• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.2
• /
• pp.200-207
• /
• 2009

This paper presents a compact, low insertion loss, sharp rejection and wide band microstrip band pass filter that is composed rectangular loop resonator and Step-Impedance-Open-Stub(SIOS). The SIOS can be reduce length about 30 % more than general 0.25 $\lambda$ open stub. And the stub can the advantage of tuning impedance magnitude. In order to demonstrate agrement of this paper prove, the optimized wide band pass filters are realized and experimented. A transmission line model used to calculate the frequency response of the new filters shows good agreement with measurements. The filter has 3 dB fractional bandwidth of 51.75 %(3.206 GHz), an insertion loss of better than 0.44 dB from 4.587 GHz to 7.793 GHz, and two rejection of greater than 30 dB within 221 MHz($4.326{\sim}4.587\;GHz$) at low frequency band, 181 MHz($7.739{\sim}7.954\;GHz$) at high frequency band. Maximum rejection characteristics of the filter are -61.8 dB at low frequency and -76.3 dB at high frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.21 no.6
• /
• pp.681-689
• /
• 2010

We will demonstrate a novel topology for the feedforward amplifier. This amplifier does not use a delay element thus providing an efficiency enhancement and a size reduction by employing a distributed element negative group delay circuit. The insertion loss of the delay element in the conventional feedforward amplifier seriously degrades the efficiency. Usually, a high power co-axial cable or a delay line filter is utilized for a low loss, but the insertion loss, cost and size of the delay element still acts as a bottleneck. The proposed negative group delay circuit removes the necessity of the delay element required for a broadband signal suppression loop. With the fabricated 2-stage distributed element negative group delay circuit with -9 ns of total group delay, a 0.2 dB of insertion loss, and a 30 MHz of bandwidth for a wideband code division multiple access downlink band, the feedforward amplifier with the proposed topology experimentally achieved a 19.4 % power added efficiency and a -53.2 dBc adjacent channel leakage ratio with a 44 dBm average output power.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.2
• /
• pp.147-153
• /
• 2009

In this paper, FSS(Frequency Selective Surface) using defect mode characteristic is proposed. The unit cell using defect mode characteristic of the proposed FSS is offered lower resonant frequency in the same cell size. The number of suitable array is optimized 13 by 13. Also, the patch antennas operated in WCDMA(Wideband Code Division Multiple Access) Tx band and Rx band are designed for the comparison. The gain value of proposed FSS-1 complex structure (the patch antenna of Tx band and FSS) is improved 3.3 dB from 9.98 dBi to 13.28 dBi in Tx band. The gain value of proposed FSS-2 complex structure(the patch antenna of Rx band and FSS) is improved 5.53 dB from 9.81 dBi to 15.34 dBi in Rx band. Also the measured impedance bandwidth($VSWR{\leq}2$) of manufactured $13{\times}13$ array antenna is from 337 MHz(1.87 to 2.21 GHz). The measured radiation gain is 11.39 dBi(1.94 GHz), 13.11 dBi(2.05 GHz), 11.09 dBi(2.14 GHz). The measured radiation efficiency is 81 %. Because the proposed FSS structure has more higher gain, it will be applied to antenna of WCDMA repeater system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.21 no.1
• /
• pp.28-35
• /
• 2010

In this paper, we designed and fabricated a ultra-wideband(UWB) bandpass filter with a good performance of a stopband, and a notched band in passband. The transformed equivalent circuit of the highpass filter was realized by distributed element. A wide-passband with 3-dB fractional bandwidth of more than 100 % was achieved by using optimum response of the HPF. For improving lower and upper stopband characteristic, a cross coupling between feed lines was employed, which was analyzed by desegmentation technique. In order to reject interference of Wireless LAN and Hyper LAN(5.15~5.825 GHz), the narrow notched(rejection) band was realized by a spurline. The fabricated BPF indicated the passband from 3.1 to 10.55 GHz and the flat group delay of less than 0.94 ns over the entire passband except the rejection band. The filter shown sharp attenuation both inside and outside the band and notched band from 5.2 to 6.12 GHz.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.7
• /
• pp.582-588
• /
• 2014

IMO and IALA have undertaken projects that GMDSS Modernization and E-navigation, which refer to "Future digital communications systems" for a more efficient transmission of voice and data communications in the VHF maritime mobile service. ITU has also resolved in WRC-07 Resolution 357 to study the use of spectrum-efficient technologies in order to provide for the operation of ship and port security and maritime safety systems. IALA and ITU WP5B have coordinated for the technical developments and the spectrum issues. Recommendation ITU-R M.1842-1 has approved by WP5B meeting. This revision provides a wideband data service both 50kHz and 100kHz in the VHF maritime mobile service. This paper has studied E-navigation, its needs for data exchange that includes explanations of the current methods for transmitting data by VHF that based in land mobile radio service. A further technologies trend is estimated for Recommendation ITU-R M.1842-1, that is based on the land mobile radio standards with some tailored to fit the needs of the maritime mobile service.

