Showing papers in "Iet Microwaves Antennas & Propagation in 2016"

Design, characterisation and fabrication of a broadband polarisation-insensitive multi-layer circuit analogue absorber

Abstract: A broadband polarisation-independent circuit analogue absorber comprising multi-layer resistive frequency selective surfaces (FSS) has been presented in this study. The proposed structure consists of a periodic arrangement of square loops loaded with lumped resistors and these square loops are printed on dielectric substrates separated by an air spacer. The simulated result shows the reflectivity below -10 dB in the frequency range from 4.96 to 18.22 GHz (fractional bandwidth of 114.40%) under normal incidence, covering C, X, and Ku bands. An equivalent circuit analysis has been introduced to characterise the proposed absorber, which shows good matching with the full-wave analysis. The effects of the individual FSS layers and the air spacer have been studied and several parametric variations have been carried out to examine the sensitivity of the design parameters on the absorption bandwidth. Finally, the designed absorber has been fabricated and measured in anechoic chamber, which shows good agreement between the experimental results and the simulated responses, under different angles of incidence as well as for various polarisation angles.

CPW-fed hexagonal Sierpinski super wideband fractal antenna

Abstract: A compact hexagonal Sierpinski fractal antenna for super wideband applications is presented. It consists of hexagonal radiation patch with two iterations of Sierpinski square slots and coplanar waveguide feeding. An impedance bandwidth of 3.4–37.4 GHz is achieved. The achieved bandwidth ratio is 11:1. Desirable radiation performance characteristics including relatively stable and omni-directional radiation patterns are obtained over this range. A good agreement is achieved between the simulated and experimental results. The designed antenna has advantages of wider bandwidth and miniaturised size over the previously reported structures.

3D-printed planar graded index lenses

Abstract: The authors introduce two flat graded-index (GRIN) lens designs in this study. First of these is a thick lens, which was designed and fabricated by using the three-dimensional (3D)-printing technique. Second, a thin dial-a-dielectric (DaD) lens, which uses state-of-the-art artificially engineered dielectric materials for design and for which they present only the simulated results, with plans to fabricate it in the future. Both designs overcome the difficulties faced in finding desired commercial off-the-shelf materials, either for 3D-printing or for fabricating conventional GRIN lenses. The lenses comprise of several concentric dielectric rings with bespoke relative permittivities for transforming spherical waves into plane waves and vice versa. The 3D-printed thick flat lens is low-cost and light-weight, but provides broadband and high gain performance. Measurement results show that the realised gain of the thick lens is 9–11 dB over the frequency band of 12–18 GHz. The designed DaD lens has the desirable characteristics of low loss, low reflection and broadband properties.

Decoupled frequency diverse array range–angle-dependent beampattern synthesis using non-linearly increasing frequency offsets

Abstract: The frequency diverse array (FDA) using linearly increasing frequency offsets has received much attention, but it has a range and angle coupled beampattern. This study proposes a new uniform linear FDA with non-linearly increasing frequency offsets to decouple the range–angle-dependent beampattern. Square increasing and cubic increasing frequency offsets are suggested for the FDA. In doing so, the range and angle of targets are solely estimated without ambiguities by the multiple signal classification algorithm. Numerical results show that the proposed approach outperforms the existing approach using logarithmically increasing frequency offsets in both focusing transmit energy and target localisation performance, especially in the range dimension.

Characterisation by Gaussian processes of finite substrate size effects on gain patterns of microstrip antennas

Abstract: A procedure is presented for characterising the effects of varying finite substrate/ground plane size on the gain properties of microstrip antennas by means of Gaussian process regression (GPR). Two kinds of microstrip antenna were considered, namely a probe-fed patch antenna on both thin and thick dielectric substrates, and an L-probe-fed patch on a thick air substrate. CST Microwave Studio was used to generate training and test data for the GPR models. Frontal E and H-plane gain patterns could be predicted with normalised root-mean-square errors (RMSEs) of <1.8% for the thin-substrate probe-fed patch and the L-probe-fed patch; for the thick-substrate probe-fed patch, RMSEs were 2.1 and 2.8% for the two principal plane gain patterns, respectively. Furthermore, the GPR models could predict patterns at least two orders of magnitude faster than it took to obtain them via direct simulation in CST. Such models are expected to be useful in CAD-based environments for rapidly obtaining estimates of substrate/ground-plane size effects on gain characteristics in lieu of time-consuming full-wave simulations.

