Muhammad Yusof Ismail | Universiti Tun Hussein Onn Malaysia (original) (raw)

Papers by Muhammad Yusof Ismail

The demand for low cost and less weight antenna with compact broadband features in communication ... more The demand for low cost and less weight antenna with compact broadband features in communication system is rapidly increasing. In this work, the possibility of employing dual gap on square patch reflectarray antenna for bandwidth improvement is presented. The introduction of dual gap attached on square patch is shown to improve the bandwidth performance from 315 MHz to 397 MHz.

Reconfigurable reflectarray antenna is one of the options proposed in this work that can be used ... more Reconfigurable reflectarray antenna is one of the options proposed in this work that can be used as an active antenna in order to allow the change in the frequency of operation and hence, the dynamic phase control of resonant elements. The capability of realizing frequency tuning using slots embedded into patch elements is presented. In this study, the change in resonant frequency and phase distribution has been investigated using frequency tuning strategy within X-band frequency range. This further enhances the feasibility of reflectarray antenna of realizing electronic beam scanning. The results obtained from commercially available CST computer model demonstrate that the energy reflected with a minimum simulated reflection loss of -0.6233 dB Moreover, the maximum attainable phase range of 4.922 rad allows the beam to be scanned up to an angle of 26 degrees. Analysis of the frequency tuning capability of resonant elements using CST computer software will be integrated with measurement using waveguide simulator to show the reliability of the change in frequency and phase distribution.

This paper presents a simple and effective technique for the scattering parameter measurements of... more This paper presents a simple and effective technique for the scattering parameter measurements of infinite tunable reflectarrays in X-band frequency range. Tunable reflectarrays have been designed by using different types of slot configurations embedded in the patch elements. The scattering parameter measurements have been carried out using waveguide simulator technique and the measured results are found out to be in close agreement with the analysis carried out using Finite Element Method (FEM) and Finite Integral Method (FIM) techniques. A maximum change of 17% (10GHz to 8.3GHz) in the resonant frequency has been demonstrated by using rectangular and circular slots. Furthermore the achievable dynamic phase range of 314° demonstrates a feasibility of employing the proposed slot configurations for the design of active tunable reflectarray antennas.

This paper presents a thorough investigation of the effects of substrate thickness on the perform... more This paper presents a thorough investigation of the effects of substrate thickness on the performance of infinite reflectarrays. The reflectarrays designed in the X-band frequency range are investigated in terms of electric field intensity, reflection loss and reflection phase performance. It has been demonstrated that the electric field intensity decreases from 3.42e5V/m to 2.34e5V/m as the thickness of the substrate is increased from 0.2mm to 2.0mm. The measured reflection loss has been shown to decrease from 15dB to 2.25dB as the substrate thickness is changed from 0.127mm to 0.381mm. Furthermore the effect of substrate thickness on the reflection phase performance has also been demonstrated by waveguide scattering parameter measurements.

There has been much interest recently in developing reconfigurable reflectarray antenna for tunab... more There has been much interest recently in developing reconfigurable reflectarray antenna for tunable microwave applications. Liquid crystal (LC) has been given much attention due to its dielectric anisotropy property which allows the change in the frequency and hence the reflection phase. In this paper, the phase agility of the periodic array using K15 nematic liquid crystal as the dielectric permittivity is presented. Numerical and experimental results at X-band are used to compare the plane wave scattering parameter from a two patch reflectarray cell of 500 µm. A tunable dynamic phase range of 221° is achieved over a broad band of 170 MHz which also gives a tunability of 0.39.

In this paper we demonstrate that the anisotropic property of liquid crystal can be exploited to ... more In this paper we demonstrate that the anisotropic property of liquid crystal can be exploited to control the phase of signals that are reflected from a reflectarray cell. Numerical and measured results at X-band are used to compare the plane wave scattering from two reflectarray cells which are constructed on liquid crystal film of thickness 200 mum and 500 mum.

Iet Microwaves Antennas & Propagation, 2007

Experimental results at X-band are used to compare the electromagnetic scattering from a printed ... more Experimental results at X-band are used to compare the electromagnetic scattering from a printed reflectarray cell, which is constructed on 500 mm thick layers of three different nematic state liquid crystals. It is shown that a small voltage can be used to vary the permittivity of the tunable substrate and thereby control the phase of the reflected signals. Numerical results using Ansoft HFSS are compared with the measured phase, resonant frequencies and signal attenuation for two orientations of the liquid crystal molecules. Data fitting is employed to quantify the loss tangent and the permittivity values of the three anisotropic specimens. The performance trade-offs that are imposed by the use of commercially available materials are discussed, and the computer model is used to specify the electrical properties of a liquid crystal mixture, which can provide a signal loss of ,1 dB and a dynamic phase range of 3008 from the patch elements at 10 GHz.

Electronically steerable antenna systems are required for many applications including communicati... more Electronically steerable antenna systems are required for many applications including communication systems and radar. Normally these employ diode phase shifters to create the required aperture distribution. In this paper we show how the anisotropy property of liquid crystal (LC) material can be exploited to provide an integrated phase shifter for a printed patch antenna such as a reflectarray (N. Misran et al., 2003). This offers a simpler alternative to semiconductor devices and has the potential to overcome the limitations of existing phase shifter technology in the millimeter and submillimeter wave bands. In this paper we demonstrate the relationship between the LC thickness and the attainable phase range for a patch element in which the change in LC permittivity can be obtained by applying a dc voltage between the patch conductor and the ground plane. Simulations for different LC substrate thicknesses were carried out using the transmission line model (TLM) MICROSTRIPES and the finite element model (FEM) Ansoft HFSS. Measurements the scattering parameters of a 200 μm and a 500 μm thick patch reflectarray have been performed using waveguide simulator technique to demonstrate the validity of the predictions.

