Patent Publication Number: US-6989785-B2

Title: Low-profile, multi-band antenna module

Description:
FIELD OF THE INVENTION 
     The present invention relates to low-profile antennas, and more particularly to low-profile antennas with multi-band capabilities. 
     BACKGROUND OF THE INVENTION 
     Vehicles are receiving an increasing number of wireless services, such as cellular phone service, satellite radio, terrestrial radio, and Global Positioning System (GPS) service. As additional wireless services become available, a vehicle must be equipped to accommodate the different types of signals. Multi-band antennas are widely used in vehicles. When designing multi-band antennas, designers focus on cost, aesthetics, and aerodynamics. 
     Conventional multi-band antennas have a single receiving element with a broad bandwidth and are designed to receive signals from all bands of interest. However, it is difficult to make a single receiving element receive multiple bands because each wireless service requires a different radiation pattern. 
     Other multi-band antennas have a single module that includes multiple antenna receiving elements. Each antenna element receives a different service at a given frequency. The signals received by each antenna element are sent to different receivers using separate cables. However, as the number of cables increases, the cost increases. Additionally, certain combinations of antenna receiving elements can cause interference. 
     In addition to cost, the overall dimensions of the antenna are important. A large number of antenna receiving elements increases the size of the antenna module. As the size increases, the aerodynamic drag increases, which may cause wind noise and/or reduce fuel economy. 
     SUMMARY OF THE INVENTION 
     A low-profile multi-band antenna module according to the present invention includes a first antenna that transmits first radio frequency (RF) signals in a first RF band. A second antenna transmits second RF signals in a second RF band. A first RF multiplexer combines the first and second RF signals for transmission. The first antenna, second antenna, and first RF multiplexer are arranged on a panel. 
     In other features, a transmission line has a first end that communicates with the first RF multiplexer and transmits the first and second RF signals. A second RF multiplexer communicates with a second end of the transmission line and separates the first and second RF signals. The first and second RF multiplexer implement out-of-band rejection to minimize interference between the first and second RF signals. The first RF signals are transmitted from the second RF multiplexer to a first transceiver and the second RF signals are transmitted from the second RF multiplexer to a second transceiver. At least one of the first antenna and the second antenna communicates with at least one amplifier. The transmission line supplies direct current (DC) power to at least one amplifier. 
     In still other features of the invention, the first and second antenna are arranged on the panel in an orientation that minimizes electrical interference between the first and second antenna. A combination of the first and second antenna minimizes interference between the first and second RF band. At least one of the first antenna and the second antenna radiates circular polarization and vertical polarization that is ideal for satellite radio communication. At least one of the first antenna and the second antenna radiates circular polarization that is ideal for global positioning system (GPS) satellite communication. At least one of the first antenna and the second antenna radiates vertical polarization that is ideal for terrestrial communication. 
     In yet other features, the first RF band is an industrial, scientific, and medicine (ISM) band, the second RF band is a satellite radio band, and the second antenna suppresses interference from the ISM band and is located adjacent to the first antenna. The first RF band is a personal communications services (PCS) band, the second RF band is a satellite radio band, and the second antenna suppresses interference from the PCS band and is located adjacent to the first antenna. The first RF band is a PCS band, the second RF band is a GPS band, and the first and second antenna are located at opposite ends of the panel to minimize coupling between the first and second antenna. The first RF band is a satellite radio band and the first antenna is located near a center of the panel. The first RF band is a first ISM band at a first frequency, the second RF band is a second ISM band at a second frequency, the first antenna is located adjacent to the second antenna, the first antenna suppresses interference from the second ISM band, and the second antenna suppresses interference from the first ISM band. The first RF band is a GPS band, the second RF band is an ISM band, and the first antenna suppresses interference from the ISM band and is located adjacent to said second antenna. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a prior art multi-band antenna module with a single receiving element; 
         FIG. 2  is a prior art multi-band antenna module with multiple receiving elements; 
         FIG. 3  is a top plan view of an exemplary multi-band antenna module; 
         FIG. 4  is a bottom plan view of the multi-band antenna module of  FIG. 3 ; 
         FIG. 5  is a graph showing the relative power of an interferer in the PCS band received by a satellite radio band antenna as function of frequency; 
         FIG. 6  is a graph showing the relative power of an interferer in the ISM band at 2450 MHz received by a satellite radio band antenna as a function of frequency; 
         FIG. 7  is a graph showing coupling between a GPS band antenna and an ISM band antenna at 2450 MHz as a function of distance; 
         FIG. 8  is a graph showing coupling between an ISM band antenna at 5800 MHz and a GPS band antenna as a function of distance; 
         FIG. 9  is a graph showing coupling between a GPS band antenna and a PCS band antenna as a function of distance; 
         FIG. 10  is a graph showing coupling between a satellite radio band antenna and an ISM band antenna at 2450 MHz as a function of distance; 
         FIG. 11  is a graph showing coupling between a satellite radio band antenna and an ISM band antenna at 5800 MHz as a function of distance; and 
         FIG. 12  is a graph showing coupling between a satellite radio band antenna and a PCS band antenna as a function of distance. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. 
