Abstract:
This invention presents new and alternative design techniques of single feed Dual/Tri ISM band PIFA for wireless system applications. To attain the advantages of and in accordance with the purpose of the present invention, dual and/or tri ISM band PIFA antennas are provided. In particular, an antenna comprises at least a ground plane, a radiating element, a short, and a feed tab. The short provides a connection between the ground plane and the radiating element. The feed tab connected to the radiating element provides RF power and provides initial impedance match. While the feed tab provides initial impedance match, additional impedance match and frequency control are obtained by the inclusion of one or more of a parasitic element, a slot, tuning stubs, and capacitive elements.

Description:
FIELD OF THE INVENTION 
     The present invention relates to Planar Inverted F-Antenna (PIFA), and in particular, to a single feed dual or tri ISM band PIFA of narrow width having a compact ground plane. 
     BACKGROUND OF THE INVENTION 
     The world has witnessed a rapid progress in wireless communication. The emerging technology of short range radio links (such as the Bluetooth protocol or the like) and local area network system applications have caused a renewed focus on the industrial scientific medical (“ISM”) frequency band. Conventionally, ISM band RF data communication devices use external antenna. But these devices could use internal antenna to avoid protruding external antenna. Internal antennas have several advantages such as being less prone to external damage, a reduction in overall size of the handset, and increased portability. 
     Among the various choices for internal antennas, the planer inverted F-antenna (“PIFA”) appears to have great promise. Relative to other internal antennas, the PIFA is generally lightweight, easy to adapt and integrate into a device chassis, has moderate range of bandwidth, has omni directional radiation patterns in orthogonal principal planes for vertical polarization, versatile for optimization, and multiple potential approaches for size reduction. 
     The PIFA also finds useful applications in diversity schemes. Its sensitivity to both the vertical and horizontal polarization is important for mobile cellular/RF data communication applications because of the absence of fixed orientation of the antenna 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. 
     Regarding the single ISM band PIFA technology, the thrust of research has been on optimal performance with the miniaturization in the sizes of both the antenna and the ground plane. Recently, however, there is a gradual shift of the emphasis from the existing single ISM band operation to dual or tri ISM band operating covering the frequency ranges of 2.4-2.5, 5.15-5.35, and 5.47-5.725 GHz. This calls for the development of dual or tri ISM band antennas for applications in wireless communication. There exists a continued interest and requirement for the compact dual and/or tri ISM band PIFA for emerging applications of RF data wireless systems comprising laptop computer and other handheld electronic devices, such as, for example, PDAs, electronic games, cellular phones, etc. 
     Unlike the case of PIFA for cellular applications, in wireless RF data communication systems, there exist variations on the sizes of the radiating element and ground plane as well as on the choice of preferred placement of the PIFA within the device. 
     In the majority of single feed cellular dual band PIFAs, quasi-physical partitioning of the radiating element facilitates dual frequency operation. Conventionally, a slot (straight, inclined, or L-shaped) forms a quasi-physical partitioning of the radiating element to facilitate the desired physical partitioning of the PIFA structure. When the system requirements impose stringent restrictions on the allowable width of the radiating element or ground plane, such as, for example, widths as low as about 1 to about 3 mm, the conventional dual band PIFA design invoking hitherto proven slot technique can prove to be a difficult, if not impossible, task. 
