Abstract:
The present invention provides a miniature, built-in multi-band antenna which is suitable for use in future compact mobile terminals. According to exemplary embodiments, a semi built-in printed antenna is provided which includes patch elements of different sizes and capable of being tuned to different frequency bands. An internal patch element is located on a printed circuit board (PCB) within a communication device and another patch element is located outside the PCB. On each patch element is formed a slot which divides the patch element into sub-parts. Each sub-part of the internal patch element is structured so as to be resonant at a frequency in the same frequency band to which the internal patch element is tuned. Each sub-part of the external patch element is similarly structured but having a resonance with a larger bandwidth than the internal patch element and at a frequency band to which the external patch element is tuned. As a result, a high efficiency, broad band, multi-band, and surface mountable low profile antenna can be realized.

Description:
RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 09/112,366 to Ying, filed Jul. 9, 1998 and entitled “Miniature Printed Spiral Antenna for Mobile Terminals”, U.S. patent application Ser. No. 09/112,152 to Ying, filed Jul. 9, 1998 and entitled “Twin Spiral Dual Band Antenna”, and U.S. patent application Ser. No. 09/212,259 to Ying, filed Dec. 16, 1998 and entitled “Printed Multi-Band Patch Antenna,” all of which are incorporated by reference in their entireties herein. 
    
    
     BACKGROUND 
     The present invention relates generally to radio communication systems and, in particular, to built-in antennas which can be incorporated into portable terminals and which allow the portable terminals to communicate within different frequency bands. 
     The cellular telephone industry has made phenomenal strides in commercial operations in the United States as well as the rest of the world. Growth in major metropolitan areas has far exceeded expectations and is rapidly outstripping system capacity. If this trend continues, the effects of this industry&#39;s growth will soon reach even the smallest markets. Innovative solutions are required to meet these increasing capacity needs as well as maintain high quality service and avoid rising prices. 
     Throughout the world, one important step in the advancement of radio communication systems is the change from analog to digital transmission. Equally significant is the choice of an effective digital transmission scheme for implementing the next generation technology, e.g., time division multiple access (TDMA) or code division multiple access (CDMA). Furthermore, it is widely believed that the first generation of Personal Communication Networks (PCNs), employing low cost, pocket-sized, cordless telephones that can be carried comfortably and used to make or receive calls in the home, office, street, car, etc., will be provided by, for example, cellular carriers using the next generation digital cellular system infrastructure. 
     To provide an acceptable level of equipment compatibility, standards have been created in various regions of the world. For example, analog standards such as AMPS (Advanced Mobile Phone System), NMT (Nordic Mobile Telephone) and ETACS and digital standards such as D-AMPS (e.g., as specified in EIA/TIA-IS-54-B and IS-136) and GSM (Global System for Mobile Communications adopted by ETSI) have been promulgated to standardize design criteria for radio communication systems. Once created, these standards tend to be reused in the same or similar form, to specify additional systems. For example, in addition to the original GSM system, there also exists the DCS1800 (specified by ETSI) and PCS1900 (specified by JTC in J-STD-007), both of which are based on GSM. 
     However, the most recent evolution in cellular communication services involves the adoption of additional frequency bands for use in handling mobile communications, e.g., for Personal Communication Services (PCS) services. Taking the U.S. as an example, the Cellular hyperband is assigned two frequency bands (commonly referred to as the A frequency band and the B frequency band) for carrying and controlling communications in the 800 MHz region. The PCS hyperband, on the other hand, is specified in the United States to include six different frequency bands (A, B, C, D, E and F) in the 1900 MHz region. Thus, eight frequency bands are now available in any given service area of the U.S. to facilitate communication services. Certain standards have been approved for the PCS hyperband (e.g., PCS1900 (J-STD-007)), while others have been approved for the Cellular hyperband (e.g., D-AMPS (IS-136)). 
