Showing papers in "Iet Microwaves Antennas & Propagation in 2013"

Joint wireless communication and radar sensing systems - state of the art and future prospects

Abstract: The historical development and current state-of-the-art of various joint wireless communication and radar sensing systems are reviewed and discussed in this study. Different kinds of systems are categorised according to their modulation waveforms and duplex schemes. Pros and cons of each category are highlighted. To showcase the current research advances, several demonstration systems are introduced with emphasis on proposed research contributions in this emerging area, and their performances are compared with respect to both communication and radar modes. Also, a number of challenges are identified for the near future system developments and applications.

Microwave imaging for brain stroke detection using Born iterative method

Abstract: Microwave imaging reconstruction is applied to an anatomically realistic, numerical head phantom using the Born iterative method for detection of a haemorrhagic stroke within the brain tissues. A forward model is used to estimate back-scattered signals which are subsequently used in the image reconstruction process. Image reconstruction using excitation signals at 850 MHz is shown to produce the emulated stroke with a high contrast particular to the estimated conductivity profile.

Inkjet printed dipole antennas on textiles for wearable communications

Abstract: This study presents an inkjet printed textile antenna realised using a novel fabrication methodology. Conventionally, it is very difficult to inkjet print onto textiles because of surface roughness. This study demonstrates how this can be overcome by developing an interface coated layer which bonds to a standard polyester cotton fabric, creating a smooth surface. A planar dipole antenna has been fabricated, simulated and measured. This study includes DC resistance, RF reflection coefficient results and antenna radiation patterns. Efficiencies of greater than 60% have been achieved with only one layer of conducting ink. The study demonstrates that the interface layer saves considerable time and cost in terms of the number of inkjet layers needed whilst also improving the printing resolution.

Genetic-based design of a tetra-band high-efficiency radio-frequency energy harvesting system

Abstract: In this study, we exploit genetic algorithms to design a rectenna required to harvest ambient radio-frequency (RF) energy from four different RF bands in critical (ultra-low power) conditions. For this purpose a set of multi-resonant annular-ring patch antennas are pixel-wise described inside an electromagnetic simulator to provide the `population' of individuals among which the genetic tool is able to select the most adapted one with respect to the design specifications. The further use of circuit-level non-linear simulation tool, based on Harmonic balance technique, allows the rigorous multi-band design of the whole rectenna system in RF stationary conditions at several received power levels. The result is a novel compact, lightweight and highly efficient tetra-band rectenna, able to harvest RF energy from GSM 900, GSM 1800, UMTS and WiFi sources available in the ambient. At these frequency bands high radiation efficiency is desired as an essential prerequisite for optimally handling very low-power densities. Very good agreement with measurements of both the radiating and rectifying designs is demonstrated in real office scenarios. Finally the rectenna is connected to a power management unit and the resulting assembly is tested in terms of stored energy while harvesting from a mobile cell-phone call.

Inkjet-printed antennas, sensors and circuits on paper substrate

Abstract: Inkjet-printing is a very promising technology for the development of microwave circuits and components. Inkjet-printing technology of conductive silver nanoparticles on an organic flexible paper substrate is introduced in this study. The paper substrate is characterised using the T-resonator method. A variety of microwave passive and active devices, as well as complete circuits inkjet-printed on paper substrates are introduced. This work includes inkjet-printed artificial magnetic conductor structures, a substrate integrated waveguide, solar-powered beacon oscillator for wireless power transfer and localisation, energy harvesting circuits and nanocarbon-based gas-sensing materials such as carbon nanotubes and graphene. This study presents an overview of recent advances of inkjet-printed electronics on paper substrate.

Study of Q-factors of ridge and groove gap waveguide resonators

Abstract: The gap waveguide technology for millimeter waves applications has been recently presented. The new structure is made by generating a parallel plate cut-off region between an artificial magnetic conductor (AMC) and a metallic plate. Propagating waves will be only allowed to follow a metal ridge or groove surrounded by the AMC. The gap waveguide can be made of only metal and does not need any contact between the metal joints compared to standard waveguides. In this study, a study of Q-factors of resonators made in ridge and groove gap waveguides are presented. The resonators are made of copper and the AMC used is a textured surface of metallic pins. Simulated and measured unloaded Qs are presented and compared with Q of a standard rectangular waveguide. High Q-factors are measured for the prototypes presented, approaching 90-96% of the simulated values. Furthermore, it is shown how the lid of pins can easily stop the leakage loss at the joints of the circuit, which is the typical cause of reduced Q-factor of standard waveguides at high frequency.

