3,479,615
`R. v. GARVER
`Nov. 18, 1969
`WARACTOR CONTINUOUS PHASE MODULATOR HAVING A RESISTANCE
`IN PARALLEL WITH THE WARACTOR
`Filed Oct. 20, 1966
`
`
`
`/W/AW706,
`aaaaz M. Gaevate
`
`sy. T &ze--ó- a7726Avay16
`
`£ 2.
`
`Page 1 of 4
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`GOOGLE EXHIBIT 1008
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`

`

`United States Patent Office
`
`3,479,615
`Patented Nov. 18, 1969
`
`3,479,615
`VARACTOR CONTINUOUS PHASE MODULATOR
`HAVING A RESISTANCE IN PARALLEL WITH
`THE VARACTOR
`Robert V. Garver, Boyds, Md., assignor to the United
`States of America as represented by the Secretary of
`the Army
`Filed Oct. 20, 1966, Ser. No. 588,693
`Et, C. H.03e3/20
`U.S. C. 332- -30
`14 Claims
`
`5
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`O
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`5
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`ABSTRACT OF THE DISCLOSURE
`A varactor diode modulator is used to provide high
`frequency phase modulation without degradation of phase
`linearity or efficiency. The varactor diode reactants is ad
`justed by selecting diode parameters that will approxi
`mate a tan 6 curve as the voltage is varied. The diode is
`then attached to one part of circulator or similar plural
`channel device to provide an approximate linear relation
`ship between voltage and phase shift. A resistor is con
`nected in parallel with the varactor diode to produce a
`reflection coefficient that remains constant with variations
`of input voltage, thereby overcoming the problem of
`change in attenuation with change in phase. A 360 de
`gree modulation is achieved without the use of a second
`circulator by connecting a second varactor in parallel
`with the first and separating the two varactors by a quar
`ter wavelength line.
`
`20
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`25
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`30
`
`-assimaa
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`2
`An additional object of this invention is to provide a
`means which will yield at least 360 degree phase modella
`tion in one configuration whereby a sawtooth modulating
`signal applied thereto will produce single-sideband mod
`ulation.
`Still another object of this invention is to provide an
`improved microwave phase modulator which requires a
`minimum of space and few components.
`An additional object of this invention is to provide a
`continuous diode phase modulator in which insertion loss
`remains constant with variations in voltage.
`Briefly, in order to realize the above and other objects
`a varactor diode modulator is used. The varactor diode
`used has a reactance that is adjusted by selecting didoe pa
`rameters that will approximate a tan 6 curve as the voltage
`is varied. This diode is then attached to one part of a
`circulator or similar plural channel device to provide ap
`proximately a linear relationship between voltage and
`phase shift. To overcome the problem of change in at
`tenuation with change in phase a resistor is connected in
`parallel with the varactor diode which will produce a re
`flection coefficient that remains constant regardless of in
`put voltage variations. In order to obtain 360 degree mod
`ulation without using a second circular or similar device
`a second varactor diode is connected in parallel with the
`first mentioned varactor diode, the two being separated
`by a quarter wavelength line.
`The specific nature of the invention, as well as other
`objects, aspects, uses and advantages thereof, will clear
`ly appear from the following description and from the
`accompanying drawings, in which.
`FIGURE 1 is the equivalent circuit of a varactor diode.
`FIGURE 2 is a superposition of the curve representing
`the normalized reactance of the varactor diode and the
`% tan 6 curve.
`FIGURE 3 is a schematic diagram of a typical embodi
`ment of the invention.
`FIGURE 4 is a representation of the addition of two
`tan 8 functions to provide a tan 26 function.
`FIGURE 5 is a schematic diagram of another typical
`embodiment of my invention which will produce 360
`degree modulation.
`Referring to FIGURE 1, varactor diode 10, when
`mounted in a transmission line, has an equivalent circuit
`which includes Series inductance 11, junction capacitance
`12, series resistance 14, and cartridge capacitance 16.
`The effects introduced by capacitance 16 and resistance
`14 are either negligible or they can be made negligible.
`Capacitance 16 can be tuned out by resonating it with
`a parallel inductor at any given frequency of operation,
`and in this particular application spreading resistance 14
`has been found to be negligibly small. For this reason
`capacitance 16 and resistance 14 can be ignored, and the
`reactance of the diode may be represented as follows:
`
`40
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`50
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`55
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`This invention relates to phase modulators, and in par
`ticular, those phase modulators that utilize diodes.
