Showing papers in "Iet Microwaves Antennas & Propagation in 2008"

Enhanced two-antenna structures for universal mobile telecommunications system diversity terminals

Abstract: The design of several universal mobile telecommunications system multi-antenna systems with radiators having a high isolation, a high total efficiency and a low envelope correlation is presented. First, two planar inverted-F antennas (PIFAs), closely positioned at the top edge of a small ground plane whose size is representative of the printed circuit board of a mobile phone, are described. A technical solution is then proposed to increase the isolation between the antennas and enhance their total efficiency when still keeping them closely spaced. The technical solution is based on an optimal neutralisation technique, applied between the antennas of the structure. Several optimal systems, based on different parameters, are fabricated and measured. The simulated and measured S-parameters are presented in addition to the gain radiation patterns, the surface currents on the structure and the theoretical and experimental total efficiencies. The envelope correlation coefficients are also computed using two different equations. It is then demonstrated that, with the help of the neutralisation technique, a system composed of two closely spaced PIFAs located at the top edge of a small ground plane can lead to a high total efficiency and a low envelope correlation coefficient. In conclusion, this technique can be easily implemented at the terminal side of a wireless link and may enhance its diversity gain and multiple input multiple output performance.

Analytical equivalence between substrate-integrated waveguide and rectangular waveguide

Abstract: Rectangular waveguide (RW) with sidewalls of vertical conducting cylinders (i.e. SIW, substrate-integrated waveguide) becomes popular with the advent of low-temperature co-fired ceramic structure; its analysis is usually numerical, or modal, leading to empirical design formulas. However, its analytical equivalence to the common RW of the solidwall is identified; in other words, analytical design formulas of the SIW and the equivalent RW of solid sidewalls are the same. The equivalence is established on comparing the surface impedances along the side walls, of the SIW and of an RW through analytical continuation. The equivalence formulas, propagation and cut off frequency show very good agreement with the results from both numerical simulations and measurements of hardware experiments, and over wide frequencies. The good agreements are easily understood on the basis of the conformal maps and the variational principle.

Cavity-backed archimedean spiral antenna with strip absorber

Abstract: The characteristics of an Archimedean spiral (ARSP) antenna backed by an extremely shallow cavity (0.07 wavelength at the lower operating design frequency of 3 GHz) are analysed. It is revealed that the presence of the cavity causes noticeable variation in the antenna characteristics at low frequencies. To restore the wideband characteristics inherent to the ARSP, a ring-shaped strip absorber (R-ABS) is placed under the spiral arms. It is found that the wideband antenna characteristics are successfully restored with the use of the R-ABS. Subsequently, the R-ABS is divided into two arc-shaped strip absorbers and the volume of each is reduced by decreasing the arc-angle ARC from 180deg (corresponding to an R-ABS) to 0deg (corresponding to a cavity without an absorber). It is shown that when the arc-angle is chosen to be greater than deg ARC =90=, the antenna characteristics obtained for = ARC =180= are reproduced. Theoretical results are confirmed using results from experimental work.

Wideband microstrip antennas with sandwich substrate

Abstract: A broadband microstrip antenna with low–high–low (sandwich) dielectric constant substrate combination using a microstrip line-via feed is presented for ultra-wideband applications. The proposed antenna consists of three dielectric substrates; low dielectric constant substrates that contain the microstrip feed line as well as parasitic patches and a high dielectric constant substrate that contains the driven patch. To achieve a large impedance bandwidth, parasitic patches and microstrip line-via combination feed to the driven patch in the multilayered microstrip antenna are used. The proposed antenna designed, fabricated and measured on the sandwich substrate. The antenna has measured 10 dB return loss bandwidth of 46.9% and directive gain >5.2 dBi at boresight across the impedance bandwidth. The total height of antenna is 5.77 mm or 0.077λo at 4 GHz.

Design of sharp-rejection, compact, wideband bandstop filters

Abstract: A general procedure is described to design a sharp-rejection wideband bandstop filter by using interference of the signals propagating through two parallel transmission line segments having different electrical lengths and characteristic impedances. Bandwidth and rejection level of the filters can be controlled by changing the impedances of the lines. A simple transmission line model is used for filter analysis. Design graphs are presented. Theoretical prediction is verified by fabricating two filters in microstrip technology. Good agreements is obtained among theoretical prediction, full-wave simulation and measurements.

