New Papers from Ali Darwish

Instructor Ali Darwish has co-authored a couple of new papers recently. The most recent one, A Broadband 1-to- N Power Divider/Combiner With Isolation and Reflection Cancellation appears in the IEEE MTT Transactions. You must be a member of the IEEE Microwave Theory and Techniques society to get free access.

A novel 1-to- N broadband “ iπ-wave” power divider/combiner with reflection cancellation is presented and demonstrated. The new iπ-wave structure provides reflection cancellation and output port isolation with 1-to- N (arbitrary N) signal splitting or N-to-1 summing. It has low loss due to its use of low-impedance transmission lines and provides a relative bandwidth of 50%-200%. The concept is studied theoretically and demonstrated experimentally with several 1-to-4 dividers. The divider/combiner pair provides power amplifiers with broadband operation and well-matched input/output impedances. The concept can be implemented in hybrid circuits or monolithic microwave integrated circuits (MMICs).

His other article, Channel Temperature Analysis of GaN HEMTs With Nonlinear Thermal Conductivity appears in the IEEE Transactions on Electron Devices.

This paper presents an enhanced, closed-form expression for the thermal resistance, and thus, the channel temperature of AlGaN/gallium nitride (GaN) HEMTs, including the effect of the temperature-dependent thermal conductivity of GaN and SiC or Si substrates. In addition, the expression accounts for temperature increase across the die-attach. The model's validity is verified by comparing it with experimental observations. The model results also compare favorably with those from finite-element numerical simulations across the various device geometric and material parameters. The model provides a more accurate channel temperature than that from a constant thermal conductivity assumption; this is particularly significant for GaN/Si HEMTs where the temperature rise is higher than in GaN/SiC. The model is especially useful for device and monolithic microwave integrated circuit designers in the thermal assessment of their device design iterations against required performance for their specific applications.

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