     A conventional dual band PIFA  70  with a single feed is illustrated in FIGS. 13A and 13B. Dual band PIFA  70  has a radiating element  301  and a ground plane  302 . An L-shaped slot  303  on the radiating element  301  creates a quasi-physical partitioning of the radiating element  301 . The segment on the radiating element  301  with dimensions of length (L 1 ) and width (W 1 ) resonates at the lower frequency band of the multi band operation. Conventionally, dual band (2.4-2.5/5.15-5.35 GHz) PIFA  70  has operating dimensions of lengths between 19.16-18.38 mm for (L 1 ) and between 12.07-11.58 mm for (W 1 ). The segment on the radiating element  301  with dimensions of length (L 2 ) and width (W 2 ) resonates at the upper frequency band of the multi band operation. Conventionally, the partition results in typical operating dimensions between 8.93-8.59 mm for (L 2 ) and 5.63-5.41 mm for (W 2 ). A power feed hole  304  is located on the radiating element  301 . A connector feed pin  305   a , used for feeding radio frequency (RF) power to the radiating element  301 , is inserted through the feedhole  304  from the bottom surface of the ground plane  302 . The connector feed pin  305   a  is electrically insulated from the ground plane  302  where the feed pin passes through the hole in the ground plane  302 . The connector feed pin  305   a  is electrically connected to the radiating element  301  with solder at  306   a . The body of the feed connector  305   b  is connected to the ground plane  302  at  306   b with solder. The connector feed pin  305   a  is electrically insulated from the body of feed connector  305   b . A through hole  307  is located on the radiating element  301 . A conductive post  308  is connected to the radiating element  301  at  309   a  with solder. The conductive post  308  also is connected to the ground plane  302  at  309   b  with solder. The dual band impedance match of the radiating element  301  is determined by the diameter of the connector feed pin  305   a , the diameter of the conductive shorting post  308  and the separation distance between the connector feed pin  305   a  and the conductive shorting post  308 . The main disadvantage of the configuration of the multi band PIFA  70  is the lack of simple means of adjusting the separation of lower and upper resonant frequency bands. The change in the separation of the resonant frequency bands requires the repositioning of the slot  303 . The above configuration is also associated with a constraint on the realizable bandwidth centered on the dual resonant frequencies of the PIFA  70 . 
     Thus, it would be desirous to develop a dual or tri band PIFA antenna using a relatively compact antenna construct. In a related study and yet distinct from the proposed invention, the design of a single feed tri band PIFA or dual cellular and non cellular (GPS or ISM) applications has been reported in U.S. patent application Ser. No. 10/135,312, filed Apr. 29, 2002, of Kadambi et al., titled “A Single Feed Tri Band PIFA with Parasitic Element,” which is incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     This invention presents new and alternative design techniques of single feed Dual/Tri ISM band PIFA for wireless system applications. To attain the advantages of and in accordance with the purpose of the present invention, dual and/or tri ISM band PIFA antennas are provided. In particular, an antenna comprises at least a ground plane, a radiating element, a short, and a feed tab. The short provides a connection between the ground plane and the radiating element. The feed tab connected to the radiating element provides RF power and provides some frequency control. While the feed tab provides some frequency control, additional frequency control is obtained by the addition of one or more of a parasitic element, a slot, tuning stubs, and capacitive elements. 
    
    
     The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention, and together with the description, serve to explain the principles thereof. Like items in the drawings are referred to using the same numerical reference. 
     FIG. 1 shows an embodiment of a PIFA illustrative of the present invention; 
     FIG. 2 shows VSWR and impedance characteristics of a sample PIFA  10 ; 
     FIG. 3 shows another embodiment of a PIFA illustrative of the present invention; 
     FIG. 4 shows VSWR and impedance characteristics of a sample PIFA  20 ; 
     FIG. 5 shows still another embodiment of a PIFA illustrative of the present invention; 
     FIG. 6 shows VSWR and impedance characteristics of a sample PIFA  30 ; 
     FIG. 7 shows a further embodiment of a PIFA illustrative of the present invention; 
     FIG. 8 shows VSWR and impedance characteristics of a sample PIFA  40 ; 
     FIG. 9 shows yet a further embodiment of a PIFA illustrative of the present invention; 
     FIG. 10 shows VSWR and impedance characteristics of a sample PIFA  50 ; 
     FIG. 11 shows still a further embodiment of a PIFA illustrative of the present invention; 
     FIG. 12 shows VSWR and impedance characteristics of a sample PIFA  60 ; and 
     FIG. 13 shows a conventional slotted PIFA. 
    
    
     DETAILED DESCRIPTION 
     The present invention will be described with reference to FIGS. 1-12. Using a combination of tuning devices and shorted parasitic elements, with or without slots in the radiating element, this invention presents the design of a dual and/or tri ISM band PIFAs having a relatively compact construct. The tuning devices and parasitic elements in the present invention can control the resonant frequency and the bandwidth of the dual and/or tri ISM frequency of operation. The location, the size (height, length, and width, also referred to as dimensions) and the relative orientation of the parasitic element and or tuning devices with respect to the radiating element control the tuning performance. Non limiting embodiments of the present invention have radiating elements and ground planes (as explained further below) with similar widths. While different widths are possible, it has been found that keeping the widths consistent results in a more compact structure. Further, the exemplary dimensions provided in this application are largely dictated by manufacturing tolerances; thus, the range of possible dimensions provided should be considered non limiting examples. 
