Article comprising a phase shifter having a movable dielectric element

A phase shifter including a phase-shifting slab having a phase-shifting member is used in conjunction with a quasi-TEM transmission line having at least one active line and one ground. In some embodiments, the phase-shifting slab is inserted between the active line and the ground. The phase-shifting member is advantageously configured so that as it is advanced between the active line and the ground plane, a varying amount of dielectric material passes therebetween. Varying the amount of dielectric material between the active line and the ground changes the effective dielectric constant of the transmission line. Such a change in the effective dielectric constant causes a change in the propagation velocity of a signal traveling through the transmission line. In that manner, a phase shift is introduced in the signal relative to other signals. The phase-shifting slab advantageously comprises at least one impedance-matching member that decreases or eliminates an impedance mismatch that occurs between air-suspended and dielectrically-loaded regions of the transmission line. In some embodiments, the impedance mismatch is decreased or eliminated over the entire phase-shifting range. Decreasing the impedance mismatch may advantageously reduce the incidence and severity of signal reflections.

FIELD OF THE INVENTION 
The present invention relates to telecommunications. More particularly, the 
present invention relates to a phase shifter for use in conjunction with a 
phased-array antenna for the purpose of beam steering/tilting. 
BACKGROUND OF THE INVENTION 
A phased-array antenna is a directive antenna having several individual, 
suitably-spaced radiating antennas, or elements. The phased array 
generates a radiation pattern ("beam") having a main lobe and side lobes 
that is determined by the collective action of all the radiating elements 
in the array. The response of each radiating element is a function of the 
specific phase and amplitude of a signal applied to the element. By 
varying the relative phases of the signals applied to the individual 
radiating elements, the beam can be advantageously changed in azimuth 
("beam steering"), elevation ("beam tilting") or both. 
Beam steering/tilting has a number of applications. Of major significance 
is its application to the field of wireless telecommunications. The 
geographic area serviced by a wireless telecommunications system is 
partitioned into a number of spatially-distinct areas called "cells." Each 
cell usually has an irregular shape (though idealized as a hexagon) that 
depends on terrain topography. Typically, each cell contains a base 
station, which includes, among other equipment, radios and antennas that 
the base station uses to communicate with the wireless terminals in that 
cell. Due to instantaneous geographic variations in communications 
traffic, it may be desirable, at times, to adjust the geographic coverage 
of a particular base station. This can be accomplished by beam 
steering/tilting. 
There are a variety of different ways to obtain a relative phase change 
between the signals applied to the various antenna elements for beam 
steering/tilting. The change in phase .phi. experienced by an 
electromagnetic wave of frequency f propagating with a velocity v through 
a transmission line of length l is given by the expression: 
.phi.=2.pi.fl/v. As is well known to those skilled in the art, the 
velocity v of an electromagnetic wave is a function of the permeability 
.mu. and the dielectric constant .epsilon. of the medium in which the wave 
propagates. Thus, phase can be changed by altering frequency, line length, 
propagation velocity, permeability or dielectric constant. 
Devices for causing a differential phase change ("phase shifters") 
utilizing the aforementioned phase-shifting techniques are known. One type 
of phase shifter utilizes switchable delay lines having different lengths. 
Such a phase shifter is usually big and expensive. Moreover, due to the 
discrete nature of such a device, an error in desired phase will typically 
be present. A second type of device is a solid-state hybrid-coupled-diode 
phase shifter. Such devices suffer from high insertion loss and 
nonlinearity. As a result of such high insertion loss, amplifiers are 
required at the top of a base station tower to increase signal levels. At 
the high power levels required for transmission, such amplifiers are 
heavy, big and expensive. Such amplifiers are considerably smaller and 
less expensive at "receive" power levels, although it is still generally 
undesirable to have such active RF electronics at the top of a tower. 