`A need now exists in microwave technology for linear,
`hysteresis-free, high efficiency, high modulation fre
`quency, constant insertion loss phase modulators. Pres
`ently ferrite modulators are extensively used; however
`these require high power low frequency modulating sig
`nals, and such requirements severely limit the usefulness
`of this type of modulator. Further, because they are fer
`rite devices they will behave as one would expect ferrite
`devices to behave in that they exhibit pronounced hy
`sterisis characteristics. To overcome the difficulties en
`countered with ferrite modulators varactor diode continu
`ous phase modulators are now being extensively used, but
`these too have disadvantages. Varactor diode modulators
`have a pronounced non-linear relationship between phase
`and voltage and are subject to severe insertion loss varia
`tions with change in phase. C. S. Kim, et al. (Digest of
`Technical Papers, 1966 International Solid State Circuits
`Conference) have disclosed a varactor diode phase mod
`ulator in which phase and voltage have a linear relation
`ship; however variations in insertion loss with change in
`phase were still found to be present. Further, the lineari
`zation of the phase response of this device was accom
`plished using many space consuming components, for ex
`ample, two diodes and six quarter wavelength lines were
`required for 180 degree modulation. Such a technique
`would produce a prohibitively large structure at low
`60
`frequencies. Even a larger number of components would
`be required in such a device to produce 360 degree mod
`ulation.
`It is therefore an object of this invention to provide a
`microwave phase, modulator in which the phase is a linear
`function of the applied modulating voltage.
`Another object of this invention is to provide a phase
`modulator requiring a very low power modulating signal.
`A further object of this invention is to provide a phase
`modulating means in which high frequency modulation
`may be accomplished without degradation of phase lin
`earity or efficiency.
`
`X =oL- min V
`
`where:
`V=normalized value of the diode voltage, e.g. V=0
`at the contact potential and V= 1 at the breakdown
`voltage,
`?y-/2 (typically), and
`C min=capacitance of the varactor junction at or near
`the maximum possible reverse bias voltage.
`This expression can be normalized to yield the follow
`ing expression:
`w=XC minoLC min-V%
`As shown in FIGURE 2 this normalized reactance
`expression when plotted as a function of V can be super
`imposed on the 38 tan 6 curve 22 when plotted as a func
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`Page 2 of 4
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`

`

`where: Z=characteristic impedance of the transmission
`line. It will be found that the center of this curve will not
`coincide with the center of the Smith chart. Therefore, it
`will be readily seen that the magnitude of the reflection
`coefficient will change with changes in V. If one should
`plot the normalized admittance of the diode, it will be
`found that the center of this curve in relation to the center
`of the reactance curve and the center of the Smith chart
`will be positioned so that by adding conductance to the
`admittance a curve may be obtained that has its center
`at the center of the Smith chart. The magnitude of the
`conductance so added may be found by the equation:
`
`O
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`20
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`3,479,615
`4.
`3
`circuitry used to obtain 360 degree modulation. The radio
`tion of 8/90. The normalized reactance can as well be
`frequency energy to be modulated enters circulator 50
`plotted on a Smith chart, where incremental changes in
`through port 51 and emerges from port 51. Circulator 50
`V will produce like incremental changes in the phase
`is connected to the diode network through port 51' and
`angle of the reflection coefficient. The equation of this
`transmission line 52 which must be adjusted to have a
`curve is:
`characteristic impedance of Z/2 in order to provide the
`desired linearity of phase shift and constancy of insertion
`loss. Varactor diodes 57 and 62 are separated by quarter
`wavelength line section 53 and connected thereto by ter
`minals 57 and 62, respectively. The other terminals, 57'
`and 62' of the varactor diodes are connected, respective
`ly, to transmission lines 58 and 63 to which are connected
`capacitors 59 and 64. Capacitors 59 and 64 provide an
`R.F. short circuit to ground for the transmission lines to
`which they are connected thereby providing a certain
`amount of necessary inductance. Short lengths of trans
`mission line 54 and 55 are connected to the inputs of
`varactor diodes 62 and 57, respectively, at one end and
`to ground at the other end whereby by properly adjusting
`the impedance of each line section the cartridge capac
`itance of the particular diode to which each line section
`is connected can be parallel resonated. Parallel resistances
`56 and 61 are connected in parallel with line sections 55
`and 54, respectively and as discussed with relation to FIG
`URE 3 provide the necessary admittance to maintain
`constant insertion loss with changes in voltage. Modula
`tion voltage is introduced into the network by fine wires
`60. The operation of this embodiment is similar to the
`operation of the embodiment of FIGURE 3 differing
`only in that a 360 degree phase shift is now possible with
`a linearity of plus or minus five degrees, because of the
`second varactor diode.
