Buy issue PDF
- $135.90
IET Microwaves, Antennas & Propagation
Volume 5, issue 4, 21 March 2011
Volumes & issues:
Volume 5, issue 4
21 March 2011
-
- Author(s): Z.H. Firouzeh; R. Moini; S.H.H. Sadeghi; R. Faraji-Dana
- + Show Description
-
Hide details
-
p.
379
–385
(7)
This study presents a robust and efficient approach for derivation of non-symmetrical closed-form Green's functions for microstrip structures. In this method, the discrete complex image technique is used to extract the closed-form expressions for stratified Green's functions. The surface-wave poles in these expressions are first extracted using a recursive contour integration method. The remainder is then approximated by a series of complex exponentials using either the Prony's method or the generalised pencil-of-function (GPOF) along the extended rooftop-shaped path in kρ-plane. An analytical identity is subsequently employed to obtain the new spatial-domain Green's functions. For calculation of the integral of GzxA with respect to x, it is observed that only a single approximate Green's function can accurately represent both the near and far fields. Moreover, the method generates accurate results in the near-field region when z′≠z and ρ→0. A two-part expression for the non-symmetrical potential GzxA is introduced as well. This two-part approximation is very accurate and computationally fast for the entire range of distances, especially when z=z′≠0 or z′≠z. - Author(s): P. Sobis; J. Stake; A. Emrich
- + Show Description
-
Hide details
-
p.
386
–392
(7)
Two compact and simple to design differential phase shifter topologies, based on high/low-impedance transmission-line sections and open-ended coupled-line sections, are presented for the first time. The basic circuit theory for single section topologies is reviewed, leading to design equations and graphs for direct circuit synthesis. Balanced topologies and multiple section designs are also proposed improving the performance and feasibility of the phase shifters. Two planar microstrip single section differential phase shifter hybrids, at a centre frequency of 12 GHz and a 45 and 135° phase difference have been designed and manufactured. The designs have a simulated 0.5 dB amplitude and 1° phase imbalance over more than 25 and 40% bandwidth, respectively. Experimental results verify the circuit performance and feasibility of the proposed differential phase shifters. - Author(s): A.L. Amadjikpè; D.J. Chung; S. Courrèges; P. Eudeline; A. Ziaei; J. Papapolymerou
- + Show Description
-
Hide details
-
p.
393
–401
(9)
A two-pole evanescent-mode waveguide narrow-band filter digitally tunable with micro-electromechanical system (MEMS) switches is demonstrated. A design approach for a prescribed frequency shift and tuning range is elaborated using a simple equivalent circuit model. The validity of the proposed frequency tuning concept is proved through simulation and measurement of a prototype. The measured tunable filter achieves three resonant states around 3 GHz, with an average frequency tuning of 20 MHz between each state, a fractional 1-dB bandwidth of 1.2–1.5% and better than 2.1 dB insertion loss. The measured unloaded quality factor (Q) of the filter varies from 315 to 460 over the frequency tuning range. - Author(s): S.I. Latif; L. Shafai; C. Shafai
- + Show Description
-
Hide details
-
p.
402
–411
(10)
When microstrip antennas are miniaturised, because of high ohmic losses, their gain and efficiency drop significantly. In this study, a new technique is presented to improve these two important parameters of such antennas, where multiple laminated conductors are used to form the conducting patch. The technique essentially reduces the ohmic losses, and consequently improves the gain and efficiency. At first, a planar conductor is studied to show that using multiple laminated conductors, instead of a single conductor of the same thickness, losses can be reduced. The same technique is then used in several miniaturised microstrip antennas, in order to reduce their ohmic losses. It is shown that this process enhances the gain and efficiency of these antennas progressively, by increasing the number of layers in the lamination. Simulation studies on two miniaturised antennas have provided about 1.5 and 2.4 dB improvement in the gain, and from 30 to 40.7% improvement in the efficiency. Experimental investigations are also conducted and confirmed the simulated results. For a microstrip square ring antenna, a measured gain enhancement of 2.16 dB at 2.2 GHz is obtained, by laminating only the ring with four conducting layers. - Author(s): K. Konstantinou; S. Kang; T. Brown; C. Tzaras
- + Show Description
-
Hide details
-
p.