Uniplanar polarisation diversity antenna for ultra-wideband systems

Abstract: A new compact, uniplanar, polarisation-diversity, monopole-like slot antenna for ultra-wideband (UWB) systems is presented. The proposed design effectively integrates orthogonally fed slot antennas, utilising the uniplanar nature of coplanar waveguide without degrading the time-domain characteristics and diversity performance. To achieve high isolation between the ports, a strip is integrated diagonally in the ground plane. Furthermore, by loading arc shaped slot resonators on the feeding structures, the proposed antenna successfully rejects the undesired subband, assigned for IEEE 802.11a and HIPERLAN/2. The measured results demonstrate that the antenna provides a 2:1 voltage standing wave ratio (VSWR) band from 2.76 to 10.75 GHz whereas showing rejection in the frequency band 4.75-6.12 GHz, along with an inter-port isolation better than 15 dB. The proposed radiator displays a nearly omnidirectional radiation pattern, along with a moderate gain and efficiency. The envelope correlation coefficient discloses a good diversity performance across the UWB spectrum. Furthermore, the time-domain analysis shows minimum dispersion to the radiated pulse. In addition, the experimental analysis indicates that the proposed design is less disposed to the housing effects when mounted in metallic casing. All these features make the proposed antenna a viable candidate for UWB dual-polarised multiple-input-multiple-output applications.

Antenna design exploiting adjoint sensitivity-based geometry evolution

Abstract: The authors present a new approach for evolutionary antenna design. Through exploiting efficient adjoint sensitivity analysis techniques, the antenna structure evolves to better satisfy the design constraints. The coordinates of a selected number of control vertices are chosen as optimisation parameters thus enabling evolution to arbitrary shapes. The authors approach is illustrated through the design of a number of microstrip structures.

Effect of the fabrication parameters on the performance of embroidered antennas

Abstract: Simulated and measured microstrip patch antennas produced using embroidery techniques have been presented. The antennas use a standard microwave substrate material. The effect of stitch direction and stitch density is described and a clear requirement to understand how the currents flow in an antenna, so that the stitch direction can be correctly chosen is shown. Two different simulation approaches for these antennas are discussed and one is linked to measurement results, pointing to a simplified model for simulating embroidered patch antennas.

Dual band-notched small monopole antenna with novel W-shaped conductor backed-plane and novel T-shaped slot for UWB applications

Abstract: In this study, a novel method for designing a new monopole antenna with dual band-notched characteristic for UWB applications has been presented. The proposed antenna consists of a square radiating patch with a modified T-shaped slot, and a ground plane with two E-shaped slots and a W-shaped conductor backed-plane. By cutting two E-shaped slots in the ground plane, additional resonance is excited and hence much wider impedance bandwidth can be produced, especially at the higher band, which results in a wide usable fractional bandwidth of more than 130% (2.73%13.3 GHz). In order to generate single band-notched characteristic, the authors use a W-shaped conductor backed-plane structure on the other side of the substrate. In addition, by cutting a modified T-shaped slot in the radiating patch and microstrip feed-line, a dual band-notched function is achieved. The measured results reveal that the presented dual notch band monopole antenna offers a very wide bandwidth with two notched bands, covering all the 5.2/5.8 GHz wireless local area network, 3.5/5.5 GHz WiMAX and 4 GHz C bands. The designed antenna has a small size of 12 % 18 mm 2 . Good voltage standing wave ratio (VSWR) and radiation pattern characteristics are obtained in the frequency band of interest. Simulated and measured results are presented to validate the usefulness of the proposed antenna structure for ultra-wideband (UWB) applications.

Directional modulation transmitter radiation pattern considerations

Abstract: A pattern synthesis approach is applied to a directional modulation (DM) system. A systematic synthesis procedure is suggested which ensures optimal constellation patterns production along pre-specified communication directions, whereas simultaneously conserving energy dispersal in other directions. In this study, the properties of DM systems synthesised from Gaussian magnitude far-field radiation pattern templates are used to illustrate performance benefits with regards to DM bit error rate response compared with those achieved by a conventional steered array.

