Patent Publication Number: US-6670923-B1

Title: Dual feel multi-band planar antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     U.S. patent application Ser. No. 10/135,312, filed Apr. 29, 2002 by Govind R. Kadambi and Jon L. Sullivan entitled SINGLE FEED TRI BAND PIFA WITH PARASITIC ELEMENT, incorporated herein by reference 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to antennas, and more specifically to antennas for use within handheld or portable wireless communication devices or handsets. 
     2. Description of the Related Art 
     State of the art cellular communication systems generally require handsets that provide both a multi-band and a multi-system capability. That is, there is a growing need for multi-purpose cellular handsets that can be utilized in cellular applications such as Advanced-Mobile-Phone-Service (AMPS), Personal-Communications-Service (PCS), Global-System-For-Mobile-Communication (GSM), Distributed-Communications-System (DCS) and Industrial Scientific Medical (ISM), and that can also be utilized in non cellular applications such as Global-Positioning-System (GPS) and Bluetooth (BT) (Bluetooth is the code name for an open specification to standardize data synchronization between disparate personal computer and handheld personal computer devices). 
     Current advances in cellular communication technology also provide an emphasis on providing an antenna that is internal to a cellular handset, to thereby utilize the inherent advantages that are provided by such an antenna that is buried with the wireless communication device. 
     The structure and arrangement that is provided by the present invention includes a planar inverted-F antenna (PIFA). 
     A PIFA is a compact, low profile, microstrip antenna, and it is called an inverted-F antenna because a side view of the antenna resembles the letter F facing down. U.S. Pat. Nos. 6,072,434, 6,218,991 and 6,222,496, incorporated herein by reference, are examples of PIFAs. 
     Multi-Band PIFAs are of interest to the mobile wireless communication industry. In a multi-band PIFA a choice between providing a single antenna feed, or providing multiple antenna feeds, tends to be dependent on system requirements. However, from the standpoint of antenna design, the choice between providing a single antenna feed or multiple antenna feeds has both merits and demerits. 
     In a single antenna feed, multi-band, PIFA providing a required bandwidth at multiple resonant frequencies generally leads to antenna design complexities. 
     On the other hand, a multi-band PIFA having multiple antenna feeds tends to diminish antenna design complexities since the design of a plurality of individual radiating/receiving elements, each having a separate feed, tends to be less difficult. However, multiple antenna feeds encounter the problem of mutual coupling between the individual radiating/receiving elements of a multi-band. PIFA. There is also a concern that a multi-band PIFA with multiple antenna feed ports may have its performance compromised due to mutual coupling and poor isolation between the PIFA&#39;s various resonant bands. 
     Hence, in spite of the reduced design complexities that are provided by a multi-band PIFA having multiple feeds, such a PIFA has not been a choice for practical applications, mainly due to the mutual coupling problem. In view of this, techniques that reduce the mutual coupling between the individual radiating/receiving elements of such as multi-band PIFA are important. 
     Past research on dual-feed, dual-band, PIFAs has emphasized optimizing the PIFA for cellular applications. However, most of the prior art dual-feed, dual-band, PIFAs exhibit an isolation of only about 15 dB. 
     Further improvement in the isolation that is provided by a dual-feed. dual-band, PIFA has been realized by increasing the physical separation between the antenna&#39;s multiple radiating/receiving elements. However, such an option contradicts the desirable requirement that the overall physical volume that is occupied by the PIFA be small. 
     Therefore, techniques which accomplish the desired objective of improved isolation without increasing the overall volume and/or linear dimensions of a multi-band PIFA are needed by the art. 
     The design and application of a dual-feed, dual-band, PIFA for cellular or mobile communication have been dealt with in the following publications, wherein the publications generally deal with the design of PIFA for cellular bands such as the AMPS/PCS or GSM/DCS bands. 
     [1] Z. D. Liu, P. S. Hall and D. Wake, “Dual-Frequency Planar Inverted-F Antenna”, IEEE Trans. Antennas and Propagation Vol. AP-45, No. 10, pp. 1451-1458, October 1997. 
     [2] C. B. Rowelland R. D. Murch,“A Compact PIFA Suitable for Dual-frequency 900/1800—MHz Operation”, IEEE Trans. Antennas and Propagation Vol. AP-46, No. 10, pp.596-598, April 1998. 
