United States Patent [191
`Wolfson et a1.
`
`[54] PHASE SHIFT DEVICE USING
`VOLTAGE-CONTROLLABLE DIELECI'RICS
`
`[75]
`
`[73] Assignee:
`
`Inventors: Ronald I. Wolfson, Los Angeles;
`Clifton Quan, Arcadia; Donald R.
`Rohweller, Torrance, all of Calif.
`Hughes Aircraft Company, Los
`Angeles, Calif.
`Appl. No.: 10,943
`Filed:
`Jan. 29, 1993
`
`[21]
`[22]
`[51]
`[52]
`
`[53]
`
`[56]
`
`............ .. H01P 1/18; 1101p 3/08
`1111. cm ....
`US. Cl. .................................... .. 333/161; 333/26;
`333/139
`Field of Search ............. .. 333/156, 140, 153, 151,
`333/33, 34, 116, 133
`References Cited
`U.S. PATENT DOCUMENTS
`3,448,410 6/1969
`4,375,054 2/1983
`5,032,805 7/ 1991
`..
`5,075,646 12/1991
`5,212,463 5/1993 Babbitt et al. ..................... .. 333/161
`
`OTHER PUBLICATIONS
`Cohn, “Shielded Coupled—Strip Transmission Line”,
`
`llllllllllllllllllllllll|||IllllllllllllllllllllllllIllllllllllllllllllllll
`5,355,104
`Oct. 11, 1994
`
`US005355104A
`Patent Number:
`Date of Patent:
`
`[11]
`[45]
`
`IEEE Trans. Microwave Theory Tech., MTT-3, pp.
`29-38, Oct. 1955.
`“A Broad-Band E-Plane 180° Millimeter-Wave Balun
`(Transition),” R. W. Alm et al., IEEE Microwave and
`Guide Wave Letters, vol. 2, No. 11, Nov. 1992, pp.
`425-427.
`Primary Examiner-Seungsook Ham
`Attorney, Agent, or Firm—L. A. Alkov; W. K.
`Denson-Low
`ABSTRACT
`[57]
`A length of strip transmission line uses two symmetri
`cally spaced center conductors between two ground
`planes. These conductive strips produce an even-mode
`electric ?eld between the two groundplanes when ex
`cited in-phase and an odd-mode electric ?eld when
`excited in anti-phase relationship. For the latter case,
`the phase velocity of the odd-mode is signi?cantly af
`fected by the electric ?eld in the gap region between the
`conducting strips. By varying the relative dielectric
`constant of a material located in the gap region, e.g?;by
`means of a voltage-controllable dielectric such as bari
`um-titanate compositions, the phase velocity and,
`hence, the phase shift of an RF signal propagating
`through the strip transmission medium can be con
`trolled.
`
`14 Claims, 5 Drawing Sheets
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`Page 1 of 11
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`Oct. 11, 1994
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`U.S. Patent
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`Page 6 of 11
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`
`PHASE SHIFI‘ DEVICE USING
`VOLTAGE-CONTROLLABLE DIELECTRICS
`
`5
`
`15
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`25
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`35
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`40
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`45
`
`BACKGROUND OF THE INVENTION
`The present invention relates to RF phase shift de
`vices, and more particularly to a device capable of pro
`ducing a continuous, reciprocal, differential RF phase
`shift with a single control voltage.
`Conventional phase shifters use either ferrites or PIN
`diodes to switch the phase characteristics of a transmis
`sion line. While recent developments in miniaturized,
`dual-toroid, ferrite phase shifters have allowed their
`integration into microstrip circuits to achieve reciprocal
`operation, PIN-diode phase shifters are still widely
`used. Depending on the particular application require
`ments, the digital phase bits are traditionally con?gured
`from one of the following circuit types: I) switched line;
`2) loaded line; 3) reflective (e. g., hybrid coupled); or 4)
`high-pass/low-pass ?lter.
`A number of these circuits are typically connected in
`series to form a device that provides 360 degrees of
`differential phase shift. Circuit losses, along with para
`sitic elements of the PIN diodes and the bias networks
`required, increase the RF insertion loss above that of an
`equivalent, straight through, transmission line. Phase
`setting accuracy is limited to one-half of the smallest
`phase bit increment and results in phase quantization
`sidelobes that may be objectionable. Average power
`handling capability is primarily limited by the maximum
`allowable temperature rise due to RF losses concen
`trated in the diode junction area. Cost, size, weight and
`reliability of the driver circuits and associated power
`supplies become important issues, as each phase bit
`requires a separate driver and control power for the
`PIN diodes can be substantial in a large array.