Design and implementation of a substrate integrated waveguide phase shifter

Abstract: The design and implementation of a phase shifter based on the substrate integrated waveguide (SIW) technique operating at 10 GHz are presented. The proposed phase shifter consists of a SIW section with two inserted metallic posts. The phase shifting in this configuration is achieved by changing the diameter and the position of these posts. Numerical simulations have been carried out for different diameters and positions, which have shown good agreement with the theory. A parametric study was also conducted to assess the impact of errors made on the diameter and position of the two metallic posts. To prove the concept, prototypes were fabricated and measured. Experimental results agree well with simulations and SII was better than -14 dB, S21 better than -1.08 dB and the phase error was less than 1.5deg.

Size reduction and bandwidth enhancement of snowflake fractal antenna

Abstract: A new small-size and wideband fractal antenna in the shape of a snowflake is proposed. Various iterations of this fractal antenna with probe feed and capacitively coupled feed are compared and an optimised design is presented. It is shown that, with an air-filled substrate and capacitive feed, an impedance bandwidth >49% and, with a slot-loading technique, a reduction of about 70% in patch surface size compared with an ordinary wideband Koch fractal antenna are achievable. The simulation via a finite-element programme, and measured results on the return loss and the E and H-plane radiation patterns of the proposed antennas are presented and shown to be in good agreement.

New CPW-fed monopole antennas with both linear and circular polarisations

Abstract: A low-profile, planar, circularly polarised monopole antenna with a shorting sleeve strip fed using a coplanar-waveguide transmission line for wireless communication in the digital communication system and the global positioning system bands is studied. By utilising the coupling effect between the monopole antenna and sleeve, two excited resonant modes, including the monopole and travelling-wave modes, cover the 1.57- and 1.8-GHz bands. Through modification with antennas of various geometrical parameters, the proposed antenna exhibits the wide bandwidth in the desired frequency bands, which has a bandwidth of 45% at 1.6%GHz for an input reflection coefficient of less than %10%dB. Meanwhile, the antenna has a 3-dB axial ratio bandwidth of 5%. Details of the design considerations for the proposed antennas are described, and the results of the antenna performances obtained are presented and discussed.

Frequency-invariant pattern synthesis of conformal array antenna with low cross-polarisation

Abstract: Despite their potential and promising advantages over classical planar arrays, conformal arrays also present many challenges to the antenna designer, including varying element normal due to curvature, serious cross-polarisation effect, limited operational bandwidth and so on. A uniform method for the element polarised pattern transformation of arbitrary 3D conformal arrays is presented based on Euler rotation. A space-time-polarisation filter structure is proposed for the pattern synthesis of conformal array, in which the finite impulse response (FIR) filters assigned to every element are used to acquire the frequency-invariant array pattern and the element polarisation diversity in array global coordinates is used to depress the cross-polarisation level. The optimal weight vector is obtained by alternating projection method. The alternating projection method is a powerful and attractive method for the pattern synthesis in that it requires relatively smaller amount of computation burden and a wide variety of desirable constraints can be freely implemented in a -visible- way, which is usually impossible for other optimisation method. The pattern synthesis method proposed has established a unified frame for the frequency-invariant and low cross-polarisation pattern synthesis of conformal array. Simulation results are provided to demonstrate the effectiveness and behaviour of the proposed method.

Equivalent circuit for the microstrip ring resonator suitable for broadband materials characterisation

Abstract: A simple equivalent circuit of the edge coupled microstrip ring resonator is developed based on both circuit and electromagnetic theory. The new model extends the work done by previous authors by including the effects of radiation loss, the coupling gap and the feed network as well as extending the frequency range by including higher-order modes. The model accurately predicts the resonant frequencies of the ring including the effects of dispersion and thick conductors. The equivalent circuit allows measurement of the resonance frequencies and the Q factors to be made independently of the coupling gap dimensions, which traditionally have been difficult to accurately model. A method of determining radiation loss is also presented, which has often been incorrectly neglected in the past. Experimental results support the accuracy of the equations and measurements on alumina rings that demonstrate a frequency accuracy of better than 1% over 12 resonant modes in the frequency range 3-33 GHz.