Co-designed substrate-integrated waveguide filters with patch antennas

Abstract: A new approach to integrate high-quality ( Q )-factor three-dimensional vertical cavity filters with patch antennas into a single unit is presented. This integrated filter/antenna system exhibits small footprint, high efficiency and enhanced bandwidth. The patch antenna is designed to provide an additional transmission pole for the filtering function and works as a highly efficient radiator. In addition, this integrated patch antenna with a filter can achieve a bandwidth larger than that of a standalone patch antenna with the same geometry. A prototype three-pole Chebyshev filter/antenna is demonstrated at X band. The centre frequency and fractional bandwidth of the filter/antenna system are 10.27 GHz and 8.7%, respectively. Owing to the high Q factor ( ~650) of the cavity resonator and near loss-less transition between the antenna and filter, the overall efficiency of the filter/antenna system is simulated to be as high as 91.8%. The reduced footprint, enhanced bandwidth and low-loss performance of these integrated filter/antenna systems make them particularly useful for phased array applications. Prototypes of the filter/antenna systems as well as a filter/antenna array are fabricated and measured. An excellent agreement between the simulated and measured results is observed.

Optimisation of antenna arrays using the cuckoo search algorithm

Abstract: The goal of this article is to introduce and use the cuckoo search (CS) as an optimisation algorithm for the electromagnetics and antenna community. The CS is a new nature-inspired evolutionary algorithm (EA) for solving N-dimensional optimisation problems. Compared with other nature-inspired algorithms, the CS algorithm is easy to understand and implement and has minimum number of parameters to tune. Different examples are presented that illustrate the use of the CS algorithm, and the results are compared with results obtained using other optimisation methods. Preliminary results suggest that the CS algorithm can in some cases outperform other EAs, at least for the examples studied in this article.

Millimetre-wave waveguide reflectometers for early detection of skin cancer

Abstract: Millimetre-wave (mm-wave) reflectometry is an efficient technique for diagnosis of human tissue disease such as early stage skin cancer. Two sets of non-invasive and in-package reflectometers operating at 42 and 70 GHz are designed, fabricated and successfully tested with different kinds of samples. The tests are performed for a number of liquids, and pure water at different temperatures. Also, the proposed WR-22 device is tested over skin at different locations. The clinical trial tests are performed on a number of volunteer patients who suffered from Basal cell carcinoma. The proposed devices are easy-to-fabricate, and provide a low-cost solution for fast and accurate skin cancer detection. Furthermore, the proposed technology has the potential to be used for fast tissue inspection during a surgery

Enhancing the security of communication via directly modulated antenna arrays

Abstract: A new approach to enhance the security of data transmission using direction dependent antenna modulation based on an array with wide element spacing combined with directional array elements is presented. For illustrative purposes, the system investigated, and reported here, consists of an array of only two elements but the approach is general and can be extended to multi-element array systems. It is shown that by increasing the element spacing of an array the directional error rate characteristics of the system, in a given direction, can be significantly improved. Furthermore, the directly modulated system shows superior error rate performance to that of an equivalent, conventionally modulated, system in the grating lobe directions. The error rate characteristics of the proposed system are analysed for two scenarios: firstly when the angular separation between an eavesdropper and the intended recipient is small and secondly for the case when a potential eavesdropper is located much closer to the transmit antenna than the intended recipient.

Realisation of new single-layer triple-mode substrate-integrated waveguide and dual-mode half-mode substrate-integrated waveguide filters using a circular shape perturbation

Abstract: A method of ‘mode shifting’ is presented for realisation of triple-mode and dual-mode filters, in which the resonant frequency of one mode is shifted near to the resonant frequency of another mode using a perturbation. To realise a triple-mode filter, a single-layer substrate-integrated waveguide (SIW) square cavity is perturbed by introducing vias at the middle of the structure. This perturbation causes mode shifting of the dominant mode (TE101) near to the next modes (TE102 and TE201). Operation of this triple-mode resonator is analysed and resonant frequencies of the perturbed cavity are obtained theoretically. A triple-mode filter is realised using this resonator and the filter is modelled by a coupling matrix based on the global eigenmodes. Moreover, by using the mode shifting technique, a novel dual-mode bandpass filter with half-mode SIW (HMSIW) structure is presented. Both the triple-mode SIW and dual-mode HMSIW filters are fabricated on a single-layer substrate using a printed circuit board process.

