Metasurfaces that manipulate electromagnetic waves have gained significant attention in recent years. The focus has primarily been on planar devices, while many applications require curved surfaces. In this study, the authors propose an analysis approach for cylindrical cascaded (multilayer) metasurfaces. The approach combines the concept of sheet impedance in the spectral domain with a new transmission matrix formulation that is applicable to stratified, canonical curved geometries. Approximate formulas for the sheet impedance of common planar, metallic patterns are also adapted to curved geometries. The reported analysis approach allows one to determine the optimal spectral-domain, azimuthal dependence of a sheet impedance, as well as the best geometrical elements to obtain the required azimuthal variation. The results are verified through several cylindrical metsurface examples.

A body contacting substrate integrated waveguide (SIW) slot antenna with 1 GHz cut-off frequency is presented for deep tissue thermometry. The SIW is shorted at one end and fed by an exponentially tapered microstrip line with a defected ground structure. An inclined (137°) off-centred, asymmetric twin slot (23.3×3 mm²) etched on the SIW ground plane is optimised for resonance at 1.3 GHz and directional power deposition over 1.2–1.4 GHz. Antenna measurements indicate >10 dB return loss and high immunity to ambient electromagnetic interference. Antenna brightness temperature measurements indicate the ability to detect a 10 mm diameter hot spot with a temperature rise of 0.6°C at 45 mm depth from the phantom surface.

The capability of complementary capacitively loaded loop (CCLL) metamaterial (MTM) to miniaturise printed slot antenna is examined. This study presents a planar compact antenna with the overall size of 15 × 9 mm² for handheld/portable applications. The antenna is comprised of four sections: coupled-fed, a parasitic line, a CCLL-MTM, and a slot. It is shown that CCLL-MTM exhibits a magnetic behaviour through the frequency band of 2820–3200 MHz, which causes antenna miniaturisation while simultaneously helps radiation enhancement. To validate the simulation results, a prototype of the antenna is fabricated and tested. Good agreement between the simulation and measurement results is obtained.

A novel, high-power optically controlled microwave switch is presented. The switch uses integrated illumination of a silicon superstate through a low-loss glass substrate which reduces losses related to the plasma conductivity tail in the silicon. Numerical electromagnetic modelling is used to design the switch and good agreement between measured and simulated results has been achieved. The switch is then characterised using a two-tone non-linearity test at 2 GHz and a third-order intercept point of +72 dBm is obtained with 10 W per tone.

This study presents the design, accurate characterisation, and performance comparison for multilayer thin-film microstrip (TFMS), coplanar waveguide (CPW), and substrate integrated waveguides (SIW) lines and interconnects for various transverse dimensions, which are fabricated on thin dielectric layers, using advanced ceramic-based photoimageable thick-film technology. The influence of ground-plane width on multilayer finite-ground planar transmission lines (TFMS and CPW) and the influence of cavity dimensions on SIW have been experimentally studied. This includes the variation of characteristic impedance and attenuation with normalised ground-/cavity-width and extending frequency to beyond 110 GHz (180 GHz, for SIW). Contrary to conventional fence-post, metal-filled trenches have been used for SIW, showing high performance (loss of 0.2 dB/mm at 110 GHz, even for a thin dielectric) and suitable for operation beyond 180 GHz, the highest frequency reported for off-chip integration in MCMs. Further, for the first time, comprehensive comparative performances of traditional microstrip, TFMS, CPW, and SIW, in circuit/system design perspective, have been presented for enabling proper selection of transmission media and interconnect with optimum transverse/ground width, and development of compact and high performance millimetre-wave multichip module front-ends economically.

