Electronic system locates interferences in radar reception. System utilizes well known frequency-modulated continuous-wave technique to locate objects with nonlinear impedances. FM transmitter generates signal through bandpass filter which eliminates higher order harmonics around carrier frequency

Frazier, M. J.

Morissette, S.

Sea, R. G.

English

An apparatus is described for locating an electrically nonlinear object and determining the distance to the object by transmitting an FM signal in the vicinity of the nonlinear object causing a signal of a higher harmonic to be reflected by the nonlinear object. A receiver is provided for receiving the higher harmonic reflected signal. It is compared with the initial exciting signal so as to produce a signal, the amplitude of which is directly proportional to the distance to the object

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ATTN OF: GP
(NASA-Case-KSC-10108) JUNCTION RANGE
FINDER Patent (IIT Research Inst.) 6 p
CSCL 14B
N73-25U6
^
00/14
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05101 .
TO: KSI/Scientific & Technical Information Division
Attention: Miss Winnie M. Morgan
FROM: GP/Office of Assistant General Counsel for
Patent Matters
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
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The following information is provided:
U.S. Patent No. : 3, 73ei.E(p7
J///M/S JiS?;
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA patent Case No.
of
*
NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
Yes A* / No / /
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
inventor (author) appears at the heading of column No. 1 of
the Specification, following the words "... with respect to
an invention of ..."
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Enclosure
Copy of patent cited above
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United States Patent
Low et al.
[in 3,732,567
[45] May 8,1973
[54] JUNCTION RANGE FINDER
[76] Inventors: George M. Low, Deputy Adminis-
trator of the National Aeronautics
and Space Administration with
respect to an invention of; Sarto
Morissette, Thetford Mines,
Quebec, Canada; Ronald G. Sea,
Newport Beach, Calif.; Marvin J.
Frazier, Wood Dale, III.
[22] Filed: Sept. 21, 1970
[21] Appl. No.: 73,922
[52] U.S. Cl 343/14, 343/6.8 R, 343/17.5
[51] Int. Cl G01s9/23
[58] Field of Search 343/14, 5 SG, 6.5 R,
343/17.5, 6.8 R
[56]
2,935,743
3,079,557
References Cited
UNITED STATES PATENTS
5/1960 Glegg 343/14 X
2/1963 Crabtree 343/6.8 R X
2,929,057 3/1960 Green 343/14
3,508,828 4/1970 Froome 343/14 X
3,087,153 4/1963 Richards 343/6.5 R X
3,444,509 5/1969 Rubega et al 340/3 R
2,907,023 9/1959 Skinner 343/14
3,217,322 11/1965 Kabelletal 343/17.5
3,098,971 7/1963 Richardson 343/6.8 R
Primary Examiner—Benjamin A. Borchelt
Assistant Examiner—Harold Tudor
Attorney—James O. Harrell and John R. Manning
[57] ABSTRACT
An apparatus for locating an electrically nonlinear ob-
ject and determining the distance to the object by
transmitting an FM signal in the vicinity of the non-
linear object causing a signal of a higher harmonic to
be reflected by the nonlinear object. A receiver is pro-
vided for receiving the higher harmonic reflected
signal and comparing such with the initial exciting
signal so as to produce a signal, the amplitude of
which is directly proportional to the distance to the
object.
2 Claims, 2 Drawing Figures
'J-O1
PATENTEDNAY 81973 3,732,567
SHEET 1 OF 2
INVENTORS
MARVIN J. FRAZIER
5ARTO MORISSETTE
BV RONALD G. SEA
ATTORNEY
PATENTED HAY 3137
SHEET 2 OF 2
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BY
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MARVIN J. FRAZIER
5ARTO MORISSETTE
RONALD G. SEA
ATTORNEY
__, -, -M »•"
3,732,567
1 2
JUNCTION RANGE FINDER correcting such using an apparatus constructed in ac-
The invention described herein was made in per- cordance with the present invention. This apparatus in-
formance of work under a NASA Contract and is sub- eludes the following basic parts: (1) a generator for
ject to the provisions of Sections 305 of the National generating a frequency modulating exciting signal of a
Aeronautics and Space Act of 1968, Public Law 5 predetermined fundamental frequency, (2) a trans-
85-568 (72 Stat. 435,402 U.S.C.P. 2457). mining means for transmitting the exciting signal in the
The invention relates to an apparatus for locating vicinity of a nonlinear object for causing a signal of a
electrically nonlinear objects which sometime occur at higher harmonic to be reflected by the nonlinear ob-
joints between metallic structures, and more particu- ject> (3) a receiver for receiving the higher harmonic