Developments in retrodirective array technology

Abstract: There has been significant interest in retrodirective antennas, especially considering the wealth of applications that could be significantly enhanced, or created, by the use of such technology. There is enormous potential for retrodirective antennas where complicated automatic tracking systems would benefit from being replaced by much simpler systems. Retrodirective array technology offers one solution pathway since it can offer extremely fast tracking with relatively simple circuitry. Retrodirective or self-steering arrays are suited for low radio frequency (RF) power mobile terminal use particularly on or between un-stabilised vehicles. In this type of operational scenario, high degrees of relative movement are expected, and power consumption and weight of the antenna must be kept to a minimum. In this study, the authors give a brief historical review of basic retrodirective technology and elaborate on some recent developments at Queens University of Belfast associated with retrodirective antenna technology in relation to, two-way communications, ultrafast RADAR, microwave imaging, spatial power transmission, mitigation of multipath effects and spatial encryption.

Resemblance between gap waveguides and hollow waveguides

Abstract: There is a lack of suitable numerical ports for the gap waveguides This study studies the resemblance between the ridge/groove gap waveguide and the conventional hollow ridge/rectangular waveguide, respectively, by using numerical analysis The dispersion diagrams and characteristic impedances are compared and found to be similar within the stopband of the parallel-plate modes Therefore conventional hollow waveguides can be used as ports in numerical analysis of gap waveguides In addition, this means that the geometry of circuit components in hollow ridge/rectangular waveguides can be used as a good starting point when designing ridge/groove gap waveguide components

Unidirectional wideband circularly polarised aperture antennas backed with artificial magnetic conductor reflectors

Abstract: The reflection coefficient phase is studied for four different artificial magnetic conductors (AMCs) having canonical frequency selective surface (FSS)-type two-dimensional periodic structures to be used as back reflectors for an aperture antenna. The bidirectional circularly polarised (CP) radiation of the octagonal-shaped aperture (OSA) antenna is made unidirectional using these AMC surfaces as ground planes. The antenna height measured from the upper surface of AMC reflector to the OSA radiator is chosen to be small to realise low-profile antenna: 0.0825λ o at the lowest analysis frequency of 4.5 GHz. Different antenna parameters like voltage standing wave ratio (VSWR) of 2, 3-dB axial ratio (AR) bandwidth, gain, and front-to-back ratio are studied and compared for these four AMCs and the conventionally used perfect electric conductor (PEC) ground plane as back reflectors. Four different aperture shapes with fixed aperture perimeter are designed to integrate with the square-loop AMC as back reflector to realise a low-profile unidirectional wideband CP aperture antenna. Hexagonal-shaped aperture antenna over the square-loop AMC shows the largest measured 3-dB AR bandwidth of 23.33% (5.65-7.05 GHz), VSWR of 2 bandwidth of 36.67% (5.16-7.36 GHz), and the gain of around 7 dBic over the band for overall antenna volume of 0.72λ o × 0.60λ o × 0.19λ o at 6.0 GHz.

Novel closely spaced planar dual-band frequency-selective surface

Abstract: A novel, dual-band frequency-selective surface (FSS) is presented. The designed and fabricated FSS structure has closely spaced operation bands and high selective frequency response at each operation band. Two-dimensional compact U-shaped slot resonators are used in each FSS unit cell to obtain this ability. Also, each slot resonator is composed of straight slot section at the centre connected to two U-shaped arms at each end. The dimensions of the slot resonators are optimised using via full-wave electromagnetic simulations using CST Microwave Solver. The proposed FSS structure is independent of incident polarisation and angle because of 90° rotation of the unit cell. The validity of the proposed FSS is confirmed by both simulation and measurement results. In the experimental verification, a waveguide measurement setup is chosen. Both measurement and simulation results show that the FSS structure operates at the designed frequencies of 8.80 and 9.54 GHz, which are very close to each other.