     Referring to  FIG. 1 , a first prior art multi-band antenna module  10  includes a single receiving element  12  with a broad bandwidth. The single receiving element  12  is mounted on a ground plane  14  and has a broad radiation pattern  16  designed to receive signals from all bands of interest. The received signals are transmitted on a single cable  18  to a set of filter banks  20 , where the signals are filtered and distributed to their appropriate receivers. While a single receiving element  12  and a single cable  18  are used, it is difficult for a broad radiation pattern  16  to receive all of the desired signals. Many radio frequency (RF) services require different radiation patterns at specific frequencies. 
     Referring now to  FIG. 2 , a second prior art multi-band antenna module  28  includes a group of receiving elements  30 - 1 ,  30 - 2 , and  30 - 3  mounted on the ground plane  14 . The group of receiving elements  30 - 1 ,  30 - 2 , and  30 - 3  produces a combination of radiation patterns  32 - 1 ,  32 - 2 , and  32 - 3 . Each receiving element  32 - 1 ,  32 - 2 , or  32 - 3  receives signals for a wireless service at a specific frequency. The signals are routed to an appropriate receiver on individual cables  34 - 1 ,  34 - 2 , and  34 - 3 . While signals for different wireless services are received, each service uses an individual cable  34 - 2 ,  34 - 2 , or  34 - 3 , which is costly and aesthetically displeasing. 
     Referring now to  FIGS. 3 and 4 , an exemplary multi-band antenna module  42  according to the present invention includes a global positioning system (GPS) band antenna  44 , a first industrial, scientific, and medicine (ISM) band antenna  46  that operates at a first frequency, a second ISM band antenna  48  that operates at a second frequency, a satellite radio band antenna  50 , and a personal communications services (PCS) band antenna  52  mounted on a panel  54 . The first ISM band antenna preferably operates at 2450 MHz, and the second ISM band antenna preferably operates at 5800 MHz. The satellite radio band antenna  50  radiates circular polarization and vertical polarization. The circular polarization is directed overhead, and the vertical polarization is directed towards the horizon. This enables the satellite radio band antenna  50  to communicate with satellites and terrestrial repeaters. The satellite radio band antenna  50  is preferably a cavity-backed crossed-slot antenna, such as the antenna described in “Crossed-Slot Antenna for Mobile Satellite and Terrestrial Radio Receptions”, Ser. No. 10/409,513, filed Apr. 8, 2003, which is hereby incorporated by reference in its entirety, and can be constructed in many shapes including circular and rectangular. 
     The GPS band antenna  44  radiates circular polarization directed overhead. This enables the GPS band antenna  44  to communicate with satellites. The GPS band antenna  44  is preferably a dielectric-loaded patch antenna. The first ISM band antenna  46 , the second ISM band antenna  48 , and the PCS band antenna  52  radiate vertical polarization directed toward the horizon and no signal towards zenith. This radiation pattern is ideal for terrestrial communication and is similar to that of a monopole antenna. The first ISM band antenna  46 , the second ISM band antenna  48 , and the PCS band antenna  52  are preferably center-fed patch antennas, such as the antenna described in “Low-Profile Antenna”, Ser. No. 10/408,004, filed Apr. 4, 2003, which is hereby incorporated by reference in its entirety. Center-fed patch antennas are low-profile and preferably constructed using low-cost stamped sheet metal or printed circuit techniques. An important feature of the multi-band antenna module  42  is that it is low-profile. All of the antennas  44 ,  46 ,  48 ,  50 , and  52  are less than six millimeters tall and are optimized to produce the radiation pattern for their required services. 
     The positioning of the antennas  44 ,  46 ,  48 ,  50 , and  52  on the panel  54  is important because of interference and coupling between the antennas  44 ,  46 ,  48 ,  50 , and  52 . The PCS band antenna  52  and the GPS band antenna  44  are located at opposite ends of the panel  54  due to their high coupling. The satellite radio band antenna  50  is located in the center of the panel  54  due to its large size. The first ISM band antenna  46  is located adjacent to the second ISM band antenna  48  because a receiver for either antenna is typically designed to allow for interference from the other. The first ISM band antenna  46  and the second ISM band antenna  48  are located adjacent to the satellite radio band antenna  50 . The satellite radio band antenna  50  has unique suppression capabilities in the ISM band at 2450 MHz and is narrow-band enough to suppress most of the radiation from the ISM band at 5800 MHz. The satellite radio band antenna  50  also suppresses radiation from and is located adjacent to the PCS band antenna  52 . The first ISM band antenna  46  and the second ISM band antenna  48  do not receive significant interference from and are located adjacent to the GPS band antenna  44 . 