Compact multi-band polarisation-insensitive metamaterial absorber

Abstract: In this study, a novel multi-band metamaterial absorber has been proposed which is ultra-thin, compact, polarisation-insensitive and wide-angle absorptive. The proposed structure comprises two concentric metallic rings printed on a dielectric substrate which is backed by a metal ground plane. The proposed structure exhibits four distinct absorption peaks at 4.11, 7.91, 10.13 and 11.51 GHz with peak absorptivities of 98.81, 99.68, 99.98 and 99.34%, respectively, under normal incidence. The designed absorber is polarisation insensitive due to four-fold symmetry, which has been confirmed by simulation and measurement studies. Moreover, the structure shows high absorption (over 90%) for oblique incident angles up to 45° for both transverse-electric and transverse-magnetic polarisations. The surface current distributions at the four absorption frequencies have been illustrated to explain the absorption mechanism of the structure. In addition, several parametric variations are performed to observe the effects of the geometrical dimensions on the absorption performance. The free space measurement method has been utilised to measure the responses of the fabricated structure, which are in good agreement with the simulated results. The proposed ultra-thin (∼0.013λ 0 thin corresponding to lowest absorption frequency) absorber is anticipated to be useful in various potential applications like stealth technology, electromagnetic interference, electromagnetic compatibility and wireless communication.

Design of a uniplanar printed triple band-rejected ultra-wideband antenna using particle swarm optimisation and the firefly algorithm

Abstract: A compact planar monopole antenna is proposed for ultra-wideband applications. The antenna has a microstrip line feed and band-rejected characteristics and consists of a ring patch and a partial ground plane with a defective ground structure of rectangular shape. An annular strip is etched above the radiating element and two slots, one C-shaped and one arc-shaped, are embedded in the radiating patch. The proposed antenna has been optimised using bio-inspired algorithms such as the particle swarm optimisation and the firefly algorithm, based on a new software algorithm (Antenna Optimizer). Multi-objective optimisation achieves rejection bands at 3.3-3.7 GHz for Worldwide Interoperability for Microwave Access, 5.15-5.825 GHz for the 802.11a wireless local area network system or HIPERLAN/2, and 7.25-7.745 GHz for C-band satellite communication systems. Validated results show wideband performance from 2.7 to 10.6 GHz with S 11 <; -10 dB. The antenna has compact dimensions of 28 × 30 mm 2 . The radiation pattern is comparatively stable across the operating band with a relatively stable gain except in the notched bands.

Periodic array of complementary artificial magnetic conductor metamaterials-based multiband antennas for broadband wireless transceivers

Abstract: This study presents the empirical results of a low-profile light-weight antenna based on a periodic array of the complementary artificial magnetic conductor metamaterial structure, which is realised by loading the antenna with E-shaped slits and inductive microstrip lines grounded using metallic via-holes. The finalised prototype antenna operates over a broadband of 0.41–4.1 GHz, which corresponds to a fractional bandwidth of 165.84%, and has dimensions of 40 × 35 × 1.6 mm3 or 0.054λ 0 × 0.047λ 0 × 0.0021λ 0, where λ 0 is free-space wavelength at operating frequency of 410 MHz. The finalised antenna has a peak gain and radiation efficiency of 4.45 dBi and 85.8%, respectively, at 2.76 GHz. At the lower operating frequency of 410 MHz, the gain and radiation efficiency are 1.05 dBi and 32.5%, respectively, which is normally highly challenging to realise with very small antennas. The planar nature of antenna enables easy integration with wireless transceivers.

Microwave and millimetre wave antipodal Vivaldi antenna with trapezoid-shaped dielectric lens for imaging of construction materials

Abstract: High-quality microwave and millimetre wave imaging of construction materials and structures requires ultra-wideband (UWB) techniques to provide high-range resolution as well as a reasonable penetration depth. A modified compact microwave and millimetre wave UWB antipodal Vivaldi antenna is designed and presented in this study. First, the conventional antipodal Vivaldi antenna is designed as a reference antenna. Then, to provide the desired frequency range (3.4-40 GHz) with increased gain at its lower frequencies, the slit edge technique is applied, thus creating a periodic slit edge antipodal Vivaldi antenna (PSEAVA). Finally, a trapezoid-shaped dielectric lens (TDL) as an extension of the substrate is added and optimised to increase gain and directivity at higher frequencies of the frequency range, creating PSEAVA with a TDL (PSEAVA-TDL). The results show that the PSEAVA-TDL has the highest gain (up to 16 dB) and front-to-back ratio (up to 37.5 dB), and the narrowest half power beamwidth (down to 11.7°). A prototype of the proposed PSEAVA-TDL with compact size of 40 × 90 × 0.508 mm 3 is fabricated and applied for the imaging of samples made of construction materials. High-range resolution images of the samples are obtained with this antenna by using synthetic aperture radar algorithm.