Synthesis of ultra-wideband bandpass filter employing parallel-coupled stepped-impedance resonators

Abstract: To design an ultra-wideband (UWB) bandpass filter with the fractional bandwidth (FBW) up to 110% (31%106%GHz), a new filter prototype consisting of multi-stage parallel-coupled stepped-impedance resonators (SIRs) is synthesised based on the transmission-line theory rather than the conventional multi-mode property Asymmetrical SIRs are employed instead of the conventional symmetrical/quasi-symmetrical ones, so that an extra degree of freedom is introduced in circuit parameter selection As a result, the minimum dimension of the coupling gaps between the adjacent SIRs is successfully enlarged to be more than 01%mm, which alleviates the requirement on fabrication precision A simple equivalent circuit for this filter prototype is represented in the form of distributed parameters and the corresponding Chebyshev filtering function is derived as well The relation between the number of poles in passband, N p , and the stage of the filter, n , is summarised to be N p =3 n +2 To validate the newly derived synthesis theory, a one-stage UWB filter is first synthesised to compare with the previously published results obtained by the electromagnetic (EM) simulator Furthermore, a two-stage filter is synthesised to successfully meet the Federal Communications Commission (FCC)+s indoor/outdoor spectrum specifications The fabricated UWB filter exhibits a compact size of 2658+mm in total length, low insertion loss (09+dB at 685+GHz), flat group delay (05+01+ns), good stopband characteristics (+S21+++40+dB at 1+2+GHz) and steep skirt property (+28+dB/GHz) as well It should be noted that the proposed filter prototype can be also used to realise aUWB filter with an FBW even greater than 110+

Sub-wavelength resonators: on the use of metafilms to overcome the λ size limit

Abstract: Metamaterials - in particular, double negative materials - have been used in the design of electromagnetic resonators as a means to overcome the classical lambda/2 size limitation. The surface equivalent of a metamaterial is a so-called metafilm - a surface distribution of suitably chosen electrically small scatterers. In this paper we illustrate how metafilms can be used to overcome the lambda/2 size limit in order to design resonators of very small dimension. We present expressions that relate the polarisability densities of the scatterers of the metafilm needed to achieve in principle any desired resonator size. To validate the analytical results, comparisons to full-wave simulations of resonators containing various metafilms are shown. The effect of loss is investigated, and it is shown that smaller resonator size is achieved at the expense of lower Q (quality factor). The results can be scaled; that is, the dimensions of the scatterers can range from relatively large to relatively small, depending on the frequencies of interest.

Millimetre-wave monopulse antenna incorporating substrate integrated waveguide phase shifter

Abstract: A compact planar E-plane monopulse antenna is proposed and realised at 36.5 GHz for millimetre-wave radar or direction-finding system application, which is built on the substrate integrated waveguide (SIW) technology. A phase shifter having a non-uniform SIW width configuration is self-consistently made of a periodically embedded via array and it can achieve good performances over a relative broad bandwidth. A 180deg directional coupler incorporating this proposed phase shifter structure is developed in the design of an integrated feeding network for the monopulse antenna. Four elements array based on the configuration of antipodal linearly tapered slot antenna is designed as radiator, offering a pair of 'sum' and 'difference' beams along the long direction of the substrate. Measured gain of the 'sum' beam is higher than 16 dBi, whereas the zero depth of the 'difference' beam is lower than -38 dB. This type of monopulse antenna presents an excellent candidate in the development of intelligent millimetre-wave directional- finding system.

Triple-band wireless local area network monopole antenna

Abstract: A triple-band Bluetooth (BT) and wireless local area network (WLAN) monopole antenna has been proposed based on concepts called capacitive loading/de-loading and inductive loading/de-loading. It has been demonstrated that BT and triple-band WLAN operations, including the BT 2.4 GHz (2.4-2.484 GHz), the WLAN IEEE 802.11 2.4 GHz (2.4-2.484 GHz), 5.2 GHz WLAN (5.15-5.35 GHz) and WLAN 5.8 GHz (5.725- 5.825 GHz) can be achieved by using the monopole antenna with an overall size 8.0 x 11.5 x 1.0 mm 3 , which is one of the most compact WLAN monopole antennas covering the three frequency bands.

