The presented survey was conducted in six European countries as an online study. A total of 2454 subjects participated. Two main research questions were investigated: firstly, how does the cognitive, moral, and affective framing of radio frequency electromagnetic field (RF EMF) exposure perception influence RF EMF risk perception? Secondly, can the deployment of mobile phone base stations have greater acceptance with RF EMF exposure reduction? The findings with respect to the first question clearly indicated that the cognitive framed exposure perception is the main determinant of RF EMF risk perception. The concomitant sensitivity to exposure strength offers an opportunity to improve the acceptance of base stations by exposure reduction. A linear regression analysis supported this assumption: in a fictional test situation, exposure reduction improved the acceptance of base stations, operationalized as the requested distance of the base station from one?s own home. Furthermore, subjects with high RF EMF risk perception were most sensitive to exposure reduction. On average, a 70% exposure reduction reduced the requested distance from about 2000 meters to 1000 meters. The consequences for risk communication are discussed.
Zhu F, Gao S, Ho ATS, Brown TWC, Li JZ, Xu JD (2011) LOW-PROFILE DIRECTIONAL ULTRA-WIDEBAND ANTENNA FOR SEE-THROUGH-WALL IMAGING APPLICATIONS, PROGRESS IN ELECTROMAGNETICS RESEARCH-PIER 121 pp. 121-139
A compact-size planar antenna with ultra-wideband (UWB) bandwidth and directional patterns is presented. The antenna can be fabricated on a printed circuit board (PCB). On one side of the PCB, it has a circular patch, and on the other side it has a slot-embedded ground plane with a fork-shaped feeding stub in the slot. Directional radiation is achieved by using a reflector below the antenna. To reduce the thickness of the antenna, a new low-profile antenna configuration is proposed. Three types of directional UWB antennas are analyzed. The distance between the antenna and the reflector is 12 mm (0.16 »0, »0 is the free space wavelength at the lowest frequency). In order to validate the design, a prototype is also fabricated and measured. Measured results agree well with the simulated ones. The measured results confirm that the proposed antenna features a reflection coefficient below -10 dB over the UWB range from 4.2 GHz to 8.5 GHz, a maximum gain around 9 dBi, a front-to-back ratio over 17 dB and pulse fidelity higher than 90% in the time domain. Thus it is promising for see-through-wall imaging applications.
Goulianos AA, Brown TWC, Stavrou S (2010) Power Delay Profile modelling of the ultra wideband
off-body propagation channel, IET Microwaves, Antennas and Propagation 4 (1) pp. 62-71
A novel dual-polarized broadband antenna array for S-band is presented. This antenna is composed of 6 × 2 microstrip antenna elements with a hybrid feed-line network providing an isolation e 18.6 dB between the H- and V-ports. The operative bandwidth is from 3.15 to 3.25 GHz, and the peak measured gain is approximately 19 dBi. The array is suitable for spacecraft operation because of the selected materials, its low profile (~8 mm thickness), and light weight. It has potential applications in synthetic aperture radar (SAR), remote sensing, and wireless communications.
This paper presents the design of a novel multipath mitigating ground plane for Global Navigation Satellite System (GNSS) antennae. Firstly, the concept of a compact low multipath
cross plate reflector ground plane (CPRGP) is presented. In comparison to the choke ring and Electromagnetic Band Gap (EBG) ground planes, the proposed CPRGP has compact size, low mass, wide operational bandwidth and simple configuration. The proposed CPRGP is then integrated with a circularly polarized dual-band GNSS antenna in order to assess the multipath mitigating performance over two frequency bands.
Measurement results of the proposed CPRGP with GNSS antenna achieves a front to back ratio (FBR) over 25 dB at L1 (1.575 GHz) and L2 (1.227 GHz) bands and maximum backward cross polarization levels below -23 dB at both bands. Antenna phase centre variation remains less than 2 mm across both L1 and L2 bands. Furthermore, the performance comparison of the proposed CPRGP with the commercially available pinwheel
antenna and the shallow corrugated ground plane is presented, showing the advantages of CPRGP for high precision GNSS applications.
Makaratat K, Brown TWC, Stavrou S, Evans B (2010) Complex correlation on linear array angle-of-arrival estimation measurement of ultra wideband propagation channels, IET MICROWAVES ANTENNAS & PROPAGATION 4 (9) pp. 1354-1369 INST ENGINEERING TECHNOLOGY-IET
Due to the disability of the traditional complex natural resonant method, the characteristic polarisation state method is proposed to determine egg quantity in a box with a two by three egg configuration. Parameters are investigated for different egg quantity scenarios and the results show a potential way to determine number in terms of characteristic angle ².
Eggers PCF, Brown TWC, Olesen K, Pedersen GF (2007) Assessment of capacity support and scattering in experimental high speed vehicle to vehicle MIMO links, The 65th IEEE Vehicular Technology Conference pp. 466-470 IEEE
Preliminary results on the use of the vehicle to vehicle MIMO channel in a rural highway environment are presented. This is looked at both in terms of the available spatial multiplexing through singular value decomposition and also angular distribution within the channel. Results indicate a strong predominant line of sight link in general while instances of scattering from other vehicles will cause changes in the Doppler spectrum as well as beamforming jitter.