412
–418
(7)
The evaluation of communication systems with low-height terminals requires path loss models that are applicable to low-height links. For the terminology low-height, the range 0.5 (mobile-) to 3 m (fixed-node) above ground is considered. Herein, empirical non-time-dispersive propagation models for relaying systems with low-height terminals are proposed. The models consist of line-of-sight and non-line-of-sight branches. Single- and two-slope modelling approaches were examined. The models take into account the effect of frequency, transmitter and receiver height and environment. They are complemented by shadowing and fast-fading distribution and correlation statistics. The performance of the models in producing accurate estimations is evaluated by comparison with sets of independent data. - Author(s): E. Garcı́a; C. Delgado; L. Lozano; F. Cátedra
- + Show Description
-
Hide details
-
p.
419
–425
(7)
A study on the parameters of an approach that combines the characteristic basis function method and the multilevel fast multipole algorithm is presented. This approach is a very efficient scheme for the rigorous computation of electrically large problems. An analysis of the configuration parameters of the method to obtain accurate results reducing CPU time is shown. Non-uniform rational B-splines surfaces are employed for the representation of the geometry and the characteristic basis functions are described in terms of curved rooftops generated in the parametric space. The associated macro-testing functions are defined as aggregations of curved razor–blade functions. - Author(s): S. Shahid; J.A.R. Ball; C.G. Wells; P. Wen
- + Show Description
-
Hide details
-
p.
426
–432
(7)
Methods to determine resonant cavity Q-factor from vector network analyser reflection data are often quite complex. This study presents a simple method which makes use of two least squares algorithms applied sequentially. Firstly, a circle is fitted to the data, which is then projected onto a linear frequency scale using the Ginzton technique. A straight line is fitted to the projected data, and the loaded Q-factor and the resonant frequency are obtained from the line coefficients. The method has been tested on both synthetic and experimental data, and compared with the Kajfez QZERO software, and the results are shown to be accurate to a fraction of 1%. - Author(s): Z.-s. Qi; Y. Guo; B.-h. Wang
- + Show Description
-
Hide details
-
p.
433
–442
(10)
Owing to the curvature of the conformal carrier, the polarisation diversity of element patterns is one of the most distinct characteristics of conformal array manifolds. Consequently, direction-of-arrival (DOA) estimation with conformal array antennas always couples with the estimation of the polarisation. Based on the fourth-order cumulants of the array outputs and an elaborately designed array structure, an estimation of signal parameters via rotational invariance techniques-based blind DOA estimation algorithm with respect to polarisation diversity is proposed for conformal array antennas, in which the displacement vectors required by ESPRIT are acquired by utilising ‘virtual array elements’ derived from actual array elements by ‘virtual cross-correlation computation’. Owing to the fact that these distance vectors used in algorithm implementation are not affected by element patterns and source polarisation, the 2D DOA estimates are decoupled from polarisation and obtained with no need for exact knowledge of array element polarised patterns. The proposed method achieves high-resolution 2D DOA estimation and is applicable to cylindrical, conical and spherical conformal carriers. The array set-up examples of conical, cylindrical and spherical carriers are presented for demonstration and the Monte-Carlo simulation results of DOA estimation with cylindrical conformal array are also provided to illustrate the effectiveness of the proposed algorithm. - Author(s): F. Gong; C. Li; J. DeGroat
- + Show Description
-
Hide details
-
p.
443
–449
(7)
This study proposes a new wide band quadrature coupler structure using a lumped-element technique. The theoretical operating conditions of the proposed structure are also analysed. The operating bandwidth is extended and the phase shift difference error is reduced by introducing two matching frequency points. When the designed centre frequency is 6 GHz, a theoretical calculation shows that the operating bandwidth is 2 GHz and the phase shift error ranges from −5.9 to 1.76°. A coupler with 6 GHz centre frequency is also designed in a 0.13 µm CMOS process and simulated using Cadence Spectre. The active area of the coupler is 560 µm×640 µm. The post-layout simulation shows that the operating bandwidth has strong tolerance to the process variations. - Author(s): T.A. Denidni; Z. Weng
- + Show Description
-
Hide details
-
p.
