Micro-internal antenna

Information

  • Patent Grant
  • 6342860
  • Patent Number
    6,342,860
  • Date Filed
    Friday, February 9, 2001
    23 years ago
  • Date Issued
    Tuesday, January 29, 2002
    22 years ago
Abstract
A Planar Inverted F Antenna (PIFA) is disclosed comprising a radiating element and a ground plane positioned on a bottom cover. A Radome is positioned over the radiating element and the ground plane with the bottom cover and the Radome enclosing the radiating element and the ground plane. The ground plane is positioned below the radiating element and a conductive shorting strip extends between one end of the radiating element and one end of the ground plane. A feed lead extends from one side of the radiating element and has a base portion which protrudes outwardly of the Radome for connection to the center conductor of a RF power feeding cable. The radiating element includes a first horizontally disposed portion, a second horizontally disposed portion, and a substantially vertically disposed portion extending therebetween. The first substantially vertically disposed portion of the radiating element functions as a first capacitive loading plate with the second horizontally disposed portion of the radiating element functioning as a second capacitive loading plate. A dielectric block is positioned between the second horizontally disposed portion of the radiating element for providing dielectric loading to the radiating element.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to a Planar Inverted F Antenna (PIFA) and in particular to a method of designing a single band PIFA as an encapsulated module with a localized ground plane and multiple external lead contacts for easy integration to the chassis of a radio communication device.




2. Description of the Related Art




With the rapid progress in wireless communication technology and the ever-increasing emphasis for its expansion, wireless modems on laptop computers and other handheld radio devices will be a common feature. The technology using a short-range radio link to connect devices such as cellular handsets, laptop computers and other handheld devices has already been demonstrated [Wireless Design On-line Newsletter, Vol. 3, Issue 5, Nov. 22, 1999]. The ISM band (2.4-2.5 GHz) is the allocated frequency band for such applications. The performance of the antenna placed on devices like a cellular handset or a laptop computer is one of the critical parameters for the satisfactory operation of such a radio link. Therefore the performance characteristics of the antenna located on communication devices assumes significant importance in the evolving technology of wireless modems.




Recently, in the cellular communication industry, there has been an increasing emphasis on internal antennas instead of conventional external wire antennas. The concept of an internal antenna stems from the avoidance of a protruding external radiating element by the integration of the antenna into the device itself. Internal antennas have several advantageous features such as being less prone to external damage, a reduction in overall size of the handset with optimization, and easy portability. In most internal antenna designs, the printed circuit board of the communication device serves as the ground plane of the internal antenna. Among the various choices for internal antennas, a PIFA appears to have great promise. The PIFA is characterized by many distinguishing properties such as relative light weight, ease of adaptation and integration into the device chassis, moderate range of bandwidth, Omni-directional radiation patterns in orthogonal principal planes for vertical polarization, versatility for optimization, and multiple potential approaches for size reduction. The PIFA also finds useful applications in diversity schemes. Its sensitivity to both vertical and horizontal polarization is of immense practical importance in mobile cellular/RF data communication applications because of absence of the fixed antenna orientation as well as the multi-path propagation conditions. All these features render the PIFA to be a good choice as an internal antenna for mobile cellular/RF data communication applications.




A conventional prior art single band PIFA assembly


100


is illustrated in

FIGS. 9 and 10

. The PIFA


100


shown in

FIG. 9 and 10

consists of a radiating element


101


, a ground plane


102


, a power feed hole


103


is located corresponding to the radiating element


101


, a connector feed pin


104


, and a conductive post or pin


105


. The connector feed pin


104


serves as a feed path for radio frequency (RF) power to the radiating element


101


. The connector feed pin


104


is inserted through the feed hole


103


from the bottom surface of the ground plane


102


. The connector feed pin


104


is electrically insulated from the ground plane


102


where the pin passes through the hole in the ground plane


102


. The connector feed pin


104


is electrically connected to the radiating element


101


at


106


with solder. The body of the feed connector


107


is electrically connected to the ground plane


102


at


108


with solder. The connector feed pin


104


is electrically insulated from the body of the feed connector


107


. A through hole


109


is located corresponding to the radiating element


101


, and a conductive post or pin


110


is inserted through the hole


109


. The conductive post


110


serves as a short circuit between the radiating element


101


and the ground plane


102


, The conductive post


110


is electrically connected to the radiating element


101


at


111


with solder. The conductive post


110


is also electrically connected to the ground plane


102


at


112


with solder. The resonant frequency of the PIFA


100


is determined by the length (L) and width (W) of the radiating element


101


and is slightly affected by the locations of the feed pin


104


and the conductive post or shorting pin


110


. The impedance match of the PIFA


100


is achieved by adjusting the diameter of the connector feed pin


104


, by adjusting the diameter of the conductive shorting post


110


, and by adjusting the separation distance between the connector feed pin


104


and the conductive shorting post


110


.