     [3] P. Kabacik and A. A. Kucharski,“Optimizing the radiation Pattern Of Dual Frequency Inverted F Planar antennas”, JINA conference, pp.655-658, 1998. 
     [4] P. Song, P. S. Hall, H. Ghafouri-Shiraz and D. Wake, “Triple-Band Planar Inverted F Antenna”, IEEE-APS Symposium, 1999, Orlando, pp.908-911. 
     Above cited reference [1] discusses an achievable isolation between the two feed ports of a GSM/DCS band PIFA. Specifically, isolation between the two ports as reported in [1] is of the order of about 15 dB. Any improvement in the isolation, while maintaining the overall volume of the PIFA, is at the expense of gain at one of the antenna ports. 
     To the contrary, the present invention improves the isolation (18-19 dB) between the two feed ports of two-antenna assemblies that are constructed and arranged in accordance with the present invention, without degrading the gain at the individual antenna ports. Further, the present invention does not increase the overall physical volume that is occupied by the multi-band antenna structure. 
     The design of a GSM/DCS/ISM Tri Band PIFA with two and three feed ports is described in above cited reference [4]. In this reference, multiple antennas are each of the PIFA type with all of the radiating elements lying on a single surface that is parallel to a ground plane. Prior art FIGS. 1-3, discussed below, show this type of arrangement. 
     In an embodiment of the present invention a multi-band, two-antenna assembly or module provides a combination of a PIFA and an inverted-F antenna (IFA) whose radiating elements are located in an orthogonal orientation. 
     An IFA is also known as a shunt-driven inverted-L antenna transmission line having an open end. That is, an IFA is a version of an inverted-L antenna having with the freedom to tap the input along the antenna&#39;s horizontal wire in order to achieve a degree of control over the antenna&#39;s input impedance. 
     FIG. 1 is a top view of a prior-art multi-band PIFA  10  having multiple feeds. FIG. 2 is a section view of PIFA  10  taken on line  2 — 2  of FIG. 1, and FIG. 3 is a section view of PIFA  10  taken on line  3 — 3  of FIG.  1 . Multi-band PIFA  10  includes two separate feeds, one feed for each if its two frequency bands. 
     PIFA  10  includes radiating/receiving elements  11  and  12  that resonate at the two separate frequency-bands. Radiating/receiving elements  11  and  12  occupy a common plane, and they are positioned above and generally parallel to a ground plane element  13 . An L-shaped slot  14  provides both physical and electrical separation between the two radiating/receiving elements  11  and  12 . 
     A first hole  15  is provided in the relatively large area radiating/receiving element  11 , and a conductive feed pin  16  is inserted through hole  15 . Feed pin  16  is used to feed radio frequency (RF) power to radiating/receiving element  11 . Feed pin  16  is electrically insulated from ground plane element  13  at the location whereat feed pin  16  passes through a hole that is provided in ground plane element  13 . 
     A second hole  17  is provided in radiating/receiving element  11 . A conductive post  18  which functions as a short circuit between radiating/receiving element  11  and ground plane element  13  is inserted through hole  17  and through a hole that is provided in ground plane element  13 . Post  18  extends generally parallel to feed pin  16 . 
     Radiating/receiving element  11 , having the relatively larger dimensions of length (L 1 ) and width (W 1 ), resonates at the lower frequency band of multi-band PIFA  10 . 
     Impedance matching of radiating/receiving element  11  is determined by the diameter of feed pin  16 , by the diameter of shorting post  18 , and by the distance that separates feed pin  16  and shorting post  18 . 
     Radiating/receiving element  12 , having the relatively smaller dimensions of length (L 2 ) and width (W 2 ), resonates at the higher frequency band of multi-band PIFA  10 . 
     A first hole  19  is provided in radiating/receiving element  12 . A conductive feed pin  20  is inserted through hole  19  and is used to feed RF power to radiating/receiving element  12 . Feed pin  20  is electrically insulated from ground plane element  13  at the location whereat feed pin  20  passes through a hole that is provided in ground plane element  13 . 
     A second hole  21  is provided in radiating/receiving element  12 , and a conductive post  22  that passes through hole  21  provides a short circuit between radiating/receiving element  12  and ground plane element  13 . Post  22  extends generally parallel to feed pin  20 . 
