# Choy Yoong Tham's research while affiliated with Wawasan Open University and other places

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## Publications (39)

The latest generation of Cassegrain radio astronomy antennas is designed for multiple frequency bands with receivers for individual bands offset from the antenna axis. The offset feed arrangement typically has two focusing elements in the form of ellipsoidal mirrors in the optical path between the feed horn and the antenna focus. This arrangement a...

p class="BodyTextKeep"> We present an analysis on the performance of the Cassegrain and Gregorian on-axis, off-axis and offset antennas. In our study, we have adopted the design parameters for the Cassegrain configuration used in the Atacama Large Millimeter Array (ALMA) project. Modifications on the original parameters are made so as to meet the d...

In this chapter, the characteristics of the propagation of waves in superconducting waveguides are investigated. To compute the propagation constant, the complex conductivity of the superconductor is incorporated into the set of characteristic equations which describes the propagation constant of waves in the waveguide. An important outcome from th...

The open educational resources (OER) movement has gained momentum in the past few years. With this new drive towards making knowledge open and accessible, a large number of OER repositories have been established and made available online throughout the world. However, the inability of existing search engines such as Google, Yahoo!, and Bing to effe...

We present an analysis on the performance of wave coupling from a
rectangular waveguide to a probe. In order to enable maximum coupling of
fields to the probe, we have carefully computed and designed the
appropriate height and position of the probe. Comparisons and analysis
of the efficiency of wave coupling using coaxial-line and microstrip
probes...

The Open Educational Resources (OER) movement has gained momentum in the past few years. With this new drive towards making knowledge open and accessible, a large number of OER repositories have been established and made available online throughout the globe. However, despite the fact that these repositories hold a large number of high quality mate...

As an open and distance learning (ODL) institution, Wawasan Open University (WOU) employs a blended approach for delivering courses to its undergraduate and postgraduate students, who are entirely adult learners. In this approach, the use of a learning management system (LMS) is absolutely crucial for student support as well as the enhancement of t...

Open educational resources (OER) are a global phenomenon that is fast gaining credibility in many academic circles as a possible solution for bridging the knowledge divide. With increased funding and advocacy from governmental and nongovernmental organisations paired with generous philanthropy, many OER repositories, which host a vast array of re-s...

Being an Open Distance Learning (ODL) institution, Wawasan Open University (WOU) employs a
blended approach for delivering courses to its undergraduate and postgraduate students who are
entirely adult learners. In this approach, the use of a Learning Management System (LMS) is
absolutely crucial for student support as well as the enhancement of the...

We present a novel and accurate approach to compute the loss of electromagnetic waves propagating in a Microstrip line. A set of transcendental equation is derived by matching the tangential fields with the surface impedance at the dielectric-air and dielectric-conductor interfaces. The propagation constant is obtained by numerically solving for th...

Hence, in using phasor representation in equations relating field quantities, the partial derivatives with respect to t and z may be replaced by products with jω and jkz, respectively; the common factor exp[j(ωt + kzz)] can be dropped. Here, the propagation constant kz is a complex variable, which consists of a phase constant βz and an attenuation...

We present an accurate approach to compute the attenuation of waves, propagating in circular waveguides with lossy and superconducting walls. A set of transcendental equation is developed by matching the fields at the surface of the wall with the electrical properties of the wall material. The propagation constant kz is found by numerically solving...

We present a full wave analysis to compute the propagation constant of electromagnetic waves traveling in a normal and superconducting microstrip transmission line. The transverse wavenumber in the dielectric substrate is obtained as the root of a set of transcendental equation, derived by matching the tangential fields at the dielectric-conductor...

We present a fundamental and accurate approach to compute the attenuation of electromagnetic waves propagating in a rectangular waveguide with imperfect conducting walls. The wavenumbers in the x and y directions, i.e. k<sub>x</sub> and k<sub>y</sub>, respectively, are first computed as roots of the transcendental equations developed by matching th...

We present a simple technique to compute the attenuation of electromagnetic waves propagating in waveguides with imperfect conducting walls. The propagation constant can be computed by numerically solving the transcendental equations, derived from the surface impedance of the walls and substituting the results into the dispersion relation. Good agr...

This paper presents a full-wave analysis on the wave propagating in a superconducting stripline with a large width-to-separation ratio. A set of transcendental equation is derived, by matching the ratio of the tangential electric and magnetic fields, respectively, with the surface impedance of the strip. The propagation constant can be obtained by...

