A Design Method for Microstrip Directional Couplers Loaded With Shunt Inductors for Directivity Enhancement

Seungku Lee,Yongshik Lee IEEE 2010 IEEE transactions on microwave theory and techniqu Vol.58 No.4

<P>An accurate design method is proposed for directivity enhancement of microstrip directional couplers loaded with shunt inductors. The parasitic effects of junction discontinuities in various parts of such microstrip directional couplers have critical effects especially on the directivity, and therefore they must be taken into account. Without proper modeling of these parasitic effects, directivity enhancement becomes extremely difficult especially for weak coupling levels. The demonstrated method of analysis can be applied to obtain exact designs of all previous microstrip directional couplers that are loaded symmetrically with series and/or shunt reactance for directivity enhancement, regardless of the coupling levels. Based on the proposed method, a 20-dB microstrip directional coupler is designed at 2.4 GHz. A maximum directivity of 56 dB has been measured, which is an improvement of 48 dB over a conventional microstrip directional coupler. A 16.3% bandwidth at 2.4 GHz has been measured in which the directivity remains above 20 dB, while the maximum variation in the coupling level is 0.5 dB. This is the first work to demonstrate directivity of more than 50 dB for a 20-dB microstrip directional coupler.</P>

Generalized Miniaturization Method for Coupled-Line Bandpass Filters by Reactive Loading

Seungku Lee,Yongshik Lee IEEE 2010 IEEE transactions on microwave theory and techniqu Vol.58 No.9

<P>This paper presents a generalized miniaturization method for coupled-line bandpass filters by reactive loading, including the series-inductive loading method that is proposed in this work. It is shown that bandwidth reduction seen in the previous miniaturization method of shunt-capacitive loading is a special case. In fact, one can choose a coupled-line filter to be miniaturized with its bandwidth reduced, expanded, or maintained after miniaturization. The ratio of the bandwidths before and after miniaturization plays an important role in determining the even-/odd-mode impedance, as well as the reactance levels after miniaturization. Therefore, the freedom in choosing the bandwidth ratio provides a great flexibility in miniaturizing coupled-line filters since one can choose an appropriate bandwidth ratio to maintain the impedance and reactance at practical levels after miniaturization. The proposed generalized miniaturization method enables filter designs focused on size reduction, improved stopband response, low-cost fabrication, or a combination of these, which are verified by experimental results.</P>

An Inductor-Loaded Microstrip Directional Coupler for Directivity Enhancement

Seungku Lee,Yongshik Lee IEEE 2009 IEEE microwave and wireless components letters Vol.19 No.6

<P>A directivity-enhancement technique is demonstrated for a microstrip directional coupler. By loading the coupler with shunt inductors, the phase velocities of the even and odd modes are altered in such a way that an isolation null is achieved. Compared with other compensation techniques for directivity enhancements, the proposed method provides the advantages of being simple yet easily application to high frequencies. For a 10 dB directional coupler at 0.9 GHz, a maximum directivity improvement of nearly 38 dB is measured over the conventional counterpart.</P>

A Uniform Coupled-Line Dual-Band Filter With Different Bandwidths

Seungku Lee,Yongshik Lee IEEE 2010 IEEE microwave and wireless components letters Vol.20 No.10

<P>This letter presents a planar dual-band bandpass filter (BPF) of adjustable bandwidths. The proposed method of simultaneously designing the J-inverters and the resonators enables a BPF to have bandwidth control, without any structural modification to the uniform coupled lines loaded with shunt stubs. A systematic design approach is introduced along with experimental results that verify the proposed method.</P>

A Planar Dual-Band Filter Based on Reduced-Length Parallel Coupled Lines

Seungku Lee,Yongshik Lee IEEE 2010 IEEE microwave and wireless components letters Vol.20 No.1

<P>A planar dual-band filter is demonstrated that is based on reduced-length parallel coupled lines. By reactively loading a reduced-length coupled line, a dual-band performance is obtained. The dual-band filter is developed by cascading these dual-band coupled lines. A complete set of design equations is provided that can be applicable to an arbitrary number of filter stages. Experimental results for a Chebyshev-type dual-band filter with center frequencies at 2.4 and 5.2 GHz are in excellent agreement with the full-wave simulated results.</P>

Cataracts are Associated with the Coexistence of Moderate to Severe Obstructive Sleep Apnea and Diabetes Mellitus

Lee Seungku,윤대위,김진관,서영우,신철 대한수면학회 2020 sleep medicine research Vol.11 No.2

Background and Objective: The individual presence of diabetes mellitus (DM) or obstructive sleep apnea (OSA) is significantly associated with cataract formation, but few studies have examined the association of cataracts with comorbid DM and OSA. Our aim in this study was to confirm the relationship between cataracts and the individual presence of DM or OSA in a large population-based cohort study and evaluate the association between cataracts and the coexistence of OSA and DM. Methods: We included 699 individuals who were enrolled in the Korean Genome and Epidemiology Study and who underwent both nocturnal polysomnography and cataract diagnosis in the study. We assessed the presence and severity of OSA by means of unattended home sleep monitoring. DM was diagnosed based on the fasting blood-glucose level or by the use of antihyperglycemic medications. Cataracts were diagnosed according to the Lens Opacities Classification System III. Results: The prevalence of cataracts tended to increase as OSA worsened. Diabetes patients had a higher prevalence of cataracts than did normal subjects. In multivariate analysis, there was no significant association of cataracts with DM or OSA alone. In the joint analysis of DM and OSA, however, the odds for cataracts were significantly higher in the DM patients with moderate to severe OSA than in the DM patients without OSA, indicating a significant synergy of moderate to severe OSA and DM on cataracts. Conclusions: The concurrent presence of DM and moderate to severe OSA was associated with cataracts. Thus, OSA should be considered in the prevention or treatment of diabetic cataracts.