     Impedance matching of radiating/receiving element  12  is determined by the diameter of feed pin  20 , by the diameter of shorting post  22 , and by the distance that separates feed pin  20  from shorting post  22 . 
     Multi-band PIFA  10  illustrated in FIGS. 1-3 provides several disadvantages. For example, adequate isolation between the two frequency bands requires that a relatively large physical separation be provided between the two radiating/receiving elements  11  and  12 , thus necessitating a relatively large width for L-shaped slot  14 . This increased width of L-shaped slot  14  decreases the overall effective dimensions of PIFA  10 , thereby reducing the bandwidth as well as the gain of PIFA  10 . 
     In addition, any change that may be made in the frequency-separation that exists between the two resonant frequency bands of PIFA  10  involves a change in the linear dimensions L and W of the two radiating elements  11  and  12 . 
     Z. D. Liu, P. S. Hall and D. Wake, “Dual Frequency Planar Inverted—F Antenna”, IEEE Trans. Antennas and Propagation, Vol. AP-45, No. 10, pp. 1451-1548, Oct. 1997 describes a multi-band PIFA with separate feeds that is structurally configured similar to PIFA  10 . 
     P. Kabacik and A. A. Kuchaski, “Optimizing the Radiation Pattern of Dual Frequency Inverted—F Planar Antennas”, JINA Conference, pp.655-658, 1998 (hereinafter referred to as:Kabacik et al) also describes a multi band PIFA having separate feeds that is similar to PIFA  10 . However in Kabacik et al, instead of providing an L-shaped slot that separates the two radiating/receiving elements, as in PIFA  10 , an annular slot is proposed by Kabacik et al. 
     The problem of mutual coupling within a dual-feed, multi-band, PIFA is a severe constraint or drawback for the utility of such an antenna in system applications. It is possible to improve the isolation between the multiple radiating/receiving elements of a multi-band PIFA by increasing the separation distance between the radiating/receiving elements. In view of an emphasis on reducing the physical size of internal cellular antennas, this recourse of providing an increased physical separation between the radiating/receiving elements is not a practical solution. 
     SUMMARY OF THE INVENTION 
     The present invention provides a two-antenna assembly, one antenna of which is a PIFA. The second antenna of the two-assembly is contained within a physical volume that is occupied by the PIFA, such that the overall physical volume that is occupied by a two-antenna assembly in accordance with the invention is equal to the physical volume of the PIFA. 
     In embodiments of the invention, the second antenna&#39;s radiating/receiving element is mounted between the radiating/receiving element of the PIFA and a ground plane element, and the second antenna&#39;s radiating/receiving element extends in a plane that is perpendicular to both the plane of the radiating/receiving element of the PIFA and the plane of the ground plane element. 
     In other embodiments of the invention, the second antenna&#39;s radiating/receiving element is mounted between the radiating/receiving element of the PIFA and a ground plane element, and the second antenna&#39;s radiating/receiving element extends in a plane that is parallel to both the plane of the radiating/receiving element of the PIFA and the plane of the ground plane element. 
     The present invention provides a combined PIFA/IFA two-antenna assembly whose construction and arrangement retains the physical volume of the PIFA, and in addition minimizes the mutual coupling between the radiating/receiving elements of the two-antenna PIFA/IFA assembly. 
     In accordance with the invention, the PIFA portion of the two-antenna assembly is designed for dual resonance (i.e. AMPS/PCS resonance or GSM/DCS resonance) in the cellular frequency bands. 
     The PIFA is constructed and arranged such that the plane of the PIFA&#39;s radiating/receiving element is parallel to a flat or planar ground plane element, thereby providing a physical space between the PIFA&#39;s radiating/receiving element and its ground plane element. 
     In accordance with the invention, the second antenna portion (the IFA portion) of the two-antenna assembly operates in a frequency band for a non-cellular application (i.e. ISM or GPS), and the second antenna portion is constructed and arranged such that its radiating/receiving element is located in the space that exists between the radiating/receiving, element and the ground plane element of the PIFA. 
     In an embodiment of the invention the plane of the second antenna&#39;s radiating/receiving element extends generally parallel to the plane of the PIFA&#39;s radiating/receiving element. 
     In other embodiments of the invention the plane of the second antenna&#39;s radiating/receiving element extends generally perpendicular to the plane of the PIFA&#39;s radiating/receiving element. 
