Tim Brown

Dr Tim Brown

Senior Lecturer in RF Antennas and Propagation
CEng, PhD
+44 (0)1483 689810
06 CII 01


University roles and responsibilities

  • Director of Postgraduate Studies
  • IET Student Advisor
  • Exchange Programmes Coordinator
  • Course organiser for short courses on Antennas and Propagation, RF Systems and Circuits, Microwave Engineering and 5G Communications
  • Contact person for the Electronics and Amateur Radio Society
  • Marketing and outreach support


    Research interests

    Research collaborations



    Mohsen Khalily, Tim W. C. Brown, Rahim Tafazolli (2019)Machine Learning Based Approach for Diffraction Loss Variation Prediction by the Human Body, In: IEEE Antennas and Wireless Propagation Letters Institute of Electrical and Electronics Engineers (IEEE)

    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 angles.

    Ben Allen, Tim W. C Brown, Timothy D Drysdale (2021)Experimental evaluation of a linear angular momentum multiplexed radio link for moving platforms, In: Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences477(2254) Royal Society

    Linear angular momentum multiplexing (LAMM) has recently been proposed for high spectral-efficiency communications between moving platforms, such as between trains and ground infrastructure. We present performance results obtained from a scale experimental system comprising a 2 × 2 antenna system operating at 2.35 GHz. The link transmitted two independent video streams, using RF pre-coding and software-defined radios to modulate and up/down-convert the signals. Linear motion is introduced to demonstrate the translation-invariance of the technique. We interpret the measured data with the aid of an analytical model to show that crosstalk between the two channels is at levels low enough to consistently support the video streams without interruption. Specifically, our results show spectral efficiency is consistently higher when LAMM coding is enabled compared with an uncoded channel.

    FABIEN HELIOT, TIM W C BROWN (2022)On the Exposure Dose Minimization of Multi-antenna Multi-carrier System Users, In: IEEE transactions on vehicular technology IEEE

    —From the fourth generation (4G) of cellular systems onward, wireless personal devices (WPDs) support multi-input multi-output (MIMO) communication. However, the impact of MIMO communication on the electromagnetic field (EMF) of WPD users has yet to be fully understood and analyzed at the system level. In this paper, we first provide a generic model for assessing the individual exposure dose of multi-antenna WPD users in a multiuser multi-carrier communication system. An optimization framework for minimizing this exposure dose is then developed based on our exposure model. This framework helps us to identify a new criterion, i.e., the ratio between the normalized exposure dose and the channel to noise ratio (CNR), as the main system level criterion for minimizing the individual exposure dose of multi-antenna WPD users. This criterion is further integrated in the design of two novel centralized resource allocation schemes that take advantage of the multiple antennas at the WPD to minimize the per-user exposure dose, when full or limited knowledge of each user channel is available. Our new schemes can significantly reduce the individual exposure dose of WPD users (by approximately 80%) in comparison with the most relevant existing resource allocation schemes. Our results also provide insights into the logarithmic relationship between the per-user exposure dose and the number of receive antennas (or the number of time slots), and how such a parameter can be exploited to further reduce the exposure and/or provide a higher SE while maintaining a low exposure dose. Index Terms—EMF exposure dose, MIMO, Multi-carrier system , SAR, optimization.

    Ali Ali, Mohsen Khalily, Tim W C Brown, Rahim Tafazolli (2022)Beam-steering Capability for OAM-based Reflectarray at 5G-mmWave frequencies, In: IET microwaves, antennas & propagation Wiley

    This paper demonstrates the ability of the reflectarray antenna (RA) to perform orbital angular momentum (OAM) beamsteering with low divergence angles at the fifth generation (5G) millimetre-wave (mmWave) bands. To provide steered OAM beams, it is necessary to regulate the scatterer’s geometries smoothly throughout the focal area to follow the required twisted distribution. The traditional numerical method to compensate for the phase is modified to enable the 3D scanning property of OAM beams, so it is possible to avoid the feeder blockage and produce high-gain steered OAM beams. Likewise, reducing the inherent beam divergence of OAM beams can be obtained by examining the most satisfactory phase distribution of the scatterers by fitting the focal length. The simulated radiation pattern is validated by the measured radiation pattern of the fabricated RA in the frequency range between 28.5 GHz and 31.5 GHz.