Investigation of hybrid elliptical antenna arrays

Abstract: Novel types of antenna arrays constructed from combination of linear and elliptical antenna arrays are presented. These types are called elliptical, concentric elliptical, elliptical cylindrical and elliptical coaxial cylindrical arrays where only the array factors are considered. The effect of the element factor can be considered separately and combined to the array factor. The expression for the array factor of elliptical array has been obtained. Then, array factors of other three types are derived by the combination of linear and elliptical array properties. Their directivities and sidelobe levels are simulated in various current distributions. The effect of ellipse eccentricity, element spacing and number of elements are calculated and compared with those parameters.

Synthesis and applications of new left handed microstrip lines with complementary split-ring resonators etched on the signal strip

Abstract: A new type of left handed microstrip lines implemented by means of complementary split-ring resonators (CSRRs) is proposed. The CSRRs are etched on the signal strip alternating with series gaps. Additionally, shunt connected stubs are introduced for the first time to the previous structure. The combination of these three elements, that is, the series gaps, the CSRR and the shunt inductance, enhances design flexibility. By this means, the ground plane is left unaltered and narrow band artificial transmission lines with good performance and compact dimensions can be synthesised. The lumped element equivalent circuit model of the structure is proposed and validated. To demonstrate the applicability of these new left handed transmission lines, two compact microwave components have been designed and fabricated: (i) a narrow band power divider and (ii) a band pass filter. The resulting power divider is 75% smaller than the conventional implementation and 50% smaller than previous power dividers implemented by means of CSRRs. The band pass filter performance is comparable to that of previous CSRR-based filters with ground plane etching, whereas its size is smaller. This work represents a significant progress on the design of microwave components based on CSRRs, that is, the approach is opened to those systems where the ground plane cannot be etched.

Design of square patch antenna with a notch on FR4 substrate

Abstract: Simulation and measured results of a square patch antenna with a notch to search their possible application on modern communication systems including WiMax systems are presented. The antennas are designed on an FR4 substrate and the notch angle is varied under different conditions. It is found that on varying the notch angle from 180deg to 164deg, antennas resonate at a single frequency but on reducing the notch angle further, antennas start resonating at two frequencies with improved bandwidth. The optimum performance of an antenna is obtained when the notch angle is set to 151deg. Different radiation parameters of the antennas under varying conditions are analysed and their possible applications in modern communication systems are investigated.

Compact double-mode cross-coupled microstrip bandpass filter with tunable transmission zeros

Abstract: A compact double-mode cross-coupled microstrip bandpass filter with an asymmetric frequency characteristic and three transmission zeros is presented. The bandpass filter consists of a cross-coupled gap and a double-mode resonator of a half-wavelength line with a shunt-stepped-impedance open stub. In comparison to the conventional square loop dual-mode resonator, the proposed double-mode resonator achieves a 59% size reduction. The parametric studies on the electrical length of the open stub and the capacitance of the cross-coupling are provided in order to gain a better insight into the transmission poles and zeros. Then, a bandpass filter is designed, fabricated and tested to validate the design concept. From 2.3 to 2.5 GHz, the return loss is better than 10 dB and the insertion loss is <1.5 dB. There are three transmission zeros in the upper stopband at 2.8, 3.4 and 4.9 GHz.

Determination of the complex permittivity of textiles and leather in the 14-40 GHz millimetre-wave band using a free-wave transmittance only method

Abstract: A free-wave, transmission only technique for the determination of complex permittivity in the millimetre (mm)-wave band 14-40 GHz of planar samples of textiles is presented. With this method an accurate alignment of source and detector horns is not required and time gating methods to reduce or remove standing wave interference between horns is replaced by a data smoothing process. The technique is novel as phase information from the transmitted wave is not required to determine the complex permittivity. The textiles investigated are denim (cotton) and cow leather (two colours, red and beige). This method is shown to be simple to set up, easy to use and fast when compared with other methods such as free-wave reflectance and transmittance or Fabry-Perot cavity and gives results which are accurate enough for most of the practical applications. A significant difference in the absorption of mm-wave power between the two leather samples is observed. This can be explained by the different chemical composition of the two leather samples, investigated using a scanning electron microscope with electron dispersive spectrometry and which is almost certainly a result of the colouring process employed.