Design of a four-element multiple-input–multiple-output antenna for compact long-term evolution small-cell base stations

Abstract: This study presents a multiple-input-multiple-output (MIMO) antenna for compact small-cell base stations operating in the long-term evolution (LTE) standard. This MIMO antenna comprises four unit antenna elements, targeted at the frequency band of LTE700/850/900 (698-960 MHz). In comparison with the state-of-the-art MIMO antennas covering these frequency bands, the proposed design enables the maximum number of antenna elements, yet it occupies a compact volume of only π × 80 2 × 50 mm 3 ( π × 0.18 2 × 0.11 λ 3 ), which is the most miniature electrical configuration to date. The unit antenna element consists of a monopole antenna with a sleeve attached to each side, fed by a coaxial cable. Since the spacing between antenna elements is so small (0.24 λ ), this work uses four miniature and wideband defected ground structures (DGSs) to reduce the mutual coupling; moreover, although the DGSs adversely alter the impedance matching of unit element, the authors applied multi-objective fractional factorial design to achieve isolation enhancement and bandwidth preservation simultaneously. Accordingly, the optimised MIMO antenna shows desired -10 dB impedance bandwidth and sufficient isolation in the targeted frequency band. In addition, the radiation patterns, antenna efficiency, and the signal correlation coefficients are measured and evaluated.

Compact reconfigurable multiple-input-multiple-output antenna for ultra wideband applications

Abstract: This study presents a two element multiple-input-multiple-output (MIMO) reconfigurable antenna for ultra wideband (UWB) applications. Each individual antenna is composed of a modified square radiating patch. The array can be reconfigured by either placing antenna elements orthogonally for corner installation or by placing them back-to-back for compact three-dimensional (3D) modules. The design is fabricated on FR4 substrate having dimensions 40 mm × 37.5 mm × 1.5 mm. Port isolation greater than 20 dB in the complete band is achieved by introducing an efficient decoupling structure in the ground plane. Performance parameters such as S-parameters, radiation patterns, envelope correlation coefficient, total active reflection coefficient and channel capacity loss indicate that the proposed MIMO design is a suitable candidate for high data rate UWB applications. The proposed solution is suitable for non-planar designs around wall corners or for compact 3D structures where side-by-side placement is not practical due to size constraints.

Higher-mode textile patch antenna with embroidered vias for on-body communication

Abstract: This study presents a wearable textile higher-mode microstrip patch antenna (HMMPA) that has been designed to radiate omni-directionally at 2.4 GHz Industrial Scientific and Medical (ISM) band. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that plays an important role in generating the optimal mode for on-body radiation. The embroidery technique enabled a side-fed low-profile antenna which could be placed directly against the body. The proposed textile HMMPA antenna performance is compared with a probe-fed HMMPA antenna fabricated with rigid copper radiating parts, for both free space and on-body conditions. The on-body antenna performance has been tested by performing near-field measurements of the antenna on a full-body specific anthropomorphic mannequin phantom in an anechoic chamber. Results show that the proposed textile HMMPA antenna with vias made from conductive thread can radiate on-body with good efficiency while minimising the radiation in the broadside direction.

Alternative surface integral equation-based characteristic mode analysis of dielectric resonator antennas

Abstract: Dielectric resonator antennas are widely used in wireless communication systems. A theory of characteristic modes (CMs) for modal analysis of dielectric resonators is highly demanded. Although a few earlier studies had proposed CM theory for modelling scattering from dielectric bodies, the physical characteristics of these CMs and their eigenvalues are not as clear as that of those for conducting bodies. This study revisits the CM theory for dielectric resonators. Following the Poynting's theorem and the PMCHWT (Poggio, Miller, Chang, Harrington, Wu, and Tsai) equation, two generalised eigenvalue equations are formulated. The resultant eigenvalues possess clear physical meanings that are the same as those of perfectly electrically conducting problems. In addition, other possible CM formulations based on the PMCHWT equation are also discussed. Mathematical proofs are given in the Appendix to show how to formulate CM theory to physically describe the fundamental resonant modes of dielectric resonators. Numerical results are given to show the proposed CM formulations are effective in solving resonant frequencies and modal fields for dielectric resonators.