Mansor MF, Brown TWC, Evans BG (2010) Satellite MIMO Measurement With Colocated Quadrifilar Helix Antennas at the Receiver Terminal, IEEE Antennas and Wireless Propagation Letters 9 pp. 712-715
Pedersen GF, Andersen JB, Eggers PCF, Brown TWC, Neilsen JO, Yamamoto A, Hayashi T, Ogawa K (2007) Small Terminal MIMO Channels with user interaction,
Goulianos A, Brown TWC, Stavrou S, Evans BG (2010) Power Delay Profile Modelling on the UWB Off-Body Propogation Channel, IET Journal on Microwaves, Antennas and Propogation 4 (1) pp. 62-71 IEEE
This study presents a statistical power delay profile (PDP) model for the evaluation and design of ultra
wideband (UWB) off-body communication systems. The analysis is based on extensive real-body measurements
carried out in the frequency range between 3.5 and 6.5 GHz. Due to the dependence of the radio propagation
channel on the body region (i.e. front, side and back), we gradually develop separate stochastic tapped-delay-line
models for each body region. Based on the newly estimated parameters, channel simulation methods are
provided for each of the proposed models. Finally, several comparisons between the empirical data and the
simulations results are presented, by means of key properties of the recorded PDP profiles.
Makaratat K, Stavrou S, Brown TWC (2007) Study of UWB multipath clusters based signal array processing, 2007 (11961)
The increasing interest in using the Near Field Communications (NFC) technology  at 13.5MHz is growing rapidly in the area of contactless payments, as well as numerous other applications, between devices that are within 10cm distance apart. However, there is growing concern that the use of such devices for contactless payments invites problems with regards to using metallic objects in the vicinity of the two devices to act as ?rogue? antennas and eavesdrop information whilst a financial transaction is taking place. This paper will present aspects of designing H-antennas both for the two devices while also identifying the means by which rogue antennas can be designed from real life metallic structures such as a trolley.
This paper presents the design and development of
a dual-band switched-beam microstrip array for Global Navigation Satellite System (GNSS) applications such as ocean reflectometry and remote sensing. In contrast to the traditional Butler matrix, a simple, low cost, broadband and low insertion loss beam switching feed network is proposed, designed and integrated with a dual band antenna array to achieve continuous beam coverage of ±25° around the boresight at the L1 (1.575 GHz) and L2 (1.227 GHz) bands. To reduce the cost, microstrip lines and PIN diode based switches are employed. The proposed switched beam network is then integrated with dual-band step-shorted annular ring (S-SAR) antenna elements in order to produce a fully integrated compact-sized switched beam array. Antenna simulation results show that the switched beam array achieves a maximum gain of 12 dBic at the L1 band and 10 dBic at the L2 band. In order to validate the concept, a scaled down prototype of the simulated design is fabricated and measured. The prototype operates at twice of the original design frequency i.e. 3.15 GHz and 2.454 GHz and the measured results confirm that the integrated array achieves beam switching and good performance at both bands.
Zhu F, Gao S, Ho ATS, Brown TWC, Li J, Wei G, Xu J (2013) Planar Ultra- wideband Antenna with wideband characteristics,
Quantification of distortion effects on UWB system performances in terms of positioning error is analysed in this research. UWB multipath distorted channels are simulated in each frequency subband, over 2-11 GHz. Its characteristics are modelled corresponding to multipath clusters along the propagation paths. The classification of clusters and physics. based distortion mechanisms are generalized to be included into the simulation algorithm. Finally, distortion impacts on system performances regarding to frequency dependent characteristics and positioning errors are investigated.
Makaratat K, Brown TWC, Stavrou S (2008) Modified UWB Spatio-Temporal Channel Simulation Including Pulse Distortion and Frequency Dependence, IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS 7 pp. 553-556 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Goulianos AA, Brown TWC, Evans BG, Stavrou S (2009) Wideband Power Modeling and Time Dispersion Analysis for UWB Indoor Off-Body Communications, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 57 (7) pp. 2162-2171 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
This paper focuses on a preliminary study to determine the quantity of eggs in a fridge using ultra wideband (UWB) impulse responses in the near field. First of all this paper investigates the detectable positions of an egg when placed 1 cm above a UWB antenna array element. Secondly, one egg with six possible configurations on an array are constructed and coupling information is initially obtained for understanding the effect of egg locations. Reflection coefficient and mutual coupling between elements with a random quantity of eggs are analyzed from which a correlation coefficient is derived and used in a different number of eggs present.
To mitigate potential interferences with coexisting wireless systems operating over 3.3-3.6 GHz, 5.15-5.35 GHz, or 5.725-5.825 GHz bands, four novel band-notched antennas suitable for ultra-wideband (UWB) applications are proposed. These include UWB antennas with a single wide notched band, a single narrow notched band, dual notched bands, and triple notched bands. Each antenna comprises a half-circle shaped patch with an open rectangular slot and a half-circle shaped ground plane. Good band-notched performance is achieved by using high permittivity and low dielectric loss substrate, and inserting quarter-wavelength horizontal/vertical stubs or alternatively embedding quarter-wavelength open-ended slots within the feed line. The results of both simulation and measurement confirm that the gain suppression of the single and multiple band-notched antennas in each desired notched band are over 15 dB and 10 dB , respectively. The radiation pattern of the proposed triple band-notched design is relatively stable across the operating frequency band. © 1963-2012 IEEE.