`It is therefore an object of the present invention to
`provide an RF phase shift device that produces a con
`tinuous, reciprocal, differential RF phase shift with a
`single control voltage.
`SUMMARY OF THE INVENTION
`In accordance with the invention, an RF phase shifter
`includes ?rst and second spaced groundplanes and ?rst
`and second spaced conductors disposed between the
`groundplanes. The conductors are separated by a gap in
`which a dielectric material is disposed. The dielectric
`material is characterized by a variable relative dielectric
`constant, which may be modulated by application of dc
`electric ?eld.
`The device includes means for applying a variable
`electric ?eld to the dielectric material to set the dielec
`tric constant at a desired value in order to provide a
`desired phase delay through the device. When the con
`ductors are excited in phase, the dielectric constant of
`55
`the dielectric has only negligible effect on the propaga
`tion velocity of the RF signal; however, when the con
`ductors are excited in anti-phase relationship, the effect
`is substantial.
`The means for applying an electric ?eld comprises
`?rst and second electrodes, the dielectric material being
`disposed between the electrodes, and the means for
`applying a variable electric ?eld across the dielectric
`material includes a means for applying a voltage across
`the electrodes. Preferably the electrodes are the ?rst
`and second conductors.
`In one preferred form, the groundplanes, the conduc
`tors and the dielectric material comprise a suspended
`
`65
`
`1
`
`5,355,104
`
`2
`stripline transmission line. The ?rst and second conduc
`tors can be arranged in either a coplanar, edge-coupled
`relationship or in a parallel, width-coupled relationship.
`In accordance with another aspect of the invention,
`the device can be con?gured in a true-time-delay device
`that provides large differential time delays, where the
`time delay is variable, in dependence on the magnitude
`of the electric ?eld across the dielectric material.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`These and other features and advantages of the pres
`ent invention will become more apparent from the fol
`lowing detailed description of an exemplary embodi
`ment thereof, as illustrated in the accompanying draw
`ings, in which:
`FIGS. 1 and 2 are cross-sectional illustrations of an
`RF phase shifter in accordance with this invention em
`ploying respectively width-coupled and edge-coupled
`lines constructed in air-dielectric suspended stripline.
`FIGS. 3 and 4 illustrate electric ?eld lines of the
`device of FIG. 2 when excited in phase and in anti
`phase relationship, respectively.
`FIG. 5 is a graph illustrating the relative dielectric
`constant of compositional mixtures of Ba1_xSrxTiO3 as
`a function of temperature.
`FIG. 6 is a graph showing that a calcium dopant
`reduces the dielectric constant peak that occurs at the
`Curie temperature and broadens the usable temperature
`range of BST.
`FIG. 7 is a graph illustrating that the variation of the
`relative dielectric constant of porous BST is a broad
`function of temperature without the sharp peaks that
`occur in the high-density BST compositions.
`FIGS. 8 and 9 are respective plan and cross-sectional
`views of an RF phase shifter embodying the present
`invention.
`FIG. 10 shows a true-time-delay device embodying
`the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`Overview of the Invention
`Voltage-controlled dielectrics offer an attractive al
`ternative to traditional solid-state and ferrite phase-shift
`devices for the design of electronically scanned array
`antennas. Either liquid crystals, or ferroelectric materi
`als which operate in either the ferroelectric or paraelec
`tric domain, can provide the desired change in dielec
`tric constant with an applied dc electric ?eld. A large
`class of such ferroelectric materials exists: BaSrTiOg
`(BST), MgCaTiO3(MCT), ZnSnTiO3(ZST) and BaOP
`bO-NdZO3-TiO3 (BPNT), to name just a few. Recently
`developed sol-gel processes make it feasible to engineer
`high-purity compositions with special microwave char
`acteristics. BST has received the most attention, with
`properties that include voltage-controlled dielectric
`constant tunable over a 2:1 ratio, relative dielectric
`constant ranging from about 20 to over 3,000 and mod
`erate microwave loss tangent from 0.001 to 0.050.