     In order to provide a Tri band two-antenna assembly within the volume that is occupied by the PIFA, in one embodiment of the invention the perpendicular-oriented radiating/receiving element of the IFA is placed (generally underneath a radiating or non-shorted edge of the PIFA&#39;s planar radiating/receiving element. This results in a orthogonal disposition of the planar radiating/receiving element of the PIFA and the planar radiating/receiving element of the IFA. 
     Apart from the orthogonal orientation of the two planar radiating/receiving elements, a slot contour within the radiating/receiving element of the PIFA also improves the isolation between the two feed ports that are individually provided for the PIFA and the IFA. 
     In other embodiments of the invention the above-described perpendicular-oriented radiating/receiving element of the IFA is placed under a non radiating or shorted edge of the PIFA&#39;s radiating/receiving element. This arrangement also results in an orthogonal disposition of the planar radiating/receiving elements of the PIFA and the IFA, this orthogonal orientation also providing isolation between the feed port of the PIFA and the feed port of the IFA. 
     In addition, neither of the above constructions and arrangements require that an increased physical separation be provided between the radiating/receiving elements of the PIFA. 
     This invention provides a dual-feed Tri-band (AMPS/PCS/ISM band or GSM/DCS/ISM band) two-antenna assembly having good gain, having a reasonable bandwidth and having improved isolation, such as −18 dB, between the multiple feed ports of the two-antenna assembly. 
     This invention provides a dual-feed Tri-band (AMPS/PCS/GPS bands) two-antenna assembly having good gain, having a reasonable bandwidth and having improved isolation better than −18 dB between the multiple feed ports of the two-antenna assembly. 
     In accordance with the invention the physical volume that is required by the IFA is physically placed within the volume that is required by the PIFA. In such an arrangement, the radiating/receiving element of the IFA is located under the radiating/receiving element of the PIFA, and the radiating/receiving element of the IFA may be either parallel-to or perpendicular-to the radiating/receiving element of the PIFA. 
     Although the advantage of improved isolation is reduced when the radiating/receiving element of the IFA is under and parallel-to the radiating/receiving element of the PIFA, this construction and arrangement in accordance with the invention improves the gain within the ISM band of the IFA, and in addition the bandwidth of both the PIFA and the IFA is improved. 
     This invention provides a bandwidth characteristic and an isolation characteristic for several planar, compact, dual-feed, Tri band/Quad band. two-antenna assemblies having utility in both cellular and non-cellular applications. 
     Within the spirit and scope of this invention, the invention can also be utilized to improve the isolation performance of a dual-feed, dual-band, PIFA two-antenna assembly wherein the PIFA provides for either AMPS or GSM operation, and wherein the IFA provides for PCS or DCS or ISM or GPS operation. 
     An important feature of the invention is minimizing the coupling between the two-antenna assembly&#39;s multiple radiating/receiving elements, which in turn improves the isolation between the individual feed ports that are provided for each of the radiating/receiving elements. 
     The present invention provides a two-antenna assembly that is formed by a new and an unusual combination of a PIFA and an IFA. The construction and arrangement of the two-antenna assembly results in minimizing the mutual coupling between the two antenna feed ports, without increase in the physical volume that is required by the PIFA itself. The present invention&#39;s technique for improving the isolation between the two antenna feed ports also retains the desirable physical compactness requirement of a multi-band two-antenna assembly. 
     The present invention&#39;s improvement in isolation between the two antenna feed ports that individually support the cellular band and the noncellular band does not result in a deterioration of the radiation/polarization characteristics of the radiating/receiving elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a top view of a prior art multi-band PIFA having multiple feeds. 
     FIG. 2 is a section view of the PIFA of FIG. 1 taken on line  2 — 2  of FIG.  1 . 
     FIG. 3 is a section view of the PIFA of FIG. 1 taken on line  3 — 3  of FIG.  1 . 
     FIG. 4 is an exploded top view that shows only the PIFA portion of a two-antenna assembly in accordance with the present invention. 
     FIG. 5 is an enlarged side section view that shows the planar radiating/receiving element of a second antenna mounted on an outer surface of one of the long-walls of the PIFA&#39;s box-shaped dielectric carriage shown in FIG. 4, such that this second radiating/receiving element is located generally under the radiating edge of the PIFA&#39;s radiating/receiving element, and such that the plane of this second radiating/receiving element extends generally perpendicular to the plane of the PIFA&#39;s radiating/receiving element and to the plane of the ground plane element. 
