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This paper introduces a transmission line model analysis for dielectric-loaded self-resonant structures (SRSs). Equivalent circuit models, besides their fast computational time, usually offer some insights into the underlying physics of the electromagnetic structures, hence simplifying and improving the design and optimization criteria of these structures. A systematic approach for deriving impedance expressions of SRS on and within multi-layer dielectric media is presented. The process of extracting equivalent circuit parameters from impedance expressions is explained. The trends of equivalent circuit parameters are studied with different dielectric medium properties and various angles of incidence for an SRS with multiple resonant states highlighting the effect of changing the physical and electrical dimensions on the equivalent circuit parameters. The transmission line model responses are compared to full-wave simulation results, and model accuracy is assessed using the mean absolute error criteria. Furthermore, a new simplified method for calculating the forward transmission coefficient of an SRS within multi-layer media is proposed. This expression offers fundamental insights into the factors contributing to the $S_{21}$ response. Finally, experimental measurements for SRS embedded in a multi-layer dielectric media inside a waveguide is conducted and compared to the equivalent model with very good agreement.

5G technology provides users with a significantly better experience and is a key enabler of massive connectivity between people-to-people and people-to-machines as well as machines-to-machines. The low -latency transmission promised by 5G opens up the possibilities for implementing remote healthcare, self -driving cars, and virtual reality/augmented reality. 5G technology includes fully digital beamforming, multiple access technologies, and massive multiple-input-multiple-output (MIMO) to deliver higher data rates, higher bandwidth, and lower latency. Antenna along with other microwave systems plays an important role in achieving key features of 5G technology. Unlike a single base station antenna array technology, in 1990, the modern antenna system has evolved from a passive to an active antenna system with integrated radios and digital baseband processing units.

This paper presents a quad-band frequency agile antenna, with independent and concurrent frequency tunability in each band, for a tunable, concurrent, quad-band single chain radio receiver for 5G New Radio (NR). More specifically, the antenna comprises of four planar slots etched in a ground plane and fed through a single microstrip feedline, without any impedance matching network. The structure is optimized to maximize isolation between the individual slots and their respective resonant frequencies. Furthermore, a novel high order harmonic suppression method is demonstrated, which controls the current distribution via creating a fictitious short circuit in the slot antenna–enabling the antenna to achieve a much wider tuning range. Numerical simulations are verified using experimental implementation and measurements, with good agreement observed. The four slots resonate around the 830 MHz, 1.8 GHz, 2.4 GHz and 3.4 GHz frequency bands, which are independently tuned (using a varactor diode in each slot) to achieve tuning ranges of approximately 64%, 66%, 27% and 33%, respectively. More importantly, the contiguous four bands covers a total frequency tuning from 0.6 to 3.6 GHz i.e. a tuning range of approximately 143%. Finally, far-field measurements are performed and the antenna is evaluated in over-the-air testbed (quad-band radio receiver), which measures the Error Vector Magnitude performance for the individual channels. Good performance is observed, confirming acceptable isolation performance between the four bands. The data reported in this paper is available, from ORDA-The University of Sheffield Research Data Catalogue and Repository, at https://doi.org/10.15131/shef.data.11219000.v1 .

This study describes an experimental investigation into improving the detectability of self-resonant structures. Passive self-resonant structures have been used as an alternative to active devices in many applications including radio-frequency identification (RFID) due to their long lifetime and low manufacturing cost. They can be used to store information in terms of the presence or the absence of resonance peaks at a given frequency window. This work investigates practical validation of gain enhancement techniques, aiming to improve the resonance characteristics of passive RFID tags to increase their read range and allow them to operate in highly lossy mediums. Two passive resonator designs are studied: a uniform cross-shaped resonator and a folded (gammadion) cross having a physical aperture 45% less than that of the uniform cross. Arrays of elements have been used to improve the detectability of the structure. Measurement settings have also been investigated in order to achieve higher levels of detectability.

