HK1036364B - Flexible diversity antenna - Google Patents

Description

Flexible diversity antenna

Technical Field

The present invention relates generally to antennas, and more particularly to antennas for use in communication devices.

Background

Antennas for personal communication devices, such as radiotelephones, may not function adequately when in close proximity to the user during operation or when the user is moving during operation of the device. The movement of a user or a close object during radiotelephone operation can produce signal quality degradation or signal strength fluctuations, known as multipath fading. Diversity antennas have been designed to work in conjunction with the main antenna of a radiotelephone to improve signal reception.

Many popular handheld wireless telephones are being miniaturized. In practice many modern models are only 11 to 12 cm long. Unfortunately, as radiotelephones decrease in size, their internal space decreases accordingly. The reduction in internal space makes the bandwidth and gain requirements required for existing types of diversity antennas to achieve radiotelephone operation more difficult, as its size can be reduced accordingly.

One type of diversity antenna is known as a Planar Inverted F Antenna (PIFA). PIFAs are known by their name resembling the letter F and in particular include several layers of rigid material formed together to provide a radiating element having a conductive path therein. The layers and elements of a PIFA are typically mounted directly on a molded plastic or sheet metal support structure. Because of its rigidity, bending and forming the PIFA into its final shape for placement in the small area of a radiotelephone is somewhat difficult. In addition, PIFAs are prone to damage when the device in which they are installed is subjected to impact forces. Impact forces can fracture the layers of the PIFA and can impede operation or even cause failure.

Because of the generally non-planar design, various steps of stamping, bending, and etching may be required to manufacture the PIFA. Thus, fabrication and assembly are typically performed in a somewhat costly batch-type process. In addition, PIFAs typically use shielded signal feeds, such as coaxial cables, to connect the PIFA to the RF circuitry within the radiotelephone. Shielding the signal feed between the RF circuitry and the PIFA during assembly of the radiotelephone typically involves manual installation, which increases the cost of manufacturing the radiotelephone.

Summary of The Invention

It is therefore an object of the present invention to provide a PIFA that can be easily adapted to the internal area of a small communication device, such as a radiotelephone.

It is another object of the present invention to provide a PIFA that can have sufficient gain and bandwidth performance for use within a wireless telephone.

It is a further object of the present invention to provide a PIFA that is less susceptible to damage from impact forces to devices in which the PIFA is internally mounted.

It is another object of the present invention to simplify radiotelephone assembly and thereby reduce radiotelephone manufacturing costs.

These and other objects of the present invention are provided by a flexible diversity antenna which may have gain and bandwidth capabilities suitable for use in small communication devices such as radiotelephones. A core of flexible material, such as silicone, has electrical conductors embedded within it and is surrounded by a first layer of flexible dielectric material. At one end of the antenna, a first layer of dielectric material is surrounded by a conductive material, such as a copper or nickel fabric. The conductive material is flexible and replaces the rigid material elements commonly used in PIFAs.

The conductive material is preferably surrounded by a second layer of flexible dielectric material. The antenna parts surrounded by the conductive material function as tuning elements, while the antenna parts not surrounded by the conductive material function as radiating elements. Preferably, the electrical conductors within the core extend along a sinuous path between the radiating element and the tuning element.

A flexible signal feed is incorporated with the antenna and extends outwardly from the flexible core. The signal feed is electrically connected to an electrical conductor embedded within the flexible core. The signal feed is surrounded by a layer of flexible material, preferably the same material as the flexible core. The flexible material is surrounded by a layer of dielectric material. Surrounding the layer of dielectric material is a layer of conductive material that acts as a shield for the signal feed. The layer of conductive material may be surrounded by a layer of another dielectric material.

The operation for manufacturing the flexible diversity antenna having a predetermined impedance includes: forming a planar antenna element having an electrical conductor embedded in an elastomeric core, a first layer of dielectric material surrounding the elastomeric core, a portion of the first layer of dielectric material surrounded by conductive material, and a second layer of dielectric material surrounding the conductive material; and then folding the planar antenna element into a shape for assembly in an electronic device, such as a radiotelephone. The resilient core and the layers of material layered for stacking around the core are bent before folding the planar antenna element into a shape for assembly in an electronic device. During the bending operation, structuring of the surface of the second layer of dielectric material may be achieved.

