• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.35D no.5
• /
• pp.40-47
• /
• 1998

This paper report sthe design, fabrication and characterization of an AlGaAs/GaAs HBT (heterojunction bipolar transistor) with an air-bridge isolation structure which is made to improve high frequency characteristics for the application to the mobile communication system in the next genration. We found that the size, shape and structure of HBT have an effect on the high frequency operation. The measured dc and ac characteristics of the four type HBTs were compared and analyzed. An E-type HBT with an air-bridge structure by undercut etching exhibited .beta.=56, $V_{off-set}$ = 0.3 V, B $V_{CEO}$=7.0V with $f_{T}$=40 GHz and $f_{max}$=45GHz at a collector current density of 7.1*10$^{4}$ A/c $m^{2}$.>.

• Korean Journal of Crystallography
• /
• v.11 no.4
• /
• pp.191-194
• /
• 2000

Bi/sub 12/SiO/sub 20/, Bi/sub 12/GeO/sub 20/ and Bi/sub 12/O/sub 20/ compounds with the sillenite crystal structure were synthesized and sintered into the dense ceramic bodies. An analyses of the microwave dielectric properties of the Si, Ge and Ti sillenites showed a permittivity (e) of ∼40 and a negative temperature coefficient of the resonant frequency for all analogues (from -20 to -40 ppm/K). The Qxf value of the Si and Ge sillenites was measured to be ∼8.000 GHz. The Ti analogue shows a significantly lower Qxf value(∼2.500 GHz) and is sensitive to the heat-treatment conditions. By increasing the sintering temperature the size of the grains increases, which correlates with an increase in the Qxf value.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.1
• /
• pp.69-72
• /
• 2004

A bandpass filter has been designed by employing the PBG structure and the aperture on the ground together in this paper. The harmonics of band pass filter have been suppressed by employing the PBG structure and the bandwidth of it has been broadened by using the aperture on the ground. The three kinds of PBG structures has been combined to suppress the harmonics of the filter The center frequency of filter is 2.2 GHz and the bandwidth has been increased from $40\%$ by the aperture and all harmonics were suppressed about 35dBc by the PBG. The insertion loss has been reduced 3.0dB to 2.6dB.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.1
• /
• pp.65-68
• /
• 2004

The performances of millimeter wave Power amplifier have been improved by using PBG (photonic bandgap structure) in this paper. The PBG structure has been optimized to obtain the lowpass characteristics in Ka band and employed at output port of Ka band power amplifier. The harmonics of the power amplifier have been suppressed by the PBG of output port and the proposed PBG has suppressed the second harmonic to 40dBc around 50 GHz. The improvements of IMD and PAE of the amplifier employing the PBG structure are obtained $15\%$ and $25\%$, compared with those of the conventional Ka band power amplifier, respectively.

• Proceedings of the KSRS Conference
• /
• 2007.10a
• /
• pp.378-381
• /
• 2007

Analyses of Tropical Rainfall Measuring Mission (TRMM) microwave radiometer (TMI) and precipitation radar (PR) data show that the rainfall inhomogeneity, represented by the coefficient of variation, decreases as rain rate increases at the low resolution (the footprint size of TMI 10 GHz channel). The rainfall inhomogeneity, however, is relatively constant for all rain rates at the high resolution (the footprint size of TMI 37 GHz channel). Consequently, radiometric signatures at lower spatial resolutions are characterized by larger dynamic range and smaller variability than those at higher spatial resolution. Based on the observed characteristics, this study develops a low-resolution (${\sim}40{\times}40$ km) rainfall retrieval algorithm utilizing realistic rainfall distributions in the a-priori databases. The purpose of the low-resolution rainfall algorithm is to make more reliable climatological rainfalls from various microwave sensors, including low-resolution radiometers.

