Rockwell Science Center Collaboration
The quasi-optical power amplifier is to make use of spatial power combining technique to combine the output power of hundreds of transistors in an efficient manner. A detail discussion of spatial power combining technique can be found in [1]. The project involves design and fabrication of monolithic grid amplifiers as shown in Fig. 1. The design of grid amplifier makes use of infinite periodic array and plane wave incident and radiated assumptions. Each unit cell consists of a differential amplifier pair. The transistors are fabricated on a GaAs substrate using a 0.18mm pHEMT process. The fabricated grid amplifier is about 1cm by 1cm in size and consists of 256 differential amplifiers. The power combining is done by allowing the output power of each differential pair to freely radiate into free space and collect the power by lens and scalar feed horn antenna.
Quasi-Optical Power AmplifierI

This amplifier has maximum gain of 8dB at 37GHz with power added efficiency of 20% and maximum output power of 5W [2]. The same amplifier can also be converted into an oscillator by feeding part of the output energy into input using an angled polarizer [3]. A different approach of feeding and collecting power is under development by making use of over-moded waveguide. A prototype grid amplifier fed by over-moded waveguide is shown in Fig. 3. The mode converter is used to transfer power from standard waveguide into over-moded waveguide in a controlled fashion such that the phase and magnitude distribution across the grid amplifier surface is maximally uniform. The output power is radiated into free space and collected by horn antenna or dish antenna. The next step would be to feed and collect power on both sides using over-moded waveguide. The collecting unit again has to be able to impose maximally flat distribution across the grid aperture in order to maximize the efficiency of the grid.

References:

[1] Active Quasi-optical arrays for Solid-state Power Combining, R.A. York and Z.B. Popovic' -John Wiley & Sons.

[2]A 5-Watt, 37-GHz Monolithic Grid Amplifier , B. Dickman, D.S. Deakin, D. Rutledge, E. Sovero -IEEE Intl. Microwave Symposium, 2000.

[3]A 1-Watt, 37-GHz Monolitich Grid Amplifier , B. Dickman, J.J. Rosenberg, D. Rutledge, E. Sovero and D.S. Deakin -IEEE Intl. Microwave Symposium, May 20-25, 2001, Phoenix, AZ.


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updated March 4, 2001