Makaratat K, Brown TWC, Stavrou S (2007) Estimation of time of arrival of UWB multipath clusters through a spatial correlation technique, IET MICROWAVES ANTENNAS & PROPAGATION 1 (3) pp. 666-673 INSTITUTION ENGINEERING TECHNOLOGY-IET
Goulianos AA, Brown TWC, Stavrou S (2008) Ultra-wideband measurements and results for sparse off-body communication channels, 2008 Loughborough Antennas and Propagation Conference, LAPC pp. 213-216
This paper presents a measurement-based statistical channel model for describing UWB off-body propagation and is valid for the frequency range from 3.5 to 6.5 GHz. This model is expressed with respect to both radial and azimuth coordinates, and is physically motivated by creeping wave propagation around smooth convex surfaces, such as the human body. Consequently, it maintains the exponential decay path loss trend with respect to the body orientation angle. Furthermore, it is shown that the same model can be used for RMS delay spread prediction, by simply applying the appropriate parameters resulting from time dispersion analysis. Therefore, delay spread results are presented for threshold values of 10 and 20 dB within the peak of each power delay profile. Following the presented modeling method model parameters can be used as criterion for characterization of respective dense multipath channels. ©2008 IEEE.
Antenna diversity has been used as a method to mitigate multipath fading. For mobile communications, this has usually been at the base station, but there is an increasing demand for diversity antennas to be implemented at the mobile. In this case, there is often a main antenna, as in any other handset, and also a smaller diversity antenna. With such antennas, it is difficult for both to maintain high mean effective gain (MEG), which is a disadvantage to the overall system performance. Also, implementing more than two elements usually increases the handset volume. An intelligent quadrifilar helix antenna (IQHA) (see Leach, S.M. et al., IEE Proc. on Microwaves, Antennas and Propag., vol.147, no.3, p.219-23, 2000) is based on four helix antenna elements that can be combined to allow beam steering towards satellites and terrestrial base stations. Combining the elements in an appropriate fashion gives scope for a four-branch diversity system. The paper investigates why an IQHA provides good diversity potential. An IQHA is primarily an angular diversity system and it is shown that the equal gain combining (EGC) method (see Saunders, S.R., "Antennas and Propagation for Wireless Communication Systems", Wiley, 1999) provides the highest system gain since there is a significant increase in MEG. The analysis is carried out both for the standard sized IQHA and the reduced-size meandered IQHA.
Zhu F, Ho ATS, Brown TWC, Li J, Wei G, Xu J (2013) Miniaturized dual- polarized ultra-wideband tapered slot antenna,
Zhu, F, Gao S, Ho ATS, Abd-Alhameed RA, See CH, Brown TWC, Li J, Wei G, Xu J (2014) Ultra-Wideband Dual-Polarized Patch Antenna with Four Capacitively Coupled Feeds, IEEE Transactions on Antennas and Propagation
novel dual-polarized patch antenna for ultra-wideband (UWB) applications is presented. The antenna consists of a square patch and four capacitively coupled feeds to enhance the impedance bandwidth. Each feed is formed by a vertical isosceles trapezoidal patch and a horizontal isosceles triangular patch. The four feeds are connected to the microstrip lines that are printed on the bottom layer of the grounded FR4 substrate. Two tapered baluns are utilized to excite the antenna to achieve high isolation between the ports and reduce the cross-polarization levels. In order to increase the antenna gain and reduce the backward radiation, a compact surface mounted cavity is integrated with the antenna. The antenna prototype has achieved an impedance bandwidth of 112% at (|S11| d -10 dB) whereas the coupling between the two ports is below -28 dB across the operating frequency range. The measured antenna gain varies from 3.91 to 10.2 dBi for port 1 and from 3.38 to 9.21 dBi for port 2, with a 3-dB gain bandwidth of 107%.
The evaluation of communication systems with low-height terminals requires path loss models
that are applicable to low-height links. For the terminology low-height, the range 0.5 (mobile-) to 3m (fixed-node) above ground is considered. Herein, empirical non-time-dispersive propagation models for relaying systems with low-height terminals are proposed. The models consist of line-of-sight and non-line-of-sight branches. Single- and two-slope modelling approaches were examined. The models take into account the effect of frequency, transmitter and receiver height, and environment. They are complemented by shadowing and fast-fading distribution and correlation statistics. The performance of the models in producing accurate estimations is evaluated by comparison with sets of independent data.
Zhu F, Gao S, Ho ATS, Brown TWC, Li J, Wei G, Xu J (2013) Cavity-backed Dual-polarized Antenna for Ultra-wideband Radar Systems,
Goulianos AA, Brown TWC, Stavrou S (2008) A novel path-loss model for UWB off-body propagation, pp. 450-454
Brown TWC, Ekpe UM (2010) When is Clarke's approximation valid?, IEEE Antennas and Propagation Magazine 52 (3) pp. 171-181 IEEE
For several years since the publication of Clarke's model on small-scale fading in 1968, the well-known approximation relating the square of the magnitude of the complex correlation to being approximately equal to envelope correlation has been applied ; to several aspects of modern-day radio. There are cases in the literature where a negative envelope correlation has been reported, which is in contradiction to the approximation applied by Clarke. This therefore raises the question of why the envelope correlation is negative, and, also, does the Clarke assumption always hold? The authors are unaware of any literature that addresses this subject. As such, some experimentation with synthetic data as well as measured data is used to investigate the conditions under which the approximation is valid. Channel conditions are also analyzed, to investigate how the system is valid.