In this paper, a novel tunable tri-band antenna\ud is presented for concurrent, multi-band, single chain radio\ud receivers. The antenna is manufactured on a 50×100 mm FR4\ud printed circuit board (PCB), and is able to provide three concurrent,\ud independently tunable operating bands covering a frequency\ud range from 600 MHz to 2.7 GHz. The antenna performance\ud is investigated for both numerical and experimental methods\ud when using, first, varactor diodes and, second, digitally tunable\ud capacitors (DTCs) to tune frequencies, which shows the antenna\ud gain can be improved by up to 2.6 dBi by using DTCs. A\ud hardware-in-the-loop test-bed provides a system level evaluation\ud of the proposed antenna in a direct RF digitized, concurrent,\ud tri-band radio receiver. By measuring the receiver’s error vector\ud magnitude, we demonstrate sufficient isolation between concurrent\ud bands achieving 30 MHz of aggregated bandwidth as well\ud as strong resilience to adjacent blockers next to each band. The\ud data reported in this article are available from the ORDA digital\ud repository (https://doi.org/10.15131/shef.data.5346295).

Novel arrangements of active frequency selective surfaces (AFSSs) with integrated voltage control wiring are proposed for bistate (transparency/reflectance) operation at specified frequencies. The AFSSs are comprised of passive arrays of intertwined patterns of slots in a conductor screen and an active dipole array with p-i-n diodes placed on either the same or opposite sides of a thin dielectric substrate. Simulation and measurement results show that such AFSSs exhibit good isolation (~15 dB) between the translucency and reflection states at normal incidence that slightly decreases at oblique incidence. The proposed AFSSs maintain the high angular and polarization stability over broad fractional bandwidths inherent to the constituent periodic arrays of intertwined conductor patterns with substantially subwavelength unit cells. The merits of these AFSS arrangements also include resilience to parasitic effects of real switches, whose insertion loss in the ON state only enhances the AFSS ON/OFF isolation. Such AFSSs are essential elements for reconfiguring and controlling the electromagnetic architecture of buildings.

A low-profile quad-band loaded-slot antenna with independently controllable frequency bands is presented in this paper. Four slots are carefully designed to generate four separate frequency resonances, which were independently tuned by employing varactor diodes in each slot. The proposed concept was simulated using a full-wave solver and validated through measurements. The results show that each of the four bands can be independently controlled by altering the bias voltage of the respective varactor diode. Overall, the measured frequency tuning of the 1st, 2nd, 3rd, and 4th bands were 450–750 MHz, 600–1200 MHz, 1200–2100 MHz and 2100–2700 MHz, respectively. The proposed antenna has good potential for applications in the concurrently tunable multiband radio systems, including 5G.

A low-profile tri-band slot antenna with enhanced tuning range is presented in this paper. Tri-band frequency agility is obtained using three varactor-loaded slots on a planar structure. The tuning range of the proposed antenna is enhanced by suppressing the higher-order resonance modes, especially by controlling the surface currents and creating a fictitious ground on the antenna. Following full-wave simulations, a prototype was developed and measured to validate the concept. Results show a tuning range from 600MHz to 3300MHz, which is a 600 MHz increase in the overall tuning range than previously reported.

A concurrent, tunable, triple-band, single chain radio receiver for 5G radio access networks is presented and its performance is evaluated in a hardware-in-the-loop test-bed. The test-bed emulates a 5G heterogeneous network supporting three independently tunable, wideband, simultaneous connections over a frequency range from 600 MHz to 2.7 GHz. The single chain receiver is able to achieve an aggregate bandwidth of 93.75 MHz, 31.25 MHz per band, and a net data rate of 187.5 Mbit/s through the use of single-carrier QPSK transmissions. The receiver demonstrate sufficient isolation between the concurrent transmissions as well as strong resilience to adjacent blockers through the use of a small guard band.

A concurrent, tunable, tri-band, single chain radio receiver for 5G radio access networks is evaluated. The three concurrent bands are independently tunable over a frequency range from 600 MHz to 2.7 GHz. A hardware-in-the-loop test-bed provides a system level evaluation of the proposed receiver using direct RF digitization. The test-bed emulates a 5G heterogeneous network supporting three wideband, simultaneous connections. By measuring the receiver EVM, we demonstrate sufficient isolation between concurrent bands achieving 60 MHz of aggregated bandwidth as well as strong resilience to adjacent blockers.

This invited paper considers a key next step in the design of radio architectures aimed at supporting low energy consumption in 5G heterogeneous radio access networks. State-of-the-art mobile radios usually require one RF transceiver per standard, each working separately at any given time. Software defined radios, while spanning a wide range of standards and frequency bands, also work separately at any specific time. In 5G radio access networks, where continuous, multiband connectivity is envisaged, this conventional radio architecture results in high network power consumption. In this paper, we propose the novel concept of a concurrent multiband frequency-agile radio (CM-FARAD) architecture, which simultaneously supports multiple standards and frequency bands using a single, tunable transceiver. We discuss the subsystem radio design approaches for enabling the CM-FARAD architecture, including antennas, power amplifiers, low noise amplifiers and analogue to digital converters. A working prototype of a dual-band CM-FARAD test-bed is also presented together with measured salient performance characteristics.

