WO2015120240A1

WO2015120240A1 - Tunable dielectric resonator antenna

Info

Publication number: WO2015120240A1
Application number: PCT/US2015/014766
Authority: WO
Inventors: Kristi Pance; Karl SPRENTALL
Original assignee: Rogers Corp
Current assignee: Rogers Corp
Priority date: 2014-02-06
Filing date: 2015-02-06
Publication date: 2015-08-13
Anticipated expiration: 2016-08-06

Abstract

A tunable dielectric resonator antenna includes a coupler in electrical communication with an input, a ground plane coupled to an end of the coupler, a first dielectric resonator at least partially surrounding the coupler and an actuator that moves the ground plane relative to an end of the first dielectric resonator to vary a fundamental frequency of the tunable dielectric resonator.

Description

TUNABLE DIELECTRIC RESONATOR ANTENNA

BACKGROUND OF THE INVENTION

[0001] The subject matter disclosed herein relates to antennas and, more particularly, to a tunable dielectric resonator antenna.

[0002] An antenna (or aerial) is an electrical device which converts electric power into radio waves, and vice versa. Typically an antenna consists of an arrangement of couplers (elements), electrically connected (often through a transmission line) to the receiver or transmitter. Current is forced through the antenna by a transmitter to create an oscillating magnetic field around the antenna elements that radiate away from the antenna into space. During reception, oscillating fields of an incoming radio wave exert force on antenna elements, causing them to move back and forth, creating oscillating currents in the antenna. In the same way, during the reception, the incoming waves, excites oscillating fields and currents on the antenna elements.

[0003] A dielectric resonator antenna (DRA) is a radio antenna mostly used at microwave frequencies and higher, that consists of a block of dielectric material of various shapes that serve as a resonator, a coupler (e.g., a wire or other metallic element) and a ground plane to which the coupler is mounted. The resonator may be formed of a ceramic or other dielectric material.

[0004] In operation, waves (radio or micro, for examples) are introduced into the inside of the resonator material from the transmitter circuit via the coupler and bounce back and forth between the resonator walls, forming standing waves. The walls of the resonator are partially transparent to radio waves, allowing the waves to radiate into space.

[0005] In a similar manner, radio or other waves outside of the dielectric may enter into the region within the resonator walls. The waves may then be detected by the coupler and interpreted by a receiving circuit (which may the same circuit as the transmitter circuit in some cases.

[0006] Today's ever increasing reliance on wireless communication has seen an marked increase in the demand for antennas. Some applications also require that these antennas be tunable. BRIEF DESCRIPTION OF THE INVENTION

[0007] According to embodiments of one aspect of the present invention, a tunable dielectric resonator antenna comprising a coupler in electrical communication with an input, a ground plane coupled to an end of the coupler, a first dielectric resonator at least partially surrounding the coupler, and an actuator that moves the ground plane relative to an end of the first dielectric resonator to vary a fundamental frequency of the tunable dielectric resonator is disclosed.

[0008] Also disclosed is a tunable dielectric resonator antenna that includes a plurality of dielectric resonator slices each separated from one another, a plurality of metal fins, each fin being disposed between two different dielectric slices, an actuator that causes the fins to move relative to the dielectric resonator slices to vary a fundamental frequency of the antenna, and a coupler that provides a signal to an area surrounded by the slices.

[0009] Also, methods of operating and tuning the above antennas are disclosed.

[0010] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

[0011] The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0012] FIG. 1 is a block diagram of embodiment of an antenna;

[0013] FIG. 2 is block diagram of an example of split resonator section;

[0014] FIG. 3 shows an example of an antenna having slices and fins according to one embodiment;

[0015] FIG. 4 shows a block diagram of an antenna having slices and fins according to one embodiment; and

[0016] FIGs. 5 and 6 show a block diagram of how the fins of FIGs. 3-4 may be moved.