     Each one of the frequency bands specified for the Cellular and PCS hyperbands is allocated a plurality of traffic channels and at least one access or control channel. The control channel is used to control or supervise the operation of mobile stations by means of information transmitted to and received from the mobile stations. Such information may include incoming call signals, outgoing call signals, page signals, page response signals, location registration signals, voice channel assignments, maintenance instructions, hand-off, and cell selection or reselection instructions as a mobile station travels out of the radio coverage of one cell and into the radio coverage of another cell. The control and voice channels may operate using either analog modulation or digital modulation. 
     The signals transmitted by a base station in the downlink over the traffic and control channels are received by mobile or portable terminals, each of which have at least one antenna. Historically, portable terminals have employed a number of different types of antennas to receive and transmit signals over the air interface. For example, monopole antennas mounted perpendicularly to a conducting surface have been found to provide good radiation characteristics, desirable drive point impedances and relatively simple construction. Monopole antennas can be created in various physical forms. For example, rod or whip antennas have frequently been used in conjunction with portable terminals. For high frequency applications where an antenna&#39;s length is to be minimized, another choice is the helical antenna. 
     It is commercially desirable to offer portable terminals which are capable of operating in widely different frequency bands, e.g., bands located in the 800 MHZ region and bands located in the 1900 MHZ region. Accordingly, antennas which provide adequate gain and bandwidth in both frequency bands will need to be employed in portable terminals. Several attempts have been made to create such dual-band antennas. 
     For example, U.S. Pat. No. 4,571,595 to Phillips et al. describes a dual-band antenna having a sawtooth-shaped conductor element. The dual-band antenna can be tuned to either of two closely spaced apart frequency bands (e.g, centered at 915 MHz and 960 MHz). This antenna design is, however, relatively inefficient since it is so physically close to the chassis of the mobile phone. 
     Japanese patent no. 6-37531 discloses a helix which contains an inner parasitic metal rod. In this patent, the antenna can be tuned to dual resonant frequencies by adjusting the position of the metal rod. Unfortunately, the bandwidth for this design is too narrow for use in cellular communications. 
     Dual-band, printed, monopole antennas are known in which dual resonance is achieve by the addition of a parasitic strip in close proximity to a printed monopole antenna. While such an antenna has enough bandwidth for cellular communications, it requires the addition of a parasitic strip. Moteco AB in Sweden has designed a coil matching dual-band whip antenna and coil antenna, in which dual resonance is achieved by adjusting the coil matching component (¼ λ for 900 MHz and ½ λ for 1800 MHz). This antenna has relatively good bandwidth and radiation performances and a length in the order of 40 mm. A non-uniform helical dual-band antenna which is relatively small in size is disclosed in copending, commonly assigned U.S. patent application Ser. No. 08/725,507, entitled “Multiple Band Non-Uniform Helical Antennas.” 
     Presently, antennas for radio communication devices, such as mobile phones, are mounted directly on the phone chassis. However, as the size and weight of portable terminals continue to decrease, the above-described antennas become less advantageous due to their size. Moreover, as the functionality of these future compact portable terminals increases, the need arises for a built-in miniature antenna which is capable of being resonant at multiple frequency bands. 
     Conventional built-in antennas currently in use in mobile phones include microstrip antennas and planar inverted-F antennas. Microstrip antennas are small in size and light in weight. The planar inverted-F antenna (PIFA) has already been implemented in a mobile phone handset, as described by K. Qassim, “Inverted-F Antenna for Portable Handsets”, IEE Colloqium on Microwave Filters and Antennas for Personal Communication Systems, pp.3/1-3/6, Feb. 1994, London, UK. More recently, Lai et al. have published a description of a meandering inverted-F antenna (WO 96/27219). This antenna has a size which is about 40% of that of the conventional PIFA antenna. 
     FIGS. 1A and 1B illustrate the conventional planar patch antenna compared to the meandering inverted-F antenna described in Lai et al. The conventional planar patch antenna of FIG. 1A has both a size and length equal to, for example, a quarter wavelength of the frequency to which the antenna is to be made resonant. The conventional planar patch antenna also has a width W. The meandering inverted-F antenna, illustrated in FIG. 1B, also has a length equal to a quarter wavelength of the resonant frequency and a width equal to W; however, the size of the meandering inverted-F antenna is reduced to about 40% of the size of the conventional planar patch antenna. This reduction in size is attributable to the antenna&#39;s meandering shape. 
