Phase locked, pulsed oscillator apparatus, for example, for radar use, comprises a pulsed r.f. oscillator, a pulse repetition frequency (PRF) generator and a pulse shaping network. The PRF generator pulsed output signal of frequency, f.sub.1, is reshaped by the pulse shaping network to provide to the input gate of the r.f. oscillator a train of triggering pulses each having a very fast rise time, t.sub.r, which caues the triggering pulses to exhibit significant harmonic power near the r.f. oscillator's free running frequency, f.sub.FR. The reshaped pulses provided by the pulse shaping network gate the r.f. oscillator on and off and cause coherency of the pulsed oscillator output signal relative to the PRF generator output signal. The reshaped pulse rise time, t.sub.r, is preferably less than about 3-4, and more preferably is about two, times the oscillator output signal period, l/f.sub.FR. The peak turn on voltage, V.sub.p, of the reshaped pulses is preferably about twice the average voltage, V.sub.avg, of such pulses. PRF generator frequency, f.sub.1, may be modulated in a manner enabling the communication of information by the r.f. oscillator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to the field of pulsed oscillator 
apparatus and more particularly to phase-locked or PRF coherent, pulsed 
radio frequency oscillator apparatus as are commonly used in radar 
systems. 
2. Discussion of the Prior Art 
Radar systems, as is well known, have been extensively used in military and 
civilian applications since about World War II. Representative radar uses 
include the location and tracking of airborne aircraft and missles and of 
such natural phenomenae as tornados, hurricanes and storm fronts. 
As is also well known, radar operates generally by the emission of 
electromagnetic waves, ordinarily produced by a radio frequency (r.f.) 
oscillator. These emitted waves are reflected towards the source by many 
types of objects, including those mentioned above. The reflected waves are 
received and compared with the transmitted waves with respect to wave 
phase and/or frequency, the differences being used to compute the location 
and velocity, if any, of the reflecting object relative to the radar 
transmitter. For ease in discrimination between transmitted and reflected 
waves, the r.f. oscillator of the radar transmitter is typically pulsed so 
as to provide a train of time separated pulses, each of which is, however, 
sufficiently long to include a number of the waves at the oscillator 
frequency. 
Since information as to a detected object's location and velocity often 
depends upon minute differences between the transmitted and reflected 
waves or signals, it can readily be understood that the transmitted signal 
should be time-invariant in frequency and each pulse should be phase 
coherent. Accordingly, pulsed r.f. oscillators used in radar systems are 
commonly locked in phase to a precise, pulsed output of, for example, a 
crystal-type oscillator which may be a pulsed repetition frequency (PRF) 
generator. 
In the past, such phase locking of the pulsed r.f. oscillators as are used 
in radar systems, has involved the use of relatively extensive, associated 
high frequency digital circuitry, which, for example, may cause the 
oscillator frequency to be an integral multiple of the PRF generator pulse 
frequency. As a result, such radar systems are not only comparatively 
costly, but also require relatively large amounts of power. 
The need, however, exists in various important applications for small, 
relatively low cost and low power consuming radar apparatus. Typical of 
such applications is scoring apparatus for airborne, towed targets and/or 
pilotless drones used for gunnery practice. For applications such as 
these, the airborne scoring radar, which is configured for determining 
projectile miss distances within a pre-selected range, is subject to 
damage or destruction by target hits. Therefore, low cost of the scoring 
radar system is particularly desirable as is small size so as to lessen 
the probability of being hit by projectiles. Low power consumption of the 
radar system may also be an advantage for on-board scoring radar. 
A need consequently exists in many instances for small, low cost radar 
systems and hence for small, low cost pulsed r.f. oscillator apparatus 
associated with such radars. 
An object of the present invention is, therefore, to provide a pulsed r.f. 
oscillator, the output signal of which is coherent with respect to an 
associated PRF generator output signal, by reshaping the output pulse 
signal of the PRF generator and injecting the reshaped signal into the 
r.f. oscillator. 