     Designing a compact PIFA without using conventional slot techniques to partition the radiating element, while also restricting the allowable height and width, is formidable. Thus, to maintain a compact structure, the present invention is capable of incorporating a slot into the radiating element. In conventional dual band PIFA designs, the contour, size, and position of the slot play an important role. For a chosen contour and position of the slot, the size of the slot can be a tuning parameter to control the resonance of the PIFA. The variation in the size, contour and position of the slot influences the lower and upper resonant frequencies of the PIFA. Identification of the other specific parameters which facilitate rather independent control of the lower and upper resonance characteristics of the dual and/or tri band PIFA can enhance the ease of antenna tuning in many design applications. With this in view, this invention proposes the design of extremely narrow width dual and/or tri ISM band PIFA invoking both a slot and a parasitic element with a desirable provision to independently control the lower and the upper resonance to accomplish the feature of ease of tuning. The relative independent tuning of the upper and lower resonance characteristics of the dual or tri band of this invention is realized by the selective placement of tuning stubs of appropriate and pre-desired sizes. This invention also presents a feasibility of applying the slot technique in the design of compact dual and/or tri ISM band PIFA with extremely narrow width. 
     In most of the research publications and patents on PIFA technology, the major success has been the design of a single feed PIFA with dual resonant frequencies resulting essentially a dual band PIFA. In view of the inherent bandwidth limitation associated with conventional PIFA designs, most of the prior art single feed dual band PIFAs exhibit useful and desirable performance to cover only two frequency bands. U.S. Pat. No. 5,926,130 and the paper by Liu et al. entitled “Dual Frequency Planar Inverted—F Antenna” IEEE Trans. Antenna and Propagation, Vol. AP-45, No. 10, pp. 1451-1548, October 1997, incorporated herein by reference, are examples of the prior art single feed dual band PIFA. FIG. 13, herein, illustrates a prior art configuration of a conventional single feed dual band PIFA. 
     The design proposed in this invention realizes the tri band operation of the PIFA by using the L-shaped as well as T-shaped slot. Although the application of L-shaped slot is common in many single feed dual band PIFA designs, use of the T-shaped slot in the PIFA is novel. Further, this invention also suggests the combination of shorted parasitic element and the slot on the radiating element to accomplish single feed dual or tri ISM performance of the PIFA. 
     Now to FIG. 1, a PIFA  10  illustrative of one embodiment of the present invention is shown. FIG. 1A shows PIFA  10  in a bent configuration having a radiating element  11 , a ground plane  12 , a feed tab  13  formed of a first conductive material, such as a copper strip, a short  14  formed of a second conductive material, which could be the same or different from the first conductive material, and a shorted parasitic element  15  formed of a third conductive material, which could be the same or different from the first and second conductive material. FIG. 1B shows PIFA  10  in a flat configuration. Thus, PIFA  10  could be made using a single piece of metal appropriately cut and bent into the proper configuration. As can be seen in FIGS. 1A and 1B, PIFA  10  does not contain a slot, although one of ordinary skill in the art on reading the disclosure would understand a slot could be incorporated into the design. 
     Feed tab  13  has a first feed tab edge  13   a  connected to radiating element  11 . In the bent configuration, feed tab  13  has a second feed tab edge  13   b  residing above ground plane  12 . A feed tab gap fg exists between second feed tab edge  13   b  and ground plane  12 . A conventional coaxial cable power feed (not shown) attaches a center conductor of the coaxial cable to second feed tab edge  13   b  to supply power to the radiating element. An outer shield of the coaxial cable attaches to ground plane  12 . Short  14  has a first short edge  14   a  attached to radiating element  11  and a second short edge  14   b attached to ground plane  12  providing a short between radiating element  11  and ground plane  12 . Short  14  facilitates a quarter wavelength operation for radiating element  11 . Parasitic element  15  has a first parasitic edge  15   a connected to ground plane  12 . In the bent configuration, parasitic element  15  has a second parasitic edge  15   b  residing below radiating element  11 . A parasitic element gap pg exists between second parasitic edge  15   b  and radiating element  11 . A short gap sg exists between the parasitic element  15  and short  14 . Parasitic element  15  forms the tuning element to control an upper resonant frequency of radiating element  11 . As shown by the flat configuration, parasitic element  15  and feed tab  13  are on opposite sides of short  14 . 