450
–458
(9)
A novel dielectric resonator antenna (DRA) is proposed for ultrawideband (UWB) applications, where a simple rectangular dielectric resonator is excited by a bevel-shaped patch connected to a coplanar waveguide (CPW) feeding line. It is found that the bandwidth of the resonant modes can be expanded by using a CPW-fed ground and bevel-shaped patch, and thus a UWB performance can be achieved. Experimental and numerical results were carried out, showing a good agreement. The measured results demonstrate that the proposed DRA achieves an impedance bandwidth more than 3:1, covering the frequency range from 3.1 to 10.6 GHz, which is suitable for UWB applications. Furthermore, to minimise the potential interferences between the UWB system and narrowband systems, such as world interpretability for microwave access and WLAN, UWB DRAs with single band-notched and dual band-notched characteristics were designed, fabricated and measured. The measurement results show good performances in terms of VSWR, antenna gain and radiation pattern. With these features, the proposed antennas are expected to be good candidates in various UWB systems. - Author(s): H.-H. Chen; R.-C. Hsieh; Y.-T. Shih; Y.-H. Chou; M.-H. Chen
- + Show Description
-
Hide details
-
p.
459
–467
(9)
A series of investigations on improving the spurious performance of a coaxial combline filter are presented. An equivalent circuit is developed to model the transverse electromagnetic (TEM) resonant frequencies, both the fundamental and higher-order modes, of a stepped-impedance coaxial resonator (SIR) with a tuning screw. Further, a series of EM simulations based on the finite-element method are conducted to study the higher-order resonances involving both TEM and TE11 modes propagating in the high- and low-impedance sections, respectively, in the SIR. These investigations complete the design of the individual SIR with good spurious performance. The couplings of the fundamental and higher-order resonant modes between a pair of SIRs are also studied to obtain a coupling scheme with good suppression on the coupling of the higher-order resonant modes. Two five-pole Chebyshev filters are then designed and compared based on the above investigations. One of the filters is fabricated and measured to verify these investigations. The measured and simulated results share good agreement. - Author(s): I.H. Naqvi; P. Besnier; G.E. Zein
- + Show Description
-
Hide details
-
p.
468
–475
(8)
Time reversal (TR) is regarded as a potential future transmission scheme for ultra-wideband (UWB) communication systems. However, the need for a perfect channel estimation is regarded as one of the main drawbacks of a TR system. It is assumed that in the case of a time-varying channel or imperfect channel estimation, the performance of the TR scheme degrades enormously. Based on this assumption, the time-reversal scheme is not considered suitable for such environments. Here, the robustness of a TR system in a time-varying channel environment is studied. The experiments are performed for a time-varying channel environment for fixed terminals and for a displaced terminal with a stationary channel environment. The results show that if the channel maintains some partial correlation with the previous channel, the TR system can perform robustly. - Author(s): Y. Wang; H. Xia; Q. Cao
- + Show Description
-
Hide details
-
p.
476
–481
(6)
An analysis of the numerical stability and dispersion properties of the latitude–longitude and geodesic finite-difference time-domain (FDTD) algorithms in modelling the earth–ionosphere system is presented. To the best of the authors' knowledge, it is the first time the properties are analysed via rigorous theoretical derivations. Furthermore, both the analytical and experimental results are compared for the two algorithms. It is found that the geodesic FDTD algorithm has a looser stability limitation than that of the latitude–longitude FDTD algorithm. After the theoretical derivation and the numerical analysis, the global electromagnetic phenomenon was clearly exhibited using the two different algorithms, revealing the correctness of the theoretical analysis and the experiments. Additionally, the potential applications of the two algorithms are briefly proposed. - Author(s): V. Koudelka; Z. Raida
- + Show Description
-
Hide details
-
p.