larly to produce a signal that is proportional to the 10 reflected signal, (4) a filter means coupled to the
distance between a station and the object. receiver for passing a predetermined harmonic portion
Complex electronic systems which comprise a mul-
 of Ae received signal, (5) means coupled to the
tiplicity of radiating transmitters and receivers can ex- generating means for multiplying the exciting signal in
perience interference due to electrical nonlinearities in
 order to produce a signal of the same frequencies as the
the immediate radiation environment of the system.
 signal passed by ^ m^T means (6) a flrst mixer for
Often the immediate radiation environment of such
 mixing ^ multiplied excited signal with the filtered
an electronic system contains many metallic structures
 reflected signal in order to produce a combined signal,
or objects. When two metallic surfaces make apparent
 (?) ^^^ means for ^ ,^ ,5 ^ combined signal
physical contact, the electrical impedance of the con- ^
 (g) a discriminator coupled to ^ output of the
tacting surface ,s quite often nonlinear, amplifying means for producing a signal having an am-
Such nonlinear characteristics of objects can often
 |itude ^ ^ ^onal to ^  distance to ^  non.
cause incorrect information to be transmitted or inter- linear object
fere with the transmission of such information In Accordingly, it is an important object of the present
launchmg space vehicles and similar complicated elec-
 25 invention to ovide m apparatU8 for locating electri.
tromc systems it is imperative that the signals being cally nonlinear objects
transmitted be received with a minimum of distortion
 Another . ^ object of ^  ni invention is
and interference. The reasons for such is obvious in
 to provide M atus for generating a signal and
that such interference could possibly cause an mcor-
 receivin a si^ of a y^ harmonic M & to com.
rect command to be sent to the space vehicle. •
 30 ^ ^ ^^ fa Qrder to ate a CQm
It has been found that metallic objects compnsed of
 sipi ^ ^ of which ig proportional to the
two or more constituent parts which have been
 distance to the nonlinear object,
fastened together non-ideally m the fabrication of the ^^
 objects ^ ^^ of ^  invcntion wffl
t^cteristSs P°SSeSS n°nhnear C 6CtnCal become more apparent from a reading of the following
C
 Sobjecte possessing this nonlinear characteristic " d^led description and appended^ claims, taken in
. . * i « • ! • • • » u conjunction with the accompanying drawings wherein:have been found to reflect signals impinging thereon _i_ , . . . .. • . • ?.
having frequencies of a higherharmonic but mathe- nGJ. ls a 8chemaU4C d-agram showing the exciting
matically related, to the exciting signal. wave *""* ^ mitted m the vKuiity of a nonlinear
It has also been found that if a metallic object is 40 ^ ^ a reflected harmonic wave being received
located in the near environment of a system radiating fr°™ ** Sen^lg ^ OOn' *"* .
radio frequency energy, the electromagnetic waves , nG 2 »a Woc^ dMW™ni «"^tratmg an apparatus for
radiated by the system will cause currents which are locatmg electncally nonlmear otyects.
linearly related to the electromagnetic wave to flow in
 fc Referm« '" «no« 0«ail to FIG. 1 of the drawings,
the object. If the object is electrically nonlinear, as in 45 *« aPP^tus can be constructed to be portable so that
the case of ah assembled metallic object, the current u can •* moved ^ ^^V ™«> ** vicinity where it is
which flows in the object will contain frequency com- desired to detect Junctions that are electrically non-
ponents which were not in the original electromagnetic lmear' As can »* seen- ** apparatus 10 transmits an
wave exciting signal 12 which, when reflected by a junction
The current flowing in the object at the new frequen- 50 14 that is electrically nonlinear produces an elec-
cies cause an electromagnetic wave containing tromagnetic wave 16 that is of a higher harmonic than
frequencies of a higher harmonic to be reflected from Ae exciting wave. In the particular example illustrated
the object. m FIG. 1, the junction possessing the electrically non-
interference thus created due to electrical non- '«near characteristics is located where the fin 18 of a
linearities in metallic objects in the near radiation en- S5 missile 20 joins the main body thereof. After the junc-
vironment of an electronic system is referred to in »»<>" ha» been detected and located it can be modified
general terms as a nonlinear environment interference. *° correct the nonlinear characteristics by changing the
Such interference can be quite severe for complex manner in which the two pieces of metal are joined,
systems, and can seriously degrade the performance of The technique utilized in the subject invention is