A third type of phase shifter uses a ferrimagnetic material (a ferrite). It 
is known that the permeability of a ferrite can be changed by varying an 
applied D.C. magnetic field. Such a permeability change results in a 
change in the propagation speed of an electromagnetic wave traveling 
through the ferrite, resulting in phase shift. Traditionally, ferrite 
phase shifters have been quite large, heavy and expensive. More recently, 
thin-film ferrites has been utilized for such shifters, which reduces 
their size and weight. Such thin-film-based ferrite phase shifters 
disadvantageously become nonlinear, however, at high power levels. A 
fourth type of phase shifter utilizes a "sliding contact" technique. In 
one implementation of a sliding-contact phase shifter, coaxial lines 
"telescope" into or out of one another such that the line length of the 
phase shifter, and hence the phase imparted thereby, is changed. Such 
phase shifters, commonly referred to as "line-stretcher" phase shifters, 
suffer from corrosion and electrical contact problems over time. 
Due to the explosive growth of wireless communications, there is a growing 
need for steerable/tiltable linear phased-array antennas. To meet that 
need, it would be desirable to have a phase shifter that avoids the 
drawbacks of the prior art. 
SUMMARY OF THE INVENTION 
A phase-shifter in accordance with an illustrative embodiment of the 
present invention comprises a phase-shifting slab having a phase-shifting 
member, advantageously comprised of a dielectric material. The present 
phase-shifter is used in conjunction with a quasi-transverse 
electromagnetic (TEM) transmission line that comprises a signal-carrying 
("active") line and a ground plane spaced therefrom. In use, the 
phase-shifting slab is inserted between the active line and the ground 
plane. The presence of the phase-shifting member between the active and 
ground plane provides a "dielectric loading" to the transmission line. The 
phase-shifting member is advantageously configured so that as it is 
advanced between the active line and the ground plane, a varying amount of 
dielectric material passes therebetween. Varying the amount of dielectric 
material between the active line and the ground plane changes the 
effective dielectric constant of the transmission line. A change in the 
effective dielectric constant causes a change in propagation velocity of a 
signal traveling along the line. In that manner, a signal may be phase 
shifted relative to another signal in another line. 
As used herein, the phrase "phase-shifting range" refers to a range of 
relative phase-shift that can be imparted by a phase shifter (e.g., 0 to 
2.phi., -1.phi. to 2.phi., etc.). The range is defined by the relative 
phase shift imparted by the phase-shifting member at a first and a second 
position. In the first position, the phase-shifting member is not present 
between the active line and the ground plane (or, more properly, the 
phase-shifting member does not interact with an electromagnetic field 
generated between the active line and the ground plane due the presence, 
in the active line, of a signal). In the second position, the 
phase-shifting member is positioned between the active line and the ground 
such that it provides the maximum dielectric loading that it is capable of 
providing to the transmission line. 
The phase-shifting slab advantageously comprises at least one 
impedance-matching member that decreases a change in impedance ("impedance 
mismatch") occurring between air-suspended (i.e., no phase-shifting slab 
between active line and ground) and dielectrically-loaded regions of the 
transmission line. 
As is known in the art, impedance refers, in the present context, to the 
ratio of the time-averaged value of voltage and current in a given section 
of the transmission line. This ratio, and thus the impedance of each line 
section, depends on the geometrical properties of the transmission line, 
such as, for example, active line width, the spacing between the active 
line and the ground, and the dielectric properties of the materials 
employed. If two lines section having different impedance are 
interconnected, the difference in impedances ("impedance step" or 
"impedance mismatch") causes a partial reflection of a signal traveling 
through such line sections. "Impedance matching" is a process for reducing 
or eliminating such partial signal reflections by disposing a "matching 
circuit" between the interconnected line segments. As such, impedance 
matching establishes a condition for maximum power transfer at such 
junctions. 
