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A 6-18 GHz gallium nitride (GaN) non-uniform distributed amplifier (NDA) monolithic microwave integrated circuit with high power density is implemented with compact four-way combined power. The drain lines and gate lines are shared among the combined NDAs. Sharing drain (or gate) lines reduces the drain (or gate) line length by half, while keeping the same characteristic impedances and eliminates bulky and lossy power combiners, such as Wilkinson combiners. The proposed four-way NDA was fabricated using a commercial 0.25 μm GaN high electron mobility transistor (HEMT) process. It shows average continuous wave output power of 20.8 W and average associated gain of 10.7 dB from 6 to 18 GHz under 33 V drain bias. When pulsed input power and pulsed DC bias are simultaneously supplied to the NDA, the output power increases to 26 W, on average. To the best of the authors' knowledge, the highest RF power and power density among the reported GaN power amplifiers with an octave bandwidth higher than the Ku-band is represented in this work.

An experimental study was performed on spray characteristics of spray diesel (D100) and biodiesel blend (BD65) injected into an atmospheric chamber. A qualitative analysis of spray images was conducted through exploiting the image processing with common image processing software. The results showed that the posterization of the images offered more detailed qualitative information on the spray compared to the more commonly-used threshold method. The posterized images showed the existence of layers in the spray with its transition at different grey levels. At lower injection, the spray tip penetration of BD65 was slightly lower than D100, whereas at high injection pressure, spray tip penetration of BD65 was higher than D100. Although BD65 had lower maximum velocity, the higher density of biodiesel may have resulted in greater momentum that enabled BD65 to have longer spray tip penetration at higher injection pressure. At higher injection pressure, the spray angle of BD65 tended to be less than that of D100.

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