The diversity antenna according to the invention can be manufactured in a planar structure, which can facilitate mass automated production. In addition, repetitive impedance characteristics can be obtained by selecting materials and controlling the thickness of the various material layers. Because of the use of flexible dielectric and conductive materials, the antenna can be formed in a variety of shapes to fit within a small area during radiotelephone assembly.

In contrast to known diversity antennas, the present invention is able to achieve gain and bandwidth for wireless telephone operation for a given size and location. Using the present invention, antenna designers have a greater degree of design flexibility than known diversity antennas. Additionally, conductive material may be selectively added to produce a stripline transmission line medium of controllable impedance over the antenna section.

Previous relatively rigid antenna assemblies PIFAs generally have not made them easily foldable to fit into the small space within a communication device. In contrast, diversity antennas according to the present invention have a flexible design, allowing the antenna to conform to the small space constraints of current wireless telephones and other communication devices. The flexible design of the present invention may also reduce the likelihood of damage caused by impact forces. In addition, the present invention eliminates the need for a separate coaxial cable to connect the antenna to the signal circuitry within the device in conjunction with an integrated, flexible signal feed. Thus, the assembly cost of the communication device, such as a radiotelephone, may be reduced.

Brief description of the drawings

Fig. 1 illustrates a typical PIFA used in a wireless telephone.

Fig. 2 is a plan view of a flexible PIFA according to aspects of the present invention.

Fig. 3 is a perspective view of the PIFA shown in fig. 2 illustrating a tuning section having a folded design.

Fig. 4 is a cross-sectional view of the PIFA illustrated in fig. 2 along line 4-4.

Fig. 5 is a cross-sectional view of the PIFA illustrated in fig. 2 taken along line 5-5.

Fig. 6 is a cross-sectional view of the PIFA illustrated in fig. 2 taken along line 6-6.

Fig. 7A and 7B schematically illustrate operations for manufacturing a flexible diversity antenna according to aspects of the present invention.

Detailed description of the invention

The present invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements.

As known to those skilled in the art, an antenna is a device for transmitting and/or receiving electrical signals. The transmitting antenna generally includes a feed assembly that senses or illuminates an aperture or reflective surface to radiate an electromagnetic field. The receive antenna generally includes an aperture or surface that focuses the incident radiation field onto a collection feed, producing an electronic signal proportional to the incident radiation. The amount of power received or radiated by the antenna depends on the aperture area and is described in terms of gain. The radiation pattern of an antenna is usually indicated using polar coordinates. The Voltage Standing Wave Ratio (VSWR) is related to the impedance matching of the antenna feed point to the feed line or transmission line. To radiate RF energy with minimal loss, or to transfer received RF energy to a receiver with minimal loss, the impedance of the antenna should be matched to the transmission line or feed impedance.

Radiotelephones typically employ a primary antenna that is operatively connected to a transceiver that is operatively associated with signal processing circuitry located on an internal printed circuit board. To maximize the power transferred between the antenna and the transceiver, the transceiver and antenna are preferably interconnected such that the respective impedances are substantially "matched," i.e., electrically tuned to filter out or compensate for undesired antenna impedance components to provide a 50 ohm (or desired) impedance value at the circuit feed.

As known to those skilled in the art, diversity antennas may be used in conjunction with a main antenna in a radiotelephone to prevent dropped calls due to fluctuations in signal strength. The signal strength may change as the user moves between cells in the cellular telephone network, the user wanders between buildings, interference from stationary objects, etc. Diversity antennas are designed to collect signals that the main antenna cannot collect by spatial, directional, bandwidth or gain diversity.

One type of diversity antenna known in the art is the Planar Inverted F Antenna (PIFA) and is illustrated in fig. 1. The illustrated PIFA10 includes a radiating element 12 in a spaced-apart relationship with a ground plane 14. The radiating element is also grounded at ground plane 14 as shown at 16. The powered RF connection 17 extends from the underlying circuit through the ground plate 14 to the radiating element 12 at 18. The PIFA is tuned to the desired frequency by adjusting the following parameters that can affect gain and bandwidth: changing the length of the radiating element 12; changing the gap H between the radiating element 12 and the ground plate 14; and varying the distance D between the grounded and powered RF connections. Other parameters known to those skilled in the art may also be adjusted to tune the PIFA and will not be discussed further.