Wideband, low profile P- and Ku-band shared aperture antenna with high isolation and low cross-polarisation

Abstract: This study describes the design of a wideband, low-profile shared aperture antenna operating at P-band and Ku-band. This antenna operates with dual-linear polarisation in P-band and single-linear polarisation in Ku-band. In this antenna design, it consists of one P-band microstrip patch antenna and an 8 × 8 Ku-band aperture-coupled patch array. The antenna covers from 330 to 420 MHz in the P-band and from 14.27 to 16.20 GHz in Ku-band with |S11| better than − 10 dB, which translates to 24 and 13% bandwidth in P- and Ku-band, respectively. The overall height of the antenna is about 80 mm, approximately 0.09λ at the lowest frequency. The cross polarisation is better than − 20 dB in the P-band and − 26 dB in the Ku-band. There is virtually no coupling between the P- and Ku-band. The measured gain varies from 6.5 to 7.5 dBi in the P-band and from 22.5 to 23.4 dBi in Ku-band.

Robust mask-constrained linear array synthesis through an interval-based particle SWARM optimisation

Abstract: An innovative strategy for the robust design of linear antenna arrays is presented. Being the array elements characterised by tolerance errors, the synthesis is aimed at determining the intervals of values fitting the user-defined mask constraints on the radiated power pattern. With reference to the upper and lower bounds of the power pattern analytically determined for given tolerances through interval analysis, the nominal excitations of the array elements are then optimised by means of a global stochastic optimiser suitably customised to deal with interval numbers. A set of numerical examples is reported to show the behaviour of the proposed method as well as to assess its potentials in dealing with the robust synthesis of pencil and shaped beams.

Planar wideband inphase power divider/combiner using modified Gysel structure

Abstract: The design of a wideband inphase power divider/combiner is presented. It uses a modified Gysel structure for an increased band and a reduced number of isolation resistors to only one. The power divider has a simple structure that does not use any slots in the ground plane, and is thus fully compatible with microstrip circuits. Moreover, the device uses one external isolation resistor, and thus it is suitable for high-power microwave applications because of the easy connection of the isolation resistor to a suitable heat sink. A theoretical analysis is presented to find the values of the design parameters for wideband performance. The simulated and experimental results of the designed divider show 69% fractional bandwidth assuming 15 dB of isolation as a reference.

Stable and compact multiband frequency selective surfaces with Peano pre-fractal configurations

Abstract: This work presents a fractal design methodology for frequency selective surfaces (FSSs) with Peano pre-fractal patch elements. The proposed FSS structures are composed of periodic arrays of metallic patches printed on a single-layer fibreglass dielectric. The shapes presented by pre-fractal patches allow one to design compact FSSs that behave like dual-polarised band-stop spatial filters. On the other side, the space-filling and self-similarity properties of Peano fractals became possible various configurations for patch elements. An FSS parametric analysis is performed in terms of the fractal iteration-number and cell-size of pre-fractal patches. To validate the used methodology four FSS prototypes are built and tested in the range from 1.0 to 13.5 GHz. Experimental characterisation of the FSS prototypes is accomplished through three different measurement setups with commercial horns and circular monopole microstrip antennas. Results show that the proposed FSS presents most of the desired features for spatial filters: compact design, multiband responses, dual-polarisation, excellent angular stability and facility for reconfiguration.

Small-size printed coupled-fed antenna for eight-band LTE/GSM/UMTS wireless wide area network operation in an internal mobile handset

Abstract: A simple small-size printed antenna for eight-band long-term evolution (LTE)/GSM/UMTS wireless wide area network operation in an internal mobile handset application is proposed. Occupying a compact size of 15 × 40 mm2 on the ungrounded region of the system circuit board and a low profile of 4 mm, the presented antenna is a coupled-fed configuration. With the longer branch of the feeding strip, a λ/4 resonant mode at around 2.7 GHz can be obtained to cover the desired LTE2500 operation. A fundamental λ/4 resonant mode over the desired lower band of LTE700/GSM850/900 can also be generated at 750 MHz by the long meandered coupling strip (length of about 113 mm). Moreover, two additional higher-order resonant modes at around 1.75 and 2.25 GHz can also be obtained by the coupling strip. By including a chip inductor L at the feeding point, the impedance matching over the lower and upper bands can be improved in order to achieve the two wide operating bands of 698–960 and 1710–2690 MHz. With the following properties of small size, ease of fabrication and good radiation characteristics, the proposed antenna is a good candidate for the fourth LTE mobile phone applications.