In the prior art techniques of PIFA design (Murch R. D. et al, U.S. Pat. No. 5,764,190; Korisch I. A., U.S. Pat. No. 5,926,139) the center conductor of the coaxial cable from the RF source is directly connected to the radiating element of the PIFA at the feed point. Further, in all these designs, the feed point of the PIFA is always drawn away from the shorted edge of the radiating element and is located within the central surface of the radiating element. Therefore, the feed cable from the RF source has to pass through the interior region (between the radiating element and the ground plane) of the PIFA. Such a prior art-feeding scheme of the PIFA will prove to be tedious and cumbersome in the final integration process. An alternative scheme of a PIFA design that circumvents such a tedious feed assembly is always desirable. From the structural and fabrication point of view, an avoidance of a feed cable extending through the interior region of the PIFA is preferred. This invention described hereinafter provides an encapsulated PIFA module in which the feed assembly is confined to the exterior of the module and hence overcomes the existing shortcomings in the final integration process of the prior art.




Keeping in pace with the rapid progress in mobile cellular communication technology, the future design of the cellular handset shall have the provision of more than one antenna to fulfill the additional requirement of BlueTooth (BT) applications. The placement of the additional internal antenna should be accomplished without necessitating any change in the overall size of the handset. The consideration of mutual coupling often warrants the placement of the cellular and BT antennas at different locations on the device chassis with a very small volume earmarked for the BT antenna. In cellular communication applications, multiple antennas may be required to utilize the phone chassis as a common ground plane. In such an application., the internal BT antenna will be an integral part of device chassis. Therefore such an additional internal antenna (for BT applications) such as a PIFA should have the desirable feature of simplified adaptability to the device chassis. A design of such an internal PIFA as a separate module with surface mountable features will be of great importance to facilitate a much simplified integration process.




SUMMARY OF THE INVENTION




A compact, lightweight, single band PIFA has been designed in an encapsulated modular form. The present invention emphasizes the feed assembly of the PIFA confined only to the exterior of the module. In the instant invention, one of the external leads of the encapsulated PIFA module facilitates the connection of the feed point of the PIFA to the RF source point of the radio device. The localized ground plane of the PIFA and the ground potential of the chassis of the radio device are connected by the other external leads.











BRIEF DESCRIPTION OF THE DRAWING





FIG. 1

is a perspective view of a cellular telephone handset having the micro-internal antenna of this invention mounted therein;





FIG. 2

is a perspective view of the antenna of this invention mounted on a chassis;





FIG. 3

is a partial exploded perspective view of the first embodiment of the antenna of this invention;





FIG. 4

is a partial perspective view of the antenna of

FIG. 3

without the Radome;





FIG. 5

is a frequency response chart that depicts the characteristics of the VSWR of the antenna of

FIG. 4

;





FIG. 6

is a perspective view of a second embodiment of the invention;





FIG. 7

is an exploded perspective view of the antenna of

FIG. 6

;





FIG. 8

is a frequency response chart that depicts the characteristics of the VSWR of the antenna of

FIG. 6

;





FIG. 9

is a top view of a prior art antenna; and





FIG. 10

is a partial sectional view as seen on lines


10





10


of FIG.


9


.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




In

FIG. 1

, the numeral


8


refers to a conventional cellular telephone handset including a chassis


9


. In the accompanying text, the numeral


10


refers to the first embodiment of an encapsulated single band PIFA, as seen in

FIGS. 2-4

. The PIFA


10


includes a radiating element


11


that is located above a ground plane


12


. An external metallic lead


14


, which is a feed tab of the PIFA, serves as an electrical path for radio frequency (RF) power to the radiating element


11


. The feed tab or lead


14


is electrically insulated from the local ground plane


12


by means of the notch


15


formed in the ground plane


12


. The notch


15


formed in the ground plane


12


of the PIFA


10


is such that the feed tab


14


does not touch the ground plane


12


. The feed tab


14


is also electrically insulated from the chassis


9


of the device by means of the notch


16


formed in the device chassis


9


. The location and the size of the notch


16


on the device chassis


9


are such that the base


17


of the feed tab


14


does not touch the device chassis


9


(FIG.


