Azremi Abdullah Al-Hadi
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Preferred name
Azremi Abdullah Al-Hadi
Official Name
Azremi, Abdullah Al-Hadi
Alternative Name
Abdullah Al-Hadi, Azremi
Al-Hadi, Azremi A.
Al-Hadi, A. A.
Azremi, A. A. H.
Main Affiliation
Scopus Author ID
57194469675
Researcher ID
A-6983-2015

Research Output

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  • Publication
    Deployable Linear-to-Circular Polarizer Using PDMS Based on Unloaded and Loaded Circular FSS Arrays for Pico-Satellites
    ( 2019)
    Hidayath Mirza
    ;
    Toufiq Md Hossain
    ;
    Ping Jack Soh
    ;
    Mohd Faizal Jamlos
    ;
    Muhammad Nazrin Ramli
    ;
    Azremi Abdullah Al-Hadi
    ;
    Emad S. Hassan
    ;
    Sen Yan
    In this paper, flexible and deployable double-sided linear-to-circular polarizers designed on polydimethylsiloxane are proposed for the first time to the best of our knowledge. ShieldIt textile is used as the conducting element of the two designs based on two different unit cell arrays: a loaded circular patch unit cell or an unloaded circular patch unit cell, both backed by a generic rectangular element on its reverse side. This is in contrast to conventional frequency-selective structure-based linear-to-circular polarizers implemented using rigid substrates, which are multi-layered and requires inter-layer physical spacing. This complicates their implementation using flexible substrates and in a deployable format. Upon implementation of this double-sided polarizer, their final performances are evaluated in terms of the phase difference, conversion efficiency, 3-dB axial ratio (AR), and ellipticity bandwidth (from 40° to 45°). Measurements indicated good agreements with simulations, and both structures exhibited more than 90% of conversion efficiency from 2.34 to 3 GHz (for the loaded circular unit cell) and from 2.36 to 3 GHz (for the unloaded circular unit cell). In terms of ellipticity, a bandwidth of 8.67% is observed for the unloaded design and 13.82% for the loaded design. The unloaded structure exhibited a fractional 3-dB AR bandwidth of 36.36% (from 1.98 to 2.86 GHz) in simulations, and 32.64 % (from 2.00 to 2.78 GHz) when evaluated experimentally. Conversely, the loaded design showed only 12.58%. An equivalent circuit model is proposed and validated via a comparison between the circuit and full-wave simulations. Finally, the performances of these polarizers are also assessed under different bending conditions due to the use of flexible materials, prior to the proposal of a suitable deployment mechanism.
  • Publication
    A flexible wearable linear-to-circular polarizer for GNSS application
    (Institute of Electrical and Electronics Engineers (IEEE), 2020)
    Hidayath Mirza
    ;
    Ping Jack Soh
    ;
    Rais Ahmad Sheikh
    ;
    Azremi Abdullah Al-Hadi
    ;
    Toufiq M Hossain
    ;
    Sen Yan
    This paper presents a single-layered fabric-based flexible linear-to-circular polarizer for GNSS application operating at 1.575 GHz. The structure presented here is based on a square aperture with an E-shaped patch structure on the reverse side. The size of the structure is 0. 21λ0 ×0. 26λ0 × 0. 01λ0 The complete structure is flexible, and the frequency of operation is centered at 1.575 GHz, with a minimum value of the axial ratio achieved is 0.06 dB. The 3 dB axial ratio fractional bandwidth is 3.81% (1.54-1.60 GHz) and the conversion efficiency fractional bandwidth covering 90% is 5.09% (1.53 to 1.61 GHz).
