Blip scan analyzer

An improved signal processing technique for providing rapid evaluation of rget echoes on a pulse by pulse basis. An analyzing circuit is constructed to receive pulse echoes from a signal transmitting system and convert the pulses to provide amplitude data through a pulse height to pulse width converter. When used in a radar system, each echo pulse is converted to a fixed amplitude pulse with a pulse width proportional to the echo amplitude as the antenna sweeps by the target. The pulses are thereafter transmitted to a display device in place of the normal radar video. The resultant display provides a real time two-dimensional amplitude pattern which enhances target detectability in the presence of noise and in multiple target environments.

BACKGROUND OF THE INVENTION 
The present invention relates to a signal processing system and more 
particularly to a wave shaping technique for permitting the rapid 
evaluation of signal echo amplitude data on a pulse by pulse basis. 
Generally, in signal processing systems such as radar or sonar systems, 
wherein echo signals are utilized to provide target information, various 
techniques have been proposed to improve the ability of the system to 
resolve multiple targets with less interference from system 
characteristics or noise. With the advent of track-while-scan computers, 
target location and estimation techniques have become particularly 
important in providing a basis for identifying targets under different 
environmental conditions. Most prior target detectors and location 
estimators relay upon the shape of the antenna scan profile and the number 
of hits per scan (with the particular antenna pattern), as the antenna 
passes through the area of the target, to provide accurate target 
detection. The accuracy of such detectors and estimators, however, is 
dependent upon the reproducibility of the target echo pattern for a given 
antenna pattern. While conventional radar displays have been constructed 
to provide target echo patterns that provide strong signals and minimal 
interference in accordance with the above scanning, various problems have 
been encountered which limit the system performance. In particular, 
certain disturbances which occur with relatively great frequency have a 
significant effect on the target echo pattern so that weaker echoes are 
modified significantly from those of strong signal echoes. In addition, 
disturbances such as multipath transmissions, which are more unpredictable 
and occur with less frequency, also provide significant echo distortion 
which alters target echo patterns. As a result, the standard radar display 
devices have been ineffective in providing signal data output which will 
provide for increased target detection or improved signal content of 
target echo patterns for use by detection and estimation devices. 
In view of the present trend toward computerized command control systems, 
there is therefore a real need for more effective techniques for providing 
patterns which will facilitate evaluation by target detection and location 
processors. Such techniques are required to allow the automatic tracking 
of targets for coordination with vehicle control systems for quick 
response to multiple threats. These automatic target detectors, however, 
must be able to obtain precise target amplitude versus azimuth data in 
order to increase the effectiveness of data analysis. The data should be 
obtained from the particular vehicle signaling system and must be able to 
account for multipath effects on apparent amplitude pattern of the target. 
In dealing with this problem, previous techniques have utilized cathode 
ray tube displays (A-scopes) and high speed rapidly advancing photographic 
film with limited success. Still other techniques have utilized sample and 
hold devices which require the manual positioning of a ranging gate to 
enclose a signal target or, alternatively, expensive memory systems to 
acquire data on many targets. All such techniques have suffered from high 
expense, difficulty in use, and lengthy post acquisition data processing 
which has curtailed their effectiveness. Consequently, application to real 
time threats in multiple target environments has been severely limited. 
Accordingly, the present invention has been developed to overcome the 
shortcomings of the above-known and similar techniques and to provide a 
wave shaping technique for obtaining target amplitude versus azimuth 
information for use with target detection and location estimation 
processors. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a signal processing 
technique which will improve the capability of target detection in 
multiple target and noisy environments. 
Another object of the invention is to provide a signal processing technique 
for evaluating signal echo amplitude information on a pulse to pulse 
basis. 
A further object of the invention is to provide a signal processing 
technique which provides pulse amplitude to pulse width conversion. 
Still another object of the invention is to provide an improved target 
signature in a signal processing system. 
Yet another object of the invention is to provide a pulse amplitude to 
pulse width conversion technique which may be incorporated in radar 
display devices for providing precise amplitude profiles from the range 
and azimuth circuitry. 
