Tunable PIFA antenna

[0002] 1. Field of the Invention

[0003] The present invention relates to a planar inverted F antenna (PIFA) for wireless communication devices such as wireless modems, cellular telephones, personal digital assistants, etc. More particularly, the present invention relates to the method of mechanically tuning the resonant frequency and/or the antenna input impedance of the antenna.

[0004] 2. Description of the Related Art

[0005] A planar inverted F antenna continues to be used in various wireless communication devices, which are made in different packages using different printed circuit boards (PCBs). This means that the antenna has to be redesigned for every single application, thus reducing the benefits of high-volume manufacturing. However, if there was a way of mechanically tuning the same basic antenna design to the different package/PCB combinations, then that same antenna design could be used in various applications with reduced unit cost of manufacturing it. To the best of applicants' knowledge, no such mechanical tuning mechanisms for PIFA antennas have been proposed so far.

[0006] A method of tuning a PIFA antenna by adjusting the volume and proximity of a dielectric material to the feed and shorting pins and/or capacitive-loading plates of the antenna is described. The present invention permits the antenna to be tuned to suit variations in applications such as where the ground plane varies in size or where there is a frequency shift required due to the different materials used to make the chassis in which the antenna is mounted. In one embodiment of the invention, the PIFA antenna includes a movable tuning member in the form of a selectively rotatable rotor having a semi-circular rotor vane provided thereon. In another embodiment, a selectively movable block or slug is utilized as the movable tuning member. In still another embodiment of the invention, the frame which supports the movable tuning members in the other embodiments has a slot molded thereinto. The size and position of the slot can be altered, thereby providing a range of antennas based on the same patch and mold tool.

[0007] A principal object of the invention is to provide a means of selectively varying or changing the resonant frequency and/or input impedance of an antenna without having to redesign and make a new antenna.

[0008] A further object of the invention is to provide a single antenna which can cover a wider frequency range than was previously available.

[0009] Still another object of the invention is to provide an antenna wherein it is possible to replace a number of antennas with a single selectively variable design, thereby reducing unit cost in volume manufacturing as well as the antenna design time.

[0010] These and other objects will be apparent to those skilled in the art.

[0011] FIG. 1 is a perspective view of a cellular telephone having the tunable PIFA antenna mounted therein;

[0012] FIG. 2 is a perspective view illustrating the tunable PIFA antenna;

[0013] FIG. 3 is a perspective view of the antenna of FIG. 2;

[0014] FIG. 4 is an exploded perspective view of the antenna of FIGS. 2 and 3;

[0015] FIG. 5 is a perspective view of a second embodiment of the tunable antenna;

[0016] FIG. 6 is an exploded perspective view of the antenna of FIG. 5;

[0017] FIG. 7 is a perspective view of a third embodiment of the tunable antenna;

[0018] FIG. 8 is an exploded perspective view of the tunable PIFA antenna of FIG. 7;

[0019] FIG. 9 is a perspective view of a fourth embodiment of the tunable antenna;

[0020] FIG. 10 is an exploded perspective view of the antenna of FIG. 9;

[0021] FIG. 11 is a perspective view of a fifth embodiment of the tunable antenna;

[0022] FIG. 12 is an exploded perspective view of the antenna of FIG. 11; and

[0023] FIG. 13 is a partial side view of the antenna of FIG. 11.

[0024] One embodiment of the PIFA antenna is referred to by the reference numeral 10 while other embodiments of the PIFA antenna will be referred to by the reference numerals 10′, 10″, 10′″, and 10″″. Inasmuch as antennas 10′, 10″, 10′″, and 10″″ are identical to antenna 10 except for the design of the tunable portion of the antenna, only antenna 10 will be described in detail with “′”, “″”, “′″”, and “″″”, referring to identical structure on antennas 10′, 10″, 10′″, and 10″″, respectively.

