Geophysical Survey Systems, Inc.

Henning F Harmuth

A digital sliding correlator having means for producing a series of time-shifted stored copies of a digital character, means responsive to said shifted, stored copies of the character for multiplying said shifted, stored copies by the input signal or the sign-inverted counterpart of the input signal, a first set of integrators and a second set of integrators, means for supplying to the first set of integrators first portions of said multiplied signals and for supplying to said second set of integrators second portions of said multiplied signals, and means for combining the outputs of said integrators.

Sliding correlator for nanosecond pulses

An improved driving circuit for a large-current radiator avoids the need to dissipate large powers in the driving circuit by drawing a certain energy value from a power supply to a storage capacitor and then feeding this energy to the radiating antenna. A constant current source provides, when a switching circuit coupled to the radiator is opened, a current to counter the tendency of the radiator otherwise to maintain continuity of current through the switching circuit, keeping to a minimum the voltage across the switching circuit so that essentially no energy will need to be dissipated in the driving circuit. By choosing the stored energy value carefully one can make it just large enough to cover the radiated energy but leave essentially no energy to be dissipated in the radiator driving circuit.

Efficient driving circuit for large-current radiator

An electromagnetic signal having originally the time variation of a rectangular pulse is radiated into a lossy medium with conductivity .sigma.. It is distorted by the medium to the distorted electromagnetic pulse f(.sigma.,y,t) when it travels the distance y/2, in time t/2, from a transmitter to a scattering or reflecting target and the same distance y/2, in time t/2, back to the receiver. The time variation f(.sigma.,y,t) of the distorted pulse can be calculated for any conductivity .sigma. and distance y using the conductivity .sigma. known from previous measurements to determine the range to the target distorted pulse f(.sigma.,y,t). Consequently, distorted pulses f(.sigma.,y.sub.n,t) can be computed and compared to the received distorted pulse f(.sigma.,y,t). The computed pulse f(.sigma.,y.sub.n, t) that is most similar to the received pulse f(.sigma.,y,t) determines the distance y.sub.n /2 to the scattering or reflecting object, which is the range to the target. The comparison between the computed, distorted signals and the actually received signal can be done by cross-correlation. If cross-correlation is used, the peak amplitude or the energy of the received signal becomes unimportant which means the physical size or radar cross-section of the target has no effect on the distance determination.

Range information from signal distortions

A method for generating a sequence of short radar pulses and a method plus apparatus for detecting those same short pulses when backscattered, even though they are heavily distorted by a target and have additive noise and unwanted signals superimposed on them. The method applies to pulses of long or short duration, including durations of 1 nanoseconds (1 ns) or less. The pulses are transmitted without the fine structure marking of a sinusoidal wave carrier, but organized into a coarse structure that results from incorporating them within a highly unconventional type of character, wherein a plurality of positive-going and negative-going pulses are transmitted such that each pulse is spaced apart from its neighbors. Each pulse is short, so the return signal is highly distorted. The sequence of positive-going and negative-going pulses are organized into a pattern of non-contiguous pulses that constitute a new type of 'character', which may be thought of as a 'spaced-apart-character'. This 'spaced-apart-character' is organized into a large coarse structure marking, so that a) the total transmitted energy is large, b) a receiver can selectively distinguish the wanted return signal from noise and unwanted signals, and c) reflections from targets longer than L=.DELTA.tc/2 are rejected.

Selective reception of carrier-free radar signals with large relative

Method and apparatus for generating and receiving carrier-free radar pulses that can be detected even though they are heavily distorted by a target and have additive noise superimposed on them, or are in an environment of unwanted signals. The method is especially applicable to signals that are based on pulses with a duration of 1 nanosecond (ns) or less. The radar signature of typical targets from such signals is very large, which makes it hard to selectively receive return signals unless they are marked. Fine structure marking is not effective for such short duration pulses. A method for organizing the signal with coarse structure marking is described that allows the radar receiver to discriminate heavily distorted wanted signals from unwanted signals and noise without requiring large peak power at the transmitter. The disclosed method involves placing positive-going and negative-going pulses together in a pattern of contiguous pulses to form a character. Generating one or more time-delayed replicas of the character and summed selected ones together to form a signal with coarse structure marking. The delay time of each replica may vary and some replicas may have their polarity reversed before summing, but all are based on pulses that are short enough to imply that most return pulses would not be recognized by a receiver. However, the coarse structure of this invention marks the signal for selective reception. It renders the characters within it recognizable, and thereby enables the transmission of pulses without a fine structure marking which might otherwise be absorbed by the atmosphere.

Detection of radar signals with large radar signatures

The extraction of radar targets, in particular airplanes or cruise missiles, from clutter is typically based on the target's velocity relative to the ground. Equipment using this principle is usually referred to as a doppler processor or moving target indicator. In situations where severe clutter is encountered, as for example where a look-down radar is trying to find low-flying cruise missiles, extraction of the target solely through its velocity relative to the ground is generally unsatisfactory. A similarly situated human observer looking down can recognize a target both from its motion and the characteristic shape of a fuselage with wings. The principle of this 'shape recognition' or 'pattern recognition' is here applied to radar by utilizing the so-called radar signature of the target. The conventional small-relative-bandwidth radar which uses signals that are amplitude modulated onto a sinusoidal carrier does not yield enough of a radar signature for this application but the so-called 'carrier-free radar' does. Carrier-free radar is also known as 'impulse radar', 'nonsinusoidal radar', or 'large-relative-bandwidth radar'.

Extraction of radar targets from clutter

A method of detecting an object that may be coated with material for preventing or attenuating reflections of incident electromagnetic waves is disclosed in which pulses of electromagnetic wave energy are generated with a large relative bandwidth in the band from about 0.1 GHz to about 12.0 GHz. Preferably, the generated pulses have a pulse duration in the range from 0.1 nanosecond to 1 nanosecond. Those pulses of electromagnetic wave energy are directed toward the object and reflections of those pulses of electromagnetic wave energy which are incident on the object are detected by receiving apparatus. The method enables coated objects to be differentiated from uncoated objects.

Large relative bandwidth radar

An antenna is disclosed that is especially useful for radiating and receiving non-sinusoidal electromagnetic waves. The antenna is an efficient and distortion-free radiator of electromagnetic pulses that do not use a sinusoidal carrier. The antenna's size is independent of frequency and the antenna, therefore, can be of small size relative to the wavelength of the radiated electromagnetic waves. When used for reception of electromagnetic wave energy, the antenna performs with low distortion. The basic concept underlying the invention is the modification of the Hertzian electric dipole into an antenna structure that can carry large currents without requiring a large driving voltage. Antennas for the transmission or reception of sinusoidal waves achieve that goal by employing resonant structures. The invention achieves the same result by changing the Hertzian electric dipole into a loop that forms a Hertzian magnetic dipole and preventing the undesirable magnetic dipole radiation by shields of conducting and absorbing materials.

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Potomac, MD, United States of America

Henning F Harmuth