     FIG. 6 is an enlarged side section view that shows the planar radiating/receiving element of a second antenna mounted on an outer surface of one of the long-walls of the PIFA&#39;s box-shaped dielectric carriage shown in FIG. 4, such that this second radiating receiving element is located generally under the non-radiating edge of the PIFA&#39;s radiating/receiving element, and such that the plane of this second radiating/receiving element extends generally perpendicular to the plane of the PIFA&#39;s radiating/receiving element and to the plane of the ground plane element. 
     FIG. 7 is an enlarged side section view that shows the planar radiating/receiving element of a second antenna mounted on one of the long-walls of the PIFA&#39;s box-shaped dielectric carriage shown in FIG. 4, such that this second radiating/receiving element is located under and extends generally parallel to the PIFA&#39;s radiating/receiving element, and such that the plane of this second radiating/receiving element extends generally parallel to the plane of the ground plane element. 
     FIG. 8 shows an embodiment of the invention wherein the radiating/receiving element of FIG.  4 &#39;s PIFA includes only a single L-shaped slot, the position and the dimensions of this single slot operating to control the resonance characteristics of the PIFA&#39;s lower frequency band and upper frequency band. 
     FIG. 9 shows another embodiment of the invention wherein the radiating/receiving element of FIG.  4 &#39;s PIFA includes only a single L-shaped slot, the position and the dimensions of this single slot operating to control the resonance characteristics of the PIFA&#39;s lower frequency band and upper frequency band. 
     FIG. 10 shows two other embodiments of the invention wherein the IFA&#39;s radiating/receiving element is selectively located on the inside surface, or on the outside surface, of a selected one of the two walls of the FIG. 4 dielectric carriage that extend generally parallel to the major axis of the ground plane element, and wherein the capacitive loading plate that is shown located on this selected wall in FIG. 4 has been moved to the wall of the dielectric carriage that underlies the radiation edge of the PIFA&#39;s radiating/receiving element and that extends generally perpendicular to the major axis of the ground plane element. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 4 is an exploded top and side view that shows only the PIFA portion  30  of a two-antenna assembly that is constructed and arranged in accordance with the present invention. 
     PIFA  30  includes four basic structural elements, i.e. (1) a rectangular, flat and metallic ground plane element  31 , (2) a four-wall, box-shaped and relatively rigid dielectric carriage  32  whose four walls  38 - 41  define a box-shaped open cavity  33 , (3) a generally flat and metallic radiating/receiving element  34 , and (4) a coaxial feed cable  35  having an RF connector  36  at one end and an exposed and upward-extending centrally located metal conductor  37  at the other end. 
     The four side edges of radiating/receiving element  34  rest on and are physically supported by the top surface of the four walls  38 - 41  of dielectric carriage  32 , such that a plane that is occupied by radiating/receiving element  34  is generally parallel to a plane that is occupied by ground plane element  31 . 
     Ground plane element  31  is in the form of a rectangle having a major axis  58  and a minor axis  59 . 
     Dielectric carriage  32  is in the form of a rectangle having two parallel and relatively long walls  38  and  39  that extend generally parallel to the minor axis  59  of ground plane element  31 , and having two parallel and relatively short walls  40  and  41  that extend generally parallel to the major axis  58  of ground plane element  31 . 
     Each of the four walls  38 - 41  of dielectric carriage  32  include an outer surface and inner surface that faces open cavity  33 . 
     The bottom surface of the four walls  38 - 41  that form dielectric carriage  32  provide a planar and box-shaped surface on which metallic ground plane element  31  is mounted such that the long wall  38  of dielectric carriage  32  is located closely adjacent to the short edge  42  of ground plane element  31 , and such that the two short walls  40  and  41  of dielectric carriage are respectively located closely adjacent to the two long edges  43  and  44  of ground plane element  31 . 
     As stated above, the top surface of the four walls  38 - 41  that form dielectric carriage  32  provide a planar box-shaped surface on which metallic radiating/receiving element  34  is mounted. 
     Radiating/receiving element  34  is of generally the same box-shape as dielectric carriage  32 , and a conductive metal strip (not shown) is provided to short the edge  50  of radiating/receiving element  34  to ground plane element  31  at or adjacent to its edge  42 . 