Referring now to fig. 2, a planar diversity antenna 20 in accordance with a preferred embodiment of the present invention is illustrated. The antenna 20 has an F-shape and includes a tuning section 22 and an adjacent radiating section 24 as shown. The antenna 20 is preferably manufactured in a planar design as shown in fig. 2. Prior to assembly within a communication device, the flexible antenna is folded to conform to the interior space of the device.

Fig. 3 illustrates an antenna 20 having a tuning section 22 folded under a radiating element 24 so that the antenna has a suitable design for assembly within a particular communication device. Fig. 3 also illustrates a shielded flexible signal feed 28 oriented substantially transverse to the radiating element 24 so as to be in the proper orientation for connection with signal circuitry within a communication device. Flexible diversity antennas according to the present invention can be formed in a variety of shapes as needed to facilitate installation in various interior spaces of devices such as radiotelephones.

Referring to fig. 2, a continuous electrical conductor 26 extends between tuning element 22 and radiating element 24 and functions as an antenna element for transmitting and receiving electrical signals. In the illustrated embodiment, the electrical conductor 26 extends from the tuning element end 22a to the opposite radiating element end 24a in a curved shape.

A flexible shielded RF or microwave signal feed 28 is integrally connected to the radiating element 24 of the antenna 20 as shown. The shielded signal feed 28 has a similar structure to the radiating element 22, as will be described in detail below. An electrical conductor 30 is contained within the flexible signal feed 28 and has opposite ends 30a and 30 b. Electrical conductor 30 is electrically connected at end 30a to electrical conductor 26 of radiating element 24 at location 29, as shown. The opposite end 30b is preferably designed to be assembled to the circuit board by conventional connection techniques including soldering, displacement connectors, conductive elastomers, metal pressure contacts, and the like.

The flexible signal feed 28 may be designed in various orientations to facilitate assembly within wireless telephones and other electronic devices. Conventional diversity antennas typically require a shielded signal feed from the main circuit board in the radiotelephone. Coaxial cables are commonly used for this purpose. However, coaxial cables are relatively expensive and require manual assembly. The present invention is advanced because the shielded signal feed 28 is mounted as an integral part of the antenna 20.

Referring now to fig. 4, a cross-sectional view of the radiating element 24 of the antenna 20 of fig. 2 along the line 4-4 is illustrated. The electrical conductors 26 are enclosed within a flexible core 34. The flexible core is preferably formed of an elastomeric material such as silicone. Preferably, the flexible core is also formed of a dielectric material having a dielectric constant between 1.8 and 2.2. A first layer of flexible dielectric material 32 surrounds the elastomeric core 34 as shown. Preferably, the first layer of dielectric material has a dielectric constant between 1.8 and 2.2. The first layer of flexible dielectric material may be formed from a non-metal, a fabric, or a knitted fabric. Polyester or Liquid Crystal Polymer (LCP) fabrics capable of withstanding processing temperatures of 120 ℃ are exemplary dielectric materials for the first dielectric layer 32.

Referring now to fig. 5, a cross-sectional view of the tuning element 22 of the antenna 20 of fig. 2 along line 5-5 is illustrated. A layer of flexible conductive material 36 surrounds the first layer of dielectric material 32. The conductive material 36 is preferably a metallized fabric. The metallized fabric is preferably a material having high strength and high temperature handling capability. Exemplary metallized fabrics include, but are not limited to, polyester or Liquid Crystal Polymer (LCP) textiles with copper-plated fibers, followed by an outer layer of nickel; a nickel and copper fabric formed from metal-plated fibers or a metal-containing felt structure; carbon fiber fabrics formed from fiber or felt structures. Alternatively, the first layer of dielectric material 32 may be partially plated on the outer surface with a metallic conductive material.

Preferably, the metallized fabric 36 is laminated to the first layer of dielectric material 32 having a resilient material such as silicone. The silicone fills the voids of the metallized fabric to enhance the bending characteristics. As is known to those skilled in the art, silicone resins provide stable flexibility with high extensibility at various temperatures, particularly at low temperatures. The conductive material 36 may then be surrounded by a second layer of flexible dielectric material 38 as shown. The second layer of dielectric material 38 may be formed from a non-metallic polymer into a film, or a fabric or knitted fabric. A Polyetherimide (PEI) film, polyester, or Liquid Crystal Polymer (LCP) fabricated fabric that can withstand 120 deg. processing temperatures is an exemplary dielectric material for the second layer of dielectric material 38.