  • Publication
    Design of a quad band CPW-fed compact flexible patch antenna for wearable applications
    (IEEE, 2020)
    Bashar Bahaa Qas Elias
    ;
    Ping Jack Soh
    ;
    Azremi Abdullah Al-Hadi
    ;
    Rahil Joshi
    ;
    Yuepei Li
    ;
    Symon K. Podilchak
  • Publication
    An ultrawideband full flexible 4 elements DGS based MIMO antenna for Sub-6 GHz wearable applications
    (IEEE, 2024-03)
    Bikash Chandra Sahoo
    ;
    Azremi Abdullah Al-Hadi
    ;
    Saidatul Norlyana Azemi
    ;
    Surentiran Padmanathan
    ;
    Sadia Afroz
    ;
    Wee Fwen Hoon
    ;
    Soh Ping Jack
    ;
    Che Muhammad Nor Che Isa
    ;
    Soumya Ranjan Mishra
    In this article, a compact wearable quad element MIMO antenna is presented operating at 4.5 GHz for 5G n77, n78, and n79 bands with the use of polyester substrate with a size of 80 × 82 × 0.4 mm3. Here T-shaped defected ground structure (DGS) technique has been utilized to improve the impedance bandwidth along with the reduction of the mutual coupling between the radiating elements. The antenna is evaluated in terms of reflection coefficient, gain, efficiency, and radiation pattern. The proposed MIMO antenna attained a maximum simulated gain of 4.3 dBi, and an efficiency of 96 % in the resonating band.
  • Publication
    Performance study of a MIMO mobile terminal with upto 18 elements operating in the sub-6 GHz 5G band with user hand
    (IEEE, 2020-01)
    Ahmed Mohamed Elshirkasi
    ;
    Azremi Abdullah Al-Hadi
    ;
    Ping Jack Soh
    ;
    Mohd Fais Mansor
    ;
    Rizwan Khan
    ;
    Xiaoming Chen
    ;
    Prayoot Akkaraekthalin
    This paper investigates the performance variation when a different number of antenna elements (AEs) is integrated onto a single MIMO mobile terminal, both in free space and when held in a user hand in data mode. Starting with a minimum of two AEs, this investigation assessed the performance of the MIMO terminal with every additional two AEs (up to 18 AEs) in terms of envelope correlation coefficient (ECC), efficiency, multiplexing efficiency, capacity and maximal ratio combining (MRC). The integrated MIMO antennas are identical and operate between 5 and 6 GHz for 5G applications. Results indicated that ECC increased with the number of AEs. However, ECC remains less than 0.32 for the case of 18 AEs in both free space and with a user hand. Meanwhile, the free space efficiency of about 90 % for the two AEs is observed to decrease with the increasing number of AEs to about 50 % with 18 AEs. However, the efficiency of elements changes with user hand depending on the level of interaction between each element and the hand. Direct blockage of AEs by the hand resulted in efficiencies of as low as 5 %, while at the same time, other AEs retained an efficiency of up to 75 %. At the center frequency of 5.5 GHz, the free space capacity is 11.1, 49.5 and 83.2 bit/s/Hz with two, ten and 18 AEs, respectively. However, the use of the mobile terminal in the proximity of the user hand degraded these levels by 11 % (two AEs), 35 % (10 AEs) and 31 % (18 AEs). Finally, multiplexing efficiency showed that capacity degradation is caused mainly by the degradation of AEs efficiency, whereas the impact of low correlation between AEs is found to be an insignificant factor. In addition to the capacity analysis, gain and diversity gain of the maximal ratio combining technique was also investigated.