The impedance-matching member can be designed to eliminate impedance 
mismatch, but only at one specific frequency. As signal frequency deviates 
from the one frequency, the impedance mismatch between the 
dielectrically-loaded and air-suspended regions begins to increase. Even 
in such cases, as long as the impedance-matching member's design bandwidth 
is not exceeded, the incidence and severity of signal reflections that 
occur due to the increasing impedance mismatch are reduced relative to 
those experienced with conventional phase shifters not possessing an 
impedance-matching member. 
To the extent that conventional phase shifters use impedance-matching 
"circuits," such circuits are usually incorporated in the active line. 
Moreover, such circuits are typically useful over a relatively small 
portion of the phase shifter's useful range of phase shift. To avoid 
significant impedance mismatch when conventional phase shifters are 
operated in regions in which the impedance-matching circuit is of marginal 
effectiveness, such conventional phase shifters are usually comprised of 
low dielectric constant materials. Such phase shifters need to be 
relatively large to cause a desirably-wide range of phase shift. 
In some embodiments of phase shifters in accordance with the present 
invention, the impedance-matching member is advantageously configured such 
that the impedance mismatch is eliminated, or, depending upon signal 
frequency, substantially reduced, over the full phase-shifting range. Such 
full-range impedance matching allows the present phase shifters to be 
comprised of high dielectric constant materials, and therefore smaller 
than most conventional phase shifters. Alternatively, for a given size, 
the present phase shifters provide a greater range of phase shift. 
In some illustrative embodiments, the phase-shifting member is configured 
to have a continuous, regular change in width, while maintaining a uniform 
dielectric constant and thickness throughout. In some such embodiments, a 
phase-shifting slab is formed from a single piece of dielectric material, 
wherein the phase-shifting member has the same thickness as the slab, 
which thickness is typically reduced, as appropriate, to create one or 
more impedance-matching members. Such monolithic impedance-matched 
phase-shifting slabs are simple and inexpensive to manufacture. Moreover, 
due to the continuous, advantageously linear change in the width of the 
phase-shifting member, there is a linear change in the amount of 
dielectric material positioned between the active line and the ground as 
the slab is advanced therebetween. That regular change results in a linear 
change in phase shift with appropriately- directed slab movement.

DETAILED DESCRIPTION OF THE INVENTION 
Phase shifters described in this specification are used in conjunction with 
a transmission line that includes at least one signal-carrying ("active") 
line and at least one ground plane. As used herein, the term "transmission 
line" refers to quasi-transverse electromagnetic (TEM) transmission lines. 
For wireless telecommunications applications, typically in the range of 
about 0.5 to 5 gigahertz (GHz), quasi-TEM transmission lines, such as 
microstrip (one ground) or strip lines (two grounds) are usually employed. 
For the sake of brevity, most illustrative embodiments of the present 
description show a phase shifter used in conjunction with a microstrip 
line. It should be understood, however, that in some embodiments, phase 
shifters in accordance with the present invention are used in conjunction 
with strip lines. Regardless of transmission-line configuration, in some 
embodiments, the active line is advantageously air-suspended (i.e., no 
dielectric material disposed between the active line and ground). Among 
any other benefits, such air-suspension reduces signal loss and allows for 
effective interaction between the phase-shifting member and an 
electromagnetic field generated by a signal propagating through the active 
line. 
FIGS. 1A & 1B, 1C & 1D, and 1E& 1F depict respective top and 
cross-sectional views for each of three illustrative configurations of a 
phase-shifting slab having a phase-shifting member comprised of a material 
having a suitable dielectric constant for use in a phase shifter. 
Phase-shifting members for use in conjunction with the present invention 
are advantageously physically adapted to provide a continuous, 
regularly-varying phase shift when moved between an active line and a 
ground plane. More particularly, the various configurations of 
illustrative phase-shifting members provide a continuous, 
regularly-varying change in effective dielectric constant of a 
transmission line. In some embodiments, the regular variation is 
advantageously linear. 