`FIGS. 1 and 2 illustrates two con?gurations for im
`plementing the invention in air-dielectric suspended
`stripline. Coupled conductive strips separated by a volt
`age-controllable dielectric are centered between
`groundplanes. FIG. 1 illustrates width-coupled lines.
`Conductive strips 22 and 24 of width w and thickness t
`are separated by a voltage-controllable dielectric 26 of
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`Page 7 of 11
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`20
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`25
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`5,355,104
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`width s. The dielectric constant e, of the dielectric 26
`exceeds 1.
`FIG. 2 illustrates edge-coupled lines. Conductive
`strips 22’ and 24’ of width w and thickness t are centered
`between the groundplanes 28’ and 30’, and are separated
`by a voltage-controllable dielectric 26' of width s.
`The coupled strips 22 and 24 of the width-coupled
`case, as well as the coupled strips 22’ and 24’ of the
`edge-coupled case, produce an even-mode electric ?eld
`when excited in phase (FIG. 3) and an odd-mode elec
`tric ?eld when excited in anti-phase relationship (FIG.
`4). The phase velocity of the even mode is essentially
`unaffected by the dielectric 26 or 26' because little or no
`electric ?eld exists in the gap between the conductive
`strips. The phase velocity of the odd mode, however, is
`signi?cantly affected by the large electric ?eld within
`the dielectric. Thus, by varying the relative dielectric
`constant in the gap region, phase velocity and hence
`phase shift of an RF signal propagating through the
`transmission medium can be modulated. The same basic
`principles can also be applied to solid-dielectric stripline
`or to microstrip transmission lines.
`Normally, both strip are fed in-phase as a conse
`quence of the symmetry of the microwave structure.
`The odd-mode, which is usually undesirable, can be
`introduced by some type of asymmetry, e. g., geometric,
`or an unbalance in amplitude or phase. Typically, both
`even and odd modes coexist in proportion to the degree
`of unbalance that exists. The invention operates most
`effectively when the odd mode predominates. A mi
`30
`crostrip-to-balanced-stripline transition is actually a
`balun that introduces a 180 degree phase shift between
`the width-coupled strips and forces the odd mode to
`propagate. A type of 180 degree balun for edge-coupled
`strips is described by R. W. Alm et al., “A Broad-Band
`E-Plane 180° Millimeter-Wave Balun (Transition), ”
`IEEE Microwave and Guide Wave Letters, Vol. 2, No.
`11, November 1992, pages 425-427. As those strips are
`fed from opposite walls of the input waveguide, a 180
`degree phase reversal occurs.
`It has been shown that those ferroelectric materials
`with the largest microwave electro-optic coefficients
`also have the largest dielectric constants, e.g.,
`Ba1_xSrxTiO3. The major challenge in developing
`these materials for microwave applications is reduction
`45
`of absorption losses, which have both intrinsic and ex
`trinsic contributions. The intrinsic contribution is due to
`lattice absorption, whereas the extrinsic contribution is
`due to anion impurities, cation impurities and domain
`wall motion. The solution-gelatin (sol-gel) process can
`produce materials with lower RF losses by reducing
`their orientational dependence through randomization.
`Furthermore, as the sol-gel process does not require the
`high-temperature processing normally associated with
`ceramics, contamination by impurities can be more
`55
`carefully controlled.
`The key electrical properties of dielectric materials
`for phase shifter applications are 6,, the relative dielec
`tric constant; A6,, the change in relative dielectric con
`stant that can be obtained with an applied electric ?eld;
`and tan 8, the microwave loss tangent.
`The range of relative dielectric constants selected for
`BST is well below the maximum speci?ed value of
`about 3,000. The rationale for using materials with
`lower relative dielectric constants is that the odd-mode
`65
`coupled stripline circuit described above performs well
`with values of dielectrics in this range; materials with
`lower 6, will have lower than 8; and it is easier to formu
`
`4
`late low-dieelectric-constant materials that are stable
`over a wide temperature.
`Ferroelectric materials are characterized by a sponta
`neous polarization that appears as the sample is cooled
`through a phase transition temperature known as the
`Curie temperature, TC. The relative dielectric constant
`of such a material exhibits a sharp maximum near
`T=Tc, caused in most materials by the condensation of
`a temperature-dependent or “soft” lattice vibration
`mode. As the sample temperature reaches Tc, the long
`and short-range forces acting on individual ions in the
`lattice become nearly balanced, resulting in large ampli
`tudes and diminished vibration frequency of the mode.