Chambers P, Brown TWC (2014) Experimental investigation of precoding for EM
exposure reduction, pp. 2464-2468 IEEE
Reduction of human exposure to electromagnetic
(EM) radiation from communications devices without compromising link quality is of importance as people spend more and more time using devices with wireless connectivity. This paper considers the idea of designing a low complexity baseband precoder to reduce user EM exposure for the user scenario of a laptop making an uplink connection to an access point terminal in a picocell environment. The design of the precoder is supported by channel sounding measurements and a ten-fold reduction in user exposure is indicated.
Zhu F, Gao S, Ho ATS, Brown TWC (2013) Compact Size Asymmetric Linearly Tapered Slot Antenna for Portable Ultra-Wideband Imaging Radar System,
The frequency spectrum offered by television white spaces provides an attractive solution to supplying extra bandwidth within large wireless local area networks or wireless backhaul links. However, it is still necessary to ensure for deployment purposes that the primary users, broadcasting services in this case, do not interfere with the white space devices but more importantly that the white space devices do not interfere with the television receivers or television re-transmitters. Given the increased use of vertical polarization as opposed to horizontal polarization in digital television transmission, this paper investigates the benefits of using horizontal as opposed to vertical polarization for white space devices operating within a restricted area. For white space devices such as access points or backhaul links placed at a high height, use of horizontal polarization will reduce their vulnerability to interfere with the primary user regardless of what polarization it has, while also they will be less susceptible to interference from the primary user in locations where vertically polarized television transmitters are deployed.
Zhu F, Gao S, Ho ATS, Brown TWC, J Li, J-D Xu (2013) Asymmetric UWB Aperture Antenna with Triple Band-Notched Function,
Brown TWC, Saunders SR (2001) Modelling polarisation diversity at the mobile terminal, ELEVENTH INTERNATIONAL CONFERENCE ON ANTENNAS AND PROPAGATION, VOLS 1 AND 2 (480) pp. 432-435 INST ELECTRICAL ENGINEERS INSPEC INC
Soodmand S, Brown TWC, Gluhak A (2013) Evaluation of HF band NFC/RFID antennas for smart shelf applications,
The rationale for this Letter is to present a method which would enhance the resolution and accuracy of timing advance (TA) in 2G GSM TDMA and 3G UMTS TDD networks. The method would enable a stationary or slow-moving mobile station (MS) to determine its location using trilateration, with enhanced resolution and accuracy. An outstanding feature of the method is that the only changes required are to software. Low resolution TA samples would be processed into enhanced resolution measurements by applying fractional bit perturbations (dither) over an extended sampled measurement period. The existing TA mechanism and word length for ensuring correct MS uplink arrival times would remain unchanged. It is proposed that enhanced timing advance (ETA) could provide a low risk, low cost alternative to location finding technologies such as angle of arrival, time of arrival, enhanced observed time difference, uplink time difference of arrival and GPS, at the same time satisfying the FCC mobile E-911 accuracy requirement.
This paper presents an assessment of how successful an eavesdropping attack on a contactless payment transaction can be in terms of bit and frame error rates, using an easily concealable antenna and low-cost electronics. Potential success of an eavesdropping attack largely depends on the correct recovery of the data frames used in the ISO 14443 standard. A near-field communication inductive loop antenna was used to emulate an ISO 14443 transmission. For eavesdropping, an identical inductive loop antenna as well as a shopping trolley modified to act like an antenna were used. The authors present and analyse frame error rates obtained with the authors equipment over a range of distances, up to 100 cm, well above the official maximum operating distance depending on the magnetic field strength.
Brown TWC, Eggers PCF, Olesen K, Pedersen GF (2010) Artificial Wideband Multi User Channels for Rural High Speed Vehicle to Vehicle Links, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 29 (1) pp. 29-36 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
A new model of inductively coupled high frequency radio frequency identification (HF
RFID) reader antennas is presented in this paper based on the idea of using the self resonance
frequency (SRF) of a small multi turn coil. The introduced multi turn small self resonant coil (MT
SSRC) antenna is mathematically analyzed in terms of SRF, number of turns, dimensions and dielectric
characteristics of the insulation, where present. Based on the analysis, a compact planar
version of MT SSRC antennas having two turns, the two turn planar SSRC (TTP SSRC), is investigated
and the dependency of the SRF to the antenna dimension is observed. A TTP SSRC antenna
operating at 13.56 MHz is fabricated and is compared with an old model of HF RFID antennas;
an optimized Q factor and a more uniform near field pattern is obtained for the new antenna. The
benefits of the obtained optimized Q factor and uniform near pattern is explained for smart shelf
application. Also, a number of TTP SSRC antennas operating at a distinct frequency, 13.56MHz
here, are fabricated on different substrates and it is shown that the Q factor and dimension of the
TTP SSRC antenna could be controlled and adjusted based on the dielectric characteristics of the
substrate. The new antenna prototype has a beneficial application to smart shelf applications in HF
Detection of packages or storage containers relies heavily on the use of radio frequency identification (RFID) tagging, though such technology provides no means to determine the quantity of items within them. This paper presents a comprehensive study of ultra wideband (UWB) detection in the reactive near field as a low cost, low power way of detecting solid items within a package to complement RFID. For proof of concept, egg boxes within a smart fridge are used as a chosen test case. Simulations and measurements are carried out to evaluate the filtering of the UWB impulse response from which it can resolve the quantity of eggs in a box, using an array of sensors either attached to the package or placed underneath. Correlation coefficients are derived as a metric of this filtering in a reactive near field detection scenario. The robustness of the approach is further evaluated by considering other food cluttered around and above the egg box. The results show smart packages which detect an item directly above the sensor are not affected by surrounding clutter.