     However, as mobile phones become smaller and smaller, both conventional microstrip patch and PIFA antennas are still too large to fit future phone chassis. In copending, commonly assigned U.S. patent application Ser. No. 09/112,366, entitled “Miniature Printed Spiral Antenna for Mobile Terminals”, a printed spiral built-in antenna with a matching post was proposed. The size of the antenna was reduced to 20-30% of the conventional PIFA antenna, which is less than {fraction (1/10)} th  of a wavelength, in order to make it suitable for future mobile phones. 
     In addition to a reduced antenna size, next generation mobile phones will require the capability to tune to more than one frequency band for cellular, wireless local area network, GPS and diversity. In copending, commonly assigned U.S. patent application Ser. No. 09/112,152, entitled “Twin Spiral Dual Band Antenna”, a multiple band, built-in antenna was proposed which is suitable for future mobile phones. The built-in antenna comprises two spiral conductor arms which are of different lengths and capable of being tuned to different frequency bands. In this design, the bandwidth of the antenna is smaller because thin strip lines are used as radiators. In order to increase bandwidth of the antenna, a compensation method is used by introducing a resistor loading technique on the matching bridge. While this approach leads to a wider bandwidth, it also results in a loss of gain. This antenna is designed for use in two frequency bands. 
     In copending, commonly assigned U.S. patent application Ser. No. 09/212,259, entitled “Printed Multi-Band Patch Antenna”, another new type of dual band patch antenna is disclosed. In contrast to the twin spiral dual band antenna which uses thin strip lines as radiators, the multi-band patch antenna uses patches with slot cutting. The patches are used as radiators and facilitate a wider bandwidth. The multi-band patch antenna is also designed for two frequency bands. 
     There continues, however, to exist a need for an efficient, miniature, built-in antenna which is capable of tuning to multiple frequency bands while simultaneously having a broad bandwidth in each of those multiple frequency bands. In addition, such antennas should be capable of tuning to a number of different frequency ranges within plural bands. 
     SUMMARY 
     The present invention overcomes the above-identified deficiencies in the art by providing a miniature, semi built-in multi-band printed antenna which is suitable for use in future compact mobile terminals by facilitating operation in at least three frequency ranges. According to exemplary embodiments, a semi built-in multi-band printed antenna is provided which includes patch elements of different sizes and capable of being tuned to different frequency bands. On each patch element is formed a slot which divides the patch element into sub-parts. Each sub-part of a patch element is structured so as to be resonant at a frequency in the same frequency band to which the patch element is tuned. As a result, a high efficiency, broad band, multi-band, and surface mountable low profile antenna can be realized which can be used in three frequency ranges where one of the frequency ranges is outside one of the two frequency bands. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and features of the present invention will be more apparent from the following description of the preferred embodiments with reference to the accompanying drawings, wherein: 
     FIGS. 1A and 1B illustrate a conventional planar patch antenna compared to the conventional meandering inverted-F antenna; 
     FIG. 2 illustrates an exemplary radio communication device in which the antenna of the present invention may be implemented; 
     FIG. 3 illustrates a printed dual band two-patch antenna on a PCB; 
     FIG. 4 illustrates an antenna configuration in which each patch part is formed of three sub-parts; 
     FIGS. 5A and 5B illustrate the process of forming a broad band, multiple band antenna; 
     FIG. 6 a  illustrates a semi built-in multi-band printed antenna of the present invention; 
     FIG. 6 b  illustrates the EM field of an antenna located on a printed circuit board (PCB); 
     FIG. 6 c  illustrates the EM field of an,antenna located outside the PCB; 
     FIG. 7 illustrates a top view of a rectangular semi built-in multi-band printed antenna according to the present invention; 
     FIG. 8 illustrates a top view of a semi built-in multi-band printed antenna of the present invention with an arcuate high-band element; 
     FIG. 9 illustrates a top view of a semi built-in multi-band printed antenna of the present invention with the high-band element having a projecting end; and 
     FIG. 10 illustrates a top view of a semi built-in multi-band printed antenna of the present invention with an end of the high-band element being a meander line forming a stub. 