This work presents an analysis of a reconfigurable self-resonant structure using an equivalent circuit model. Reconfiguring the electrical length of the structure results in uniquely identifiable changes to its forward and reflected frequency response. Equivalent circuit models are known to reduce computational time drastically and to provide an insight into the physics of the electromagnetic problem. Equivalent circuit parameters have been calculated for different states of the self-resonant structure. The responses of these equivalent circuits are compared to a full-wave simulation with very good agreement.

In this paper, a switchable textile communication system working at 2.45 GHz ISM band is presented and studied for different locations within a realistic on-body environment. A 3D laser scanner is used to generate a numerical phantom of the measured subject to improve the accuracy of the simulations which are carried out for different body postures. For the off-body communications, the system is acting as an aperture coupled microstrip patch antenna with a boresight gain of 1.48 dBi. On-body communication is achieved by using a textile stripline, which gives approximately 5 dB transmission loss over 600 mm distance. The system is switched between on and off-body modes by PIN diodes. Common issues, such as shape distortion and body detuning effects which the textile antenna may experience in realistic use are fully discussed. Robust antenna performance is noted in the on-body tests, and an additional 3 dB transmission coefficient deduction was noticed in the most severe shape distortion case.

A new type of multiband shark-fin antenna printed on 1.6 mm thick FR4 for automotive applications is presented. The antenna is mounted over a 1 m × 1 m-metal ground plane which represents a car’s roof. The overall size of the antenna is 57 mm × 40 mm × 1.6 mm which is λ/6.5 × λ/9 × λ/231.5 at the lowest frequency of operation of 0.810 GHz. The antenna is in the form of a single-sided PCB and has a measured gain of 0–6.7 dBi over the entire range of 0.810–5.84 GHz covering the mobile telephone bands (GSM, DCS and PCS), both GPS bands and Bluetooth, WiFi and V2X bands on −6 dB measured reflection coefficient criteria. The measured co-polar radiation patterns in the azimuth (XZ-plane) and elevation (YZ-plane) planes depict omnidirectional radiation behaviour.

A miniature platform tolerant antenna is presented which is suitable for low frequency applications. A Split Ring Resonator (SRR) antenna loaded with lumped capacitances is proposed, and the antenna is compact, low proflle and easy to fabricate. It has a maximum dimension of ‚/9 and i10dB bandwidth of 1%. Miniaturized artiflcial magnetic conductor surfaces (AMCs) are designed using capacitance loaded metal patches with individual elements measuring just ‚=70. Placing the SRR above the AMC improves the bandwidth to between 1.5 and 3.5% dependent on the overall size of the AMC and produces a platform tolerant antenna measuring 0.11‚£0:17‚£0:019‚. The performance of the antenna over an AMC with and without vias is studied and discussed. The AMC mounted antenna performances in free space and over a ground plane are also compared.

The performance of a 2 × 2 microstrip patch array under crumpling conditions is presented. The antenna array was manufactured on textile material, and three cases of crumpling resembling real applications are discussed. The performance of the individual patch elements correlate with the overall performance of the array. Frequency shifts of up to 6% are measured for the array when crumpled, the boresight gain is reduced by up to 6 dB with significant changes in directivity and efficiency, up to 20%. The overall efficiency for the textile array increases for crumpling in one plane but falls in the other.

A compact multiband tunable PIFA system using a varactor as an active tuning component is presented covering 88-2175 MHz. The antenna was designed to cover the mobile telephone bands (GSM850, 900, 1800, 1900, UMTS) by controlling the value of the capacitance across the gap in the slotted PIFA and two broadcast bands, FM radio (76-108 MHz) & mobile television DVB-H (470-702 MHz), were added by designing an appropriate matching circuit into the system. The antenna measured λ/15 × λ/43 × λ/19 at 470 MHz and was easily integrated into a small mobile phone handset. Simulations are verified by measurements.

