Kyu-Song Lee

Miniaturization of log-periodic dipole array antenna using triangular meander structure

This paper has been designed the miniaturized LPDA antenna applying the triangular meander structure. To reduce the basic LPDA antenna, four dipole elements for low frequency band of the basic LPDA antenna were changed into triangular meander structure except for the other elements to keep the performance of high frequency band. The proposed antenna was miniaturized up to 60 % compared with the basic LPDA antenna. The average gain was measured as 6.69 dBi.

Design and Implementation of Wideband Ultra-Fast High Precision Frequency Synthesizer for ELINT Equipment

본 논문은 2.5 ㎒ 간격으로 광대역 주파수를 발생하며 응답 시간이 400 nsec 이하인 초고속 이산(discrete)주파수 합성기를 제안한다. 제안한 주파수 합성기는 고정 주파수 위상 제어 루프(PLL)와 주파수 분배기를 이용해 16개의 기준 신호를 생성하고, 이들을 선택하여 주파수 혼합하는 방식으로 710～1,610 ㎒ 내에서 2.5 ㎒ 간격의 이산 주파수 신호를 고속으로 생성한다. 제작된 주파수 합성기의 주파수 천이 응답 시간은 평균 350 nsec, 고조파를 비롯한 모든 불요파 신호는 －60 ㏈c 이하, 위상 잡음 특성은 －94 ㏈c/㎐ @100 ㎐, 출력 세기는 평균 21.5 ㏈m, 평탄도는 2.65 ㏈ 이하로 측정되었다. 또한 주파수 천이 응답 속도를 측정하는 새로운 기법의 측정 방법이 제안되었다.

Phase Noise Analysis of 2.4 GHz PLL using SPD

In this paper, phase noise analysis result for 2.4 GHz PLL(phase locked loop) using SPD(sample phase detector) is proposed. It can be used for high performance frequency synthesizer’s LO(local oscillator) to extend output frequency range or for LO of offset PLL to reduce a division rate or for clock signal of DDS(direct digital synthesizer). Before manufacturing, theoretical estimation of PLL’s phase noise performance should be performed. In order to calculate phase noise of PLL using SPD, Leeson model is used for modeling phase noise of VCO(voltage controlled oscillator) and OCXO(ovened crystal oscillator). After theoretically analyzing phase noise of PLL, optimized loop filter bandwidth was determined. And then, phase noise of designed loop filter was calculated to find suitable OP-Amp. Also, the calculated result of phase noise was compared with the measured one. The measured phase noise of PLL was -130 dBc/Hz @ 10 kHz.

A Study on Miniaturization of a Log-Periodic Dipole Array Antenna

In this paper, we studied miniaturization of LPDA(Log-Periodic Dipole Array) antenna used for VHF and UHF bands. To miniaturize the LPDA antenna, in this study, the radiation elements in a low frequency were changed into a triangular meander structure which has small current cancelation effect at feed part. For the triangular meander structure, an isosceles triangular and right triangular meander structures were proposed and the LPDA antennas were miniaturized by using the two meander structures. Also, the simulated and measured results were compared for the two miniaturized LPDA antennas. As a result, the isosceles triangular meander and right angle triangular meander structure applied LPDA antennas were reduced up to 60.5 % and 72.4 % compared a basic LPDA antenna, respectively. Consequently, we confirmed that the triangular meander structure is suitable for miniaturization of a LPDA antenna.

A VHF Band 4 Channel Phase Discriminator

In this paper, a VHF band multi channel phase discriminator for direction finding equipment using tripple baseline interferometer technique is proposed. In order to measure simultaneously phase difference between IF(Intermediate Frequency) signals of the direction finding equipment, phase discriminator was designed to have parallel structure with multi channel, the phase correlator of phase discriminator was designed with I, Q mixer for reducing number of components. And digital LUT(Look Up Table) was applied for compensating error of phase discriminator due to phase unbalance of RF components. The measured phase accuracy of fabricated phase discriminator was 2 degree RMS(Root Mean Square) at 30 dB SNR condition, which is superior to the phase accuracy of conventional product.

Design of VHF-Band Wideband 4-Way 90° Power Divider

This paper described the design and fabrication of broadband 4-way power divider which has a phase difference between output ports in 20100 MHz VHF-band. A 4-way power divider was designed using 4-way in-phase power divider which consisted of three 2-way in-phase power dividers and two second-order all pass filters which gives phase difference between output ports. The measured insertion loss was less then 6.6 dB, return loss and isolation were better than 19 dB, and phase error between phase difference outputs was less than 1.