Open Access
Optimum power transfer in RF front end systems using adaptive impedance matching technique
(Nature Research, 2021) Alibakhshikenari, Mohammad; Virdee, Bal S.; Azpilicueta Fernández de las Heras, Leyre; See, Chan H.; Abd-Alhameed, Raed; Althuwayb, Ayman Abdulhadi; Falcone Lanas, Francisco; Huynen, Isabelle; Denidni, Tayeb A.; Limiti, Ernesto; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Matching the antenna’s impedance to the RF-front-end of a wireless communications system is challenging as the impedance varies with its surround environment. Autonomously matching the antenna to the RF-front-end is therefore essential to optimize power transfer and thereby maintain the antenna’s radiation efficiency. This paper presents a theoretical technique for automatically tuning an LC impedance matching network that compensates antenna mismatch presented to the RF-front-end. The proposed technique converges to a matching point without the need of complex mathematical modelling of the system comprising of non-linear control elements. Digital circuitry is used to implement the required matching circuit. Reliable convergence is achieved within the tuning range of the LC-network using control-loops that can independently control the LC impedance. An algorithm based on the proposed technique was used to verify its effectiveness with various antenna loads. Mismatch error of the technique is less than 0.2%. The technique enables speedy convergence (< 5 µs) and is highly accurate for autonomous adaptive antenna matching networks.
Open Access
A metasurface-based single-layered compact AMC-backed dual-band antenna for off-body IoT devices
(IEEE, 2021) Ahmad, Sarosh; Paracha, Kashif Nisar; Sheikh, Yawar Ali; Ghaffar, Adnan; Butt, Arslan Dawood; Alibakhshikenari, Mohammad; Soh, Ping Jack; Khan, Salahuddin; Falcone Lanas, Francisco; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
In this article, a compact printed monopole dual-band antenna using artificial magnetic conductor (AMC)-plane with improved gain and broader bandwidth, applicable for off-body internet of things (IoT) devices is presented. The monopole antenna consists of two C-shaped resonators connected through a U-shaped monopole, parasitic elements, discrete ground circular rings and a co-planar waveguide (CPW) feedline. Each artificial magnetic conductor (AMC) unit cell consists of a slotted circular and a square stubs, designed with two zero-crossing phases for improving the radiation characteristics and to achieve the high gain. The overall size of the proposed AMC-backed antenna is 44.4 mm ×44.4 mm ×1.6 mm with electrical dimensions of 0.75λ g × 0.75λ g× 0.027λ g. This AMC-backed antenna featured measured bandwidths of 9.6% and 12.4% with improved measured gain values of 4.88 dB and 4.73 dB at 2.45 GHz and 5.8 GHz, respectively. The specific absorption rate (SAR) values are analysed and found to be 1.58 W/kg at 2.45 GHz and 0.9 W/kg at 5.8 GHz. Therefore, the proposed AMC-backed antenna is useful for off-body IoT devices operating at 2.45 and 5.8 GHz industrial, scientific, and medical (ISM) band applications.
Open Access
Dual-polarized highly folded bowtie antenna with slotted self-grounded structure for sub-6 GHz 5G applications
(IEEE, 2021) Alibakhshikenari, Mohammad; Virdee, Bal S.; See, Chan H.; Shukla, Panchamkumar; Mansouri Moghaddam, Sadegh; Zaman, Ashraf Uz; Shafqaat, Samia; Akinsolu, Mobayode O.; Liu, Bo; Yang, Jian; Abd-Alhameed, Raed; Falcone Lanas, Francisco; Limiti, Ernesto; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
In this paper, a novel dual-polarized highly-folded self-grounded Bowtie antenna that is excited through I-shaped slots is proposed for applications in sub-6GHz 5G multiple-input-multiple-output (MIMO) antenna systems. The antenna consists of two pairs of folded radiation petals whose base is embedded in a double layer of FR-4 substrate with a common ground-plane which is sandwiched between the two substrate layers. The ground-plane is defected with two I-shaped slots located under the radiation elements. Each pair of radiation elements are excited through a microstrip line on the top layer with RF signal that is 180° out of phase with respect to each other. The RF signal is coupled to the pair of feedlines on the top layer through the I-shaped slots from the two microstrip feedlines on the underside of the second substrate. The proposed feed mechanism gets rid of the otherwise bulky balun. The Bowtie antenna is a compact solution with dimensions of 32 32 33.8 mm3. Measured results have verified that the antenna operates over a frequency range of 3.1-5Ghz and exhibits an average gain and antenna efficiency in the vertical and horizontal polarizations of 7.5 dBi and 82.6%, respectively.