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular circuits, circuit components, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, and circuits are omitted so as not to obscure the description of the present invention. 
     FIG. 2 illustrates an exemplary radio communication device  200  in which the built-in multiple band patch antenna of the present invention may be implemented. Communication device  200  includes a chassis  210  having a microphone opening  220  and speaker opening  230  located approximately next to the position of the mouth and ear, respectively, of a user. A keypad  240  allows the user to interact with the communication device, e.g., by inputting a telephone number to be dialed. The communication device  200  also includes a built-in patch antenna assembly  250 , the details of which will be described below. 
     FIG. 3 illustrates an exemplary built-in patch antenna assembly according to the present invention. The exemplary built-in patch antenna assembly comprises two patch parts  305  and  310 , each having a different size. The two patch parts  305  and  310  are attached to the printed circuit board (PCB)  315  via a dielectric substrate  320  and are connected to opposite sides of a matching bridge  330 . A slot  340  is formed in each patch part  305  and  310  which divides the patch parts into sub-parts  345 ,  350  and  355 ,  360 , the importance of which is discussed in detail below. The patch parts  305  and  310  are positioned over the PCB  315  and form slots between the patch parts and the PCB  315 . One skilled in the art will appreciate that the patch parts form the main radiators (or sensors) of the present antenna system. 
     As evident from FIG. 3, the patch parts  305  and  310  are fed by the feeding pin  325 . The built-in antenna also includes a matching bridge  330  positioned between the feeding pin  325  and the grounded post  335 . The matching bridge  330  acts to tune the antenna and forms a small loop antenna between the feeding pin  325  and grounded post  335 . Tuning of an antenna refers to matching the impedance seen by an antenna at its input terminals such that the input impedance is seen to be purely resistive, i.e., it will have no appreciable reactive component. The tuning of the antenna system of the present invention is performed by measuring or estimating the input impedance associated with an antenna and providing an appropriate impedance matching circuit (i.e., the matching bridge). The matching of the antenna, according to the present invention, can be adjusted by changing the length of the matching bridge  330 . This is accomplished by simply changing the location of the grounded post  335 . The length of the matching bridge is generally in the order of 0.01λ to 0.1λ. 
     It is evident from FIG. 3 that the two patch parts  305  and  310  of the antenna system are of different sizes. By controlling the size of the patch parts, the antenna is capable of being tuned to different frequency bands. The first patch part  305  of the multiple band antenna is of a size (generally a quarter wavelength of the frequency band to which the patch part is to be tuned) so as to be resonant at frequencies in a first lower band, and the second patch part  310  is of a size so as to be resonant at frequencies in a second higher band. The two patch parts can be made resonant at any frequency. For example, the first band may be the GSM band and the second band may be the DCS band. Some of the possible combinations of low and high bands may include GSM+PCS, GSM+WCDMA, DCS+WCDMA, GSM+GPS, GSM+ISM, or any other combination of lower and higher frequency bands. 
     As set forth above, each patch part  305  and  310  includes a slot  340  which acts to separate the patch part into sub-parts. Each sub-part of a patch part is resonant at a different frequency within the same frequency band to which the patch part is tuned. For example, if the first patch part  305  is of a size that enables it to be resonant at frequencies in the GSM band, then the sub-parts of patch part  305  could be made resonant at different frequencies within the GSM band. As a result, a broader bandwidth can be achieved. 
     One skilled in the art will appreciate that, as an alternative, three or more subparts can be formed in each patch part. FIG. 4 illustrates an exemplary configuration in which each patch part is formed of three sub-parts. As illustrated, the first patch part  405  is cut into three sub-parts  405 A- 405 C and the second patch part  410  is also cut into three sub-parts  410 A- 410 C. Each of the sub-parts can be made resonant at a different frequency within the same frequency band to which their respective patch part is resonant. As such, broader bandwidth can be achieved by such a configuration, however, tuning is more difficult. 