2


). The notch


16


on the device chassis


9


is realized by the removal of the metallization of the chassis over the area underlying the base


17


of the feed tab


14


. The top end of the feed tab


14


is electrically connected to the radiating element


11


at


18


. A conductive strip


19


serves as a short circuit between the radiating element


11


and ground plane


12


. The conductive strip


19


is electrically connected to the radiating element


11


at


20


arid is electrically connected to the ground plane


12


at


21


. The radiating element


11


is bent 90° at


22


to form a vertical plane


23


. The vertical plane


23


is again bent 90° at


24


to form a lower horizontal plane


25


. The horizontal plane


25


is at a specific distance above the ground plane


12


. The horizontal plane


25


serves a capacitive loading plate for the radiating element


11


. The Radome


26


, which encapsulates the PIFA


10


, includes two separate parts with identical dielectric material property. The top cover


27


of the Radome


26


fully encloses the radiating element


11


and the local ground plane


12


of the PIFA


10


. The top cover


27


of the Radome


26


is designed to have a combination of a flat planar contour


28


and an inclined planar contour


29


resulting in a wedge shaped geometry along


30


. The surface of the top cover


27


of the Radome


26


with flat planar contour


28


is flush with the unbent portion of the radiating element


11


. The surface of the top cover


27


with an inclined planar contour


29


is designed so as to enclose the vertical section


23


and lower horizontal section


25


of the radiating element


11


. The bottom cover


31


of the Radome


26


comprises a flat surface designed to be in flush with the lower surface of the ground plane


12


of the PIFA. The bottom cover


31


of the Radome


26


, the ground plane


12


of the PIFA


10


, the radiating element


11


of the PIFA and the top cover


27


of the Radome


26


are held together at specified height and locations through the two supporting dielectric blocks


32


and


33


. The supporting dielectric block


32


connects the bottom cover


31


and the top cover


27


of the Radome


26


at


34


and


35


, respectively, The supporting dielectric block


32


, while connecting the bottom cover


31


and top cover


27


, passes through a close fitting hole


36


on the ground plane


12


as well as a close fitting hole


37


on the radiating element


11


. The supporting dielectric block


33


holds the lower horizontal section


25


of the radiating element


11


at a predetermined height from the ground plane


12


. The supporting dielectric block


33


with base


38


on the bottom cover


31


passes through a close fit hole


39


on the ground plane


12


and extends vertically up to touch the lower horizontal section


25


of the radiating element


11


.




The integration of the encapsulated module of the PIFA


10


to the device chassis


9


is carried out in two steps (FIG.


4


). In the first step, the PIFA module is placed at the desired location on the device chassis


9


and the external metallic tabs


40


and


41


of the PIFA module are connected to the device chassis


9


at


42


and


43


by solder. In the second step, the center conductor


44


of the RF input cable


45


is connected to the base


17


of the external feed tab


14


at


46


. The outer conductor


47


of the RF input cable


45


is soldered at numerous pre-selected locations on the device chassis


9


to prevent any radiation from the cable. The inner conductor


44


and the outer conductor


47


of the cable


45


are separated from the insulator


48


of the cable


45


.




The PIFA


10


configuration illustrated in

FIGS. 2-4

functions as an encapsulated single band PIFA. The dimensions of the radiating element


11


, the vertical plane


23


, the lower horizontal plane


25


, the location of the shorting strip


19


, the width of the shorting strip


19


, the material property of the Radome


26


and the relative position of the PIFA


10


on the device chassis


9


are the prime parameters that control the resonant frequency of the PIFA. The bandwidth of the single band PIFA


10


is determined by width of the feed tab


14


, the location of the feed tab


14


, the location of the shorting strip


13


, the width of the shorting strip


19


, the material property of the Radome


26


, and the linear dimensions of the radiating element


11


including the height of the PIFA. The measured resonant frequency is lower than the resonant frequency of the PIFA with only the radiating element


11


alone. The lowering of the resonant frequency of the PIFA


10


is due to the capacitive loading offered by the vertical plane


23


and lower horizontal plane


25


. Further reduction of the resonant frequency is due to the dielectric loading caused by the encapsulation of the entire PIFA


10


within Radome


26


.




In its final configuration ready for the integration (FIGS.


2


and


4


), the encapsulated PIFA


10


module will have three external leads protruding out of the Radome


17


. The RF power input cable


45


is easily assembled to the PIFA module by connecting the center conductor


44


of the cable


45


to the protruding base


17


of the feed tab


14


through a solder connection (FIG.