Reflectarrays are becoming a potentially attractive replacement of parabolic reflectors for high gain requirements. A large reflectarray consists of thousands of elements. To predict their performance a simulation model is required which is very cumbersome to build manually due to a large number of elements. It takes exhaustive efforts, keen attention to details and significant amount of time to build such a simulation model. When several iterations of modelling are required it worsens the issue even further. We have presented here an algorithm as an automated solution to this problem by interfacing Matlab® with an electromagnetic simulation software. It is very generic, time efficient and makes the modelling easy with least intervention of the designer.
Microstrip printed reflectarrays are becoming a potential replacement of parabolic reflector and phased array antennas due to their simple design, low cost and ease of manufacture to attain high gain and wide angle beam pointing at millimeter waves (mm-waves). Significant challenges are faced while implementing continuous phase reflectarrays at mm-waves. However, discretizing the required reflection phase provides a practically implementable solution. This contribution addresses the selection of phase states and its scattering in a phase discretized mm-wave reflectarray. The performance of two 1.5 bit phase quantized reflectarrays having closely spaced geometrical features is analyzed at 60 GHz. This study provides a better understanding to achieve a wider bandwidth response in practically implementable mm-wave reflectarrays.
Millimeter wave (mm-wave) bands are becoming potentially attractive candidates for next generation communication systems. It is envisioned that high gain smart antennas will be one of the key enabling technologies for such systems. At mm-wave bands, where electrical size of an individual antenna becomes very small, the inclusion of a reconfigurable mechanism in the antenna becomes a great challenge due to real estate constraints. In these scenarios a designer has to decide on the number of bits in a phase shifter for antenna beam steering which will result in an optimum design. This contribution addresses the issue of phase quantization in mm-wave high gain reflectarray smart antennas to achieve an optimum performance. Implementing coarse phase quantization greatly reduces the complexity at mm-wave bands. A case study is presented to highlight the effects of coarse phase quantization using various numbers of bits.
In this digital era, the usage of smart phones and mobile devices is becoming a norm in society with mobile communication quickly transitioned from voice oriented transmission to picture transmission to a more complex live video streaming. This latest development has demanded more
capacity and higher bandwidth in communication links. Static links, which are the focus of this thesis, are an integral part of this mobile system in delivering high capacity data transmission using backhauls or nomadic links. Multi polarised antennas with multiple-input multiple-output (MIMO) multiplexing can be employed to greatly enhance the capacity of a mobile system, especially at frequencies lower than 6 GHz, using their compact size.
A practical antenna inherently exhibits elliptical polarisation though it may be designed to form linear or circular polarisation. Little attention has been given to this aspect of polarised waves as they have always been deemed as unwanted polarisation, although in practice, any antenna is elliptically polarised as it can never be perfectly circularly or linearly polarised. This work therefore aims to deliberately exploit this opportunity by forming antennas with elliptical polarisation to identify the advantages of doing so in order to improve orthogonality in comparison with linear polarisation. It was found that in order to achieve perfect orthogonality, it was more practical to set the magnitudes and phases of the co-polar and cross-polar linear components, which resulted in an
improved co to cross polar ratio more than 20 dB better than linear polarisation in free space.
A dual elliptically polarised antenna prototype was designed and evaluated in this work, which was evaluated both in free space and within an indoor measurement campaign. Results concluded that at short distances with low scattering in the channel and directional antennas, elliptically polarised antennas provide improved multiplexing gain over dual linear polarisations.
Key words: Elliptical Polarisation, MIMO, Multiplexing, static wireless links, degrees of freedom, dual polarised antenna.
Reflectarray antennas are a potential candidate solution to realize high gains at millimetre waves (mm-waves). A reflectarray contains a large number of spatially illuminated unit cells. The performance of a good reflectarray design is manifested by the behaviour of its comprising unit cells. An established technique to characterise a unit cell is by placing it inside a waveguide to achieve periodic boundary conditions. This usually requires custom waveguide products; making the tests difficult and expensive. Additionally, when the unit cells are reconfigurable as in a smart reflectarray it is hard to take the DC bias lines out of the waveguide without using custom made waveguide parts. This contribution address the issue of unit cell placement inside the waveguide and proposes simple unit cell structures to avoid custom made waveguide parts. The idea was verified by measuring a series of unit cells at mm-waves in various configurations and a practically acceptable agreement was found. The proposed structures greatly simplify the reconfigurable unit cell testing.
A steady increasing trend towards millimetre waves (mm-waves) for next generation communication has initiated an intensive research in the field of mm-wave antenna technologies. Reflectarray antennas being one of the potential candidates offer significant advantages over parabolic and phased array antennas at mm-wave bands. In a well-designed reflectarray, the overall performance is mainly determined by its comprising unit cell(s). Most of the recent reflectarray designs are based on printed microstrip technology. It is well known that surface waves get generated in printed microstrip technology and contribute to loss in the radiated signal power in the intended direction. This paper analyses the effect of surface waves in the reflection properties of a printed microstrip millimetre wave reflectarray unit cell. The analytical results are compared with measured data at 32 GHz and an excellent agreement was observed. It was observed that surface waves, though generally considered to have malign effects in antennas, play a significant positive role in the reduction of reflection loss magnitude at unit cell level.
