Browsing by Author "Özipek, Ulaş"

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Open Access
A 6-18 GHz GaN power amplifier MMIC with high gain and high output power density
(IEEE, 2019) Sütbaş, Batuhan; Özipek, Ulaş; Gürdal, A.; Özbay, Ekmel
A three-stage reactively-matched 6-18 GHz power amplifier MMIC design is presented. The design effort is focused on obtaining a low-loss output matching network for a high output power density. Active unit cells consist of an 8×125 μm transistor stabilized with a symmetrical parallel RC circuit. The wideband amplifier is fabricated using our in-house 0.25 μm GaN on SiC HEMT process. The fabrication technology details and overall device performance are reported. Experimental results show that the MMIC has a minimum gain of 22 dB and a maximum gain of 26.5 dB across the operation band. An average output power density higher than 3.3W/mm with an associated average power-added efficiency of 22.5% is achieved. The MMIC demonstrates output power greater than 9.5 W at the center frequency. This design is distinguished from recent studies with its low-ripple high gain and high output power density.
Open Access
Design of an X-band GaN based microstrip MMIC power amplifier
(2019-02) Özipek, Ulaş
RF power amplifiers are crucial components of modern radar and communication systems. However, their design poses some challenges due to device limitations in high power and high frequency regime, as well as inherent difficulties of designing for nonlinear large-signal device operation. Gallium Nitride (GaN) based High Electron Mobility Transistors (HEMT) are promising candidates due to their superior material qualities, high power densities and ability to operate up to mm-wave frequencies. In this thesis, 0.25 μm GaN on SiC microfabrication process of Bilkent University Nanotechnology Research Center (NANOTAM) is presented. Transistor characterization procedure is demonstrated. Ideal transistor layout for design goals is selected and the transistor gate structure is optimized for X-band performance. A model library for microstrip passive circuit elements based on electromagnetic simulations has been developed. Finally, design and measurements of an X-band microstrip Class AB two-stage Monolithic Microwave Integrated Circuit (MMIC) PA, based on the same process are presented in detail. With die sizes smaller than 4.3 mm by 2.3 mm, fabricated MMICs operate at 8.5 - 11.5 GHz band with 24 dB small-signal gain. More than 13.5 W (41.3 dBm) output power (P6dB) and 31 - 38 % power-added efficiency are achieved throughout the 8.5 - 11 GHz band in pulsed mode on-wafer measurements.
Open Access
A high gain and high efficiency 15 W X-Band GaN power amplifier MMIC
(IEEE, 2019) Gürdal, Armağan; Özipek, Ulaş; Sütbaş, Batuhan; Özbay, Ekmel
An X-band microstrip power amplifier MMIC based on our 0.25 μm AlGaN/GaN on SiC process technology is presented in this work. Fabrication steps, HEMT structure and typical device performance are demonstrated. Design procedure of the three-stage power amplifier MMIC with a compact size of 4.7 mm × 2.7 mm is described. Small-signal measurements of the fabricated MMICs typically show 36 dB gain with 5 dB ripple and input/output return losses better than 16 dB and 7 dB from 8.5 GHz to 12 GHz band, respectively. Typical output power of 15 W at 6 dB compression with 37%-44% power added efficiency is achieved under pulsed operation. MMIC power measurements performed at different base plate temperatures and bias conditions are also provided. This design exhibits significantly higher gain and much better input return loss compared to MMICs in the literature with similar size, efficiency and output power parameters.
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Kıbrıs Barış Harekatı sürecinin teknoloji gelişimine etkisi
(Bilkent University, 2012) Nergiz, Tahsin Can; Oğuz, Dilara; Özçelik, Özhan; Özipek, Ulaş; Özkayalar, Deniz