     The two opposite edges  51  and  52  of radiating/receiving element  34  are bent about 90-degrees downward in order to form two metallic capacitive loading plates  53  and  54  for radiating/receiving element  34 , one loading plate  54  for tuning a lower resonant frequency of radiating/receiving element  34 , and the other loading plate  53  for tuning an upper resonant frequency of radiating/receiving element  34 . 
     Radiating/receiving element  34  also includes a first inclined slot  55  that provides a reactive loading that operates to lower the resonant frequency of the lower frequency band, and a second slot  56  that provides a reactive loading that operates to lower the resonant frequency of the upper frequency band. 
     Coaxial feed cable  35  and its RF connector  36  provide an electrical connection to radiating/receiving element  34 . That is, the exposed center metal conductor  37  of feed cable  35  extends generally 90-degrees upward and passes through ground plane element  31  in such a manner that conductor  37  is insulated from ground plane element  31 . Conductor  37  then passes adjacent to the outer surface of the long wall  38  of dielectric carriage  32 , whereupon conductor  37  electrically connects to a metal tab (not shown) that extends generally 90-degees downward from the edge  50  of radiating/receiving element  34   
     In FIG. 4, the edge  50  of radiating/receiving element  34  that is shorted to ground plane element  31  can be called a non-radiating edge. whereas the opposite edge  57  of radiating/receiving element  34  can be called a radiating edge. 
     FIG. 5 is an enlarged side section view that shows the planar radiating/receiving element  60  of a second antenna that generally occupies the cavity or space  33  that is shown in FIG. 4 between the radiating/receiving element  34  of PIFA  30  and ground plane element  31 . 
     In this embodiment of the invention the radiating/receiving element  60  of the second antenna is mounted on the inner surface  61  of the long-wall  39  of the box-shaped dielectric carriage  32  that is shown in FIG.  4 . In this embodiment of the invention the second radiating/receiving element  60  is located generally under the radiating edge  57  of the PIFA&#39;s radiating/receiving element  34 , such that the plane of this second radiating/receiving element  60  extends generally perpendicular to the plane of radiating/receiving element  34  and the plane of ground plane element  31 . 
     In FIGS. 5-7 the structural member that includes ground plane element  31  may be in the form of a printed circuit board (PCB) having a metal sheet that is located either on the top of or on the bottom of the PCB. 
     Feed to the second antenna that is formed by radiating/receiving element  60  and ground plane element  31  (an IFA) is provided by a coaxial cable  63  whose center metal conductor  62  is insulated from ground plane element  31 , is electrically connected to radiating/receiving element  60 , and extends into cavity  33 . 
     A relatively narrow metal strip  64  electrically connects a point on radiating/receiving elements  60  to ground plane element  31 . 
     FIG. 6 is an enlarged side section view of another embodiment of the invention wherein the planar radiating/receiving element  70  of a second antenna (an IFA) is mounted on the outer surface  71  of the long-wall  38  of the box-shaped dielectric carriage  32  that is shown in FIG.  4 . 
     In this embodiment of the invention the second radiating/receiving element  70  is located generally under the non-radiating edge  50  of the PIFA&#39;s radiating/receiving element  34 , such that the plane of this second radiating/receiving element  70  extends generally perpendicular to the plane of the PIFA&#39;s radiating/receiving element  34  and to the plane of ground plane element  31 . 
     Again, the second radiating/receiving element  60  of the second antenna generally occupies the cavity or space  33  that is shown in FIG. 4 between the radiating/receiving element  34  of PIFA  30  and ground plane element  31 . 
     Feed to the second antenna that is formed by radiating,/receiving element  70  and ground plane element  31  is provided by a coaxial cable  72  whose center metal conductor  73  is insulated from ground plane element  31  as it passes through around plane element  3   1 , is electrically connected to radiating,/receiving element  70 , and extend external to cavity  33 . A relatively narrow metal strip  74  electrically connects a point on radiating/receiving elements  70  to ground plane element  31 . 
     FIG. 7 shows an embodiment of the invention wherein the planar radiating/receiving element  77  of a second antenna is again mounted between the PIFA&#39;s radiating/receiving element  34  and ground plane element  31 . However in this embodiment of the invention the plane of radiating/receiving element  77  extends generally parallel to the plane of radiating/receiving element  34  and to the plane of ground plane element  31 . 