Open Access
A frequency reconfigurable compact planar inverted-F antenna for portable devices
(Hindawi, 2022) Ghaffar, Adnan; Altaf, Ahsan; Aneja, Aayush; Li, Xue Jun; Khan, Salahuddin; Alibakhshikenari, Mohammad; Falcone Lanas, Francisco; Limiti, Ernesto; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
In this paper, a low-profile, compact size, inexpensive, and easily integrable frequency reconfigurable antenna system is proposed. The proposed antenna consists of an inverted-F shape antenna, capacitors, and switching PIN diodes. The designed antenna element is fabricated on easy available and less expensive FR-4 substrate ( εr = 4.4, tan δ = 0.02). The switching diodes are incorporated within the radiating structure of the antenna design, and by changing the different states of PIN diodes, frequency reconfigurable response is achieved. While adjusting the different states of the diodes, the antenna resonates between 0.841 GHz and 2.12 GHz and covers six different frequency bands. The proposed system has compact size of . The gain of the antenna is between 1.89 and 2.12 dBi. The measurement results shows the good agreement with simulated results for different key performance parameters. Additionally, the proposed antenna shows omni-directional far-field characteristics for various different frequencies.
Open Access
Virtual antenna array for reduced energy per bit transmission at Sub-5 GHz mobile wireless communication systems
(Elsevier, 2023) Alibakhshikenari, Mohammad; Virdee, Bal S.; Mariyanayagam, Dion; García Zuazola, Ignacio Julio; Benetatos, Harry; Althuwayb, Ayman Abdulhadi; Alali, Bader; Xu, Kai-Da; Falcone Lanas, Francisco; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
This paper presents an innovative technique to synthesize a virtual antenna array (VAA) that consumes less energy than conventional antenna arrays that are used in mobile communications systems. We have shown that for a specific spectral efficiency a wireless system using the proposed virtual antenna array consumes significantly less energy per bit (∼3 dB) than a wireless system using a conventional multiple-input multiple-output (MIMO) array. This means the adoption of the proposed VAA technology in smartphones, iPad, Tablets and even base-stations should significantly reduce the carbon footprint of wireless systems. The proposed VAA is realized by employing a pair of linear antenna arrays that are placed in an orthogonal configuration relative to each other. This orthogonal arrangement ensures the radiation is circularly polarized. The size of the standard radiating elements constituting the VAA were miniaturized using the topology optimization method. The design of the VAA incorporates substrate integrated waveguide (SIW) and metasurface technologies. The function of SIW in the design was twofold, namely, to reduce energy loss in the substrate on which the VAA is implemented, and secondly to mitigate unwanted electromagnetic interactions between the neighboring radiating elements and thereby enhancing isolation which otherwise would degrade the radiation characteristics of the array. Metasurface technology served to effectively increase the effective aperture of the array with no impact on the footprint of the array. The consequence of SIW and metasurface technologies was improvement in the gain and radiation efficiency of the array. The proposed four orthogonal 4-element VAA covers the entire sub-5 GHz frequency range, and it radiates bidirectional in the azimuth plane and omni-directional in the elevation plane. Moreover, it is relatively easy to design and fabricate. The proposed VAA has dimensions of 0.96λ0 × 0.96λ0 × 0.0016λ0 at mid-band frequency of 3 GHz. VAA has a measured gain of 25 dBi and radiates with 90% efficiency. The average isolation between the linear arrays constituting the virtual array is better than 27 dB.
Open Access
A comprehensive survey on 'circular polarized antennas' for existing and emerging wireless communication technologies
(IOP Publishing, 2022) Nadeem, Iram; Alibakhshikenari, Mohammad; Babaeian, Fatemeh; Althuwayb, Ayman Abdulhadi; Virdee, Bal S.; Azpilicueta Fernández de las Heras, Leyre; Khan, Salahuddin; Huynen, Isabelle; Falcone Lanas, Francisco; Denidni, Tayeb A.; Limiti, Ernesto; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Circular polarized (CP) antennas are well suited for long-distance transmission attainment. In order to be adaptable for beyond 5G communication, a detailed and systematic investigation of their important conventional features is required for expected enhancements. The existing designs employing millimeter wave, microwave, and ultra-wideband (UWB) frequencies form the elementary platform for future studies. The 3.4-3.8 GHz frequency band has been identified as a worthy candidate for 5G communications because of spectrum availability. This band comes under UWB frequencies (3.1-10.6 GHz). In this survey, a review of CP antennas in the selected areas to improve the understanding of early-stage researchers specially experienced antenna designers has presented for the first time as best of our knowledge. Design implementations involving size, axial ratio, efficiency, and gain improvements are covered in detail. Besides that, various design approaches to realize CP antennas including (a) printed CP antennas based on parasitic or slotted elements, (b) dielectric resonator CP antennas, (c) reconfigurable CP antennas, (d) substrate integrated waveguide CP antennas, (e) fractal CP antennas, (f) hybrid techniques CP antennas, and (g) 3D printing CP antennas with single and multiple feeding structures have investigated and analyzed. The aim of this work is to provide necessary guidance for the selection of CP antenna geometries in terms of the required dimensions, available bandwidth, gain, and useful materials for the integration and realization in future communication systems.