Compact amplifier assemblies of a type now being developed for operation at frequencies of hundreds of gigahertz comprise multiple amplifier units in parallel arrangements to increase power and/or cascade arrangements to increase gains. Each amplifier unit is a monolithic microwave integrated circuit (MMIC) implementation of a pair of amplifiers in differential (in contradistinction to single-ended) configuration.

Heretofore, in cascading amplifiers to increase gain, it has been common practice to interconnect the amplifiers by use of wires and/or thin films on substrates. This practice has not yielded satisfactory results at frequencies >200 Hz, in each case, for either or both of two reasons:

  • Wire bonds introduce large discontinuities.
  • Because the interconnections are typically tens of wavelengths long, any impedance mismatches give rise to ripples in the gain-vs.-frequency response, which degrade the performance of the cascade.

Heretofore, it has been very difficult to achieve net increases in power by combining the outputs of amplifiers at frequencies >100 GHz. The only successful approach that has been even marginally successful has involved the use of waveguide combiners designed and fabricated as components separate from the amplifiers. At these frequencies, even waveguides exhibit high losses that can easily dissipate any power gained by combining outputs.

In the present development, neither thin-film nor wire interconnections are used for cascading, and separate component waveguide combiners are not used for combining power. Instead, the amplifier units are designed integrally with the waveguides and designed to be embedded in the waveguides. The underlying concept of differential-amplifier MMICs designed integrally with and embedded in waveguides and the advantages of the differential over the single-ended configuration were reported in “Differential InP HEMT MMIC Amplifiers Embedded in Waveguides” (NPO-42857) NASA Tech Briefs, Vol. 33, No. 9 (September 2009), page 35. The novel aspect of the present development lies in combining the integration and embedment concepts with the cascading and parallel-combining concepts to obtain superior performance. In an amplifier assembly of the present type, there is no need for interconnecting wires or thin-film conductors nor for separate waveguide power combiners because the waveguide in which the MMICs are embedded is the connecting medium. Because the distance between successive MMICs in a cascade is only a fraction of a wavelength, cascading can be highly efficient and ripple in gain versus frequency is reduced to a minimum. Moreover, power combining can be highly efficient because it is accomplished simply by placing MMICs side by side within the waveguide.

This work was done by Pekka Kangaslahti and Erich Schlecht of Caltech for NASA’s Jet Propulsion Laboratory. For more information, contact This email address is being protected from spambots. You need JavaScript enabled to view it..

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management JPL Mail Stop 202-233 4800 Oak Grove Drive

Pasadena, CA 91109-8099 E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-44394, volume and number of this NASA Tech Briefs issue, and the page number.

NASA Tech Briefs Magazine

This article first appeared in the December, 2010 issue of NASA Tech Briefs Magazine.

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