Ali Araghi

Dr Ali Araghi

Postgraduate research student

Academic and research departments

Institute for Communication Systems.


Demos Serghiou, Mohsen Khalily, Vikrant Singh, Ali Araghi, Rahim Tafazolli (2020)Sub-6 GHz Dual-Band 8×8 MIMO Antenna for 5G Smartphones, In: IEEE Antennas and Wireless Propagation Letters Institute of Electrical and Electronics Engineers (IEEE)

In this letter, a dual-band 8x8 MIMO antenna that operates in the sub-6 GHz spectrum for future 5G multiple-input multiple-output (MIMO) smartphone applications is presented. The design consists of a fully grounded plane with closely spaced orthogonal pairs of antennas placed symmetrically along the long edges and on the corners of the smartphone. The orthogonal pairs are connected by a 7.8 mm short neutral line for mutual coupling reduction at both bands. Each antenna element consists of a folded monopole with dimensions 17.85 x 5mm2 and can operate in 3100-3850 MHz for the low band and 4800-6000 MHz for the high band ([S11] ˂ -10dB). The fabricated antenna prototype is tested and offers good performance in terms of Envelope Correlation Coefficient (ECC), Mean Effective Gain (MEG), total efficiency and channel capacity. Finally, the user effects on the antenna and the Specific Absorption Rate (SAR) are also presented.

Sohail Payami, Mohsen Khalily, Ali Araghi, Tian Hong Loh, David Cheadle, Konstantinos Nikitopoulos, Rahim Tafazolli (2020)Developing the First mmWave Fully-Connected Hybrid Beamformer with a Large Antenna Array, In: IEEE Access Institute of Electrical and Electronics Engineers

Millimeter wave (mmWave) systems with effective beamforming capability play a key role in fulfilling the high data-rate demands of current and future wireless technologies. Hybrid analog-todigital beamformers have been identified as a cost-effective and energy-efficient solution towards deploying such systems. Most of the existing hybrid beamforming architectures rely on a subconnected phase shifter network with a large number of antennas. Such approaches, however, cannot fully exploit the advantages of large arrays. On the other hand, the current fully-connected beamformers accommodate only a small number of antennas, which substantially limits their beamforming capabilities. In this paper, we present a mmWave hybrid beamformer testbed with a fully-connected network of phase shifters and adjustable attenuators and a large number of antenna elements. To our knowledge, this is the first platform that connects two RF inputs from the baseband to a 16 8 antenna array, and it operates at 26 GHz with a 2 GHz bandwidth. It provides a wide scanning range of 60, and the flexibility to control both the phase and the amplitude of the signals between each of the RF chains and antennas. This beamforming platform can be used in both short and long-range communications with linear equivalent isotropically radiated power (EIRP) variation between 10 dBm and 60 dBm. In this paper, we present the design, calibration procedures and evaluations of such a complex system as well as discussions on the critical factors to consider for their practical implementation.

Ali Araghi, Mohsen Khalily, Pei Xiao, Arash Kosari, Houman Zarrabi, Rahim Tafazolli (2018)Millimeter-Wave MIMO Balanced Antipodal Vivaldi Antenna Design for Autonomous Cars, In: IEEE ISNCC 2018 : 2018 IEEE International Symposium on Networks, Computers and Communications Institute of Electrical and Electronics Engineers (IEEE)

This paper introduces a millimeter-wave multipleinput- multiple-output (MIMO) antenna for autonomous (selfdriving) cars. The antenna is a modified four-port balanced antipodal Vivaldi which produces four directional beams and provides pattern diversity to cover 90 deg angle of view. By using four antennas of this kind on four corners of the car’s bumper, it is possible to have a full 360 deg view around the car. The designed antenna is simulated by two commercially full-wave packages and the results indicate that the proposed method can successfully bring the required 90 deg angle of view.

ALI ARAGHI, MOHSEN KHALILY, PEI XIAO, RAHIM TAFAZOLLI, David R. Jackson (2021)Long Slot mmWave Low-SLL Periodic-Modulated Leaky-Wave Antenna Based on Empty SIW, In: IEEE Transactions on Antennas and Propagation Institute of Electrical and Electronics Engineers (IEEE)

