Abstract:
An antenna unit is disclosed. The antenna unit includes a wire antenna element and a patch antenna element. The wire antenna element creates a null at low-elevation angles to provide directional antenna patterns in azimuth planes. Nulls of the terrestrial signal pattern are directed toward the passenger compartment of a vehicle to create a larger spatial region for reception of terrestrial signals.

Description:
TECHNICAL FIELD  
   The present invention generally relates to an antenna unit that has directional reception capabilities. 
   BACKGROUND OF THE INVENTION  
   It is known in the art that automotive vehicles are commonly equipped with audio radios that receive and process signals relating to amplitude modulation/frequency modulation (AM/FM) antennas, satellite digital audio radio systems (SDARS) antennas, global positioning system (GPS) antennas, digital audio broadcast (DAB) antennas, dual-band personal communication systems digital/analog mobile phone service (PCS/AMPS) antennas, Remote Keyless Entry (RKE) antennas, Tire Pressure Monitoring System antennas, and other wireless systems. 
   Currently, it is known that patch antennas are employed for reception of GPS [i.e. right-hand-circular-polarization (RHCP) waves] and SDARS [i.e. left-hand-circular-polarization (LHCP) waves]. SDARS patch antennas may be considered to be a ‘single element’ antenna that incorporates performance characteristics of ‘dual element’ antennas that essentially receives terrestrial and satellite signals. SDARS—offer digital radio service covering a large geographic area, such as North America. Satellite-based digital audio radio services generally employ either geo-stationary orbit satellites or highly elliptical orbit satellites that receive uplinked programming, which, in turn, is re-broadcasted directly to digital radios in vehicles on the ground that subscribe to the service. SDARS also use terrestrial repeater networks via ground-based towers using different modulation and transmission techniques in urban areas to supplement the availability of satellite broadcasting service by terrestrially broadcasting the same information. The reception of signals from ground-based broadcast stations is termed as terrestrial coverage. Hence, an SDARS antenna is required to have satellite and terrestrial coverage with reception quality determined by the service providers, and each vehicle subscribing to the digital service generally includes a digital radio having a receiver and one or more antennas for receiving the digital broadcast. GPS antennas, on the other hand, have a broad hemispherical coverage with a maximum antenna gain at the zenith (i.e. hemispherical coverage includes signals from 0° elevation at the earth&#39;s surface to signals from 90° elevation up at the sky). Emergency systems that utilize GPS, such as OnStar™, tend to have more stringent antenna specifications as they also incorporate cellular phone communication antennas. 
   Unlike GPS antennas which track multiple satellites at a given time, SDARS patch antennas are operated at higher frequency bands and presently track only two satellites at a time. Thus, the mounting location for SDARS patch antennas makes antenna reception a sensitive issue with respect to the position of the antenna on the vehicle. As a result, SDARS patch antennas are typically mounted exterior to the vehicle, usually on the roof, or alternatively, inside the vehicle in a hidden location. Even further, although patch antenna circular polarization patterns are generally omni-directional in the azimuth plane so that reception does not favor any particular direction, antenna reception may be limited due to antenna position relative to the vehicle. 
   Having a null in a certain direction reduces the signal reception to a smaller spatial region. As a result, some portion of the antenna&#39;s reception becomes useless and thereby limits the functionality of the antenna. In one scenario, orientation of a patch antenna in a diversity application may lead to the deployment of additional antennas positioned throughout the vehicle to cover all directions of possible signal reception. 
   Thus, when mounted inside a vehicle, conventional patch antennas have inherent performance issues relating to directionality of the reception. Accordingly, it is therefore desirable to provide an antenna unit that improves the directionality of patch antenna gains at low elevation angles to improve the terrestrial reception, and, in a diversity application, reduce the number of patch antennas needed to compensate for nulls in the pattern. 
