Patent Description:
The Third Generation Partnership Project (3GPP) has developed and is developing standards for Fourth Generation (<NUM>) (also referred to as Long Term Evolution (LTE)) and Fifth Generation (<NUM>) (also referred to as New Radio (NR)) wireless communication systems. Such systems provide, among other features, broadband communication between network nodes, such as base stations, and mobile wireless devices (WD), as well as communication between network nodes and between WDs.

Referring to <FIG>, in order to communicate with multiple WDs 8a, 8b, 8c (referred to collectively as WDs <NUM>) in different spatial directions, the network node <NUM> may be equipped with an RF front end having a phased array antenna <NUM> with antenna elements <NUM>, phase shifters <NUM> and a beamformer <NUM>. The beamformer <NUM> determines for each phase shifter <NUM> an amount of phase shift to be introduced by the phase shifter <NUM> in the path toward an antenna element <NUM>. By selecting and implementing the phase shift in each path, a beam of the phased array antenna <NUM> can be steered toward one or more specific directions toward different WDs <NUM>. For example, the phase shifters <NUM> can cause the beam to steer toward a particular elevation direction.

The phase shifters <NUM> can be adjusted to achieve different phases by varying a wiper arm <NUM> in a wiper arm configuration, as shown in <FIG>, or by varying an overlap of striplines, as shown in <FIG>. In <FIG>, two parallel striplines 22a and 22b are overlapped by a U-shaped stripline <NUM>. Phase is adjusted by moving the U-shaped stripline <NUM> to the left or right in <FIG>. When stripline <NUM> is moved to the left, there is more overlap and less phase shift, whereas when stripline <NUM> is moved to the right, there is less overlap and more phase shift. This is sometimes referred to as a trombone phase shifter. A disadvantage of the configuration of <FIG> is large return loss, whereas a disadvantage of the configuration of <FIG> is a need for shielding, which uses greater volume and increased weight.

Document <CIT> discloses a phase shifter that is provided with: at least one reference conductor to which a reference potential is supplied; a first line conductor which faces the reference conductor so as to constitute a transmission path, and to which a signal is inputted; a second line conductor which is disposed on the first line conductor side so as to face the reference conductor and to constitute the transmission path, and from which a signal is outputted; and a third line conductor which is electrically connected to the first and second line conductors in such a manner as to be able to move relative to the first and second line conductors, and which faces the reference conductor so as to constitute the transmission path, wherein at least one of the first, second, and third line conductors has a portion in which the characteristic impedance is different from that in other portions.

Document <CIT> discloses an adjustable constant impedance phase shifter. In the adjustable constant impedance phase shifter a conductive circuit path is arranged between a conductive sheet and a parallel plane that is parallel to the conductive sheet; an edge of a dielectric plate and an edge of a conductive plate are adjoined such that the dielectric plate and the conductive plate form a slide member; and the slide member is movably arranged along a slide path between the circuit element and the conductive sheet so that any point of the conducting circuit path is consistently enclosed between the slide member and the parallel plane, and so that the relative permittivity of a medium adjacent to a point on the conductive circuit path is simultaneously changed as the slide member is moved.

Some embodiments advantageously provide a system for high performance stripline phase shifters in a radio frequency (RF) front end.

According to the present disclosure, sliding phase shifters according to the independent claims are provided. Developments are set forth in the dependent claims.

In some embodiments, a trombone-type stripline is provided with shielding by vias and an upper ground plane. Such shielding is lighter and smaller in volume than known shielding. In some embodiments, the sliding portion of the stripline phase shifter is tapered to provide return loss over the phase shift range that is improved over known methods. In some embodiments, the sliding portion of the sliding phase shifter and/or the fixed portion of the sliding phase shifter are tapered in the direction of motion to provide performance in the presence of mechanical misalignment that is improved over known methods. In particular, in some embodiments, the fixed portion is wider than the sliding portion to provide improved performance in the presence of mechanical misalignment between the fixed portion and the sliding portion as compared with using fixed and sliding portions having the same width. In some embodiments, a non-linear stripline is used to achieve greater phase shift per unit of motion of the sliding portion of the sliding phase shifter. In some embodiments, a sliding dielectric portion overlaps a fixed portion to achieve a desired phase shift.

According to one aspect, a sliding phase shifter includes a fixed dielectric having first striplines to couple power into the sliding phase shifter. The sliding phase shifter also includes a sliding dielectric having second striplines electrically slidingly coupled to the first striplines, an amount of phase shift of a signal being determine by an amount of overlap of the first striplines and the second striplines, a width of the second striplines being at least partially tapered along a portion of the second striplines.

