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Showing papers in "Iet Microwaves Antennas & Propagation in 2012"


Journal ArticleDOI
TL;DR: A novel RF power harvesting front-end whose conversion efficiency is significantly improved at low RF power levels (<;-20 dBm) as compared to existing technologies is designed, making a game changing technology for powering mobile devices.
Abstract: This study is focused on equipping wireless devices (including sensors) with novel, high-efficiency circuitry to harvest and convert ambient radio frequency (RF) power to direct current (dc). Key components of this technology are (a) miniaturised antenna and (b) high-efficiency rectifying circuit. The first is responsible for capturing the RF waves, and the latter converts the RF energy to dc. A major challenge is the design of novel circuitry to generate a battery-like voltage from very low incoming RF energy. Under this study, the authors designed a novel RF power harvesting front-end whose conversion efficiency is significantly improved at low RF power levels (<;-20 dBm) as compared to existing technologies. Thus, the new circuitry can harvest ambient and widely available RF energy, making a game changing technology for powering mobile devices. In this study, the authors demonstrate this technology by using it to power a commercially available temperature and humidity meter with an LCD display. The latter is powered using nothing more than ambient WiFi signals in an office environment.

171 citations


Journal ArticleDOI
TL;DR: In this paper, the authors considered the antenna as a helix with a dielectric resonator core and derived the height of the helix using the Hansen-Woodyard condition for an end-fire array.
Abstract: The present thesis considers two different subjects in the research area of electromagnetics. The first part is concerned with antenna design and the second with radar absorbers and rasorber.In the first part, a novel excitation technique for cylindrical dielectric resonator antennas is introduced to produce circular polarization. The exciter is a tape helix that is wound around the dielectric resonator and is fed by a coaxial probe. The helix excites the HE11σ modes in phase quadrature in the cylindrical dielectric resonator antenna. The height of the helix is determined using the Hansen-Woodyard condition for an end-fire array based on the phase velocity of the surface wave traveling along the dielectric resonator side wall. This phase velocity is estimated from the phase velocity in an infinitely long dielectric rod with the same permittivity and radius as the dielectric resonator antenna. The helical exciter is required to operate in the helix axial mode. The height of the helix is usually taller than the height of the dielectric resonator core. Using this type of excitation, a 3 dB axial-ratio bandwidth of 6.4% was achieved for a sample design with dielectric constant er ~ 11. The achieved 3 dB axial-ratio bandwidth is greater than that typical of other reported single feed cylindrical dielectric resonator antennas. A prototype of the sample design is fabricated and measured and a good agreement between simulation and measurement is observed. Furthermore, two approaches for the enhancement of the 3 dB axial ratio bandwidth are proposed: removing the central portion of the cylindrical dielectric resonator and using stacked cylinders. The advantages and limitations of each approach are discussed. Another perspective on the proposed design is to consider the antenna as a helix with a dielectric resonator core. In this perspective, the effects of the dielectric core on the helix antenna are discussed.The second part of the thesis is concerned with the design of thin wideband electromagnetic planar absorber for X- and KKu-band which also has a polarization sensitive transparent window at frequencies lower than L-band. The design is based on a two layer capacitive circuit absorber with the backmetal layer replaced with a polarization sensitive frequency selective surface. The structure is studied for normally incident waves with two orthogonal linear polarizations. The structure is optimized to have high transparency at low frequencies for one of the polarizations and at the same time good absorption efficiency for both polarizations at the high-frequency band. For one of the polarizations a -1.9 dB transmission with a transmission loss of less than 10% at 1 GHz as well as a 2.25:1 (75%) bandwidth of -20 dB reflection reduction are achieved. For the other polarization we obtained more than 3:1 (100%) bandwidth of -19 dB absorption. Compared with our earlier design based on a Jaumann absorber, we succeed in significantly reducing the transmission loss at the transparent window. Furthermore, the module of absorption quality is extensively improved. The improvements are based on using periodic arrangements of resistive patches in the structure design. The investigation of the structure for oblique angles of incidence and non-ideal materials is also accomplished.