482
–489
(8)
In this study, exploitation of artificial neural networks for an efficient solution of a simple electromagnetic compatibility problem is discussed. Two parallel dielectric layers are penetrated by a perpendicular electromagnetic wave. A standing wave is formed between layers. Radial basis function networks are employed to estimate the electric field intensity between the layers for both the harmonic wave and the pulse wave illumination. The electrical parameters of dielectric layers can influence the field distribution inside the investigated structure. Probabilistic neural networks are used to classify parameters of layers related to critical intensities of internal fields. Classification abilities of probabilistic networks are compared with a conventional k-NN method both for a dense training set and a sparse one. - Author(s): G. Felic; C. Thomas; E. Skafidas
- + Show Description
-
Hide details
-
p.
490
–494
(5)
In this study, an antenna design technique that includes wire bond interconnection for 60-GHz antenna–chip integration is investigated. The presented technique is unique as it does not require additional matching elements to deal with wire bond interconnection effects on the antenna input impedance matching bandwidth. As the reactance of the bonding wires is compensated by design of the antenna circuit, the matching bandwidth is not significantly reduced. To the authors’ knowledge, this is the first antenna design presented for integration with a 60-GHz CMOS chip using wire bond interconnection without a compensation network. - Author(s): A.O. Karilainen; P.M.T. Ikonen; C.R. Simovski; S.A. Tretyakov; A.N. Lagarkov; S.A. Maklakov; K.N. Rozanov; S.N. Starostenko
- + Show Description
-
Hide details
-
p.
495
–502
(8)
Dielectric or magneto-dielectric materials can be used to miniaturise antennas, but there are many important parameters that must be considered when selecting which material to use. The authors discuss these figures of merit and a rigorous method to compare antennas with different material fillings. A meandered planar inverted-F antenna (PIFA) loaded with magneto-dielectric and dielectric materials is presented as an example antenna for testing. The magneto-dielectric material used is composed of mylar substrate and Fe–SiO2 sheets. Measurement results for the permeability of the material are presented. The radiation mechanism of the meandered PIFA is studied, and the proper position for dielectric and magneto-dielectric filling is discussed and identified. Miniaturisation by commercial dielectric and the presented magneto-dielectric fillings is measured and compared at the same resonance frequency using the radiation quality factor as the figure of merit. It is seen, that the antenna can benefit from the magneto-dielectric filling material in terms of the radiation quality factor only if the placement of the antenna filling is carefully selected.
Robust and efficient method for evaluation of the non-symmetrical components of the Green's functions for microstrip structures
High/low-impedance transmission-line and coupled-line filter networks for differential phase shifters
Two-pole digitally tunable evanescent-mode waveguide narrow-band filter with radio frequency micro-electromechanical systems switches
Gain and efficiency enhancement of compact and miniaturised microstrip antennas using multi-layered laminated conductors
Measurement and modelling of the propagation channel between low-height terminals
Analysis of the parameters of an approach that combines the characteristic basis function method and the multilevel fast multipole
Reflection type Q-factor measurement using standard least squares methods
Blind direction-of-arrival estimation algorithm for conformal array antenna with respect to polarisation diversity
Analysis and design of a wideband lumped-element quadrature directional coupler for complementary metal-oxide semiconductor implementation
Hybrid ultrawideband dielectric resonator antenna and band-notched designs
Investigations on improving the spurious performance of a coaxial combline filter
Robustness of a time-reversal ultra-wideband system in non-stationary channel environments
Stability and dispersion analysis of the finite-difference time-domain algorithms in modelling the earth–ionosphere system
Evaluation of electromagnetic immunity of layered structures by neural networks
Design of co-planar waveguide-fed slot/patch antenna with wire bond for a 60-GHz complementary metal-oxide-semiconductor transceiver
Experimental studies on antenna miniaturisation using magneto-dielectric and dielectric materials
