Dr James Kelly

Lecturer in Microwave Antennas
MEng (Hons), PhD, PG Cert ULT, MIEEE
Wednesdays 1-2pm


Areas of specialism

Microwave Antennas

University roles and responsibilities

  • Additional Learning Support (ALS) Tutor for Electronic Engineering


    Research interests

    Research projects



    Idris IH, Hamid MR, Jamaluddin MH, Rahim MKA, Kelly JR, Majid HA (2014) Single-, dual- and triple-band frequency reconfigurable antenna, Radioengineering23(3)pp. 805-811
    The paper presents a frequency reconfigurable slot dipole antenna. The antenna is capable of being switched between single-band, dual-band or triple-band operation. The antenna incorporates three pairs of pindiodes which are located within the dipole arms. The antenna was designed to operate at 2.4 GHz, 3.5 GHz and 5.2 GHz using the aid of CST Microwave Studio. The average measured gains are 1.54, 2.92 and 1.89 dBi for low, mid and high band respectively. A prototype was then constructed in order to verify the performance of the device. A good level of agreement was observed between simulation and measurement.
    Borja A, Kelly JR (2015) Reconfigurable Microwave Circuit Based on a Single Triangular Microstrip Patch, 2015 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETINGpp. 2253-2254 IEEE
    Kelly JR, Borja AL (2014) Hardware block for use in programmable microwave function arrays, Electronics Letters50(15)pp. 1076-1077
    Ultimately, the research presented will lead to the development of a microwave integrated circuit that is analogous to a field programmable gate array. An early step towards the development of this technology is presented. Specifically, a 3-port device, based on a single resonant element, namely a microstrip square patch, is described. The device operates simultaneously as a filter and an antenna. Filter performance is obtained between ports 1 and 2. Antenna performance is obtained on port 3. © 2014 The Institution of Engineering and Technology.
    Wang Z, Kelly JR, Hall PS, Borja AL, Gardner P (2014) Reconfigurable parallel coupled band notch resonator with wide tuning range, IEEE Transactions on Industrial Electronics61(11)pp. 6316-6326
    This paper presents a new form of reconfigurable band notch resonator with a wide tuning range. The whole structure consists of a through line and two parallel coupled resonators. This paper presents an accurate lumped element equivalent circuit for the parallel coupled resonator. The mechanism giving rise to the wide tuning range is also investigated. The first harmonic of the fundamental stop-band is analyzed and compared with that of the varactor-coupled resonator. Measurement results show that the stop-band of the filter can be tuned from 0.6 to 4.0 GHz. This is achieved by varying the capacitance of two pairs of varactor diodes. The stop-band tuning range is restricted by the capacitance variation which can be achieved using the varactor diode. The potential tuning range of a filter based on this resonator is greater than one decade. © 1982-2012 IEEE.
    Wei JD, Chen XZ, Kelly JR, Cui YZ (2015) Blast furnace stockline measurement using radar,IRONMAKING & STEELMAKING42(7)pp. 533-541 MANEY PUBLISHING
    Kelly JR, Borja A (2015) Reconfigurable Microwave Circuit Based on Three Triangular Microstrip Patches, 2015 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETINGpp. 2251-2252 IEEE
    Chen G, Xiao Pei, Kelly James, Li B, Tafazolli Rahim (2017) Full-Duplex Wireless-Powered Relay in Two Way Cooperative Networks,IEEE Access5pp. 1548-1558 IEEE
    This paper investigates a full duplex wirelesspowered two way communication networks, where two hybrid access points (HAP) and a number of amplify and forward (AF) relays both operate in full duplex scenario. We use time switching (TS) and static power splitting (SPS) schemes with two way full duplex wireless-powered networks as a benchmark. Then the new time division duplexing static power splitting (TDD SPS) and full duplex static power splitting (FDSPS) schemes as well as a simple relay selection strategy are proposed to improve the system performance. For TS, SPS and FDSPS, the best relay harvests energy using the received RF signal from HAPs and uses harvested energy to transmit signal to each HAP at the same frequency and time, therefore only partial self-interference (SI) cancellation needs to be considered in the FDSPS case. For the proposed TDD SPS, the best relay harvests the energy from the HAP and its self-interference. Then we derive closed-form expressions for the throughput and outage probability for delay limited transmissions over Rayleigh fading channels. Simulation results are presented to evaluate the effectiveness of the proposed scheme with different system key parameters, such as time allocation, power splitting ratio and residual SI.