According to this aspect, in some embodiments, the sliding dielectric has a first ground plane on at least part of one side of the sliding dielectric and has the second striplines on an opposite side of the sliding dielectric facing the fixed dielectric, and wherein the sliding dielectric further comprises vias extending from the one side to the opposite side of the sliding dielectric, the vias encompassing at least a portion of a perimeter surrounding the first and second striplines. In some embodiments, the sliding phase shifter further includes a second ground plane below at least a portion of the second striplines, a separation between the first ground plane and the second ground plane being selected to achieve an impedance of the second striplines that matches an impedance of the first striplines. In some embodiments, the second ground plane is limited in extent so as to expose at least a portion of the first striplines to the first ground plane. In some embodiments, the separation is selected so that a return loss is below a threshold for all positions of the sliding dielectric within a frequency band of operation. In some embodiments, the sliding phase shifter further includes a ground coupling strip along the perimeter, the ground coupling strip terminating one end of the vias. In some embodiments, the second striplines are narrower than the first striplines. In some embodiments, the taper is selected to achieve an insertion loss that is above a threshold for all positions of the sliding dielectric within a frequency band of operation. In some embodiments, the first striplines are at least partially tapered in width along a direction of propagation of the first striplines. In some embodiments, the taper is linear.

According to another aspect, a sliding phase shifter includes a fixed dielectric structure having first striplines. The sliding phase shifter also includes a sliding dielectric structure. The sliding phase shifter is configured to provide a change in phase shift of a signal when the sliding dielectric structure slides over the first striplines to change an amount of overlap of the sliding dielectric and the first striplines. The sliding dielectric structure has a first region with a first ground plane above a level of the first striplines and having a second region with a dielectric slab above the level of the first striplines and below a second ground plane.

According to this aspect, in some embodiments, the first striplines follow a curved path. In some embodiments, the curved path is sinusoidal. In some embodiments, the first ground plane is separated from the first striplines by air. In some embodiments, the dielectric slab is configured to cover an entire length of the first striplines in a minimum delay position. In some embodiments, a dielectric constant of the dielectric slab is higher than a dielectric constant of a dielectric of the fixed dielectric structure. In some embodiments, the fixed dielectric structure has a third ground plane below the first striplines and a signal trace in a same plane as the third ground plane, the signal trace being coupled to the first striplines by a via. In some embodiments, a height of the first ground plane, a height of the second ground plane and a height of the third ground plane are selected to provide an insertion loss that exceeds a threshold in a frequency band of operation. In some embodiments, a height of the first ground plane, a height of the second ground plane and a height of the third ground plane are selected to provide a return loss that falls below a threshold in a frequency band of operation. In some embodiments, the second ground plane is above the first region and the second region, a ground coupling strip surrounds a perimeter of the sliding dielectric structure and a plurality of vias around the perimeter, the vias extending from the ground coupling strip to the second ground plane.

Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to high performance stripline phase shifters in a radio frequency (RF) front end. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

As used herein, relational terms, such as "first" and "second," and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements.

Returning to the drawing figures, where like reference designators refer to like elements, <FIG> shows a perspective view of one embodiment of a sliding phase shifter <NUM> according to principles set forth herein. The sliding phase shifter <NUM> has a fixed dielectric <NUM>, over which is situated a sliding dielectric <NUM>. Vias <NUM> form a circumferential pattern around the perimeter of the fixed stripline <NUM> and the sliding stripline <NUM>. Vias <NUM> are also positioned in the center region in the area between sliding stripline <NUM> and fixed striplines <NUM>. At one end, e.g., a bottom, of the vias <NUM> is a ground coupling strip <NUM> and at the opposite end, e.g., a top, of the vias <NUM> is a top ground plane <NUM>. The ground coupling strip <NUM> is positioned around the perimeter of the fixed stripline <NUM> and sliding stripline <NUM>. The vias <NUM> extend from the ground coupling strip <NUM> to the top ground plane <NUM>.

The combination of the vias <NUM>, the ground coupling strip <NUM> and top ground plane <NUM> forms a shield around the fixed stripline <NUM> and sliding stripline <NUM> of the sliding phase shifter <NUM>. A partial ground plane <NUM> is under a portion of the sliding stripline <NUM>. The partial ground plane <NUM> has an opening <NUM> exposing the fixed stripline <NUM>, forming a ground plane transition <NUM>. <FIG> shows the sliding stripline <NUM> overlapping at <NUM> the fixed stripline <NUM>.