such a system. similar to that employed in the CW-FM radar ahimitry.
It is possible to materially reduce the interference However, in the altimitry application the receiver
generated by nonlinear environment by locating the responds to energy which is back scattered from all ob-
structure or objects which are nonlinear and modifying jects within the antenna beam. The back scattered
the structure to eliminate the nonlinear contacts. . energy is at the same frequency as the transmitted
In accordance with the present invention, it has been signal from the FM source. The apparatus constructed
found that the difficulties encountered with electrically in accordance with the present invention is only con-
nonlinear objects may be overcome by locating and cerned with detecting energy which is at a frequency
3,732,567
3 4
different from that being transmitted which is a charac- criminator is used for this application rather than a
teristic of the reflected wave from an electrically non- .frequency counter to circumvent the fixed error in-
linear junction. Altimiters and radar systems illustrat- herent in frequency counting schemes, which is
ing circuitry similar to that referred to above are dis- deleterious for short range measurements,
closed in U.S. Pat. No. 2,929,057 granted to Green on 5 In the following discussion, delays in circuit com-
Mar. 15, 1960, and U.S. Pat. No. 3,217,322 granted to ponents will be ignored, since they would be calibrated
Kabell et al. on Nov. 9, 1965. out in a practical system. The trippler 32 output v,(f) is
Referring in more detail to FIG. 2 of the drawings, an
FM transmitter 22 generates a wave defined by the v,(/) = sin [ 3wj + (3pl2fm) an Wmt}
equation v, (r) = v, sin [w,t + (0/2/m) sin wm t], which 10 This signal v,(t) is combined in the first mixer 34
is the common expression for frequency modulated
 with the output of the local oscillator 36 signal to
wave of modulated frequency fm = wm!2ir. The carrier produce a signal vz(f) which is
frequency is/fl = wo/2ir, and the total frequency excur-
sion is given by /3 . The signal generated by the trans-
 15 v2(/) = sin [(3w0- WIF)t + (3ft/2fm) sin Wmt ]
mitter is passed through a bandpass filter 24 centered
 There are many other mixer output frequencies,
at/0 and is then transmitted or radiated from the trans- however, the signal in v2(/) is selected by the filter
m itting antenna 26 in order to eliminate any higher har- which follows the mixer
monies of/, produced in the transmitter.
 The signal fa Vj(/) fa combined m Ae Kemd mixer
Assuming a nonlinear structure is located at a range 20
 40 ^ ^ received signal VB(O to produce a mixer
or distance R from the system antenna 26, the trans-
 output centered at the rp frequency and given by
milled or exciting wave propagates to the nonlinear ob-
ject in time r/2 — R/c, wherein c is the velocity of light. v3( t) = cos [ Wlrt — ( 3/3//m) sin ( Wmr/2 ) cos wn (t —
Thus, the wave impinging on the object 14, such as il- r/2) — 3w0r ]
lustrated in FIG. 1 is given by 25 ^ ^
 i a n g- J n l B M t _in_this_dejfeJopmenVthe_
Es(t) = Asm[wo( t - r /2 ) + (P/2fm)smwm(t-r/2)] target ranges are such that r«l/fm. Therefore, sin
(Wm r/2) = Wm r/2 to a very good approximation, and
where (A) can be considered a constant for the present
 v^t) can ^ rewritten as
discussion. The exciting wave Es causes currents at the 3Q
same frequency to flow in the majority of the vehicle v3(f) = cos [ W,rt — STT/JTCCS Wm (t — r/2) ]
structure 20, however, if the structure, such as the joint . . , , _„. . , . . _. ,
... .. ,. . - . : where the phase angle 3 W0r has been ignored. The last1 4 , i s nonlinear currents a t t h e harmonics o f t h e above - . « , , - « _ . / • _ • • ,
wave Es are produced; specifically, the subject inven- «*»"*" for v'(/) 'I* fr^uency modulated signal at
tion is interested in the third harmonic current which is 35 ^ ^T^u TJ* T? "^T '?•tO r C°"'given bv vement level by the IF amplifier 42; limited in a hmiter
to reduce unwanted amplitude modulation, and then
i'3 (f) = B sin [ 3w0 (/ — r/2) + (3/3/2/m) sin wm (t—r/2) impressed upon a frequency discriminator 46. The out-
] put of the discriminator is
This current causes a wave linearly related to it to be *0
 v<> (t) = 3irKfir cos Wm (t — r/2)
radiated. This wave is sensed by a receiving antenna 28,
however, due to the distance or range R, the received where K is a constant dependent on the discriminator
signal vr (t) is delayed another time increment r/2 = characteristics. Relation v. (t) is a signal at frequency
R/c. Thus, the received waveform is given by fm = Wml2r . For the purpose of the invention, the
45
 time delay in vc (t) is unimportant. The signal has an
