Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2001-07-19
2003-09-16
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S131000, C330S295000
Reexamination Certificate
active
06621374
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to power division and combination, and more particularly to power divider/combiners usable at radio frequencies including microwave and millimeter-wave frequencies.
BACKGROUND OF THE INVENTION
Modern communications often require broad bandwidth transmissions in order to accommodate very high data rates. These transmissions are made using electromagnetic or light signals. Regardless of the form of the transmission, substantial electronic amplifier power is often required at the transmitting end of a transmission path. If the transmission is by way of electromagnetic transmission lines, the lines are subject to significant losses at the high frequencies implied by broad bandwidth, and reamplification may be required at various points along the path. If the transmission path includes free-space propagation from one antenna to another, the transmission losses can be significant, which requires significant transmitted power to maintain the received signal above ambient noise levels. The production of photonic signals by means of lasers or other optoelectric devices is subject to significant inefficiencies. All of the losses and inefficiencies, in turn, require that electronic power amplification be performed.
As solid-state devices have improved over the years, the amount of power which an individual solid-state device can produce within a given frequency band has increased. As a result, a power level at a given frequency band which at one time might have required the paralleled outputs of several solid-state devices may now require only one solid-state device. However, with each advance in the power-handling capability of solid-state devices, the requirements of power, frequency and bandwidth have also increased, so that there is continuing need for electronic power amplifiers. The higher frequency and bandwidth requirements, in turn, tend to make parasitic reactances more important, and to require that the structures of the amplifiers become smaller, notwithstanding that the power requirements are remain high. Thus, in this context, the term “power” means that more than one solid-state device is required to produce the total output power of the amplifier, regardless of the actual power level.
The paralleling of amplifiers is old in the art. For example, vacuum-tube audio amplifiers using push-pull output stages were common at one time, and continue to find niche applications. Cable-television and similar amplifiers operating in the frequency range from about 50 to about 220 MHz. using both simple paralleled stages and push-pull amplifier stages, have been in use for forty years, and are known in the art. Such cable television amplifiers were generally fabricated in the form of discrete-component assemblages on printed-circuit boards.
The paralleling of two amplification devices ordinarily requires the division of the signal to be amplified into two portions, application of each portion of the signal to be amplified to one of the two amplifier devices, and the combining of the amplified output signals from the two devices. In general, signal dividers and signal combiners are passive devices which use the same types of structure, so that a signal divider for use at a given frequency and power level can generally be used as a signal combiner, and similarly a signal combiner can generally be used as a signal divider, simply by reversing the input and output ports. Those skilled in the art know that the phasing of the signals to be combined must be made in such a manner as to prevent cancellation, and that phase can be controlled at any location between the division of the signal into two portions and the combining point.
Power division in the abovementioned cable television amplifiers was generally done in one of two ways, namely by a pair of resistive power dividers coupled to the signal source, with their taps coupled to the divided-signal utilizing apparatuses, or by a center-tapped hybrid transformer arrangement wound on a magnetic core, with the center tap coupled to the source and the ends of the windings coupled to the divided-power utilization devices. It is common, in such arrangements, to couple an isolation resistor across the divided-power ports. It should be noted that the resistive power divider is lossy, in that half of the signal power is wasted as heat in the resistors, so the less lossy center-tapped hybrid was used almost exclusively for power combining.
In the field of microwave power amplification, U.S. Pat. No. 4,701,716, issued Oct. 20, 1987 in the name of Poole describes a scheme for paralleling distributed amplifiers such as travelling-wave tubes in such a manner as to maximize the bandwidth of the resulting combined system. In the Poole arrangement, distributed microwave 3 dB hybrids in the form of coupled quarter-wave transmission lines are used for the power dividers and combiners. Such distributed transmission-line hybrid arrangements are well known in for use in microwave systems.
While paralleling two output devices can provide about a doubling of the amplifier output power for a given level of distortion, yet more power may be required for certain applications. For such higher-power applications, the paralleling of more than two devices may be required. U.S. Pat. No. 4,315,222, issued Feb. 9, 1982 to Saleh describes a power combiner arrangement in which the output power from a plurality of amplifier modules is combined at a single junction. Each amplifier is coupled to the junction by a transmission line having an electrical length of one quarter wavelength (&lgr;/4) at a frequency within the operating frequency range. U.S. Pat. No. 4,755,769, issued Jul. 5, 1988 in the name of Katz describes a composite amplifier including four signal amplifiers. A four-way power divider divides the signal to be amplified into four equal-amplitude, equal-phase portions, and each of the portions is applied to the input port of one amplifier. The amplified output signals are combined at a combining port by way of a scheme using the impedance transformation attributes of quarter-wavelength transmission lines. While details of the power divider are not specified in the Katz patent, one possible scheme for four-way power division is an arrangement similar to his combining arrangement, namely a cascade of two stages of transmission-line segments, including a first stage of division into two signal portions, followed (in the direction of the flow of signal in such an amplifier) by a second stage of division into two parts of each of the two divided signals, for a total of four divided signals.
Power division and combination can be performed by simple connection of two or more load or source devices, respectively, to a common source or load, respectively. Such simple junction-type splitter/combiners suffer from the problem of impedance mismatch, which tends to cause a portion of the input signal power to be reflected rather than going to the output ports of the splitter/combiner. A paralleled power amplifier generally similar to the Katz paralleled amplifier is described in U.S. Pat. No. 4,780,685 issued Oct. 25, 1988 in the name of Ferguson. The Ferguson arrangement uses tapped transmission lines as impedance transformers to improve the impedance match between a common 50-ohm output transmission line and plural transmission lines combined at a combining node.
An arrangement for combining a large number of individual amplifier modules into a composite microwave amplifier is described in U.S. Pat. No. 4,641,106, issued Feb. 3, 1987 in the name of Belohoubek et al. In the Belohoubek arrangement, radial transmission lines with quarter-wavelength slots are used for the division of the signal to be amplified into plural portions, and also for combining of the amplified signals. The Belohoubek et al. arrangement includes isolation resistors coupled between each individual transmission path and the next.
Another arrangement for combining a large number of amplifiers is described in U.S. Pat. No. 4,965,530, issued Oct. 23, 1990 in the na
Higgins Thomas Patrick
Sturzebecher Dana Jay
Duane Morris LLP
Lockheed Martin Corporation
Pascal Robert
Takaoka Dean
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