Communications: directive radio wave systems and devices (e.g. – Radar transponder system – Iff or sif
Reexamination Certificate
1965-04-05
2002-07-16
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar transponder system
Iff or sif
C342S013000, C342S017000, C342S019000, C342S082000, C342S085000
Reexamination Certificate
active
06420995
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a silent operating radar, i.e., a radar that detects a target and its position without the countermeasure operator located at the target being able to detect the presence of the radar.
More specifically, this invention relates to a silent operating radar that provides transmitted signals with characteristics which allow optimum processing by the radar while taking advantage of limitations inherent in typical radar interception receiving equipment located at the target.
Today, the problems of modernized warfare have increased to the point that high speed aircraft or other craft well-equipped with newly developed electronic countermeasure receivers and jammers can quickly penetrate areas to be defended. Prior to this invention, invading aircraft or other craft have had the benefit of knowing that they were being detected because of the large signal power levels utilized in the tracking radar. Once they determined that they were in fact being observed, they would enter evasive patterns and also utilize their countermeasure electronics to jam the tracking radar. Furthermore, they would be able to launch missiles to home in the radar signal and thereby cause the radar's destruction. This advantage that the target aircraft has had is removed by the usage of a radar system employing the invention to be described. With the utilization of the invention the invading craft can no longer determine that their presence has been detected. Not knowing that they have been detected, the invading craft does not take evasive measures. He can not turn on his electronic countermeasure equipment to mislead the radar nor can he turn on his jamming equipment since these would give away his presence. Jamming and ECM equipment is only employed by the hostile craft only after he has been detected. Again, since the invader has not detected the presence of a radar, he has no reason to attempt to utilize radar homing missiles to destroy the radar.
The ability to operate a radar system in a silent mode is similarly important where ocean going vessels are involved since the presence and location of a moving fleet or submarine is critical to the success of an invading aircraft. As has been mentioned, once the invading aircraft is aware that it is being observed it can rely on its countermeasures equipment to mask its actual position. This advantage is present whether the tracking radar is ground-based, flying, or on ocean-going vessel. While the range of silent operation may be lessened by the size of the tracking radar's host craft and related antenna, the principle of this invention applies equally as well to them as with ground-based radars. Furthermore, the invention could also be utilized against search ships as well as aircraft.
SUMMARY OF THE INVENTION
The remainder of the description will be related to a ground-based radar but it should be understood that the invention is not limited to a ground-based environment but can be utilized in ships or aircraft having the capacity to handle such equipment.
The invention to be described more fully hereafter removes completely the possibility that the oncoming craft will be able to detect the presence of an operating ground-based radar. This has been accomplished through the utilization of equipment providing transmission signals with specific characteristics that allow optimum processing while taking advantage of limitations inherent in typical signal receiving equipment. In addition, the ground-based radar utilizing the concept of the invention is optimized to efficiently detect and process a target's reflected signals.
It is well known that the receivers at the target making an approach have only to overcome a one-way path loss with reference to the transmitted radar signal, while the ground-based radar has the additional loss inherent in the reflected radar signal from the incoming target. This reflected loss is measured as the fourth power of the radial distance from the target to the ground-based radar, while the one-way path loss to the target is on the order of a second power loss based on the radial distance from the radar to the target. Since the ground-based radar receives what is in essence a two-way path loss, the ground-based radar must be optimized to a point at which the advantage held by the target because of path loss considerations is overcome.
This invention provides a range of self-protection around the ground-based radars. This self-protection range may be defined as an intermediate range within which radar intercept receiver systems having set operating characteristics cannot detect the presence of the ground-based radar system. This aforementioned self-protection comes about due to the ground-based radar's detection advantage over the approaching target.
Where high energy per cycle is transmitted the target receiver operator can detect the presence of the ground-based radar by slowly sweeping the bandwidth until the strong signal is identified. In this type of strong transmitted signal environment the transmitted signal only experiences a one-way path loss while a return echo from the plane experiences a second path loss, previously noted. If the ground-based radar has the same receiver capabilities as the target's receiver, the target could detect, the fact that it was being searched for before the ground-based radar could detect the target's presence.
The invention to be described makes use of transmitted low energy per cycle signals which take the form of wide-band, purely random noise. In addition the ground-based radar, in accordance with the invention, has optimized all radar reception advantages to a point where even an extremely weak return signal can be detected though buried in the wide band noise originally transmitted and then reflected, whereas the target radar, because of space limitations, the size of the antenna and weight limitations cannot be optimized to have anywhere near the overall sensitivity and capacity to discriminate as a ground-based radar.
With the aforementioned transmission characteristics it becomes apparent that where a low energy signal per cycle is transmitted, there is some point near the ground-based radar where the one-way path loss is insufficient to prevent the target from detecting the low energy signal. Further removed from the ground-based radar, the target cannot detect the presence of the ground-based radar but the transmitted signals are still being reflected by the target. At this point the optimized ground-based radar functions to detect even the very weak reflected signals, experiencing a two-way path loss. There is of course a specific distance through which the reflected signal can pass before it is attenuated to a point where the ground-based radar even with optimized receivers cannot detect the reflected signal. The just mentioned specific distance represents the ground-based radar's detection advantage over the target. The distance from the near point, where the target can detect the presence of a signal being transmitted, and the specific distance just noted defines the ground-based radar's region of self-protection. This may be referred to as intermediate self-protection range or the volume that it defines about the ground-based radar may be termed a self-protection shell.
It is therefore apparent that as the energy per cycle changes by way of increase or decrease, the dimensions of the self-protection range or shell will change. The operator of the ground-based radar therefore has the ability to increase or to decrease the range being searched in a manual manner or automatically in a programmed manner to be described in detail more fully hereafter.
The silent ground-based radar involved here will transmit a spread spectrum which is essentially noise and then use coherent integration and correlation detection to extract information from the return echo. The fact that optimum detection is possible is brought about because the radar can maintain a record of the signal it has transmitted long
Goulder Morton E.
Richmond Martin R.
Long Daniel J.
Sotomayor John B.
Systems Information and Electronic Systems Integration Inc.
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