Communications: directive radio wave systems and devices (e.g. – Testing or calibrating of radar system – By monitoring
Patent
1997-01-29
1998-10-06
Pihulic, Daniel T.
Communications: directive radio wave systems and devices (e.g.,
Testing or calibrating of radar system
By monitoring
H03L 707, H03B 2100
Patent
active
058183841
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for and method of generating a coherent signal whose amplitude, frequency and phase can be accurately controlled.
Generally, in the development of a modern complex system such as a radar system, employing sophisticated high technology, it becomes necessary to simulate part of the real world the system is ultimately designed to work in. Simulation of a system, or part thereof, is useful because the necessity of supplying actual physical real world conditions is avoided. Simulation also provides the system designer a much lower cost alternative for approximating real world conditions. The most common use of simulation systems or simulators is in the testing of systems whereby testing without the use of a simulator would be either too cost prohibitive or impossible. In addition, the accuracy of software simulation is limited as compared to live testing.
Simulation systems are virtually a required component in the design and development of complex systems in such fields as radar and communications. For example, the design of radar and communication systems typically employ coherent signals in their design. The development of such systems typically requires the capability to simulate coherent signals for testing purposes. It would be virtually impossible to test these systems during development without the use of simulation equipment.
For example, coherent moving target indicator (MTI) radars or coherent pulse doppler radars typically employ coherent detection to determine the doppler frequency shift caused by a moving target. The doppler frequency shift of a moving target is directly related to its speed. In a coherent radar system the same oscillator signal used to generate the transmitted signal is used as the reference signal in the receiver section of the radar. Thus, the received echo signal from the target is always coherent with the internal reference signal used to determine the speed of the target.
The requirements of a radar target simulator and, more specifically, the signal generator portion thereof, include accurate control of the amplitude, frequency and phase of the simulated echo return signal. In addition, the simulated echo return signal must be coherent with the signal transmitted by the radar. Amplitude control of the simulated target signal is necessary because the echo return signal almost always has a lower amplitude due to wave propagation and due to the reflection characteristics of the target. Frequency control is required because the frequency of the return echo signal from a moving target is different from the frequency of the transmitted radar signal. This difference is due to the motion of the target and is called the doppler frequency. In addition, it is desirable to be able to control the phase of the simulated echo return signal for a variety of reasons. For example, moving targets may cause not only a frequency shift but may also cause a phase shift in the echo return signal. In addition, it might be desirable to stress the radar receiver section, including its signal processing capabilities, by phase shifting the return signal in certain ways.
An additional common systems requirement is calibration or compensation of electrical components in a circuit. Often, it is desirable to be able to calibrate or compensate a device for certain conditions or parameters.
A coherent signal generator is disclosed in German patent application 3145532. A local oscillator having a frequency f.sub.1 is mixed with a coherent oscillator signal f.sub.0. The resultant signal is filtered, amplified and heterodyned with a second local oscillator signal having a frequency equal to the sum of frequency f.sub.1 and a doppler frequency shift f.sub.D. The resultant mixer output signal is filtered and constitutes the output of the signal generator. Although the frequency component of the output signal can be controlled to simulate doppler shifts, there is no provision for controlling the phase of the output signal.
SUMMA
REFERENCES:
patent: 4818064 (1989-04-01), Youngquist et al.
patent: 5019793 (1991-05-01), McNab
patent: 5408201 (1995-04-01), Uriya
patent: 5518400 (1996-05-01), Otoide et al.
Friedman Mark M.
Pihulic Daniel T.
State of Israel-Ministry of Defense Armament Development Authori
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