Ultra wideband loop antenna on contact with human body tissues

Abstract: Human body tissues have a strong effect on the antenna operation in wireless body area networks (WBANs). In this study, the authors present the deep investigations of the effect of body tissue thicknesses on the performance of an ultra wideband (UWB) loop antenna by simulations when the antenna is operated on contact with tissues. The planar UWB loop antenna is designed for the examinations, which is targeted to be used in UWB WBAN applications. The effect of tissue thicknesses on the antenna performance is analysed and characterised in the terms of reflection coefficient S 11 , gain and total antenna efficiency, group delay, radiation patterns and specific absorption rate by simulations. A parametric layered human body tissue model with the frequency-dependent behaviour is exploited in the investigations. Further, the reflection coefficient of the presented antenna is measured in the different locations of the author's body. The main aim of these investigations is to demonstrate how the thickness of outermost body tissues affects the antenna performance.

Mechanically reconfigurable antennas using an anisotropic carbon-fibre composite ground

Abstract: The authors present reconfigurable antennas based on anisotropic reinforced continuous carbon fibre composite (RCCFC) material. By the rotation of the anisotropic RCCFC ground plane, the current distribution can be changed to select a desirable mode of resonance and suppress unwanted modes. Hence, the RCCFC ground plane behaves as a mode filter in the proposed reconfigurable antennas. Several types of probe-fed reconfigurable microstrip-patch antennas are presented, including the RCCFC conductivity characteristics, the principle of reconfigurable operation and the simulated and measured performance. The outstanding mechanical strength of RCCFC materials along with the promising radiation characteristics of these reconfigurable antennas make them good candidates for radio cognitive and military applications.

Direction-of-arrival estimation for uncorrelated and coherent signals in the presence of multipath propagation

Abstract: The authors propose a novel direction-of-arrival (DOA) estimation method for signals that are uncorrelated, partially coherent or fully coherent in the presence of multipath propagation. First, uncorrelated and coherent signals are distinguished by the rotational invariance techniques as well as the property of the moduli of eigenvalues. The DOAs of the uncorrelated signals are then estimated based on their related eigenvalues. Finally, the singular value decomposition of virtual steering vectors is used to estimate the DOAs of the coherent signals while avoiding the cross-term effects. The effectiveness and efficiency of the proposed method are demonstrated by the simulation results.

Generalised correction to the friis formula: quick determination of the coupling in the fresnel region

Abstract: A simple yet effective correction term to the Friis formula is presented to improve its accuracy in the Fresnel region. Based on the concept of gain reduction factor, the proposed asymptotic term with an empirical coefficient can be widely applied to a variety of antennas without lengthy calculations. The information required in the computation is only the antenna gain, separation and wavelength for the boresight scenarios. Case studies of several representative antennas using full-wave simulations show that the accuracy of the estimated power transmission levels between two antennas in the Fresnel region can be improved by up to 2-5 dB, for both boresight and off-axis cases. Measurement results using two horn antennas also confirm the validity of the proposed correction term.

Reduced and conventional size multi-band circular patch antennas loaded with metamaterials

Abstract: In this study, a novel technique to achieve multi-band performance for both reduced and conventional size circular microstrip patch antennas loaded with metamaterial has been proposed Incorporation of symmetric slotting concept with the concept of additional mode modification for both MNG (µ negative) and ENG (ɛ negative) metamaterial loaded circular patch antennas have been shown The use of metamaterial creates an unconventional mode, whereas symmetrical slotting not only modifies another band but also improves the gain by around 1 dB of unconventional mode for MNG loaded antenna Design algorithms for metamaterial loaded circular patch antennas have been developed to achieve size reduction and highly directive multiband property Based on these design algorithms, at first a reduced size triple band circular patch antenna loaded with MNG metamaterial has been shown where around 35% size reduction is achievable Later, a triple band conventional size circular patch antenna partially loaded with ENG metamaterial has been designed with high gain and directive performances for all three bands compared to previously reported such antennas