   SUMMARY OF THE INVENTION  
   The inventors of the present invention have recognized these and other problems associated with patch antennas. To this end, the inventors have developed an antenna unit comprising a wire antenna element and a patch antenna element. Nulls of the terrestrial signal polarization pattern are directed toward the passenger compartment of a vehicle to create a larger spatial region for reception of terrestrial signals that propagate toward the vehicle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1A  illustrates a top view of an antenna unit according to an embodiment; 
       FIG. 1B  illustrates a cross-sectional view of the antenna assembly according to  FIG. 1A ; 
       FIG. 2A  illustrates a top view of an antenna unit according to another embodiment; 
       FIG. 2B  illustrates a cross-sectional view of the antenna assembly according to  FIG. 2A ; 
       FIG. 3A  illustrates a top view of an antenna unit according to another embodiment; 
       FIG. 3B  illustrates a cross-sectional view of the antenna assembly according to  FIG. 3A ; 
       FIG. 4A  illustrates a top view of an antenna unit according to another embodiment; 
       FIG. 4B  illustrates a cross-sectional view of the antenna assembly according to  FIG. 4A ; and 
       FIG. 5  illustrates potential antenna unit configurations for a diversity application. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT  
   The above described disadvantages are overcome and a number of advantages are realized by the inventive antenna unit, which is generally illustrated at  10 ,  100 ,  200 ,  300  in  FIGS. 1A–4B . Essentially, the antenna unit  10 ,  100 ,  200 ,  300  improves directional linear polarization patterns at low-elevation angles, particularly at 0°, of a wire antenna element  12 ,  102 ,  202 ,  302  while maintaining circular polarization characteristics of a patch antenna element  11 ,  111 ,  211 ,  311 . Referring initially to  FIGS. 1A and 1B , the antenna unit  10  generally includes a straight-wire antenna element  12  soldered to a patch antenna element  11 . The patch antenna element  11  includes a single feed pin  14  ( FIG. 1B ) extending through a high dielectric substrate  18  that electrically couples a bottom metallization  16   b  to a top metallization  16   a  where the straight-wire antenna element  12  is soldered. The top and bottom metallizations  16   a,    16   b  may include any desirable metallization, such as, for example, a silver conductive film. 
   As seen more clearly in  FIG. 1A , the straight-wire antenna element  12  is positioned in an off-centered configuration about a central area, C, of the antenna unit  10 . More specifically, the straight-wire antenna element  12  is off-centered about the top metallization  16   a,  which is seen more clearly at the intersection of dashed lines, D, that defines the central area, C, of the antenna unit  10 . Additionally, as seen more clearly in  FIG. 1B , the single feed pin  14  is off-centered from the straight-wire antenna element  12 . Although the single feed pin  14  is off-centered from the straight-wire antenna element  12 , the feed pin  14  may be aligned with the straight-wire antenna element  12 , if desired. The height, H, of the straight-wire antenna element  12  from top metallization  16   a  is less than free-space quarter wavelength due to the presence of high dielectric substrate  18  which makes the straight-wire antenna element  12  appear electrically longer. For example, the straight-wire antenna element  12  may include a height, H, approximately equal to, for example, 2 mm positioned over the high dielectric substrate  18  having a thickness, T, approximately equal to, for example, 5 mm, that makes the height, H, physically appear to be 10 mm high rather than 2 mm. 
   Alternate embodiments of the antenna unit  10  are seen generally at reference numerals  100 ,  200 ,  300  in  FIGS. 2A–4B . Each antenna unit  100 ,  200 ,  300  includes a top metallization  106   a,    206   a,    306   a  that is electrically connected to a bottom metallization  106   b,    206   b,    306   b  through a substrate  108 ,  208 ,  308  by a single feed pin  104 ,  204 ,  304 . As illustrated, the antenna unit  100  includes a helical antenna element  102  ( FIGS. 2A ,  2 B) and the antenna unit  200  includes a cross antenna element  202  ( FIGS. 3A ,  3 B) that are each soldered to the top metallization  106   a ,  206   a , respectively. The cross antenna element  202  generally includes a straight-wire stem portion  212  and an X-shaped cross portion  210 . Alternatively, the antenna unit  300  includes a top-loaded monopole element  302  ( FIG. 4A ,  4 B) joined directly to the single fed pin  304 . The top-loaded monopole element  302  generally includes a top plate  310 , a first stem  312  soldered to the top metallization  306   a , and a second stem  314  that is electrically coupled to the feed pin  304 . 