    Uchendu Iyemeh Egwenike, Kelly James (2017) Ultrawide isolation bandwidth Compensated Power Divider for UWB applications,Microwave and Optical Technology Letters59(12)pp. 3177-3180 John Wiley & Sons
    This article presents design analyses for achieving an ultrawide isolation bandwidth compensated power divider (CPD). The CPD offers improvement in complexity, size and insertion when compared with alternative techniques for increasing isolation bandwidth. A prototype CPD with -15dB isolation bandwidth of 114% was fabricated and measured to validate the analyses.
    Wang Z, Hall P, Kelly JR, Gardner P (2017) Wideband Frequency Domain and Space Domain Pattern Reconfigurable Circular Antenna Array,IEEE Transactions on Antennas and Propagation65(10)pp. 5179-5189 IEEE
    This paper presents a wideband circular antenna array with a frequency domain and space domain reconfigurable radiation pattern. A wideband circular array antenna is designed with omni-directional radiation pattern, in azimuth direction, throughout the whole frequency band. The antenna array consists of eight TEM horn antennas. The antenna array exhibits an omni-directional azimuthal radiation pattern when all eight ports are excited with signals of the same magnitude and phase. The antenna array is fed through eight reconfigurable bandstop filters and a power splitter. This enables it to provide an omni-directional azimuthal pattern along with a single directional pattern null in a given spatial direction and at a certain frequency. Both the spatial direction and the frequency can be altered. The antenna works from 0.8 GHz to 3.0 GHz. The antenna array will be useful in combating interference in wideband communication systems. It will also be of value in surveillance military applications.
    da Costa I, Filgueiras H, Kelly J, Arismar Cerqueira S, Xiao P (2018) Mechanical Beam Steering Circular Patch Antenna,EuCAP 2018 Proceedings
    This work reports preliminary results and a prototype of an innovative mechanical beam steering circular patch antenna for 5G indoor cellular access networks with sub6 GHz operation. The beam steering is achieved using 18 screws installed around the circular patch radiator, working as a reflector by proper managing the screws position and height. The new antenna can steer its main beam over 360º in azimuth plane and from -30º to 30º in the elevation plane with gain up to 8.01 dBi at 4.6 GHz.
    Allayioti Marion, Kelly James R., Mittra Raj (2018) Beam and Polarisation Reconfigurable Microstrip Antenna Based on Parasitics,Microwave and Optical Technology Letters60(6)pp. 1460-1464 Wiley
    This paper presents a dual-notch polarization and beam reconfigurable microstrip antenna. It uses parasitics which incorporate switches to steer its beam away from boresight and dual-notches which, again, incorporate switches to reconfigure between linear and circular polarization. The antenna is a low profile microstrip patch antenna which only uses a single feed, allowing it to be compact and simple in terms of its structure.
    Alqurashi K. Yahya, Filgueiras H.R.D., da Costa I. F., Cerqueira S. Jr. Arismar, Xiao Pei, Chen Zhe, Wong Hang, Kelly J.R. (2018) Millimeter Wave Beam Steerable/Reconfigurable Liquid Metal Array Antenna,Proceedings of ICEAA - IEEE APWC - FEM 2018pp. 814-815 Institute of Electrical and Electronics Engineers (IEEE)
    Users within mobile networks require ever increasing data rates. However, the frequency spectrum, reserved for mobile networks, is highly saturated. The millimeter wave spectrum, by contrast is relatively under utilised. Nonetheless, this area of the spectrum suffers from higher propagation losses, necessitating the use of highly directional antennas. To support mobility these antennas require beam steering capabilities. For several applications wide beam scanning capability is required. A valuable approach for increasing the beam scanning range is to use element factor plus array factor control [1]. Although several authors have presented designs based on this approach the lobe performance of those antennas is generally quite poor. In this paper we seek to address that issue.