102 citations


Journal ArticleDOI
TL;DR: In this paper, a method for designing miniaturised multi-band filters using the complementary split-ring resonators (CSRRs) is proposed and demonstrated on the basis of substrate integrated waveguide (SIW) technology.
Abstract: A novel method for designing miniaturised multi-band filters using the complementary split-ring resonators (CSRRs) is proposed and demonstrated on the basis of substrate integrated waveguide (SIW) technology. By loading different types of CSRRs on the waveguide surface, multiple passbands propagating below the waveguide cutoff frequency can be generated separately. The proposed structures allow relatively independent control over the centre frequency and the coupling coefficient. The working principle is illustrated by the equivalent circuit and the filter coupling methodology is introduced for design purpose. Two types of dual-passband filters, a triple-band and a quadruple-band filter are designed and fabricated to validate the proposed concept. These filters are showing advantages in terms of compact size, good selectivity and stopband rejection, as well as the easy integration capability with other circuits.

74 citations


Journal ArticleDOI
TL;DR: In this article, a comprehensive comparison of a wide collection of compact microstrip resonant cells (CMRCs) found in the extensive body of literature has been presented, which has led to the selection of the most promising CMRC geometry for the efficient miniaturisation of modern microwave components.
Abstract: A comprehensive comparison of a wide collection of compact microstrip resonant cells (CMRCs) found in the extensive body of literature has been presented. The evaluation of different CMRC designs has led to the selection of the most promising CMRC geometry for the efficient miniaturisation of modern microwave components. To showcase the vital effectiveness of the approach, the initially selected CMRC has been notably improved and applied to an exemplary microwave component, that is, a branch-line coupler, to obtain its size reduction without degradation in its performance. Exemplary prototype circuits have been designed to mimic the frequency characteristics of a classic coupler, simultaneously presenting a substantial 75, 80 and 85% surface area reduction. The best solution obtained has been experimentally validated. The measured in-band results are in excellent accordance with the theoretical characteristics, whereas the broadband performance depicts an additional effect, that is, the strong suppression of unwanted signals in 2.6-7 GHz frequency band. The multi-step CMRC evaluation and improvement procedure proposed presents an efficient design methodology for novel compact circuit topologies developed in microstrip technology.

73 citations


Journal ArticleDOI
TL;DR: In this paper, an ultra wideband (UWB) antenna is presented whose frequency characteristics can be reconfigured electronically to have either a single- or dual-band notch function to block interfering signals from C-band satellite communications systems, IEEE 802.11a and HIPERLAN/2 WLAN systems for example.
Abstract: An ultra-wideband (UWB) antenna is presented whose frequency characteristics can be reconfigured electronically to have either a single- or dual-band notch function to block interfering signals from C-band satellite communications systems, IEEE802.11a and HIPERLAN/2 WLAN systems for example. The proposed antenna is excited using a circular ring resonator fabricated on one side of the dielectric substrate with a circular slot etched on the ground plane. To realise a single- or dual-band notch characteristic the antenna includes a semi-circular parasitic strip located above the circular ring, and a T-shaped stub is located near the inner edge of circular ring. The parasitic strip and T-shaped stub are connected to the circular ring via PIN diodes to give the antenna reconfigurable capability by configuring the PIN diodes in a prescribed combination of ON and OFF states. It is shown that there is virtually no change in the antenna's E -plane and H -plane radiation patterns for the various PIN diode switching conditions. The proposed antenna's performance has been verified by measurements.

72 citations


Journal ArticleDOI
TL;DR: The authors carry out a numerical study that aims at finding a trade-off between the design cost and reliability of the SBO algorithms and demonstrates that the use of multiple models of different fidelity may be beneficial to reduce the designcost while maintaining the robustness of the optimisation process.
Abstract: Electromagnetic (EM) simulation has become an important tool in the design of contemporary antenna structures. However, accurate simulations of realistic antenna models are expensive and therefore design automation by employing EM solver within an optimisation loop may be prohibitive because of its high computational cost. Efficient EM-driven antenna design can be performed using surrogate-based optimisation (SBO). A generic approach to construct surrogate models of antennas involves the use of coarse-discretisation EM simulations (low-fidelity models). A proper selection of the surrogate model fidelity is a key factor that influences both the performance of the design optimisation process and its computational cost. Despite its importance, this issue has not yet been investigated in the literature. Here, the authors focus on a problem of proper surrogate model management. More specifically, the authors carry out a numerical study that aims at finding a trade-off between the design cost and reliability of the SBO algorithms. Our considerations are illustrated using several antenna design cases. Furthermore, the authors demonstrate that the use of multiple models of different fidelity may be beneficial to reduce the design cost while maintaining the robustness of the optimisation process. Recommendations regarding the selection of the surrogate model coarseness are also given.