     PIFA  10  functions as a single feed dual ISM band PIFA. The resonant frequency of the lower frequency band and the bandwidth center for radiating element  11  are determined by the dimensions of radiating element  11 , the size of ground plane  12 , the location and width of feed tab  13  on radiating element  11 , and the width of short  14  and the distance between radiating element  11  and ground plane  12 . 
     The resonant frequency of the lower frequency band and the bandwidth of radiating element  11  are determined by the location and width of shorted parasitic element  15  on ground plane  12 , the gap pg, the gap sg, and the height of PIFA  10 . While parasitic element  15  tunes the upper frequency band, it has little or no influence on tuning the lower frequency band. The coaxial cable power feed (not shown) attached to second feed tab edge  13   b influences the tuning of the upper frequency band, also. 
     Thus, different elements tune the radiating element&#39;s lower frequency band and upper frequency band. This allows the upper and lower frequencies to be varied separately. 
     A single feed dual ISM band PIFA  10  tuned to lower and upper frequencies of 2.4-2.5 and 5.15-5.35 GHz was designed and tested. FIG. 2 shows plots of VSWR and the impedance characteristics of a possible PIFA  10  with these frequencies. The VSWR plot indicates satisfactory bandwidth for the dual ISM Band operation of PIFA  10 , which is devoid of the conventional slot configuration. Using the parasitic element, a traditional single band PIFA can be made into a dual band PIFA without increase in the overall size or volume of the antenna. As can be seer, from the flat configuration, shown in FIG. 1B, PIFA  10  is designed so that a single sheet can be bent to form the antenna, although multiple sheets and solder could be used also. The results shown in FIG. 2 are based on radiating element  11  having dimensions 3(W)×30(L)×12(H) mm and ground plane  12  having dimensions 3(W)×42(L). These dimensions are exemplary, however, and one of ordinary skill in the art would understand the dimensions could vary over a wide range. The width of the radiating element can be as small as 2 mm and it can be as wide as 8-9 mm. The smallest width of the ground plane should be just the width of the radiating, element itself. The maximum width of the ground plane can be slightly or much bigger than the width of the radiating element. The minimum length of the ground plane should be just the length of the radiating element, itself. The maximum width of the ground plane can be slightly or much bigger than the length of the radiating element. It is pertinent to point out that any reduction in the width of the radiating element needs to be adequately compensated by a proportional or corresponding increase in the length of the radiating element to realize the multi band resonance of PIFA  10 . In general, the increase in the size of the ground plane has the effect of decreasing the resonant frequencies. The above observation holds good uniformly to all the further embodiments of this invention also. 
     FIGS. 3A and 3B show a Tri ISM band PIFA  20 . PIFA  20  operates over frequency ranges 2.4-2.5 GHz, 5.15-5.35 GHz, and 5.47-5.725 GHz. PIFA  20  contains radiating element  11 , ground plane  12 , feed tab  13 , short  14 , parasitic element  15 , and a tuning stub  16 . PIFA  20  may have a feed tab extension  13   c  attached to feed tab  13 . FIG. 3B shows PIFA  20  in a flat configuration. 
     Feed tab  13  has a first feed tab edge  13   a  connected to radiating element  11 . In the bent configuration, feed tab  13  has a second feed tab edge  13   b  that resides above ground plane  12 . In this example, second feed tab edge  13   b  has a protrusion  13   c  attached to it and extending toward ground plane  12 . While shown rectangular, protrusion  13   c  could have other geometric configurations, such as semi-circular, square, elliptical, triangular, or the like. Short  14  has first short edge  14   a  connected to radiating element  11  and second short edge  14   b  connected to ground plane  12  to provide a short between radiating element  11  and ground plane  12 . In this case, parasitic element  15  has a first parasitic edge  15   a  connected to ground plane  12  opposite short  14 . In other words, second short edge  14   b  is connected to a first end of ground plane  12  and first parasitic edge  15   a  is connected to a second end of ground plane  12  opposite the first end. Parasitic element  15  extends above ground plane  12  parallel to short  14 . Parasitic element  15  has a second parasitic edge  15   b  that resides in the plane of radiating element  11 . A bend in parasitic element  15  exists at second parasitic edge  15   b . While shown as extending at a 90 degree angle, parasitic element  15  could angle forwards or away from short  14 , also. A generally horizontal portion  15   d  of parasitic element  15  extends from second parasitic edge  15   b  to third parasitic edge  15   c . Horizontal portion  15   d  is shown parallel to ground plane  12 , although horizontal portion  15   d  could angle away or towards ground plane  12 . A radiating element to parasitic element gap rpg exists between radiating element  11  and parasitic element  15 . As can be seen, parasitic element forms an L-shape. PIFA  20  also contains a tuning stub  16 . Tuning stub  16  has a first tuning stub edge  16   a  connected to radiating element  11  between first short edge  14   a  and first feed tab edge  13   a . Tuning stub  16  has a second tuning stub edge that resides above ground plane  12 . A tuning stub gap ts exists between ground plane  12  and second tuning stub edge  16   b . A gap tsft exist between stub  16  and tab  13 . As can be seen in FIG. 3A, short  14  and parasitic element  15  exist at opposite ends of ground plane  12  and run parallel to each other at a width equal to radiating element  11 . 
