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A Flexible Circuit Circulator/Isolator

IP.com Disclosure Number: IPCOM000009060D
Original Publication Date: 2002-Aug-05
Included in the Prior Art Database: 2002-Aug-05
Document File: 2 page(s) / 42K

Publishing Venue

Motorola

Related People

Robert R. Kornowski: AUTHOR [+3]

Abstract

Circulators/Isolators are commonly employed in Solid State R.F. (Radio Frequency) P.A. (Power Amplifier) Assemblies to protect the active devices in the amplifier output circuitry from the potentially damaging effects of load malfunction. Circulators/Isolators are also used to reduce the magnitude of reverse-traveling interfering signal energy that can play against the nonlinearity of the power amplifier output device/s and thereby produce I.M.D. (Intermodulation Distortion).

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A Flexible Circuit Circulator/Isolator

By Robert R. Kornowski Robert R. Kornowski and Daniel J. Buntley

 
 

Circulators/Isolators are commonly employed in Solid State R.F. (Radio Frequency) P.A. (Power Amplifier) Assemblies to protect the active devices in the amplifier output circuitry from the potentially damaging effects of load malfunction. Circulators/Isolators are also used to reduce the magnitude of reverse-traveling interfering signal energy that can play against the nonlinearity of the power amplifier output device/s and thereby produce I.M.D. (Intermodulation Distortion). The associated circuit topology in this Isolator/Circulator application environment is typically comprised of planar microstrip structures that have co-resident R.F. “hot” and R.F. ground conductor systems wherein all of these constructions are collectively attached to a common heat sink structure. Owing to the physical mass and dissipation factor of a high power (200 Watt) Circulator’s/Isolator’s ferrous junction, and to the heat that is dissipated by the Circulator’s/Isolator’s load resistor when responding to a fault condition, the Circulator’s/Isolator’s housing design and electrical interconnection schemes end up being constrained to the point that R.F. functionality is compromised in order to accommodate the need for secure mounting and adequate heat sinking. The C.T.E. (Coefficient of Thermal Expansion) differences that typically exist in such application environments also necessitates some means of mediation to assure long-term reliability. Collectively, these conditions result in compromised designs wherein the R.F. ground current is conveyed through less than ideal “nut-and-bolt” conduction pathways and the R.F. “hot” current is conveyed through delicate inductive interconnection devices (“Omega Straps”) that provide the physical compliance which is needed to reconcile the systemic C.T.E. differences (see Figure 1).

Various schemes have historically been employed to mitigate the prior noted difficulties, but they also introduce new complications.   For example, a pair of R.F. ground Omega Straps can be symmetrically attached to the Circulator/Isolator housing on each side of the R.F. “hot” Omega Strap at the input/output ports to reduce the variability effects of “nut-and-bolt” R.F. ground current conveyance. This scheme, however, triples the number of delicate inductive interconnection devices that are needed for each electrical connection. In addition to increasing the cost of the Circulator/Isolator, this connection scheme necessitates expensive packaging to protect the delicate Omega Straps during transport and is subject to handling damage (deformation) when out of the package. Another scheme involves the application of capacitors to reduce the electrical discontinuity of the R.F. input/output port connections by tuning-out the Omega Strap inductance. While tuning does reduce the discontinuity of the R.F. connection, it also adds cost and complexity to the...