AM/FM dual grid antenna

[0001] This invention generally relates to vehicle radio antennas and more specifically relates to vehicle radio antennas which are integrated with the vehicle windows.

[0002] In order to enhance a vehicle's aesthetic qualities, it is common to integrate vehicle radio antennas with one or more of the vehicle's windows (commonly known as hidden antenna systems or on-glass AM/FM antenna systems). Unlike mast (i.e. rod) antennas, on-glass antenna systems do not introduce any external vehicle protrusions and they typically offer excellent mechanical stability and satisfactory reception performance. Although on-glass antennas are widely used, they do suffer from various drawbacks. Specifically, on-glass antennas are difficult to design because a small change in a vehicle's body design can radically change the reception performance of the antenna.

[0003] On-glass antenna systems are usually fabricated by printing metallic conductors on an inner surface of the back-glass or the side-glass (FIG. 1) of a vehicle window. A low-noise-amplifier (LNA) circuit is typically mounted in close proximity to the on-glass antenna and is electrically coupled to the on-glass antenna to amplify the weak signal received by the antenna before it is sent to the radio receiver for further conditioning. The on-glass antennas are typically fed vertically (close to the vehicle roof) so that the LNA circuit can be housed in the vicinity where the vehicle roof intersects the window.

[0004] Referring to FIG. 2, it is also known to locate on-glass antennas on the back glass 3 (i.e. rear windshield glass) of a vehicle, V, to provide an AM/FM antenna system. As illustrated, the rear windshield glass 3 includes a plurality of horizontally-fed wires 4 that function as a defroster grid to melt or snow and ice from the glass 3. Additional grid lines (not shown) that are on or, in close proximity to the horizontal defroster grid lines 4 may also be used as the AM/FM antenna system. However, such additional grid line are generally not adequate to provide a desired signal reception performance.

[0010] Referring to FIG. 3, an AM/FM antenna 10 is shown located on a rear-windshield glass 11. Although the illustrated embodiment is disclosed in conjunction with a rear-windshield glass implementation, it is to be understood that the illustrated embodiment is not limited to a rear-windshield glass implementation and that the illustrated embodiment can just as easily be implemented on the side glass or front-windshield of a vehicle, V.

[0011] The AM/FM antenna consists of two separate wire-grid structures 12a, 12b. The first grid structure 12a, which is the FM antenna, utilizes the already existing defroster grid, which includes a plurality of horizontally-disposed wires 14a–14d and an added modification defined by a plurality of vertical wires 16a–16d and a defroster grid perimeter defined by side wires 20a, 20b and upper and lower wires 20c, 20d. The FM antenna 12a also includes a main feed 18 that extends generally horizontally and connects to the defroster-grid perimeter at the side wire 20a. As illustrated, the vertical wires 16a–16d intersect the horizontally disposed wires 14a–14d to connect the upper and lower wires 20c, 20d.

[0012] The second grid structure 12b, which is the AM antenna, is located above the FM antenna 12a. The AM antenna 12b includes a main feed 22 that extends generally horizontally and is connected to a bifurcated wire feed fork that includes a side wire 24a and upper and lower wires 24b, 24c. As illustrated, the AM antenna 12b is electromagnetically coupled to the bifurcated wire feed fork. A plurality of vertical wires 28a–28c intersect a plurality of horizontally disposed wires 30a–30c to connect the upper and lower wires 26b, 26c.

[0013] The side wire 26a, the upper and lower wires 26b, 26c, the vertical wires 28a–28c, and the horizontally-disposed wires 30a–30c, form multiple loop structures, which is shown for example, at the arrow, L, which is formed by the wires 28a, 28c, 30b, 30c. Accordingly, the loop structures, such as L, aid the directionality of the FM antenna pattern over its entire frequency range. Directionality is defined as the difference between maximum and minimum gains in a radiation pattern. For example, if the maximum gain is +3 dBd at 45° but the minimum gain is −8 dBd at 143°, then directionality is 11 dB. Typically, automotive original equipment manufacturers (OEM) specify the directionality at 15 dBd.

[0014] As illustrated, the AM antenna 12b includes a generally defined ‘open end,’ which is designated generally at 32, such that the horizontally-disposed wires 30a–30c are not connected by a vertical wire, which is similar to the side wire 26a that connects the upper and lower wires 26b, 26c. As illustrated, the FM and AM grids 12a, 12b, although spatially separated, are electromagnetically-coupled. The location of the AM antenna grid 12b also provides a uniform ground for FM antenna 12b, which, as a result, improves overall FM antenna performance.

[0015] Referring to FIG. 4, another embodiment of the invention is disclosed generally at reference numeral 100, which includes a remote keyless entry (RKE)/tire pressure monitoring (TPM) antenna 12c located substantially above the AM antenna 12b. The RKE/TPM antenna 12c includes a feed line 50 and an antenna element 75. The horizontal length of the antenna element 75 is not relatively long enough and the inverted T-structured spacing from the vehicle roof (not shown) formed by the feed line 50 does not interfere with the operation of the AM antenna 12b. Therefore, by being able to locate the RKE/TPM antenna 12c on the same glass 11 as the FM and AM antennas 12a, 12b, additional design flexibility is enabled without compromising the operation of the FM or AM antennas 12a, 12b.

[0016] All of the embodiments disclosed herein have a preferred range of antenna conductor width of 0.25 mm to 1.50 mm. However, it will be appreciated that other conductor widths may be used if desired. As such, it is recognized that those skilled in the art may make various modifications or additions to the embodiments chosen here to illustrate the present invention, without departing from the spirit of the present invention. Accordingly, it is to be understood that the subject matter sought to be afforded protection hereby should be deemed to extend to the subject matter defined in the appended claims, including all fair equivalents thereof.