     The positioning of the antennas  44 ,  46 ,  48 ,  50 , and  52  on the panel  54  is also important because one or more of the antennas  44 ,  46 ,  48 ,  50 , and  52  may contain built-in amplifiers. This is especially true for the satellite radio band antenna  50  and the GPS band antenna  44 , which are receive-only antennas. The satellite radio band antenna  50  and the GPS band antenna  44  receive weak signals from distant satellites and typically include integrated low-noise amplifiers. The integrated low-noise amplifiers can easily be saturated and require the antennas  44 ,  46 ,  48 ,  50 , and  52  to have low inter-element coupling. The input to low-noise amplifiers is often unfiltered and relies upon the inherent out-of-band rejection capabilities of the antenna. The amplified signal may need further filtering, so out-of-band signals are rarely a problem in the receiver system. Therefore, the signals from the antennas  44 ,  46 ,  48 ,  50 , and  52  may be combined onto a single cable using an RF multiplexer. 
     A first RF multiplexer  56  is mounted on the bottom side of the panel  54  in  FIG. 4 . The panel  54  is formed as a printed circuit board to minimize the size of the multi-band antenna module  42 , and feed holes  58  connect the antennas  44 ,  46 ,  48 ,  50 , and  52  to feed circuits  60 . The feed circuits  60  connect the feed holes  58  to the first RF multiplexer  56 . The first RF multiplexer  56  combines the signals from the antennas  44 ,  46 ,  48 ,  50 , and  52  for transmission. A second RF multiplexer  62  is located remote from the multi-band antenna module  42 . The second RF multiplexer  62  separates the signals from the antennas  44 ,  46 ,  48 ,  50 , and  52  to be transmitted on cables  64  to separate transceivers. A transmission line  66  connects the first RF multiplexer  56  and the second RF multiplexer  62 . The panel  54  includes amplifiers  68  for one or more of the antennas  44 ,  46 ,  48 ,  50 , and  52 . The amplifiers  68  may contain multiple internal amplifiers and filters. A power cable  70  is connected to the second RF multiplexer  62 . The power cable  70  supplies direct current (DC) power that is transmitted over the transmission line  66  to power the amplifiers  68 . The first RF multiplexer  56  and the second RF multiplexer  62  preferably include out-of-band rejection to filter the signals from the antennas  44 ,  46 ,  48 ,  50 , and  52 , or, in the alternative, additional filters are used. Combining all of the signals from the antennas  44 ,  46 ,  48 ,  50 , and  52  and a DC supply on the transmission line  66  results in a simpler design and a lower installation cost. 
     Referring now to  FIGS. 5 and 6 , the ability of the satellite radio band antenna  50  to suppress the PCS band and the ISM band at 2450 MHz is illustrated.  FIG. 5  shows an interferer signal  78  tuned to the PCS band, indicated at  80 , and a received signal  82  by the satellite radio band antenna  50  at different frequencies.  FIG. 6  shows an interferer signal  84  tuned to the ISM band at 2450 MHz, indicated at  86 , and a received signal  88  by the satellite radio band antenna  50  at different frequencies. The satellite radio band is indicated at  90  in  FIGS. 5 and 6 . The suppression is important because the satellite radio band antenna  50  has a sensitive amplifier, and it is important not to saturate it. The PCS band antenna  52 , the first ISM band antenna  46 , and the second ISM band antenna  48  transmit and receive signals. Therefore, it is important that as little energy as possible from those bands leaks into the satellite radio band antenna  50 . It is difficult to isolate the ISM band and the satellite radio band because the frequencies are close together. The signal rejection in the 2.45 GHz band is particularly strong due to a sharp dip  92  in the satellite radio band antenna  50  sensitivity. This significantly helps to isolate the bands. 
     Referring now to  FIGS. 7–12 , there is a risk of the transmission of one of the antennas  44 ,  46 ,  48 ,  50 , and  52  saturating the amplifier of another antenna since many of the antennas include integrated amplifiers. The coupling between antennas that transmit and receive and those that only receive are especially critical. The coupling between each of the antennas  44 ,  46 ,  48 ,  50 , and  52  is small, even for short separation distances. In most cases the coupling is less than −20 dB, which is desirable. 
       FIG. 7  shows the GPS band antenna coupling  100  and the first ISM band antenna coupling  102 .  FIG. 8  shows the GPS band antenna coupling  104  and the second ISM band antenna coupling  106 .  FIG. 9  shows the GPS band antenna coupling  108  and the PCS band antenna coupling  110 . Because of the high coupling, the GPS band antenna  44  and the PCS band antenna  52  are located at opposite ends of the panel  54 .  FIG. 10  shows the satellite radio band antenna coupling  112  and the first ISM band antenna coupling  114 . The coupling between the satellite radio band antenna  50  and the first ISM band antenna  46  would be much greater if the satellite radio band antenna  50  did not have suppression abilities for the ISM band.  FIG. 11  shows the satellite radio band antenna coupling  116  and the second ISM band antenna coupling  118 .  FIG. 12  shows the satellite radio band antenna coupling  120  and the PCS band antenna coupling  122 . Most of the coupling occurs in the satellite radio band, where the PCS band antenna  52  does not transmit. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.