2


). The PIFA


10


module can easily be adapted to the device by connecting the external tabs


40


and


41


to the device chassis


9


at


42


and


43


, respectively, by solder (FIG.


4


). Thus, the proposed modular design of PIFA


10


of this invention greatly simplifies the task of integration of the PIFA to the device. Further, it can easily be inferred that the design of the PIFA


10


module has the distinct advantage of feed assembly which is confined only to the exterior dimensions of the module. The suggested modular design of this invention circumvents the hitherto imposed shortcoming of the feed assembly (cable) passing through the interior region of the PIFA. The result of the tests conducted on the single band PIFA


10


, illustrated in

FIGS. 2-4

, referred to as the first embodiment of this invention, is shown in FIG.


5


.

FIG. 5

illustrates the VSWR plot of the single band PIFA


10


resonating in the ISM band (2400-2500 MHz). The dimensions of the single band PIFA


10


are: Length=16 mm, Width=5.5 mm and Maximum Height=4.5 mm. The projected semi-perimeter of the single band PIFA


10


is 21.5 mm as compared to the semi-perimeter of 30.61 mm of a conventional single band PIFA


110


resonating in the ISM band.




The second embodiment of the invention is illustrated in

FIGS. 6 and 7

. The single band PIFA


50


illustrated in

FIGS. 6 and 7

is similar to the PIFA


10


, but has an additional slot


51


formed in the radiating element


11


(FIG.


7


). Further, there is a dielectric block


52


of pre-desired dielectric constant placed between the lower horizontal section


25


and the ground plane


12


. The supporting block


33


passes through a tight fit hole


53


on the dielectric block


52


in addition to passing through the tight fit hole


39


on the ground plane


12


. Also, the external leads


40


and


41


of PIFA


50


, for connecting the ground plane


12


of the PIFA


10


to the device chassis


9


, are absent. Therefore, the ground plane


12


of the PIFA


50


module is not connected to the ground potential of the device chassis


9


resulting in the physical isolation of the PIFA


50


from the device chassis


9


. As a consequence, the effective size of the ground plane for the optimum performance of the PIFA


50


is merely the size of the localized ground plane


12


itself. This is in contrast to the relatively large effective ground plane for the PIFA


10


of the first embodiment of this invention where the localized ground plane


12


of the PIFA


110


is directly connected to the device chassis


9


. Therefore, the significant feature of the design of PIFA


50


is the extremely small size of the ground plane


12


. In actuality, the size of the ground plane


12


is comparable to the linear dimensions of the radiating element


11


of the PIFA


50


. The size of the ground plane


12


has significant effect on the resonance characteristics and the gain performance of the PIFA. To achieve the resonance in the ISM band despite the miniaturization both in size of the PIFA


50


and the size of the ground plane


12


, the dielectric loading of the PIFA


20


has also been incorporated through the dielectric block


52


. Provision has been made for connecting the outer conductor


47


of the RF input cable


45


to the external tab


54


to offer a ground potential to the PIFA


50


. The external tab


54


is a protrusion of the ground plane


12


of the PIFA


50


. All the other elements of the single band PIFA


50


illustrated in

FIGS. 6 and 7

are identical to the single band PIFA


10


illustrated in

FIGS. 2-4

which has already been explained while covering the first embodiment of this invention. Further redundant explanation of the single band PIFA


50


illustrated in

FIGS. 6 and 7

will therefore be omitted.




The slot


51


is positioned between the vertical plane


23


and the shorting strip


19


and is located corresponding to a position on the radiating element


11


of the PIFA


50


as illustrated in FIG.


7


. The choice of the location of the slot


51


illustrated in

FIG. 7

has been with a specific purpose to offer reactive loading effect to the radiating element


11


. Hence the size and position of the slot


51


will control the resonant frequency of the PIFA


50


. In its final configuration ready for the integration (FIGS.


6


and


7


), the encapsulated PIFA


50


module will have two external leads protruding out of the Radome


26


. The RF power input cable


45


is easily assembled to the PIFA module by connecting the center conductor


44


of the cable


45


to the protruding base


17


of the feed tab


14


through a solder connection (FIG.


7


). The shield (outer conductor)


47


of the cable


45


is soldered to the protruding external tab


54


. From this, it can easily be inferred that the design of the PIFA


50


module has the distinct advantage of feed assembly, which is confined only to the exterior dimensions of the module. The suggested modular design of this invention circumvents the hitherto imposed shortcoming of the feed assembly (feed cable) passing through the interior region of the PIFA. The result of the tests conducted on the single band PIFA


50


illustrated in

FIGS. 6 and 7

referred to as the second embodiment of this invention is shown in FIG.


