Haengseon Lee

A Photon Modeling Method for the Characterization of Indoor Optical Wireless Communication

In this paper, an analysis method for optical wave propagation based on photon model is presented for the characterization of optical wireless communication environment. In contrast to radio waves, optical waves have very short wavelengths, so that material properties become important and often cause diffuse reflections. Channel models including diffuse reflections and absorption effects due to material surface textures make conventional electromagnetic wave analysis methods based on ray tracing consume enormous time. To overcome these problems, an analysis method using photon model is presented that approximates light intensity by density of photons. The photon model also ensures that simulation time is within a predictable limit and the accuracy is proportional to the number of total photons used in the simulation.

ACCELERATED THREE DIMENSIONAL RAY TRACING TECHNIQUES USING RAY FRUSTUMS FOR WIRELESS PROPAGATION MODELS

In this paper, accelerated techniques for three dimensional ray tracing using the concept of ray frustums are presented for the fast characterization of wireless communications, where various radio propagation paths such as wall-transmitted wave and scattered wave from buildings and ground are generated. To accommodate such scatterers, objects are modeled by triangulated meshes, and potential ray paths are searched and stored in the form of ray frustums. The presented acceleration techniques using the frustums include sorting of triangulated surfaces, hashing functions and space partitioning. The validity of the method is verifled by comparison with measurement data.

A Simple Method of Estimating the Radiated Emission From a Cable Attached to a Mobile Device

When a mobile device is connected to cables for charging power or transmitting data, the radiated emission from the attached cables, which are typically effective electromagnetic interference (EMI) antennae at certain frequencies, can cause serious system-level EMI problems. The measurement of system-level radiation during compliance and precompliance tests is not only a time-consuming task, but also requires expensive facilities such as a semianechoic chamber. This paper proposes a simple method of predicting far-field radiation from cables attached to mobile devices at the early stage of the design and development phase without using an EMI chamber. The method combines radiation characterization of a simple box-source-cable geometry using full-wave simulations with the measurement of the real common-mode current flowing through the cable. The proposed method was applied to mobile phones to estimate the far-field radiated emissions, which were compared with the measurement results. The accuracy of the predicted results was evaluated using the feature selective validation technique, indicating good agreement and correlation.

An Ultra-Wideband Antenna Design Using Sierpinski Sieve Fractal

A trapezoid ultra-wideband antenna using Sierpinski sieve fractal was proposed to reduce the size and expand the bandwidth of the antenna. The effect of the fractal iteration factor (Kn) on the return loss of the antenna was simulated. The return loss, group delay, and path loss (|S 21|) of the antenna were simulated and measured to show that the proposed antenna may be used well for UWB applications with the wide operating bandwidth and good impedance matching. The radiation characteristics of dipole-like pattern and gain variation (2–4 dBi) were obtained over the frequency band.

Crosstalk Reduction Effect of Asymmetric Stub Loaded Lines

In this paper, a crosstalk reduction technique is proposed which utilizes asymmetric stub loaded lines. With small periodic stubs in a transmission line, the coupling strength and the phase velocity of the coupled line are modified without significant change in signal transmission property. We investigate the effect of the asymmetric structure on the crosstalk reduction by measurements and simulation. We also present a simple numerical formulation using a coupled line theory which agrees well with the measurement.

Generation and Distribution of 1.25 Gb/s Ultrawideband Doublet Pulses Based on the Combination of Nonlinear Polarization Rotation and Parametric Amplification

We propose an alternative photonic scheme to generate a doublet ultrawideband (UWB) pulse, which is based on the combined use of nonlinear polarization rotation (NPR) and optical parametric amplification (OPA). The proposed scheme uses NPR together with OPA in a highly nonlinear dispersion-shifted fiber to produce an ideal transfer function with which input Gaussian pulses are successfully converted into doublet pulses. An experimental demonstration was carried out to verify the working principle. The system performance of the generated UWB doublet pulses was assessed by propagating them over a 20-km-long fiber link, followed by wireless transmission. Error-free transmission was successfully achieved at a data rate of 1.25 Gb/s.

A Dual-Band Combline Bandpass Filter Loaded by Lumped Series Resonators

This letter presents a dual-band combline bandpass filter (BPF) loaded by lumped series resonators. The proposed filter configuration can easily generate two desired passbands by controlling the resonant frequencies of the comblines as well as the series resonators. Furthermore, the skirt frequency characteristics between the two passbands are improved by transmission zeros introduced by source-load coupling via a lumped element capacitor. Two-pole dual-BPF with center frequencies of 1.2 and 1.54 GHz is designed and the measured results agree well with simulated results.

Design of Ultra Wideband Monopole Antenna Using Parasitic Open Loops

We have proposed a novel ultra wideband monopole antenna using parasitic open loops for UWB applications. The proposed antenna consists of a center monopole, two symmetrical open loops, and CPW feeding. The combining technique of orthogonal electric and magnetic dipoles is used to design the proposed antenna. Symmetrical structure is the key concept for achieving an ultra wideband impedance matching and very low dispersion over the operating frequency band (3.1 ∼ 4.8 GHz). The group delay was measured as a function of the azimuth angle φ. The radiation patterns are very close to those of a conventional dipole antenna and the simulated antenna gain varies from 2 dBi to 3.2 dBi over the operating frequency range.

Dispersion relation of corrugated circular waveguides

Electromagnetic propagation in corrugated waveguide has been of considerable interest because it supports balanced HE11 mode. The HE11 mode has excellent characteristics for the feed of parabola antenna. In this paper, we obtain dispersion relation of all possible propagation modes by Fourier transform method which is applicable to other general periodic structures. Unlike other methods based on anisotropic surface impedance, the fields are expressed through a series of modal eigenfunctions in the corrugation. The residue calculus is utilized to relate the modal magnetic currents in rapidly-converging series and to show the equivalence of the method to Floquet theorem.

Polarizabilities of an annular aperture in a thick conducting plane

The polarizabilities of an annular aperture in a thick conducting plane are obtained for electric and magnetic cases. The polarizabilities are important parameters to describe the waveguide coupling by apertures. The Hankel transform is applied to express the scattered and transmitted potentials. The problem is solved by a combination of the analytic and numerical methods. The resulting series solution is fast convergent and very efficient for numerical computation. The numerical calculations are performed to illustrate the behavior of polarizabilities in terms of the aperture size and conductor thickness.