[0025] In the drawings, the numeral 11 refers to the printed circuit board (PCB) in a wireless communication device which may be a cellular telephone, laptop computer, modem, personal digital assistant, etc, which is generally indicated by the reference numeral 12. The PIFA antenna 10 includes a carrier frame 14 having support legs 16 extending therefrom. A circular recess 18 is formed in frame 14 as is a circular opening 20. The numeral 22 refers to a movable tuning member which includes a rotor 24 having a screwdriver slot 26 formed in one end thereof. The other end of rotor 24 is rotatably received by the opening 20, as seen in FIGS. 3 and 4. A semi-circular rotor vane 28 is provided on rotor 24 for rotation therewith. Rotor vane 28 is constructed of a high-dielectric constant material. Patch 30 is positioned over frame 14 so that the end of the rotor 24 having the screwdriver slot 26 formed therein protrudes through opening 32 of patch 30. Patch 30 includes a feed pin 34 and a ground pin 36 which are soldered or otherwise electrically connected to PCB 11 in conventional fashion. Frame 14 is mounted on the PCB 11 by solder, clips, screws, or such other means as may be convenient.

[0026] The rotor vane 28 is shaped such that when the rotor 24 is rotated, there is a variation in mass and proximity of dielectric material to the feed pin 34 and ground pin 36. The effect of this variation is to vary the frequency response of the PIFA antenna 10. Thus, PIFA 10 is provided with a way of tuning the resonant frequency and/or the antenna input impedance thereof. The design of PIFA 10 enables the antenna to replace a range of antennas with a single design with the single design having the capability of being selectively adjusted to meet the requirements of a specific design.

[0027] PIFA antenna 10′ varies somewhat from the design of PIFA antenna 10 in that the movable tuning member 22 of PIFA antenna 10 has been replaced by a selectively slidable toothed block or slug 38. In PIFA 10′, the frame 14′ has a toothed slot 40 formed therein which communicates with the opening 42 formed in patch 30′. The teeth 44 on block 38 engage the teeth 46 in slot 40 to selectively maintain the block 38 in position. The longitudinal movement of the high-dielectric block 38 with respect to the feed pin 34′ and ground pin 36′ also provides a way of tuning the resonant frequency and/or the antenna input impedance by varying the volume and proximity of a dielectric material with respect to the feed and shorting pins 34′ and 36′, respectively.

[0028] In the PIFA antenna 10″, the movable tuning member is in the form of a threaded plug or screw 48 comprised of a high-dielectric constant material. Plug 48 is threadably received in threaded bore 50 in frame 14″. The longitudinal movement of the plug 48 with respect to the feed pin 34″ and ground pin 36″ provides a way of selectively tuning the resonant frequency and/or the antenna input impedance by varying the volume and proximity of a dielectric material with respect to the feed and shorting pins 34″ and 36″, respectively.

[0029] Yet another embodiment of the PIFA antenna is illustrated in FIGS. 9 and 10 and is referred to by the reference numeral 10′″. In PIFA 10′″, the frame 14′″ is provided with a slot 52 molded thereinto. The molding tool used to mold frame 14′″ can be configured so that the size and position of the slot can be altered, thereby providing a range of antennas based on the same patch and mold tool.

[0030] Still another embodiment of the PIFA antenna is illustrated in FIGS. 11-13 and is referred to by the reference numeral 10″″. In PIFA 10″″, the frame 14″″ is provided with a transverse bore 54 formed therein which rotatably receives a transverse rotor 56 which is semi-circular in profile so that the volume of an air gap below the patch 30″″ may be selectively varied as shown. In this way, the PIFA 10″″ is effectively capacitively loaded with a variable capacitor.

[0031] In PIFA antennas 10, 10′, 10″, 10′″, and 10″″, the movable tuning members will be formed from a high-dielectric constant material while the remaining components may be constructed of low-dielectric constant materials. In PIFA antennas 10, 10′, 10″, 10′″, and 10″″, it is recommended that the tolerances be such that the movable tuning members will remain in place if the wireless communication device is bumped, dropped, etc. Further, some form of holding members could be employed if needed to maintain the tuning members in place once they have been adjusted.

[0032] Thus it can be seen that a novel tunable PIFA antenna has been provided which accomplishes at least all of its stated objectives of the invention.