• Journal of Satellite, Information and Communications
• /
• v.4 no.1
• /
• pp.1-7
• /
• 2009

As the information age comes out, the aspect of future war brings about the many changes in terms of war-fighting environment. Accordingly, information superiority and intelligence-centric warfare have been important and new war-fighting concept such as NCW(network centric warfare) have been turned up. This paper proposed all-weather core-strategy communications systems guaranteeing not only the real-time transmission of the information collected in a battlefield and expansion, automation, and rapidity of a battlefield but also broadband, mobility, survivability, and flexibility. The proposed military satellite communications system is classified into wideband mass capacity link, survivability, and the system supporting OTM(on the move) communication for the real-time transmission of battlefield information. This paper analyzed the essential operation concepts and core schemes of the U.S. Army's next generation system, TSAT(Transformational Satellite Communication System). Base on the analysis results, this paper proposed that the architecture of next generation military satellite communications systems for NCW have to provide the data rate, anti-jamming capability, network control and management capability which are optimally adaptable for the wireless channel environments such as jamming and interference and to support the variety of platforms like high-speed mobile vehicles, micromini devices, super-high speed unmanned aerial vehicles. Finally, this paper also proposed that next generation military satellite communications systems need the technologies such as the adaptable multi-antenna, laser link, and next-generation anti-jamming waveform.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.7
• /
• pp.1-7
• /
• 2016

In this paper, the design methodology of a corrugated conical horn antenna is proposed to be obtain wide-band properties over the full range of frequencies in the Ku-band. In order to improve the properties of the corrugated conical horn antenna, such as its gain, VSWR, co-polarization to cross-polarization ratio and wide-bandwidth, two types of mode matching converters are implemented within it. One is located at the end of the circular waveguide, while the other is positioned in front of the horn-flare section. The properties of the antenna are analyzed and compared according to the position of the proposed converters through simulations. In the comparison of the antenna performance in the case where the VSWR, co-polarization to cross-polarization ratio and antenna gain over the Ku band of 12-18 GHz are less than 2, greater than 30dB and 20dB respectively, the former antenna exhibits greater stability and a wider frequency band than the latter from the viewpoint of transmitting and receiving signals simultaneously. Therefore, considering the gain, VSWR, radiation pattern and bandwidth, the horn antenna structure in which the mode matching converter is implemented inside the circular waveguide has better performance than the other.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.8A
• /
• pp.801-809
• /
• 2010

Limitation of optical phase conjugation for implementation of wideband and long-haul WDM transmission system is symmetric distribution of optical power and local dispersion with respect to optical phase conjugator (OPC). This limitation forces OPC to place at midway of total transmission length. This paper shows that the limitation of optical phase conjugation is overcame by applying optimal net residual dispersion (NRD) into transmission links based in inline dispersion management (DM). Optimal NRD related with OPC position is decided by combination of precompensation and postcompensation. It is confirmed that optimal NRD depends on launch power of WDM channels and system performance criterion as well as OPC position. That is, in case of 1 dB eye opening penaty (EOP) as a performance criterion for WDM channels with 0 dBm launch power, it is confirmed that OPC is allowed to place at anywhere of 1000 km by applying best NRD related with exact OPC position into transmission links. And, it is confirmed that, under 3 dB EOP criterioin for WDM channels with 3 dBm launch power, OPC is allowed to place at 350~700 km by applying NRD between 100 ps/nm and 200 ps/nm into transmission links, though that NRD value is not best combination of precompensation and postcompensation.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.11
• /
• pp.635-639
• /
• 2016

In the devices used in the microwave frequency band, the gain decreases as the frequency increases due to the parasitic component. To compensate for these characteristics, a linear gain equalizer with an opposite slope is needed in wideband systems, such as those used for electronic warfare. In this study, a linear gain equalizer that can be used in the 18 ~ 40GHz band is designed and fabricated. Circuit design and momentum design (optimizations) were carried out to reduce the errors between design and manufacturing. A thin film process is used to minimize the parasitic components within the implementation frequency band. A sheet resistance of 100 ohm/square was employed to minimize the wavelength variation due to the length of the thin film resistor. This linear gain equalizer is a structure that combines a quarter wavelength-resonator on a series microstrip line with a resistor. All three 1/4 wavelength short resonators were used. The fabricated linear gain equalizer has a loss of more than -5dB at 40GHz and a 6dB slope in the 18 ~ 40GHz band. By using the manufactured gain equalizer in a multi-stage connected device such as an electronic warfare receiver, the gain flatness degradation with increasing frequency can be reduced.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.47 no.5
• /
• pp.43-51
• /
• 2010

Attenuation coefficients of medical ultrasound not only reflect the pathological information of tissues scanned but also provide the quantitative information to compensate the decay of backscattered signals for other medical ultrasound parameters. Based on the frequency-selective attenuation property of human tissues, attenuation estimation methods in spectral domain have difficulties for real-time implementation due to the complexicity while estimation methods in time domain do not achieve the compensation for the diffraction effect effectively. In this paper, we propose the modified VSA method, which compensates the diffraction with reference phantom in time domain, using adaptive bandpass filters with decreasing center frequencies along depths. The adaptive bandpass filtering technique minimizes the distortion of relative echogenicity of wideband transmit pulses and maximizes the signal-to-noise ratio due to the random scattering, especially at deeper depths. Since the filtering center frequencies change according to the accumulated attenuation, the proposed algorithm improves estimation accuracy and precision comparing to the fixed filtering method. Computer simulation and experimental results using tissue-mimicking phantoms demonstrate that the distortion of relative echogenicity is decreased at deeper depths, and the accuracy of attenuation estimation is improved by 5.1% and the standard deviation is decreased by 46.9% for the entire scan depth.