Improvement in the signal-to-noise ratio of Nuclear Magnetic Resonance (NMR) systems may be achieved either by increasing the signal amplitude or by decreasing the noise. The noise has multiple origins ? not all of which are strictly ?noise?: incoherent thermal noise originating in the probe and pre-amplifiers, probe ring down or acoustic noise and coherent externally broadcast radio frequency transmissions. The last cannot always be shielded in open access experiments. In this paper, we show that pulsed, low radio-frequency data communications are a significant source of broadcast interference. We explore two signal processing methods of de-noising short
Measurements in the range of 10-20GHz, 22-
30GHz and 50-67GHz are presented in this paper that show
the benefit of using gaps in building infrastructure to
substantially improve the penetration loss in the order of 10dB
or more. Increasing the frequency substantially improves the
opportunity to penetrate through the same size gap as it
becomes electrically larger. The measurement setup used in
this work involves the use of a ground floor infrared reflector
glass door whereby the effect of the gaps can be compared both
by closing the door and sealing the gaps with a conductor in
order to identify the difference in penetration. Simulations
were also carried out to verify the waveguiding and standing
wave effects in the gaps.
Future communication systems employing
massive multiple input multiple output will not have the ability
to use channel state information at the mobile user terminals.
Instead, it will be necessary for such devices to evaluate the
downlink signal to interference and noise ratio (SINR) with
interference both from the base station serving other users
within the same cell and other base stations from adjacent
cells. The SINR will act as an indicator of how well the precoders
have been applied at the base station. The results
presented in this paper from a 32 x 3 massive MIMO channel
sounder measurement campaign at 2.4 GHz show how the
received bit error rate and error vector magnitudes can be
used to obtain a prediction of both the average and
dynamically changing SINR.
This article reports two contributions related to reflectarray antenna design at millimeter waves (mm-waves). First, a closed form analytical formulation is provided for the prediction of reflection properties of square/rectangular mm-waves reflectarray unit cells based on various quality factors and the theory of waveguide coupled resonators. To ensure a high accuracy at mm-waves, the effects of fringing fields, surface waves, metal conductivity, and metal surface roughness are included in the analysis. This analysis program greatly facilitates the parametric studies of a unit cell's constituting parameters to converge on an optimum design solution. Secondly, the concept of phase quantization is proposed for a cost effective realization of mm-waves reflectarrays. The developed formulation in the first contribution was used to design two 3 bit phase quantized, single layer, 19 wavelength, passive reflectarrays at 60/GHz. The test results are compared with simulations and a very good agreement was observed. These findings are potentially useful for the realization of high gain antennas for mm-wave inter-satellite links in small satellite platforms.
A new simple and accurate model defined as shield
edge diffraction is derived and validated suitable for frequencies
above 10GHz diffracting around obstructions that are narrow
compared to the Fresnel zone width. The model includes new
simple Fresnel diffraction parameters similar to those used with
traditional knife edge diffraction, which can in the same way be
integrated into deterministic and empirical path loss models.
Capability of the model extends beyond current single and
double knife edge models whereby it includes the effects of the
antennas? far field distances as well as their gain and phase
patterns, which subsequently have a severe effect on the
diffraction loss in short range links. The models are validated
using both anechoic chamber as well as real environment based
measurements at 10-12GHz and 26GHz.
Next generation wireless communication systems are expected to support unprecedented extremely high data transfer rates. This objective requires wider bandwidths which are presently only available at the millimeter waves (mm-waves) spectrum (30-300 GHz). Due to stringent propagation impairments, mm-waves mainly rely on the line of sight communication links which require high gain and wide angle beamsteeering smart antennas to maintain their performance. Owing to the complexity and losses in array beamformers, the realization of a high gain wide angle electronic beamsteering antenna solution at mm-waves becomes a key challenge.
This research provides a potentially competing novel high gain electronic beamsteering antenna solution for mm-waves in the form of a phase quantized smart reflectarray consisting of high performance reconfigurable unit cells. Novel contributions of this research are: (a) Analysis of mm-wave reflectarray unit cells including the effects of fringing fields, surface waves, finite metal conductivity and metal surface roughness. (b) New measurement techniques for mm-wave reflectarray unit cells to ease the alignment, orientation, and DC biasing issues. (c) Characterization of PIN diodes at 10 GHz and 60 GHz for their ON/OFF state models extraction from measurements. (d) Design of three state implicit phase shifter reflectarray unit cell at 60 GHz, reduction in its DC bias lines, and an optimization technique to improve polarization purity of a multi-state reconfigurable unit cell. (e) A fast algorithm to prepare the electromagnetic simulation model of large reflectarrays. (f) Conception and measurement based validation of phase quantized reflecarrays and their performance matrix. (g) Conception and measurement based analytical solution of low DC power consuming smart reflectarrays.
The resulting solution is agile, simple to implement, do not necessarily require multiple RF chains, enables wide angle electronic beamsteering (+-78 degree), is scalable for any gain/frequency requirements, can be made foldable for smaller satellite platforms, is very reliable, and consumes low DC power. This smart reflectarray platform can implement any phase only synthesis technique for radiation pattern control including single/multiple pencil beams, contoured beams, and their scanning over wider angles. Findings of this research would potentially benefit next generation terrestrial/air/space communication systems and radars.