A single-to-differential low-noise amplifier (LNA) is proposed for low-power medical devices in the frequency band of 401–406 MHz. The proposed LNA avoids the use of surface acoustic wave (SAW) filter and additional balun in RF receiver front-end. The LNA comprises inductive degeneration common source (IDCS) technique (stage I) and a cascaded common source circuit (stage II). The stage-II is stacked on top of stage-I. The proposed balun LNA incorporates single to differential (SD) conversion for minimum gain and phase error. A compensation bias circuit is proposed to minimise variations in parameters of LNA against process corners, supply voltage and temperature (PVT). An upsurge balun LNA is designed in UMC 0.18-µm CMOS technology, the DC power consumption is 290 µW under a supply voltage of 1 V and the minimum noise figure is 3 dB. The die area of LNA including buffers and bias circuit is 850 µm × 978 µm. The worst-case post layout simulation results show a gain and phase error of 0.8 dB and 10°. The percentage variation of gain and NF against PVT is reduced by 55 and 48%. Furthermore, the balun LNA has out of band rejection at the roll-off rate better than 70 dB/dec.

This study describes the design of a metamaterial planar antenna for multi-octave band operation. The metamaterial unit-cell comprises L-shaped slit which is etched inside a rectangular patch with a grounded inductive spiral. The slit essentially behaves as a series left-handed capacitance and the spiral as a shunt left-handed inductance. The antenna was modelled and optimised for impedance bandwidth, gain and efficiency performance using commercial three-dimensional full-wave electromagnetic simulation tools. The antenna has a measured impedance bandwidth of 6.02 GHz for S ₁₁<−10 dB. This corresponds to a fractional bandwidth of 172.49%, which is higher than multiband planar antennas reported to date. The antenna has a maximum gain and efficiency performance of 3.7 dBi and 73%, respectively, at 3.25 GHz. The physical footprint of the antenna is comparable to other wideband planar antennas reported to date. The overall size of the antenna is 0.037λ ₀ × 0.027λ ₀ × 0.002λ ₀ and 0.25λ ₀ × 0.18λ ₀ × 0.017λ ₀, where λ ₀ is free-space wavelength at 0.48 and 3.25 GHz, respectively.

A compact, wideband, omnidirectional, vertically polarised antenna without electrostatic discharge problems is proposed in this study for 4G long-term evolution applications. The proposed antenna is composed of three identical basic radiators separated by an angle of 120°. The basic radiator is based on a slot loop which is a wideband and DC ground structure. By bending the basic radiators, the antenna achieves better impedance matching and lower gain variation in the horizontal plane in a compact size. The proposed antenna reaches a fractional bandwidth of 45.5% for the voltage standing wave ratio (VSWR) <1.5, a peak gain from 2.4 to 3.8 dBi with a gain ripple around 2 dB in the omnidirectional plane. It operates from 1700 to 2700 MHz, covering most 4G long-term evolution frequency bands. Both simulation and measurement of a prototype is done in this study to verify the antenna performance.

This study addresses the problem of explicit size reduction of multi-band antennas by means of simulation-driven optimisation. The principal difficulty of electromagnetic (EM)-based miniaturisation of multi-band antennas is that several resonances have to be controlled independently (both in terms of their frequency allocation and depth) while attempting to reduce physical dimensions of the structure at hand. The design method of choice in this work is feature-based optimisation (FBO) framework. The methodology has been shown as appropriate for handling multi-band antenna responses. The primary objective of the optimisation process is the footprint area of the antenna. At the same time, design requirements pertinent to reflection characteristics are handled by means of a penalty function approach. The properties of the FBO framework, namely ‘flattening’ of the functional landscape, allows to keep the design optimisation costs at acceptable levels of few dozens of evaluation of the EM simulation model of the antenna. For the sake of demonstration, two antenna structures are considered, a dual-band patch antenna, and a triple-band dipole antenna. Considerable size-reduction ratios are achieved, over 50% and almost 30% for the first and the second structures, respectively. Numerical results are validated experimentally.

The contribution of this work is twofold: the authors developed an accurate model to solve the vector wave equation of radially-layered inhomogeneous waveguides based on spline function expansions and automated grid construction by genetic programming, and thenemployed this model to analyse the propagation of electromagnetic waves within oil wells. The developed model uses a spline expansion of the fields to convert the wave equation into a quadratic eigenvalue problem where eigenvectors represent the coefficients of the splines and eigenvalues represent the propagation constant of the eigenmode. The present study compared the proposed model using the classical winding number technique. The results obtained for the first eigenmodes of a typical oil well geometry were more accurate than those obtained by the winding number method. Moreover, the authors model could find a larger amount of eigenmodes for a fixed azimuthal parameter than the standard approach.