In the present context, the effective dielectric constant .epsilon..sub.eff 
is given by: 
EQU .epsilon..sub.eff =(c.sub.o /c.sub.e).sup.2 [ 1] 
where: c.sub.o is the phase velocity in the air-suspended line 
(phase-shifting member is not present between the active line and the 
ground); and 
c.sub.e is the phase velocity in the dielectrically-loaded line 
(phase-shifting member is disposed between the active line and the 
ground). 
As noted in the Background section of this Specification, changing the 
effective dielectric constant of a medium through which an electromagnetic 
wave travels changes the speed of propagation of that wave. A phase shift 
therefore results. 
In one embodiment, a continuous, advantageously linearly-varying phase 
shift is obtained using phase-shifting member 4a, shown in FIGS. 1A & 1B. 
Phase-shifting member 4a is configured as a trapezoid (quadrilateral with 
one set of parallel sides). Phase-shifting member 4a advantageously varies 
linearly in width w between first end 8a and second end 10a, as depicted 
in FIG. 1 and has a constant thickness t.sub.a (see FIG. 1B). As 
phase-shifting member 4a is moved in a direction indicated by direction 
vector 12, the amount of dielectric material between microstrip line 2 and 
ground plane 6 changes since width w varies (see FIG. 1A). As such, 
effective dielectric constant .epsilon..sub.eff changes and a phase shift 
is obtained. 
In other embodiments, phase-shifting members having other shapes varying in 
width and suitable for providing a regularly-varying phase response are 
suitably used. For example, the phase-shifting member can have a 
triangular configuration, as in many of the illustrative embodiments 
described later in this specification. 
In a second embodiment, a continuous, advantageously linearly-varying phase 
shift is obtained using phase-shifting member 4b, shown in FIGS. 1C & 1D. 
Rather than changing the width of phase-shifting member 4b, its thickness 
t.sub.b is varied between first end 8b and second end 10b as depicted in 
FIG. 1D. As phase-shifting member 4b is moved in a direction indicated by 
direction vector 12 between active line 2 and ground plane 6, the amount 
of dielectric material passing therebetween changes since thickness 
t.sub.b varies. As a result, effective dielectric constant 
.epsilon..sub.eff changes and a phase shift is again obtained. 
In a third embodiment, a continuous, regularly-varying phase shift is 
obtained using phase-changing member 4c, shown in FIGS. 1E & 1F. 
Phase-shifting member 4c is uniformly shaped, with no changes in width or 
thickness. To obtain a change in effective dielectric constant, the 
dielectric constant .epsilon. of slab 4c itself varies regularly between 
end 8c and end 10c. Thus, when slab 4c is moved between active line 2 and 
ground plane 6 along a direction indicated by direction vector 12, 
effective dielectric constant .epsilon..sub.eff changes and a phase shift 
is once more obtained. 
Those skilled in the art will recognize that in the illustrative phase 
shifters shown in FIGS 1A-1F, there is an impedance mismatch as a signal 
travels along active line 2 from an air-suspended region (i.e., 
phase-shifting member absent) to a dielectric-loaded region (i.e., 
phase-shifting member present). Such impedance mismatch in active line 2 
may undesirably result in partial reflections of a signal traveling 
therethrough. The effective dielectric constant of the transmission line 
is a function of the dielectric constant of the material, and the amount 
of such material, disposed between the active line and the ground plane. 
In accordance with the present invention, the line impedance is changed, 
and impedance mismatch is reduced or avoided, by providing at least one 
impedance-matching member that is insertable between the active line and 
the ground plane. When so inserted, the impedance-matching member provides 
a dielectric loading suitable for reducing or eliminating potential 
impedance mismatch, such as between air-suspended and dielectric-loaded 
regions of the transmission line. The impedance-matching member is 
advantageously incorporated into a phase-shifting slab of the present 
phase shifters. 