Time domain energy measures associated with the currents and charges induced on the elements of multiple straight parallel wires located horizontally above dielectric medium are calculated. The mathematical model is based on a set of coupled space-time Hallen integral equations for halfspace problems. Currents and charges along the wires are obtain...

The ALMA telescope will be an interferometer of 64 antennas, which will be situated in the Atacama desert in Chile. Each antenna will have receivers that cover the frequencies 30 GHz to 970 GHZ. This frequency range is divided into 10 frequency bands. All of these receiver bands are fitted on a cartridge and cooled, with bands 1 and 2 at 15K and th...

The ALMA telescope will be an interferometer of 64 antennas, which will be situated in the Atacama desert in Chile. Each antenna will have receivers that cover the frequencies 30 GHz to 970 GHZ. This frequency range is divided into 10 frequency bands. All of these receiver bands are fitted on a cartridge and cooled, with bands 1 and 2 at 15K and th...

The transient behavior of thin wires with nonlinear resistive load in the presence of a dielectric half-space is analyzed directly in the time domain. The nonlinear wire problem is formulated by the space-time Hallen integral equation. The effect of a two-media configuration is taken into account via the space-time reflection coefficient appearing...

A root-mean-square (rms) measure of effect of nonlinear loading on the transient response of thin wires is proposed. The transient behavior of nonlinearly loaded wires is analyzed directly in the time domain. The problem is formulated via the space-time Hallen integral equation. The equation is solved by the space-time Galerkin Bubnov boundary elem...

Analysis of the human body exposed to low frequency and high frequency electromagnetic fields is presented in this work. The formulation of the problem is based on a simplified thick wire model of the human body. The current distribution induced in the body is determined by solving the Pocklington integral equation for a straight thick wire via the...

The feasibility of making single-chip, superconducting detectors for submillimetre-wave astronomical inteferometry is demonstrated. An experimental device based on back-to-back corrugated horns, and back-to-back finline transitions, was fabricated. The detector was illuminated at 350 GHz, using a coherent laboratory source, and 0.6° fringes were me...

We present results from an interferometer using a single chip, beam com- bining, superconducting detector. The interferometer consists of back to back corrugated horns feeding a back to back finline transition. The beams are combined in microstrip using a directional coupler. The detector was illumi- nated by a coherent source in the far field at f...

We describe a methodology that makes the computational intensive boundary element method/the method of moments feasible for analysing transients on PCBs. The methodology uses a combination of three modelling techniques to reduce the computational demand as well as to overcome the numerical difficulty due to the electrically small dimensions at low...

We present rigorous analysis qf guided propagation in cylindrical waveguides with finite conductivity and superconducting walls. Our calculations are based on a method by Stratton which solves Maxwell's equations in cylindrical coordinates. The transcendental equation gives the complex propagation constant as a function of frequency, geometry and c...

Thin-wire antenna model of the human body exposed to the transient excitation is presented in the paper. The analysis is based on the solution of the corresponding integral equation and it is carried out directly in the time domain (TD) . The integral equation is handled via the TD Galerkin-Bubnov scheme of the boundary element method. Numerical re...

We describe a procedure for modeling the optical behaviour of planar, bolometric imaging arrays. Arrays of this kind are being developed for the next generation of ground-based and space-borne, submillimetre-wave and far-infrared, astronomical telescopes. A unique feature of the scheme is that the partially coherent vector fields associated with th...

The transient analysis of wires having a nonlinear load in the presence of a half-space is carried out directly in the time domain. The nonlinear wire problem is formulated by the time domain Hallen integral equation. The effect of a two-media configuration is taken into account via the reflection coefficient appearing within the integral equation...

The transient response of a structure may be obtained directly by solving a problem in the time domain. However, there are certain advantages in obtaining the time-domain waveform from frequency-domain data. Taking samples to characterize the frequency spectrum of a resonant structure with no prior knowledge of its behavior, poses difficulty. There...

We outline a procedure for modelling the behavior of partially-coherent long-wavelength optical systems. The procedure is of considerable importance to microwave background astronomy, where sequences of high-throughput optical components are often used. In the paper, we give a symbolic description of the basic method, and illustrate its use by calc...

Measures of the time-domain energy associated with the current and
charge on thin wires, located over a conductive halfspace, are
evaluated. The solution is obtained from a time-domain version of the
Hallen integral equation, solved by a time-marching procedure. The
energy measures involve spatially integrating the square of the current
and charge...

The main difficulty in modelling transients via the frequency domain in highly resonant structures is to extract the complete
information from its frequency response spectrum. The selection of suitable values for the number of samples and the frequency
resolution determines the accuracy of the result. However, neither of these parameters are known...