결합 선로 이중 대역 필터의 대역폭이 줄지 않는 설계 방법

이승구(Seungku Lee),하정제(Jungje Ha),이용식(Yongshik Lee) 한국전자파학회 2010 한국전자파학회논문지 Vol.21 No.3

본 논문에서는 분로 스터브가 연결된 결합 선로로 구성된 이중 대역 필터의 새로운 설계 방법을 제안한다. 이중 대역 필터가 단일 대역 필터와 두 목표 주파수에서 같은 응답 특성을 갖는 조건에 기반한 기존 설계 방법과는 달리 제안하는 설계 방법은 두 필터가 같은 전파 상수와 같은 영상 임피던스를 갖는 조건을 바탕으로 한다. 이는 기존 설계 방법과는 달리 대역폭이 줄어들지 않는 설계 방법으로 복잡한 과정을 통한 대역폭 보상이 필요없으므로 보다 간단한 설계가 가능한 장점이 있다. 또한 새로운 이중 대역 필터 설계 방법을 제공함으로써 보다 유연한 설계를 가능하게 한다. 실험적 검증을 위하여 중심 주파수가 1 ㎓와 3.5 ㎓인 이중 대역 체비셰프필터를 설계 및 제작하였으며, 측정 결과는 전자기 모의실험 결과와 매우 일치하는 우수한 특성을 보인다. This paper proposes an improved filter synthesis method for dual-band filters based on coupled lines loaded with shunt stubs. The conventional design method relies on equality of the response of the conventional single-band filter and its dual-band counterpart at two frequencies. On the other hand, the proposed method is based on equivalence of the propagation constants and the image impedances of the two filters. Therefore, the proposed method does not suffer from bandwidth reduction phenomena, which requires complex compensating process in the conventional method. Also, the alternative design parameters provided by the demonstrated method enable to construct dual-band filters with more flexibility. For experimental verification, a Chebyshev type dual-band filter with center frequencies at 1 ㎓ and 3.5 ㎓ is designed and fabricated. The measured results are in excellent agreement with the full-wave simulated results.

BLE 비콘 위치 추정을 위한 로봇 경로 탐색 기법

이가진(Lee Gajin),이범준(Lee Beomjun),김승구(Kim Seungku) 한국통신학회 2025 한국통신학회 학술대회논문집 Vol.2025 No.6

한글문자 자동인식에 관한 연구

이범천(Bumchun Lee),김정국(Jungkuk Kim),이승구(Seungku Lee) 한국정보과학회 1981 정보과학회논문지 Vol.8 No.4

한글은 구조적 특수성과 자모의 유사성, 그리고 필체의 다양성등에 의해 자동인식에 있어서 많은 문제점을 내포하고 있다. 최근에 연구 보고된 바 있는 한글인식기법들은 크게 두가지의 범주로 분류될 수 있다. 첫째 방법은 자모를 추출한 후에 Syntactic rule에 의해 인식하는 것이며 두번째 방법은 Tree grammar를 이용하여 자모추출과 인식을 동시에 수행하는 것이다. 본 연구는 후자를 보완한 것으로써 다음의 기법을 제안하였다. 우선 Tree grammar의 Terminal V_T를 line segment direction과 그 segment의 starting node의 degree의 pair(V_(TL), V_(TD))로 확장하여 인접상태의 정보를 포함하는 grammar를 정의하였고 이를 Top-down parsing에 의해 초성의 segment와 인식을 동시에 수행하고 종성의 인식을 행하였다. 모음의 인식을 위하여는 별도의 segmentation algorithm을 적용하였다. 이러한 방법은 이미 연구된 Tree grammar를 이용한 인식방법에서 문제가 되고 있는 ambiguity의 대부분을 제거할 수 있으며 보다 높은 인식률을 얻을 수 있다. 약간의 제약이 가해진 필기체가 실험에 사용되었으며 그 결과 96%의 인식률을 얻을 수 있었다. 제안된 기법은 자모들이 상호 연결되어 있는 경우에 매우 효율적이고 본 연구실에서 현재 진행되고 있는 Tree grammar inference를 이용한 learning system으로 확장 보강되면 제한없는 필기체의 인식에 사용될 수 있을 것으로 기대된다. Algorithms to reduce ambiguities in the recognition process for Korean characters are proposed. Terminal symbols are redefined to accomodate the complicated line connectivity informations by representing them with the pair (Vtl, Vtd), where Vtl is the degree of the starting point of that line segment. Segmentation and recognition of the consonant can be parallelly processed by top-down parsing, Algorithms for the recognition of vowels are also developed which work for the patterns with the first consonant removed. 96% of the recognition ratio has been obtained through the experimentation with the restricted handwritten characters.

이종 통신기술을 활용한 Zigbee 채널 평가 방법

이헌국(Lee Heon Guk),임진묵(Lim Jin Mook),김승구(Kim Seungku) 한국통신학회 2017 한국통신학회 학술대회논문집 Vol.2017 No.6