Theory of self-adjoint S-parameter sensitivities for lossless non-homogenous transmission-line modelling problems

Abstract: The authors present, for the first time, a comprehensive theory for self-adjoint S-parameter sensitivities of non-homogenous transmission-line modelling problems. They show that wideband S-parameter sensitivities can be efficiently calculated without carrying out any adjoint simulations. The N p original simulations used to calculate the S-parameters of an N p -port electromagnetic structure supply the sensitivities as well. The authors also present their approach for two different types of nodes utilised in transmission-line modelling. The efficiency and accuracy of their algorithms are illustrated through a number of examples. Good match is obtained between their self-adjoint sensitivities and those calculated using finite differences at the response level.

Bandwidth-dependent modelling of small-scale fade depth in wireless channels

Abstract: In this paper, the relation between small-scale fade depth and channel bandwidth in an indoor environment is investigated. The fade depth, a measure of the signal power variability over a local region in space, is evaluated for narrowband, wideband and ultrawide-band channels. The experimental analysis is based on frequency-domain measurements in the 3.1–10.6 GHz microwave band. Physical insight into the fading process is provided, and the effect of increasing bandwidth and temporal resolution is discussed. A dual-slope empirical model is developed, which accurately describes the relationship between fade depth and channel bandwidth. It is demonstrated that the fade depth, considered at the three standard deviation values, converges to about 4 dB at 1 GHz bandwidth, and a further increase in bandwidth yields only a marginal improvement in fade mitigation.

5 bit, silicon-based, X-band phase shifter using a hybrid pi/t high-pass/low-pass topology

Abstract: A hybrid pi/t bit passive topology is presented to enable a significant reduction in the die area for a high-pass/low-pass phase shifter is presented. A hybrid-topology 5 bit digital X-band phase shifter was designed, fabricated and tested using a 200 GHz, 0.13 mum SiGe bipolar complementary metal oxide semiconductor (BiCMOS) technology. Size and performance characteristics are presented as a contrast to an all-pi phase shifter recently presented by Comeau et al. using the same SiGe BiCMOS technology and design goals. With similar bit passive performance to the all-pi design, the hybrid shifter allows for a total shifter die-area reduction of 50.5%. The absolute phase error of the shifter was less than plusmn13 from 8 to 12 GHz, with an average insertion loss of -20 dB.

Compact dual-band tunable microstrip antenna for GSM/DCS-1800 applications

Abstract: A compact single feed dual-band electronically tunable microstrip antenna for operation in GSM/DCS-1800 system is presented. The antenna consists of two resonant elements designed separately and integrated while preserving their designed bands. The two bands are separately tuned using two biasing control circuits. A significant size reduction and bandwidth selection are achieved using a varactor diode as a voltage control capacitance. The design and implementation is carried out on a foam substrate of thickness 2.44 mm and with a dielectric constant 1.2. Simulation and experimental results show that the required bandwidth of the GSM/DCS-1800 system can be easily covered with voltage changes from 1 to 3 V, which is suitable for mobile hand phones.

Negative permittivity meta-material microstrip binomial low-pass filter with sharper cut-off and reduced size

Abstract: A binomial low-pass filter provides the flattest pass-band response but slow attenuation transition. A design for improving the roll-off performance based on the negative-epsiv property of complementary split-ring resonators is presented, whilst maintaining the filter pass-band performance. By properly designing and integrating the complementary split-ring resonators with the low-pass filter, not only can the roll-off of the filter be significantly improved, but also the filter size further reduced. The measured results indicate that the proposed structure achieves a flat pass-band with no ripples as well as has a selectivity of 32 dB/GHz. This significantly exceeds the 17 dB/GHz selectivity of the conventional design. Furthermore, the proposed filter has a size smaller by 16%.

Reduction of ground-plane-dependent effects on microstrip-fed printed rectangular monopoles

Abstract: Methods to mitigate the strong dependence of impedance bandwidth on the ground- plane size for a rectangular printed planar monopole is described. It is shown that the bandwidth limitation may be overcome by introducing feed-line asymmetry, which alters the purity and the Q of the higher frequency modes and by ground-plane augmentation, which effects the lower frequency modes. A method of extending the ground plane without increasing the overall antenna size is shown to improve both the bandwidth and gain and also to enable the use of significantly smaller ground planes. The effects of these techniques on radiation pattern are discussed.

