Tech Briefs

Submillimeter-Wave Amplifier Module With Integrated Waveguide Transitions

This technique can be used in submillimeter-wave imaging in homeland security, weapons detection, and commercial test equipment.

To increase the usefulness of monolithic millimeter-wave integrated circuit (MMIC) components at submillimeter-wave frequencies, a chip has been designed that incorporates two integrated, radial E-plane probes with an MMIC amplifier in between, thus creating a fully integrated waveguide module. The integrated amplifier chip has been fabricated in 35-nm gate length InP high-electron-mobility-transistor (HEMT) technology. The radial probes were mated to grounded coplanar waveguide input and output lines in the internal amplifier. The total length of the internal HEMT amplifier is 550 μm, while the total integrated chip length is 1,085 μm. The chip thickness is 50 μm with the chip width being 320 μm.

altThe internal MMIC amplifier is biased through wirebond connections to the gates and drains of the chip. The chip has 3 stages, employing 35-nm gate length transistors in each stage. Wire bonds from the DC drain and gate pads are connected to off-chip shunt 51-pF capacitors, and additional off-chip capacitors and resistors are added to the gate and drain bias lines for low-frequency stability of the amplifier. Additionally, bond wires to the grounded coplanar waveguide pads at the RF input and output of the internal amplifier are added to ensure good ground connections to the waveguide package.

The S-parameters of the module, not corrected for input or output waveguide loss, are measured at the waveguide flange edges. The amplifier module has over 10 dB of gain from 290 to 330 GHz, with a peak gain of over 14 dB at 307 GHz. The WR2.2 waveguide cutoff is again observed at 268 GHz. The module is biased at a drain current of 27 mA, a drain voltage of 1.24 V, and a gate voltage of +0.21 V. Return loss of the module is very good between 5 to 25 dB. This result illustrates the usefulness of the integrated radial probe transition, and the wide (over 10-percent) bandwidth that one can expect for amplifier modules with integrated radial probes in the submillimeter-regime (>300 GHz).

This technology was developed for a submillimeter-wave imaging system under the DARPA SWIFT program, in collaboration with Northrop Grumman Corporation. Submillimeter-wave imaging has many applications to homeland security, hidden weapons detection, airport security, detection of bio-weapons, as well as potential applications in commercial test equipment. This technology is partially a semiconductor chip product and partially a waveguide module. The semiconductor is not fixed in its final form, but the module is essentially fixed in its final form.

This work was done by Lorene Samoska, Goutam Chattopadhyay, David Pukala, Todd Gaier, Mary Soria, and King Man Fung of Caltech and William Deal, Gerry Mei, Vesna Radisic, and Richard Lai of Northrop Grumman Corporation for NASA’s Jet Propulsion Laboratory. The contributors would like to acknowledge the support of Dr. Mark Rosker and the Army Research Laboratory. This work was supported by the DARPA SWIFT Program and Army Research Laboratory under the DARPA MIPR no. 06-U037 and ARL Contract no. W911QX-06-C-0050. NPO-45088

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