    Tim Brown, Mohsen Khalily (2018)Integrated Shield Edge Diffraction Model for Narrow Obstructing Objects, In: IEEE Transactions on Antennas and Propagation IEEE

    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.

    M. Mansour, T. Brown, B. Evans (2018)Vertical Array of Orthogonal Circular Polarised Quadrifilar Helix Antenna for Satellite MIMO System, In: Proceedings of 2018 IEEE International RF and Microwave Conference (RFM 2018) Institute of Electrical and Electronics Engineers (IEEE)

    This paper investigates the effects of Ground Plane on the Performance of Multipath Mitigating Antennas for GNSS.

    Ben H. Allen, Tim W.C Brown, Tim D. Drysdale (2019)A New Paradigm for Train to Ground Connectivity Using Angular Momentum, In: IEEE Xplore Institute of Electric and Electronics Engineers

    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.

    Ghulam Ahmad, Tim W.C. Brown, Craig I. Underwood, Tian H. Loh (2018)An investigation of millimeter wave reflectarrays for small satellite platforms, In: Acta Astronautica151pp. 475-486 Elsevier

    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.

    Ghulam Ahmad, Tim Brown, Craig Underwood, Tian Hong Loh (2017)How coarse is too coarse in electrically large reflectarray smart antennas?, In: 2017 International Workshop on Electromagnetics: Applications and Student Innovation Competitionpp. 135-137 IEEE

    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.

    T. A. Hill, J. R. Kelly, M. Khalily, T. W. C. Brown (2019)Conformal Transmitarray for Scan Loss Mitigation with Thinned Reconfiguration, In: Proceedings of the 2019 13th European Conference on Antennas and Propagation (EuCAP) Institute of Electrical and Electronics Engineers (IEEE)

    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.

    Tim Brown, D Humphreys, M Hudlicka, T Loh (2018)Prediction of SINR using BER and EVM for Massive MIMO Applications, In: EuCAP 2018 Proceedings IEEE

    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.

    TWC Diakos, TP, Briffa, JA, Brown, Wesemeyer, S (2013)Eavesdropping near-field contactless payments: a quantitative analysis, In: TP Diakos (eds.), IET Journal of Engineering

    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.

    Ghulam Ahmad, Craig Underwood, Tim Brown, TH Loh (2017)Role of Surface Waves in Improving the Reflection Properties of a Millimetre Wave Reflectarray Unit Cell, In: LAPC 2017 Proceedings The Institution of Engineering and Technology

    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.

    UM Ekpe, TWC Brown, BG Evans (2011)Channel characteristics analysis of the dual circular polarized land mobile satellite MIMO radio channel, In: Proceedings - 2011 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications, APWC'11pp. 781-784
    AA Goulianos, TWC Brown, S Stavrou (2010)A novel path-loss model for UWB off-body propagationpp. 450-454

    A novel, multi-slope dual breakpoint model for predicting path-loss in Ultra-Wideband (UWB) off-body communication channels, is proposed. This model is based on real-body measurements, carried out in the frequency range between 3.5GHz-6.5GHz, in an anechoic chamber. New parameters that describe this specific propagation environment are presented and evaluated. Results show that the first breakpoint point angle lies in the lit region of the transmitter and increases exponentially with distance until it rises to its threshold value. Based on this finding the near and far field areas for BAP (Body to Access Point) channels are defined. In addition, newly estimated decay coefficients suggest severe degradation as the receiver moves in between the two critical angles. Finally, techniques for model expansion in two dimensions are discussed.