61 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed an approach based on the optimisation of the pulse sequence modulating the static excitations of the array elements to exploit pattern multiplication effects such that the sideband level of the harmonic pattern term related to the array factor is balanced by the element pattern distribution.
Abstract: The reduction of the power losses in the sideband radiation of directive time-modulated linear arrays is addressed. The approach is based on the optimisation of the pulse sequence modulating the static excitations of the array elements to exploit pattern multiplication effects such that the sideband level of the harmonic pattern term related to the array factor is balanced by the element pattern distribution. A set of representative numerical results is reported and discussed to illustrate the potentialities and the limitations of the proposed approach.

55 citations


Journal ArticleDOI
TL;DR: Paper-based inkjet-printed ultra wideband (UWB) fractal antennas are presented in this article, where a miniaturized UWB monopole, which uses a fractal matching network and is the smallest reported inkjet printed UWB printed antenna to date, and a fourth-order Koch snowflake monopole which utilises a Sierpinski gasket fractal for ink reduction, are demonstrated.
Abstract: For the first time, paper-based inkjet-printed ultra-wideband (UWB) fractal antennas are presented Two new designs, a miniaturised UWB monopole, which utilises a fractal matching network and is the smallest reported inkjet-printed UWB printed antenna to date, and a fourth-order Koch Snowflake monopole, which utilises a Sierpinski gasket fractal for ink reduction, are demonstrated It is shown that fractals prove to be a successful method of reducing fabrication costs in inkjet-printed antennas, while retaining or enhancing printed antenna performance

55 citations


Journal ArticleDOI
TL;DR: In this paper, a multi-resonant unit cell based on liquid crystals is proposed for reconfigurable reflectarray antennas, which is made up of three parallel dipoles in the same cell and a tunable liquid crystal as substrate.
Abstract: A multi-resonant unit-cell based on liquid crystals is proposed for reconfigurable reflectarray antennas. The proposed reflectarray element is made up of three parallel dipoles in the same cell and a tunable liquid crystal as substrate. The performance of the multi-resonant unit cell is compared with that of a single-resonant element in a frequency band from 30 to 40 GHz, showing a significant improvement in bandwidth, range of phase and losses. For a commercial liquid crystal, the proposed element provides a phase range greater than 360 within a 7.4 bandwidth and losses lower than 4.7 dB. These results represent a significant improvement with respect to the single-resonant unit cell based on the same liquid crystal. Finally, the proposed multi-resonant element is validated by measuring the phase response and losses in an X-band waveguide simulator.

52 citations


Journal ArticleDOI
TL;DR: In this paper, a low-cost inkjet-printed patch antenna sensor that can passively detect crack formation, orientation and shape by means of resonant frequency shifts in the two resonant modes of the antenna is presented.
Abstract: Monitoring fatigue cracking of large engineering structures is a costly and time-intensive process. The authors' present the first low-cost inkjet-printed patch antenna sensor that can passively detect crack formation, orientation and shape by means of resonant frequency shifts in the two resonant modes of the antenna. For the first time, the effect of non-linear crack shapes on the parallel and perpendicular resonant modes of a patch antenna is quantified with simulation and measurement. This study presents a step towards fully integrated, low-cost, conformal and environmentally friendly smart skins for real-time monitoring of large structures.