This paper describes a technique that makes the computational
intensive moment method (MM) competitive for analyzing transients on
PCBs. The technique uses equivalent wires to model the conducting tracks
at low frequencies, 2-D sheet impedance approximation for the dielectric
substrate and dynamic adaptive sampling to obtain the frequency spectrum

Transient behaviour of two coupled wires immersed in a two-media
configuration is analysed. The active wire is excited by a
time-dependent voltage source. As the wires are identical, the symmetry
of the configuration is exploited, and two coupled wires are considered
as two single-wire problems. Each mode is represented by the
corresponding space-t...

We present a simple and fundamental technique to compute the attenuation of electromagnetic waves propagating in lossy rectangular waveguides with imperfectly conducting wall. A set of transecendental equations is derived by matching the tangential electric and magnetic fields at the surface of the wall with the constitutive properties of the wall...

## Citations

... The main-reflector of THz wave Cassegrain antenna is a rotating paraboloid, and the sub-reflector is a rotating hyperboloid. The machining and grinding process is adopted to process the mainreflector and sub-reflector to meet the requirements of THz wave antenna for high precision and high surface finish of reflector [14]. The main parameters of 360 GHz Cassegrain antenna design are presented in Table 2. ...

... While designing a radio telescope antenna, various parameters need to be considered. These parameters such as bandwidth, gain, directivity, beam width, and radiation pattern characterize an antenna's performance [5]. The radiation pattern is the essential parameter of antennas that allows designers to compare different solutions and assess their usefulness in wireless communication systems. ...

... Waveguide loss in a resistive-walled waveguide for the TE nm mode is given by (8) [22], where α has units of Nepers/meter (Np/m) and 1 Np=(1/20)•ln(10) dB ≈ 0.115 dB, a is the broad wall width, b is the narrow wall height, R is the sheet resistance of the waveguide wall calculated from eqns (2),(3), and (4), f c is the cutoff frequency (9), η = (μ/ε) 1/2 is the intrinsic impedance of free space, and the ratio β/k is given by (10). The computation of (8) is only valid for frequencies reasonably above cutoff [23]; at frequencies near or below cutoff, a boundary matching method must be used for accurate results. ...

... In [12], the configuration of a probe in a waveguide has already been carefully designed for full-wave coupling to a 50 Ω coaxial cable. Hence, we adopt identical parameters as those in [12], with the rectangular probe replaced by the hammerhead. ...

... The most apparent simplification found in these literatures is allowing the solution for Helmholtz equation to be separated into pure and modes, where p and q represent respectively the number of maxima of the electric fields in the x and y directions of the waveguide. In a practical dielectric waveguide, however, a superposition of these two modes is necessary to satisfy the boundary conditions [34][35][36]. Among these available techniques, Marcatili's approach [19][20][21] turns out to be the most widely implemented. ...

... depicts the structure of a circular waveguide. At the boundary of the waveguide where radius r = a, the tangential electric E t and magnetic H t fields in the waveguide are related to the electrical properties of the wall material by[14] -[16] ...

... e MOOC online learning system is a network platform with huge online courses available based on online teaching that also expands students' education pathways at all levels. However, the management of these platforms necessitates a high level of skill and money, making them challenging to establish and manage in institutions [8]. ...

... In [4] and [5], analysis on the performance of superconducting circular waveguides has been performed based on Mattis-Bardeen theory. Since the equations are derived from Bardeen, Cooper and Schrieffer BCS weak coupling theory, it takes into account the presence of the gap energy. ...

... At some specific plane z the electrical field E(x, y, t, z) is registered and then whole broadband wavefront propagation dynamic could be revealed by means of methods of digital holography. This scheme is based on the concept of THz PTDH described and experimentally approved in [27] In terms of spatial coordinates the registration of E(x, y, t, z) can be performed by 2D raster scanning procedure [54] or by using detector's matrix array [57]. Then the inverse problem could be solved, reconstructing the spatio-temporal and spatio-spectral information of THz field in the object plane z 0 or in any other plane z. ...

... Fig. 2 shows contours of LO sideband rejection as a function of the amplitude and phase imbalances in a balanced mixer. Our single chip balanced mixer is based on the back-toback finline layout previously used by Campbell et al [6] as the basis for a 350 GHz bolometric interferometer. A single split mixer block is used, incorporating Pickett-Potter horn-reflector (PPHR) antennae [7] coupled to either end of a 160 × 320 µm waveguide. ...

Reference: A 700 GHz single chip balanced SIS mixer