    Borja A. L., Kabiri Yasin, Belenguer A., Kelly J. R. (2018) Programmable Multi-Functional RF/Microwave Circuit for Antenna and Filter Operation,IEEE Transactions on Antennas and Propagation66(8)pp. 3865-3876 Institute of Electrical and Electronics Engineers (IEEE)
    This paper describes a multi-functional microwave device that can be reconfigured to behave either as a filter or an antenna. The device is based around a single resonant element, referred to as a building block element that is connected to 4 ports. The resonant element is a microstrip square patch working in the 2.45 GHz unlicensed Industrial Scientific and Medical (ISM) band used for IEEE 802.11 WiFi. The proposed building block is simple in its design and construction. The paper also presents devices composed of three building blocks, which can realize more complex filtering and antenna mode performance. In addition, PIN diodes have also been incorporated into the devices in order to facilitate electronic control. Measured results, pertaining to fabricated prototypes, show that filter and antenna operation can be achieved, in the same device at a frequency of around 2.45 GHz with acceptable insertion loss and efficiency. In the future, it is anticipated that this could lead to a new paradigm, namely a device that is analogous to a field programmable gate array (FPGA) operating in the microwave frequency regime.
    Kelly James R., Tanha Mandana Ardeshir (2018) Reconfigurable 26GHz Liquid Metal Antenna Capable of Low Loss Continuous Beam Steering,Proceedings of the 2018 IEEE Conference on Antenna Measurements and Applications, 3-6 September 2018, Västerås, Sweden Institute of Electrical and Electronics Engineers (IEEE)
    For this first time this paper presents a concept for a high gain millimeter wave beam steerable antenna that supports continuous steering over a 360° scan range and promises to yield extremely low power losses. The concept does not require phase shifters which suffer from high insertion losses at millimeter wave frequencies or mechanical movement, in the conventional sense, which has the disadvantages of poor reliability and slow response times due to high inertia.
    Millimetre wave beam and polarization reconfigurable antennas for future wireless communications are investigated in this thesis. The millimetre wave frequency spectrum has recently attracted large attention from researchers and the industry of wireless communications. Millimetre wave frequencies is considered to be the frequency spectrum between 30 GHz and 300 GHz. However, the industry considers the spectrum above 10 GHz as millimetre wave, due to the fact that it shows similar propagation characteristics with the spectrum above 30 GHz. The aforementioned spectrum of frequencies offers a lot of advantages compared to lower frequency spectrum, due to the fact that it offers large and mostly unexploited bandwidths. The need for very high data rates, in future wireless communications, increases the need for bandwidth. Millimetre wave frequencies can be used to fulfill future bandwidth demands. Although millimeter wave frequencies offer several advantages and good potential for future wireless communications, they also impose several challenges. This thesis discusses the need for highly directive and beam reconfigurable antennas for such high frequencies. It also discusses how an antenna design can benefit from being circularly polarised for several wireless communication applications and how antennas for future wireless communications must be able to reconfigure several parameters, without compromising the performance, cost and size, giving the exibility to a wireless terminal to operate in several different modes. This thesis proposes novel reconfigurable antennas for portable devices, which can be used at millimetre wave frequencies, and which offer high gain, wide steering range, low scan loss and multi-parameter reconfigurability; essential characteristics that antennas designed for future wireless communications should offer.
    Hill Timothy A., Kelly James R. (2019) 28 GHz Taylor Feed Network for Sidelobe Level Reduction in 5G Phased Array Antennas,Microwave and Optical Technology Letters61(1)pp. 37-43 Wiley