52 citations


Journal ArticleDOI
TL;DR: In this paper, a multi-band printed dipole antenna loaded with reactive elements is proposed, where the reactive loading of the dipole is inspired by the Epsilon-negative (ENG) and double negative metamaterial inclusions, which enable the loaded dipole to operate in multiuser bands.
Abstract: A compact multi-band printed dipole antenna loaded with reactive elements is proposed The reactive loading of the dipole is inspired by the Epsilon-negative (ENG) and double negative metamaterial inclusions, which enable the loaded dipole to operate in multi-band The reactive loads are realised by two rake-shaped split ring resonators facing each other Investigations reveal that the loaded dipole radiates at two or three separated bands depending on symmetrical or asymmetrical loading and load locations The new resonance frequencies are lower than the natural resonance frequency of the conventional half-wavelength dipole In this range of frequencies, the radiation efficiency of the composite antenna is high In order to validate the simulation results, a prototype of the proposed printed dipole is fabricated and tested The agreement between the simulated and measured results is quite good

Journal ArticleDOI
TL;DR: In this paper, a reduced size rat-race coupler incorporating a bandpass frequency response characteristic is presented and designed based on substrate-integrated waveguide (SIW) technology.
Abstract: A reduced size rat-race coupler incorporating a bandpass frequency response characteristic is presented and designed based on substrate-integrated waveguide (SIW) technology. By use of electric- and magnetic-coupling structures between adjacent SIW cavity resonators, a conventional rat-race coupler and a bandpass filter with a 200-MHz bandwidth at a centre frequency of 7.75 GHz can be integrated as one component resulting in miniaturisation. A design process based on the coupled-resonator network is introduced to synthesise such a bandpass coupler with desired bandwidth, return loss and coupling. A Butler matrix and a six-port junction with bandpass response are then developed based on the proposed rat-race coupler. They represent excellent candidates for miniaturised transceiver and direct conversion systems. The measured results are in good agreement with the simulated predictions.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a quadruple band notch antenna with four pairs of meander lines working as resonators for ultra-wide band (UWB) antennas, which can be adjusted independently using the dimensions of the corresponding MLs.
Abstract: In this study, the design of multiple band notch for compact ultra-wide band (UWB) antennas is proposed. The antenna consists of an elliptical radiator, a microstrip-feed line and a ground plane. Four pairs of meander lines (MLs), working as resonators, are added to the antenna to produce a quadruple band notch characteristic, yet without increasing the overall antenna size. Two types of feeding techniques, direct-connected feed and parallel-coupled feed, are used in the resonators. The centre frequencies and bandwidths of the individual notches can be adjusted independently using the dimensions of the corresponding MLs. For verification, the proposed antenna is also fabricated and measured. The return loss, peak gain, efficiency and radiation pattern of the band-notch antenna are studied using both computer simulation and measurement. The pulse responses of the band-notched antennas are also measured and compared with those of single-, double- and triple-band-notch antennas.

Journal ArticleDOI
TL;DR: In this article, a frequency reconfigurable multiple-input multiple-output (MIMO) antenna with coupled conductors and an isolation improvement structure located between the two antennas is presented.
Abstract: A frequency reconfigurable multiple-input multiple-output (MIMO) antenna is presented. The proposed MIMO antenna consists of two reconfigurable printed monopole antennas with coupled conductors and an isolation improvement structure located between the two antennas. In order to change the operating frequency, PIN-diodes are embedded in the antennas. According to the on/off state of the PIN-diode, the resonant frequency is changed between the WLAN band (2400-2483 and 5150-5350-MHz) and the m -WiMAX band (3400-3600-MHz). The proposed isolation technique produces an S 21 of less than -20-dB for both service bands. Simulation and measurement results confirm the antenna performance. Peak gains of 3.81-dBi at 2.4-GHz, 1.87-dBi at 5.2-GHz and 5.15-dBi at 3.5-GHz are found. Radiation efficiencies are greater than 58.85- over all of the operating frequency bands. The measured envelope correlation coefficient (ECC) and the mean effective gain (MEG) are suitable for use in MIMO antenna systems.

Journal ArticleDOI
TL;DR: In this paper, a novel metamaterial topology called M-band nested U-ring resonator (M-NURR) is proposed to provide multiple band operation with an electrically small and geometrically simple unit cell design.
Abstract: In this study, a novel metamaterial topology, called M-band nested U-ring resonator (M-NURR), is proposed to provide multiple band operation with an electrically small and geometrically simple unit cell design. The M-NURR unit cell has M-nested and unconnected U-shaped metal rings printed on a dielectric substrate where each ring is primarily associated with a distinct LC type resonance frequency where L and C stand for inductance and capacitance, respectively. Therefore this M-NURR topology has the novel property that each of these resonance frequencies can be controlled almost independently by adjusting the arm length of the associated U-ring. In this study, three different M-NURR structures (for M=1, 2, 3) are designed, fabricated and characterised both numerically and experimentally with very good agreement. The suggested sub-wavelength M-NURR metamaterial topology is anticipated to be useful in the design of miniaturised multi-band mobile communication devices as it makes the fine tuning of operation frequencies possible by a simple parametric adjustment.