    A D Abeygunasekera, C E Free, T Brown (2007)A Novel Dual-Ring Multi-Layer Circular Polarized Antenna

    A novel circular polarized antenna structure capable of high radiation efficiency, and suitable for use in multilayer microwave circuits is presented. The antenna uses dual ring feed system to enhance radiation. Data is provided for a prototype antenna working at 10 GHz.

    SALMAN BEHBOUDI AMLASHI, MOHSEN KHALILY, TIM W C BROWN, PEI XIAO, RAHIM TAFAZOLLI (2021)Graphene-based Reconfigurable Reflecting Surface for Future Communications

    —In this paper, a reflecting metasurface is proposed to control the reflection angle by manipulating the chemical potential (CP) of graphene. The surface can operate in three anomalous reflection modes for θ = 45 • , 60 • and 75 • while it is illuminated with a normal incident electromagnetic wave (EMW). Moreover, by tuning the chemical potential of graphene sheets the proposed surface can switch off the reflection mode of operation by absorbing the incident EM power.

    Mona Ibrahim, C Pardi, Tim Brown, Peter McDonald (2018)Active elimination of radio frequency interference for improved signal-to-noise ratio for in-situ NMR experiments in strong magnetic field gradients, In: Journal of Magnetic Resonance287pp. 99-109 Elsevier

    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

    A new modelling method suited to the dual circular polarised (MIMO) channel applicable to land mobile satellite (LMS) communications in line of sight cases is presented. In this scenario, it is necessary to apply correlated fading to the co-polarised and cross- polarised channels separately in order to model the evident polarization multiplexing in such channels found from measurement data. Comparisons between model and measured data for satellite elevations of 30o are presented for validation. Influence of the vehicle interior on the channel model is also analysed.

    Ghulam Ahmad, Tim Brown, Craig Underwood, Tian Hong Loh (2017)An efficient algorithm for electrically large reflectarray antenna design automation, In: 2017 International Workshop on Electromagnetics: Applications and Student Innovation Competitionpp. 133-134 IEEE

    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.

    AA Goulianos, TWC Brown, S Stavrou (2010)Power Delay Profile modelling of the ultra wideband off-body propagation channel, In: IET Microwaves, Antennas and Propagation4(1)pp. 62-71

    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 λ0, λ0 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.

    Muhammad Ali Jamshed, Fabien Heliot, Tim Brown (2019)A Survey on Electromagnetic Risk Assessment and Evaluation Mechanism for Future Wireless Communication Systems, In: IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biologypp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)

    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.

    Tim W. C. Brown, Ben H. Allen, Tim D. Drysdale, Upasana K. Dagia (2020)Linear Angular Momentum Multiplexing – Conceptualisation and Experimental Evaluation with Antenna Arrays, In: Proceedings Royal Society London A ROYAL SOCIETY

    Linear Angular Momentum Multiplexing is a new method for providing highly spectrally efficient short range communication between a transmitter and receiver, where one may move at speed transverse to the propagation. Such applications include rail, vehicle and hyperloop transport systems communicating with fixed infrastructure on the ground. This paper describes how the scientific concept of linear angular momentum multiplexing evolves from orbital angular momentum multiplexing. The essential parameters for implementing this concept are: a long array at least at one of the ends of the link; antenna element radiation characteristics; and the array element spacing relative to the propagation distance. These parameters are also backed by short range measurements carried out at 2.4GHz used to model the Rice fading channel and determine resilience to multipath fading.

    B Bhandari, S Gao, T Brown (2009)Meandered Variable Pitch angle Printed Quadrifilar Helix Antenna, In: Proceedings of Loughborough Antennas and Propagation Conferencepp. 325-328

    A new method of meandered variable pitch angle printed Quadrifilar Helix Antenna (MVPQHA) is described. This type of antenna helps in reducing the size of the printed quadrifilar helix antenna (PQHA) and makes the bandwidth of the antenna broader. The new type of antenna is compared with other existing types of printed quadrifilar helix antenna in terms of size, return loss and bandwidth.