In this study, a simple antenna with rotational symmetric bow-tie dipole structure is proposed. The polarization of this antenna varied with the frequency, and is named frequency-selective polarization antenna (FSPA). It is evolved from a basic bow-tie dipole structure. After symmetrically cutting off two ellipses and rotational symmetrically incising two wide slits on the two arms of the bow-tie dipole, FSPA is achieved. The lower linearly polarized (LP) and circularly polarized (CP) waves are produced by the larger tip. In the same way, the upper LP and CP waves are generated by the smaller tip. It can not only generate right-hand circular polarization and left-hand circular polarization with center frequencies of 2.40 and 5.30 GHz, but also radiate different LP waves as a dipole at two different bands. This antenna can get an impedance bandwidth (S ₁₁<−10 dB) of 98.7% from 1.9 to 5.65 GHz, the 3 dB axial ratio bandwidths can reach 8.3% (2.3–2.5 GHz) and 13.3% (4.9–5.6 GHz). The antenna peak gains at CP bands are 2.1 and 4.4 dBic, respectively. The peak gains at LP bands are 2.4 and 3.0 dBi, respectively. Furthermore, the radiation patterns perform well within these frequency bands.

In this study, a new design of a planar ultra-wideband (UWB) monopole antenna with a rose-curve contour shape is proposed. The rose-curve circumference of the monopole is expressed in polar coordinates as: . This function enables a flexible and easy to control layout, which directly affects the antenna's response. The arguments of the function are specified based on a simple deterministic design rule and the outputs of a parametric study. The antenna covers the 3.1–11 GHz band and has an ultra-miniaturised size of 864 mm³ when realised on a RT/Duroid 6010LM substrate of 0.635 mm thickness. To add dual-notch characteristics to the proposed antenna, a complementary dual-band split ring resonator inclusion is etched on the antenna's patch near the feeding line. The inclusion is designed to operate at the two Wi-Fi and ISM frequency bands, 3.5 and 5.8 GHz, respectively. These centre band frequencies are determined using a new hybrid method that utilises the resonant and non-resonant design approaches of metamaterial structures. Simulated and measured return loss values, radiation patterns and gain values for the proposed antennas (with and without notching) are in very good agreements, and demonstrate satisfactory performance.

The authors present a triple-band metamaterial absorber operating at mm wave frequency band. The absorber is composed of periodic unit cells, which consists of a new pattern and a ground plane, placed in two sides of a dielectric substrate made of polyimide film. To best understand the absorption mechanisms, full-wave simulation results for the electric field, surface current, and power loss distributions are presented. The experimental results, for a transverse electric-polarised normal incident wave, show three distinctive absorption peaks, at frequencies 101.25, 108.75, and 129 GHz with absorptivities of 92.5, 94.9, and 88.6%, respectively. The absorber is independent of the wave polarisation, where high absorption is achieved for a wide range of oblique angles of incidence.

A novel compact four bands hybrid filtering antenna composed of a hybrid radiator and a four bands bandpass filter is presented. The hybrid radiator is constructed using the micro-strip line fed, the square-ring and the T-stub near the ground plane. The proposed four bands bandpass filter is composed of two parts, one is two-step impedance resonators (SIRs) and the other is the tuning stub transition structure. With tuning stub transition structure, two SIRs effectively match to 50 Ω hybrid radiator. Furthermore, the geometry of the proposed filter is U-shaped with the micro-strip fed around the hybrid radiator. The evolution of the hybrid radiator and the construction of the four bands bandpass filter using the two SIRs and the transitions are discussed in detail. The proposed filtering antenna not only possesses numerous operation bands with good band edge gain selectivity but also reduces the occupied size in the modern communication device. The overall size of the proposed filtering antenna is 33 mm × 36.4 mm × 0.508 mm, and the operation frequencies are 1.8/2.45/3.5/5.2 GHz bands for GSM1800/WLAN/WiMAX applications. The measured results agree with simulated outcomes.

