Patent Publication Number: US-11038248-B2

Title: Apparatus forming a strip line and dielectric part

Description:
FIELD OF INVENTION 
     The present subject matter relates to a phase shifter and more specifically to an electro-mechanical phase shifter. This phase shifter can be used within mobile radio antennas, but also for any Radio Frequency (RF) device requiring a phase shift. 
     BACKGROUND 
     The key technical requirements of Base Station antennas for radio communication applications are high gain, high quality horizontal-plane (H-plane) and vertical-plane (V-plane) patterns. Gain and vertical-plane patterns requirements (i.e. tilt value, control of lobes, capability of null fields) are mainly a function of the antenna length and are controlled via the feeding network of the antenna. 
     Variable Electrical Tilt (VET) antennas have capability of tilt variation, i.e. of main lobe position variation versus the horizon. The adjustment of this tilt position may be achieved through several techniques applied to the antenna feeding network, using active and/or passive devices. The main component needed to achieve such tilt variation is a phase shifter device. 
     The present application deals with passive phase shifter devices, particularly the family of phase shifters using dielectric materials. At least two “dielectric materials” have to be considered with such technique: a solid device (the so-called “phase shifter”) and air (or vacuum). Displacing the solid dielectric material over a propagation line—so replacing the air dielectric—creates a phase variation. 
     The antenna phase shifted feeding network type used today may comprise several dielectric parts, called phase shifters, these parts may sliding under a stripline, or over a microstrip line, as described within the published patent application US2004/0080380 and the U.S. Pat. No. 6,816,668. 
     Considering that with such an implementation, each radiating element of the panel antenna may be unitary phase shifted, improving performance of such antenna and stability considering the radiating elements. 
     The phase shifter of the state of the art comprises the following drawbacks:
         This construction requires that the dielectric phase shifter parts must slide transversally, while the central actuator is mechanically moved within the axis of the antenna. This implies the use in specific mechanical parts that will realize the axial-to-transversal mechanical efforts transmissions. These parts have a non-negligible cost, and moreover are a source of additional friction, increase backlashes, and other mechanical malfunctions created by the plurality of parts and associated tolerances. These drawbacks are particularly unwanted considering high frequency systems, such as LTE.   The standard unitary dielectric phase shifters design may achieve phase shift ranges of about ˜60° (i.e. for one dielectric device), resulting in the entire phase shifted feeding network the capability to achieve for the antenna a tilt variation of about 10°. Performing higher phase shift ranges such as 100 or 120° is feasible—permitting to reach a 15° antenna tilt range for example—but at either cost of a wider mechanical dielectric part, or/and, the use of a bigger dielectric value. For high frequency scope, as wavelengths are reduced, increasing dimensions isn&#39;t a valid option, and, increasing the dielectric value will impose a higher sensitivity regarding the dielectric part positioning and tolerances.   If the Electrical plane patterns are good in terms of value and stability, it is nevertheless difficult to achieve stable Side Lobes Suppression over −20 dBc versus the antenna main beam.       

     The proposed electro-mechanical phase shifter reduces the three above mentioned drawbacks and is able to deeply reduce the general radio frequency and mechanical constraints related to present Phase Shifter devices, and particularly regarding high frequency bands such as at least 3.5 GHz. 
     SUMMARY OF THE INVENTION 
     Various embodiments of phase-shifters are proposed that can solve the previously described problems. More specifically, some embodiments provide a phase-shifter. 
     This summary is provided to introduce concepts related to examples of phase-shifter. 
     In one implementation, an apparatus forming a phase-shifter is described. The apparatus comprises a strip line and a moving dielectric part. The moving dielectric part surrounds the strip line and is adapted to move only along a longitudinal axis of the strip line. 
     Within this apparatus the size of the area of the strip line surrounded by the moving dielectric part is modified when the moving dielectric part moves along the longitudinal axis. 
     In one implementation, an antenna is described. The antenna comprises an apparatus forming a phase shifter and the apparatus is placed in a housing of which one of the faces is formed by a chassis of the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is given with reference to the accompanying drawings. In the drawings, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which: 
         FIG. 1  presents a phase-shifter. 
         FIG. 2  presents a phase-shifter. 
         FIGS. 3 - a ,  3 - b , and  3 - c  present a phase-shifter. 
         FIG. 4  presents a phase-shifter. 
         FIGS. 5 - a ,  5 - b ,  5 - c ,  5 - d ,  5 - e , and  5 - f  present examples of other phase shifters impedance transformer designs. 
         FIGS. 6 - a ,  6 - b , and  6 - c  presents a phase-shifter at different positions. 
         FIGS. 7 - a  and  7 - b  present another embodiment of the phase shifter. 
     
    
    
