Hitherto, glass antenna for receiving AM radio broadcast waves and FM radio broadcast waves has often been formed on a rear window glass of an automobile, since it requires a relatively large area for obtaining a good reception gain. Furthermore, since a rear window glass of an automobile is often formed on its central region with defogging heating strips, in case that a glass antenna is formed on a rear window glass, it has been forced to be formed on a blank space above or below the defogging heating strips.
Furthermore, in most cases, reception has been conducted by forming one antenna on a blank space above the defogging heating strips for receiving AM broadcast waves and FM broadcast waves, and an antenna of these AM-band/FM-band has taken a grounded antenna pattern having one feed point.
Furthermore, in the case of receiving radio waves of AM radio broadcast waves and radio waves of FM radio broadcast waves by a glass antenna, as shown in FIG. 9, in many cases, an antenna amplifier has been provided generally between an antenna feed point and a tuner, and an electromotive force insufficient to be input to the tuner has been amplified, and it has been input to the tuner.
Alternatively, as shown in FIG. 10, an impedance matching circuit has been formed in order to minimize the reduction loss of the reception gain by a feeder line between the antenna feed point and the tuner to maintain the electromotive force that becomes sufficient to be input to the tuner, thereby inputting it to the tuner.
In the case of sharing antennas of AM broadcast waves and FM broadcast waves, in many cases, with respect to the amplifier, an AM broadcast wave amplifier and an FM broadcast wave amplifier are separately provided, thereby amplifying the received power and then inputting it to the tuner. Alternatively, also with respect to the impedance matching circuit, in many cases, the reduction due to the loss of the reception sensitivity is suppressed by an AM broadcast wave impedance matching circuit and an FM broadcast wave impedance matching circuit in the route that transmits radio waves received by an antenna to the tuner.
As one in which a glass antenna is formed on an upper blank space of a vehicular rear window glass and an amplification is conducted by an amplifier, for example, there is described in Patent Publication 1 an amplifier attachment structure of a vehicular glass antenna, which has a glass antenna in which an antenna conductor is formed at a predetermined position of a vehicular window glass plate and an amplifier for amplifying the reception sensitivity of the glass antenna, and in which the amplifier is directly connected to a feed terminal portion of the glass antenna by means such as soldering, brazing or a conductive adhesive bonding, thereby reducing the gain loss due to the capacity loss at a feed line portion between the glass antenna and the amplifier.
With respect to forming an impedance matching circuit between a vehicular glass antenna and a tuner, for example, Patent Publication 2 describes a four-terminal circuit as an impedance matching circuit.
Patent Publication 1: a microfilm of Japanese Utility Model Application 63-89982 (Japanese Utility Model Laid-open Publication 2-13311)
Patent Publication 2: Japanese Patent Laid-open Publication 2001-313513