Another object of the present invention is to provide a PRF coherent, 
pulsed r.f. oscillator apparatus in which the output signal of a PRF 
generator is reshaped to provide an oscillator triggering signal that has 
substantial harmonic power near the free running frequency of the 
oscillator so that the reshaped signal controls the phase of the 
oscillator signal and also triggers the oscillator on and off. 
Still another object of the present invention is to provide a PRF coherent, 
pulsed r.f. oscillator apparatus in which the pulsed output signal of a 
PRF generator is reshaped to provide an oscillator triggering signal which 
has a very fast rise time. 
Yet another object of the present invention is to provide a PRF coherent, 
pulsed r.f. oscillator apparatus in which the pulsed output signal of a 
PRF generator is reshaped to provide an oscillator triggering signal which 
has a rise time which is no more than several times longer than the period 
of the pulsed oscillator signal. 
Further objects, advantages and features of the present invention will 
become apparent to those skilled in the art from the following decription 
when taken in conjunction with the accompanying drawings. 
SUMMARY OF THE INVENTION 
PRF coherent, pulsed oscillator apparatus, according to an embodiment of 
the present invention, comprises a pulse repetition frequency (PRF) 
generator having pulse output signals of a frequency, f.sub.1, with an 
associated period, T.sub.1, equal to 1/f.sub.1, and a pulsed oscillator 
having a free running frequency, f.sub.FR, which is approximately equal to 
N times the PRF generator output signal frequency, f.sub.1, wherein N is 
an integer. Included in the apparatus are pulse shaping means connected 
for receiving the PRF generator output signals and for the shaping thereof 
into reshaped pulse signals having a preselected, sharp rise time, 
t.sub.r, the pulse shaping means being connected to the pulsed oscillator, 
preferably to the base of a transistor input, for the providing of the 
reshaped pulsed signals thereto. The reshaped pulse rise time, t.sub.r, is 
selected to impart significant harmonic power to the reshaped pulses near 
the free running frequency of the pulsed oscillator in combination with 
configuration of the pulsed oscillator for causing triggering on of the 
pulsed oscillator and for causing an output signal of the pulsed 
oscillator to have pulse-to-pulse consistency such that each output pulse 
bears the same relationship to the reshaped pulse as any other output 
pulse does. 
The reshaped pulse signal rise time, t.sub.r, is preferably less than about 
four times, and more preferably less than about twice, the length of the 
pulsed oscillator output signal period. In a particular embodiment, the 
pulsed oscillator output signal frequency, is about 3.245 GHz, the 
reshaped signal rise time is about 0.6 nsec, and the PRF generator output 
signal frequency is about 2.86 MHz. 
Also, preferably, the reshaped pulse signal has a peak turn-on voltage, 
V.sub.p, which is at least about twice as great as an average voltage, 
v.sub.avg, of the reshaped pulse signal, the reshaped pulse signal peak 
turn-on voltage, V.sub.p, being preferably equal to between about 0.2 and 
about 0.4 volts. 
PRF generator output signal pulse width, Pw, and hence that of the reshaped 
signal, is selected to be substantially greater than the pulsed oscillator 
output signal period. According to an embodiment, the reshaped pulse 
signals have a pulse width, P.sub.w, which is between about 50 and about 
100 nsec for a pulsed oscillator output signal frequency of about 3.245 
GHz. 
Also, according to an embodiment of the invention, means may be provided 
for modulating the output signal of the PRF generator, and accordingly 
thereby modulating the output signal of the pulsed oscillator, in a manner 
encoding information into such output signals.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention may be better understood by a brief examination of an 
exemplary, known-type of phase-locked, pulsed r.f. oscillator apparatus 10 
depicted, in block diagram form, in FIG. 1. Shown comprising oscillator 
apparatus 10 are a pulsed r.f. oscillator 12, a pulse repetition frequency 
(PRF) generator 14, a low power, continuous wave (c.w.) oscillator 16, a 
loop filter 18, a divide by N (.div.N) circuit 20 and a mixer 22. A pulsed 
output signal 24 (more particularly described below) of r.f. oscillator 12 
is provided, for example, to a radar transmitting antenna, not shown. 