<FIG> show two top views of the sliding phase shifter <NUM>. <FIG> shows the sliding phase shifter <NUM> with the sliding stripline <NUM> being in a minimum delay position with respect to the fixed stripline <NUM> to provide minimum phase shift. <FIG> shows the sliding phase shifter <NUM> with the sliding stripline <NUM> in a maximum delay position with respect to the fixed stripline <NUM> to provide maximum phase shift. Minimum and maximum used herein refer to the minimum and maximum with respect to the functional extremes, i.e., phase shift, achievable with the particular structure.

<FIG> shows a side view of the sliding phase shifter <NUM>. The sliding dielectric <NUM> exhibits surface Ls1 and surface Ls2. Surface Ls1 carries the ground coupling strip <NUM>. Surface Ls2 carries the top ground plane <NUM>. The fixed dielectric <NUM> includes a lower portion 28a and an upper portion 28b. The lower portion 28a includes surface L1, which has a ground plane <NUM>. The fixed dielectric <NUM> may be part of a printed circuit board (PCB) that has the fixed dielectric <NUM>. The lower portion 28a also includes surface L2 which is not metallized to the left of the ground plane transition <NUM> and is metallized to form a partial ground plane <NUM> to the right of the ground plane transition <NUM>. The fixed stripline <NUM> ground separation <NUM>, which is the separation between L1 and Ls2, may be designed so that the fixed stripline <NUM> exhibits a first impedance. The partial ground plane <NUM>, is closer to the top ground plane <NUM> and creates a sliding stripline <NUM> ground separation <NUM>, which is the separation between L2 and Ls2, that exhibits a second impedance. A width and taper of the sliding stripline <NUM>, as well as the height of the partial ground plane <NUM> and ground separation <NUM>, may be designed so that the second impedance closely matches the first impedance, in order to reduce reflection by the sliding phase shifter <NUM>. Note that <FIG> shows only the vias <NUM> in the sliding dielectric part <NUM>. In some embodiments, there may also be vias <NUM> that extend from the lower ground plane <NUM> to the upper most level L3 of the fixed dielectric <NUM>. There may also be vias that connect the fixed stripline <NUM> to signal traces on another level that carry a signal into the sliding phase shifter <NUM>. A thin dielectric layer <NUM>, such as a solder mask or Teflon®, may lie between layers Ls1 and L3 to reduce passive intermodulation (PIM) and to reduce friction.

<FIG> shows a top view of the sliding phase shifter <NUM> where at a base of the sliding stripline <NUM>, the width of the sliding stripline <NUM> is a first value t1. At an end of the sliding stripline <NUM>, the width of the sliding stripline <NUM> is a second value t2, which is less than the first value t1. In some embodiments, t1=<NUM> and t2=<NUM>. In some embodiments, the fixed stripline may also be tapered, with a narrow end having width t3 and a wider base width t4. In some embodiments, t3=<NUM> and t4=<NUM>. In <FIG>, the sliding stripline <NUM> is shifted to the right by, for example, <NUM>. This illustrates that when the sliding stripline <NUM> is narrower than the fixed stripline <NUM>, the fixed stripline <NUM> encompasses the sliding stripline <NUM> when there is side-to-side motion within design tolerances. By ensuring overlap of the fixed stripline <NUM> and the sliding stripline <NUM>, better phase shifter performance, as indicated by return loss, insertion loss or delay linearity, can be achieved than the performance that can be achieved, if there is any non-overlap.

As a consequence of making t2 less than t3, the impedance of the sliding stripline <NUM> would differ substantially from the impedance of the fixed stripline <NUM>, but for the positioning of the partial ground plane <NUM> to match these impedances.

<FIG> is a graph of return loss versus frequency for three different positions of the sliding stripline <NUM>, where <NUM> indicates the minimum delay position of the sliding stripline <NUM> shown in <FIG>. <FIG> is a graph of insertion loss versus frequency for <NUM> different trace transition widths with the sliding stripline in the minimum delay position By tapering the width of the sliding stripline <NUM> from t1 to t2, and/or tapering the width of the fixed stripline <NUM> from t3 to t4, undesired nulls or a large increase in the insertion loss over an operating frequency band can be avoided.

<FIG> shows a perspective view of another embodiment of sliding phase shifter <NUM>. The sliding phase shifter <NUM> has a sliding dielectric structure <NUM> that has an Ls2 ground plane <NUM>. A fixed dielectric structure <NUM> has a stripline <NUM> (delay line trace) on a level L4. The stripline <NUM> is shown in <FIG> as a pair of physically parallel sine waves, with one side of the stripline <NUM> being a sine wave and the opposite side of the stripline <NUM> being a cosine wave. Although the stripline <NUM> is non-linear, because of its symmetry it provides a linear change in phase shift when the sliding portion is moved relative to the fixed portion. Other non-linear traces can be employed. An advantage of the non-linear stripline <NUM> is that more phase change per unit of movement of the sliding dielectric structure <NUM> can be achieved. A pair of straight traces <NUM> on another level L3 provides an interface with an external circuit. In operation, as the sliding dielectric structure <NUM> moves from a maximum delay position, such as shown in <FIG>, to a minimum delay position as shown in <FIG>, the phase shift decreases.