In this paper, empty substrate integrated waveguides (ESIW) technology is applied to design long slot leaky-wave antennas (LWAs). First, a uniform-aperture structure is presented and its limitations on forming the beam are studied. Then, a sinusoidal curve is employed to modify the geometry of guided-wave structure which divides the slot into a number of segments, making a periodic aperture. After that, a method is proposed to regulate the guided waves inside the ESIW. To this end, a modulation function is derived to simultaneously determine the local amplitude and segment length of the physical sinusoidal curve at each individual points on the structure. This results in manipulating the phase constant (_) and leakage rate (_) across the aperture which ultimately controls both the tilt angle and side-lobe-level (SLL) of the constructed beam. The slot is placed on the centerline of the broad wall of the ESIW in order to reduce the cross polarization. The structure is designed to operate at 35 GHz with SLL = 􀀀30 dB and a backward tilt angle of _m = 􀀀20 deg. Finally, the proposed LWA is simulated and a fabricated design is measured. A good agreement is observed between the theoretical, simulated, and measured performance of the antenna.

Amir Arayeshnia, Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Trapped Microstrip-Ridge Gap Waveguide for Standalone Millimeter Wave Structures, In: EUCAP 2020

This paper presents a novel design of trapped microstrip-ridge gap waveguide by using partially filled air gaps in a conventional microstrip-ridge gap waveguide. The proposed method offers an applicable solution to obviate frustrating assembly processes for standalone high-frequency circuits employing the low temperature co-fired ceramics technology which supports buried cavities. To show the practicality of the proposed approach, propagation characteristics of both trapped microstrip and microstrip-ridge gap waveguide are compared first. Then, a right-angle bend is introduced, followed by designing a power divider. These components are used to feed a linear 4-element array antenna. The bandwidth of the proposed array is 13 GHz from 64~76 GHz and provides the realized gain of over 10 dBi and the total efficiency of about 80% throughout the operational band. The antenna is an appropriate candidate for upper bands of WiGig (63.72~70.2) and FCC-approved 70 GHz band (71~76 GHz) applications.

Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Multiple-Beam mmW-Slotted-Waveguide Leaky Wave Antenna with Control on Polarization, In: 2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting Institute of Electrical and Electronics Engineers (IEEE)

By performing the Floquet-mode analysis of a periodic slotted waveguide, a multiple-beam leaky wave antenna is proposed in the millimetre-wave (mmW) band. Considering the direction of surface current lines on the broad/side-walls of the waveguide, the polarization of constructed beams are also controlled. The simulation results are well matched with the initial mathematical analysis.

Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Holographic-Based mmW-Wideband Bidirectional Frequency Scanning Leaky Wave Antenna, In: EUCAP 2020

Utilizing the holography theory, a bidirectional wideband leaky wave antenna in the millimetre wave (mmW) band is presented. The antenna includes a printed pattern of continuous metallic strips on an Alumina 99:5% sheet, and a surface wave launcher (SWL) to produce the initial reference waves on the substrate. To achieve a bidirectional radiation pattern, the fundamental TE mode is excited by applying a Vivaldi antenna (as the SWL). The proposed holographic-based leaky wave antenna (HLWA) is fabricated and tested and the measured results are aligned with the simulated ones. The antenna has 22:6% fractional bandwidth with respect to the central frequency of 30 GHz. The interference pattern is designed to generate a 15 deg backward tilted bidirectional radiation pattern with respect to the normal of the hologram sheet. The frequency scanning property of the designed HLWA is also investigated.

Shadi Danesh, Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Millimeter Wave Phased Array Antenna Synthesis Using a Machine Learning Technique for Different 5G Applications, In: Proceedings of the 2020 IEEE International Symposium on Networks, Computers and Communications (ISNCC'20) Institute of Electrical and Electronics Engineers (IEEE)

A machine learning (ML) technique has been used to synthesis a linear millimetre wave (mmWave) phased array antenna by considering the phase-only synthesis approach. For the first time, gradient boosting tree (GBT) is applied to estimate the phase values of a 16-element array antenna to generate different far-field radiation patterns. GBT predicts phases while the amplitude values have been equally set to generate different beam patterns for various 5G mmWave transmission scenarios such as multicast, unicast, broadcast and unmanned aerial vehicle (UAV) applications.

Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Study on the Location of mmWave Antenna for the Autonomous Car?s Detection and Ranging Sensors, In: EUCAP 2020

The effect of vehicle’s proximity on the radiation pattern when the RADAR’s antenna is mounted on the body of autonomous cars is analysed. Two directional radiation patterns with different specifications are placed at different locations of a realistic car body model. The simulation is performed based on ray-tracing method at 77 GHz, the standard frequency for self-driving applications. It is shown that to obtain a robust RADAR sensor, the antenna radiation pattern is better to have relatively higher gain and lower side-lobe-level (SLL), than narrower halfpower- beamwidth (HPBW) and higher front-to-back (F/B) ratio. Both academia and industry can benefit from this study.