The authors present a new asymmetric structure using an optimisable coil configuration and circuit model to eliminate frequency splitting and increase high-efficiency transfer distance in wireless power transfer (WPT) via magnetic resonance coupling. A pair of non-identical coils is proved theoretically and optimised to limit the coupling coefficient. The series–shunt mixed-resonant circuit structure is adopted to promote the performance of WPT system. The advantages and characteristics of the asymmetric system using mixed-resonant circuit structure based on appropriate non-identical coils are depicted by numerical calculation and simulation. Moreover, the WPT system is finally set up to verify the theory prediction. All the calculated and experimental results show that frequency splitting is suppressed in close distance effectively. Moreover, the high-efficiency transfer distance is proved to exceed the triple diameter of receiving coil. Therefore, a relatively high-efficiency and long-distance WPT system, which can be a good candidate for charging portable electronics, is obtained by selecting suitable circuit parameters and appropriate non-identical coils.

In this study, a novel electrically steerable planar array antenna based on liquid crystal (LC) is elaborately designed, fabricated and measured. The occupied area and undesired coupling of the meander line phase shifter are reduced by chamfering appropriately. Combined with the electrically tunable LC material, the miniaturised phase shifter achieves 146° phase shift and 122.7°/dB frequency-dependent figure-of-merit. Utilising in series phase shifters, power dividers and in parallel patches, the proposed antenna features compact configuration 41° continuous wide beam scanning range from forward to backward at the satellite communication band 12.5 GHz. At the same time, it maintains satisfactory reflection coefficient and impedance bandwidth at each angle. Finally, the measurements validate the scanning of the beam by electrically tuning the phase shift between the radiating elements.

Along the years, RADAR absorbing materials (RAM's) have been widely introduced in aeronautic applications and platforms. However, this kind of materials presents three main problems for certain applications when they are intended to be used in real operations. First, they must be scalable from a laboratory sample to actual size, at a reasonable cost. Second, they must be able to work without metal backing for applications in non-metallic vehicles or other objects which surface might not be flat. Indeed, they should also be flexible and surface adaptable. Finally, their absorbing properties against electromagnetic fields should be preferably characterised under real conditions, that is, in free space (FS), in order to design and fabricate an appropriate material for the intended application. In this study, a self-developed, low-cost, bilayer, X-band RAM, composed of a lower layer of polyaniline silicon rubber and a top layer of silicon rubber with graphite was characterised in a bistatic anechoic chamber called BIANCHA, and the results are presented, analysed and compared with software simulation and with the typical single polarisation waveguide measurement method, showing the adequacy of FS measurements for the development of this type of RAM.

In this study, a new compact broadband two-port multiple-input–multiple-output (MIMO) antenna using shared radiator is proposed. The radiator making an angle of 135° from X-axis is symmetrically shared by two tapered microstrip feed lines in orthogonal polarisations. The shared radiator MIMO antenna is more compact as compared with conventional MIMO antenna which uses separate radiator for each port. The proposed antenna is designed on low-cost FR4 substrate (dielectric constant = 4.4, and loss tangent = 0.02) of size 39 × 39 mm² and provides a bandwidth of 136.63% (2.4–12.75 GHz) with reflection coefficients, S ₁₁/S ₂₂ less than or equal to −10 dB and values of mutual coupling between antenna ports S ₂₁/S ₁₂ less than or equal to −15 dB. Through the utilisation of end-loaded meandered line stub attached to modified curved ground plane, low mutual coupling between antenna ports is achieved. The simulated results for input and radiation characteristics of the proposed MIMO antenna are compared with corresponding experimental results.

