New UWB 1:2 Power Divider with Flat In-Band Splitting and Bandpass Filtering Functions

Thai Hoa Duong,Ihn Seok Kim 한국전자파학회JEES 2010 Journal of Electromagnetic Engineering and Science Vol.10 No.1

This paper introduces a new U.S. ultra-wideband(UWB: 3.1~10.6 GHz) 1:2 power divider based on a single section Wilkinson type configuration. The divider provides very flat in-band power splitting, high isolation, low insertion loss, sharp roll-off bandpass filtering, and DC blocking characteristics. The circuit consists of a λ/4 Y resonator, three capacitively coupled λ/2 short-circuited lines, and a resistor between the two output ports. The circuit structure was simulated with ADS and HFSS, and realized with low-temperature co-fired ceramic(LTCC) green tape, which has a dielectric constant of 7.8. |S11| better than 10 ㏈, |S21| and |S31| less than 3.2 ㏈, with both |S22| and |S32| measured as better than 12 ㏈ for the whole UWB band. Measurement results agree closely with HFSS simulation results. The power divider has a compact size of 4×9×0.6 ㎣.

Nighttime LED Taillight Detection Method with Optical Camera Communication System

Thai-Hoa Huynh(후인 타이호아),Myungsik Yoo(유명식) 한국통신학회 2020 韓國通信學會論文誌 Vol.45 No.9

THE INFLUENCE OF PRODUCT-COUNTRY IMAGE ON THE PERCEIVED QUALITY: AN EMPIRICAL STUDY FROM VIETNAMESE CONSUMERS

Hoa Hong Pham,Ngoc Thai Pham,Duy Vu Nguyen 글로벌지식마케팅경영학회 2016 Global Marketing Conference Vol.2016 No.7

Although country-of-origin has been a controversial topic in literature, there has been little research effort to explain the nature linkage between country-of-origin and perceived quality from consumers in emerging markets. Drawing on the notion of country-of-origin, this study proposes the concept of product-country-image which is operationalized with the three components of cognitive, affective and conative. Structural equation modeling is employed to explore the relationship between the product-country-image and perceived quality. The findings indicate that only ‘affective components’ are positively related to ‘conative components’ among three pairs. What is more, structural equitation modeling demonstrated that the influence of product-country image on perceived quality is simultaneously regardless of the level of consumers’ familiarity with a foreign country’s product. Using data collected from 348 Vietnamese consumers, this study generates new insights for academics and practitioners.

New Elliptic Function Type UWB BPF Based on Capacitively Coupled <tex> $\lambda/4$</tex> Open T Resonator

Thai Hoa Duong,Kim, I.S. IEEE 2009 IEEE transactions on microwave theory and techniqu Vol.57 No.12

<P>This paper introduces two new circuit structures for European and U.S. ultra-wideband (UWB) bandpass filters (BPFs) with sharp roll-off characteristics. The circuit structures consist of capacitively coupled three parts in stripline structure, a λ/4 open T resonator, a λ/4 short-circuited line, and input and output lines. We show first that ultra wide bandpass property is basically obtained from the T resonator with a capacitively coupled λ/4 short-circuited line, which provides two attenuation poles at lower and upper cutoff frequencies. Two identical capacitively coupled input/output lines, which can be λ/4 length open ends or λ/2 length short ends, with the T resonator are adopted to suppress lower and higher frequency components outside of the passband. There is coupling between the input and output lines providing two additional transmission zeros in the lower and upper transition bands of the filter. Since the coupling between the T resonator with the λ/4 short-circuited line and the input/output lines limits the bandwidth of the filter to the European UWB band, both the λ/4 short-circuited line and the input/output lines are inserted between the two stacked T resonators for the U.S. UWB band. The filter structures are simulated with ADS and HFSS and realized with low-temperature co-fired ceramic (LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results.</P>