`In this temperature range, linear restoring forces on the
`ions in the lattice become very small and applied elec
`tric ?elds can induce signi?cant linear and non-linear
`electro-optic coef?cients at microwave frequencies.
`The major dif?culty in working with ferroelectric
`materials at or near the Curie temperature in order to
`achieve large changes in relative dielectric constant
`with applied voltage is that because of the sharp maxi
`mum, the material is extremely temperature sensitive.
`This is illustrated in FIG. 5 for compositional mixtures
`of Ba1_xSrxTiO3, where increasing proportion of
`SrTiO3 has been introduced to reduce the Curie temper
`ature below that of pure BaTiO3, about 120° C. Note
`that for the material compositions shown, the relative
`dielectric constant changes by about 2:1 over a tempera
`ture range of 20° C.
`The addition of certain dopants, e.g., calcium, broad
`ens the usable temperature range, as shown in FIG. 6.
`Further temperature stabilization of the BST is
`achieved when the dielectric constant is reduced, either
`by porosity or dilution in a low-loss dielectric polymer.
`FIG. 7 shows the variation in relative dielectric con
`stant for a sample of porous BST that was measured
`over the temperature range of —40° C. to + 100° C.
`Modeling of non-linear materials such as BST com
`positions becomes more dif?cult when porosity is in
`creased in order to reduce the relative dielectric con
`stant. Other factors that complicate the analysis are the
`change in dielectric constant with applied electric ?eld
`and effects due to the shift in Curie temperature. The
`sol-gel processing technique, however, can dramati
`cally improve the microstructure of the material with a
`consequent reduction in the microwave loss tangent.
`A ferroelectric phase shifter in accordance with this
`invention works on the principle that the relative di
`electric constant of a ferroelectric material is controlled
`by an externally applied dc electric ?eld, which in turn
`changes the propagation constant of a transmission line.
`The dc bias is applied by means of a pair of electrodes,
`generally parallel to one another, with the ferroelectric
`material in between. The bias electrodes can either be
`an integral part of the RF transmission circuit, or imple
`mented especially to provide the bias function. It is
`generally preferable to avoid separate electrodes, as
`they must be carefully arranged so as not to interfere
`with the RF ?elds; otherwise, interactions can produce
`large internal re?ections, moding or excessive insertion
`loss of the RF signal. Certain RF transmission struc
`tures, such as coaxial lines, parallel-plate waveguides
`and coupled-strip transmission lines have existing con
`ductors that can be used as bias electrodes.
`There are several other considerations when imple
`menting dc bias in the transmission structures. First, a
`dc block is required to prevent the dc bias voltage from
`shorting out or damaging sensitive electronic circuits,
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`5,355,104
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`5
`such as ampli?ers or diode detectors. The dc block can
`be a small gap in the transmission line or a high-pass
`?lter that couples through the RF but open-circuits the
`dc. Second, a bias port must be provided for introduc
`ing the dc bias without allowing RF leakage. This is
`generally accomplished by means of a high-impedance
`inductive line or a low-pass ?lter. The bias line should
`generally be located orthogonal to the RF electric ?eld
`in order to minimize coupling and prevent shorting out
`the latter.
`For experimental hardware, it is often convenient to
`use a commercially available monitor tee/dc block in
`order to eliminate the bias port design effort. Such com~
`ponents are readily available, e.g., from MA-COM
`/Omni-Spectra, as part numbers 2047-6010 through
`2047-6022. For production hardware, an integral bias
`port design is preferred to reduce size, weight, insertion
`loss and cost.
`
`10
`
`6
`and 62, thereby providing a means to apply a dc electric
`?eld across the dielectric 73B.
`The length of the phase shift region 72 is selected 30
`with the voltage range supplied by the source 82, to
`provide at least 360 degrees of phase shift at the lower
`frequency edge of the frequency band of interest; at
`higher frequencies the device will provide more than
`360 degrees phase shift.
`The microstn'p-to-balanced-stripline transition serves
`as a balun that can be designed to produce an anti-phase
`condition between the two conductive strips over an
`operating band of an octave or more. The balun pro
`duces the anti-phase condition in the following manner.