• Proceedings of the IEEK Conference
• /
• 2003.11c
• /
• pp.323-326
• /
• 2003

본 논문은 무선 음성/영상 송수신용 RF모듈 설계 및 제작하였다. RF 주파수는 정보통신부에서 고시한 영상전송용 2410, 2430, 3450, 2470MHz 사용하였으며 IF 주파수는 479.5MHz를 사용하였다. 설계 및 제작된 RF 모듈은 FR-4 재질인 유전체 4.6, 두게 0.8mm, 양면구조의 기판을 사용하여 50mm x 40mm 크기로 제작되었다. 설계된 송신기 모듈은 ＋5V 단일전원으로 9±1dBm의 출력과 주파수허용편차 50×10/sup -6/이하, 스퓨리어스 발사강도 기본주파수의 평균전력보다 40dB이하의 성능을 만족하였다. 수신기 모듈은 +5V 단일 전원으로 -80dBm이하의 수신감도로 만족할만한 성능을 보였다.

• Journal of electromagnetic engineering and science
• /
• v.18 no.2
• /
• pp.88-93
• /
• 2018

Radio frequency (RF) and microwave power is one of the key quantities in the framework of electromagnetic measurement standards. Therefore, the stability of the power standard is essential to users' reliable measurements in various areas. Coaxial and waveguide thermistor mounts are used as transfer standards of RF and microwave power. Over decades, the effective efficiencies of thermistor mounts have been measured using coaxial and waveguide microcalorimeters in the frequency range of 10 MHz-40 GHz. The measurement uncertainty of the effective efficiency is evaluated. Results show that the power standards have been well maintained within the measurement uncertainty.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.48 no.12
• /
• pp.91-96
• /
• 2011

In this paper, a low-power direct-conversion transmitter based on current-mode operation, which satisfies the IEEE 802.15.4 standard, is proposed and implemented in a $0.13{\mu}m$ CMOS technology. The proposed transmitter consists of DACs, LPFs, variable gain I/Q up-conversion mixer, a divide-by-two circuit with LO buffer, and a drive amplifier. By combining DAC, LPF, and variable gain I/Q up-conversion mixer with a simple current mirror configuration, the transmitter's power consumption is reduced and its linearity is improved. The drive amplifier is a cascode amplifier with gain controls and the 2.4GHz I/Q differential LO signals are generated by a divide-by-two current-mode-logic (CML) circuit with an external 4.8GHz input signal. The implemented transmitter has 30dB of gain control range, 0dBm of maximum transmit output power, 33dBc of local oscillator leakage, and 40dBc of the transmit third harmonic component. The transmitter dissipates 10.2mW from a 1.2V supply and the die area of the transmitter is $1.76mm{\times}1.26mm$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.9
• /
• pp.1039-1046
• /
• 2007

In this paper, a coupled-defected ground structure(C-DGS) using negative inductive coupling is proposed and a bandstop filter(BSF) using C-DGS is designed and fabricated. The proposed C-DGS is the closely-located DGS cells for the negative coupling, the negative coupling of ground currents between adjacent DGS cells greatly improves the stopband characteristics. The proposed BSF utilizing the sharp cutoff response of the C-DGS has a -10 dB rejection band from 4 GHz to 11.3 GHz. A maximum attenuation rate is -64.3 dB/GHz in 3 cell structure, -108 dB/GHz in 5 cell structure. The C-DGS BSF shows the improved attenuation rate 3.8 times in 3 cell structure, 2.4 times in 5 cell structure, Also, the C-DGS BSF is reduced to 35.2 % and 40 % of the DGS BSF, respectively, due to the closely-located DGS cells. We fabricated the single gate mixer using C-DGS BSF. The single gate mixer has 6.6 dB conversion gain.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.4B
• /
• pp.388-396
• /
• 2002

In this paper, An aperture-coupled microstrip patch antenna operating at WLL frequency range(Rx : 2.3∼2.33Ghz, Tx : 2.37 ∼2.4Ghz) for WLL repeater is designed and fabricated. FR-4 epoxy substrate with 4.7 relative permittivity is inserted between feed-line and patch plane. Aperture-coupled structure is employed for consideration of bandwidth improvement and gain\`s characteristics. Air gap is arranged at each layer for bandwidth extension and radome is used as a protector in the upper patch. In this paper, both 1 port and 2 port are designed as 1$\times$2 array antenna which uses T-junction and λ$\_$g//4 transformer. Here, 1 port is used as transmitting/receiving antenna and 2 port is used as receiving antenna. Functionally independent two antennas using space diversity arrange slots between two antennas in order to be placed at the same place. As a result, we obtained a excellent isolation below -40dB and return loss is reduced by means of slots arrangement between patch and antenna.