Multistatic microwave imaging with arrays of planar cavities

Abstract: The authors present a multistatic imaging system at microwave frequencies based on arrays of planar cavity sub-apertures, or panels. The cavity imager consists of sets of transmit and receive panels, loaded with radiating irises distributed over the sub-apertures in an aperiodic pattern. This frequency-diverse aperture produces distinct radiation patterns as a function of frequency that encode scene information onto a set of measurements; images are subsequently reconstructed using computational imaging approaches. Similar to previously reported computational imaging systems, the cavity-based imager presents a simple system architecture, minimising the number and expense of components required in traditional microwave imaging systems. The cavity imager builds on previous frequency-diverse approaches, such as the recently reported metamaterial and air-filled cavity systems, by utilising frequency-diverse panels for both the transmit and receive sub-apertures of the imaging system. Though the panel-to-panel architecture has greater sensitivity to calibration error, this implementation nevertheless increases mode diversity and, in the context of a computational imaging system, results in improved image reconstructions.

Improvement of microstrip patch antenna gain and bandwidth at 60 GHz and X bands for wireless applications

Abstract: A method has been proposed to simultaneously enhance the gain (14 dB), bandwidth (BW) (12.84% of the operating central frequency) and efficiency (94%) of a microstrip patch antenna. The antennas have been designed based on the patch size improvement technique to improve the fabrication tolerance. The designed prototypes have been fabricated by conventional low cost printed circuit board etching method and tested at X-band (8-12 GHz) and 60 GHz band (57-66 GHz) frequencies. Antennas' overall performance is maintained across their operating frequency range. The tested antennas for 60 GHz band convince the requirements for multi-gigabits/s data rate wireless local area network and wireless personal area network applications recommended by IEEE 802.11ad and IEEE 802.15.3c standards. In all cases the simulation and the measured results are in good agreement.

Reconfigurable narrow-frame antenna for LTE/WWAN metal-rimmed smartphone applications

Abstract: A reconfigurable narrow-frame coupled-loop antenna capable of providing hepta-band long term evolution/wireless wide area network (LTE/WWAN) for metal-rimmed smartphone applications is proposed. The ground clearance of this proposed antenna is only 7 × 70 mm 2 which is promising for narrow-frame smartphone applications. Moreover, this proposed antenna can realise the miniaturisation by employing a positive intrinsic negative diode (PIN diode), which can provide two working states. When the PIN diode is OFF, it can provide coverage for GSM850/DCS/PCS/UMTS2100/LTE2300/2500 operations. When the PIN diode is ON, the obtained bands are GSM900/DCS/PCS/UMTS2100/LTE2300/2500. Hence, by combining these two working states, GSM850/900/DCS/PCS/UMTS2100/LTE2300/2500 operations are achieved. In addition, the feasibility of realising decoupled multi-antennas is demonstrated and its performances are well-suited for future smartphone applications. Detailed design considerations of the proposed antenna are described. Both experimental and simulated results are also presented and discussed.

Design of multi-band bandpass filters based on stub loaded stepped-impedance resonator with defected microstrip structure

Abstract: The design of multi-band bandpass filters (BPFs) employing stub loaded stepped-impedance resonator with defected microstrip structure (SL-SIR-DMS) is presented in this study for the first time. The proposed SL-SIR-DMS is created by embedding DMS on the low-impedance line of the SL-SIR. It is found that different defected structures can lead to different frequency responses. In addition, by using DMS, tri-band and even quad-band responses can be easily achieved without increasing the resonator size. As verification, one tri-band SL-SIR-DMS and one quad-band SL-SIR-DMS are designed and analysed using even/odd-mode method. Subsequently, one tri-band BPF and one quad-band BPF have been developed with pseudo-interdigital coupling to realise good out-of-band performance. The predicted results are compared with measured ones and good agreement is achieved. Compared with BPFs using only SL-SIR, the proposed filters with DMS are more compact due to the slow-wave characteristic. Compared with the BPFs using defected ground structure to improve the stopband performance, the proposed ones can realise comparable wide stopbands but maintaining the signal integrity on the ground plane for packaging purpose.