`When an RF signal is applied to either coaxial connec
`tor 52 or 54, a current is caused to flow in the center
`conductor and attached microstrip line that lies above
`the suspended groundplane. This current produces an
`image current sheet that ?ows in the opposite direction,
`but which is spread across the width of the suspended
`groundplane. As the latter tapers down to match the
`width of the microstrip line above, the image current
`density increases until both currents are equal in magni
`tude and in anti-phase relationship. The even-mode and
`odd-mode impedances of the coupled lines can be deter
`mined from the physical parameters “b,” “w,” “s” and
`“e,” using well-known relationships given in the paper
`by S. B. Cohn, “Shielded Coupled-Strip Transmission
`Line,” IEEE Trans Microwave Theory Tech , MTT-3,
`pp. 29-38, Oct. 1955. The even-mode phase velocity in
`the phase shift region 72 will usually be on the order of
`only one percent less than the velocity in free space.
`The phase velocity of the odd mode, on the other hand,
`is much more noticeably affected by the dielectric 73B
`in the phase shift region 72. The ratio of phase velocities
`for the two modes is given by:
`
`rzmzo/cmzn?
`
`(1)
`
`where V00 is the odd-mode velocity, Voe is the even
`mode velocity, 6, is the relative dielectric constant of
`the material in the gap region, and the relative dielectric
`constant of the air-stripline structure is taken equal to
`one.
`The groundplanes 56 and 58 serve as a rigid housing
`both to enclose the dielectric-?lled strip transmission
`lines and to support the RF input and output connec
`tors. The two outer dielectric layers 73A and 73C are
`each made from high-purity alumina sheets metallized
`on both surfaces. The suspended microstrip ground
`plane 60 that tapers down to form the lower coupled
`strip transmission line 64 is etched on the metallized
`topside of the bottom layer 73C using conventional
`photolithographic techniques. The 50-ohm microstrip
`and upper coupled-strip transmission line 62 is similarly
`etched on the bottom side of the top layer 73A. The
`middle layer 73B is an unmetallized ferroelectric dielec
`tric sheet. When the three dielectric layers 73A, 73B
`and 73C are stacked between the metal groundplanes 56
`and 58, the voltage-controllable dielectric 73B lies be
`tween the conducting strips 62 and 64 that form the
`microstrip and coupled-strip transmission lines. As
`these metallized conductors are not directly connected
`to one another, they are used as electrodes for introduc
`ing the control voltage across the variable dielectric
`sample.
`The device 50 can be compensated for input- and
`output-port mismatch caused by changes in relative
`
`20
`
`25
`
`DESCRIPTION OF PREFERRED
`EMBODIMENTS
`FIGS. 8 and 9 show an analog phase shifter 50 based
`on the even-mode/odd-mode principle described
`above. The coaxial input and output connectors 52 and
`54 at either end of the unit 50 transition into a conven
`tional, unbalanced, microstrip transmission line that is
`suspended between two groundplanes 56 and 58. The
`metallization that forms the suspended microstrip
`groundplane at either connector tapers down in width
`to form a balanced, two-conductor stripline transmis
`sion line at the center of the device. The lower conduc
`tor 60 nominally forms the microstrip groundplane
`adjacent to the connectors 52 and 54, but as shown,
`tapers down in width to form, with the upper conductor
`62, microstrip-to-balanced-stripline transitions 68 and
`70. In general, the linewidths of the coaxial connector
`center conductor and the microstrip line will be differ
`ent, requiring a transition, e.g., a taper or step~trans
`former for matching impedances. The lower conductor
`60, and if necessary the upper conductor 62, transition
`to width w to provide the balanced stripline in the phase
`shift region 72.
`Gaps 64 and 66 are formed in the upper conductor 62
`as do blocks in the RF line.
`A voltage controllable dielectric 73B is disposed
`between the conductors 60 and 62 in the region 72.
`Preferably, the voltage controllable dielectric not only
`extends into the transitions from connector to connec
`tor, but also extends sideways beyond the upper and
`lower conductors 60 and 62. This con?guration is pre
`ferred because: 1) the hardware will be easier to fabri
`cate and assemble; 2) if the dielectric does not extend
`into the transition region, a hugh discontinuity is cre
`ated that will require special matching; and 3) negligible
`RF ?elds exist in the high dielectric material except for
`the region that lies between the coupled lines. Extend
`ing the voltage controllable dielectric into the transition
`regions will contribute to the overall differential phase
`shift; however, most of the phase shift still occurs
`within the “phase shift region” because of the favorable
`anti-phase relationship there.