In this paper, a compact, broadband, planar array antenna with omnidirectional radiation in horizontal plane is proposed for the 26 GHz fifth-generation (5G) broadcast applications. The antenna element is composed of two dipoles and a substrate integrated cavity (SIC) as the power splitter. The two dipoles are placed side-by-side at both sides of the SIC and they are compensated with each other to form an omni-directional pattern in horizontal plane. By properly combing the resonant frequencies of the dipoles and the SIC, a wide impedance bandwidth from 24 to 29.5 GHz is achieved. To realize a large array while reducing the complexity, loss and size of the feeding network, a novel dual-port structure combined with radiation and power splitting functions is proposed for the 1st time. The amplitude and phase on each element of the array can be tuned, and therefore, the grating lobes level can be significantly reduced. Based on the dual-port structure, an 8-element array with an enhanced gain of over 12 dBi is designed and prototyped. The proposed antenna also features low profile, low weight and low cost, which is desirable for 5G commercial applications. Measured results agree well with the simulations, showing that the proposed high-gain array antenna has a broad bandwidth, omni-directional pattern in horizontal plane, and low side-lobes.
The Internet of things (IoT) refers to uniquely identifiable objects and their virtual representations
in an Internet-like structure to be managed and inventoried by computers. Radio-frequency
identification (RFID) - a prerequisite for the IoT - is an automatic way for data transaction in
object identification and is used to improve automation, inventory control and checkout
operations. An RFID system consists of a reader device and one or several tags. Smart reader
systems are building blocks for cutting edge applications of RFID and as a subdivision of these
systems, RFID smart shelf solutions are started to be implemented for large-scale item-level
management where characteristics of reader antennas are critical issue.
This work focuses on designing optimised reader antennas for high frequency (HF) RFID
smart shelf systems which operate based on inductive coupling between the tag and the reader
antennas and have good performance in crowded environments. Firstly, an approach is presented
to increase band-width of HF RFID reader antennas to improve the reception of sub-carrier
frequencies. A fabricated enhanced band-width antenna at 13.56 MHz is evaluated for its
capability in being used for smart shelf applications. The obtained band-width supports sub-carrier
frequencies for all the HF RFID standards to be detected easier and thus leads to increased
identification range. It is shown the HF RFID technology is capable of identifying the distance of
tagged books based on the received magnetic field intensity.
Secondly, multi turn small self resonant coil (MT SSRC) antennas are introduced and analysed
as a new model of inductively coupled reader antennas. Based on the analysis, two turn planar
SSRC (TTP SSRC) antennas having similar dimension with the current HF RFID reader antennas
are investigated. Fabricated TTP SSRC antenna operating at 13.56 MHz is resulted to optimised Q
factor and more uniform near field pattern in comparison with the similar antennas. Also, a
number of TTP SSRC antennas operating at a distinct frequency, 13.56MHz, are fabricated on
different substrates and it is shown the desired Q factor and antenna dimension can be obtained
based on the dielectric characteristics of the substrate.
A conformal transmitarray with thinned control is
presented, operating at 28 GHz. Its side panels are rotated to
align with the maximum steering angle, increasing the gain
and reducing the scan loss. The transmitarray is fed by an
8-element linear phased array antenna. Beam focusing to +/-
53 degrees is demonstrated for two different directions, using
combinations of crossed-slot unit cells. A unit cell placement rule
is proposed to significantly reduce (i.e. thin) the required number
of reconfigurable unit cells. A filling factor of 43% was achieved
compared to a fully populated design. This reduces the cost and
biasing complexity. By minimising scan loss, this antenna could
improve the performance of 5G small-cell access points.
The accurate measurement of electromagnetic exposure and its application is expected to become more and more important in future wireless communication systems, given the explosion in both the number of wireless devices and equipments radiating electromagnetic-fields(EMF)and the growing concerns in the general public linked to it. Indeed, the next generation of wireless systems aims at providing a higher data rate,better quality of service(QoS), and lower latency to users by increasing the number of access points,i.e.densification, which in turn will increase EMF exposure. Similarly, the multiplication of future connected devices,e.g. internet of things(IoT)devices, will also contribute to an increase in EMF exposure. This paper provides a detailed survey relating to the potential health hazards linked with EMF exposure and the different metrics that are currently used for evaluating,limiting and mitigating the effects of this type of exposure on the general public. This paper also reviews the possible impacts of new wireless technologies on EMF exposure and proposes some novel research directions for updating the EMF exposure evaluation framework and addressing these impacts in future wireless communication systems. For instance, the impact of mmWave or massive-MIMO/beamforming on EMF exposure has yet to be fully understood and included in the exposure evaluation framework.
This paper presents a machine learning (ML) based
model to predict the diffraction loss around the human body.
Practically, it is not reasonable to measure the diffraction loss
changes for all possible body rotation angles, builds and line
of sight (LoS) elevation angles. A diffraction loss variation
prediction model based on a non-parametric learning technique
called Gaussian process (GP) is introduced. Analysed results state
that 86% correlation and normalised mean square error (NMSE)
of 0.3 on the test data is achieved using only 40% of measured
data. This allows a 60% reduction in required measurements in
order to achieve a well-fitted ML loss prediction model. It also
confirms the model generalizability for non-measured rotation
This paper presents two different designs for frequency reconfigurable antennas capable of continuous tuning. The radiator, for both antenna designs, is a microstrip patch, formed from liquid metal, contained within a microfluidic channel structure. Both patch designs are aperture fed. The microfluidic channel structures are made from polydimethylsiloxane (PDMS). The microfluidic channel structure for the first design has a meander layout and incorporates rows of posts. The simulated antenna provides a frequency tuning range of approximately 118% (i.e. 4.36 GHz) over the frequency range from 1.51 GHz to 5.87 GHz. An experimental result for the fully filled case shows a resonance at 1.49 GHz (1.3% error compared with the simulation). Experienced rheological behavior of the liquid metal necessitates microfluidic channel modifications. For that reason, we modified the channel structure used to realise the radiating patch for the second design. Straight channels are implemented in the second microfluidic device. According to simulation the design yields a frequency tuning range of about 77% (i.e. 3.28 GHz) from 2.62 GHz to 5.90 GHz.