     Tuning stub  16  controls the resonance and the bandwidth characteristics of the upper frequency band of radiating element  11 . Otherwise, PIFA  20  is similar in operation as PIFA  10 . PIFA  20  functions as a single feed Tri ISM band PIFA. The resonant frequency of the lower frequency band and the bandwidth of radiating element  11  are determined by the dimensions of radiating element  11 , the size of ground plane  12 , the location and the width of feed tab  13 , the separation distance between the shorting  14  and the tuning stub  16 , the width of short  14 , as well as by the distance between ground  12  and radiating element  11 . Further, gap rpg influences the lower resonant frequency. 
     The resonant frequency of the upper frequency band and the bandwidth of radiating element  11  are determined by the location and width of feed tab  13 , gap fg, gap tsft, as well as the distance between ground  12  and radiating element  11 . Parasitic element  15  has little influence on the upper resonant frequency. Connecting a conventional power cable to feed tab  13  can influence the upper resonant frequency. 
     FIG. 4 shows a VSWR and impedance characteristic of a sample PIFA  20  having radiating element dimensions of 3(W)×35(L)×10(H) mm and ground plane dimensions of 3(W)×35(L) mm with operating frequencies of 2.4-2.5 GHz, 5.15-5.35 GHZ, and 5.47-5.725 GHz. The possible variation in the width of the radiating element ranges from a very small value of 2 mm to as wide as 8-9 mm. The width of the ground plane should be just the width of the radiating element or larger than the width of the radiating element. These dimensions are exemplary, however, and one of ordinary skill in the art would understand the dimensions could vary over a wide range. These plots demonstrate satisfactory bandwidth for a PIFA  20  covering Bluetooth protocols, Hiper LAN frequency bands as well as the 5.15-5.35 GHz bandwidth. Similar to PIFA  10 , PIFA  20  is a single band PIFA without a slot in the radiating element, and without an increase in the overall physical size or volume of a conventional single band PIFA structure. 
     FIGS. 5A and 5B show single feed Tri ISM band PIFA  30 . PIFA  30  has radiating element  11 , ground plane  12 , feed tab  13 , short  14 , a slot  17 , and first conducting strip  19 , second conducting strip  21 , and third conducting trip  22 . Unlike PIFAs  10  and  20 , PIFA  30  has a slot  17  on radiating element  11 , making radiating element  11  potentially wider in this embodiment than the widths associated with PIFA  10  and  20 . However, PIFA  30  does not need a parasitic element, although one of ordinary skill in the art would recognize a parasitic element could be included. In this case, radiating element  11  has a T-shaped slot  17 . Slot  17  can have various configurations, such as the L-shaped slot shown in FIGS. 9 and 11. T-shaped slot  17  facilitates the quasi-physical partitioning of radiating element  11  to realize the multi frequency operation of PIFA  30 . 