     In the present document, the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or implementation of the present subject matter described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. 
     DETAIL DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  presents an embodiment of the apparatus of the present subject matter. The apparatus forms a phase-shifter. The apparatus comprises a strip line  101  and a moving dielectric part  102 . The moving dielectric part  102  surrounds the strip line  101  and is adapted to move only along a longitudinal axis  103  of the strip line. The strip line is also known as propagation line. Wherein the size of the area of the strip line  101  surrounded by the moving dielectric part  102  is modified when the moving dielectric part  102  moves along the longitudinal axis  103 . 
     In order to have the size of the area of the strip line  101 , surrounded by the moving dielectric part  102 , modified, when the moving dielectric part  102  moves along a longitudinal axis  103 , the strip line  101  can have an L (see enlarged view of the  FIG. 2 ) shape or a triangular shape  204 . 
     This embodiment allows a “perfect” mechanical position of phase shifter versus the propagation line. So using this embodiment allows the phase-shifter to work at high frequency bands such as at least 3.5 GHz. 
     In an embodiment the apparatus also comprises a guide or guiding means. These guiding means are configured to guide the movement of the moving dielectric part  102  along the longitudinal axis  103  of the strip line  101 . 
       FIG. 2  presents another embodiment of the phase shifter. In this embodiment the guiding means are constituted of a key  201  placed along a parallel axis  202  to the longitudinal axis  103  of the strip line  101  and a keyway  203  realize within the moving dielectric part  102 . The key  201  is configured to be fixed with respect to the strip line  103  and to cooperate with the keyway  203 . The key  201  is also configured to allow the movement of the moving dielectric part  102  only along the longitudinal axis  103  of the strip line  101 . The keyway is also known as a slot. 
     In an embodiment, the key  201  is fixed to the strip line  101  at  206  and  207 , or the key  201  and the strip line  101  may be both fixed to a ground plate  205  at  206 - 208 . 
     In an embodiment, the key  201  is a clip made for example of plastic dielectric. 
     In an embodiment where the key is inserted, the key may have a length at least equal to the width of the strip line, and made from the same dielectric material as the phase shifter device. This avoids any modification of the strip line area where the key is inserted. In this embodiment a slot (or keyway) is placed all along the phase shifter at the corresponding position of the clip, in order to be able to slide the phase shifter along the longitudinal axis. Within this embodiment, there is no modification of the general radio frequency construction and so the phase shifter behavior may not be modified compared to phase-shifter of the state of the art. 
       FIG. 3 - a  presents another embodiment of the phase-shifter. In this embodiment the guiding means are constituted of a second dielectric part  301  configured to be static with respect to the strip line and arranged to allow the movement of the moving dielectric part  102  only along a longitudinal axis  103  in  FIGS. 1 and 2  of the strip line  101 . 
       FIG. 3 - b  present the size of the different elements of the phase shifter according to one embodiment. This phase-shifter is capable of convenient radio frequency performances from 3.4 GHz up to 4.2 GHz. This phase shifter is realized using a suspended stripline mode. A PCB—here a single side ROGERS RT DUROID 5870 (high frequency laminate) of 0.254 mm thick, 0.35 microns of copper—is placed at the center of two metallic ground planes (not represented here) i.e. one at the top and one at the bottom, spaced here of 7.2 mm. On each sides of this PCB are placed one fix dielectric Phase Shifter, which may be positioned at the top and bottom, and one top moveable dielectric Phase Shifter and one bottom moveable dielectric Phase Shifter—made here of a dielectric material of a dielectric constant of 4. 
       FIG. 3 - c  depicted top views of the  FIG. 3 - a  Phase Shifter topology sliding 30 mm in an axial movement (min, avg, max), including second dielectric part  301 , moving dielectric part  102 , and strip line  101 . One of the Phase shifters is kept fixed and the second one is translating. 
       FIG. 4  presents an embodiment of the phase shifter in which the moving dielectric part  102  also comprises an impedance transformation part  401  and a fixed impedance part  402 . In other words, within this embodiment, the moving dielectric part is made of three main areas. The first area is the impedance transformation part. The second area is relative to a fixed impedance area. Considering that the transmission line is continuously displacing below the third area, a modification made on the third area at a certain position will not have or have low influence at another position. So, some variations may be created on the dielectric part, as thicknesses variations, all along the third area in order to create some “fine tunings” of the input and output impedances. 
       FIGS. 5 - a  to  5 - f  present respectively examples of other phase shifters impedance transformer designs  501 - 506  of a phase shifter impedance transformer that will permit to achieve the same kind of performances. The phase shifter of the present subject matter can be used with different impedance transformer section. 
     In an embodiment the moving dielectric part  102  in  FIGS. 1 and 2  are constituted of two identical parts the first part placed over the strip line and the second part placed under the strip line. 
     In another embodiment the strip line  101  in  FIGS. 1 and 2  is made by etching a metal layer of a printed circuit board. 
     An embodiment of the present subject matter is an antenna that comprises the apparatus of any of the preceding embodiments. The phase-shifter is placed in a housing of which one of the faces is formed by a chassis of the antenna. 
     In other words the different embodiments of the phase shifter may guarantee the “perfect” mechanical position of the moving dielectric part versus the propagation line. Indeed the extra parts (for example the key and keyway) inserted in the different elements of the phase-shifter, and are cause of increasing the mechanical tolerances between the dielectric phase shifters and the propagation line. 
     In an embodiment and ensure that the phase shifter mechanical positioning is directly referenced to the propagation line, a small part, called “guide” or key may be inserted directly onto the line. 
       FIG. 6 - a ,  6 - b  and  6 - c  presents respectively the phase shifter at min  601 , mid 602 and max  603  mechanical positions of a phase shifter impedance transformer. 
       FIGS. 7 - a  and  7 - b  present another embodiment of the phase shifter impedance transformer. This phase shifter is made with a microstrip. All the phase shifters of the previous embodiments can work with microstrip instead of stripline or suspended stripline. Within this embodiment a Taconic TLX PCB (0.787 mm thick) is used to realize a 50 Ohms microstrip line (copper trace width is about 2.25 mm for 35 microns thick). Over this PCB is placed two 2 mm thick dielectric elements, made of a material with a dielectric constant of about 10. 
     One other object of the present subject matter is an antenna comprising one of the phase-shifter previously described. This phase-shifter is placed in a housing of which one of the faces is formed by a chassis of the antenna.