An electrically small tunable split ring resonator antenna is presented. The resonance of the antenna is dependent on the resonance of the split rings. By loading the split ring with varactor diodes, the antenna operating frequency can be reduced and tuned. By applying a DC voltage of 1 to 9 V, the antenna is capable of tuning within the frequency range of 365 MHz to 500 MHz with the measured reflection coefficient of ${-}10$ dB. The antenna is compact and low profile. At the operation frequency of 365 MHz, it measures $0.095 \lambda \times 0.046 \lambda \times 0.001\lambda$ , where $\lambda$ is the free space wavelength.

An automated, low-field disturbance probe positioning system for measuring 3-D electric field distributions inside vehicles or similar resonant environments is described. Correlations between measured and simulated electric field distributions for a simple rectangular cavity demonstrate that the probe positioner has little impact on the measured field levels. Comparisons between measurements and simulations for a real vehicle indicate that the predicted field population distributions are within the estimated uncertainties of the measurements.

In order to meet the high data rate, low latency and high energy efficiency requirements, the future radio units must utilise the frequency spectrum available at certain geographical location efficiently with a minimum amount of hardware. This requires frequency agility and concurrent multi-standard operation capabilities at the base and mobile terminals. To utilise the TV white spaces for mobile and wireless communication and enable their carrier aggregation with sub GHz LTE bands, this paper presents a single-chain, reconfigurable, RF digitising, dual- band receiver comprised of a tunable dual-band antenna, a reconfigurable digital down converter, a baseband processing unit and wideband LNA and ADC in the form of an oscilloscope. The presented dual-band receiver is tested through a hardware- in-the-loop test-bed which shows that up to 20 MHz aggregate bandwidths can be achieved. The receiver is able to provide equivalent error vector magnitude (EVM) performance across a wide range of frequencies avoiding any inter-band interference.

Frequency selective surfaces have been widely used to control radio propagation within buildings. In this paper we consider the application of a sparse FSS for improved coverage of radio signals between two isolated adjacent rooms. The scattering lobes which will occur from a sparse FSS design can therefore be exploited to alter the coverage pattern within the second room.

Understanding radio channel path characteristics is a very important factor for ensuring quality of service and high data rates for indoor wireless communication systems. Obstacles such as human occupants, doors, walls, windows, etc. all have a significant impact on received signals strengths and will contribute to fading, multipath and shadowing effects. This paper studies the effects of changes within a building, such as opening and closing doors, and the movement and number of human occupants, on indoor signal propagation at 5.8 GHz. The effects of different obstacles inside the rooms are compared and highlight which has the most significant effect on the received electric field strength.

Among the different assets tracking solutions Radio Frequency IDentification RFID is a promising technology for in-car communications due to its relatively low cost deployment and real time monitoring and processes. In this paper, a hidden, miniature, narrow band antenna of dimensions 0.18λ×0.20λ×0.005λ is presented which is easy to manufacture using conductive paint sprayed over a car body. The design relies on a resonator, a negative image of the radiator for improved efficiency when in close proximity to ground planes and is suited for use in radio frequency identification networks using the unlicensed RFID band (865.6- 867.6 MHz) is described. The term miniature comes from the fact that the antenna is physically small given the low proximity and insensitivity to the ground plane which facilitates a possible coating layer over the antenna for hidden applications.

An independently tunable low-profile dual-band high-impedance surface (HIS) antenna system is presented which employs a single layer cross bow-tie dual-band tunable HIS ground plane with a printed wideband monopole antenna designed to cover the UHF band. The unit cell of the proposed HIS ground plane is 19.71 mm by 19.71 mm with thickness of 1.74 mm. Simulations of the HIS ground plane have illustrated that either single or dual-band reconfigurable reflection phase resonances can be achieved between 0.95 GHz and 2.45 GHz by controlling C1 (4.55 pF~0.6 pF) and C2 (4.55 pF~0.6 pF) independently which represent the two groups of varactor diodes mounted on the surface elements of the HIS. Simulations with the wideband antenna 4 mm above the HIS ground plane illustrate an effective tunable operational bandwidth from 1.07 GHz to 2.75 GHz with a dual-band capability. Parametric studies indicate the radiation efficiency of the system increases as the antenna height is increased and the diode resistance is reduced. The radiation efficiency also increases with the frequency in general over the tunable frequency range and with the optimum parameters typical values from -4 dB to -2 dB can be achieved. The proposed HIS ground plane and the wideband antenna have been fabricated with Toshiba 1SV245 varactor diodes and it has shown an effective tunable bandwidth from 0.9 GHz to 2.8 GHz approximately with the dual band capability.