The dielectric constant of the phase-shifting members and 
impedance-matching members for use in the present phase shifters will 
suitably be in a range of about 2 to 15. While materials with a lower or 
higher dielectric constant can be used, an increase in size of the 
phase-shifting members (with decreasing dielectric constant), and an 
increase in sensitivity to mechanical tolerances and slab positioning 
(with increasing dielectric constant), generally makes the use of such 
materials less desirable. Materials suitable for use as the phase-shifting 
and impedance-matching members are well known to those skilled in the art. 
FIGS. 2A & 2B depict respective top and cross-sectional views of phase 
shifter 100a in accordance with a first illustrative embodiment of the 
present invention. Phase shifter 100a comprises phase-shifting slab 40a 
(hereinafter "slab"), comprising phase-shifting member 42a advantageously 
having a triangular shape. As slab 40 is moved in a direction between 
active line 2 and ground 6 in the direction indicated by direction vector 
120 (see FIG. 2A), a continuous phase shift results in a signal 
propagating within active line 2 relative to another signal traveling in 
another active line (not shown). 
Slab 40a further comprises two impedance-matching members 50a.sub.1, 
50a.sub.2 suitable for reducing or eliminating impedance mismatch. In the 
illustrative embodiment shown in FIGS. 2A & 2B, the phase-shifting member 
42a and the impedance-matching members 50a.sub.1, 50a.sub.2 are 
advantageously formed from a single dielectric slab having a first 
thickness. The thickness of phase-shifting member 42a is equal to the 
first thickness. Slab thickness is simply stepped (i.e., reduced) as 
appropriate, on both sides of phase-shifting member, to create two 
impedance-matching members 50a.sub.1, 50a.sub.2 having thickness tt.sub.a 
(see FIG. 2B) that provide a dielectric loading suitable for reducing or 
avoiding impedance mismatch. The width of each impedance-matching member 
advantageously provides 90 degrees of phase. 
As is known to those skilled in the art, no simple expression describes the 
relation between the thickness and width of a layer of dielectric material 
and that layer's effect on line impedance. The required calculations can 
be performed using a "method-of-moment" calculation known to those skilled 
in the art. Such calculations are rather tedious and are usually performed 
with the aid of a software "tool." In particular, an electromagnetic (EM) 
simulator, such as Momentum.TM., available from Hewlett-Packard Company of 
Palo Alto, Calif.; IE3D.TM., available from Zeland Software of Frement, 
Calif.; and Sonnet.TM., available from Sonnet Software of Liverpool, N.Y., 
may be used for this purpose. 
Line impedance Z.sub.t of each impedance-matching member is given by the 
expression: 
EQU Z.sub.t =(Z.sub.a Z.sub.d).sup.1/2 [2] 
where: Z.sub.a is the line impedance of the air-suspended portion of the 
active line; and 
Z.sub.d is the line impedance of the dielectrically-loaded of the active 
line. 
Referring to FIG. 2B, Z.sub.d is the line impedance for region 20 of active 
line 2 and Z.sub.a is the line impedance for region 24 of active line 2. 
In the illustrative embodiment shown in FIGS. 2A & 2B, only one 
impedance-matching member is disposed one each side of phase-shifting 
member 42a of slab 40a. In other embodiments (not shown), multiple 
impedance-matching members having a reduced width relative to the 
impedance-matching members 50a.sub.1, 50a.sub.2 are located in the same 
regions. In those other embodiments, each successive impedance-matching 
member is thicker than the previous one. The use of such multiple 
impedance-matching members advantageously provides a more gradual 
impedance transition for broadband applications when signal frequency 
deviates from the impedance-matching design center frequency. The 
impedance of the impedance-matching member "k" is given by: 
EQU Z.sub.k =(Z.sub.k+1 Z.sub.k-1).sup.1/2 [ 3] 
FIGS. 2C & 2D depict respective top and cross-sectional views of phase 
shifter 100b in accordance with a second illustrative embodiment of the 
present invention. Phase shifter 100b includes slab 40b. Slab 40b is moved 
between active line 2 and group plane 6 in a direction indicated by 
direction vector 120 (see FIG. 2C) between active line 2 and ground 6 to 
cause a continuous phase shift in a signal propagating within active line 
2 relative to another signal traveling in another active line. 