Journal ArticleDOI
TL;DR: In this paper, a set of substrate-integrated cavity-backed patch antennas of alternative topologies is proposed using the substrateintegrated waveguide (SIW) technology, where the cavity backing the patch is emulated using array of plated through via holes.
Abstract: A set of substrate-integrated cavity-backed patch antennas of alternative topologies is proposed. Using the substrate-integrated waveguide (SIW) technology, the cavity backing the patch is emulated using array of plated through via holes. The proposed topologies have the potential to widen the inherent limited bandwidth of the conventional patch from typically 2% to about 15% depending on the height of the backing cavity. Additionally, the cavity enhances the antenna gain by about 2 dB, as the cavity is very effective in suppressing the unwanted surface waves, thus improving the radiation efficiency. Meanwhile, the proposed SIW topology has a low fabrication cost, as the whole structure could be attained using conventional printed circuit board processing. Design parameters of the SIW cavities are thoroughly investigated in this study, demonstrating their leakage characteristics. Four different structures are investigated corresponding to the different combinations of rectangular or circular patches backed by rectangular or circular SIW cavities. Detailed design guidelines are presented for the SIW cavities to ensure minimum leakage losses and for the radiating elements to achieve a desired fractional bandwidth. Based on experimental prototypes, a thorough comparative study between the four different topologies is presented demonstrating the attractive characteristics of each topology as far as gain, bandwidth, cross-pol level and mutual coupling.

Journal ArticleDOI
TL;DR: In this paper, two compact wideband differential bandpass filters based on the double-sided parallelstrip line (DSPSL) and transversal signal-interaction concepts are proposed.
Abstract: Two compact wideband differential bandpass filters based on the double-sided parallel-strip line (DSPSL) and transversal signal-interaction concepts are proposed in this study Two transmission zeros and good harmonic suppression can be achieved for the first wideband differential DSPSL filter, because of the two transmission paths with different lengths for input/output ports In addition, another improved common suppression wideband differential DSPSL filter with two 180/ phase inverters is introduced Four λ /4 shorted lines are added to improve the passband transmission characteristic for the two differential DSPSL filters Two prototypes with 3/dB fractional bandwidth of 94 and 1176/, and return loss greater than 15/dB for differential mode are designed and fabricated The measured results show good agreement with the theoretical expectations

Journal ArticleDOI
TL;DR: In this paper, the switching sequence is optimized to keep constant the instantaneous directivity of the main beam, while generating a desired average radiation pattern at the frequency of the impinging signal, to avoid the spreading of the desired signal power into the harmonics generated by the on-off commutations of the switches.
Abstract: As of the periodic on–off modulation of the static excitations, the number and the positions of the active elements in time-modulated arrays can vary significantly within the modulation period and the radiated pattern can drastically differ instant-by-instant. Since the fluctuations of the antenna gain could severely affect the behaviour of the received signal and its correct retrieval, the switching sequence is here properly optimised to keep constant the instantaneous directivity of the main beam, while generating a desired average radiation pattern at the frequency of the impinging signal. This allows one to avoid the spreading of the desired signal power into the harmonics generated by the on–off commutations of the switches. A set of representative results concerned with a benchmark linear case is reported and discussed to show the effectiveness of the proposed approach also in comparison with state-of-the-art solutions.