PRF generator 14, which may be, or include, a crystal controlled 
oscillator, provides a pulsed output signal 30 having a frequency, 
f.sub.1, each of the pulses 32 provided thereby having the same pulse 
width, P.sub.w. PRF generator output signal 30 is fed, through an 
electrical conduit 34, to a gating input of pulsed r.f. oscillator 12, 
such oscillator being gated on for a time equal to P.sub.w, by each PRF 
generator pulse 32. As a result, output signal 24 of pulsed r.f. 
oscillator 12 comprises a series of pulses 36, each of which have a pulse 
width, P.sub.w. 
Pulsed r.f. oscillator 12 has a natural or free-running frequency, 
f.sub.FR, which is selected by oscillator design or adjustment to be 
approximately equal to an integral number, N, times PRF generator output 
frequency, f.sub.1. However, as above-mentioned, the free running 
frequency, f.sub.FR, tends to drift with time, for example, due to heating 
of oscillator 12. On the other hand, for proper radar operation it may be 
desired that pulsed r.f. oscillator 12 have an output frequency, f.sub.2, 
which is the integer N times PRF generator frequency, f.sub.1 ; that is, 
that f.sub.2 be coherent relative to f.sub.1. 
Since oscillator output frequency, f.sub.2 is normally much greater than 
PRF generator output frequency, f.sub.1, (since f.sub.2 =Nf.sub.1), output 
signal 24 of oscillator 12 comprises the sequence of pulses 36, each 
having a pulse width equal to P.sub.w, during which the oscillator 
provides a signal 38 having a frequency, f.sub.2. 
Coherency of r.f. oscillator output signal, f.sub.2, with respect to PRF 
generator frequency, f.sub.1, as well as phase locking of oscillator 
output signal 38 so that each pulse 36 starts with the same phase of 
signal 38, is provided by c.w. oscillator 16, .div.N circuit 20, mixer 22, 
and loop filter 18. To this end, an output of c.w. oscillator 16 is 
connected to an input of r.f. oscillator 12 by a conduit 40. The output of 
c.w. oscillator 20 is connected, by a conduit 42 to .div.N circuit 20, the 
output of the latter being provided to mixer 22 through a conduit 44. Also 
provided to mixer 22, through a conduit 46 is the output of PRF generator 
14. Connected between mixer 22 and c.w. oscillator 16, by conduits 48 and 
50 is loop filter 18, the loop filter being connected, by conduit 50, to a 
VCU input of the c.w. oscillator. Within mixer 22 output signal 30 of PRF 
generator 14, at frequency, f.sub.1, is mixed with the divided by N output 
signal frequency of c.w. oscillator 16 and any phase difference between 
the two signals results, through loop filter 18, in a signal to c.w. 
oscillator 16 causing its frequency to increase or decrease so as to be N 
times f.sub.1. 
It has, of course, been known that PRF generator signal 30 cannot, by 
itself, be used to trigger and phase lock pulsed oscillator 12 and to 
cause output signal frequency, f.sub.2, of the r.f. oscillator to be 
coherent with signal frequency, f.sub.1, of the PRF generator. Thus, the 
relatively complex, exemplary circuitry illustrated in FIG. 1, and 
described above, has been developed for such purposes. 
However, it has now been discovered by the present inventor that the pulsed 
output signal of a PRF generator (corresponding to PRF generator 14) can 
be reshaped to provide triggering of an associated pulsed r.f. oscillator 
(corresponding to r.f. oscillator 12) in a manner providing coherency 
between the pulsed oscillator output signal and the output signal of the 
PRF generator. 