In this proof of concept study we employ numerical and measured results at X- band to demonstrate... more In this proof of concept study we employ numerical and measured results at X- band to demonstrate that the dielectric anisotropy of nematic state liquid crystal can be exploited to produce electronically controlled phase shifters for printed reflectarray antennas. Phase agility is realized by inserting a layer of liquid crystal in the region between the resonant patch array and the conductive ground plane. Applying a low frequency biasing voltage produces a small change in the permittivity of the substrate and this is shown to create a large shift in the phase of the reflected signal. Ansoft HFSS version 10.0 is employed to study the scattering behaviour of the array elements in the range 9Â¿11 GHz using the dielectric properties of commercially available liquid crystals. The simulated phase range, bandwidth and reflection loss are shown to be in close agreement with measurements that were obtained from a waveguide simulator. The most significant impact of this new active control strategy is in the mm and sub-mm wave band and therefore a technique is proposed for characterising the electrical performance of liquid crystals at these frequencies. This paper summarises the progress that has been made in the first stage of a collaborative academic/industrial project to investigate the feasibility of creating high frequency beam scanning reflectarray antennas for future space science instruments.

Electronics Letters, 2007

... 1403– 141 3 Martin, N., Laurent, P., Christian, P., Gelin, P., and Huret, F.: &#x27;P... more ... 1403– 141 3 Martin, N., Laurent, P., Christian, P., Gelin, P., and Huret, F.: &#x27;Patch antenna adjustable ... 299–702 4 Hu, W., Ismail, MY, Cahill, R., Gamble, HS, Dickie, R., Fusco, VF, Linton ... 509–511 5 http://www.liquidcrystals.merck.de accessed April 2007 6 Moessinger, A., Marin, R ...

Electronics Letters, 2006

ABSTRACT Numerical and measured results are employed at X-band to demonstrate that the electrical... more ABSTRACT Numerical and measured results are employed at X-band to demonstrate that the electrical properties of nematic state liquid crystal can be exploited to produce phase shifters for beam scanning printed reflectarray antennas with a tunable range greater than 180°.

Space Science and …, Jan 1, 2011

Abstract This paper presents an investigation of bandwidth enhancement of a concentric split ring... more Abstract This paper presents an investigation of bandwidth enhancement of a concentric split ring square reflectarray element in terms of phase and return loss versus frequency graph performance. The performance of element&amp;amp;#x27;s phase response is then to be ...

ijeei.org

Lumped components are used to represent the reflectarrays designed using different commercially a... more Lumped components are used to represent the reflectarrays designed using different commercially available materials. The loss performance and the effect of material properties on the reflectarray antennas are discussed in terms of the lumped components which are used in the equivalent circuit analysis. The bandwidth performance of reflectarrays designed with different materials is discussed using reflection loss and reflection phase plots obtained by equivalent circuit analysis. Furthermore the results obtained by equivalent circuit modeling are compared with the results obtained using CST Microwave Studio simulations and a close agreement between all the results has been demonstrated. The dielectric permittivity (ε r ) of materials investigated in this work ranges between 2.08 to 13 and the loss tangent (tanδ) values vary from 0.0003 to 0.025 while the reflection loss values obtained by equivalent circuit analysis varied from 0.179 dB to 6.875 dB and a variation in 10% and 20 % bandwidth is observed from 84 MHz to 360 MHZ and 126 MHZ to 540 MHz respectively based on the respective material properties.

… Engineering (ICICI-BME …, Jan 1, 2011

Abstract A novel element is developed in this research namely single square element for a reflect... more Abstract A novel element is developed in this research namely single square element for a reflectarray antenna. This element is modified by using a square hole instead of circle hole for a conventional ring element shape. A series of physical size element is investigated ...

… , 2007. APMC 2007. …, Jan 1, 2007

Applied Physics …, Jan 1, 2010

Concrete is basic construction material used for numerous sort of structure. However, in the main... more Concrete is basic construction material used for numerous sort of structure. However, in the mainstream crucial structures have to be designed as self-protective such as nuclear plants, Power plants, Weapon Industries, weapons storage places, water retaining structures like dams, & etc., which provides protection against any tragedy incident or intentionally produced horrible incidents such as dynamic loading, incident occurs in nuclear plants, terrorist attack, war, missile attack, and etc. This paper questioningly is paying concentration on judgment on minimum required kinetic energy for scabbing on the concrete structures generated by flat nosed hard missile using curve fitting empirical study. Argue overcome from this newly developed empirical formula can be used for making design recommendations and design procedures for determining the dynamic reaction of the target to frustrate scabbing.

Abstract Reflectarray antennas provide a low cost, low volume and low profile way for different t... more Abstract Reflectarray antennas provide a low cost, low volume and low profile way for different type of applications but due to limited phase ranges and high reflection loss performance their use is limited in the field of satellite and earth observatory systems. In ...

Space Science and …, Jan 1, 2009

Abstract An analysis of phase variation and phase range of concentric split ring square element ... more Abstract An analysis of phase variation and phase range of concentric split ring square element for broadband reflectarray antenna is presented in this paper. This element is the combination of a single square element and a ring element where the square element is the ...