Journal ArticleDOI
TL;DR: In this article, a dual-band 2-2 MIMO antenna system for the 700-MHz band of the long-term evolution (LTE) wireless standard is presented.
Abstract: The use of multiple-input-multiple-output (MIMO) antenna systems will be required by next generation wireless systems to achieve their high throughput data transmissions. In this work, the authors present the design and fabrication of a 2 - 2 MIMO antenna system for the 700-MHz band of the long-term evolution (LTE) wireless standard. The MIMO antenna system is based on a novel 4-shaped antenna geometry that is compact in size and covers two bands of operation. The dual-band 2 - 2 MIMO antenna system covers the 734-790-MHz and the 2307-2475-MHz LTE and industrial, scientific and medical (ISM) bands. It occupies an FR-4 material substrate size of 58-110-1.56-mm 3 . The antenna has frequency tuning capabilities without changing the over all size of the MIMO system substrate. Several isolation enhancements methods were investigated, and the values of the correlation coefficient (|ρ| max ) were within the LTE requirements. The maximum obtained gain for a single operating antenna at 770 and 2380 MHz was 5 and 4.5 dBi, respectively.

Journal ArticleDOI
TL;DR: In this article, a common-gate low-noise amplifier (LNA) that uses the current-reuse technique and is intended to achieve both ultra-wideband and low power consumption is proposed.
Abstract: A common-gate (CG) low-noise amplifier (LNA) that uses the current-reuse technique and is intended to achieve both ultra-wideband and low-power consumption is proposed. The CG amplifier enables wide-band input matching with low transconductance and low frequency-independent noise figure (NF) when employed at the input stage compared with the common-source amplifier. The current-reuse technique is adopted in order to reduce the power dissipation while achieving reasonable power gain. In addition, a shunt and series peaking technique is adopted to obtain wide bandwidth. The proposed LNA achieves a 3-dB bandwidth from 2.4 to 11.2 GHz, a maximum power gain of 14.8 dB, a minimum NF of 3.9 dB and a third-order input intercept point of −11.5 dBm while consuming 3.4 mW from a 1.5 V supply. A 0.18-μm CMOS process is utilised to fabricate the LNA.

Journal ArticleDOI
TL;DR: In this paper, two identical radiating elements, both comprising one electric and one magnetic dipole, were optimized numerically to obtain equally strong radiation from the electric and magnetic dipoles, and the optimised prototype was then manufactured and its radiation properties were measured.
Abstract: We study the possibility of creating a Huygens source antenna for linear polarisation with good matching to a 50 Ω feeding cable. For this purpose, we design two identical radiating elements, both comprising one electric and one magnetic dipole. The dimensions of these radiating elements are optimised numerically to obtain equally strong radiation from the electric and magnetic dipoles. The optimised prototype is then manufactured and its radiation properties are measured.

Journal ArticleDOI
TL;DR: In this article, a novel optimisation algorithm biogeography-based optimisation (BBO) for thinning large multiple concentric circular ring arrays is presented, which aims to achieve an array of uniformly excited isotropic antennas that will generate a narrow beam with minimum relative sidelobe level (SLL).
Abstract: This study presents a novel optimisation algorithm biogeography-based optimisation (BBO) for thinning large multiple concentric circular ring arrays. The objective is to achieve an array of uniformly excited isotropic antennas that will generate a narrow beam with minimum relative sidelobe level (SLL). BBO is a new comprehensive force based on the science of biogeography. Biogeography is the schoolwork of geographical allotment of biological organisms. BBO utilises migration operator to share information between the problem solutions. The problem solutions are known as habitats and sharing of features is called migration. In this study, the authors propose pattern synthesis method to reduce the SLLs with narrow beamwidth (BW) by making the ring array thinned using the BBO algorithm. The thinning percentage of the array is kept equal to or more than 50% and the BW is kept equal to or less than that of a fully populated, uniformly excited and 0.5λw, spaced concentric circular ring array of same number of elements and rings. The results obtained are compared with previous published results of modified particle swarm optimisation and differential evolution with global and local neighbourhoods.