     More specifically, FIG. 7 is an enlarged side section view that shows the planar radiating/receiving element  77  of a second antenna penetrating a slot  78  that is provided in the long wall  39  of the PIFA&#39;s box-shaped dielectric carriage  32 , generally midway between the PIFA&#39;s radiating/receiving element  34  and ground plane element  31 . As such, this second radiating/receiving element  77  is located under and extends generally parallel to the PIFA&#39;s radiating/receiving element  34 , and such that the plane of the second radiating/receiving element  77  extends generally parallel to the plane of ground plane element  31 . 
     As discussed above relative to FIGS. 5 and 6, the second radiating/receiving element  77  of the second antenna generally occupies the cavity or space  33  that is shown in FIG. 4 between the radiating/receiving element  34  of PIFA  30  and ground plane element  31 . 
     Feed to the second antenna that is formed by radiating/receiving element  77  and ground plane element  31  is provided by a coaxial cable  79  whose center metal conductor  80  is insulated from ground plane element  13 , is electrically connected to radiating/receiving element  77 , and is located external of cavity  33 . A relatively narrow metal strip  81  electrically connects a point on radiating/receiving elements  77  to ground plane element  31 . 
     While the FIG. 7 second antenna that is made up of radiating/receiving element  77  and ground plane element  31  may be called a PIFA, because the dimension of radiating/receiving element  77  as measured along the major axis  58  of ground plane element  31  is small compared to its dimension along the minor axis  59  of ground plane element  31 , this second antenna can be called an IPA. 
     In summary, the present invention provides a two-antenna assembly that is formed by the new and unusual structural combination of a first antenna (see PIFA  30  of FIG. 4) and a second antenna (see FIGS. 5,  6  and  7 ). 
     The construction and arrangement of this two-antenna assembly results in minimizing the mutual coupling between the two antenna feed ports (see the first feed port  35  of FIG. 4, and the second feed port  63  of FIG. 5, or  72  of FIG. 6, or  79  of FIG.  7 ), without increase in the overall physical volume that is required by the construction and arrangement of the first antenna itself. 
     The present invention&#39;s technique for improving the isolation between the two antenna feed ports that are provided for the two-antenna assembly also retains a desirable physical compactness requirement of a multi-band two-antenna assembly. 
     The present invention&#39;s improvement in the isolation that is provided between the two antenna feed ports that individually support the cellular band (see PIFA  34 ) and the non-cellular band (see the second antenna of FIG. 5, FIG. 6 or FIG. 7) does not result in the deterioration of the radiation/polarization characteristics of the two radiating/receiving elements (see  34  of FIG. 4, and  60  of FIG. 5, or  70  of FIG. 6, or  77  of FIG.  7 ). 
     FIG. 8 shows an embodiment of the invention wherein the radiating/receiving element  34  of FIG.  4 &#39;s PIFA includes a single L-shaped slot  85 , the position and the dimensions of this single L-shaped slot  85  operating to control the resonance characteristics of the PIFA&#39;s lower frequency band and upper frequency band. 
     For example, a two-antenna assembly having the FIG. 8 PIFA radiating/receiving element  34  provides an AMPS/PCS/GPS, dual-feed, two-antenna assembly that includes a PIFA and an IFA. 
     In FIG. 8, instead of providing FIG.  4 &#39;s slot  55  that is inclined to the major axis  58  of ground plane element  31  and FIG.  4 &#39;s slot  56  that extends generally parallel to major axis  58 , the PIFA radiating/receiving element  34  of FIG. 8 provides an L-shaped slot  85  whose first portion  86  extends generally parallel to major axis  58  and whose second portion  87  extends generally perpendicular to major axis  58 . 
     The open edge of L-shaped slot  85  (i.e. the open end of first slot portion  86 ) lies on the non-radiating edge  50  of radiating/receiving element  34 , this open edge of L-shaped slot  85  lies to the left of the point  88  whereat radiating/receiving element  34  is connected to ground plane element  31 , and this open edge of L-shaped slot  85  lies to the left of the point  89  whereat the PIFA&#39;s feed conductor  37  of FIG. 4 is connected to radiating/receiving element  34 . 
