Haider R. Khaleel

A Compact Polyimide-Based UWB Antenna for Flexible Electronics

In this letter, we present a compact ultrawideband (UWB) antenna printed on a 50.8-μm Kapton polyimide substrate. The antenna is fed by a linearly tapered coplanar waveguide (CPW) that provides smooth transitional impedance for improved matching. The proposed design is tuned to cover the 2.2-14.3-GHz frequency range that encompasses both the 2.45-GHz Industrial, Scientific, Medical (ISM) band and the standard 3.1-10.6-GHz UWB band. Furthermore, the antenna is compared to a conventional CPW-fed antenna to demonstrate the significance of the proposed design. A parametric study is first performed on the feed of the proposed design to achieve the desired impedance matching. Next, a prototype is fabricated; measurement results show good agreement with the simulated model. Moreover, the antenna demonstrates a very low susceptibility to performance degradation due to bending effects in terms of impedance matching and far-field radiation patterns, which makes it suitable for integration within modern flexible electronic devices.

Compact Polyimide-Based Antennas for Flexible Displays

In this paper, we present two compact ultra thin and flexible printed monopole antennas intended for integration with flexible displays, such as flexible organic light-emission displays (FOLEDs) and active matrix electro-phoretic displays (AM-EPDs). The proposed antennas are designed to provide Wireless local area network (WLAN) and Bluetooth connectivity for flexible displays. The first design is a dual band antenna operating at 2.45 GHz and 5.2 GHz while the second is a single band antenna operating at 2.4 GHz. Both antennas were printed on a Kapton polyimide-based substrate with dimensions (35 mm×25 mm) and (26.5 mm×25 mm) for the dual and single band respectively. Antenna properties, such as gain, far-field radiation patterns, scattering parameter S11 are provided. Moreover, the effect of folding/bending was performed experimentally on both designs to study its influence on the antennas performance. The proposed compact, thin and flexible designs along with antennas characteristics are perfectly suitable for integration into flexible displays for WLAN and Bluetooth connectivity.

Wearable Yagi microstrip antenna for telemedicine applications

This paper presents a button shaped antenna based on a microstrip Yagi array. The proposed antenna is suitable for Wireless Body Area Network (WBAN) and telemedicine applications operating at 2.45 GHz. Antenna properties, such as far-field radiation patterns, coupling coefficient, measured by the scattering parameter S11, and gain are provided. Moreover, the simulated performance of the proposed antenna is compared to circular and rectangular patch button shaped antennas having similar sizes. Design and simulations are performed using CST Microwave Studio software which is based on the Finite Integration Technique (FIT). The proposed antenna achieved a gain of 6.7 dB, (F/B) ratio of 11.7 dB and a semi-directional radiation pattern required for on body and off body applications.

Flexible printed monopole antennas for WLAN applications

In this paper, we present two thin/flexible printed monopole antennas for Wireless Local Area Network (WLAN) applications. The first design is a single band antenna which operates at 2.4 GHz while the second one is a dual band antenna operates at 2.5 GHz and 5.2 GHz. The dimensions of the proposed antennas are: (26.5 mm × 25) and (35 mm × 25) mm for the single band and dual band respectively. Antenna properties, such as gain, far-field radiation patterns, coupling coefficient, expressed in terms of the scattering parameter S11 are provided. Design and simulations are performed using CST Microwave Studio software which is based on the Finite Integration Technique (FIT). Moreover, the effect of folding the antenna was performed experimentally on both designs to study its influence on the antenna performance. The achieved gain for the single band antenna is 1.8 dB with a measured bandwidth of 270 MHz. The dual band antenna achieved a gain of 1.8 dB and 4 dB at 2.5 GHz and 5.2 GHz respectively, and measured bandwidths of 305 MHz and 480 MHz at the first and second band respectively. The proposed thin and flexible designs along with antennas characteristics are suitable for integration into flexible technologies for WLAN applications.

Mutual coupling reduction of dual-band printed monopoles using MNG metamaterial

In this paper, a μ-Negative metamaterial (MNG) is utilized for mutual coupling reduction between dual-band printed monopole antennas used in Multiple Input Multiple Output (MIMO). A dual-band MNG metamaterial is designed to specifically possess negative effective permeability at the two resonant frequencies where the antennas are operating. MNG is inserted between the two printed monopoles (back to back) to decrease the correlation between them. The printed monopole antennas were designed to operate in the Wireless Local Area Network (WLAN) bands 2.45 GHz and 5.2 GHz. Antenna characteristics such as, scattering parameters far-field radiation patterns with and without the presence of MNG are provided. The design of the MNG unit cell and its effective constitutive parameters are also provided. Design and simulations are conducted using Ansofts HFSS software which is based on the Finite Element Method (FEM). The proposed technique achieved a 14 dB reduction in mutual coupling at 2.45 GHz and 13 dB at 5.2 GHz. A gain of 2 dB higher than the normal case at the second band is observed while it is maintained the same on the first band. Furthermore, the MNG based antenna system maintains a relatively low profile (16 mm) which is convenient for compact systems and hand-held devices.

