Wideband bandpass filter using unpowered HEMT amplifiers

A wideband bandpass filter using unpowered, packaged HEMT amplifiers is proposed and implemented. The key idea is to utilize very small parasitic capacitances of the unpowered HEMT as a part of the feedback loop connecting LC resonators. At the input power of -10 dBin, the 3 dB bandwidth of the fabricated bandpass filter is 93.6% of the center frequency (1.536 GHz). Furthermore, our filter does not show appreciable spurious up to 12 GHz. These internal capacitances of the HEMT extracted from the equivalent circuit modeling are shown to be in the range of 10-500 fF. (C) 2008 Wiley Periodicals, Inc.