Orthogonal static or fixed links with polarization
multiplexing can be formed by using dual polarized antennas
with a low cross coupling from one polarization to the other. This
is limited by the level of achievable polarization purity of two
orthogonal dual polarized antennas. Any practical antenna is
inherently elliptically polarized, resulting in either circular or
linear polarization impurity. This work exploits such impurity
where simple semi directional elliptically polarized antennas are
designed to have minimal cross coupling. Results show a dual
polar static link can reach the capacity limit using elliptical
polarization, which is not reached with linear polarization.
Channel measurements both in free space and indoor
environments were carried out from 2.2 to 2.4 GHz using a
derived cross polar ratio to quantify the impact of multipath
scattering on static links.
Beam steering impairments adversely affect antenna performance at wider steering angles. Scan loss degrades the antenna gain, and hence the link budget. To address this problem, antennas designs based on phased arrays, lenses, and transmitarrays are proposed. Millimetre wave beamforming within 5G cell sectors is considered as an application scenario. Feed networks for an 8-element phased array, operating at 28 GHz, were designed using unequal power dividers. A Taylor amplitude distribution was applied to reduce the sidelobe level to -15.2 dB at boresight. Prototypes were fabricated in microstrip, using meanders to steer the beam. Cascaded Fresnel lenses were placed around the array, to enhance the gain. By tilting the lenses to align with the steered beam, the lenses increased the gain by 3.19 dB at ±52°, and by a further 1.5 dB when repositioned in simulation. Asymmetric amplitude distributions were applied to the array to prevent the main lobe from splitting. Diffraction theory was used to analyse the focusing properties of the lens arrangement. The fabricated prototype exhibited a bandwidth of 1.75 GHz. Antennas were designed and simulated for line-of-sight MIMO scenarios. An envelope correlation coefficient below 0.0356 was maintained for both designs. 2D SISO beam steering was also simulated. Achievable data rates were estimated from the antenna parameters, and the effect of interference was evaluated. Scan loss was mitigated for the two antenna rows within the focal region. A conformal transmitarray was designed, using 1-bit unit cells based on crossed-slots. A unit cell placement rule was proposed to reduce the number of electronically reconfigurable cells by 59%. A measured gain of 12.5 dBi and a simulated total efficiency of 75% were obtained at boresight and the maximum steering angle of 53°. By combining reconfigurable lenses with phased arrays, the focusing directivity is able to mitigate scan loss.
Wireless connectivity needs to be high capacity and reliable for present and future high speed land transportation systems, including rail, road and hyperloop. All such moving platforms transport a substantial number of passengers, creating high data demands in often remote areas. This paper proposes how to re-think the means by which wireless connectivity is implemented to provide wireless services to a dense number of users on a fast moving platform. The proposed concept evolves from orbital angular momentum radio modes for data multiplexing to linear or planar angular momentum instead. In this study, the wireless link is placed underneath the moving platform, a promising low-cost method that potentially could achieve 9Gbps with 15MHz bandwidth and 10dB signal to noise ratio from initial analysis carried out.
This thesis presents the feasibility of liquid metal in reconfigurable antenna applications. Unlike conventional reconfigurable antennas, liquid metal possesses the ability to reconfigure an antenna aperture in new ways largely undiscovered. In this work, the design, analysis and measurement of two liquid metal reconfigurable antennas are carried out bringing together research on materials, microfluidics and electromagnetics. In addition, a like for like comparison of applying liquid metal and PIN diode in pattern reconfigurable antennas is presented. On the RF characterisation, test fixtures are designed, analysed and measured to evaluate liquid metal and copper up to 67 GHz, and PIN diode up to 6 GHz. While various liquid metal antennas exist, the current state of the art has mainly implemented liquid metal in point-like contacts or limited confined areas.
On how liquid metal can be used to connect/disconnect large areas of metalisation and achieve radiation performance not possible by using conventional switches is demonstrated in a frequency bandwidth reconfigurable antenna. The antenna results in a 2 dB gain and 24% efficiency enhancement. The second antenna presents a frequency tunable patch antenna formed from liquid metal. The antenna reconfigures its resonance in a continuous manner. A measured total usable spectrum of 73% is achieved.
In the like for like pattern reconfigurable antennas comparison, the liquid metal shows no effect on resonance whereas PIN diodes cause 27% resonance shift. The liquid metal antenna shows up to 1.4 dB gain and 13% efficiency higher than that of the PIN diode antenna. In the RF characterisation, the diode shows up to 6.5 dB higher insertion loss than liquid metal. Liquid metal measurements up to 67 GHz show identical behaviour as of copper.
Results conclude that liquid metal has a high feasibility in reconfigurable antenna applications and its RF performance is as of a typical conductor.