In order to accomplish the above and other objects, the present technique 
utilizes a blip scan analyzer (BSA) to convert a radar video output to an 
amplitude profile on the signal processing display. The analyzer utilizes 
a capacitor charging circuit to stretch the radar video in a time 
proportionate to the video amplitude and provides a pulsed output which 
can be displayed on a standard plan position indicator (PPI) or B scan 
display device. When a radar echo is initially received, the charging 
circuit is rapidly charged to a value indicative of the amplitude of the 
echo. The circuit is subsequently allowed to discharge at a predetermined 
rate and applied to a pulse shaping circuit which will create a constant 
amplitude pulse output proportional in width to the amplitude of the echo 
pulse. The constant amplitude pulse is thereafter applied to the standard 
radar display which provides a visual output representative of the 
amplitude of the echo. Since the pulses are displayed in place of the 
radar video, they are synchronous therewith and appear on the display as 
individual line segments extending from the range of the target for a 
length proportional to each echo amplitude. The resultant amplitude 
pattern, as displayed on the output of the device as the radar tracks, 
consists of a phosphor image of all the echoes representing a target 
signature. Since the BSA is providing a two-dimensional representation of 
the target in lieu of the normal PPI displays, the target signatures 
provide improved sensitivity and target detectability for detection and 
analysis. 
Other objects, advantages and novel features of the invention will become 
apparent from the following detailed description when considered with the 
accompanying drawings wherein:

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to FIG. 1, the schematic diagram illustrates the processing 
system and technique in accordance with the teachings of the present 
invention. In the present instance, the signal processing system will be 
described with reference to a radar receiving system, although the 
teachings are equally applicable to other processing systems known in the 
art. Generally, a radar transmitter (not shown) generates a series of 
modulated pulses at a selected carrier frequency which are radiated in 
accordance with the antenna pattern and azimuth direction in a manner well 
known in the art. Upon encountering a target, such pulses are reflected to 
form a target echo signal which is received at the antenna 10 when 
positioned in the appropriate direction. The received echo signals are 
subsequently transmitted to conventional radar receiving circuitry 11 
which produces a radar video output representative of the range and 
azimuth of the target. As is known, the length of time between the 
transmission of the radar pulse and the return of the target echo signal 
is directly proportional to the range of the target, while the position of 
the antenna indicates the azimuth of the target. The signal representing 
the video output is thereafter coupled to a conventional cathode ray 
display device (such as a PPI or B scope) to visually display the target 
echo. Normally, the radar video output can be represented as a voltage 
V.sub.i (t) as is illustrated in FIG. 3a wherein the output signal 
consists of low level amplitude peaks created by noise and high amplitude 
peaks representing the target echo signal. When transmitted to the cathode 
ray tube display devices, the visual images created by the pulses on the 
phosphor screen are located at positions on the display equivalent to the 
range of the target and having an intensity proportional to the amplitude 
of the target echo signal. As can be seen, the ability of the display to 
provide effective target detection will be determined by the capability of 
an operator or processor to distinguish between high and low intensity 
light on the scope and the ability of additional threshold circuitry to 
establish a level which will eliminate noise from the display. Because of 
the variety of problems created by noise in the receiver system and 
multipath effects, the conventional display output does not readily 
facilitate effective target recognition and discrimination in multiple 
target and interference environments. 
While the above system could provide various visual interpretations, the 
problems become even more acute when the video output is to be processed 
by automated target detection and estimation processes. Because of the 
relation between the antenna pattern and target signature, most automated 
techniques are constructed to take into account the antenna pattern in 
evaluating the presence of a target upon receipt of a target echo 
amplitude pattern. Since the conventional radar video is sensitive to 
external factors, however, the similarity or dissimilarity of target echo 
patterns for a given antenna pattern cannot be insured to enable a 
statistical evaluation of the effectiveness of a detection and estimation 
technique. Accordingly, there is increased reliance on operator 
interpretation for target detection while the more accurate computer 
evaluations are neglected. 