v r ( t ) = H sin (3w0 (t - r) + (30/2/m ) sin wm (r - r) ] amplitude of 3 irKftr which is directly proportional to
wherein His a constant. the target or interference source range.
The following discussion is pertinent to the The amplitude of the output signal v0(J) can be mea-
processing of the signal vr (/) in the receiver generally 50 sured by *"> suitable device, such as a volt meter, to
designated by the reference character 30 to obtain a extract &e desired range information. Thus, by radial-
signal indicative of the range from the sending station. >ng a frequency modulated fundamental waveform,
In addition to transmitting the signal produced by the measurements made on a third harmonic reflected
FM transmitter 22, the signal is also fed to a tripler 32 signal from a nonlinear interference source will yield a
combined in a mixer 34 with the output of a local oscil- 55 signal output whose amplitude is proportional to the
later 36 at a frequency//^, which is the IF frequency, range to the interference source. All normal scattered
and then sent through a filter 38 into a second mixer returns at the fundamental frequency are rejected and
40. The purpose of the trippler 32, the mixer 34, the thus not utilized.
local oscillator 36, and the filter 38 is to produce a In some systems which experience interference due
signal v2 which varies at the same frequencies as the *° to the above mechanisms, the frequency of operation is
reflected signal picked up by the antenna 23, but sufficiently high to permit directional antennas to be
without the time delay. This is to enable the signal v, to used as an aid in locating environment nonlinearities
be mixed in the mixer 40 with the reflected signal to which can contribute to the interference. However,
produce a signal at the intermediate frequency suitable often the environment is quite complex, and it is desira-
for amplification by the amplifier 42. ble to be able to assess the approximate range to a non-
The block diagram shows the use of the frequency linear structure in addition to the general direction ob-
discriminator to extract the range information. A dis- tained by the use of directional antennas.
3,732,567
In essence, the invention applies existing FM-CW
techniques which are normally used primarily for al-
titude measurements, to the range determination of ob-
jects in the environment which are nonlinear. The dif-
ference in system implementation lies primarily in the 5
fact that for a conventional FM-CW range measure-
ment system,' the received signal is at the same frequen-
cy as the transmitted signal, while for the nonlinearity
locating scheme, the received signal is at a frequency
which is different than that transmitted by nature of the 10
conversion process in the nonlinearity. It is anticipated
that the third harmonic of the transmitted signal would
be the logical return frequency to monitor, however, a
higher harmonic or an intermodulation product
between two transmitted signals could be used instead. IS
What is claimed is:
1. Apparatus for locating an electrically nonlinear
object comprising:
A. means for generating a frequency modulated ex-
citing signal of a predetermined fundamental 20
frequency;
B. a transmitting means for transmitting said exciting
signal in the vicinity of said nonlinear object for
causing a signal of a higher harmonic to be
reflected by said nonlinear object; 25
C. a means located in close proximity to said non-
linear object for receiving said higher harmonic
reflected signal;
D. filter means coupled to said receiving means for
passing a predetermined harmonic portion of said
received signal;
E. means coupled to said generating means for mul-
tiplying said exciting signal to produce a signal of
the same frequency as said signal reflected by said
nonlinear object and filtered by said filter means;
F. a first mixer for mixing said multiplied excited
signal with said filtered reflected signal producing
a combined signal;
G. amplifier means for amplifying said combined
signal,
H. a discriminator coupled to the output of said am-
plifying means for producing a signal having an
amplitude directly proportional to the distance to
said nonlinear object, and
1. a limiter interposed between said first mixer and
said discriminator for reducing unwanted am-
plitude modulations.
2. The apparatus as set forth in claim 1, wherein said
means coupled to said generating means for multiply-
ing said exciting signal includes;
A. a tripler coupled to said generating means for
multiplying said exciting signal;
B. a local oscillator; and
C. a second mixer coupled to said tripler and oscilla-
tor for mixing the output of said local oscillator
with the output of said tripler.
30
35
40
45
50
55
60
65