Journal ArticleDOI
TL;DR: In this article, a microstrip-line dual-band bandpass filter using a stub-loaded multiple-mode resonator is presented, which is formed by loading three stubs in shunt to a simple uniform impedance resonator in the center and two symmetrical locations, respectively.
Abstract: A compact microstrip-line dual-band bandpass filter using a stub-loaded multiple-mode resonator is presented. This multiple-mode resonator is formed by loading three stubs (one short-circuited and two open-circuited stubs) in shunt to a simple uniform impedance resonator in the centre and two symmetrical locations, respectively. By properly adjusting the lengths of the three stubs, the first two resonant modes of this multiple-mode resonator can be allocated within the first passband, whereas the third and fourth resonant modes can be allocated within the second passband of the dual-band filter. This results in the formulation of a novel dual-band filter with compact-size and high isolation between passbands by incorporating this multiple-mode resonator with source-load coupling. Two coupling paths are used to control the bandwidth of each passband independently. To illustrate the concept, two dual-band filters of different frequency ratios are designed, fabricated and measured. Simulated and measured results are found to be in good agreement with each other, showing that a rejection level of 15 dB up to more than four times the first passband frequency can be obtained.

Journal ArticleDOI
TL;DR: In this paper, the authors presented the design of microwave filters based on the coupling matrix approach; determination of the matrix is based on a hybrid optimisation algorithm which may be applied to cross-coupled filters having diverse topologies.
Abstract: This study presents the design of microwave filters based on the coupling matrix approach; determination of the matrix is based on a hybrid optimisation algorithm which may be applied to cross-coupled filters having diverse topologies. Various filter responses from dual-band to quad-band are given as examples of the approach. The optimisation is performed on the coupling matrix and a genetic algorithm (GA) is employed to generate initial values for the control variables for a subsequent local optimisation (sequential quadratic programming search). The novel cost function in this study measures the difference of the frequency locations of reflection and transmission zeros between the response produced by the coupling matrix and the ideal response. The ideal response in the form of characteristic polynomials is determined from the filter specifications and generated by a recently developed iterative technique which is capable of realising multi-band filters with different return loss levels. Convergence of the coupling matrix optimisation is fast, and no initial values for the control parameters are required by the GA. An eighth-order X-band dual-band waveguide filter with all-capacitive-coupling irises has been fabricated and measured to verify the design technique. Excellent agreement between simulation and experimental result has been achieved.

Journal ArticleDOI
TL;DR: In this article, a novel transmission-line cloaking design operating at microwave frequencies is presented with special emphasis in the design placed on ease of manufacture and practicality, and the operation of the cloak is verified by studying the antenna blockage caused by the cloaked and uncloaked objects.
Abstract: Transmission-line cloaking is a simple yet wideband technique for cloaking a mesh-like object. A novel transmission-line cloak design operating at microwave frequencies is presented with special emphasis in the design placed on ease of manufacture and practicality. The operation of the cloak is verified by studying the antenna blockage caused by the cloaked and uncloaked objects. It is shown both numerically and experimentally that the designed transmission-line cloak is capable of hiding a mesh-like metal object placed inside it from the incident wave in a variety of different scenarios and within a fairly wide frequency bandwidth. Also, the agreement between simulations and measurements is shown to be very good.

Journal ArticleDOI
TL;DR: In this paper, a three-layer DRA structure is used to achieve enhanced and broadband coupling to the waveguide, and the double-summation representation of the homogeneous Green's function is extended to the multilayer case, leading to a substantial reduction in computation time for the input impedance.
Abstract: A rectangular waveguide feed to the dielectric resonator antenna (DRA) is proposed. A three-layer DRA structure is used to achieve enhanced and broadband coupling to the waveguide. The antenna topology is easy to realise and does not need additional coupling or matching elements to effectively excite the DRA. The configuration also affords ease in frequency tuning without sacrificing bandwidth or radiation performance. The full-wave Green's function approach is presented for the analysis of such multilayer structures with an arbitrary number of layers with greatly reduced computational overhead. The modes of the multilayer DRA can be identified from the analysis, which can be used to explain the broadband nature of the coupling. The double-summation representation of the homogeneous Green's function has been extended to the multilayer case, leading to a substantial reduction in computation time for the input impedance.

