Yeongseog Lim

Wide-band high-efficiency printed loop antenna design for wireless communication systems

A new wide-band high-efficiency coplanar waveguide-fed printed loop antenna is presented for wireless communication systems in this paper. By adjusting geometrical parameters, the proposed antenna can easily achieve a wide bandwidth. To optimize the antenna performances, a parametric study was conducted with the aid of a commercial software, and based on the optimized geometry, a prototype was designed, fabricated, and tested. The simulated and measured results confirmed that the proposed antenna can operate at (1.68-2.68 GHz) band and at (1.46-2.6 GHz) band with bandwidth of 1 and 1.14 GHz, respectively. Moreover, the antenna has a nearly omnidirectional radiation pattern with a reasonable gain and high efficiency. Due to the above characteristics, the proposed antenna is very suitable for applications in PCS and IMT2000 systems.

A design and fabrication of bandpass filter using miniaturized microstrip square SIR

A four-pole quasi-elliptic function bandpass filter of 1.95 GHz center frequency with 60 MHz bandwidth for IMT-2000 is designed and fabricated using the miniaturized square stepped impedance resonator (SIR). The nonuniform finite difference time domain (NUFDTD) method is used to design the resonator and to calculate the coupling coefficient of three basic structures. The size reduction of miniaturized square SIR resonator is about 50% compared with a square open loop resonator. A bandpass filter using this resonator show good microwave characteristics with harmonic suppression of about -19 dB at 4.76 GHz. The results of measurements are almost similar to those of simulation.

Design of dual polarized antenna for DCS, UMTS, WiBro base stations

In this paper, we proposed the dual polarization antenna for DCS, UMTS, and WiBro bands. To extend the impedance band width, the proposed antenna used the square loop radiators. In addition, by square loop radiators, the dimensions of an antenna are reduced. As a result of measurement after compensation, we can see that the first port is less than −14dB, the second port is less than −14dB and intra isolation is less than −25dB. Additionally, a gain of the antenna is more than 9dBi. This polarization diversity antenna element can be used to form an array antenna for a wireless communication base station.

Modified annular ring slot antenna for dual WLAN band application

In this paper, the modified annular ring slot antenna is proposed for 2.4/5-GHz dual WLAN band operation. The higher order resonant modes in the annular ring slot are used to control the second operating frequency. The proposed antenna is printed on a FR-4 substrate, and has dimensions of 50 times 50 times 1.2 [mm] with a ground plane. The frequency ratio of the two operating frequencies can be adjusted from 1.97 to 2.64 with geometric values. The measured impedance bandwidths (VSWR<2) of the proposed antenna are approximately 13.2% for the 2.4-GHz band and 40% for the 5-GHz band and the peak gains are 3.74, 4.12 and 5.25 dBi for 2.45, 5.35 and 5.8 GHz bands, respectively.

Optimization of flexible substrate for COF (chip on flexible) LED packaging

The poor thermal design of high brightness light-emitting diodes (HB-LEDs) package for the automotive exterior lighting system causes the degradation of the optical and reliability performance, also the deterioration of the cost-effectiveness. We design the flexible package substrate with the thick heat-spreading layer and thermal via-hole fully filled with the copper (FFC) for the conventional process of flexible printed circuit board (FPCB) and the extraction methodology of the heat flow is presented. Effective heat flow for thermal simulation is compensated for the optical loss between the internal and external quantum efficiency. The vertical blue LED is attached on metal core printed circuit board (MCPCB) without the molding process, and then heat distribution and optical power is, respectively, measured by using infrared camera and optical LED tester as increasing the magnitude of the input power. Detailed thermal performance of FPCB and MCPCB is verified with the heat distribution and the thermal resistance. The effects of the main factors of FPCB with filled via-holes are discussed using design of experiment (DOE) methodology. The thermal resistance and junction temperature of FPCB is, respectively, over two times and 10 °C lower than that of MCPCB.

Temperature rise in the human head and brain for portable handsets at 900 and 1800

The purpose of this paper is to calculate temperature rises in an anatomically based model of the human head and brain for handset antenna at 900 and 1800 MHz. The specific absorption rate (SAR) is initially calculated with the use of the finite-difference time-domain (FDTD) method. The temperature rises in the human head and brain are then calculated by substituting the SAR into the bio-heat equation. The steady-state maximum temperature rises in the head and brain are determined through linear extrapolation of the peak average SAR. The averaged 1 g peak SARs in the head model are 1.590 W/kg at 900 MHz and 1.515 W/kg at 1800 MHz. The maximum temperature rises are 0.160 /spl deg/C in the head and 0.054 /spl deg/C in the brain at 900 MHz and 0.124 /spl deg/C, 0.044 /spl deg/C at 1800 MHz. Computed results show higher temperature elevation is obtained at 900 MHz in comparison to 1800 MHz and temperature increases rapidly within 3 min of phone time. In addition, after 7-8 minutes of phone time it reaches about 90 % of steady-state value and the steady-state condition in 30 minutes.

A design of printed square loop antenna for omni-directional radiation patterns

In this paper, for dual band operation of both PCS and IMT2000, we propose a wideband antenna with printed square loop configuration. The proposed antenna has the CPW-feed structure on the same plane with radiating element. The calculated and measured bandwidths for 15 dB return loss are 1 GHz (1.68/spl sim/2.68 GHz) and 1.14 GHz (1.46/spl sim/2.6 GHz), respectively. The fabricated antenna has nearly omni-directional radiation pattern, and measured antenna gain of 2.67 dBi. These results confirm that proposed antenna could be used in both PCS and IMT2000 band operation.

Miniaturized bandpass filter with improved stopband characteristics using microstrip interdigital-loop resonator

A four-pole quasi-elliptic function bandpass filter is designed and fabricated using a miniaturized microstrip interdigital-loop resonator. The novel microstrip interdigital-loop resonator is able to control spurious responses in a compact size. A bandpass filter using this resonator shows good microwave characteristics with harmonic suppression of about -15 dB at 6.52 GHz, which is 3.34 f/sub 0/, where f/sub 0/ is the midband of frequency of a bandpass filter. The results of measurements are almost similar to those of simulation.

Balun-BPF using magnetically coupled interdigital-loop resonators

In this paper, we proposed the Balun-BPF(band pass filter) using the magnetically coupled resonators. The proposed Balun-BPF is a deformation of the transformer which operates like the ideal Balun in low frequency. The conventional coupled-resonator filter design theory was used for the design of a Balun-BPF. Moreover, the Interdigital-loop resonator was used to miniaturize the Balun-BPF. This Balun-BPF operated in a 2.4∼2.5 GHz band, generally used in the wireless communication. Experimental measurements are also presented to validate the theory and EM simulations.

Optimization of flexible substrate for automotive LED rear-lamp

High brightness light-emitting diodes (HB LEDs) for the automotive exterior lighting system are required to maintain the stable light output irrespective of the ambient temperature. We design the flexible substrate with the thick trace layer for heat spreader for the conventional process of printed circuit board (PCB). The performance of flexible PCB substrate with the thick copper layer of 200 um is compared with the conventional substrate attached on aluminum heat spreader of 1.5 mm and 150 W/m-K. The proposed design is analyzed in accordance with the size and thickness of heat spreader, and then the heat emission properties of the proposed substrate laminated with thick copper foil is characterized by using CFD (computational fluid dynamics) technology. The optimization of the substrate is carried out in accordance with the forward current and voltage. The thermal resistance from the top surface of LED to the plastic housing can be decreased over 1.5 times in comparison with the conventional structure while the delta forward voltage is controlled within 0. 04 V.