     Returning to FIG. 3, the patch parts  305  and  310  can be of any shape, including three dimensional. The size of the patch parts, however, should be approximately a quarter of the wavelength of the frequency to which the patch parts are to be tuned. 
     The resonant frequencies and bandwidth of the built-in multiple band patch antenna are dependent upon the area and thickness of the dielectric substrate, the type of dielectric material selected (i.e., the dielectric constant), the patch size and the size and location of the slots. One skilled in the art will appreciate that an increase in the area or thickness of the dielectric substrate or patch size or a decrease in the value of the dielectric constant results in an increase in the bandwidth which can be achieved. Moreover, the bandwidth also depends on the size and location of the slots formed in the patch parts. 
     As is evident from FIG. 3, the built-in multiple band patch antenna can be mounted at the edge of the PCB which provides for better radiation efficiency and bandwidth. In addition, the PCB space requirement for the built-in multiple band patch antenna is minimized due to its small size. 
     FIGS. 5A and 5B illustrate a technique by which the broad band, multiple band patch antenna is formed. The broad band, multiple band patch antenna can be formed from a conventional patch antenna by forming a slot in the conventional patch antenna, such as the one illustrated in FIG. 1A, along an axis of the matching bridge so that two patch parts are created, connected to opposite sides of the matching bridge (see FIG.  5 A). Each part is of a size which enables it to be resonant within a different frequency band. The larger part  505  is resonant at a lower frequency and the smaller part  510  is resonant at a higher frequency. The actual forming of the slot can be performed by, for example, any one of the following methods: cutting, etching, MID ( 3 D metalization) or chemical processing. 
     A slot is then formed in each patch part so as to divide each patch part into sub-parts (see FIG.  5 B). The slots can be of an arbitrary shape; however, slot shape also affects the achievable bandwidth. As indicated above, each sub-part of a patch part is resonant at a different frequency or frequency range within the same frequency band to which the patch part is tuned thereby increasing the bandwidth of the antenna. 
     In order to make the antenna operable in three frequency ranges, the high band patch part  510  may be modified. Specifically, the high band patch part  510  can be moved out of the PCB  315  (of FIG.  3 ). 
     As illustrated in FIG. 6 a , the high band patch element  610  is placed outside the PCB  615  according to exemplary embodiments of the present invention. This results in an increase in the equivalent volume of the antenna at the higher frequency band. A small antenna has a small volume which results in a small bandwidth. This is illustrated in FIGS. 6 b  and  6   c . With reference to FIG. 6 b , if an antenna  610  is placed on the PCB  615 , the volume  675  of the antenna is on the top side of the PCB  615 . By placing the antenna  610  outside the PCB  615  as illustrated in FIG. 6 c , the equivalent antenna volume  675  is at both the top and bottom sides of the PCB  615  which results in a greater bandwidth. The EM waves  660  corresponding to the high band antenna  610  are more easily matched to the space when the antenna is outside the PCB and result in a broader bandwidth. The EM waves  660  of the high band antenna element  610  in FIG. 6 b  radiate in the manner illustrated. The PCB, which may be made of a conducting element, prevents the waves from traveling through the PCB. In an embodiment of the present as illustrated in FIG. 6 c , the EM waves radiate on both sides of the PCB due to the location of the high band antenna  610 . The radiating elements of the high band patch may be supported by a substrate as the high band patch is moved away from the PCB. It may also be etched outside of the communication device. The substrate may be plastic for example. 
     Since the high band patch part  510  is now outside of the PCB, it may be printed in three dimensions which flexibility makes it useful for certain commercial applications. For aesthetic reasons, the handset may not be designed in the traditional rectangular or box-like shape. It may, for example, be designed with a curvature shape. Therefore, the built-in antenna will be in three dimensions. The high band element  610  can now be used to tune to both the DCS and the PCS bands while the low band element  605  is still tuned to the GSM band. 