Steeply Sloped UWB Bandpass Filter Based on Stub-Loaded Resonator

Thai Hoa Duong,Kim, I S IEEE 2010 IEEE microwave and wireless components letters Vol.20 No.8

<P>This letter introduces an ultrawideband (UWB) bandpass filter (BPF) with very sharp roll-off characteristics in stripline structure for the U.S. band (3.1-10.6 GHz). The UWB characteristic is basically obtained from capacitive coupling between a main line and a λ/2-length stub-loaded resonator. The stub-loaded resonator consists of λ/8 short-circuited and open-circuited stubs at the center of the λ/2 line. The two stubs provide two attenuation poles at lower and upper cutoff frequencies. For input and output lines, two λ/4 identical capacitively coupled lines have been installed to suppress the unwanted signals in the lower and upper stopbands. The filter has been designed with two transmission zeros at 2.4 and 11.1 GHz to provide 81- and 86-dB/GHz slopes in the lower and upper transition bands, respectively, and realized with low-temperature co-fired ceramic (LTCC) green tape that has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results. Insertion loss less than 1.1 dB and return loss better than 14 dB in the whole passband have been measured. The group delay at the center frequency is 0.26 ns, and the group delay variation within the passband is less than 0.5 ns. The size of the filter is 6 × 18 × 0.6 mm<SUP>3</SUP>.</P>

Rectangular prism pressure coherence by modified Morlet continuous wavelet transform

Thai-Hoa Le,Luca Caracoglia 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.5

This study investigates the use of time-frequency coherence analysis for detecting and evaluating coherent “structures” of surface pressures and wind turbulence components, simultaneously on the time-frequency plane. The continuous wavelet transform-based coherence is employed in this time-frequency examination since it enables multi-resolution analysis of non-stationary signals. The wavelet coherence quantity is used to identify highly coherent “events” and the “coherent structure” of both wind turbulence components and surface pressures on rectangular prisms, which are measured experimentally. The study also examines, by proposing a “modified” complex Morlet wavelet function, the influence of the time-frequency resolution and wavelet parameters (i.e., central frequency and bandwidth) on the wavelet coherence of the surface pressures. It is found that the time-frequency resolution may significantly affect the accuracy of the time-frequency coherence; the selection of the central frequency in the modified complex Morlet wavelet is the key parameter for the time-frequency resolution analysis. Furthermore, the concepts of time-averaged wavelet coherence and wavelet coherence ridge are used to better investigate the time-frequency coherence, the coherently dominant events and the time-varying coherence distribution. Experimental data derived from physical measurements of turbulent flow and surface pressures on rectangular prisms with slenderness ratios B/D=1:1 and B/D=5:1, are analyzed.

New UWB BPF with Steep Selectivity Based on T-Resonator and Capacitively Coupled λ/4 and λ/2 Line Sections

Thai Hoa Duong,Ihn Seok Kim 한국전자파학회JEES 2009 Journal of Electromagnetic Engineering and Science Vol.9 No.3

In this paper, two new circuit structures for European and U.S. ultra-wide band(UWB) bandpass filters(BPFs) with sharp roll-off characteristics are introduced. We show first that the ultra-wide bandpass property is obtained from a λ/4 open T resonator with a capacitively coupled λ/4 short-circuited line, which provides two attenuation poles at lower and upper cutoff frequencies. Then, two identical capacitively coupled input/output lines, which can be λ/4-length open ends or λ/2-length short ends, with the T-resonator, are adopted to suppress lower and higher frequency components outside of the pass band. There is coupling between the input and output lines providing two additional transmission zeros in the lower and upper transition bands of the filter. Since the coupling between the T-resonator with the λ/4 short-circuited line and the input/output lines limits the bandwidth of the filter to the European UWB band, both the λ/4 short-circuited line and the input/output lines are inserted between the two stacked T-resonators for the U.S. UWB band. The filter structures are simulated with ADS and HFSS and realized with low-temperature co-fired ceramic(LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results.

