. One of the most widespread applications in which spectrum is shared between two services is that of terrestrial and satellite-based radio communications systems, where it is of primary importance to protect sensitive earth station receivers operating to satellites in the geostationary orbit from harmful interference from terrestrial transmitters using the same frequency bands. A new model for the path loss in rain scatter has been developed in which the earth station elevation angle is now an input parameter, in order to derive more reliable and more widely applicable estimates of rain scatter interference. This paper describes the rain scatter process and the development of the new formulation, together with comparisons between the resulting predictions of path loss with those derived from the existing model. Comparisons are also given between the new model and the predicted path losses and experimental measurements of rain scatter interference obtained within the COST 210 project, which considered the influence of the atmosphere on interference between radio communications systems at frequencies above 1 GHz, and led to the rain scatter model in Recommendation P.452-9 View full abstract»

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  • Fractal antenna research at University of Birmingham

    Page(s): 724 - 727 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    The use of fractal geometry in electromagnetics has been a recent topic of interest. In antenna applications, the Minkowski loop, the Koch curve monopole, the Koch island patch, the Sierpinski carpet and the Sierpinski gasket have been reported. In particular, the fractal Sierpinski gasket monopole antenna which demonstrates a log periodic resonant property. Although the fractal structure from these mathematical functions could provide attractive multiband performance, it has become clear that such geometry requires further modification to enhance their application. However, perturbation effectively varies the structural properties, and hence electrical properties. In this paper, we present two recent developments of these fractal monopole antennas at the University of Birmingham. The first development describes the multiband behaviour of a perturbed fractal Sierpinski gasket and a perturbed Parany monopole antenna. Both antennas have a periodic ratio of 0.75 and 0.775 respectively. The first antenna demonstrates four operating bands while the latter design involves eight bands. Two methods are presented to demonstrate improvements to the inherently poor input impedance match of these antennas with a 50 Ω port. These improved feeding methods will allow further flexibility to the application of these multiband antennas. The second development looks into an alternative multi-level structure antenna which may provide bandwidth improvements without sacrificing antenna performance. The design consists of a set of self similar circular rings, as an alternative to the triangular fractal Sierpinski gasket monopole antenna. A comparison of both antennas with scale factor of 0.5 is described View full abstract»

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