`A bias port 74 is formed in sidewall 76 of device 50.
`A thin bias lead 80 runs through the bias port 74 and
`low-pass ?lter 75 to upper conductor 62, and connects
`to a dc bias source 82. The lower conductor 60 is do
`grounded at the connectors 52 and 54. The source 82
`provides a selectable dc bias between the conductors 60
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`5,355,104
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`8
`3. Precise phase-setting accuracy (provides analog
`dielectric constant of the dielectric insert material 73B.
`This matching can be accomplished by several means.
`control):
`4. True time delay (no beam squint with frequency
`The traditional approach is to use either tapers or step
`changes);
`transformers to effect an average match between the
`5. Moderate power-handling capability (power dis
`impedance extremes that are encountered with changes
`tributed over large area);
`in the dielectric constant of the ferroelectric material
`73B. The voltage-controllable material 73B could also
`6. Low control power (high electric ?eld with low
`leakage current);
`be used to improve matching by varying the dielectric
`7. High reliability (single, simple driver; bulk material
`constant along the length of the matching sections.
`device); and
`Variation of dielectric constant with position could be
`8. Low cost (single, simple driver; few discrete com
`achieved in many ways: for example, the use of material
`ponents).
`with a graded dielectric constant or segments of mate
`It is understood that the above-described embodi
`rial with different dielectric constant or control-voltage
`ments are merely illustrative of the possible speci?c
`characteristics; tapering the transmission-line width or
`embodiments which may represent principles of the
`gap distance between conducting strips; or providing
`present invention. Other arrangements may readily be
`separate electrodes with individual bias-level control at
`devised in accordance with these principles by those
`different locations along the matching sections.
`skilled in the art without departing from the scope and
`FIG. 10 shows a true-time-delay (TT D) device, simi
`spirit of the invention.
`lar in concept to the phase shifter described above,
`What is claimed is:
`except that the balanced, two-conductor transmission
`1. An RF phase shift device, comprising:
`line 118 in the time delay region 114 is made very long
`?rst and second spaced groundplanes;
`by folding it in the fashion of a meanderline. Thus, the
`a conductive housing, said housing comprising said
`device 100 includes a lower metallization layer 106 and
`?rst and second groundplanes and ?rst and second
`an upper conductor 108. The layer 106 tapers down in
`sidewalls extending generally perpendicularly to
`width adjacent each coaxial connector 102 and 104 to
`said groundplanes;
`form microstrip-to-balanced-stripline transitions 110
`?rst and second spaced conductors disposed between
`and 112. The top and bottom conductors 108 and 106
`said groundplanes, said conductors being separated
`are of equal width in the time delay region. A dc bias
`by a gap;
`circuit of similar construction to that employed for
`a dielectric material disposed in said gap, said mate
`device 50 (FIGS. 8 and 9) may be also employed with
`rial characterized by a dielectric constant which
`the device 100 to set up a dc electric ?eld of variable
`varies in value when a voltage is applied to said
`magnitude between the two conductors 106 and 108 and
`dielectric material;
`across the dielectric 116. By adjusting the magnitude of
`means for applying a control signal to said dielectric
`the electric ?eld, the relative dielectric constant of the
`35
`material to set the value of the dielectric constant at
`material 116 is also adjusted, thereby providing the
`a predetermined value in order to provide a desired
`capability of adjusting the time delay of RF signals
`phase delay region through said device;
`traversing the region 114. The amount of time delay
`means for exciting said ?rst and second conductors
`that can be achieved is limited only by the insertion loss
`by an RF signal to provide an anti-phase signal in
`that can be tolerated and the VSWR due to the multi
`said phase delay region; and
`tude of sharp bends. The VSWR of very long delay
`wherein said groundplanes, said conductors and said
`lines can be improved either by the use of sinuous lines
`dielectric material comprise a suspended stripline
`or by making the bends random instead of periodic.