The thickness of the first and second layers of dielectric material 32, 38 may be varied during manufacture of the antenna 20 to produce a controlled characteristic impedance of the electrical conductor. Characteristic impedance (Z) of RF transmission line₀) Is calculated from the geometry and dielectric constant of the material (conductor width and dielectric thickness) that makes up the line. Due to the change in geometry from stripline to microstrip transmission lines. The thickness of the layer is adjusted for the desired impedance. A more rigid dielectric material may also be added to the first and second layers of dielectric material 32, 38 to control the flexibility of the antenna 20 or to modify the dielectric constant of the antenna. Polyetherimide (PEI) films may be used where high strength and good flexibility are required. As known to those skilled in the art, PEI closely matches the dielectric constant of silicone elastomers and bonds well to silicone and various outer coating materials. The bonding of the first and second dielectric layers 32, 38 may require the use of a heat activated adhesive film. Preferably, a fluoroethylene propylene (FEP) adhesive film is used for the TFE dielectric material, and a silicone film is used for the PEI dielectric material.

The antenna 20 may be subjected to a curing process to cure the silicone or other elastomeric material used for the core 34 and to laminate the layers of material surrounding the core together. The curing process is generally carried out as recommended by the manufacturer of the bonding system used. For example: the FEP film is tacky at a temperature greater than or equal to 235 ℃; the silicone elastomer heat-curable adhesive is bondable at a temperature greater than or equal to 120 ℃; or the pressure-cured silicone elastomer adhesive may be given an accelerated bond at a temperature greater than or equal to 90 ℃. Pressure is applied through the rigid support plate as is common with adhesives that adhere to sheet materials. The surface between the material to be bonded and the support plate may be filled with a suitable resilient gasket. The compliance of the elastomeric pad helps create a seamless bonded surface. The nature or surface texture of the elastomeric patch may be used to create fold lines or bend relief points that aid in the final assembly of the antenna.

The second layer of dielectric material 38 may include surface texturing to distribute bending stresses evenly across the cross-section of the antenna 20. The score may be formed by a pressure pad used in the curing process. Pressure is applied during curing to ensure that the silicone fills the interstices between the fibers within the conductive material 36.

Referring now to fig. 6, a cross-section of the transition between the radiating portion 24 and the tuning portion 22 of the antenna 20 of fig. 2 along line 6-6 is illustrated. In the illustrated embodiment, the second dielectric layer 38 terminates just beyond the termination point of the conductive material 36. However, the second dielectric layer 38 may extend further onto the first layer of dielectric material 32. Extending the second dielectric layer 38 over the first layer of dielectric material 32 may be used to create a more uniform thickness transition (to aid in adhesion handling) or to create more rigidity in the transition portion (to aid in final assembly bending). A similar design may exist at the transition between the signal feed 28 and the radiating element 24.

A relatively rigid outer layer of material (not shown) may be used to form the environmentally compliant outer surface of the antenna 20. Various materials that may be used for the outer layer include, but are not limited to, FEP. It is desirable that the outer layer of material be resistant to abrasion or other causes of abrasion.

The operation of manufacturing a flexible diversity antenna according to the present invention is schematically illustrated in fig. 7A and 7B. A planar antenna is formed (block 100) and then folded for assembly in an electronic device (block 200). The operation of forming the planar antenna includes embedding electrical conductors in a flexible core (block 102), preferably of a meander design. The elastomeric core is then surrounded by a first layer of dielectric material (block 104). A portion or portions of the first layer of dielectric material are surrounded by the conductive material to tune the antenna to a predetermined impedance (block 106). A shielded signal feed is integrally formed with and extends outwardly from the antenna (block 108). The elastomeric core and the material used to bond the dielectric and conductive layers to the core are cured using curing techniques known to those skilled in the art, including but not limited to air curing, thermal curing, infrared curing, microwave curing, and the like (block 110). A surface texture may be created on the second layer of dielectric material during the curing process (block 112).

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims (22)

1. A diversity antenna, comprising:

a flexible silicone core surrounded by a first layer of flexible dielectric material and having ends;

a first layer of flexible conductive metallized fabric surrounding said first layer of flexible dielectric material at one of said ends;

an electrical conductor embedded within said flexible core and extending between said ends; and

an integral flexible signal feed extending outwardly from said flexible core, said signal feed being electrically connected to said electrical conductor embedded within said flexible core.