In order to overcome the noted problems associated with conventional 
display and target detection techniques, therefore, the present invention 
utilizes a blip scan analyzer 13 which operates on the radar video to 
produce a wave shape that permits rapid evaluation of search radar target 
echo amplitude data on a real time pulse by pulse basis. The circuit 13 is 
coupled to the output of the radar video circuitry 11 in such manner that 
it may be selectively inserted in series with the conventional radar 
display 12. The effect of this circuit is to provide a modified signal 
which stretches the radar video in a time proportional to the video 
amplitude and which displays the modified signal on the standard PPI or B 
scan display. As the radar sweeps by a target, each individual target echo 
is converted to a fixed amplitude pulse with a pulse width proportional to 
the amplitude of the echo in the radar video. This technique may be more 
easily visualized by reference to FIG. 3 wherein the typical waveforms 
produced during conversion of the radar video (V.sub.i (t)--) are shown. 
According to the invention, the radar video V.sub.i (t) from the output of 
11 is provided to a capacitor charging circuit of device 13 to produce a 
voltage proportional to the video amplitude. That voltage is then 
permitted to discharge at a constant rate to form a waveform (V.sub.c (t) 
corresponding to the stretched voltage waveform shown in FIG. 3. The 
voltage V.sub.c (t) is thereafter coupled to a voltage threshold circuit 
which produces a constant pulse output as long as the voltage (V.sub.c (t) 
exceeds the threshold level. The resultant signal output is a constant 
amplitude pulse having a pulse width proportional to the amplitude of the 
radar video V.sub.i (t). It should be noted that as the radar video 
amplitude increases, the pulse width of the BSA output also increases. The 
threshold voltage V.sub.DC is then set so that there is a high probability 
that a target echo signal will exceed the threshold voltage and a low 
probability that receiver noise will exceed the threshold voltage. When 
applied to the conventional radar display, the output pulses of FIG. 3 are 
synchronous with the radar pulses from the radar video. The output display 
is therefore a two-dimensional amplitude pattern consisting of constant 
intensity phosphor line segments for each pulse extending from the range 
position on the display and having a length proportional to the echo 
amplitude. 
Turning now to FIG. 2, a circuit forming the BSA 13 is schematically 
illustrated. The circuit generally consists of an operational amplifier 
U.sub.1 having its positive terminal coupled to receive the radar video 
signal V.sub.i (t) and connected through resistor R.sub.1 to ground. The 
output from U.sub.1 provides an amplified signal which is coupled to one 
terminal of capacitor C.sub.2 and the cathode of diode D.sub.1 and as 
input to the base of transistor switch Q.sub.1. The other terminal of 
C.sub.2 and the anode of D.sub.1 are coupled to the negative input of 
U.sub.1 and in series with the parallel combination of the resistor 
R.sub.2 and capacitor C.sub.3. The other terminals of C.sub.3 and R.sub.2 
are in turn coupled to the output and negative input of operational 
amplifier U.sub.2. In operation, the connection of elements C.sub.2 and 
C.sub.3 prevents overshoot of the radar video signal during charging of 
the capacitor C.sub.1. The emitter of Q.sub.1 is coupled to one terminal 
of capacitor C.sub.1, to the positive terminal of U.sub.2, and to the 
collector of Q.sub.2. The other terminal of C.sub.1 is connected to ground 
and to the base of transistor Q.sub.2 which has its emitter coupled 
through R.sub.3 to potentiometer R.sub.4 to ground. The output V.sub.c (t) 
of U.sub.2 is coupled to the negative input of operational amplifier 
U.sub.3 which has its positive input coupled through variable resistor 
R.sub.5 to regulate the threshold voltage V.sub.DC. The amplifier U.sub.3 
operates as a comparator and provides an output signal when the voltage 
V.sub.c (t) exceeds the voltage set by the resistor R.sub.5. The output of 
U.sub.3 is then coupled to a pulse driving circuit formed from transistors 
Q.sub.3 to Q.sub.5. Transistor Q.sub.3 has its base coupled to the output 
of U.sub.3, to the anode of D.sub.2, and through resistor R.sub.6 to a 
biasing voltage. The collector of Q.sub.3 is coupled to the cathode of 
D.sub.2, to the anode of D.sub.3, to the base of Q.sub.4, through the 
parallel combination of resistor R.sub.10 and capacitor C.sub.4 to ground, 
and through the resistor R.sub.7 to a biasing voltage. The emitter of 
Q.sub.3 is coupled through resistor R.sub.8 to ground, to the base of 
Q.sub.5, and to the anode of D.sub.4. The collector of Q.sub.4 is coupled 
to the cathode of D.sub.3 and through resistor R.sub.9 to a biasing 
voltage. The emitter from Q.sub.4 is coupled to the anode of D.sub.5 which 
has its cathode coupled to the cathode of D.sub.4 and to the collector of 
Q.sub.5 to provide the pulse output terminal. The emitter of Q.sub.5 is 
thereafter coupled to ground. 