To investigate highly squinted spotlight synthetic aperture radar (SAR) images of an electrically large ship target over a rough sea surface, this work focuses on the simulation analysis of SAR images from such a composite scene. For this problem, there are two key issues need to be considered, namely the simulation and the processing of SAR echoes. Considering the first issue, an efficient facet scattering model based on capillary wave modification facet scattering model and geometrical optics and physical optics hybrid method is applied to calculate the electromagnetic (EM) scattering characteristics from a real ship-ocean scene, based on which SAR echoes can be obtained. For the second issue, a non-linear frequency scaling algorithm (NFSA) is employed to efficiently process the highly squinted SAR echoes. Compared with the traditional frequency scaling algorithm, the NFSA extends the frequency scaling operation to the cubic order and makes a more accurate secondary range compression. With the solutions to the two issues, SAR images of a complicated ship-ocean scene under different incident and squint angles are presented and analysed. The reasonable results demonstrate the validity of the simulation approach and the practicability of the model for highly squinted spotlight SAR images.

This study is presented to explore the properties of multisection transdirectional coupled-line couplers (TRD CLCs) developed for bandwidth enhancement. Unlike conventional multisection contradirectional coupled-line couplers (CTD CLCs) comprising only CTD CLCs, the proposed multisection TRD CLCs may require the combination of transdirectional and CTD CLCs for some higher-order designs. The designs feature a central TRD CLC. A symmetrical structure with respect to the central coupler is proposed to meet the port assignments of transdirectional couplers with broadband performance on the magnitude difference as well as the phase difference of 90° between two output ports. It can offer multiple solutions for some multisection designs. Practical examples are presented for 3 dB multisection TRD CLCs with optimum coupling coefficients assigned to individual couplers to achieve maximum bandwidth. Periodic structures are used to implement coupled-line couplers. Simulation results indicate that the proposed multisection designs meet the required port assignments and offer wider bandwidth compared to a single design of the same coupling. The simulation results of the three-section design are verified experimentally and good agreement is observed.

Two ultra-wideband (UWB) bandpass filter (BPF) with fractional bandwidths of 30% (1.2 GHz) and 52% (2.5 GHz) are developed and named as UWB BPFs I and II, respectively. Two novel generation approaches of resonant mode (RM) are first presented and analysed, which are named as synchronous-quasi-resonance (SQR) and double-curved-route (DCR), assisting in generating more RMs with the same prototype. First, an admittance prototype and its equivalent network are proposed to realise an UWB with multi-RMs and transmission zeros (TZs), whose detailed generation mechanisms are discussed. Then, two UWB BPFs are implemented employing the same prototype and design procedures. Their distinct characteristics of frequency response show that the one employing SQR and DCR can generate three more in-band RMs and one more TZ in high rejection band over another, which leads to a 1.3 GHz wider bandwidth and 1.0 GHz more harmonic suppression. Finally, a modularised design model is proposed to build the UWB or multi-band filters requiring arbitrary numbers of RMs and TZs.

Narrowband analysis of real-life up-link (UL) and down-link (DL) trends in personal exposure to recently installed long-term evolution 1800 and other radio frequency sources in typical everyday environments is presented in this work. Results are derived by analysis and post-processing of experimental dataset consisting of 1,677,600 measurement samples, taken at a sampling frequency of 0.25 Hz. The electric field measurements were collected with calibrated personal exposure meters at 90 urban spots, including outdoor and indoor microenvironments. A robust regression from order statistics was applied, enabling the determination of more reliable mean exposure values (V/m) for each wireless and broadcast technology and microenvironment. The exposure ratio for global system for mobile communications (GSM) + long-term evolution (LTE) 1800 (UL) and GSM + LTE 1800 (down link, DL) varied between 0.004 and 0.546% in outdoor environments. The maximal electric field value for the GSM + LTE 900 (DL) was 1.77 V/m, while for GSM + LTE 1800 (DL) this value was 0.644 V/m. The cumulative distribution function of the total radio frequency exposure for the various microenvironments is presented. The research results confirm that exposure levels in an urban environment even after the LTE 1800 Re-farming deployment are far below the International Commission on Non-ionising Radiation Protection reference levels.