8


.

FIG. 8

illustrates the VSWR plot of the single feed multi-band PIFA


50


resonating in the ISM band (2400-2500 MHz). The dimensions of the single band PIFA


50


are: Length=16 mm, Width=5.5 mm and Maximum Height=4.5 mm. The projected semi-perimeter of the multi-band PIFA


50


is 21.5 mm as compared to the semi-perimeter of 30.61 mm of a conventional single band PIFA


110


resonating in the ISM band only.




As can be seen from the foregoing discussions, a novel scheme to design a single band PIFA in a modular form has been proposed and demonstrated. The suggested design of the PIFA in a modular form has the distinct advantage and the desirable feature of easy and much simplified integration to the device chassis. In the PIFA designs of this invention, the feed assembly is confined only to the exterior of the module resulting in enhanced fabrication ease. The proposed design also overcomes the tedious feed assembly of the prior art techniques of the PIFA design. The radiating element, the shorting strip, the feed tab, and the ground plane of the PIFA are so configured to facilitate the formation of the PIFA in one process of continues and sequential bending of a single sheet of metal resulting in improved manufacturability. The resonance of the PIFA in ISM band has been achieved without increasing the effective area of antenna, thereby accomplishing the miniaturization of the size of the PIFA. The concept of the slot loading technique and the partial dielectric loading has also been invoked in this invention to achieve the reduction of resonant frequency of the PIFA without increasing the size of the PIFA. The concept of partial dielectric loading involving the dielectric block over a small and selective area of the PIFA reduces the weight and cost of the PIFA. The partial dielectric loading also results in a relative reduction of the dielectric loss and hence contributes to the enhanced radiation efficiency of the PIFA. The encapsulated single band PIFA


10


and PIFA


50


as of this invention are lightweight, compact, cost-effective and easy to manufacture.




Thus the novel design technique of encapsulated single band PIFA in a modular form of this invention has accomplished at least all of its stated objectives.



Claims
  • 1. A Planar Inverted F Antenna (PIFA), comprising:a bottom cover; a radiating element having first and second ends, first and second sides, and upper and lower ends; a ground plane positioned below said radiating element having first and second ends, first and second sides, and upper and lower ends; said radiating element and said ground plane being positioned on said bottom cover; a conductive shorting strip extending between said first end of said radiating element and said first end of said ground plane; a feed lead extending from said first side of said radiating element; and a Radome positioned over said radiating element and said ground plane; said bottom cover and said Radome enclosing said radiating element and said ground plane; said feed lead having a base portion protruding outwardly of said Radome for connection to the center conductor of a RF power feeding cable.
  • 2. The PIFA of claim 1 wherein said radiating element includes a first horizontally disposed portion, a second horizontally disposed portion, and a substantially vertically disposed portion extending therebetween.
  • 3. The PIFA of claim 2 wherein said first substantially vertically disposed portion functions as a first capacitive loading plate of said radiating element.
  • 4. The PIFA of claim 3 wherein said second horizontally disposed portion functions as a second capacitive loading plate of said radiating element.
  • 5. The PIFA of claim 4 wherein said first horizontally disposed portion has a reactive loading slot formed therein.
  • 6. The PIFA of claim 5 wherein said reactive loading slot is formed in said first horizontally disposed portion between said vertically disposed portion and said shorting strip.
  • 7. The PIFA of claim 6 wherein a dielectric block is positioned between said second horizontally disposed portion of said radiating element at said ground plane for providing dielectric loading to said radiating element.
  • 8. The PIFA of claim 7 wherein said radiating element, said shorting strip, and said ground plane are of one-piece construction.
  • 9. The PIFA of claim 1 wherein said radiating element, said shorting strip, and said ground plane are of one-piece construction.
  • 10. The PIFA of claim 1 wherein a pair of tabs extend from said ground plane outwardly of said Radome for connection said ground plane to the chassis of the device in which said PIFA is being used.
  • 11. The PIFA of claim 1 wherein a tab extends from said ground plane outwardly from said Radome for connection to a RF cable.
US Referenced Citations (3)
Number Name Date Kind
5455596 Higashiguchi et al. Oct 1995 A
5550554 Erkocevic Aug 1996 A
6005524 Hayes et al. Dec 1999 A