2. A diversity antenna according to claim 1,

wherein the first layer of flexible conductive metalized fabric is surrounded by a second layer of flexible dielectric material.

3. A diversity antenna according to claim 1,

wherein the electrical conductor has a curved design throughout the flexible core.

4. A diversity antenna according to claim 1,

wherein the metallized fabric is laminated over the first layer of flexible dielectric material having a silicone elastomer.

5. A diversity antenna according to claim 2,

wherein the first and second layers of flexible dielectric material have a dielectric constant between 1.8 and 2.2.

6. A diversity antenna according to claim 1,

the flexible silicone core has a dielectric constant between 1.8 and 2.2.

7. A diversity antenna according to claim 2,

wherein the first and second layers of flexible dielectric material comprise polyetherimide films.

8. A diversity antenna according to claim 1, further comprising:

a layer of flexible material surrounding the signal feed; the outer surface of the flexible material is surrounded by three layers of materials which are sequentially from inside to outside:

a flexible dielectric material layer, a flexible conductive metalized fabric layer, and a flexible dielectric material layer.

9. A flexible diversity antenna comprising:

a flexible silicone core surrounded by a first layer of flexible dielectric material having portions with an outer surface coated with a conductive metallized fabric and having ends;

an electrical conductor embedded within said flexible core and extending between said ends; and

a signal feed extending outwardly from said flexible core, said signal feed being electrically connected to said electrical conductor embedded within said flexible core.

10. A flexible diversity antenna according to claim 9 further comprising a second layer of flexible dielectric material surrounding said portion of said first layer of flexible dielectric material plated with conductive material.

11. A flexible diversity antenna according to claim 9 wherein said electrical conductor has a meandering configuration through said flexible core.

12. A flexible diversity antenna according to claim 9, further comprising:

a flexible layer of material surrounding said signal feed; the outer surface of the flexible material is surrounded by three layers of materials which are sequentially from inside to outside:

a flexible dielectric material layer, a flexible conductive metalized fabric layer, and a flexible dielectric material layer.

13. A wireless telephone comprising:

a radiotelephone housing;

a circuit board disposed in the housing;

a flexible diversity antenna disposed in the housing, the flexible diversity antenna comprising:

a flexible silicone core surrounded by a first layer of flexible dielectric material and having ends;

a first conductive metallized textile layer surrounding one of said end portions; and

an electrical conductor embedded within said flexible core and extending between said ends; and

a signal feed extends outwardly from the diversity antenna and electrically connects the electrical conductor embedded within the flexible core to the circuit board.

14. A radiotelephone according to claim 13 wherein said first conductive metallized textile layer is surrounded by a second layer of flexible dielectric material.

15. A radiotelephone according to claim 13 wherein said electrical conductor has a curved design through said flexible core.

16. A radiotelephone according to claim 13 wherein said metallized fabric is laminated to said first layer of flexible dielectric material having a silicone elastomer.

17. A radiotelephone according to claim 13 further comprising:

a flexible layer of material surrounding said signal feed; the outer surface of the flexible material is surrounded by three layers of materials which are sequentially from inside to outside: a flexible dielectric material layer, a flexible conductive metalized fabric layer, and a flexible dielectric material layer.

18. A method of manufacturing a flexible diversity antenna having a predetermined impedance, the method comprising the steps of:

forming a planar antenna having an electrical conductor embedded in a flexible silicone core, a first layer of flexible dielectric material surrounding the flexible silicone core, a portion of the first layer of flexible dielectric material being surrounded by a conductive metallized cloth and a second layer of flexible dielectric material surrounding said conductive metallized cloth; and

folding a planar antenna into a shape for assembly within an electronic device;

wherein the step of forming the planar antenna comprises forming an integral shielded signal feed extending outwardly from the flexible core, wherein the signal feed is electrically connected to the electrical conductor embedded within the flexible core.

19. A method according to claim 18, wherein said step of forming a planar antenna comprises embedding a meander-shaped electrical conductor throughout the flexible core.

20. A method according to claim 18, further comprising the step of curing the flexible core prior to said step of folding the planar antenna into a shape for assembly within the electronic device.

21. A method according to claim 18 wherein the metallized fabric is laminated to a first layer of flexible dielectric material having a silicone elastomer.

22. A method according to claim 20, wherein said step of curing the flexible core comprises forming a surface texture on the second layer of flexible dielectric material.