A response variation (RV) element is introduced to control the consistency of an adaptive wideband beamformer's response over the frequency range of interest. By incorporating the RV element into the linearly constrained minimum variance (LCMV) beamformer, we develop a novel linearly constrained beamformer with an improved output signal-to-interference-plus-noise ratio (SINR), compared to both the traditional formulation and the eigenvector based formulation, due to an increased number of degrees of freedom for interference suppression. In addition, two novel wideband beamformers robust against look direction estimation errors are also proposed as a further application of the RV element. One is designed by imposing a constraint on the RV element and simultaneously limiting the magnitude response of the beamformer within a pre-defined angle range at a reference frequency; the other one is obtained by combining the RV element and the worst-case performance optimization method. Both of them are reformulated in a convex form as the second-order cone (SOC) programming problem and solved efficiently using interior point method. Compared with the original robust methods, a more efficient and effective control over the beamformer's response at the look direction region is achieved with an improved overall performance.

Subband method is an effective way to reduce the computational complexity of a wideband system and in this paper we study the subband design problem for fixed wideband beamformers, with an emphasis on the design of frequency invariant beamformers (FIBs). We first express the equivalent fullband beam response as a function of the subband beamformer coefficients and then formulate the design problem based on the least squares approach. One direct least squares formulation is first proposed for the design of a general wideband beamformer, and then extended to the FIB design case, followed by three further variations.

A class of adaptive beamforming algorithms with real-valued coefficients is proposed based on the uniform linear array structure by introducing a preprocessing transformation matrix. It is derived from the beamformer with a minimum mean square error (MSE) or a maximum output signal-to-interference-plus-noise ratio (SINR), depending on the specific design criteria. The key parameter of the transformation matrix takes different values for different beamforming scenarios and three representative examples are studied: the linearly constrained minimum variance beamformer (and the generalized sidelobe canceller), the reference signal based beamformer, and the class of blind beamformers based on the constant modulus algorithm. Its advantage is twofold: 1) with real-valued coefficients, the computational complexity of the overall system is reduced significantly; 2) a faster convergence speed is achieved and given the same stepsize, the system arrives at a lower MSE (or a higher output SINR).

The problem of interference cancellation may arise in the nearest future for body-area networks (BANs) whenever a certain number of BANs are led to operate in the vicinity of each other under the same spectrum band. In this paper, using the data obtained from the measurements, the performance in terms of bit error rate (BER) of three linear CDMA receiver structures is investigated for BANs: the conventional receiver, the minimum mean square error receiver, and the decorrelator receiver. We show that in synchronous scenario, the three receivers exhibit the same performance regardless of the number of supported users and SNR level. The BER performance of the linear receivers in on-body channels is better than in Rayleigh channel with the belt-chest channel exhibiting the best gain due to the presence of a stronger LOS component. Furthermore, with orthogonal codes, these receivers are shown to be robust to the MAI level increase and do not require a perfect power control.

The sample matrix inversion (SMI) beamformer suffers from performance degradation due to the finite sample size effect and the arrival angle mismatch problem. A simple technique to provide robustness to the conventional SMI beamformer is to block the desired signal from the received data before calculating the beamformer's weight vector, which leads to the subtraction-based SMI (S-SMI) beamformer. In this correspondence, closed-form approximations of the expected value of the signal-to-interference-plus-noise ratio (SINR) for the S-SMI beamformer and the SMI beamformer are derived, where the effect of both finite sample size and arrival angle mismatch are considered. Simulations show that the derived approximations are close enough to represent the true values of the SINR, when the sample size is small and the arrival direction mismatch exists.

A class of constant modulus algorithms (CMAs) subject to a conjugate symmetric constraint is proposed for blind beamforming based on the uniform linear array structure. The constraint is derived from the beamformer with an optimum output signal-to-interference-plus-noise ratio (SINR). The effect of the additional constraint is equivalent to adding a second step to the original adaptive algorithms. The proposed approach is general and can be applied to both the traditional CMA and its all kinds of variants, such as the linearly constrained CMA (LCCMA) and the least squares CMA (LSCMA) as two examples. With this constraint, the modified CMAs will always generate a weight vector in the desired form for each update and the number of adaptive variables is effectively reduced by half, leading to a much improved overall performance. (C) 2010 Elsevier B.V. All rights reserved.