   In application, the helical antenna  102  presents an inductive loading to the antenna unit, and the X-shaped cross portion  210  and top plate  310  each presents a capacitive load to the respective antenna units  200 ,  300  to electrically extend the height of the antenna unit  200 ,  300 . As illustrated in  FIGS. 2A–4B , the antenna elements  102 ,  202 ,  302  and single feed pins  104 ,  204 ,  304  are off-centered in a similar fashion as described above with respect to the straight-wire antenna element  12 . In application, the wire antenna elements  12 ,  102 ,  202 ,  302  may be off-centered from the central area, C, at any desirable distance, such as, for example, 1 mm. Because most patch antennas may have a width approximately equal to 10 mm, a shift of 1 mm, for example, is approximately equal to a 10% shift in the overall width, W, of the patch antenna  11 ,  111 ,  211 ,  311 . Although each wire antenna element  12 ,  102 ,  202 ,  302  is shown off-center, the wire antenna elements  12 ,  102 ,  202 ,  302  do not have to be off-centered, and may include any desirable positioning, such as, for example, a centered positioning. 
   The directionality of the linear polarization pattern is maintained by controlling the height of the wire antenna element  12 ,  102 ,  202 ,  302 , and by providing the single pin feed  14 ,  104 ,  204 ,  304  on the top surface of the antenna unit  10 ,  100 ,  200 ,  300  for the patch antenna  11 ,  111 ,  211 ,  311  and the wire antenna  12 ,  102 ,  202 ,  302 . 
   As explained above, circular polarization patterns are generally omni-directional. Because the antenna units  10 ,  100 ,  200 ,  300  have a small ground plane, the radiation patterns tend to become highly directional by receiving more radiation at zenith (i.e. elevation angle of 90°) and receiving less radiation patterns at lower elevation angles (i.e. elevation angles closer to 0°). In application, when any of the antenna units  10 ,  100 ,  200 ,  300  are mounted inside a vehicle, V, ( FIG. 5 ), the directional antenna power pattern is faced away from the vehicle. More specifically, the ground plane,of the antenna unit  10 ,  100 ,  200 ,  300  is faced toward the inside of the vehicle and the wire antenna element  12 ,  102 ,  202 ,  302  is faced toward the outside of the vehicle. By facing the directional antenna power pattern of the antenna unit  10 ,  100 ,  200 ,  300  away from the inside of the vehicle, the null in the power pattern may be selectively located toward the inside of the vehicle. As a result, the antenna unit  10 ,  100 ,  200 ,  300  favors a particular direction for signal reception, creating a larger spatial region for radiation patterns that propagate toward the vehicle. 
   The antennas units  10 ,  100 ,  200 ,  300 , when positioned in a vehicle as described above, may improve upon conventional vehicular diversity configurations. As known, diversity antenna applications operate on the principle such that two or more antenna units complement each other to cover the expected satellite signal from one or more satellites to increase the probability of uninterrupted reception of the satellite signals when physical obstructions, such as tall buildings or trees impede the line of sight (LOS) of at least one of the antenna units. This is accomplished by receiving a terrestrially-repeated signal of the obstructed satellite signal. As seen in  FIG. 5 , a diversity antenna application may be applied using any desirable antenna placement configuration. For example, antenna units may be located under the trunk lid in a center location (TC), a left, driver-side location (TL), a right, passenger-side location (TR), a hood location (H), a left, driver-side front quarter panel location (LFQ), a right, passenger-side front quarter panel location (RFQ), an instrument panel location (IP), an left, driver-side mirror location (LM), a right, passenger-side mirror location (RM), or any other location about the vehicle, V, desired by the antenna designer. By implementing the antenna unit  10 ,  100 ,  200 ,  300  in a diversity application such that nulls in the power pattern face the inside of the vehicle (i.e. the passenger compartment area), an improved diversity application is provided. For example, if antenna units  10 ,  100 ,  200 ,  300  are located at the LFQ, RFQ, TL, and TR locations, such that the nulls of each antenna location are faced toward the inside of the vehicle, a uniform linear polarization reception is ensured 360° about the vehicle. 
   The present invention has been described with reference to certain exemplary embodiments thereof. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the exemplary embodiments described above. This may be done without departing from the spirit of the invention. The exemplary embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is defined by the appended claims and their equivalents, rather than by the preceding description.