Amplifiers – With semiconductor amplifying device – Including plural amplifier channels
Reexamination Certificate
2000-07-18
2002-02-05
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including plural amplifier channels
C330S286000
Reexamination Certificate
active
06344777
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to high power microwave and millimeter wave RF sources, and, more particularly, to a high power RF amplifier structure that combines the RF power output of a large number of individual semiconductor millimeter wave RF amplifiers to achieve higher power levels within a physically compact package.
BACKGROUND
The microwave and millimeter wave (MMW) frequency range has long been the range of choice for various electronic devices, such as radar, satellite up-link and down-link transmitters, LMDS ground station transmitters and smart munitions. To achieve RF at frequencies in that range, as example, at 35 GHz, millimeter microwave integrated circuit (“MMIC”) devices have been developed to produce and/or amplify RF signals with reasonable levels of efficiency. Many of those MMIC devices employ high electron mobility transistors (“HEMT”) as the active element providing amplification. One example of such a high efficiency MMIC source is described in an article by Ingram et. al. (a co-inventor) appearing in the IEEE Transactions on Microwave Theory and Techniques, Vol. 45, No. 12, December 1997 at pages 2424-2430.
Although the MMIC amplifier described in the foregoing article achieved a benchmark in power level in the achievement of a six watt RF output, due to the nature of the semiconductor device and the high frequency, the high power achieved by a single such MMIC amplifier device is much less than the power levels which are achieved at the lower microwave frequencies at which the familiar magnetron or klystron devices are used. Although the RF power is relatively high for a semiconductor device at the 35 GHz frequency, that power is less than customarily desired for the typical radar and/or up link and down link communications channels. It may be said that the more power available, the better. To achieve greater RF power levels at millimeter wave frequencies, it has been necessary to combine the RF outputs of multiple numbers of MMIC amplifier devices so that the total output power from the combination is much larger than that available solely from a single MMIC amplifier.
The familiar binary combiner has typically been used for that RF combining function in those plural MMIC power amplifier combinations. In implementation of the binary combiner, RF inputted from separate sources to a pair of waveguide arms are combined by use of a Magic-T junction, and the combined output is then introduced by a third port of the Magic-T junction to another arm. In turn, the RF in that third arm is then combined by another Magic-T junction with the RF output of another like waveguide arm that introduces the combined power from a different pair of arms. The combining structure must be symmetrical. That is, each arm to a MMIC power amplifier must be of the same length as the corresponding arm associated with any other MMIC power amplifier so that the RF from separate amplifiers is equal in intensity and phase when combined at a Magic-T junction. The foregoing inverted pyramiding structure, at least theoretically, may be built up ad-infinitum to produce very high power levels.
In practice, power loss is inherent in the binary combiner structure due to the waveguide media, such as the air environment within the waveguide, resistivity of the waveguide walls and imperfection of the construction. Some portion of the RF energy heats the air and the waveguide, and is essentially lost as heat, reducing the energy that is output. That power loss serves as one limit to the size of the binary combiner and the combination of multiple power amplifiers. As the number of combining elements is increased, the power losses in the arms carrying the higher power levels become excessive, and the combining efficiency drops substantially as the number of stages in the binary combiner increases beyond eight.
A contributing factor to such loss of RF is the physical size of the assembly. Each MMIC amplifier assembly, though small, is of a finite size. To combine the outputs of multiple power amplifiers using the binary combiner technique, the power amplifiers must be arranged, as example, in a single row so as to satisfy the described requirement for symmetry in the binary waveguide combining arrangement. The number of individual power amplifiers may be represented as 2
n
, where n is equal to a whole number greater than 1. Increasing the number of amplifiers from 4 to 8 spreads the row of amplifiers over double the width than before, and, hence, requires an increase in length of the intermediate waveguide arms of the binary combiner that join the amplifiers together. Because the RF must then propagate over greater path lengths, the energy lost due to heating of air in the waveguide and dissipation on the waveguide walls, increases. Hence, the overall electrical efficiency becomes lower.
The physical size of the binary combiner becomes excessively large as the number of included power amplifier elements increase beyond eight. Eventually, the combiner loss increases exponentially beyond between eight to sixteen elements, and additional combining does not produce a net higher power. As an advantage, the present invention allows the RF of a greater number of microwave semiconductors to be combined without incurring such exponentially increasing losses. Considered separately, a large physical size is not typically desirable, since size could pose a problem in applications in which limited space is available, such as in aircraft installations. As a further advantage, the present invention provides both a high power RF amplifier and a more compact physical structure than is available with the existing high power amplifier designs that employ the binary combining structure.
A secondary effect of increased heating is that the MMIC amplifiers, which are sensitive to temperature, are adversely affected by temperature increases. Being a semiconductor material, the lower the temperature of operation, the greater is the power gain achieved. Hence, the amplifier structure typically includes cooling apparatus both active and/or passive types to conduct heat away from the amplifier. Thus, not only do loses increase when the transmission path lengths increase, but the operating efficiency of the individual amplifiers falls off, unless more active cooling can be provided. Even if greater cooling capacity is employed to maintain the amplifier efficiency, the energy expended to provide that cooling instead reduces overall system efficiency.
Accordingly, a principal object of the invention is to provide a new high power RF amplifier this is capable of providing very high power levels at millimeter and microwave frequencies with reasonable efficiency.
Another object of the invention is to provide an efficient means to combine the RF outputs of semiconductor devices to achieve ultra-high power levels in the millimeter/microwave frequency range.
A still further object of the invention is to provide an RF power combining structure whose efficiency and power level surpasses that available in designs that use binary combiners and affords a more compact physical size.
SUMMARY
In accordance with the foregoing objects and advantages, a new waveguide power combining structure is defined by a compact power module that contains numerous (
16
will be used as an example to illustrate the concept) MMIC amplifiers and novel manifold structures. The input manifold structure provides an RF feed that evenly distributes inputted RF in equal amplitude and phase to each MMIC amplifier. Each MMIC amplifier amplifies the RF power and the RF output power from each amplifier is combined in the output manifold structure of the power module from which the combined higher power level RF is output.
The individual MMIC power amplifiers are organized in four separate rows and those rows of amplifiers are stacked in layers, one over the other. The input waveguide manifold that distributes the RF to be amplified amongst all the power amplifiers and the output waveguide manifold in which the individual outputs are combined into a si
Brunner William M.
Chen Yaochung
Ingram Daisy L.
Yen Huan-Chun
Choe Henry
Goldman Ronald M.
Pascal Robert
TRW Inc.
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