Ashifa M Musthafa, Mohsen Khalily, Ali Araghi, Okan Yurduseven, Rahim Tafazolli (2022)Compact Multi-Mode Quadrifilar Helical Antenna for GNSS-R Applications, In: IEEE antennas and wireless propagation letters IEEE

In this paper, a compact circularly polarized (CP) multi-mode antenna for global navigation satellite system re- flectometry (GNSS-R) is presented. The design comprises two Quadrifilar Helical Antennas (QHAs), each fed with a ground coplanar waveguide (GCPW) and quarter wavelength power divider (QWPD) integrated feed. A hybrid staircase-shaped (SSR) QHA radial is proposed, and it is formed by serially arranging several vertical and diagonal elements. The electric field lines from the vertical elements converge constructively to radiate with the axis normal. Besides, the circular spatial offsets between the adjacent diagonal and vertical elements induce a 90 delay in the field radiated. This hybrid shape launches an unprecedented theory facilitating normal mode of operation (MOOp) in QHA and generates CP over broad elevations and azimuths (0

Mehdi Mehranpour, Saughar Jarchi, Asghar Keshtkar, Ayaz Ghorbani, Ali Araghi, Okan Yurduseven, Mohsen Khalily (2020)Robust Breast Cancer Imaging Based on a Hybrid Artifact Suppression Method for Early-Stage Tumor Detection, In: IEEE access8pp. 206790-206805 IEEE

A high-resolution conformal array for detection of small size tumors inside the breast is proposed. The array consists of a novel cavity-backed low-profile aperture-stacked-patch (LP-ASP) antennas. The proposed antenna operates from 2.2 GHz to 13.5 GHz which enables the imaging system to be exploited across a high fractional bandwidth of approximately 149%. Thanks to the wide operating bandwidth of the designed antenna, the proposed system is not only applicable for a deep penetration imaging, but also for high resolution and accurate images acquisition. The proposed single element antenna has a compact size of \mathrm {10 \times 10 \times 10.495 m}\mathrm {m}^{3} . So, it is possible to form a conformal array around the breast by applying numbers of the designed elements. Moreover, a Hybrid Artifact Suppression (HAS) method is presented to remove the artifact effects including skin reflection and mutual coupling between the elements. In this method, the artifact response of each channel is estimated using Independent Component Analysis (ICA) at the early-stage of the recorded signals. Additionally, in order to suppress the artifact data to accurately detect the malignant tumor, a Wiener filter is applied. To validate the practicality of the presented calibration algorithm in the proposed conformal array, the detection of a single spherical tumor (with a small diameter of 5 mm) within a realistic breast model in different scenarios is studied. Investigating of simulated and measured results of the designed antenna, and comparing quantitative metrics of successfully reconstructed tumor images by the proposed HAS and conventional calibration methods show the proposed system can be a good candidate for the breast cancer detection applications.

Ali Araghi, Mohsen Khalily, Okan Yurduseven, Pei Xiao, Rahim Tafazolli (2022)Guided-wave manipulation in SIW H-plane horn antenna by combining phase correction and holographic-based leakage, In: Scientific reports12(1)pp. 11234-11234

A hybrid technique is proposed to manipulate the feld distribution in a substrate integrated waveguide (SIW) H-plane horn to enhance its radiation characteristics. The technique comprises two cascaded steps to govern the guided waves in the structure. The frst step is to correct the phase of felds and form a quasi-uniform distribution in the fare section so that the gain increases and sidelobe-level (SLL) decreases. This is obtained by loading the structure with a novel modulated metal-via lens. Field expansion on the radiating aperture of the SIW H-plane horn generates backward surface waves on both broad walls which increases the backlobe. In the second step, these backward surface waves are recycled and directed forward with the aid of holography theory. This is achieved by adding a couple of dielectric slabs with holographic-based patterns of metallic strips on both broad walls. With this step, the backlobe is reduced and the endfre gain is further increased. Using the proposed technique, the structure is designed and fabricated to operate at f = 30GHz which simultaneously improves the measured values of gain to 11.65 dBi, H-plane SLL to − 17.94 dB, and front-to-back ratio to 17.02 dB.