A low-profile circularly polarised (CP) antenna with conical-beam radiation pattern is presented. The proposed antenna consists of a monopolar patch antenna fed by a probe in the centre and a ring-shaped array formed by eight modified parasitic patch elements. Two resonant modes of the monopolar patch which connects to a ground plane by a set of conductive shorting vias are utilised to achieve wide impedance bandwidth. A CP conical-beam radiation pattern is formed by loading the designed array. Loop current and slot resonant mode are employed to discuss the operating principle. A parametric study is carried out for the detailed design concept illustration. To verify the design, a prototype has been fabricated and measured, which shows a low profile of 0.059λ ₀, a maximum gain of 7.45 dBic, a 10-dB impedance bandwidth of 23.1%, a 3-dB axial ratio bandwidth of 9.6% and a good conical-beam radiation pattern.

A novel electronically steerable phased array antenna is developed for global positioning system/broadband global area network (GPS/BGAN) navigation applications. The array is composed of 2 × 2 printed quadrifilar helical antennas (PQHAs) integrated with digital phase shifters for beam steering over the transmit/receive bands. The feed network of each PQHA is based on a sequential rotation to achieve wideband circular polarisation (CP). An elegant control network with the embedded microcontroller is designed to provide driving bits to the phase shifters with reduced phase error. The meandered line design maintains high-performance CP radiation up to ±60° off-axis, within 1525 to 1660 MHz, and its size is 44% of the design with straight lines. The array gain is positive over 1450–1800 MHz beyond the BGAN band, with better than 13 dB return loss and <2.2 dB axial ratio. The measured broadside gain of the array exceeds 8.5 dBi at 1600 MHz, and has a wide beam steering of ∼±80° over the BGAN band. The developed antenna represents a significant technical advance to the design and manufacturing of PQHA array, it has a compact size, low cost and lightweight with a relatively large bandwidth and almost hemispherical coverage with excellent right-hand circularly polarized radiation.

This work presents a novel approach to computationally efficient Pareto front identification for variable-turn on-chip inductors. The final outcome is a set of solutions that correspond to the best trade-offs between conflicting design objectives. Here, we consider minimising inductor area and, simultaneously, maximising its quality factor, while maintaining a specified inductance value at a given operating frequency. As opposed to the typically used population-based metaheuristics requiring massive computational resources to generate the entire Pareto front in a single algorithm run, the proposed method reduces the number of necessary structure evaluations by exploiting a point-by-point strategy for determining the consecutive trade-off designs. The original design problem is a mixed-integer task involving integer and non-integer variables (here, the number of inductor windings and its geometry parameters). For the sake of computational efficiency, we develop a separate kriging interpolation model for each considered case of winding turns, and use it, instead of expensive electromagnetic simulations, to obtain the initial Pareto fronts. The non-dominated part of the concatenated initial Pareto sets is subsequently elevated (accuracy-wise) to the level of an electromagnetic analysis by means of a response correction technique. Our considerations are illustrated using a 3.5-nH variable-turn on-chip inductor realised in 65-nm CMOS technology.

A new architecture for designing a tuneable wideband absorber using an active frequency selective surface (AFSS) is presented. The proposed AFSS is composed of 2-D periodic array of two opposite directional anchor-shaped metal strips printed on a dielectric substrate with no metallic screen on the back side, where positive–intrinsic–negative diodes as active components are embedded between each two anchor-shaped strips. Biasing at different voltages to turn ON and OFF the diodes, AFSS structure can react as a switchable surface between transmissive and reflective states. While, the absorber consists of the designed AFSS structure and a metallic back-plane, separated by a foam spacer. By dynamically changing the bias voltage of the diodes, the impedance of the proposed absorber can be adjusted and match with the free space at its resonant frequencies. Doing this, the presented absorber is able to offer a tuneable reflectivity level of less than −10 dB over a wide frequency band from 7 to 13.1 GHz. The detailed design of a switchable transmissive/reflective surface and a tuneable wideband absorber are reported. Both the simulated and measured results have verified the proposed performances. Furthermore, a good agreement between the measurement and simulation results has been obtained.