  • Publication
    A triband wearable antenna for location tracking using cospas-sarsat and GNSS
    (IEEE, 2025)
    Rais Ahmad Sheikh
    ;
    Azremi Abdullah Al-Hadi
    ;
    Roy B. V. B. Simorangkir
    ;
    Thennarasan Sabapathy
    ;
    Rizwan Khan
    ;
    Prayoot Akkaraekthalin
    ;
    Surentiran Padmanathan
    ;
    Toufiq Md Hossain
    ;
    Che Muhammad Nor Che Isa
    ;
    Ping Jack Soh
    This paper presents the design of a tri-band antenna operating in the Cospas-Sarsat (C-S) and GPS/GNSS bands applicable for the Internet of Things (IoT). Implemented with flexible and robust materials, the antenna operates in three distinct frequencies: 406 MHz for C-S applications and 1227 MHz (L2) and 1575 MHz (L1) for GPS/GNSS applications. The measured 10-dB impedance bandwidth is from 1.517-1.587 MHz (in L1 band) and from 1.192-1.232 MHz (in L2 band). In C-S band, the measured 6-dB bandwidth is from 393 to 406.5 MHz. The 3 dB axial ratio (AR) bandwidth in the L1 and L2 bands are 17 MHz (1.08%) and 18 MHz (1.47%), respectively. The antenna demonstrates a measured gain of 1.61 dB at 406 MHz, exceeding the simulated gain of 0.573 dB, and features a beamwidth of 140°. The measured gains for the L2 and L1 bands closely align with the simulations, although a slight reduction in gain is observed for the L2 band. In the H-plane, zenith-directed main lobes produce measured gains of 1.61 dB for 406 MHz, 2.71 dB for L2, and 3.51 dB for L1. On the other hand, the measured efficiency for the antenna is 36.32% (in the C-S band), 54% (in L1 band) and 60.12% (in L2 band). Both measured and simulated results consistently showed good agreements in terms of gain, polarization, and efficiency. Moreover, the antenna design incorporates effective shielding against electromagnetic radiation, conforming to specific absorption rate (SAR) values of 0.046, 0.077, and 0.035 W/Kg in C-S, L1 and L2 bands respectively. Antenna integration into the life vest foam prior to placement on the human chest significantly influenced axial ratio variations. In the L1 band, the AR increased from 0.43 dB to 3.34 dB, while in the L2 band, it rose from 0.56 dB to 8.66 dB. This indicates a more pronounced effect on polarization characteristics at the lower frequency. Overall, the proposed tri-band antenna presents promising capabilities for location tracking applications, with potential for integration into wearable devices for enhanced safety and tracking functionalities.
  • Publication
    Gain Optimization of Low-Profile Textile Antennas Using CMA and Active Mode Subtraction Method
    ( 2021)
    Bashar Bahaa Qas Elias
    ;
    Ping Jack Soh
    ;
    Azremi Abdullah Al-Hadi
    ;
    Prayoot Akkaraekthalin
    This paper presents an active mode subtraction method based on the characteristic mode analysis to estimate the forward directivity based on the difference in modal significance curves. This made the optimization of the antenna gain in the design process to be more efficient. To the best of the authors' knowledge, such method is innovative and proposed in literature for the first time. This method is derived on the basis that the total radiated field of the antenna, and consequently, the directivity is mainly contributed by the excited dominant modes. To demonstrate its effectiveness, three compact, planar, and wearable antennas with increasing complexity will be designed and optimized using this method. The first is a conventional circular patch antenna operating at 5.3 GHz, whereas the second one is a planar loop antenna operating at 3.08 GHz. The third design is a crown-shaped planar antenna (CPA) with a 3 × 3 artificial magnetic conductor (AMC) plane integrated underneath to reduce potential coupling effects from the body. All three antennas are made fully using textiles with the same thicknesses: felt fabric as its substrate and ShieldIt Super as its conductive textile. For all designs, the use of the proposed method, which is validated using the method of moments, has predicted the maximum direction of radiation and its respective gain at the desired frequencies with good accuracy. Besides that, the design of the AMC plane for the CPA is also optimized using CMA prior to the integration with the antenna and a leather wrist strap. Measurements of the final crown-shaped antenna design indicated a good agreement with simulations, with an operating bandwidth of more than 240 MHz, FBR of 15.73 dB and a directional radiation pattern outward from the body.