Ali Araghi, Mohsen Khalily, Pei Xiao, Fan Wang, Rahim Tafazolli (2022)Systematic Design of a Holographic-Based Metasurface Reflector in the Sub-6 GHz Band, In: IEEE antennas and wireless propagation letterspp. 1-5 IEEE

This letter presents a systematic method to regulating the response of an artificial impedance surface. The method is based on governing the dispersion diagram to control the depth of modulation so that a meaningful pattern of scatterers is obtained on the structure. The method is applied on a holographic-based large reflective metasurface to achieve a dual-beam radiation pattern with tilt angles of \pm 45^{\circ } in the azimuth plane at f=3.5 GHz. The structure is fabricated and the measured data concur with the simulation results.

Ali Araghi, Mohsen Khalily, Mahmood Safaei, Amirmasood Bagheri, Vikrant Singh, Fan Wang, Rahim Tafazolli (2022)Reconfigurable Intelligent Surface (RIS) in the Sub-6 GHz Band: Design, Implementation, and Real-world Demonstration, In: IEEE Access Institute of Electrical and Electronics Engineers (IEEE)

Here, we first aim to explain practical considerations to design and implement a reconfigurable intelligent surface (RIS) in the sub-6 GHz band and then, to demonstrate its real-world performance. The wave manipulation procedure is explored with a discussion on relevant electromagnetic (EM) concepts and backgrounds. Based on that, the RIS is designed and fabricated to operate at the center frequency of 3.5 GHz. The surface is composed of 2430 unit cells where the engineered reflecting response is obtained by governing the microscopic characteristics of the conductive patches printed on each unit cell. To achieve this goal, the patches are not only geometrically customized to properly reflect the local waves, but also are equipped with specific varactor diodes to be able to reconfigure their response when it is required. An equivalent circuit model is presented to analytically evaluate the unit cell’s performance with a method to measure the unit cell’s characteristics from the macroscopic response of the RIS. The patches are printed on six standard-size substrates which then placed together to make a relatively big aperture with approximate planar dimensions of 120 W 120 cm2. The manufactured RIS possesses a control unit with a custom-built system that can control the response of the reflecting surface by regulating the performance of the varactor diode on each printed patch across the structure. Furthermore, with an introduction of our test-bed system, the functionality of the developed RIS in an indoor real-world scenario is assessed. Finally, we showcase the capability of the RIS in hand to reconfigure itself in order to anomalously reflect the incoming EM waves toward the direction of interest in which a receiver could be experiencing poor coverage.

ALI ARAGHI, MOHSEN KHALILY, PEI XIAO, RAHIM TAFAZOLLI (2021)Holographic-Based Leaky-Wave Structures: Transformation of Guided Waves to Leaky Waves, In: IEEE microwave magazine22(6)pp. 49-63 Institute of Electrical and Electronics Engineers
Ali Araghi, Mohsen Khalily, Amirhossein Alizadeh Ghannad, Pei Xiao, Rahim Tafazolli (2019)Compact Dual Band Antenna for Off-Body-Centric Communications, In: Proceedings of the 13th European Conference on Antennas and Propagation (EuCAP 2019) European Association on Antennas and Propagation

A compact size, dual-band wearable antenna for off-body communication operating at the both 2.45 and 5.8 GHz industrial, scientific, and medical (ISM) band is presented. The antenna is a printed monopole on an FR4 substrate with a modified loaded ground plane to make the antenna profile compact. Antennas’ radiation characteristics have been optimized while the proposed antenna placed close to the human forearm. The fabricated antenna operating on the forearm has been measured to verify the simulation results.

ALI ALI, MOHSEN KHALILY, ALI ARAGHI, RAHIM TAFAZOLLI (2021)Polarization-Insensitive Circular Reflectarray for Satellite Applications in Ka-band

A polarization-insensitive circular reflectarray antenna (RA) for long-distance wireless communications is investigated. By combining patches, dipoles, and rings, a polarization-insensitive unit cell is achieved. With a phase variation of around 314 • between 30 GHz and 32 GHz, a circular reflectarray with a radius of 400 mm is built. Simulation results indicate a maximum realized gain of 27.6 dB at 30 GHz.

ALI ALI, MOHSEN KHALILY, ALI ARAGHI, Seyed Ehsan Hosseininejad, RAHIM TAFAZOLLI (2021)A Circular Reflectarray for OAM Generation at Terahertz Regime for 6G Applications

A circular reflectarray antenna (RA) for generating Orbital Angular Momentum (OAM) modes in the Terahertz (THz) band is introduced. An interlaced unit cell is proposed to reach a phase variation of 328 at 185 GHz to 188 GHz. Combining RA, OAM, and THz technologies in one structure can be utilized to reach the future requirements of 6G networks. That is due to the additional degree of freedom that OAM beams can provide for data multiplexing in short-distance wireless communication.