<FIG> show a side view of the sliding phase shifter <NUM>. In <FIG>, the sliding dielectric structure <NUM> is in a minimum delay position. In <FIG>, the sliding dielectric structure <NUM> is in a position of increased delay as compared to the minimum delay position. The sliding dielectric structure <NUM> has a first region to the left of a transition point <NUM> and a second region to the right of the transition point <NUM>. In the first region there are two levels of the sliding dielectric structure <NUM>. The upper level has a dielectric which carries on its lower surface the Ls2 ground plane <NUM>. The lower level may be air. In the second region there is no ground plane on Ls2. Rather, the second region has a dielectric ε2, which may be the same or different from the dielectric ε1 of the fixed dielectric structure <NUM>. The stripline <NUM> is carried by the upper surface of the fixed dielectric structure <NUM> on level L4 between the air of the lower level of the first region and the fixed dielectric structure <NUM>. Note that the fixed dielectric structure <NUM> has an upper dielectric layer that carries the stripline <NUM> and a lower dielectric structure which carries the L3 ground plane. Also, a signal via <NUM> couples the traces <NUM> on level L3 to the stripline <NUM> on level L4.

When the sliding dielectric structure <NUM> is in the minimum delay position, as shown in <FIG>, the stripline <NUM> has air above it up to level Ls2 and has dielectric below it down to level L3, or another layer (not shown) between L1 and L3. The width of the stripline <NUM>, the distance between level Ls1 and Ls2, the distance between level L3 and L4, and ε1 all may be determined to achieve a constant impedance (for example, <NUM> ohms) of the stripline <NUM>. Note that Ls1 is the lower level of the gap between level Ls2 and level L4. As the sliding dielectric structure <NUM> is moved to the left (which may be as positioned by a stepper motor, for example), the stripline <NUM> becomes more completely covered by the dielectric ε2. This causes the phase shift (or delay) of the sliding phase shifter <NUM> to increase. The impedance of the stripline <NUM> that is covered by dielectric ε2 is now determined by width of the stripline <NUM>, the distance between levels Ls1 and Ls3, the distance between levels L3 and L4 and the dielectrics ε1 and ε2. These parameters may be chosen to achieve an impedance that is constant (or within upper and lower limits of the constant) over the entire range of positions of the sliding dielectric structure <NUM>. An advantage of the sliding phase shifter <NUM> is reduced sensitivity to side to side motion of the sliding dielectric structure <NUM>.

Returning to <FIG>, ground coupling strip <NUM> between level L4 and level Ls1 form a shielding box in conjunction with first vias <NUM> from level Ls1 to a ground plane on level Ls3. Second vias <NUM> extend from level L1 to level L4. Third vias <NUM> extend from level Ls2 to level Ls3, where level Ls3 is the upper surface of the sliding dielectric structure <NUM> and is at least partially metallized to provide shielding.

<FIG> illustrate various parts of the sliding phase shifter <NUM>, where GP stands for ground plane. In <FIG> the outer perimeter of each layer may be the outer boundary of a dielectric on which the indicated ground plane (GP) is carried. <FIG> illustrates an example of the L1 ground plane. <FIG> illustrates an example of the ground plane on L3. <FIG> illustrates an example of the L4 ground plane. <FIG> illustrates an example of the Ls1 ground plane. <FIG> illustrates an example of the Ls2 ground plane. <FIG> illustrates an example of the Ls3 ground plane. <FIG> shows an example of the traces <NUM> and <FIG> shows an example of the stripline <NUM>.

Thus, according to one aspect, a sliding phase shifter <NUM> includes a fixed dielectric <NUM> having first striplines <NUM> to couple power into the sliding phase shifter <NUM>. The sliding phase shifter <NUM> also includes a sliding dielectric <NUM> having second striplines <NUM> electrically slidingly coupled to the first striplines <NUM>, an amount of phase shift or delay of a signal being determine by an amount of overlap of the first striplines <NUM> and the second striplines <NUM>, a width of the second striplines <NUM> being at least partially tapered along a portion of the second striplines <NUM>.