     PIFA  30  has radiating element  11  and ground plane  12  extending generally parallel to each other. Radiating element  11  has a first edge  11   a  and a second edge  11   b . Feed tab  13  has first feed tab edge  13   a  attached to first edge  11   a  radiating element  11 . Feed tab  13  is parallel to first edge  11   a  and terminates at second feed tab edge  13   b , which resides above ground plane  12 . Contrary to PIFAs  10  and  20 , feed tab  13  is parallel to the first edge  11   a . Short  14  has first short edge  14   a  connected to radiating element  11  along a parallel edge  11   e  of radiating element  11  and second short edge  14   b connected to ground plane  12  along a parallel edge  12   e  of ground plane  12  to provide a short, which is contrary to PIFAs  10  and  20 . Short  14  and feed tab  13  reside on a first side of slot  17 . A first conducting strip  19  has a first conducting strip first edge  19   a  attached to radiating element I  1  along the same parallel edge  11   e  as short  14 , but across slot gap  18  so that it is attached on a second side of slot  17 . First conducting strip  19  has a first conducting strip second edge  19   b  that resides above ground plane  12 . Second conducting strip  21  having a second conducting strip first edge  21   a  attached to a second parallel edge  11   f  of radiating element  11  and third conducting strip  22  having a third conducting strip first edge  22   a  attached to second parallel edge  11   f  of radiating element  11 . Conducting strip  21  is opposite conducting strip  19  and conducting strip  22  is opposite short  14 . Second and third Conducting strips  21  and  22  are separated by a conducting strip gap cg. Second conducting strip  21  has a second conducting strip second edge  21   b  that resides a predetermined distance above ground plane  12 . Third conducting strip  22  has a third conducting strip second edge  22   b  that resides a predetermined distance above ground plane  12 . First conducting strip second edge  19   b , second conducting strip second edge  21   b , and third conducting strip second edge  22   b  can reside a different distances above ground plane  12 , but they could reside at the same distance. First, second, and third conducting strips  19 ,  21 , and  22  act as tuning stubs, similar to tuning stub  16  for PIFA  20 . The locations of each of the first, second, and third conductive strips enable tuning of a specific resonant band frequency. For example, conducting strips  19  and  21  have a greater influence to tune the resonance of the lower frequency band while conducting strip  22  has a greater influence on the upper band. 
     PIFA  30  functions as a single feed Tri ISM band PIFA. The resonant frequency of the lower frequency band and the bandwidth of radiating element  11  are determined by the dimensions of radiating element  11 , the distance between radiating element  11  and ground plane  12 , the size of ground plane  12 , the location and width of feed stub  13 , the width of short  14 , the position of slot  17  in radiating element  11  as well as its dimensions (including gap  18 ), the location and width of first conducting strip  19 , the predetermined distance between ground plane  12  and first conducting strip second edge  19   b , the location and width of second conducting strip  21 , and the predetermined distance between ground plane  12  and second conducting strip second edge  21   b.    
     The resonant frequency of the upper frequency band and the bandwidth of radiating element  11  are determined by the location and width of third conductive strip  22 , the predetermined distance between ground plane  12  and third conducting strip second edge  22   b , the position of the T-shaped slot  17  and the dimension of the T-shaped slot  17 . 
     FIG. 6 shows satisfactory VSWR and impedance characteristics of a sample PIFA  30  operating in the 2.4-2.5, 5.15-5.35, and 5.47-5.725 GHz range. The sample PIFA  30  has radiating element  11  dimensions of 6(W)×26(L)×6(H) mm and ground plane  12  dimensions of 6(W)×30(L) mm. The width of the radiating element can vary from as small as  2  mm to as wide as 8-9 mm. The width of the ground plane can be restricted to just the width of the radiating element or it can be larger than the width of the radiating element. For a 6 mm wide radiating element  11  of PIFA  30 , the width of the T-shaped slot  17  is about 2 mm. Once again, these dimensions are exemplary. 
     FIGS. 7A and 7B represent a PIFA  40  that combines slot  17  on radiating element  11  with parasitic element  15  on ground plane  12 . PIFA  40  comprises radiating element  11 , ground plane  12 , slot  17 , feed tab  13 , short  14 , parasitic element  15 , a first conducting strip  23 , a second conducting strip  24 , and a third conducting strip  26 . 