     The two patches, i.e., high band element  610  and low band element  605 , are connected to the matching bridge  630  from opposite directions. One end of the matching bridge  630  is an antenna feed pin  625  while the other end is the matching grounded post  635 . As described earlier, the bigger patch is the low band element  605  which is resonant at the lower frequency band and the smaller patch is the high band element  610  that is resonant at the higher frequencies. 
     Since the patch size determines the dual band resonant frequencies, the antenna of the present invention can be designed for GSM, DCS and PCS frequencies. The patches may be of any shape. Each patch may be flat and very thin giving the appearance of not being three dimensional. The high band element may also be similar in appearance to conventional antennas which are enclosed in plastic or other similar structures. 
     An edge of each of the patch elements  605  and  625  is connected to the matching bridge  630 . The remaining edges of the patch elements are not connected to the matching bridge  630 . As described above with reference to FIG. 3, the slots  340  on the patches  305  and  310  divide the patches into sub-parts. Similarly, according to exemplary embodiments of Applicant&#39;s invention, as illustrated in FIG. 6, slots  640  divide the patches  605  and  610  into sub-parts. Each of these sub-parts is resonant at a particular frequency within each frequency band for which the patch is designed. Two such sub-parts  645  and  650  corresponding to the low band element  605  and two sub-parts  655  and  660  corresponding to the high band element  610  are illustrated in FIG.  6 . These sub-parts results in wider band patch antenna as described above. The subparts may be of varius shapes. 
     With respect to the characteristics of each of the patch elements, they have been described above with respect to FIG.  3 . For instance, the bandwidth depends on the size of the patch, the shape of the patch, shape of the slots, the location of the slots, the thickness of the substrate and the substrate material. A larger patch area results in a broader bandwidth for the antenna. A larger gap between the patch and an edge of the PCB also results in a broader bandwidth for the antenna. The length of the matching bridge may be changed to adjust the matching of the antenna. 
     An antenna according to one embodiment of the present invention is illustrated in FIG. 7 in which the high band element  710  is rectangular and is located over the top edge of the PCB  715 . The space between the element  710  and the PCB  715  permits the antenna to be tuned to the PCD and DCS frequency ranges. FIG. 8 illustrates another exemplary antenna design in which the high band element  810  is also over the top edge of the PCB  815  but is formed as an arc. Similarly, in FIG. 9, the high band element  910  is over the top edge of the PCB  915  and is formed with one end projecting upward. In FIG. 10, the high band element  1010  is over the top edge of the PCB  1015  and is a meandering element which can be altered to form a stub. 
     In order to illustrate the effectiveness of the present invention, FIG. 11 sets forth results of a simulation for the exemplary dual band patch antenna illustrated in FIG.  7 . Purely for purposes of illustrating the present invention, the following values for the various parameters enumerated above for a semi built-in multi-band printed antenna may be used. The antenna, i.e., both the high and low patch elements  705  and  710  of FIG. 7, has dimensions of 30 mm×40 mm. The antenna has a height of 5 mm. The space  740  by which the high patch element  710  is separated from the PCB  715  may be 5 mm. The substrate may be plastic and may be 1 mm in thickness. The parts of the high and low element patches are made resonant at the GSM, DCS and PCS frequency ranges. 
     FIG. 11 illustrates the VSWR performance of this design. The bandwidth is 8.7% (i.e., about 80 MHz) at the GSM band for a VSWR of less than 2.35:1. In the DCS frequency band, the bandwidth is 15.6% (i.e., about 280 MHz) for a VSWR less than 3.2:1. Finally, at the PCS band, the bandwidth is 14.6 (i.e., about 280 MHz) for a VSWR of less than 3.2:1. As is evident from FIG. 11, this antenna meets the requirements of a GSM/DCS/PCS triple frequency application. 
     The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed above. For example, while the antenna of the present invention has been discussed primarily as being a radiator, one skilled in the art will appreciate that the dual band patch antenna of the present invention would also be used as a sensor for receiving information at specific frequencies. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.