To this end, a greatly simplified PRF coherent pulsed r.f. oscillator 
apparatus 60, according to the present invention, is depicted, in block 
diagram form, in FIG. 2. Generally comprising oscillator apparatus 60 are 
a pulsed r.f. oscillator 62, a PRF generator 64 and a pulse shaping 
network 66. 
In the manner above-described for PRF generator 14, PRF generator 64 
outputs a signal 68, comprising a series of pulses 70 of frequency, 
f.sub.1, and pulse width, P.sub.w. PRF generator frequency f.sub.1, may, 
by way of descriptive example, be about 2.86 MHz. Output signal 68 of PRF 
generator 64 is provided, by a conduit 72, to the input of pulse shaping 
network 64. 
As more particularly described below, pulse shaping network 66 reshapes the 
PRF generator signal 68 so as to output a reshaped signal 74 comprised of 
reshaped pulses 76 having a frequency and pulse width, P.sub.w, equal to 
those of PRF generator signal 68. Signal 74 from pulse shaping network 66 
is fed, via a conduit 78, to the input of pulsed r.f. oscillator 62. In 
response to the received reshaped signal 74 from pulse shaping network 66, 
r.f. oscillator 62 outputs a signal 80 comprised of a train of time 
separated pulses 82 having the same frequency and about the same pulse 
width, P.sub.w, as PRF generator signal 68. Each r.f. oscillator output 
pulse 82 is comprised of a number of oscillations or waves 84 having a 
frequency equal to the free running frequency, f.sub.FR, of the 
oscillation, the number of such oscillations per pulse 82 being, of 
course, dependent upon the width, P.sub.w, of such pulses. 
The present inventor has found that if reshaped pulses 76, provided by 
pulse shaping network 66, have significant harmonic power near the free 
running frequency of r.f. oscillator 62, the output signal 80 of the r.f. 
oscillator will have pulse-to-pulse consistency; that is, each r.f. 
oscillator output pulse 82 will be identical to each other pulse 82 in 
phase and shape and any such pulse will bear the same relationship to the 
reshaped pulses 76 as does any other such pulse. Since r.f. oscillator 
output signal 80 comprises a sequence of identical or repetitive pulses 82 
the Fourier spectrum elements of the output signal are multiples of PRF 
signal 68 frequency, and coherency is thus achieved between r.f. 
oscillator output signal pulses 82 and PRF generator output signal pulses 
70. The fact that the Fourier spectrum elements of r.f. oscillator output 
signal 80 are multiples of PRF signal 69 does not, however, imply that the 
period of the r.f. oscillator waves 84 is necessarily a harmonic of PRF 
output signal pulses 70. That is, r.f. oscillator frequency, f.sub.FR, 
does not necessarily equal an integral number N times PRF generator 
frequency, f.sub.1. 
The condition for reshaped pulses 76 having significant harmonic power near 
the r.f. oscillator's free running frequency, f.sub.FR, is satisfied by 
the reshaped pulses having a very fast rise time, t.sub.r, as well as 
having a high turn on voltage peak, V.sub.p, consistent with not damaging 
the input of r.f. oscillator 62 to which the reshaped pulses are provided. 
Preferably the rise time, t.sub.r of reshaped pulse 76 is no more than 
about 3 to about 4 times the period of r.f. oscillator oscillations 84, 
and is preferably only about twice such period. For an exemplary r.f. 
oscillator frequency f.sub.FR of 3.245 GHz, the signal period is about 
0.308 nsec; therefore, the rise time, t.sub.r, of reshaped pulses 76 is 
preferably no more than about 0.924 to about 1.233 nsec and is more 
preferably only about 0.6 nsec. Also, preferably, the peak turn on 
voltage, V.sub.p, is equal to at least about twice the average voltage, 
V.sub.avg of pulses 76. Since pulsed r.f. oscillator 62 is triggered on by 
the leading edge of reshaped pulses 76, the shape of the rest of each 
pulse 76 is not generally critical so long as the average voltage, 
V.sub.vag, is sufficient to keep oscillator 62 turned on. The effect on 
r.f. oscillator 62 of the very fast rise (turn on) time, t.sub.r, of 
reshaped pulses 76 is that when each such pulse 76 is received, the 
oscillator is turned on and starts outputting oscillations or waves 84, 
which are coherent with respect to PRF generator output signal 68. 