    TWC Brown, KCD Chew, SR Saunders (2012)Analysis of the diversity potential of an intelligent quadrifilar helix antenna, In: Twelfth International Conference on Antennas and Propagation: Conference Publication No. 4912pp. 194-198

    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.

    Tim Hill, James R. Kelly, Mohsen Khalily, Tim W.C Brown (2020)Cascaded Fresnel Lens Antenna for Scan Loss Mitigation in Millimeter Wave Access Points, In: IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION Institute of Electrical and Electronics Engineers

    Millimeter wave lens antennas will be essential for future wireless access. Conventionally, they increase the gain in the boresight direction only. In this paper, cascaded Fresnel zone plate lenses are combined with a phased array to increase the gain at wide steering angles of ±52°. The side lenses are tilted to align with the maximum steering angle, and cascaded to increase the focusing gain. The inner lenses increase the gain by 2.45 dB at boresight, and by 3.19 dB at the maximum steering angle. When the side lenses are repositioned, the simulated focusing gain increases to 4.69 dB. Asymmetric amplitude distributions are proposed to prevent the main lobe from splitting. An 8-dement 7-lens prototype operating at 28 GHz achieved a gain from 12.96 dBi to 15.35 dBi with a bandwidth of at least 1.3 GHz for all measured beam directions. The maximum measured azimuthal beamwidth was 27°. A design procedure and a theoretical analysis of diffraction through the lenses are provided. By increasing the SNR, this beamfonning antenna could improve the coverage of 3-sector 5G microcell base stations, and support gigabit wireless links for vehicular, rail, and satellite communications.

    S Soodmand, Tim Brown (2017)Inductively Coupled Small Self Resonant Coil (SSRC) Reader Antennas for HF RFID Applications, In: International Journal of Electronics and Communications78pp. 32-40 Elsevier

    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 RFID.

    Intan S. Zainal Abidin, Tim W, C. Brown (2020)Exploitation of Elliptical Polarization for Improved Orthogonal Static Links, In: IEEE Transactions on Antennas and Propagation68(4)pp. 3103-3110 Institute of Electrical and Electronics Engineers (IEEE)

    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.

    Tim Brown, R Xie, P Chambers (2018)Frequency Dependence of Penetration through Gaps into Buildings at mmWave, In: EuCAP 2018 Proceedings IEEE

    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.

    R Di Bari, TWC Brown, S Gao, C Underwood (2011)Dual-Polarized Printed S-Band Radar Array Antenna for Spacecraft Applications, In: IEEE Antennas and Wireless Propagation Letters10pp. 987-990 IEEE

    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 ≥ 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.

    TWC Brown, T Diakos (2011)On the design of NFC Antennas for contactless payment applications, In: Proceedings of the 5th European Conference on Antennas and Propagation (EUCAP)pp. 44-47

    The increasing interest in using the Near Field Communications (NFC) technology [1] 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.

    Demos Serghiou, Mohsen Khalily, S. Johny, M. Stanley, I. Fatadin, T.W.C Brown, N. Ridler, Rahim Tafazolli (2020)Ultra-Wideband Terahertz Channel Propagation Measurements from 500 to 750 GHz, In: 2020 International Conference on UK-China Emerging Technologies (UCET)

    This paper presents empirically based ultrawideband and directional channel measurements, performed in the Terahertz (THz) frequency range over 250 GHz bandwidth from 500 GHz to 750 GHz. Measurement setup calibration technique is presented for free-space measurements taken at Line-of-Sight (LoS) between the transmitter (Tx) and receiver(Rx) in an indoor environment. The atmospheric effects on signal propagation in terms of molecular absorption by oxygen and water molecules are calculated and normalized. Channel impulse responses (CIRs) are acquired for the LoS scenario for different antenna separation distances. From the CIRs the Power Delay Profile (PDP) is presented where multiple delay taps can be observed caused due to group delay products and reflections from the measurement bench.

