• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.5 s.96
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• pp.482-487
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• 2005

In this paper, we propose the control method of output impedance of each cascode unit cell of distributed amplifier by connecting varactors in the gate-terminal of common gate. Compared to common source unit cell, cascode unit cell has many advantages such as high gain and high output impedance as well as negative resistance loading. But if the transistor model which is used in design is inaccurate and process parameter is changed, oscillation sometimes can occur at band edge in which the gain start to drop. Therefore, we need control circuit which can prevent oscillation, although the circuit has already fabricated, and varactor connected to gate-terminal of common gate of cascode gain cell can play that part. Measured result of fabricated distributed amplifier shows the capability of contol of gain characteristic by adjusting of value of varactors, this can guarantee the stability of the circuit. The gain is $8.92\pm0.82dB$ over 49 GHz, the group delay is $\pm9.3 psec$ over 41 GHz. All transistor which has $0.15{\mu}m$ gate length is GaAs based p-HEMT, and distributed amplifier is put together with 4 stages.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.1
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• pp.23-32
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• 2008

In the VHF range, active antennas are widely used for wideband applications due to their small size. Active antenna consists of antenna elements and amplifiers, which are directly connected to each other. Gain and noise-figure characteristics are very important for good sensitivity performance, because it is located at the front end of a receiving system. In this study, we developed an active dipole antenna with 5:1 bandwidth(100${\sim}$500 MHz), which consists of a dipole antenna and a P-HEMT amplifier. To obtain required performances, the antenna and the amplifier should be designed simultaneously. In order for that, we introduced an equivalent port concept to model the 1-port dipole antenna as an equivalent 2-port system. Using the proposed equivalent port, the performance of the active dipole antenna was simulated by the ADS. In order to measure the gain and noise-figure characteristics of the antenna, we utilized the same concept of the two-port equivalent impedance model. The measurement results for typical gain, NF and VSWR in the required frequency band were 8dBi, 9dB and 1.7:1, respectively. The radiation patterns at the principal planes were same as the typical radiation pattern of a dipole antenna. By comparing the simulation results with measured ones, it is confirmed that the proposed methods works well.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.1
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• pp.15-22
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• 2008

In this paper, we propose a numerical analysis on reversed current of distributed amplifier based on transmission line theory and proposed a theory to obtain optimum transmission line length to minimize the reversed currents by cancelling those components. The reversed current is analyzed as being simply absorbed into the terminal resistance in the conventional analysis. In the proposed analysis, however, they are designed to be cancelled by each other with opposite phase by the optimal length of the transmission lint Circuit simulation and implementation using pHEMT transistor were performed to validate the proposed theory with the cutoff frequency of 3.6 GHz. From the measurement, maximum gain of 14.5dB and minimum gain of 12.3dB were achieved In the operation band. Moreover, measured efficiency of the proposed distributed amplifier is 25.6% at 3 GHz, which is 7.6%, higher than the conventional distributed amplifier. Measured output power Is about 10.9dBm, achieving 1.7dB higher output power than the conventional one. Those improvement is thought to be based on the cancellation of refersed current.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.12
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• pp.1350-1359
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• 2008

This paper presents a wideband doubly balanced resistive mixer fabricated using $0.5{\mu}m$ GaAs p-HEMT process. Three baluns are employed in the mixer. LO and RF baluns operating over an 8 to 20 GHz range were implemented with Marchand baluns. In order to reduce chip size, the Marchand baluns were realized by the meandering multicoupled line and inductor lines were inserted to compensate for the meandering effect. IF balun was implemented through a DC-coupled differential amplifier. The size of IF balun is $0.3{\times}0.5\;mm^2$ and the measured amplitude and phase unbalances were less than 1 dB and $5^{\circ}$, respectively from DC to 7 GHz. The mixer is $1.7{\times}1.8\;mm^2$ in size, has a conversion loss of 5 to 11 dB, and an output third order intercept(OIP3) of +10 to +15 dBm at 16 dBm LO power for the operating bandwidth.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.5
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• pp.796-805
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• 2000

A 30GHz band low noise amplifier module, which has linear gain of 30dB and noise figure of 2.6dB, for 30GHz satellite communication transponder was developed by use of MMIC and thin film MIC technologies. Two kinds of MMIC circuits were used for the low noise amplifier module, the first one is ultra low noise MMIC circuit and the other is wideband and high gain MMIC circuit. The pHEMT technology with 0.15$mu extrm{m}$ of gate length was applied for MMIC fabrication. Thin film microstrip lines on alumina substrate were used to interconnect two MMIC chips, and the thick film bias circuit board were developed to provide the stabilized DC bias. The input interface of the low noise amplifier module was designed with waveguide type to receive the signal from antenna directly, and the output port was adopted with K-type coaxial connector for interface with the frequency converter module behind the low noise amplifier module. Space qualified manufacturing processes were applied to manufacture and assemble the low noise amplifier module, and space qualification level of environment tests including thermal and vibration test were performed for it. The developed low noise amplifier was measured to show 30dB of minimum gain, $\pm$0.3dB of gain flatness, and 2.6dB of maximum noise figure over the desired operating frequency range from 30 to 31 GHz.

• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.1
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• pp.13-20
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• 2003

Both MgO and $Sc_2O_3$ are shown to provide low interface state densities (in the $10^{11}{\;}eV^{-1}{\;}cm{\;}^{-2}$ range)on n-and p-GaN, making them useful for gate dielectrics for metal-oxide semiconductor(MOS) devices and also as surface passivation layers to mitigate current collapse in GaN/AlGaN high electron mobility transistors(HEMTs).Clear evidence of inversion has been demonstrated in gate-controlled MOS p-GaN diodes using both types of oxide. Charge pumping measurements on diodes undergoing a high temperature implant activation anneal show a total surface state density of $~3{\;}{\times}{\;}10^{12}{\;}cm^{-2}$. On HEMT structures, both oxides provide effective passivation of surface states and these devices show improved output power. The MgO/GaN structures are also found to be quite radiation-resistant, making them attractive for satellite and terrestrial communication systems requiring a high tolerance to high energy(40MeV) protons.

• Journal of Advanced Navigation Technology
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• v.14 no.1
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• pp.20-26
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• 2010

In this paper, a frequency tripler has been designed with 100mW medium-power using P-HEMT. It is designed to obtain 7.2 GHz frequency at the output that is an integer multiple of 2.4 GHz input frequency by using nonlinear device that produces 3rd harmonic. The frequency tripler is designed by using load-pull simulation. To suppress the 2nd and fundamental, notch filter is used for the frequency tripler. The tripler is designed to obtain about 21dBm output power with 15 dBm input, i.e., 6 dB conversion gain and the suppression of 20 dBc at fundamental, and 30 dBc at the second harmonics.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.8
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• pp.1297-1304
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• 2002

The phase locked oscillator having a low phase noise and high output in Ku-band was designed. To obtain the low phase noise and high output characteristics of oscillator, the nonlinear equivalent circuits of p-HEMT was analyzed by TOM method and we have decided the trade-off bias point between the low phase noise and the output power of oscillator. The designed phase locked oscillator with prescaler for stable operation, experiment results exhibits output power of 1003m with phase noise in the phase locked state of -824BC/HB at 10mz offset from 13.250Hz, and simulation result of 1003m output power in the phase noise -840Bc/Hz at 10KHz offset frequency respectively. a good agreement has been obtained between simulations and experiments results.

• ETRI Journal
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• v.34 no.5
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• pp.649-654
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• 2012

This paper presents a novel 16-quadrature-amplitude-modulation (QAM) E-band communication system. The system can deliver 10 Gbps through eight channels with a bandwidth of 5 GHz (71-76 GHz/81-86 GHz). Each channel occupies 390 MHz and delivers 1.25 Gbps using a 16-QAM. Thus, this system can achieve a bandwidth efficiency of 3.2 bit/s/Hz. To implement the system, a driver amplifier and an RF up-/down-conversion mixer are implemented using a $0.1{\mu}m$ gallium arsenide pseudomorphic high-electron-mobility transistor (GaAs pHEMT) process. A single-IF architecture is chosen for the RF receiver. In the digital modem, 24 square root raised cosine filters and four (255, 239) Reed-Solomon forward error correction codecs are used in parallel. The modem can compensate for a carrier-frequency offset of up to 50 ppm and a symbol rate offset of up to 1 ppm. Experiment results show that the system can achieve a bit error rate of $10^{-5}$ at a signal-to-noise ratio of about 21.5 dB.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.12
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• pp.1-6
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• 2007

In this study, we have performed the channel modification of the conventional MHEMT (metamorphic high electron mobility transistor) to improve the breakdown characteristics. The Modified channel consists of the InxGal-xAs channel and the InP sub channel instead of the InxGa1-xAs channel. Since InP has the lower impact ionization coefficient in comparison with In0.53Ga0.47As, we have adopted the InP-composite channel in the modified MHEMT. We have investigated the breakdown mechanism and the RF characteristics for the conventional and the InP- composite channel MHEMTs. From the measurement results, we have obtained the enhanced on and off-state breakdown voltages of 2.4 and 5.7 V, respectively. Also, the increased RF characteristics have brought about the decreased output conductance for the InP-composite channel MHEMT. The cut-off frequency (fT) and the maximum oscillation frequency (fmax) for the InP-composite Channel MHEMT were 160 GHz and 230 GHz, respectively. It has been shown that the InP-composite channel MHEMT has the potential applications for the millimeter wave power device.