Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1999-07-20
2001-06-12
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S026000
Reexamination Certificate
active
06246299
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a signal combiner, and more particularly to a high power broadband non-directional signal combiner for use with coherent and non-coherent solid state power amplifiers.
BACKGROUND OF THE INVENTION
The development of solid-state power amplifiers for RF transmitters has created challenges to designers not present when using previous tube designs. One major problem with solid-state designs is their limited power handling capability. While high power devices have been developed, they are generally quite expensive and thus are not desirable for designs where cost is a significant factor.
One strategy for solving this dilemma has been to divide the signal to be amplified into several components and to direct these components to a like number of smaller solid-state power amplifiers. The outputs of the power amplifiers are then combined to provide an output signal level which is comparable to or higher than the output signal which could have been obtained from a single high power solid-state power amplifier.
This divide-and-conquer strategy has its own drawbacks, however. The primary drawback was that previous signal dividers and combiners had used conventional wound transformers and lumped inductive and capacitive components to achieve the required impedance matching. Such components are inherently narrow-banded and are thus impractical for applications where wide bandwidths are required. Modern solid-state power amplifiers are generally broad-banded, and conventional narrow-banded signal dividers and combiners severely limited their utility.
One solution to such narrow-banded dividers and combiners was provided by U.S. Pat. No. 4,774,481 to Edwards et al., which discloses a broadband non-directional signal combiner (non-directional meaning that the combiner can be used as either a combiner or a divider). The combiner utilizes coaxial cables interconnected in a bridge configuration, and a coaxial cable transformer. The bridge configuration increases bandwidth, while the transformer counteracts the impedance transforming characteristics of the combiner. The resulting combiner disclosed by Edwards et al. combines and divides signals across a broad range of frequencies with relatively large isolation between input ports, and a low voltage standing wave ratio. However, the combiner disclosed in Edwards et al. is not entirely flux canceling when in the coherent mode. In addition, the combiner has a relatively large number of interconnections which act as discontinuities in the circuit, which increase insertion losses.
Another solution to the problems associated with narrow-banded dividers and combiners has been proposed in commonly assigned U.S. patent application Ser. No. 09/067,852. The combiner disclosed therein utilizes coaxial cables which are wound into coils. This arrangement provides a combiner having a relatively short signal path with few discontinuities, such that insertion losses are low and relatively little inductance is required in the signal path. However, this configuration may not be able to provide as high a bandwidth as may be desired, which may be up to 50:1 or higher for example.
What is still needed, therefore, is a non-directional signal combiner which exhibits exceptional power handling ability with low insertion loss characteristics, which exhibits excellent isolation characteristics between input ports, which exhibits excellent input and output port voltage standing wave ratio characteristics, which is capable of dissipating relatively large amounts of unbalanced power, which employs flux canceling circuitry combined with transmission line mode impedance matching which inherently exhibits excellent IMD characteristics, which exhibits a usable bandwidth of a decade or more and which is rugged and reliable, and of a relatively simple design that is conducive to relatively inexpensive mass production.
SUMMARY OF THE INVENTION
An object, therefore, of the present invention is to provide a non-directional signal combiner which exhibits exceptional power handling ability with low insertion loss characteristics.
Another object of the present invention is to provide a non-directional signal combiner having the above characteristics and which exhibits improved isolation characteristics between input ports.
Another object of the present invention is to provide a non-directional signal combiner having the above characteristics and which exhibits excellent input and output port voltage standing wave ratio characteristics.
An additional object of the present invention is to provide a non-directional signal combiner having the above characteristics and which is capable of dissipating relatively large amounts of unbalanced power.
A further object of the present invention is to provide a non-directional signal combiner having the above characteristics and which employs flux canceling circuitry combined with transmission line mode impedance matching which inherently exhibits excellent IMD characteristics.
Yet another object of the present invention is to provide a non-directional signal combiner having the above characteristics and which exhibits a usable bandwidth of a decade or more.
Still another object of the present invention to provide a non-directional signal combiner having the above characteristics and which is rugged and reliable, and of a relatively simple design that is conducive to relatively inexpensive mass production.
These and other objects of the present invention are achieved by a signal combiner assembly having a common ground plane and first and second coaxial cable connectors. Each of the first and second coaxial cable connectors includes an inner conductor and an outer conductor, the outer conductors being connected to the common ground plane. First and second coaxial cables, each having an inner conductor and an outer conductor, are also provided. The inner conductor of the first coaxial cable extends between the inner conductor of the first coaxial cable connector and a sum port, while the inner conductor of the second coaxial cable extends between the inner conductor of the second coaxial cable connector and the sum port. The first and second coaxial cables passing through a hole provided in a piece of magnetic material from opposite sides of the hole. Preferably, the piece of magnetic material is formed from a ferrite and takes the shape of a toroid or squaroid.
Preferably, the signal combiner assembly also includes third and fourth coaxial cables having an inner conductor and an outer conductor. The inner conductor of the third coaxial cable extends between a first end of the outer conductor of the first coaxial cable and a second end of the outer conductor of the second coaxial cable. Similarly, the inner conductor of the fourth coaxial cable extends between a first end of the outer conductor of the second coaxial cable and a second end of the outer conductor of the first coaxial cable. Both ends of the outer conductors of both cables are connected to the common ground plane.
The signal combiner assembly also preferably includes a first dissipater extending between the first ends of the outer conductors of the first and the second coaxial cables and a second dissipater extending between the second ends of the outer conductors of the first and the second coaxial cables. Most preferably, the first and the second dissipaters comprise resistors.
It is also preferable to provide grounded capacitors connected at the sum port and at each output port and with capacitors in parallel with the first and the second dissipaters
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. The capacitors compensate for any residual reactance within the combiner.
Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
REFERENCES:
patent: 4182996 (1980-01-01), Spence
patent: 4309666 (1982-01-01), Ito et al.
patent: 4605902 (1986-08-01), Harrington
patent: 4647868 (1987-03-01), Mueller
patent: 4774481 (1988-09-01), Edwar
Glenn Kimberly E
Pascal Robert
St. Onge Steward Johnston & Reens LLC
Werlatone, Inc.
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