Novel robust beamforming algorithms are proposed to avoid signal cancellation in a multipath environment. The robustness is achieved by forcing the array responses to the signal of interest and its multipath signals in the pre-estimated clusters to be no less than unity while minimising the output power. Since the array responses to all the multipath signals are constrained, they will not cancel the signal of interest completely as in the conventional adaptive beamforming methods. The effectiveness of the proposed algorithms is verified by computer simulations.

In this paper we study the optimization process of a novel hybrid antenna, formed by a Planar Inverted-F Antenna (PIFA) and a coplanar patch in the same structure, and intended to be used in mobile communications and WIFI applications simultaneously. This hybrid device has been recently proposed and characterized in the literature, and it has been shown that it allows a bandwidth of 850MHz (49%) in the lower band and 630MHz (11.25%) in the upper band. In spite of these good performance results, the flne tuning of the joint PIFA-patch parameters in the hybrid antenna is a hard task, not easy to automatize. In this paper we propose the use of an Evolutionary Programming (EP) approach, an algorithm of the Evolutionary Computation family, which has been shown to be very efiective in continuous optimization problems. We use a real encoding of the antenna's parameters and the CST Microwave Studio simulator to obtain the performance of the antenna. The simulator is therefore incorporated to the EP algorithm as a part of the antenna's evaluation process. We will show that the EP is able to obtain very good sets of parameters in terms of the designer necessities, usually a larger bandwidth at the design frequencies. In this case, the bandwidth of

The performance of a two-element broadband beamforming structure with sensor delay-lines (SDLs) attached is studied for two adaptive implementations, in terms of the direction of the interfering signals, the inter-spacing between delay-line sensors and the length of the SDLs. Compared with the conventional broadband beamformers with tapped delay-lines (TDLs), the SDL based structure has a better performance in two aspects: its output signal to interference plus noise ratio (SINR) drops less as the inter-delay within delay-lines increases; with the same number of delays and weights it can achieve a better performance than the TDL one.

The design methodology is described for a miniaturized frequency selective surface (FSS) using lumped reactive components. Capacitive and inductive elements are utilized in metallic patches to create current loops similar to that observed in bandpass aperture type FSS. It is shown that the resonant frequency of the FSS is controlled mainly by the values of the lumped components and to a lesser extent by the distance between the components. It is insensitive to the periodicity. Issues such as the effects of component loss and oblique incidence are reported using full field predictions. Measurements are shown for an FSS with unit cell periodicity of ?/36.

An adaptive wideband beamforming structure is proposed with combined spatial/temporal subband decomposition. The received signals are first processed by a transformation matrix, and then split into a series of subbands, where independent beamformers can be operated. A special property is that some of the lower subbands can be discarded without affecting its performance, which leads to a system with a lower computational complexity and higher convergence speed.

Performance of a dual-band coplanar patch antenna integrated with an electromagnetic band gap substrate is described. The antenna structure is made from common clothing fabrics and operates at the 2.45 and 5 GHz wireless bands. The design of the coplanar antenna, band gap substrate, and their integration is presented. The band gap array consists of just 3 times 3 elements but reduces radiation into the body by over 10 dB and improves the antenna gain by 3 dB. The performance of the antenna under bending conditions and when placed on the human body are presented.

A beamspace adaptive planar array for broadband beamforming is proposed based on the frequency invariant beamforming technique. A detailed analysis is provided for both the linear arrays and the planar arrays, where two conditions are imposed: the beams should exhibit a good frequency invariant property and be linearly independent. These two conditions are not independent and there is a tradeoff between them. To improve the interference cancellation capability of the array, we may need to sacrifice the frequency invariant property to some degree for more linearly independent beams. A sufficient condition for the linear independence of the beams is derived with a DFT matrix based design proposed. Simulation results verified our analysis and the proposed method.

A novel internal, quad-band antenna placed inside a "foldable" type of mobile phone is presented. Its structure consists of a helical and a monopole element exciting two broad frequency bands. Using a simple matching circuit the proposed antenna covers several frequency bands including the global system for mobile communication (890-960 MHz), digital communication system (1710-1880 MHz), personal communication system (1850-1990 MHz), and universal mobile telecommunication system (1920-2170 MHz). It achieves a voltage standing wave ratio (VSWR) of less than three across all frequency bands with total radiation efficiency of more than 50%. Its novel design and structure occupies only 1.8 cm3 of volume making this antenna very small and very suitable for internal use inside mobile terminals.