Width, P.sub.w, of PRF generator pulses 70, and hence of reshaped pulses 
76, as above-described, determines width of oscillator output pulses 82, 
and therefore determines the number of oscillations or waves 84 per pulse 
82. Pulse width P.sub.w of pulses 70 is, by design and configuration of 
PRF generator 64, made sufficiently long to provide a sufficient number of 
oscillations 84 per output pulse 82 to assure proper operation of the 
system of which apparatus 60 forms a part. Thus, for the exemplary case in 
which r.f. oscillator frequency, f.sub.FR is 3.245 GHz and the 
corresponding period is about 0.308 nsec, pulse width, P.sub.w, may, for 
example, be selected to be between about 50 and about 100 nsec, although 
the present invention is not limited to any particular time range for 
P.sub.w. 
FIG. 3 illustrates one manner in which PRF coherent, pulsed r.f. oscillator 
apparatus 60 of the present invention may be electronically implemented. 
As shown in FIG. 3, PRF generator 64 has associated or formed therewith a 
generator portion 96 and a buffer portion 98; pulse shaping network 66 has 
associated or formed therewith a network portion 100 and an interface 
portion 102. Values of the various resistors and capacitors are as 
indicated in FIG. 3, and types of the various transistors and diodes are 
also indicated on such Figure. Inductance, L.sub.1, may, for example 
comprise 73 turns of 30 enameled wire wound on a T50-6 core. Diode D.sub.1 
is preferably a step recovery diode. 
As described above, by way of example, PRF generator 64 provides an output 
signal 68 having a frequency, f.sub.1, equal to 2.86 MHz. Output signal 
pulses 76 from pulse shaping network 66 has a pulse rise time, t.sub.r, 
equal to about 0.6 nsec, a pulse width, P.sub.w, of about 27 nsec, a pulse 
fall time, t.sub.f, of about 6.8 nsec and a peak turn on voltage, v.sub.p, 
of about 0.3 V. 
Variable capaciter, C.sub.1, of pulsed oscillator 62 is varied to adjust 
the free running frequency, f.sub.FR, of the pulsed oscillator to be about 
3.245 GHz. The very fast rise times, t.sub.r, of reshaped pulses 76 
provide sufficient harmonic energy at the oscillator's free running 
frequency, f.sub.FR, to cause oscillator 62 to start each pulse 82 at a 
fixed phase relationship with respect to reshaped pulse 76. Injection of 
the reshaped pules 76 directly into the base of pulsed oscillator 
transistor Q.sub.6 not only gates oscillator 62 on and off, but is also 
very effective in achieving coherency of the pulsed oscillator output 
signal 80 to PRF generator output signal 68. 
In some circumstances it may be desirable to also be able to use apparatus 
60 to transmit data or information. For example, if apparatus 60 is used 
in an airborne target miss distance radar, it may be desirable to use the 
apparatus also to transmit information a to the determined miss distance 
to a ground scoring station. For such purposes, as shown in FIG. 2, 
modulating means 110 are connected to PRF generator 64 by a conduit 112. 
Modulating means 110, which may be of known conventional design, may, 
therefore, be used, for example, to frequency modulate PRF generator 
frequency, f.sub.1, and hence also r.f. oscillator output signal pulses 
82, in a manner encoding information or data into oscillator output signal 
80. 
Although there has been described above a specific arrangement of a PRF 
coherent, pulsed oscillator apparatus in accordance with the present 
invention for the purpose of illustating the manner in which the invention 
may be used to advantage, it will be appreciated that the invention is not 
limited thereto. Accordingly, any and all modifications, variations or 
equivalent arrangements which may occur to those skilled in the art should 
be considered to be within the scope of the invention as defined in the 
appended claims.