According to this aspect, in some embodiments, the sliding dielectric <NUM> has a first ground plane <NUM> on at least part of one side of the sliding dielectric and has the second striplines <NUM> on an opposite side of the sliding dielectric <NUM> facing the fixed dielectric <NUM>, and wherein the sliding dielectric <NUM> further comprises vias <NUM> extending from the one side to the opposite side of the sliding dielectric <NUM>, the vias <NUM> encompassing at least a portion of a perimeter surrounding the first and second striplines <NUM>, <NUM>. In some embodiments, the sliding phase shifter <NUM> further includes a second ground plane <NUM> below at least a portion of the second striplines <NUM>, a separation between the first ground plane <NUM> and the second ground plane <NUM> being selected to achieve an impedance of the second striplines <NUM> that matches an impedance of the first striplines <NUM>. In some embodiments, the second ground plane <NUM> is limited in extent so as to expose at least a portion of the first striplines <NUM> to the first ground plane <NUM>. In some embodiments, the separation is selected so that a return loss is below a threshold for all positions of the sliding dielectric <NUM> within a frequency band of operation. In some embodiments, the sliding phase shifter <NUM> further includes a ground coupling strip <NUM> along the perimeter, the ground coupling strip <NUM> terminating one end of the vias <NUM>. In some embodiments, the second striplines <NUM> are narrower than the first striplines <NUM>. In some embodiments, the taper is selected to achieve an insertion loss that is above a threshold for all positions of the sliding dielectric <NUM> within a frequency band of operation. In some embodiments, the first striplines <NUM> are at least partially tapered in width along a direction of signal propagation of the first striplines <NUM>. In some embodiments, the taper is linear.

According to another aspect, a sliding phase shifter <NUM> includes a fixed dielectric structure <NUM> having first striplines <NUM>. The sliding phase shifter <NUM> also includes a sliding dielectric structure <NUM>. The sliding phase shifter <NUM> is configured to provide a change in phase of a signal when the sliding dielectric structure <NUM> slides over the first striplines (<NUM>) to change an amount of overlap of the sliding dielectric and the first striplines. The sliding dielectric structure <NUM> has a first region with a first ground plane <NUM> above a level of the first striplines <NUM> and having a second region with a dielectric slab <NUM> above the level of the first striplines <NUM> and below a second ground plane <NUM>.

According to this aspect, in some embodiments, the first striplines <NUM> follow a curved path. In some embodiments, the curved path is sinusoidal. In some embodiments, the first ground plane <NUM> is separated from the first striplines <NUM> by air. In some embodiments, the dielectric slab <NUM> is configured to cover an entire length of the first striplines <NUM> in a minimum delay position. In some embodiments, a dielectric constant of the dielectric slab <NUM> is higher than a dielectric constant of a dielectric of the fixed dielectric structure <NUM>. In some embodiments, the fixed dielectric structure <NUM> has a third ground plane <NUM> below the first striplines <NUM> and a signal trace in a same plane as the third ground plane <NUM>, the signal trace being coupled to the first striplines <NUM> by a via <NUM>. In some embodiments, a height of the first ground plane <NUM>, a height of the second ground plane <NUM> and a height of the third ground plane <NUM> are selected to provide an insertion loss that exceeds a threshold in a frequency band of operation. In some embodiments, a height of the first ground plane <NUM>, a height of the second ground plane <NUM> and a height of the third ground plane <NUM> are selected to provide a return loss that falls below a threshold in a frequency band of operation. In some embodiments, the second ground plane <NUM> is above the first region and the second region, a ground coupling strip around a perimeter of the sliding dielectric structure and a plurality of vias around the perimeter, the vias extending from the ground coupling strip to the second ground plane <NUM>.

Claim 1:
A sliding phase shifter (<NUM>), comprising:
a fixed dielectric (<NUM>) having first striplines (<NUM>) configured to couple power into the sliding phase shifter (<NUM>); and
a sliding dielectric (<NUM>) having second striplines (<NUM>) electrically slidingly coupled to the first striplines (<NUM>), an amount of phase shift or delay of a signal being determined by an amount of overlap of the first striplines (<NUM>) and the second striplines (<NUM>), a width of the second striplines (<NUM>) being at least partially tapered along a portion of the second striplines (<NUM>),
characterized in that the sliding dielectric (<NUM>) has a first ground plane on at least part of one side of the sliding dielectric (<NUM>) and has the second striplines (<NUM>) on an opposite side of the sliding dielectric (<NUM>) facing the fixed dielectric (<NUM>), and wherein the sliding dielectric (<NUM>) further comprises vias (<NUM>) extending from the one side to the opposite side of the sliding dielectric (<NUM>), the vias (<NUM>) encompassing at least a portion of a perimeter surrounding the first and second striplines (<NUM>).