Study on the theory and method of vortex-electromagnetic-wave-based radar imaging

Abstract: Helical phase fronts and orbital angular momentum of the vortex electromagnetic (EM) wave are applied to radar imaging at microwave frequencies and comprehensive simulations are conducted. Results demonstrate that an incrementally phased uniform circular array can be exploited to generate vortex EM wave at microwave frequencies. The imaging model based on the linear frequency modulation signal is established and the pulse-compression and fast Fourier transform methods are used to image the target in both range and azimuth dimensions. Furthermore, antenna pattern optimisation methods for imaging are studied to enhance the directivity of the emitting signal. The work can promote the significant development of novel information-rich radar imaging technology and provide staring imaging with substantial technical supports.

Dual-band single-layer quarter ring frequency selective surface for Wi-Fi applications

Abstract: This study proposes a frequency selective surface (FSS) design to be used in Wi-Fi shielding applications as either a band reject or band pass dual-band single-layer filter. The proposed design consists of a combination of basic elements, that is, ring loops/slots, and is tuned at both 2.4 and 5.2 GHz Wi-Fi frequency bands. It has a relatively stable frequency response in the aforementioned Wi-Fi bands for incidence angles ranging from 0° to 45°. Both band reject and band pass designs are presented, along with their unit cell dimensions. Simulation and model validation through measurements demonstrate the performance of the proposed FSS design. Active variants are also proposed and briefly evaluated, in simulation environment, which should allow for applications where an on-off switching is desired at 2.4 and 5.2 GHz Wi-Fi bands.

Horn antennas for generating radio waves bearing orbital angular momentum by using spiral phase plate

Abstract: The design of two new horn antennas for the generation of radio waves bearing orbital angular momentum (OAM) is presented. The OAM mode l = 1 or −1 is generated by combining the guided modes of a circular waveguide with a spiral phase plate. The authors present here two structures to generate OAM wave based on TE11 and TM01 modes. The resulting magnitude and phase patterns of the electrical field and the radiation patterns evidence the presence of waves carrying OAM.

Circularly polarised half E-shaped patch antenna: a compact and fabrication-friendly design

Abstract: Supporting circular polarisation in single-layer, single-feed, compact patch antennas is a challenging task, especially when improved bandwidths are required. The difficulty lies in simultaneously obtaining good axial ratio (AR) and impedance matching performance over the required bandwidth. Several broadband,thick-substrate circularly polarised (CP) patch designs have appeared in the literature, but their complex fabrication might not be suitable for harsh environments requiring mechanical simplicity or for high-frequency applications at X-band or higher. In this study, the authors propose a novel solution to this problem: the CP half E-shaped patch antenna. This antenna is able to utilise thick substrates to meet the bandwidth requirements of many potential applications. Furthermore, the design can be fabricated on a single-layer and uses reasonably sized gaps and line widths, making for a fabrication-friendly design. Their design example shows 5.3% AR and impedance matching bandwidth at a thickness near a tenth of a wavelength. The S11 < − 10 dB bandwidth is 35%. Their particular design example has dimensions that fit within 45% × 39% of a free-space wavelength. Furthermore, they provide an important comparison discussing the differences in operation between the linearly polarised half E-shaped patch, CP E-shaped patch, and CP half E-shaped patch.

Wearable logo-antenna for GPS–GSM-based tracking systems

Abstract: This study presents a wearable antenna for a global positioning system–global system for mobile communication (GPS–GSM)-based anti-theft tracking system to be embedded in high-cost clothing and luggage accessories (such as leather bags). To assess the feasibility of this solution, a prototype antenna was designed mimicking the shape of one of the Levi Strauss & Co.’s logos, and it was fabricated using a conductive non-woven fabric on a layer of leather. Furthermore, to cover both the GPS L1 and the GSM-1800 bands with a single radiating element, positive-intrinsic-negative (PIN) diodes were employed to reconfigure the operating frequency of the antenna. Experimental data demonstrating the feasibility of the proposed design strategy are presented and discussed.