LOW insertion Loss Multilayer Capacitively Loaded Step-Impedance Miniaturized UWB Bandpass Filter

Thai Hoa Duong,김인석 경희대학교 산학협력기술연구원 2008 산학협력기술연구논문집 Vol.14 No.-

In this paper, a low insertion loss interdigital bandpass filter with capacitively loaded stepped impedance resonators (SIR) in Low Temperature Co-fired Ceramic (LTCC) technology is introduced. By using SIR and capacitive loading structures based on E_(r)= 41. 77 substrates, a wideband interdigital bandpass filter has been realized for the frequency range from 3.1 GHz to 4.8 GHz. Measurement shows insertion loss less than 0.8 dB, return loss better than 15 dB in the pass band with the center frequency at 3.95 GHz and bandwidth ratio of 43%. The filter has a size of 2.15 x 2.6 x O.85mm^(3). 본 논문에서는, Low Temperature Co-fired Ceramic (LTCC) 기술을 이용하여 capacitively loaded stepped impedance resonators (SIR) 를 갖는 낮은 삽입손실 인터디지털 대역통과 필터를 소개한다. E_(r)= 4 1. 77을 기반으로 하는 SIR과 capacitive loading 구조를 이용함으로써,광대역 인터 디지털 대역통과 필터는 3.1 에서 4.8 GHz 의 주파수 범위에 대해서 실현이 된다. 측정값은 중심주파수 3.95GHz를 갖는 통과 대역에서 삽입 손실이 0.8 dB 보다 작고,반사 손실은 15 dB 이상이고,43% 의 대역폭 률 을 보여준다. 필터의 크기는 2.15 x 2.6 x 0.85㎣ 이다.

Understanding of unsteady pressure fields on prisms based on covariance and spectral proper orthogonal decompositions

Hoa, Le Thai,Tamura, Yukio,Matsumoto, Masaru,Shirato, Hiromichi Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.16 No.5

This paper presents applications of proper orthogonal decomposition in both the time and frequency domains based on both cross spectral matrix and covariance matrix branches to analyze multi-variate unsteady pressure fields on prisms and to study spanwise and chordwise pressure distribution. Furthermore, modification of proper orthogonal decomposition is applied to a rectangular spanwise coherence matrix in order to investigate the spanwise correlation and coherence of the unsteady pressure fields. The unsteady pressure fields have been directly measured in wind tunnel tests on some typical prisms with slenderness ratios B/D=1, B/D=1 with a splitter plate in the wake, and B/D=5. Significance and contribution of the first covariance mode associated with the first principal coordinates as well as those of the first spectral eigenvalue and associated spectral mode are clarified by synthesis of the unsteady pressure fields and identification of intrinsic events inside the unsteady pressure fields. Spanwise coherence of the unsteady pressure fields has been mapped the first time ever for better understanding of their intrinsic characteristics.

COMPETITIVENESS-BASED ECONOMIC GROWTH: THE E-GOVERNMENT IMPACT IN VIETNAM

( Hoa Thai Thi Thanh ),( Pan Suk Kim ) 한국행정학회 2016 한국행정학회 학술발표논문집 Vol.2016 No.-

This paper studies the impact of e-government on economic growth potential based on competitiveness. Within Vietnam, the rising momentum of using e-government in the government’s working agenda is geared toward contributing to the economic growth of the nation. Current literature has explored the impact of e-government on economic growth, but it is mainly cross-national or focused on developed countries. Using a panel dataset collected in 63 provinces/municipalities in Vietnam, this study attempts to fill the gap in the literature by investigating the impact of e-government in Vietnam as a case study of a developing country. Moreover, considering the systematic effect of e-government, this study uses path analysis and empirical evidence to provide illustrations of how e-government applications in Vietnam can be used as vehicles to support the competitiveness of different economic areas in Vietnam, through increasing the ability of economic governance to potentially steer economic growth at a more vigorous level.