     The FIG. 8 embodiment of the invention eliminates slot  56  of FIG. 4 whose open edge lies on the radiating edge  57  of the FIG. 4 radiating/receiving element  34 . When the radiating/receiving element  34  of the above-mentioned second antenna or IFA is placed under the radiating edge  57  of the PIFA&#39;s radiating/receiving element  34 , as shown in FIGS. 5 and 7, slot  56  of FIG. 4 has an influence on the isolation that exists between the PIFA and the IFA. In FIG. 8, the absence of FIG.  4 &#39;s slot  56  having an open slot-edge located on the radiating edge  57  of radiating/receiving element  34  improves the isolation between the PIFA and the IFA. 
     The use of the single L-shaped slot  85  shown in FIG. 8 provides an additional feature in that the position of L-shaped slot  85  influences the dual-polarization properties of the PIFA, thus providing that the radiation patterns of the PIFA&#39;s upper and lower frequency bands are oppositely polarized. 
     FIG. 9 shows another embodiment of the invention wherein the radiating/receiving element  34  of FIG.  4 &#39;s PIFA includes a single L-shaped slot  95 , the position and the dimensions of this single slot  95  operating to control the resonance characteristics of the PIFA&#39;s lower frequency band and upper frequency band. 
     That is, L-shaped slot  95  shown in FIG. 9 replaces the inclined slot  55  and the slot  56  of FIG.  4 . As was true in FIG. 8, L-shaped slot  95  controls the resonant characteristics of the PIFA in both the lower and upper frequency bands. 
     A difference between the embodiment of FIG.  9  and the embodiment of FIG. 8 is that the open end of FIG.  9 &#39;s L-shaped slot  95  (i.e. the open end of slot  95  that is located on the non-radiating edge  50  of radiating/receiving element  34 ) lies to the left of the point  88  whereat radiating/receiving element  34  is connected to ground plane element  31  (as in FIG.  8 ), but in FIG. 9 this open end of L-shaped slot  95  lies to the right of the point  89  whereat the PIFA&#39;s feed conductor  37  of FIG. 4 is connected to FIG.  9 &#39;s radiating/receiving element  34 . 
     In FIG. 9 the elimination of FIG.  4 &#39;s  56 having an open edge located on the radiating edge  57  of radiating/receiving element  34  improves the isolation between the PIFA and the IFA of the two-antenna assembly, particularly when the radiating/receiving element of the IFA is placed under the radiating edge of the PIFA&#39;s radiating/receiving element as shown in FIGS. 5 and 7. 
     However, the slot configuration of FIG. 9 does not provide the above-described dual polarization-feature, which implies that the radiation patterns of the lower and upper frequency bands have the same polarization when the slot configuration of FIG. 9 is used. 
     FIG. 10 shows two other embodiments of the invention wherein the IFA&#39;s radiating/receiving element  96  is selectively located on the inside surface, or on the outside surface, of a selected one of the two walls  40  or  41  of the FIG. 4 dielectric carriage  32  that extend generally parallel to the major axis  59  of ground plane element  31 , and wherein the capacitive loading plate  53  or  54  that is shown located on this selected one of the two walls  40  and  41  wall in FIG. 4 has been moved to the wall  39  of the dielectric carriage that underlies the radiation edge  57  of the PIFA&#39;s radiating/receiving element  34  and extends generally perpendicular to the major axis  58  of ground plane element  31 . 
     That is, FIG. 10 shows embodiments of the invention wherein the IFA&#39;s radiating/receiving element  96  is located on the inside surface (or the outside surface) of the wall  41  of dielectric carriage  32 , radiating/receiving element  96  being connected to ground plane element  31  by way of a metal tab  99 , and radiating/receiving element  96  being connected to the center conductor  98  of a feed cable  97 . 
     A similar embodiment of the invention provides that the IFA&#39;s radiating/receiving element  96  is located on the inside surface (or the outside surface) of the opposite wall  40  of dielectric carriage  32 , and is connected to ground plane element and a feed cable as shown in FIG.  10 . 
     In the FIG. 10 embodiment of the invention, the one of the two capacitive loading plates  53  or  54  of FIG. 4 that is eliminated, as above-described, can optionally be moved to the radiating edge  57  of the PIFA&#39;s radiating/receiving element  34 , as is shown in FIG.  10 . 
     While the invention has been particularly shown and described with reference to a preferred embodiment 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.