In operation, the radar video V.sub.i (t) is applied to the input of 
U.sub.1 to produce a voltage output at the base of Q.sub.1 which tracks 
the radar video. When the voltage V.sub.c (t) is less than V.sub.i (t), 
the capacitor C.sub.1 will charge through transistor Q.sub.1 with voltage 
overshoot being prevented by the specific coupling of capacitors C.sub.2 
and C.sub.3. When the value of V.sub.c (t) becomes greater than V.sub.i 
(t), transistor Q.sub.2 will act to discharge the capacitor C.sub.1 at a 
constant rate through resistors R.sub.3 and R.sub.4 to ground. The rate of 
discharge can be determined by adjusting the value of potentiometer 
R.sub.4 while the rate of charge can be controlled by changing the value 
of C.sub.1. The voltage output V.sub.c (t) is thereafter provided to 
comparator U.sub.3 and generally follows the discharge of capacitor 
C.sub.1 in the manner as shown by FIG. 3b. When the output V.sub.c (t) 
exceeds the threshold V.sub.DC as fixed by the resistor R.sub.5, the 
output from U.sub.3 will drive the circuit formed from transistors Q.sub.3 
-Q.sub.5 to produce a constant amplitude pulse output. The length of the 
pulse output will therefore be equal to the time period that V.sub.c (t) 
exceeds the threshold level V.sub.DC and will be proportional to the 
amplitude of the radar video. 
In implementing the circuit shown in FIG. 3, all amplifiers U.sub.1 to 
U.sub.3 and transistors Q.sub.1 -Q.sub.5 were biased with the identified 
voltages for the desired operational values. In this particular example, 
transistors Q.sub.1 -Q.sub.5 were type 2N2219A, D.sub.1 and D.sub.5 type 
FD333, and D.sub.2 -D.sub.4 were Schottky diodes coupled in the manner 
indicated to prevent transistors Q.sub.1 -Q.sub.5 from saturating and to 
eliminate storage time delays. In addition, pins 8 of U.sub.1 and U.sub.2 
were coupled through 30 pf capacitors to ground while pins 4 and 7 of 
U.sub.1 and U.sub.2 were connected through 0.1 .mu.F to ground. All other 
element values and connections were established as indicated in the 
drawing. 
Using the above described circuitry, the disclosed technique was capable of 
providing output pulses in response to radar video pulses having a pulse 
width of 2 ns without any significant degradation of the video display. 
While this particular response is considered desirable for normal tracking 
operations, various modifications of the element values may obviously be 
made to accommodate specific conditions necessitated by different radar 
parameters. As has been previously noted, the modified pulse output of the 
present technique allows significant increases in target detection 
sensitivity, yet only minor and inexpensive modifications to the radar 
circuitry. Such technique allows the target threshold to be easily 
modified to increase the probability of target detection. In addition, the 
previously described technique provides a target echo signal that is 
relatively independent of noise and multipath disturbances such as to 
allow the use of and evaluation of the automated target detection and 
location estimation processors. When employed as a selectable circuit in 
series with the conventional PPI or B scope, the amplitude profile 
produced provides enhanced visual target detectability and target 
signature characteristics critical for target tracking. All of these are 
advantages that have not been previously recognized in the prior art. 
While the present invention has been described with the particular 
reference to the circuit of FIG. 2, it is obvious various modifications 
can be made in accordance with the inventive teachings. The BSA circuit 13 
may therefore consist of any automated peak detecting and pulse stretching 
circuitry capable of converting the radar video to a constant amplitude 
pule having a width proportional to the amplitude. Obviously, many other 
variations and modifications of the present invention are possible in 
light of the above teachings. It is therefore to be understood that within 
the scope of the appended claims the invention may be practiced otherwise 
than as specifically described.