Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Missile or spacecraft guidance
Reexamination Certificate
1999-08-23
2001-02-06
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Missile or spacecraft guidance
C342S112000, C342S115000, C342S116000, C342S129000, C342S192000, C342S204000
Reexamination Certificate
active
06184817
ABSTRACT:
FIELD OF INVENTION
This invention relates to the generation of multiple frequencies, and more particularly to the utilization of a minimum number of base frequencies or tones, in order to generate a large number of spectrally pure preselected frequencies.
BACKGROUND OF THE INVENTION
It will be appreciated that in air defense systems, an incoming missile is countermeasured through the utilization of an interceptor missile, which is guided towards the incoming missile through attitude control and millimeter wave radar techniques. In order to be able to intercept an incoming missile with current attitude adjusting technology, it is important to be able to transmit millimeter radar signals in hundreds of frequency channels so that the frequency can be hopped amongst channels to avoid jamming. Moreover, it is important that these frequencies be selectable and available through a switching system in which the transmit frequency can be set rapidly.
In the past, master frequency generators have been employed utilizing a large number of base frequencies or tones in order to be able to synthesize the required channel. In one application, as many as 16 tones were necessary in order to generate the required frequencies with the required spectral purity. In addition to generating the 16 tones, multipliers, and dividers, mixers were combined to provide the large number of frequencies required. For instance, in one application, 100 channels are needed to be generated. The result of such a master frequency generator was that the number of parts necessary was excessive, which both added weight and resulted in high power consumption in an application, which because of its intended use, must be extremely lightweight and extremely parsimonious in its power consumption.
In general, for interceptor missiles, it is the kinetic energy of the missile that takes out the incoming missile, as opposed to explosives that utilize proximity fuses to be able to accomplish the task. Thus, it is desirable to minimize the mass of the components in the missile to be able to maximize the velocity. This is because the energy in the collision is proportional to the square of the velocity. The number of components also obviously adds considerably to the cost of the entire system, such that any system that can minimize the parts count is desirable.
In the interceptor missile application, as mentioned before, it is a requirement to generate hundreds of channel frequencies and to be able to hop between frequencies to avoid jamming. Secondly, channels permit profiling the incoming missile as to its attitude or orientation, as well as its physical characteristics, to determine the most lethal point of impact, and this requires hundreds of channels.
SUMMARY OF THE INVENTION
In order to accomplish the generation of hundreds of channels with high accuracy, low phase noise, low spurious content and fast switching, in one embodiment, five base frequencies or tones are generated, with a relationship between the tones being f
0
+/−⅛f
0
and +/−{fraction (1/16)}f
0
. After much research into the various tradeoffs between different synthesizer techniques, a solution was found which permits utilization of only five tones to generate hundreds of channels with a master frequency generator utilizing one half the parts count previously thought necessary.
In one embodiment, one first determines the desired step size between the multiple frequencies to be generated, which is usually a system requirement. With a fixed configuration of dividers and mixers designed to permit generation of a predetermined number of different frequencies with the above step size, then one can specify the center tone as being the step size x, a number reflecting the one over the base tone spacing (i.e.16), multiplied by a number determined by the specific configuration. In one embodiment, for a circuit which can generate 160 different frequencies, the center tone is step size×16×128, where the basic step size is the tone spacing divided by 128, and where the tone spacing is defined as ⅛ of the center tone.
Thus, setting the tone spacing=F
c
/16=128×step size, F
c
=16×128×step size. Having specified the center or base tone, one can generate the other four tones based on the above +/−⅛f
0
and +/−{fraction (1/16)}f
0
relationship.
In one example, with three mixers and four dividers, and with selected dividers providing a divide-by-4 or a divide-by-8 function, it can be shown that 160 different frequencies can be generated from five tones, with the frequency generated
f
agility
={fraction (41/128)}F
A
+K/4(N
1
/1+N
2
/4+N
3
/8+N
4
/32),
where F
A
is the lowest tone, where K is the tone spacing, and where N is either 0 or an integer.
It will be appreciated that in the past, the simplest way of generating multiple frequencies was to utilize a phase locked oscillator at the output frequency. This technique was, however, found to be woefully short of being able to generate the frequencies without considerable phase noise and spurious and slow switching speed.
It will also be appreciated that there are an infinite number of solutions that can be tried in order to accommodate the number of frequencies to be generated with the minimum number of tones. There are also an infinite number of combinations of multipliers, dividers, mixers and oscillators to be able to achieve the desired result. It is noted that one prior art master frequency generator has a parts count of 328 components. These components are mixers, filters, KA amplifiers, microwave amplifiers, dividers, regulators, cables and a Doppler VCO. In contradistinction to the prior master frequency generator in the subject system, in one embodiment only 155 components need be utilized.
In the preferred embodiment, a fixed oscillator is used in combination with dividers and mixers to generate the five basic tones. These five basic tones are then combined in three additional mixers to generate the hundreds of frequencies required for the above-mentioned channels. The combining circuit in one embodiment includes divide-down circuits, which in combination with the mixers, minimizes spurs by up-conversion, expansion and divide-down steps to provide the required spectral purity.
In summary, a system is provided for generating multiple frequencies in a specified frequency band, with a specified step size between frequencies, in which the spectral purity of the frequencies is assured. The switching speed between frequencies is very fast, limited only by the speed of the switches used. In one embodiment, only five tones are generated as the base for the rest of the synthesis, in which the relationship of the five tones is f
0
+/−⅛f
0
and +/−{fraction (1/16)}f
0
. The subject system may be utilized in air defense systems for generating the transmit channels to be able to permit a missile seeker to transmit a signal at the appropriate frequency. In one embodiment, spectral purity is achieved by providing a number of stages of up converting, expanding, and dividing down of an input signal.
REFERENCES:
patent: 3614627 (1971-10-01), Runyan et al.
patent: 4382258 (1983-05-01), Tabourier
patent: 5146616 (1992-09-01), Tang et al.
patent: 5239309 (1993-08-01), Tang et al.
Lockheed Martin Corporation
Sadacca Stephen S.
Sidley & Austin
Sotomayor John B.
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