`This invention may be practiced by using other plural
`channel reflection devices such as directional couplers,
`hybrid rings, or magic T's instead of a circulator. For
`example, if one of the varactor diode circuits as described
`with reference to FIGURE 3 is placed in each of the
`normally coupled arms of a 3 db coupler, reciprocal phase
`modulation of the power out of the normally isolated arm
`will be produced. Any form of electrical circuitry may be
`used to construct the invention; for example, either strip
`line, coaxial line, waveguide or any other form of TEM
`circuitry may be used. The R.F. shorting capacitors and
`input leads may be replaced by filters which can be de
`signed using state of the art techniques to permit the phase
`modulator to be controlled at very high modulation.
`It will be apparent that the embodiments shown are
`only exemplary and that the various modifications can
`be made in construction and arrangement within the scope
`of the invention.
`I claim as my invention:
`1. An improved continuous diode phase modulator hav
`ing a linear phase-voltage relationship while maintaining
`a constant insertion loss comprising:
`(a) a plural channel reflecting means,
`(b) a varactor diode,
`(c) connecting means for connecting said varactor diode
`to Said plural channel reflecting means, said reflect
`ing means including an inductive means adjusted to
`be in parallel resonance with the cartridge capacitance
`of said varactor diode,
`(d) resistance means connected in parallel with said
`varactor diode thereby establishing a constant inser.
`tion loss,
`(e) means for introducing a modulating voltage into the
`diode network connected in series with said varactor
`diode and connected to the end of said varactor diode
`opposite the end connected to said plural channel re
`flecting means, and
`(t
`sans for introducing a carrier voltage to be modu
`ated.
`2. The improved continuous diode phase modulator
`of claim 1 wherein said varactor diode has an admit
`tance characteristic selected to conform substantially to a
`tan G Curve.
`
`The result of adding conductance to the diode admittance
`in the above described manner will be that the magnitude
`of the reflection coefficient will remain constant with
`variations of V.
`30
`In FIGURE 3, in a typical embodiment of the inven
`tion, the radio frequency power to be modulated enters
`port 32 of circular 30 and emerges from port 32". The cir
`culator by means of port 32' and transmission line 31 is
`connected in series to the junction terminal of varactor
`diode 36 which arrangement allows the varactor diode to
`be represented as in FIG. 1. The other terminal 36' of
`the varactor diode is connected in series with a length of
`transmission line 37 which is R.F. short-circuited by ca
`pacitor 38 to provide the desired inductance to satisfy the
`40
`above equations. A short length of high impedance trans
`mission line 33 is connected to the input of varactor diode
`36 with its other end being connected to ground. By prop
`erly adjusting the length and characteristic impedance of
`transmission line 33 it is possible to obtain the necessary
`inductance with which cartridge capacitance 16 (FIG. 1)
`may be parallel resonated at the frequency of operation.
`The conductance which is added to make the reflection
`coefficient invariant with voltage is represented by resis
`tor 34 placed in parallel with transmission line 33 which
`must be a well-designed non-reactive resistance at the
`frequency of operation. Modulating voltage is introduced
`into the network by a fine wire 39 connected in series with
`transmission line 37 and varactor diode 36.
`In operation equal increments of voltage across the
`diode will produce equal increments of phase shift of the
`5 5
`reflection coefficient of the diode which will, in turn, pro
`vide equal increments of phase shift throughout the net
`work. By using parallel resistance 34 the magnitude of the
`reflection coefficient will remain constant thereby produc
`ing constant transmission loss in the system. This embodi
`60
`ment has the property that 180 degrees rotation on the
`Smith chart produces substantially a 180 degree phase
`change in the network. For 180 degree phase modulation
`this approximation is within plus or minus 2.6 degrees.
`FIGURE 4 demonstrates that two varactor diodes each
`having an admittance characteristic approximately con
`forming to a tan 0 function can be added to provide a
`tan 20 function and 360 degree modulation. Curves 40
`and 41 represent the two tan 0 curves which are to be
`added. The phase shift which exists between curves 40 and
`41 may be obtained by placing a quarter wavelength line
`section between the two diodes as will be discussed in
`relation to FIGURE 5. The result of this addition step is
`tan 20 curve 42.
