Kazutaka Takagi

An X-band 250W solid-state power amplifier using GaN power HEMTs

More than 250 W of peak output power (pulse width 64 mus, duty cycle 7%) is achieved with newly developed X-band solid-state power amplifier. The final stage of the SSPA consists of four 80 W class GaN power HEMTs and a low loss 4-way combiner. Compared with the conventional klystron tubes, our newly developed SSPAs are smaller, more reliable and require less amounts of occupied frequency bandwidth.

Simulation and experimental results of source harmonic tuning on linearity of power GaAs FET under class AB operation

Nonlinearity of GaAs FET amplifiers under class AB operation such as an abrupt increase of the output power against the input power can be effectively reduced by suppressing even-order harmonic distortion in the gate RF voltage. In this paper, we demonstrate the effect of the source harmonic tuning and condition for improving the linearity of power GaAs FETs under class AB operation by the source harmonic tuning technique.

X-band AlGaN/GaN HEMT with over 80W Output Power

AlGaN/GaN high electron mobility transistors (HEMTs) were developed for X-band applications. The operating voltage and temperature dependence of output power characteristics in CW operating conditions were investigated. The developed AlGaN/GaN HEMT with combined two dies of 11.52 mm gate periphery exhibits output power of over 81.3W with a power added efficiency (PAE) of 34% under VDS=30V, CW operating condition at 9.5GHz, and a gain compression level of 3dB

Ku-band AlGaN/GaN-HEMT with over 30% of PAE

AlGaN/GaN High Electron Mobility Transistors (HEMTs) were improved for X-band and Ku-band applications. The power added efficiency (PAE) was achieved over 40% for X-band and over 30% for Ku-band. The developed devices combined two AlGaN/GaN HEMTs of 12 mm gate periphery and exhibited the output power of over 50W. An AlGaN/GaN HEMT with four dies of 12 mm gate periphery was developed and exhibited the output power of over 120W.

Ku-band AlGaN/GaN HEMT with over 30W

AlGaN/GaN high electron mobility transistors (HEMTs) were developed for Ku-band applications. The operating voltage characteristics in CW operating conditions were investigated. The developed AlGaN/GaN HEMT with combined two dies of 12 mm gate periphery exhibits output power of over 30 W with a power added efficiency (PAE) of 12% under VDS = 30 V, CW operating condition at 14.25 GHz, and a gain compression level of 3 dB.

A multicenter phase II prospective clinical trial of glucocorticoid for patients with untreated IgG4-related disease

Abstract Objective: Although glucocorticoids are effective for patients with IgG4-related disease, the treatment has not yet been standardized. Therefore, the treatment strategy should be established. Patients and methods: Patients who fulfilled the comprehensive diagnostic criteria for definite IgG4-related disease were started on prednisolone (0.6 mg/kg body weight) with the dose reduced every two weeks. The subsequent maintenance dose and need for prednisolone were determined for individual patients. The primary endpoint was the complete remission (CR) rate at one year. Secondary endpoints included overall response rate (ORR), the maintenance dose, the relapse rate, and adverse events. Results: This study enrolled 61 patients. After clinicopathological review, three patients were excluded, and one, 13, and 44 patients were diagnosed with probable, possible, and definite IgG4-related disease, respectively. Of the 44 patients with definite IgG4-RD, 29 (65.9%) achieved CR, and the ORR was 93.2%. No patient was refractory to primary treatment. The most frequent adverse events were glucose intolerance. Six patients relapsed. Conclusions: Glucocorticoid treatment is usually effective for patients with IgG4-RD, and we should examine the possibility of other disorders when a patient is glucocorticoid refractory. Some patients are misdiagnosed, making central clinicopathological review of diagnosis very important in conducting clinical studies.

5-GHz band 30 watt power GaAs FETs

C-band high-power and high-efficiency GaAs FETs (field-effect transistors) have been developed. The active region of the FET chip has been highly integrated by forming long gate fingers. Four chips are power-combined efficiently by using internal matching circuits. The FETs deliver an output power at 1-dB gain-compression point of 30 W with 6.8-dB gain and 28% power-added efficiency, and a saturated output power of 33 W at 5.5 GHz. They exhibit an excellent linearity with a third-order intermodulation distortion intercept point of +55 dBm.<<ETX>>

Developing GaN HEMTs for Ka-Band with 20W

AlGaN/GaN High Electron Mobility Transistors(HEMTs) were developed for Ka-band. The developed device showed 138 GHz of fmax, which depended on the thickness of the AlGaN barrier layer and the gate length. It had a 6.4 mm gate periphery on a metal carrier plate. The output power achieved 20 W with impedance matching circuits.

GaN MMIC for Ka-Band with 18W

A Ka-band high power amplifier MMIC developed from a robust process of 0.2μm gate-length AlGaN/GaN HEMT on SiC is presented. The MMIC chip was measured across 29 to 31GHz under pulsed bias condition. At VDD=28V, The MMIC chip achieved a power added efficiency of 17% with an output power of 18W. The 2-stage amplifier GaN MMIC has 10.2dB linear gain and a die-size of 4.0mm × 5.5mm. The MMIC can realize high power Solid-State Power Amplifier.

Numerical Device Model for Reliable AlGaN/GaN HEMT Structure Design Based on Shear Stress

A numerical device model is proposed for the design of reliable AlGaN/GaN HEMT structures. In the model, shear stress due to the inverse piezoelectric effect is used to predict high-temperature DC stress test results. The calculated shear stress is compared with test results for various AlGaN/GaN HEMT structures. The comparison shows that structures passing the test have shear stress lower than 0.19 GPa under the test conditions. An AlGaN/GaN HEMT structure for the Ka band was designed so that stress would be lower than this value. The designed structure was fabricated and passed the test. These results indicate that the model can be used to design reliable AlGaN/GaN HEMT structures.