Junction range finder

June 1973	 B73-10191 
NASA TECH BRIEF S	 John F Kennedy Space Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Junction Range Finder 
The problem: 
Radar systems that are part of complex electronics 
in space vehicles and aircraft are sometimes subject 
to interference from surrounding objects. Specifically, 
objects that comprise several metallic surfaces forming 
physical junctions with each other exhibit nonlinear 
electrical impedances. The signals reflected from these 
junctions bear information which does not corre-
spond to the object distance. Wrong information of this 
nature may cause serious interferences in the radar 
reception. Naturally, these sources of interference must 
be located and corrected. 
The solution: 
An electronic system was built to locate these sources 
of interference.
Transmitter 
Antenna
How it's done: 
The system as shown in the figure utilizes a well 
known FM-CW (frequency-modulated continuous-wave) 
technique to locate objects with nonlinear impedances. 
In operation, an FM transmitter generates a signal 
through a bandpass filter which eliminates the higher 
order harmonics around the carrier frequency. The 
signal is then radiated through the transmitting antenna. 
A portion of this signal, used as a reference, is fed to a 
tripler and then combined in a mixer with a local IF 
oscillator. This signal is fed through a bandpass filter 
into the second mixer to be combined with the signal 
reflected from the target. 
When the transmitted signal strikes a nonlinear 
object, it generates electrical currents on the object 
surface. These currents produce higher order harmonics 
Heceiver 
Antenna .
	
I
Bandpass	 FM
	
Filter f0	 [Transmitter 
Carrier Frequency=f0  I	 Tripler	 I
I Local IF Mixer	
I Oscillator 
Bandpass 
I	 Filter 
Bandpass I
______ 
	
Filter 3 f0 I	 Mixer	 IF I	 1 Amplifier I	 Limiter I__.1D54immnat0r 
Block Diagram of the Junction Range Finder
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
.
https://ntrs.nasa.gov/search.jsp?R=19730000191 2020-03-17T07:09:31+00:00Z
in the reflected signal. The reflected signal is picked up 
by a directional receiver antenna designed to match 
with the third-order harmonic of the carrier. This 
signal is then mixed with the reference signal in the 
second mixer. Because the received signal is time-delayed 
with respect to the reference signal, the phase difference 
contains the object range information. The output of 
the mixer is then amplified, limited, and fed into the 
discriminator. The amplitude of the discriminator output 
is directly proportional to the distance of the object 
and is given by 
v0(t)=K AfcomR 
where is the amplitude of the discriminator output, 
K is a proportionality constant, Lf is the frequency 
deviation, Wm is the modulating frequency, R is the 
range to the object, and c is the velocity of signal 
propagation.
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Kennedy Space Center 
Code AD-PAT 
Kennedy Space Center, Florida 32899 
Reference: TSP73-10191 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,732,567). Inquiries concerning non-ex-
clusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Kennedy Space Center 
Code AD-PAT 
Kennedy Space Center, Florida 32899 
Source: Sarto Morissette, Ronald G. Sea, and 
Marvin J. Frazier of
Illinois Institute of Technology
under contract to

Kennedy Space Center
(KSC-10 108)
. 
B73-10191	 Category 02


Junction range finder

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