Slab 40b includes two impedance-matching members 50b.sub.1, 50b.sub.2 
having a thickness that advantageously varies regularly between first edge 
52 and second edge 54. Line impedance (in the transitional region) is thus 
a function of the relative position between first edge 52 and second edge 
54 of the impedance-matching member and independent of the width of 
phase-shifting member 42b (see FIG. 2C). Tapered impedance-matching 
members 50b.sub.1, 50b.sub.2 represent a logical conclusion of the use of 
an increasing number of discrete impedance-matching members. 
Referring to FIGS. 2A, 2B, 2C & 2D, phase shifters 100a and 100b having two 
identical impedance-matching members, one disposed on each side of 
respective phase-shifting members 42a and 42b, are particularly well 
suited to applications in which input impedance is substantially the same 
as the output impedance. The term "input impedance" refers to the 
impedance of the active line 2 at the leading edge of the phase-shifting 
member (e.g., loading edge 46a in FIG. 2A) and the term "output impedance" 
refers to the impedance of the active line 2 at the trailing edge of the 
phase-shifting member (e.g., trailing edge 48a in FIG.2A). In other 
applications, however, input impedance is different from output impedance. 
As such, the two impedance-matching members may require different physical 
configurations. In such applications, one of the impedance-matching 
members is advantageously implemented in active line 2 rather than in the 
slab, as is illustrated in FIGS. 2E-2H. 
FIGS. 2E & 2F depict respective top and cross-sectional views of phase 
shifter 100c in accordance with a third illustrative embodiment of the 
present invention. Phase shifter 100c includes slab 40c. Slab 40c is moved 
in a direction indicated by direction vector 120 (see FIG. 2E) between 
active line 2 and ground 6 to cause a continuous phase shift in a signal 
propagating within active line 2 relative to another signal traveling in 
another active line (not shown). 
Slab 40c has one impedance-matching member 50c, similar to 
impedance-matching member 50a previously described. An impedance "circuit" 
60c is located in active line 2 as depicted in FIG. 2E. Leading edge 46c 
of phase-shifting member 42c of slab 40c is advantageously orthogonal to 
active line 2 to facilitate impedance matching via circuit 60c. 
Line-integrated impedance circuits, such as the circuit 60c, are 
implemented in a known fashion, such as, for example, by changing active 
line width, thickness, or by changing the gap between the active line and 
the ground plane. 
It will be appreciated that in other embodiments (not depicted), the 
configuration of phase shifter 100c (FIG. 2E) can be changed wherein the 
relative positions of the impedance circuit 60c and the impedance-matching 
member 50c are reversed (i.e., the slab-integrated member 50c is located 
at leading edge 46c of the main portion 42c, and line-integrated circuit 
60c is located at trailing edge 48c). In such other embodiments, leading 
edge 46c is tapered and trailing edge 46c is orthogonal to active line 2 
(to facilitate impedance matching with circuit 60c). 
FIGS. 2G & 2H depict respective top and cross-sectional views of phase 
shifter 100d in accordance with a fourth illustrative embodiment of the 
present invention. Phase shifter 100d utilizes a single impedance-matching 
member 50d and one line-integrated impedance circuit 60c, like phase 
shifter 100c. Phase-shifting member 42d is moved between active line 2 and 
ground 6 in a direction indicated by direction vector 120 causing a 
continuous phase shift in a signal propagating in active line 2 relative 
to other signals propagating in other active lines (not shown). 
Impedance-matching member 50d has a tapered profile like members 
50b.sub.1, 50b.sub.2 (see FIG. 2D). Line-integrated impedance circuit 60d 
provides a more gradual impedance transition (relative to an impedance 
circuit that is not tapered) when signal frequency deviates from the 
impedance-matched frequency. In some embodiments, line-integrated 
impedance circuit 60d is implemented as a gradual increase in the width of 
active line 2. 