      3  26
  • Publication
    A 3.5 GHz wearable antipodal vivaldi antenna for 5G applications
    (IEEE, 2024-01)
    Sadia Afroz
    ;
    Azremi Abdullah Al-Hadi
    ;
    Surentiran Padmanathan
    ;
    Saidatul Norlyana Azemi
    ;
    Wee Fwen Hoon
    ;
    Bikash Chandra Sahoo
    ;
    Yen San Loh
    ;
    Che Muhammad Nor Che Isa
    ;
    Lun Hao Tung
    ;
    Lai Ming Lim
    ;
    Zambri Samsudin
    ;
    Idris Mansor
    ;
    Soh Ping Jack
    This paper represents a wideband wearable antenna for 5G applications. In this proposed design, an antipodal vivaldi antenna structure is implemented on a polyimide and polyester combined substrate. The 120 × 95 × 0.82 mm3 sized antenna acquired a wide bandwidth of 910 MHz with a realized gain of 5.42 dBi and efficiency of 96 percent.
      10  2
  • Publication
    A study and investigation of small antenna efficiency measurement using reverberation chamber
    ( 2006)
    Azremi Abdullah Al-Hadi
    ;
    Soh Ping Jack
    ;
    Anuar Mat Safar
    Numbers of small antennas were designed and various kind of antennas were tested for measurement. Amplitude fluctuations in signals received over mobile radio channels are typically modeled by Rayleigh distribution. The field statistics in the volume of the enclosure are shown to correspond to the Rayleigh statistics found in properly functioning reverbration chambers when a sufficiently large number of modes are excited. The purpose of this paper is to show that the antenna efficiency can be measured accurately in much faster, easier and cost effectively reverberation chamber using three different antennas (two monopole antennas with attenuator and surface mount resistor, and modified folded monopole patch antenna). It also gives an investigation of the statistical characteristics in Rayleigh communications channels by using reverberation chamber. Scattering parameters taken from the measurement of the antenna radiation efficiency using reverberation chamber is implemented into Rayleigh Probability Density Function (PDF) model and it really shows that they are in good agreement with those of theoritically predicted Rayleigh model.
      17  23
  • Publication
    Compact Multiband Reconfigurable MIMO Antenna for Sub- 6GHz 5G Mobile Terminal
    ( 2022-01-01)
    Padmanathan S.
    ;
    Azremi Abdullah Al-Hadi
    ;
    Elshirkasi A.M.
    ;
    Al-Bawri S.S.
    ;
    Islam M.T.
    ;
    Sabapathy T.
    ;
    Jusoh M.
    ;
    Akkaraekthalin P.
    ;
    Soh P.J.
    In this paper, the design of a multiband multiple-input multiple-output (MIMO) antenna with frequency and radiation pattern reconfiguration capability in the 5G sub-6 GHz band is presented. Frequency and radiation pattern reconfiguration are enabled on the antenna consisting of two planar inverted-F antenna (PIFA) elements using PIN diodes and DC biasing circuits. At the reflection coefficients of less than -6 dB, both PIFA element 1 and PIFA element 2 achieves triband with bandwidth from 220 MHz to 2330 MHz, ranging from 0.8 GHz to 6 GHz, covering cellular bands for GSM, UMTS, LTE and 5G-NR bands. Moreover, high isolation of at least -10 dB and envelope correlation coefficient with less than 0.3 between ports ensures satisfactory MIMO diversity performance. PIFA elements 1 and 2 have achieved main lobe gain ranging from 1.06 dB to 2.97 dB at their respective resonant frequencies with total efficiencies ranging from 46.2% to 74.5% achieved within the operating bandwidth. This enables a calculated channel capacity of 9.45 to 10.5 bit/s/Hz for PIFA element 1 and 9.56 to 10.23 bit/s/Hz for PIFA element 2, respectively. The percentage of channel capacity achieved over IID capacity for both PIFA elements ranges from 73.71% to 92.8%. Simulated antenna performance parameters agreed well with measurements, and potentially enables reliable and consistent data throughput for 5G mobile terminals.
      3  34