`transmission line in said region, and wherein said
`Table I shows measured data taken at 1.0 GHz on a
`second conductor tapers to a greater width on each
`45
`porous barium-strontium-titanate sample.
`side of said region to form a microstrip ground
`TABLE I
`plane of a microstrip-to-balancedstripline transi
`tion.
`Applied voltage (kV/cm)
`2. The device of claim 1 wherein said means for ap
`0
`plying a control signal comprises means for applying a
`1
`variable electric ?eld across said ?rst and second con
`2
`ductors, said dielectric material having the property
`3
`4
`that its dielectric constant is dependent upon the magni
`5
`tude of said electric ?eld.
`6
`3. The device of claim 1, wherein said ?rst and sec
`7
`ond conductors are arranged in a parallel, width-cou
`8
`pled relationship.
`9
`10
`4. The device of claim 1 wherein said device provides
`a 360 phase shift range.
`5. The device of claim 1 wherein said dielectric mate
`rial comprises a composition of BaSrTiO3.
`6. The device of claim 1 wherein said means for ap
`plying a control signal comprises means for applying a
`bias dc electric ?eld across said dielectric material.
`7. The device of claim 6 wherein said means for ap
`plying a bias dc electric ?eld comprises means for ap
`plying a voltage between said ?rst and second conduc
`tors.
`
`The invention provides a means for producing a con
`tinuous, reciprocal, differential RF phase shift by vary
`ing the dielectric properties of a material with a single
`control voltage. Key advantages of the invention in
`clude the following:
`1. Reciprocal operation (no reset required between
`65
`transmit and receive);
`2. Wideband operation (contains no resonant cir
`cuits);
`
`e,
`150
`145
`139
`132
`124
`115
`110
`106
`103
`100
`98
`
`TANS
`0.010
`0.010
`0.009
`0.009
`0.008
`0.008
`0.008
`0.007
`0.007
`0.007
`0.007
`
`5
`
`15
`
`20
`
`50
`
`55
`
`60
`
`Page 10 of 11
`
`

`
`5,355,104
`
`10
`means for applying a control signal to said dielectric
`material to set said dielectric constant at a desired
`value in order to provide a desired time delay to
`RF signals propagating along a transmission line
`de?ned by said conductors in said time delay re
`gion;
`means for exciting said ?rst and second conductors
`by said RF signals to provide an anti~phase signal i
`said time delay region;
`-
`wherein said groundplanes, said conductors and said
`dielectric material comprise a suspended stripline
`transmission line in said region, and wherein said
`second conductor tapers to a greater width on each
`side of said region to form a microstrip ground
`plane of a microstrip-to-balanced stripline transi
`tion.
`12. The device of claim 11 wherein said ?rst and
`second conductors are arranged in a parallel, width
`coupled relationship.
`13. The device of claim 11 wherein said dielectric
`material comprises a composition of BaSrTiO3.
`14. The device of claim 11 wherein said means for
`applying a control signal comprises means for applying
`a variable electric ?eld across said ?rst and second
`conductors, said dielectric material having the property
`that its dielectric constant is dependent upon the magni
`tude of said electric ?eld.
`* * * * *
`
`5
`
`8. The device of claim 7 wherein said dielectric mate
`rial is disposed in said gap within a phase shifting region
`de?ned along a section of said ?rst and second conduc
`tors, and said means for applying a voltage comprises a
`dc blocking gap de?ned in said ?rst conductor on either
`side of said region, a variable voltage source, and means
`for electrically connecting said ?rst and second conduc
`tors in said region to said voltage source.
`9. The device of claim 8 wherein said electrically
`connecting means comprises a low pass ?lter means.
`10. The device of claim 1 further comprising ?rst and
`second coaxial connectors connected to said respective
`transitions.
`11. A true-time-delay device for RF signals, compris
`mg:
`?rst and second spaced groundplanes;
`a conductive housing, said housing comprising said
`?rst and second groundplanes and ?rst and second
`sidewalls extending generally perpendicularly to
`said groundplanes;
`?rst and second spaced conductors disposed between
`said groundplanes, said conductors separated by a
`gal);
`dielectric material disposed in said gap along a time
`delay region extending along a section of said con
`ductors, said material characterized by a variable
`relative dielectric constant;
`
`20
`
`25
`
`30
`
`35
`
`45
`
`55
`
`65
`
`Page 11 of 11