[0017] The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0018] As described above, the typical dielectric resonator antenna includes a dielectric resonator that defines a cavity about a coupling element or loop. During reception/transmission there are forces in between the antenna elements generated by the oscillating electromagnetic (EM) fields. Usually, they are very weak to cause mechanical motions on the antenna elements. In embodiment disclosed herein, mechanical motions are caused by piezoelectric mechanism and aim to change the antenna resonant frequency or the oscillating fields frequency. In particular, one embodiment, varying a distance between a ground plane and the resonator allows for tuning of the antenna. That is, the resonant frequency of the antenna may be altered by varying the relationship between the resonator and the ground plane in certain embodiments disclosed herein. Also, in some embodiments the antenna resonant frequency may be altered by varying the distance between the ceramic (or ceramic parts) and a "floating" metal, not connected to the antenna electrical ground)

[0019] Referring to FIG. 1, an overhead view of one embodiment of a tunable dielectric resonator antenna 100 (antenna) is illustrated. The antenna is driven by a transmitter 101 that may also include receiving electronics and, thus, may general be referred to as transmitter/receiver. Or course, the transmitter and receiver could be separate from each other and only one of the two may be present in certain applications. It shall be understood that the transmitter/receiver 101 may be coupled to the antenna 100 by a transmission line 103. In one embodiment, the transmission line 103 is coaxial cable having an impedance that is close to or matches that of the antenna 100. Of course, a matching circuit may be provided it needed.

[0020] In the illustrated embodiment, signals enter and/or exit the antenna 100 via connection 106. To that end, the transmission line 103 may be electrically coupled to the connection 106. While the transmitter/receiver 101 is shown external to the antenna 100 it shall be understood that it may also be provided within it. For example, the transmitter/receiver and/or the transmission line 103 may be located within the housing 104. Of course, in some applications, the transmission line 103 may not be needed and can be omitted.

[0021] The antenna 100 includes a resonator 102. In the illustrated example, the resonator 102 is formed of two resonator portions 102a and 102b. These two portions may be formed, for example, by cutting a ring of resonator (e.g., dielectric) material such as in half. Other shapes could be used. Also, in one embodiment, only a single resonator portion (e.g., 102a) may be provided.

[0022] The illustrated antenna 100 includes a ground plane formed by housing 104. The housing 104 may be formed of metal (e.g., copper) in one embodiment. The housing may include connection 106 that is electrically coupled to coupler 109. In other embodiments, the coupling loops 109 are coupled to the resonator magnetic field and the antenna maybe excited via electric fields couplings i.e. capacitive plates instead of inductive loops. As illustrated the coupler 109 include two coupler portions 109a and 109b. The number of coupler portions 109a, 109b may be equal to the number of resonator portions 102a, 102b in certain embodiments. In one embodiment, the housing 104 serves a ground plane for the antenna formed by each coupler 109/resonator 102 combination (e.g., 109a and 102a form a combination). One end of each of the resonator portions 102a, 102b contacts the housing 104 while the other spaced from it by corresponding gaps gl, g2. In one embodiment, the coupler portions are an extension of central conductor of coaxial transmission line. In this embodiment, the other end has to contact the housing to provide a closed path for the excitation current (when antenna works in the transmission mode) or induced current (when antenna works in the receiving mode). The closed path (contact to the housing) helps to provide the right coupling to resonator magnetic field.

[0023] Introduction of power to the coupler 109 causes waves (radio or micro, for examples) to be introduced into the inside (e.g., cavity 110) of the resonator portions 102a, 102b. This may include exciting a magnetic field in the couplers loops which provokes magnetic and electric fields of the resonator. The frequency at which these waves bounce back and forth between the resonator walls defines a fundamental frequency of the antenna 100. It has been discovered that by varying the distance(s) gl, g2 between one end of the resonator 102a, 102b and the ground plane formed by housing 104 changes this fundamental frequency. Thus, an input signal can "matched" to the antenna 100 by adjusting the distance of the gaps gl, g2. In one embodiment, the distances gl and g2 are the same while in others, different distances may be utilized.

[0024] In one embodiment, the housing includes one or more actuators 112, 114, that serve to push/pull on the housing 104 to adjust the size of the gaps gl, g2, respectively. In one embodiment, the actuators 112, 114 are piezoelectric actuators. In another embodiment, the actuators 112, 114 could be an electropolymer actuator. Each of the embodiments disclosed herein can use one or both of these types of actuators. Of course, other actuator types may also be used.