Circularly polarised hybrid Z-shaped cylindrical dielectric resonator antenna for multiband applications

Abstract: This study presents design and analysis of a multi-band hybrid Z-shaped cylindrical dielectric resonator antenna (CDRA) with partial ground plane. The proposed antenna design consists of Z-shaped CDRA along with dual C-shaped patch. Dual C-shaped patch is used to excite TE 01δ mode, which also act as a radiator. Offset between upper and lower CDRAs is responsible for reduction in quality factor and also produce π /2 phase shift between the field lines of the proposed antenna which generates circular polarisation. The archetype of the proposed structure has been fabricated and practically validated. The proposed design operates in five frequency bands, i.e. 1.24-1.36 GHz, 2.56-2.88 GHz, 3.4-4.08 GHz, 5.08-5.72 GHz and 7.2-8.5 GHz with the fractional bandwidth of 9.23, 11.76, 18.18, 11.85 and 16.56%, respectively. Axial ratio bandwidth (AR <; 3 dB) for 7.85-8.35 GHz frequency band is 6.17%. The proposed antenna may be suitable for different wireless applications like WLAN (5.2 GHz), WiMAX (2.6/3.5/5.5 GHz) and satellite communication (7.9-8.39 GHz).

Design of dual band and dual-polarised dual band SIW cavity backed bow-tie slot antennas

Abstract: A novel design technique to implement dual band substrate integrated waveguide (SIW) cavity backed planar slot antenna is presented. The proposed antenna uses a combination of multiple SIW cavities of different size connected through coupling window in the common sidewall of the cavities. The cavities are loaded with long bow tie shaped slots to achieve higher bandwidth of the antenna. The placement of long bow tie slots helps to generate multiple hybrid modes which can be tuned by varying slot dimensions. First, two SIW cavities loaded with bow-tie slots are used to excite four closely placed hybrid modes in X band (8-12 GHz) to realise dual band response with a bandwidth of 600 MHz (7.2%) and 888 MHz (8.74%) and a gain of 5.3 and 4.4 dBi, respectively. The design is further extended using a set of four SIW cavities arranged as two pair of coupled SIW cavities along with bow-tie slots and placed in orthogonal orientation to implement dual band dual polarised slot antenna while maintaining its planar configuration. The proposed antenna exhibits a bandwidth of 390 MHz (3.9%) and 790 MHz (7.29%) with a gain of 6.1 and 5.4 dBi, respectively.

Planar meandered-F-shaped 4-element reconfigurable multiple-input–multiple-output antenna system with isolation enhancement for cognitive radio platforms

Abstract: In this study, a novel meandered reconfigurable F-shaped antenna is presented. The proposed design is a 4-element, dual mode, multiple-input-multiple-output (MIMO) antenna system. Frequency agility is achieved using P-type intrinsic N-type (PIN) diode switching while frequency tuning is realised using varactor diodes. The proposed design covers wide frequency bands below 1 GHz and is realised on a single substrate. The proposed design is compact and highly suitable to be used in cognitive radio-based wireless handheld devices. An isolation enhancement technique is applied to reduce the mutual coupling between various MIMO elements. Rectangular defected ground (GND) slots are used to reduce the mutual coupling between horizontally placed antenna elements while staircase type GND plane structure is introduced to enhance the isolation between vertically placed antenna elements. The antenna elements are also evaluated for MIMO performance metrics. The antenna system covers a size of 65 ×120 ×1.56 mm 3 .

Planar pattern reconfigurable antenna with eight switchable beams for WiMax and WLAN applications

Abstract: A planar pattern reconfigurable antenna designed for IEEE 802.11 b/g standard 2.4 GHz WiMax and WLAN applications is presented. The design is realised using a uniform arrangement of eight switch-controlled tapered strips symmetrically placed around a central circular disc on the top layer of an FR4 board. The antenna has a compact circular structure with overall diameter of 0.64(0) in the free space for 2.4 GHz. To control the radiation pattern of the antenna, each of the tapered strips is connected to the ground via a PIN diode. Depending on the switching status of the eight PIN diodes, the tapered strips work in grounded or open-ended mode and thus the antenna offers eight switchable patterns. To validate the design, the antenna is prototyped and its performance is verified in a far-field anechoic chamber. The simulated and measured results prove the antenna's reconfigurability of the main beam in eight directions with 45 degrees steps in the azimuth plane and a vertical tilting angle of 36 degrees. Over the operating band 2.35-2.61 GHz, the antenna has a stable gain of around 4.5 dBi, and front-to-back ratio of more than 18 dB. Compared with recent designs, this antenna is more compact, has larger beam deflection off the boresight and more beam steering states.