    K Makaratat, TWC Brown, S Stavrou (2007)Estimation of time of arrival of UWB multipath clusters through a spatial correlation technique, In: IET MICROWAVES ANTENNAS & PROPAGATION1(3)pp. 666-673 INSTITUTION ENGINEERING TECHNOLOGY-IET
    Chunxu Mao, Mohsen Khalily, Pei Xiao, Tim Brown, Steven Gao (2019)Planar Sub-Millimeter-Wave Array Antenna with Enhanced Gain and Reduced Sidelobes for 5G Broadcast Applications, In: IEEE Transactions on Antennas and Propagation67(1)pp. 160-168 IEEE

    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.

    TWC Brown, SR Saunders, BG Evans (2005)Analysis of mobile terminal diversity antennas, In: IEE PROCEEDINGS-MICROWAVES ANTENNAS AND PROPAGATION152(1)pp. 1-6 IEE-INST ELEC ENG
    Tim Brown, H Ma, Anthony Ho (2017)UWB Reactive Near Field Detection for Smart Packages: A Comprehensive Study using eggs, In: IEEE Transactions on Antennas and Propagation65(7)pp. 3691-3701 IEEE

    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.

    Ghulam Ahmad, Tim Brown, Craig Underwood, TH Loh (2017)Millimetre Wave Reflectarray Antenna Unit Cell Measurements, In: LAPC 2017 Proceedings Institution of Engineering and Technology

    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.

    M Maqsood,, S Gao, TWC Brown, M Unwin, R de vos Van Steenwijk, JD Xu, CI Underwood (2014)Low-Cost Dual-Band Circularly Polarized Switched-Beam Array for Global Navigation Satellite System, In: IEEE Transactions on Antennas and Propagation62(4)pp. 1-8

    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.

    Ghulam Ahmad, T.H. Loh, Tim Brown, Craig Underwood (2017)On the Phase Selection of Millimeter Wave Quantized Reflectarrays, In: Proceedings of the 2017 International Applied Computational Electromagnetics Society Symposium IEEE

    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.

    Khaled Yahya Alqurashi, Carol Crean, James R. Kelly, Tim W. C. Brown, Mohsen Khalily (2019)Liquid Metal Application for Continuously Tunable Frequency Reconfigurable Antenna, In: Proceedings of the 13th European Conference on Antennas and Propagation (EuCAP 2019) Institute of Electrical and Electronics Engineers (IEEE)

    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.

    MUHAMMAD ALI JAMSHED, TIM W C BROWN, FABIEN HELIOT (2021)Dual Antenna Coupling Manipulation for Low SAR Smartphone Terminals in Talk Position, In: IEEE transactions on antennas and propagation IEEE

    A rigorous analysis of the concept of coupling manipulation utilizing two antennas suited to modern smartphone devices in talk position for voice calls is presented. By using the optimum relative phase between the elements, they can substantially reduce the specific absorption rate (SAR) but still maintain efficiency due to the splitting of power between them and by exploiting a suitable level of inter element coupling. The same antenna elements can still be used for multiple input multiple output (MIMO) when not in talk position without heavily degrading their fundamental capacity limit but this is of secondary importance. The concept could be applied to frequency ranges used in mobile communications from 1.8 to 6 GHz where the ground plane has sufficient form factor. Extensive simulations using two planar inverted-F antennas (PIFAs) operating at 2.4 GHz are carried out to demonstrate conceptually how two antennas can be optimized to reduce SAR by over 50% compared to a single antenna element. SAR reduction is maintained regardless of the user’s head composition and how they are handling the device in talk position. Antenna prototypes are measured and compared to verify the capacity when the handset is used away from the body with two MIMO terminal antennas.