A generalised MIMO receiver configuration is presented featuring reduced hardware complexity. Beamforming in the analogue domain with real-valued weights is employed to constructively combine received signals and relax dynamic range prior to digitization. The weights then comprise the matrix inversion process that enables retrieval of the received original baseband signals for further digital processing. Simulations show the configuration has favourable dynamic range performance enabling it to both reduce required number of ADCs and their overall power consumption.

In this paper, the problem of distributed beamforming for cognitive radio systems with frequency-selective channel is studied. Our proposed scheme is based on the filter-and-forward (FF) relay beamforming approach and aims to maximize the received signal to interference plus noise ratio (SINR) at the secondary destination, while suppressing the interference introduced to the primary user. This scheme is further extended to accommodate a relay node output power constraint. Under certain conditions, the extended scheme can be transformed into two sub-schemes with lower computational complexity, where their closed-form solutions are derived. Simulation results are provided to show the performance of the proposed schemes.

A new printed antenna system mounted in an aperture in the roof of a car is evaluated for broadcast signal reception from 88-108 MHz. Results from simulations on the vehicle are compared with measurements. The overall performance of the antenna is also compared to common types of vehicle antennas, the roof monopole and a glass based antenna. Overall the average gain of the antennas was better than -3 dBi for vertical polarization and -10 dBi for horizontal while the input return loss was generally better than -2 dB before matching sections in the tuners and comparable with common automotive antennas. The antennas in the roof aperture offer an alternative place to mount antennas on automobiles

A compact multiband planar inverted-F antenna (PIFA) suitable for distributed radio-over-fiber repeater networks is modified into a planar structure. It is shown that the planar antenna performance is not degraded with respect to the original PIFA and further, a two layer design is demonstrated to offer improved feed matching. The European bands for GSM, DCS-1800, DECT, UMTS, Bluetooth and HiperLAN2 are all covered. A model of the antenna is introduced as a first stage to developing an equivalent circuit.

Compact, low-cost antennas for multiband telematics applications on vehicles are described. The multifrequency band antennas are variations on the printed inverted-F antenna (PIFA) principle. One type of PIFA is a compact variation of a conventional antenna while the other is a novel planar version customized for different mounting positions such as bumpers, window, and roof mount. In both derivations the dimensions are small and have been specifically designed for low-cost production. Each antenna was designed for mobile telephone band coverage from 890 to 2100 MHz. Results from free-space simulations are included but more work needs to be carried out as the vehicles have a significant effect on antenna performance. On-vehicle tests are described where the antennas were placed on glass and plastic areas and integrated into an existing multipurpose roof mount antenna.

A finite element model, using commercially available software, is presented to simulate the piezoelectrically induced stresses and strains in an optical fibre to be used as antenna. These stresses and strains are generated by a layer of piezoelectric polymer deposited on the cladding of a short fibre sample. The theoretical basis for the work is briefly explained and the modelling process is emphasised. Two types of fibre are investigated – circular fibre and D-fibre, and the results compared, analysed and discussed. It is shown that in the D-fibre, the stress and displacement increased by 1.46 and 115 times, respectively, in comparison with the circular fibre.

Conventional microstrip patch antennas are printed with continuous solid copper shapes and ground planes. The general properties of meshed patches are presented in this paper where both the patch itself and the ground plane are meshed. The gain, cross-polarization, bandwidth and radiation patterns are discussed for different combinations of patch and ground plane. The radiation patterns are not significantly affected by meshing the patch alone, but meshing the ground plane increases the back radiation. The gain can suffer by up to 3 dB or more when compared to a standard patch. Cross-polarization is improved providing that the correct mesh line geometry is chosen for the excitation mode. Meshing lowered the resonant frequency in some cases by up to 30% and also improves the bandwidth by a factor of up to 2.5 in some modes. Overall, the meshed patch offers a complex tradeoff between parameters but gives opportunities for improving the bandwidth and reducing the cross polarization and the antenna dimensions at the expense of the gain.

This Letter presents methods for improving the gain and efficiency of a microstrip patch antenna operating at 2.45 GHz implanted in the fat layer of the human body. Simulations using CST Microwave Studio are verified by measurements carried out in an anechoic chamber using a cut of fresh pork meat which has close electromagnetic characteristics to the human body. Using a glass lens and a parasitic ring placed on the skin the implanted antenna gain can be enhanced by almost 8.5 dB.