A new and simple method is proposed for the miniaturisation design of patch antenna utilising a low-profile mushroom type meta-substrate. The functional mushroom element is analytically studied. A simple designing rule is obtained to tailor the effective high permittivity for the element as one desires. In validation, one proof of the conceptual patch antenna is presented experimentally loaded with the mushroom meta-substrate. The antenna size is 0.18λ ₀ × 0.18λ ₀ × 0.029λ ₀. Numerical and measured antenna characteristics are in good agreement. The impedance is well matched in bandwidth of 2.1%. The measured cross-polar levels are all below −23 dB. The measured antenna gain is 5.7 dBi and the radiation efficiency is 85%. The authors remark that the meta-substrate is intrinsically compatible with printed planar fabrication technology and can be easily made using common dielectrics and metals of low cost. The designing method in this work is simple and yet promising. With the intuitive analytical rule, any other desirable high index permittivity can be further obtained for future potential compact patch antenna designs.

Empirical results of an electrically small printed monopole antenna are described with a fractional bandwidth of 185% (115 MHz to 2.90 GHz) for return-loss better than 10 dB, peak gain and radiation efficiency at 1.45 GHz of 2.35 dBi and 78.8%, respectively. The antenna geometry can be approximated to a back-to-back triangular shaped patch structure that is excited through a common feed-line with a meander-line T-shape divider. The truncated ground-plane includes a central stub located underneath the feed-line. The impedance bandwidth of the antenna is enhanced with the inclusion of meander-line slots in the patch and four double split-ring resonators on the underside of the radiating patches. The antenna radiates approximately omni-directionally to provide coverage over a large part of very high frequency, the whole of ultrahigh frequency, the whole of L-band and some parts of S-band. The antenna has dimensions of 48.32 × 43.72 × 0.8 mm³, which is corresponding to the electrical size of 0.235 λ ₀ × 0.211 λ ₀ × 0.003 λ ₀, where λ ₀ is the free-space wavelength at 1.45 GHz. The proposed low-profile low-cost antenna is suitable for application in wideband wireless communications systems.

A dielectric resonator antenna (DRA) with a full ground plane and an ultrawideband (UWB) operating bandwidth of 3.1–11.6 GHz is presented. Good return loss over a wide bandwidth is achieved, while the full ground plane directs most of the radiation into the upper hemisphere, significantly reducing undesirable radiation to the lower hemisphere. The measured results confirm a 10-dB return-loss bandwidth of 115%. Time-domain characteristics and effective isotropically radiated power (EIRP) spectra of the antenna are investigated for several types of UWB input pulses. The correlations between the input pulses and the radiated pulses in many directions were found to be excellent when the antenna is excited by a linearly chirped Gaussian pulse or a fifth-order Gaussian pulse. Nevertheless, EIRP spectrum calculations indicate that none of those pulses efficiently fill the Federal Communication Commission UWB mask when applied to this DRA. Hence, a third-order Rayleigh pulse is introduced and tuned to make efficient use of the allowed spectrum limits. Further improvement of pulse performance is investigated by varying antenna design parameters. This DRA is suitable for both impulse radio UWB systems and carrier-based UWB systems.

A compact planar quasi-Yagi antenna with a wideband microstrip-to-slotline transition and a modified bow-tie driver is designed with an enhanced bandwidth for precise indoor positioning applications. A compact interdigital capacitor loaded loop resonator with a high quality factor is placed inside the ring resonator at the end of the antenna's slot to realise band-notched characteristics over a frequency range of 5.1–6.3 GHz, thus avoiding interference from wireless local area networks (WLANs) and dedicated short-range communications (DSRCs). Measured results show that the proposed antenna obtains a relative impedance bandwidth, determined by the voltage standing wave ratio <2, higher than 122.6% (3.0–12.5 GHz) and a gain of 4.9–7.8 dBi outside of the stop band.