The classical zero-shifting technique is generalized to cover extraction of complex transmission zeros (TZs) in the form of fourth-order LC sections whereby the -and -axis TZs appear as special cases. Using this approach, bandpass filters can be synthesized in direct coupled resonator forms by pole placement instead of designing them through low-pass prototypes. By using circuit transformations, the resulting direct coupled resonator filter circuits can then be transformed into a variety of cross-coupled forms like a fully cross-coupled form or cascaded -tuplet form. It is shown that one or more finite -axis, -axis, or complex TZs can be extracted as direct coupled resonator circuit blocks, which can be converted into cross-coupled triplets, quadruplets, or other -tuplets of resonators. In particular, it is shown that a cascaded quadruplet section can be used to realize a complex TZ quadruplet = , as well as two pairs of -axis TZs, = , and = .

This work analyzes the effect of various gate structures on the DC and radio frequency (RF) performance of AlGaN/GaN high-electron mobility transistors (HEMTs). AlGaN/GaN HEMT devices with a 3 μm drain-to-source spacing, 125 μm gate width and 0.3 μm gate length in various gate structures were fabricated to achieve the desired frequency response with a robust, high yield, and repeatable process. The maximum drain current (I DS , max), maximum DC transconductance (g m), pinch-off voltage (V th), current-gain cutoff frequency (f T), maximum oscillation frequency (f max), and RF characteristics of the devices in terms of the small-signal gain and RF output power (P out) at 8 GHz were investigated. The results showed that the output power is increased by 1 dB when the gate structure is changed from field plate to gamma gate. The V th , g m , f T and f max values are maximized when the thickness of the passivation layer between the gate foot and the gate head is minimized. It is shown that the I DS,max is decreased and P out is increased when the gate recess etching process is performed.

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