    This paper presents a design procedure for a phased array feed network. The procedure is validated by designing and fabricating a set of 28 GHz 8-element beam steerable antennas. Within the feed, a Taylor n-bar amplitude taper is implemented using unequal power dividers. At boresight, the taper reduced the sidelobe level by 2.84 dB to -15.2 dB. Beam steering from 0° ? 48° is achieved using meanders. An empirical formula for the meander widths is proposed, enabling independent control of amplitude and phase. Empirical formulae for the initial parameters of the unequal dividers are also proposed. The wide transmission lines in this feed network are compatible with low-cost PCB fabrication techniques.
    Kabiri Yasin, Borja Alejandro L., Kelly James, Xiao Pei (2019) A technique for MIMO antenna design with flexible element number and pattern diversity,IEEE Accesspp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)
    This paper presents a new technique for designing Multiple Input Multiple (MIMO) Output antennas having pattern diversity. Massive MIMO is expected to form part of 5G communications and will require antennas having a very large number of elements. However, due to the size limitation, it is highly challenging to preserve high isolation between the ports. Pattern diversity technique are also highly desirable and can facilitate MIMO systems with diversity gain. However, achieving that within a compact antenna where there is limited space between the elements is also challenging. In this paper a technique is introduce and applied to 4-element and 6-element MIMO antennas. This technique can improve the isolation between the ports and it also yields pattern diversity for MIMO antennas with various numbers of elements. The technique is verified via experimental measurement.
    Dias Filgueiras Hugo Rodrigues, Kelly James R., Xiao Pei, da Costa I. F., Cerqueira S. Jr. Arismar (2019) Wideband Omnidirectional Slotted-Waveguide Antenna Array Based on Trapezoidal Slots,International Journal of Antennas and Propagation Hindawi
    This manuscript presents a novel approach for designing wideband omnidirectional slotted-waveguide antenna arrays, which is based on trapezoidal-shaped slots with two different electrical lengths, as well as a twisted distribution of slot groups along the array longitudinal axis. The trapezoidal section is formed by gradually increasing the slot length between the waveguide interior and exterior surfaces. In this way, a smoother impedance transition between waveguide and air is provided in order to enhance the array operating bandwidth. Additionally, we propose a twisting technique, responsible to improve the omnidirectional pattern, by means of reducing the gain ripple in the azimuth plane. Experimental results demonstrate 1.09 GHz bandwidth centered at 24 GHz (4.54% fractional bandwidth), gain up to 14.71 dBi over the operating bandwidth and only 2.7 dB gain variation in the azimuth plane. The proposed antenna array and its enabling techniques present themselves as promising solutions for mm-wave application, including 5G enhanced mobile broadband (eMBB) communications.
    Alqurashi Khaled Yahya, Crean Carol, Kelly James R., Brown Tim W. C., Khalily Mohsen (2019) Liquid Metal Application for Continuously Tunable Frequency Reconfigurable Antenna,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.
    Alqurashi Khaled Yahya, Kelly James R. (2018) Continuously tunable frequency reconfigurable liquid metal microstrip patch antenna,Proceedings of the 2017 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meetingpp. 909-910 Institute of Electrical and Electronics Engineers (IEEE)
    This paper presents a continuously tunable microstrip patch antenna formed from liquid metal (eutectic gallium indium). The concept and design of the antenna have been validated through computer simulation. The antenna is capable of reconfiguring its operating frequency in a continuous manner. The proposed design consists of a microstrip patch which is excited via aperture coupling. The EGaIn liquid metal is contained within a microfluidic channel which is formed within a polydimethylsiloxane (PDMS) substrate. Frequency tuning is achieved by altering the amount of fluid within the channel to vary the electrical length of the antenna. The simulated antenna provides a frequency tuning range of approximately 104% and a total usable spectrum (S11 <; -10 dB) of 105%. The antenna can be tuned from 3.21 GHz to 10.12 GHz. The maximum realized gain is 6.9 dBi and the total efficiency is 82%.
    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.

    Additional publications