Rectangular microstrip antenna with dumbbell shaped defected ground structure for improved cross polarised radiation in wide elevation angle and its theoretical analysis

Abstract: A simple and compact rectangular microstrip patch antenna (RMPA) with dumbbell shaped defected ground structure has been proposed and investigated experimentally for significant suppression of cross polarised (XP) radiation compared with maximum co-polarised gain without affecting the co-polarised radiation pattern. The investigation shows that the proposed antenna has an excellent co-polarised radiation to XP radiation isolation over wide elevation angle around the broadside for different aspect ratio (width to length ratio or W/L) of RMPA. The proposed idea is justified in the light of concrete theoretical analysis.

Compact frequency reconfigurable filtennas using varactor loaded T-shaped and H-shaped resonators for cognitive radio applications

Abstract: In this study, novel compact filtennas with large tunable frequency band are proposed for cognitive radio (CR) applications. Tunability is achieved by integrating a tunable T-shaped and H-shaped bandpass filter with a planar ultra-wideband monopole antenna. The T-shaped filter consists of a microstrip resonator loaded with a stub. The H-shaped filter is composed of two connected microstrip resonators. The proposed tuning technique for both filters is based on centrally loading the stub and the H-shaped with only a single varactor for miniaturisation. Increasing the varactor capacitance results in decreasing the even resonant mode of the resonator without affecting the dominant odd mode. Measurements results show that the proposed T-shaped and H-shaped filtennas are capable of tuning over a wide operating band of 1.68 and 1.73 GHz covering continuous bands for CR communication with 32.9% frequency tuning range (TR) from 4.26 to 5.94 GHz and with 36.7% frequency TR from 3.85 to 5.58 GHz, respectively. Moreover, the radiation patterns are stable over the operating frequency ranges. The frequency characteristics and radiation performance are successfully optimised using 3D full-wave electromagnetic simulator. The fabricated designs are measured for verification purposes. Good agreements are found between simulated and measured results.

Decoupling between ground radiation antennas with ground-coupled loop-type isolator for WLAN applications

Abstract: A compact and easy to fabricate decoupling method is proposed to yield high isolation for the multiple-input and multiple-output (MIMO) ground radiation antenna (GradiAnt) system. The proposed MIMO antenna system is comprised of two symmetrical, closely spaced, loop-type (GradiAnts) with a ground-coupled loop-type isolator inserted between them. The isolator can be seen as a series resonant circuit which is connected with lumped components to control decoupling. In the proposed MIMO GradiAnt system, a coupling null is induced due to the ground-coupled isolator, which effectively can be used for isolation enhancement between two GradiAnts. Within WLAN band, a minimum 14 dB isolation with a peak value of 42 dB at 2.42 GHz is achieved. In this manuscript, the decoupling principle and controlling mechanisms are first explained, then the antenna performances and tuning mechanisms are discussed in detail. The simulation and the measurement of the MIMO antenna, including the scattering parameters, efficiency, radiation patterns, peak gains and envelope correlation coefficients are conducted to verify the performance of the proposed MIMO system.

Terahertz band: Channel modelling for short-range wireless communications in the spectral windows

Abstract: The channel in the terahertz (THz) band is extremely frequency selective. This study demonstrates a ray-tracing method for modelling short-range propagation channels at THz band. The propagation response of sounding bandwidth and centre frequency on power delay profile (PDP) is investigated in five spectral windows with relatively low attenuations and higher available bandwidths which could possibly offer terabit-per-second links also. In this approach, a very detailed non-cubic three-dimensional model of an ultra-broadband indoor realistic office environment has been drawn up. Furthermore, the frequency-dependent standard electrical parameters for the common building materials were taken from the literature. The transmitter (Tx) and the receiver (Rx) are 10 m apart in line-of-sight scenario with exactly same height of 1.5 m above the floor. The simulations were performed using 25 dBi horn antennas at the transmitter and receiver sides, respectively, to combat high path loss. These frequency-dependent horn antennas were designed for the respective five spectral windows. Meanwhile, the corresponding channel impulse response of multipath components with spatial and temporal information such as angle of arrival, angle of departure and time of arrival has been captured to derive PDP models. Up to four reflections (i.e. fourth order) have been considered in the modelling process.