[0025] The actuators may operate in a linear manner such as illustrated by arrows A and B. As the actuators 112, 1 14 push/pull on the outer walls of the housing 104, the gaps gl and g2 vary and, accordingly, the fundamental frequency of the antenna 100 maybe varied. This allows the antenna 100 be become a so called "multiband antenna." As mentioned above, in one embodiment, it may be possible that gl and g2 are different. In such a case, the antenna 100 will have resonant frequency that is based on the resonant frequency of the combined portions.

[0026] As the embodiment of FIG. 1 operate by adjusting the gaps gl, g2 to set the fundamental frequency, a measure of those gaps may be utilized in the tuning process. For example, in one embodiment, the antenna 100 may optionally include a distance measurement device (generally shown by element 115). Examples of such devices include a rotary or slide potentiometer, plate capacitors, inductive spring measurement devices, light based measurement devices or devices that can measure standing wave parameters.

[0027] When the antenna 100 is manufactured, a look up table distances (gl, g2) versus fundamental frequency may be created. This may include connecting the antenna 100 a device capable of measuring the impedance of an antenna (e.g., an SWR measurement tool), varying gl and g2, and measuring the fundamental frequency of the antenna. In operation, the fundamental frequency is to be changed, the desired frequency can then be "looked up" in the table and the corresponding distances gl, g2 determined. The drivers can then be actuated to cause the antenna 100 to include the required distances. Of course, the distances could also be expressed as a particular voltage provided to the actuators in other embodiments. In such a case, the measurement device 115 may not be needed may not be needed in operation, just in calibration.

[0028] In another embodiment, and as illustrated in FIG. 2, one or more of the resonator portions 102 may be divided into vertical portions as well. In FIG. 2 and elsewhere herein, horizontal and vertical shall refer to the directions shown as X and Z, respectively. Also, a portion is on top of or above another portion if it is displaced further the origin in the Z direction than the other portion and is below or under if it closer to the origin. In the illustrated embodiment, portion 202a is above or on top of portion 202b and portion 202b is under or below portion 202a. [0029] The vertical portions 202a, 202b are separated by a layer of a dielectric 204 with a low dielectric constant. The number of vertical portions 202a, 202b may be increased to many more than two in some instances. Such horizontal partitioning can be used to vary the range of resonant frequencies of a particular antenna. In such a case, each vertical portion 202a, 202b may be coupled to a unique actuator. This may allow of the use of smaller actuators to achieve more frequency variation. While the number of actuators increases, total cost may decrease as actuator size increases increase cost dramatically.

[0030] With reference now to FIGs. 3 and 4, an alternative embodiment of a tunable antenna 300 is disclosed. The disclosed embodiment includes a plurality of dielectric slices 302 (e.g., formed by slicing a dielectric ring). The slices 302 are separated at least partially from each other by fins 304. In the embodiments of FIGs. 3-4, the fins are formed of a metal such as copper of another material suitable for forming a ground plane.

[0031] The fins 304 may be coupled to a movement element (e.g., element 306) that can cause rotational motion of the fins 304 within gaps 310 between the slices 302. (An example of such an element is generally shown as element 504 in FIG. 5.) In this manner, the fundamental frequency can be changed. It has been discovered that a very small change in the position of the fins 304 relative to the slices 302 can cause a large change in fundamental frequency. In this manner, a very small actuator may be utilized to achieve large band antennas. In the illustrated embodiment, a rotary actuator may be utilized to cause the desired motion.

[0032] In one embodiment, a foam or other separating material may be displaced between the fins 304 and the slices 302. The foam 310 may be disposed between the both sides of the slices 302 and the fins 304 or just one. In one embodiment, the foam keeps the fin 304 in contact with one of the slices 302 forming a particular gap when no torque is applied to the fins 304/movement element 306.