     In this case, feed tab  13  has first feed tab edge  13   a  attached to along a parallel edge  11   e  of radiating element  11 , which is similar to PIFA  10  and PIFA  20 , but contrary to PIFA  30 . Second feed tab edge  13   b  resides above ground plane  12 . Short  14  has first short edge  14   a  attached to first edge  11   a  and a second short edge  14   b  attached to a first ground plane edge  12   a  to provide a short. Residing opposite gap  18  and along parallel edge  11   e  exists first and second conducting strips  23  and  24 , respectively. First conducting strip  23  has a first conducting strip first edge  23   a  attached to parallel edge  11   e . Second conducting strip  24  has a second conducting strip first edge  24   a  attached to parallel edge  11   e , also. First and second conducting strips  23  and  24  are separated by a gap cg. First conducting strip  23  has a first conducting strip second edge  23   b  that resides a predetermined distance above ground plane  12 . Second conducting strip  24  has a second conducting strip second edge  24   b  that resides a predetermined distance above ground plane  12 . The predetermined distance for edges  23   b  and  24   b  from ground plane  12  can be the same or different. A third conducting strip  26  has a third conducting strip first edge  26   a  attached to a parallel edge  11   f  opposite first and second conducting strips  23  and  24 . Third conducting strip  26  has a third conducting strip second edge  26   b  that also resides a predetermined distance above ground plane  12 . Conducting strips  23 ,  24 , and  26  are positioned to enable tuning of the lower resonant. 
     Parasitic element  15  has a first parasitic element edge  15   a  attached to a parallel edge  12   f  of ground plane  12  (generally opposite feed tab  13 ). A second parasitic element edge  15   b  resides a predetermined distance below radiating element  11 . Parasitic element  15  influences the tuning of the upper resonant frequency. 
     PIFA  40  functions as a single feed Tri ISM band PIFA. The resonant frequency of the lower frequency band and the bandwidth center of radiating element  11  are determined by the dimensions of radiating element  11 , the distance between radiating element  11  and ground plane  12 , the size of ground plane  12 , the location and width of feed stub  13 , the width of short  14 , the position of slot  17  in radiating element  11  as well as its dimensions (including gap  18 ), the location and width of first conducting strip  23 , the predetermined distance between first conducting strip second edge  23   b  and ground plane  12 , the location and width of second conducting strip  24 , the predetermined distance between ground plane  12  and second conducting strip second-edge  24   b , and the predetermined distance between ground plane  12  and second conducting strip second edge  26   b.    
     The resonant frequency of the upper frequency band and the bandwidth for radiating element  11  are determined by the dimensions of radiating element  11 , the distance between radiating element  11  and ground plane  12 , the location and width of feed tab  13 , the position of slot  17  in radiating element  11  as well as its dimensions, and the location of the parasitic element  15  with respect to radiating element  11 . 
     FIG. 8 shows satisfactory VSWR and impedance characteristics of a sample PIFA  40  operating in the 2.4-2.5, 5.15-5.35, and 5.47-5.725 GHz range. The sample PIFA  40  has radiating element  11  dimensions of 6(W)×30(L)×6(H) mm and ground plane  12  dimensions of 6(W)×30(L) mm. The width of the radiating element can typically vary from 2-9 mm. The ground plane and the radiating element can have identical width or the width of the ground plane can be larger than the width of the radiating element. With 6 mm being the width of the radiating element  11  of PIFA  40 , the T-shaped slot  17  has a width of about 2 mm. 
     FIGS. 9A and 9B show a PIFA  50 . PIFA  50  contains radiating element  11 , ground plane  12 , a slot  27 , in this case an L-shaped slot, feed tab  13 , short  14 , parasitic element  15 , a capacitive loading element  31 , and a first conducting strip  32 . In this case, radiating element  11  has L-shaped slot  27  to facilitate the quasi-physical partitioning of radiating element  11  to accomplish the dual frequency operation. 
     Feed tab  13  has a first feed tab edge  13   a  attached to a parallel edge  11   f  of radiating element  11 . Feed tab  13  has a second feed tab edge  13   b  residing a predetermined distance above ground plane  12 . Short  14  has first short edge  14   a  attached to first edge  11  a of radiating element  11  and second short edge  14   b  attached to ground plane edge  12   a  to provide a short between radiating element  11  and ground plane  12 . Generally opposite feed tab  13  resides parasitic element  15  having first parasitic edge  15   a  attached to parallel edge  12   e . Parasitic element  15  has second parasitic edge  15   b  residing below radiating element  11  a predetermined distance. A capacitive loading element  31  has a first loading element first edge  31   a  attached to a second edge  29  of radiating element  11 . Generally, element  31  and radiating element  11  form a substantially 90 degree angle, with loading element  31  extending towards ground plane  12 . Loading element  31  is generally parallel to short  14  and has a second loading element edge  31   b  residing a predetermined distance above ground plane  12 . A first conducting strip  32  has a first conducting strip first edge  32   a  attached to parallel edge  11   f , opposite gap  28  of slot  27 , such that feed tab  13  resides on one side of gap  28  and first conducting strip  32  resides on the other. First conducting strip  32  has a first conducting strip second edge  32   b  residing a predetermined distance above ground plane  12 . 