It will be appreciated that the preferred phase-shifter configuration may 
vary as a function of the specifics of any given application (e.g., type 
of antenna feed-network, etc.). One configuration that is expected to be 
advantageous for integration with some antenna arrays comprises a 
trapezoidal phase-shifting slab and straight active line, such as has been 
described and depicted above. Several other configurations are described 
below and depicted in FIGS. 3-7. It should be understood that the 
impedance-matching members used in the illustrative phase shifters 
described below can be implemented in accordance with any of the 
previously-described configurations (e.g., a single member having uniform 
thickness, a series of members having different thicknesses, tapered 
members, etc.). Moreover, while the impedance-matching members are 
advantageously configured for eliminating or reducing the impedance step 
over the full phase-shifting range, in other embodiments, such 
impedance-matching members are configured for impedance matching over only 
a portion of the phase-shifting range of the phase shifters. 
FIG. 3 depicts a top view of phase shifter 100e having rectangularly-shaped 
slab 400a comprising phase-shifting member 420a and two impedance-matching 
members 500a.sub.1, 500a.sub.2 in accordance with a fifth illustrative 
embodiment of the invention. Phase shifter 100e is depicted with 
illustrative L-shaped active line 20. In the illustrative embodiment 
depicted in FIG. 3, the slab can be moved in the directions indicated by 
direction vectors 12 and 120. 
FIG. 4 depicts a top view of phase shifter 100f having rectangularly-shaped 
slab 400b comprising phase-shifting member 420b and, functionally, "two" 
impedance-matching members 500b.sub.1, 500b.sub.2 in accordance with a 
seventh illustrative embodiment of the invention. Phase shifter 100f is 
depicted with illustrative U-shaped active line 22. Phase shifter 100f is 
described to have "two" impedance-matching members even though such 
members are physically a single entity. The reason for that is that two 
impedance "transformations" are provided. In particular, a first 
transformation is provided for input signal 550 and a second 
transformation is provided for output signal 552. As such, phase shifter 
100f provides the functional equivalent of two impedance-matching members. 
The U-shaped configuration of active line 22 allows for additional phase 
shift relative to straight active line 2, since more line is 
dielectrically-loaded. The slab is movable in a direction indicated by 
direction vector 120. 
FIG. 5 depicts a top view of phase shifter 100g having rectangularly-shaped 
slab 400c comprising phase-shifting member 420c and, functionally, four 
impedance-matching members 500b.sub.1, 500b.sub.2, 500b.sub.3, 500b.sub.4 
in accordance with an eighth illustrative embodiment of the invention. 
Phase shifter 100g is depicted with illustrative plural U-shaped active 
line 24. Phase-shifting member 420c is moved between active line 24 and 
ground 6 in a direction indicated by direction vector 120 to cause a 
continuous phase shift in a signal propagating in active line 24 relative 
to another signal propagating in another active line (not shown). The 
plural-U configuration provides additional phase shift relative to the 
single-U configuration of phase shifter 100f. 
FIG. 6 depicts a top view of phase shifter 100h having rectangularly-shaped 
slab 400d comprising phase-shifting member 420d and one impedance-matching 
member 500a.sub.1 in accordance with a ninth illustrative embodiment of 
the invention. Phase-shifter 100h is depicted with illustrative L-shaped 
active line 26 having one line-integrated impedance circuit 600a. In the 
illustrative embodiment depicted in FIG. 6, the slab is movable between 
active line 26 and ground 6 in a direction indicated by direction vector 
120. 
FIG. 7 depicts a top view of phase shifter 100i having rectangularly-shaped 
slab 400e comprising phase-shifting member 420e and three 
impedance-matching members 500b.sub.1, 500b.sub.2, 500b.sub.3 integrated 
in a dielectric slab in accordance with a tenth illustrative embodiment of 
the invention. Phase shifter 100i is depicted with illustrative U/L-shaped 
active line 26 having one line-integrated impedance circuit 600a. Slab 
400e is movable in a direction indicated by direction vector 120. 
In the above-described and illustrated embodiments, the phase-shifting 
members had a rectangular or triangular shape. It should be understood, 
that in other embodiments, other shapes may suitably be used. 
Advantageously, such other configurations will result in a regular 
increase in phase shift as a function of slab position. 
In the phase shifters described above, the phase-shifting member is 
inserted into the "main" field located between the active line and the 
ground plane. In other embodiments, the phase-shifting member is inserted 
into the "fringing" field located on top of the active line. In such 
embodiments, the effective phase shift per unit line length is 
disadvantageously substantially smaller than that obtained when the 
phase-shifting member is inserted into the main field. Moreover, in such 
embodiments, the effective phase shift is disadvantageously very sensitive 
to relatively small variations in the gap between the phase-shifting 
member and the active line. 
FIG. 8 depicts a cross-sectional view of phase shifter 100j used with a 
transmission line advantageously having an "exposed-ground" configuration 
in accordance with an illustrative embodiment of the present invention. In 
the "exposed-ground" configuration, a portion 802 of ground plane 800 is 
closer to air-suspended active line 2 disposed on circuit board 840 than 
the rest of the ground plane 800. The portion 802 has a width 
substantially equal to that of active line 2. Such a configuration results 
in a more symmetric field distribution 820 than the "standard" ground 
plane configuration shown in the other Figures. FIG. 8 shows 
phase-shifting member 850 inserted between active line 2 and portion 802 
of ground plane 800 for phase shifting. Cover 830 is located above active 
line 2. 
Electromagnetic field distribution 920 for a "standard" ground plane 
configuration is depicted in FIG. 9. In such a standard configuration, 
there is uniform spacing between ground 6 and air-suspended active line 2 
that is disposed on circuit board 840. FIG. 9 shows phase-shifting member 
850 inserted between active line 2 and ground 6 for phase shifting. Cover 
830 is disposed above active line 2. Field distribution 920 is less 
symmetric than field distribution 820. The more symmetric field 
distribution obtained with the exposed-ground configuration advantageously 
leads to reduced variations (less sensitivity) in the effective dielectric 
constant to mechanical motion of the phase-shifting member in the 
"vertical" direction indicated by direction vector 90 (see FIGS. 8, 9). 
The exposed-ground configuration illustrated in FIG. 8 does, however, 
disadvantageously result in a slight reduction in the effective dielectric 
constant relative to the standard ground configuration. 
FIG. 10 depicts a cross-sectional view of phase shifter 100k utilized with 
a "dual-polarity" transmission line having two air-suspended active lines 
2 and 200 in accordance with an illustrative embodiment of the present 
invention. In FIG. 10, active lines 2 and 200 are shown disposed on 
circuit boards 840 and 842. Cover 830 is disposed "above" active line 2 
and ground 6 is disposed "beneath" active line 200 in FIG. 10. 
Phase-shifting member 1050 is inserted between the two active lines. Such 
a configuration provides a very highly-symmetric field distribution 1020, 
resulting in less variation in the effective dielectric constant with 
mechanical motion of the phase-shifting member along the direction vector 
90 than for the configuration illustrated in FIG. 8. 
As described in more detail in U.S. Pat. No. 5,905,462 and U.S. Pat. No. 
5,940,030, phase shifters in accordance with the illustrative embodiments 
of the present invention are readily integrated into phased-array antennas 
to steer/tilt the antenna radiation pattern. 
It is to be understood that the embodiments described herein are merely 
illustrative of the many possible specific arrangements that can be 
devised in application of the principles of the invention. Other 
arrangements can be devised in accordance with these principles by those 
of ordinary skill in the art without departing from the scope and spirit 
of the invention. It is therefore intended that such other arrangements be 
included within the scope of the following claims and their equivalents.