Vehicle-mounted antenna substrate unit

#This application claims priority to Japanese Patent Application No. 2012-067671, filed on Mar. 23, 2012, which is incorporated herein by reference in its entirety.

#1. Field of the Invention

#The present invention relates to a vehicle-mounted antenna substrate unit, and particularly to an antenna grounding structure.

#FIG. 1 is a schematic view showing a vehicle-mounted antenna according to the present invention.

#FIG. 2 is a perspective view showing an example configuration of a vehicle-mounted antenna.

#FIG. 3 is a schematic view showing a configuration of an antenna substrate unit.

#FIG. 1 schematically shows a vehicle-mounted antenna according to an embodiment of the present invention. The vehicle-mounted antenna includes an antenna element 10, substrate 12, coaxial cable 14, capacitor 18, and grounding bracket 20.

#As the antenna element 10, an element that operates in an unbalanced mode is used, such as a quarter-wavelength linear antenna element. The antenna element 10 is connected to an inner conductor of the coaxial cable 14 via the substrate 12. The coaxial cable 14 is drawn out from the substrate 12 and connected to a receiver 16 mounted on the vehicle. At an end located on the side of the antenna element 10, the outer conductor of the coaxial cable 14 is connected to a first terminal of the capacitor 18 provided on the substrate 12. The other terminal of the capacitor 18 is connected via the grounding bracket 20 to a conductor component of the vehicle, which serves as a grounding conductor. While the conductor component of the vehicle may be the body, chassis, or other parts, the following description is given assuming that the conductor component is the vehicle body.

#FIG. 2 is a perspective view showing an example configuration of a vehicle-mounted antenna. In this example configuration, a bent antenna element 22 is employed as the antenna element, and the capacitor is formed using the substrate 12 having a multi-layered structure. The bent antenna element 22 has a plurality of bent portions between one end to the other end, and has an electrical length of approximately one quarter wavelength. As an alternative to the bent antenna element 22, it is also possible to employ, as the antenna element, a straight or curved element having an electrical length of approximately one quarter wavelength. One end of the bent antenna element 22 is connected to a wiring conductor pattern on the substrate 12. The inner conductor of the coaxial cable 14 is also connected to the wiring conductor pattern on the substrate 12. In other words, one end of the bent antenna element 22 is connected to the inner conductor of the coaxial cable 14 via the wiring conductor pattern. Further, the outer conductor of the coaxial cable 14 is connected to a grounding conductor pattern on the substrate 12.