A Compact Ku Band Low Noise Amplifier
Using a Coplanar Circuit Medium
by John R. Lachapelle(1), Michael T. Murphy(2), Robert W. Jackson(3)
(1) Now at Trimble Navigation, Sunnyvale, CA:
(2) M/A-COM, Lowell, MA:
(3) University of Massachusetts, Amherst, MA
A coplanar low noise amplifier designed in cooperation with M/A-COM's
Microelectronics Division in Lowell, Massachusetts
Project Summary
A compact, 12-18 GHz, GaAs MMIC low noise amplifier has been designed and
constructed using the coplanar waveguide (CPW) circuit medium throughout. The purpose
of this work is to demonstrate that CPW can be used at these frequencies for a low noise
design and still meet the size limitations necessary for low cost production. Attractive
features include reduced back side processing, no vias, and suitability for flip chip
mounting.
The design process required topological considerations and modeling procedures that
are less well known for CPW than for other circuit mediums. For example, an important
consideration in choice of coplanar topology is the trade off between size and loss. This is
especially important in the input matching circuitry for an LNA. Another consideration is
the choice between lumped and distributed elements. A combination of electromagnetic
simulation and measured test structures was used to determine accurate lumped element
models for coplanar structures such as T-junctions, bends, and spiral inductors.
The 12-18 GHz design, constructed at M/A-COM's GaAs foundry, achieved first pass
characteristics of 12 db gain, 2.5:1 VSWR, and 4 db noise figure in an area of 1.6 mm x
1.6 mm. Thus, the modeling/design procedure has been verified. Further measurements
and more detailed modeling show that a second iteration design using the same process
would achieve 14 db gain, 2:1 VSWR and 3.5 db noise figure.
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