Randall E. Lehmann

X-Band Monolithic Series Feedback LNA

AnX-band monolithic three-stage low-noise amplifier (LNA) employing series feedback has demonstrated 1.8-dB noise figure with 30.0-dB gain and an input VSWR less than 1.2:1 at 10 GHz. The key to this design is using monolithic technology to obtain an exactly repeatable series feedback inductance to achieve a simultaneous noise match and input VSWR match.An X-band monolithic three-stage low noise amplifier (LNA) employing series feedback has demonstrated 1.8 dB noise figure with 30.0 dB gain and an input VSWR less than 1.2:1 at 10 GHz. The key to this design is using monolithic technology to obtain an exactly repeatable series feedback inductance to achieve a simultaneous noise match and input VSWR match.

X-band monolithic GaAs PIN diode variable attenuation limiter

Monolithic GaAs PIN diode attenuator/limiter circuits have demonstrated 26 dB of variable attenuation at X-band, while maintaining under 1.5 to 1 input and output voltage standing wave ratios (VSWRs). Insertion loss is 0.8 dB at 10 GHz in the zero bias condition. Passive limiting provides 15 dB of isolation at RF input power of 2.0 W CW (continuous wave). These results are obtained using a vertical pin diode process on metallorganic chemical vapor deposition (MOCVD) material.<<ETX>>

Design and fabrication of a GaAs vertical MESFET

Vertically oriented GaAs MESFETs were fabricated on thick epitaxial conductive layers grown by molecular-beam epitaxy on a semi-insulating substrate. The vertical channel pattern was defined by electron-beam lithography and included structures as small as 0.3- 0.4 µm on a total period of 1.0 µm. The vertical channels were formed by reactive ion etching, and the gate contact was formed by dual-angle evaporation. The top ohmic contacts were interconnected by a metal bridge supported by a dielectric layer. The drain characteristics displayed a drain punchthrough effect, indicating that a very short gate length was achieved. Microwave measurements indicated a maximum oscillation frequency of 12 GHz.

Monolithic MBE GaAs Pin Diode Limiter

A broadband MBE GaAs PIN/NIP diode limiter has demonstrated 15 dB of isolation with a +32.5 dBm input signal while maintaining less than 0.25 dB of small-signal insertion loss from 0.05 GHz to 14 GHz. These results were obtained by incorporating vertical GaAs PIN/NIP diodes in a shunt-loaded microstrip configuration.

X-band monolithic variable gain series feedback LNA

A description is given of an X-band monolithic four-stage low-noise amplifier (LNA) using series feedback that has demonstrated a 1.8-dB noise figure with 33.8-dB gain and greater than 40-dB gain control capability. This design features single-gate and dual-gate FETs (DGFETs) on the same chip. Gain control is achieved without degradation of input or output VSWR (voltage standing-wave ratio). The two input stages use single-gate FETs to achieve minimum noise figure, while the output stages use DGFETs for gain control capability.<<ETX>>

CFET-a new high quality MMIC control device

A new GaAs device developed for use in microwave monolithic control circuitry has been demonstrated. Known as a CFET, for Control Field Effect Transistor, this device eliminates the need for a conventional submicron gate by achieving control by use of a gate located behind the source-drain channel. The resulting capacitance is smaller than a conventional MESEET, resulting in a figure of merit of 800 GHz as compared to 250 GHz for a conventional MESFET. The device capabilities are demonstrated by measured performance of a SPDT switch providing 0.35-dB insertion loss and 20-dB isolation over the DC -10.0-GHz frequency band.<<ETX>>