`In FIGURE 5 is shown a typical embodiment of the
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`Page 3 of 4
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`10
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`5
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`20
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`3,479,615.
`5
`6
`3. The improved continuous diode phase modulator of
`varactor diode opposite the end connected to said
`claim 1 wherein said plural channel reflecting means is
`quarter wavelength transmission line, and
`is connected to said plural channel reflecting means.
`(f) means for introducing a carrier voltage to be modu
`4. The improved continuous diode phase modulator of
`lated.
`claim 1 wherein said plural channel reflecting means is
`8. The improved continuous diode phase modulator of
`a circulator.
`claim 7 further comprising parallel resistances connected
`5. The improved continuous diode phase modulator of
`across each said varactor diode thereby maintaining a
`claim 2 wherein the junction end of said varactor diode is
`constant insertion loss with variations in voltage.
`connected to said plural channel reflecting means.
`9. The improved continuous diode phase modulator of
`6. A continuous diode phase modulator utilizing a
`claim 7 wherein the end of each said varactor diode that
`minimum number of components and space and exhibiting
`is connected to said quarter wavelength transmission line
`a linear relationship between phase and voltage while
`is the junction end.
`maintaining constant insertion loss comprising:
`10. The improved continuous diode phase modulator of
`(a) a circulator,
`claim 7 wherein each said varactor diode has an admit
`(b) a varactor diode having an admittance character
`tance characteristic substantially conforming to a tan 0
`istic substantially conforming to a tan 0 curve,
`curve.
`(c) first transmission line means connecting the junction
`11. The improved continuous diode phase modulator of
`end of said varactor diode to a port on said circulator,
`claim 10 further comprising parallel resistances connected
`said transmission line means including a line section
`across each said varactor diode thereby maintaining a
`in parallel with said varactor diode having one end
`constant insertion loss with variations in voltage.
`connected to said transmission line and the other end
`12. The improved continuous diode phase modulator
`connected to a common point of potential,
`of claim 11 wherein the end of each said varactor diode
`(d) second transmission line means having one end con
`that is connected to said quarter wavelength transmission
`nected to the end of said varactor diode opposite said
`line is the junction end.
`junction end,
`25
`13. The improved continuous diode phase modulator
`(e) means for introducing a modulating voltage into
`of claim 12 wherein said transmission line connecting said
`the modulator, said last-named means being con
`plural channel reflecting device and said quarter wave
`nected to the other end of said second transmission
`length line is adjusted to have a characteristic impedance
`line means, and
`equal to one-half the characteristic impedance of the
`(f) a capacitor connected between said other end of
`remainder of the modulator circuit.
`said Second transmission line means and a common
`14. The method of obtaining 360 degree modulation
`point of potential, and
`using a single plural channel reflecting device and without
`(g) means for introducing a carrier voltage to be
`using two 180 degree modulators comprising the step of:
`modulated.
`connecting a pair of varactor diodes, one to each end
`7. An improved continuous diode phase modulator for
`of a quarter wavelength line, each of said varactor
`providing 360 degree modulation utilizing a minimum
`diodes having admittance characteristics substantially
`number of components and exhibiting a linear phase
`conforming to a tan 0 curve, so that the diode admit
`voltage relationship, comprising:
`tances add to conform to a tan 20 curve.
`(a) one plural channel reflecting means,
`(b) two varactor diodes,
`(c) a quarter wavelength transmission line connecting
`the varactor diodes, said transmission line including
`an inductive means adjacent each end whereby the
`cartridge capacitances of said varactor diodes are
`parallel resonated with said inductive means,
`(d) a transmission line means having one end con
`nected between said varactor diodes to said quarter
`wavelength transmission line adjacent to one end
`thereof and the other end to a port of said plural
`channel reflecting means, and
`(e) means for introducing a modulating voltage into the
`network connected to the other end of each said
`
`References Cited
`UNITED STATES PATENTS
`1/1969 La Rosa.
`3,422,378
`2/1958 Bargellini --------- --- 332-16
`2,822,523
`3,153,206 10/1964 Fisher ------------- 332- -30 X
`3,243,731
`3/1966 Erickson ----------- 332- -30 X
`3,304,518
`2/1967 Mackey ----------- 332-16 X
`3,373,381
`3/1968 Thomas ------------- 332-29
`ALFRED L. BRODY, Primary Examiner
`U.S. Cl. X.R.
`307-320; 328-16; 331-36; 332-16; 333-1.1
`
`30
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