     The vertical capacitive loading element  31  offers a reactive loading to the lower resonant band of PIFA  50 . First conducting strip  32  tunes the lower frequency band. The parasitic element generally controls the tuning of the upper frequency band. Otherwise, operation of PIFA  50  is similar to PIFA  40 . 
     PIFA  50  functions as a single feed Tri ISM band PIFA. The resonant frequency of the lower frequency band and the bandwidth of radiating element  11  are determined by the dimensions of radiating element  11 , the distance between radiating element  11  and ground plane  12 , the size of ground plane  12 , the location and width of feed stub  13 , the width of short  14 , the position of slot  27  in radiating element  11  as well as its dimensions (including gap  28 ), the location and width of first conducting strip  32 , the predetermined distance between ground plane  12  and first conducting strip second edge  32   b , the width of capacitive element  31  and the distance of the second loading element  31   b  above ground plane  12 . 
     The resonant frequency of the upper frequency band and the bandwidth of radiating element  11  are determined by the dimensions of radiating element  11 , the distance between radiating element  11  and ground plane  12 , the size of ground plane  12 , the location and width of feed tab  13 , the position of slot  27  and its dimensions (including gap  28 ), and the location of parasitic element  15  with respect to radiating element  11 . 
     FIG. 10 shows satisfactory VSWR and impedance characteristics of a sample PIFA  50  operating in the 2.4-2.5, 5.15-5.35, and 5.47-5.725 GHz range. The sample PIFA  50  has radiating element  11  dimensions of 3(W)×19(L)×6.5(H) mm and ground plane  12  dimensions of 3(W)×19(L). The width of the radiating element  11  can be allowed to vary between 2-9 mm. The multi ISM band PIFA  50  can incorporate the same width for both the radiating element and the ground plane. Alternatively, the ground plane can also be made much wider than that of the radiating element. With the choice of 3 mm wide radiating element  11  of PIFA  50 , the L-shaped slot  27  has a width of about 0.8 mm. 
     FIGS. 11A and 11B show a PIFA  60 . PIFA  60  contains radiating element  11  having slot  27  above ground plane  12 . While similar to PIFA  50 , explained with reference to FIGS. 9A and 9B, PIFA  60  has vertical capacitive loading plate  31  and horizontal capacitive loading plate  33  that allows PIFA  60  to be relatively narrower than PIFA  50 , as will be explained further below. 
     PIFA  60  operates similar to PIFA  50  and only the different parts will be further explained herein. Unlike PIFA  50 , radiating element  11  for PIFA  60  is somewhat longer (in the length dimension) to facilitate horizontal capacitive loading plate  33 . As shown, vertical capacitive loading plate  31  has second loading element edge  31   b  residing above ground plane  12  at a predetermined distance. Horizontal capacitive loading plate  33  has a first horizontal capacitive element edge  34   a  attached to second loading element edge  31   b  such that horizontal capacitive loading plate  33  is generally horizontal and parallel to ground plane  12 . A dielectric spacer  34  having predetermined dielectric constants and size can be placed between horizontal capacitive loading plate  33  and ground plane  12  to increase the capacitive loading. 
     FIG. 12 shows satisfactory VSWR and impedance characteristics of a sample PIFA  50  operating in the 2.4-2.5, 5.15-5.35, and 5.47-5.725 GHz range. The sample PIFA  60  has radiating element  11  dimensions of 2(W)×23(L)×6.5(H) mm and ground plane  12  dimensions of 2(W)×23(L) mm. Although the width of the radiating element  11  can be increased to 8-9 mm, any further decrease in the already very narrow width (2 mm) of the radiating element  11  of PIFA  60  is likely to result in fabrication complexities. To the best of the knowledge of the inventors, the realized design of 2 mm wide multi ISM band PIFA  60  of this invention is purported to have the least width among the published work in open literature. The proposed design can incorporate the same width for both the radiating element and the ground plane. On the contrary, the ground plane can be made much wider than that of the radiating element. The width of the L-shaped slot  27  is about 0.8 mm with the choice of 2 mm wide radiating element  11  of PIFA  60 . 
     While the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention.