Sewoong Kwon

A harmonic suppression antenna for an active integrated antenna

An inset-fed antenna with a shorting pin and slots is presented for harmonic suppression of an active integrated antenna. Its fundamental resonant frequency is 5.8 GHz. At fundamental and harmonic frequencies, return loss and radiation characteristics are measured and compared with those of the conventional microstrip patch antenna. The second and third harmonic return losses of the proposed antenna are suppressed to 6.7 dB and 17.7 dB with respect to the conventional patch antenna, respectively.

Harmonic tuning antennas using slots and short-pins

Recently active integrated antennas have been studied for more efficiency and harmonic reduction. The designed antenna provides a good radiation pattern on resonant frequency, and reduces EMI by suppression of second and third harmonics. Also it increases PAE on the power amplifier integrated antenna by operating as shorting load on harmonics.

Modeling the Indoor Channel for the MIMO System using Dual Polarization Antennas

This work presents a quasi-three dimensional MIMO channel model to predict the polarization characteristics of an indoor radio channel. The model considers not only the effects of the polarization of the transmitting and receiving antenna elements, but also the types of indoor environment scatterers. The proposed model is based on an ellipse model and a patch scattering model. Furthermore, the channel model expands the ellipse model to a quasi-three dimensional model. The proposed model is suitable for indoor MIMO channels and can expect ergodic capacities of a multi-polarized MIMO channel, which considers polarization and 3-D geometry

Study on the Measurement System for MIMO Channel Considering Urban Environment at Microwave Frequencies

In this paper, the development of wideband MIMO channel sounder and a pilot measurement result is described for research on the multi antenna radio propagation characteristics considering urban environment at microwave frequencies. We developed MIMO(BW:100 MHz) channel sounder using the high speed switching mechanism and periodic pseudo random binary signals method considering next generation mobile communication system. A pilot measurement campaign at the urban area of Bundang is presented for confirmation of system performance. From the analysis of measurement data, wideband path loss exponent of 3.7 and 8 GHz band is 1.79 and 1.76. Average RMS delay spread is 200 ns and 42 ns respectively. From the experiment results, operation of this measurement system is confirmed considering research for a coverage, SNR and channel capacity in urban environment at microwave frequencies.

Simple and Exact Closed-Form Expression for Determination of a Penetrated Ray Path in a Ray Tracing

A simple and exact closed-form equation to determine a penetrated ray path in a ray tracing is proposed for an accurate channel prediction in indoor environments. Whereas the penetrated ray path in a conventional ray tracing is treated as a straight line without refraction, the proposed method is able to consider refraction through the wall in the penetrated ray path. Hence, it improves the accuracy in ray tracing simulation. To verify the validation of the proposed method, the simulated results of conventional method, approximate method, and proposed method are compared with the measured results. The comparison shows that the proposed method is in better agreement with the measured results than the conventional method and approximate method, especially in high frequency bands.

Development of Exponential Model of Korea for Improved Altitude Estimation Performance of High-Altitude Target at Radar System

In this paper, an exponential model of Korea is proposed to minimize an altitude-error of high-altitude target due to atmosphere refraction at radar system. The relation between surface refractivity and refractivity gradient, which is extracted using the least square fit from the measured data at 7 weather stations, is applied to the exponential model. And in order to verify the proposed model, the altitude-errors for a standard atmosphere, a CRPL(Central Radio Propagation Lab.) exponential model, the proposed model are extracted and analyzed using a ray tracing. As a result, the proposed model can improve the altitude estimation performance of radar compared to conventional atmosphere refractive index models.

An Interference Analysis Method with Site-Specific Path Loss Model for Wireless Personal Area Network

In this paper, an interference analysis method with a site-specific path loss model for a wireless personal area network (WPAN) is proposed. The site-specific path loss model is based on geometrical optics and geometric probability to consider both site-specific radio propagation characteristics and a closed-form expression to obtain the mean interference from which the uniformly distributed multiple interferers are derived. Therefore, the proposed interference analysis method can achieve more computational simplicity than the Monte-Carlo (MC) simulation, which uses the ray-tracing (RT) technique. In addition, better accuracy than the conventional interference analysis model that uses stochastic method can also be achieved. To evaluate the proposed method, a signal to the interference-noise ratio with a mean interference concept for uniformly distributed interferers is calculated and compared in two simulation scenarios. As a result, the proposed method produces not only better matched results with the MC simulation using the RT technique than the conventional interference analysis model, but also simpler and faster calculation, which is due to the site-specific path loss model and closed-form expression for interference calculation.

A Study on Ray Tracing Method for Wave Propagation Prediction with Acceleration Methods

In this paper, we proposed an improved ray tracing method with an amelioration of visible tree structure, a visible face determination method, and non-uniform random test point method. In a proposed visible tree structure, it reduces tree nodes by means of merging similar nodes. In a visible face determination method, it shows that a ray hit test with a packet ray method can reduce a test time. A ray tracing method involving with a packet ray hit test method can improve a tree construction time up to 3.3 times than a ray tracing method with a single ray hit test method. Furthermore, by seeding a non-uniform and random test point on a face, tree construction time is improved up to 1.11 times. Received powers from the proposed ray tracing results and measured results have good agreement with 1.9 dB RMS error.

3D ray-tracing model including effect of inhomogeneous building surface for characterization of wireless communication channel

A ray-tracing method in conjunction with UTD (uniform theory of diffraction) has been widely used to characterize a wireless communication channel. Due to the complexity of the real situation, the ray-tracing method generally assumes buildings have homogeneous and smooth surfaces. However, in a real case, the building surface consists of many heterogeneous materials, whose shapes are also various. Hence, the scattering by the surface is much different from a homogeneous surface, which will affect the final accuracy of the ray-tracing method. In UTD, scattering mechanism by an object is mainly decomposed into two groups: reflection and diffraction. In general, the reflection in the specular direction is important, but the inhomogeneity may reduce the specular reflection drastically. In this paper, to consider the reduction of the specular reflection, we formulate the effective specular reflection based on PO (physical optics) approximation, and include the reflection in a 3D ray-tracing code. Then, we investigate the inhomogeneity effect on the final path-loss.

A Path loss and Shadow Fading modeling in Various Radio Environment of Seoul City Based on Measurement Data at 5.3GHz and 2.1GHz Bands

Recently, beyond 3G systems have been drawing a great deal of attention concerning next generation wireless services that provide 100 Mbps at high mobility and 1 Gbps at nomadic mobility environment. In order to exploit new mobile radio spectrum resource below 6 GHz bands in Korean radio environment, the first important step consists in a proper understanding of propagation characteristics in candidate bands. Therefore, we propose a channel model which is based on measured path loss data in various topographic areas of Seoul metropolitan city at 5.3 GHz and 2.1 GHz bands. The proposed model is a modified 4-ray model which can consider road side building characteristics in urban street canyon LOS environment. Compared to 4-ray model, it can predict path loss more accurately