Printed Yagi-Uda array for MIMO systems

In this paper, A Yagi-Uda antenna array consisting of four radiating elements is presented. The array elements are oriented back to back in a cross fashion to achieve a pattern orthogonality utilizing the end-fire radiation characteristics of the Yagi-Uda antennas. This technique is proposed to reduce the mutual coupling between the radiating elements which is essential to the performance of Multiple Input Multiple Output (MIMO) systems. Design and simulations are conducted using CST Microwave Studio which is based on the Finite Integration Technique (FIT). Results show that the correlation level is below -35 dB between the array elements at 5.2 GHz with about λ/4 separation distance.

A systematic approach for the design, fabrication, and testing of microstrip antennas using inkjet printing technology

We present a systematic approach for producing microstrip antennas using the state-of-the-art-inkjet printing technique. An initial antenna design based on the conventional square patch geometry is adopted as a benchmark to characterize the entire approach; the procedure then could be generalized to different antenna geometries and feeding techniques. For validation purposes, the antenna is designed and simulated using two different 3D full-wave electromagnetic simulation tools: Ansofts High Frequency Structure Simulator (HFSS), which is based on the Finite Element Method (FEM), and CST Microwave Studio, which is based on the Finite Integration Technique (FIT). The systematic approach for the fabrication process includes the optimal number of printed layers, curing temperature, and curing time. These essential parameters need to be optimized to achieve the highest electrical conductivity, trace continuity, and structural robustness. The antenna is fabricated using Inkjet Printing Technology (IJPT) utilizing Sliver Nanoparticles (SNPs) conductive ink printed by DMP-2800 Dimatix FujiFilm materials printer.

Miniaturized microstrip antenna array with ultra mutual coupling reduction for wearable MIMO systems

In this paper, a miniaturized microstrip antenna array with two patches is proposed for wearable MIMO systems. The array is designed to resonate at 4.2 GHz and 8.1 GHz for biomedical micro-sensing technology and biomedical diagnostics applications, respectively. In this paper, the use of a diagonal slot on the microstrip patch to reflect the surface current in a direction opposite to that of the neighboring patch. Moreover, the common area of the ground plane, between the two antennas, is augmented with Uniform Compact-Photonic Band Gap (UC-PBG) structures to prevent surface waves. This approach reduces the mutual coupling to −17 dB within a separation distance of 1.4 mm ≈ λ<inf>o</inf>/51, where λ<inf>o</inf> is the wavelength at 4.2 GHz. The microstrip antenna patch is consistent of rectangular part slotted with a diagonal trace and a meander trace which reduces the electrical size of the microstrip patch, when it is printed on substrate of ε<inf>r</inf> = 3.5, to λ<inf>o</inf>/18 × λ<inf>o</inf>/5. The maximum linear dimension of the antenna array is λ<inf>o</inf>/7.2 × λ<inf>o</inf>/4.3 × λ<inf>o</inf>/137. The performance of the array is characterized in terms of S-parameters, broadband gain and correlation spectra as well as the radiation patterns. The proposed antenna array provides bore-sight gain of −15.1 dBi at 4.2 GHz and −7.5 dBi at 8.1 GHz of 54.2 MHz and 81.8 MHz, respectively. The numerical model of the proposed array is simulated based on the Finite Integration Technique (FIT) using the Transient Domain (TD) solver of CST Microwave Studio.

Theoretical and Numerical Approaches for Determining the Reflection and Transmission Coefficients of OPEFB-PCL Composites at X-Band Frequencies

Bio-composites of oil palm empty fruit bunch (OPEFB) fibres and polycaprolactones (PCL) with a thickness of 1 mm were prepared and characterized. The composites produced from these materials are low in density, inexpensive, environmentally friendly, and possess good dielectric characteristics. The magnitudes of the reflection and transmission coefficients of OPEFB fibre-reinforced PCL composites with different percentages of filler were measured using a rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in the X-band frequency range. In contrast to the effective medium theory, which states that polymer-based composites with a high dielectric constant can be obtained by doping a filler with a high dielectric constant into a host material with a low dielectric constant, this paper demonstrates that the use of a low filler percentage (12.2%OPEFB) and a high matrix percentage (87.8%PCL) provides excellent results for the dielectric constant and loss factor, whereas 63.8% filler material with 36.2% host material results in lower values for both the dielectric constant and loss factor. The open-ended probe technique (OEC), connected with the Agilent vector network analyzer (VNA), is used to determine the dielectric properties of the materials under investigation. The comparative approach indicates that the mean relative error of FEM is smaller than that of NRW in terms of the corresponding S21 magnitude. The present calculation of the matrix/filler percentages endorses the exact amounts of substrate utilized in various physics applications.

Flexible CPW-IFA antenna array with reduced mutual coupling

In this paper, a flexible and extremely low profile CPW fed Inverted F Antenna (IFA) array is presented. The array consists of two radiating elements which are separated by λ/125 yet exhibit a low mutual coupling (-27dB). This is achieved by creating pattern diversity through defecting the ground plane and adding a parasitic structure. This technique is proposed to reduce the mutual coupling between the array elements which is essential to the performance of Multiple Input Multiple Output (MIMO) systems. Design and simulations are carried out using CST Microwave Studio which is based on the Finite Integration Technique (FIT). Results show that the proposed design is a reasonable candidate for flexible and wearable wireless systems.