[0033] FIG. 5 and 6 illustrate another embodiment of the present invention. This embodiment is similar to that shown in FIGs. 3 and 4 in that fins 304 are interspersed between slices 302. In this embodiment, however, the 304 are not the ground planes. Rather, the fins include metal or metal covered plastic (or other structural material). The ground plane metal 506 is fixed to the slices 302. In this embodiment, the electric field is generated by field generators 502 that are disposed, for example, on a central dividing element. As the slices are moved either rotationally (FIG. 5) or vertically (FIG. 6) as indicated by motion arrows C and D, respectively, the fundamental frequency of the antenna may vary. [0034] In the embodiment shown in FIG. 5, electrical ground is composed by horizontal (rounded) part show by element 504 at the bottom and the vertical relatively thick walls (e.g. slices 304) where the field generator 502 is placed. The field generator 502 is in contact with one of resonator slices and acts as an electric field exciter in contrast to the embodiments presented in FIG 1, 2, 4 where the coupling loop was coupled to magnetic antenna magnetic field. We notice here that metal plate 502 is connected to the central conductor of a coaxial line and electrically isolated from the slices 304.

[0035] Another difference in this embodiment is the fins 304 are metal but not part of ground. Rather, they are carried by element 504 which, in one embodiment, is non- conductive (e.g. plastic) and are isolated from each other and with no current paths in between. The arrangement preserves the antenna Q (high gain) and the radiation patterns (omnidirectional). In this embodiment one side of the metal fin is permanently in contact with the respective ceramic slice via metal shielded foam or any other simplified spring mechanism. A slight rotation of the plastic-metal block and the permanent contact side is pushed against the ceramic, releasing the other side where the air gap is created and changing the resonant frequency. In this embodiment the air gap will have z-dependent thickness, it will enhance almost linearly from 0 (top) to maximum (bottom). We notice here that the air gap sizes might be a bit different for different slices. It will not matter in the overall result because the frequency tuning will come as a collective effect from all gaps and not any of them in particular.

[0036] In the embodiment presented in FIG. 6 tuning is realized via vertical motion of the plastic-metal block. In this case the air gaps appear on both sides of the metal fin 302.

[0037] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

CLAIMS:

1. A tunable dielectric resonator antenna comprising:

a coupler in electrical communication with an input;

a ground plane coupled to an end of the coupler;

a first dielectric resonator at least partially surrounding the coupler; and

an actuator that moves the ground plane relative to an end of the first dielectric resonator to vary a fundamental frequency of the tunable dielectric resonator.

2. The antenna of claim 1, wherein the coupler is a wire.

3. The antenna of claim 1, wherein the dielectric resonator is formed of ceramic.

4 The antenna of claim 1, wherein the ground plane is an outer wall of a housing.

5. The antenna of claim 1, wherein the actuator is located within the housing.

6. The antenna of claim 1, further comprising a second dielectric resonator;

wherein the coupler includes a first coupler portion partially surrounded by the first dielectric resonator and a second coupler portion partially surrounded by the second dielectric resonator.

7. The antenna of claim 6, further comprising:

a housing having first and second outer walls;

wherein the first coupler portion includes an end electrically coupled to the first outer wall and the second coupler portion includes an end electrically coupled to the second outer wall.

8. The antenna of claim 7, further comprising:

a second actuator that moves the second outer wall relative to the second dielectric resonator.

9. The antenna of claim 1, wherein the first dielectric resonator is split into at least two sections, one disposed over the other.

10. A tunable dielectric resonator antenna comprising,

a plurality of dielectric resonator slices each separated from one another;

a plurality of metal fins, each fin being disposed between two different dielectric slices; and

an actuator that causes the fins to move relative to the dielectric resonator slices to vary a fundamental frequency of the antenna; and

a coupler that provides a signal to an area surrounded by the slices.

1 1. The antenna of claim 10, wherein the metal fins are rotated to vary the fundamental frequency.

12. The antenna of claim 10, wherein the metal fins are moved vertically relative to the slices to vary the fundamental frequency.

13. The antenna of claim 10, wherein the coupler is disposed in an area defined by the dielectric resonator slices.

14. The antenna of claim 10, wherein the coupler is metal plates carried by one of the fins.