Method for widening the reject-band in low-pass/band-pass filters by employing coupled C-shaped defected ground structure

Abstract: Two new compact defected ground structure low-pass filters with broad stop-band and low insertion loss in the pass band are presented. The structures of these new microstrip low-pass filters are simple as they are composed of a pair of DGS-slots and an openstub. One filter is realised through the multi-layer method, and the second filter by cascading. With these configurations, two LPF with compact size, wide reject band and sharp transition from pass to stop-band are realised. The design formulas are derived by using an equivalent circuit model of coupled DGS resonators. Demonstration filters are designed, fabricated and tested. The experimental results show good agreement with theoretical results and demonstrate that the required characteristics of LPF could be simply obtained through the proposed methods. Finally a simple gap-method will be used in order to transform the LPF to BPF.

Study and realisation of dual-composite right/left-handed coplanar waveguide metamaterial in MMIC technology

Abstract: A novel realisable dual composite right/left-handed (D-CRLH) coplanar waveguide (CPW) transmission line (TL) in GaAs MMIC technology demonstrated by theoretical analysis and experimental results is presented A D-CRLH TL is the dual of the conventional CRLH TL in the sense that it consists of series LC parallel tanks and shunt LC series tanks However, an ideal D-CRLH TL cannot be realised because of unavoidable parasitic effects The measured results indicated that a real D-CRLH TL exhibits a fundamentally different frequency response at higher frequency band in that a real D-CRLH TL cannot provide unlimited left handed (LH) bandwidth Instead, it has triple bands; right-handed (RH) passband at lower frequencies (DC-29 GHz), LH passband at intermediate frequencies (51 143 GHz) and RH passband at higher frequencies (above 143 GHz) The reported fully integrated D-CRLH CPW TL metamaterial has a very compact size of 22 mm 2 which leads to a small loss 15 dB within 3 dB LH passband

Frequency-selective surfaces with two sharp sidebands realised by cascading and shunting substrate integrated waveguide cavities

Abstract: Frequency-selective surfaces (FSSs) with two sharp sidebands have been investigated, which are constructed by cascading and shunting two substrate integrated waveguide cavities (SIWCs) of different sizes with periodic slots at top and bottom metal surfaces. The lower and upper sharp sidebands are induced by two transmission nulls that are generated by coupling between the slot aperture resonance and the resonances in the two cavities. Samples of the shunted SIWC-FSS with different size cavities were fabricated. Measured results are in good agreement with the predicted ones and its performance, such as high selectivity and passband bandwidth, is stable at oblique incidence.

Investigation of anisotropic negative permeability medium cover for patch antenna

Abstract: A more directional and higher gain patch antenna with an anisotropic negative permeability medium (NPM) cover is proposed. The patch antenna operates at the frequency where the permeability of split-ring resonator (SRR) is negative, and then the sideward radiation can be forbidden. It leads to a significant enhancement of designing the high gain antenna. We investigate numerically and experimentally the performance of the antenna when NPM composed of SRR is placed above the patch antenna. The measured result has a good agreement with the simulation. Compared with the conventional antenna, the result shows that the beam of antenna with the NPM cover becomes more convergent, half-power beamwidth is smaller by almost 30° in the H-plane and 10° in the E-plane and the gain is higher by 4.03 dB. Moreover, NPM cover can have applications in the other types of antenna such as monopoles, dipole antennas, leak-wave antennas and aperture antennas.

Multiple band-stop bow-tie slot antennas for multiband wireless systems

Abstract: A novel and simple design of wideband coplanar waveguide (CPW)-fed bow-tie slot antennas with multiple band-stop characteristics featuring multi-network applications is presented. A frequency stop band can be created by embedding the slot with a pair of stubs, which causes the resultant magnetic fields almost counterbalance in the slot and to be non-responsive at the desire stop band. The effects of the dimensions of the stub on the stop band are also analysed. Dual band-stop characteristic is also accomplished by embedding two pairs of stubs in the slot. Details of the proposed designs and experimental results of the constructed prototypes are presented.