Journal ArticleDOI
TL;DR: In this paper, an IWO algorithm for the synthesis of cosecant squared and contoured beam patterns is presented and compared with particle swarm optimisation algorithm results, which provides good convergence and is stable and adaptive to change for different boundary conditions in pattern synthesis applications.
Abstract: The authors present a new optimisation method for pattern synthesis of multi-feed reflector antennas in this study. By using an invasive weed optimisation (IWO) algorithm, shaped beam antennas are designed. The results of the IWO algorithm for the synthesis of cosecant squared and contoured beam patterns are presented and compared with particle swarm optimisation algorithm results. The far-field radiation patterns of reflector antennas, fed by linear and planar array of conical horn antennas, are provided by a physical optics and the error between desired and provided radiation patterns is calculated by a root mean square method. The results show that the IWO algorithm, which provides good convergence, is stable and adaptive-to-change for different boundary conditions in pattern synthesis applications.

Journal ArticleDOI
TL;DR: In this article, a planar antenna with ultrawideband (UWB) performance and dual band-notched characteristics is proposed, where the main features of the antenna are the compact dimensions and omnidirectional radiation across the whole band of operation.
Abstract: A planar antenna with ultrawideband (UWB) performance and dual band-notched characteristics is proposed. The main features of the antenna are the compact dimensions and omnidirectional radiation across the whole band of operation. The radiator of the antenna is a slotted square patch. The ground plane is located at the bottom layer, which also includes a Π-shaped conductor-backed plane used to widen the impedance bandwidth. Dual band-notched characteristics are achieved by an inverted T-shaped strip inside the slotted radiator and a pair of mirror inverted L-shaped slots at the two sides of the radiator. The measured results of the manufactured (12 × 16 mm) antenna on 1.6 mm FR4 substrate show that the antenna operates with voltage standing wave ratio (VSWR) less than two over the frequency band from 2.5 to 10.8 GHz. That wideband is featured by the existence of two notched bands (3.23-4.3 and 5-6 GHz), where the VSWR is more than nine, aimed at suppressing any interference from IEEE802.16 WiMAX (3.3-3.6 GHz), C-band systems (3.7-4.2 GHz) and IEEE802.11a WLAN (5.15-5.825 GHz). The antenna has an omnidirectional radiation across the whole UWB as validated by the measured radiation pattern and gain.

Journal ArticleDOI
TL;DR: In this paper, a miniature ultra-wideband (UWB) antenna for wireless universal serial bus (USB) dongle applications is presented, which comprises a half-circular quasi-self-complementary structure together with a triangular cut on a bent microstrip feed line.
Abstract: A miniature ultra-wideband (UWB) antenna for wireless universal serial bus (USB) dongle applications is presented. The proposed antenna comprises a half-circular quasi-self-complementary structure together with a triangular cut on a bent microstrip feed line. As a result of its simple geometry and compact size, the antenna can be easily integrated and printed on wireless USB dongle printed circuit boards. The dimension of the proposed antenna is only 16 mm×16.1 mm whereas the footprint size of the dongle board is 16 mm×60 mm, similar to that of a conventional USB flash disc. The simulated and measured results show that the antenna can achieve a UWB 10 dB impedance bandwidth with reasonable radiation properties. It also exhibits a much-reduced ground plane effect compared to the stand-alone design. In addition, a parametric study is performed to provide insights into the antenna operating mechanism.

Journal ArticleDOI
TL;DR: In this article, a robust simulation-driven design methodology of microwave circuits with complex topologies has been presented, which is suitable for a wide class of N-port unconventional microwave circuits constructed as a deviation from classic design solutions.
Abstract: A robust simulation-driven design methodology of microwave circuits with complex topologies has been presented. The general method elaborated is suitable for a wide class of N-port unconventional microwave circuits constructed as a deviation from classic design solutions. The key idea of the approach proposed lies in an iterative redesign of a conventional circuit by a sequential modification and optimisation of its atomic building blocks. The speed and accuracy of the method presented has been acquired by solving a number of simple optimisation problems through surrogate-based optimisation (SBO) techniques, which offer a satisfactory approximation of the optimal design solution. Two exemplary designs have been supplied to verify the method introduced. An abbreviated wideband quarter-wave impedance matching transformer and a miniaturised hybrid branch-line coupler have been developed. Diminished dimensions of the circuits under construction have been achieved by means of compact microstrip resonant cells. As an SBO engine, an implicit space mapping technique has been utilised. The final results have been acquired in only a fraction of time that is necessary for a direct electromagnetic (EM) optimisation to generate competitive results. An experimental validation of the method proving its high utility has been provided.