5,019,830
1 2
AMPLIFIED FM ANTENNA WITH PARALLEL BRIEF DESCRIPTION OF THE DRAWINGS
RADIATOR AND GROUND PLANE FIG. 1 is a longitudinal sectional view of an antenna
according to the present invention;
BACKGROUND OF THE INVENTION 5 FIG. 2 illustrates an electromotive force of the an
t ir u r L T • tennaofFIG. 1;
1. Field of the Invention FIG. 3 is a perspective view of the antenna of FIG. 1; The present mvent.on relates to an FM antenna and FIGS 4(1) and 4(2) show ... embodiment of the
more particularly to an FM wave receiving antenna. present invention
2. Prior Art 10 FIGS 5^ and's(2) show yet another embodiment of In prior art, metal rod type antennas and linear fold- the present invention; and
ing type antennas have been used for automobile FM FIG 6 shows a perspective view of still another
wave antennas and demountable FM broadcast receiv- object of the present invention.
ing antennas. When antenna gain should be considered,
antennas having wavelengths of J to i are most prefera- 15 DETAILED DESCRIPTION OF THE
ble, because the receiving level is abruptly reduced if INVENTION
the antenna has shorter wavelength. For this reason, In FIG. 1, a coaxial line 10 inlcudes a central core 11
antennas of 80 cm or longer have been mostly used in and an outer sheath 12. The central core 11 and the
Japan. outer sheath 12 are separated by an insulator (now
In antennas for frequencies above the VHP band, the 20 shown). The coaxial line 10 is provided substantially
rod type antenna and folding line type antenna have \ parallel to the surface of a metal conductor 20, and one
wavelength or multiples thereof in whole numbers. end of the outer sheath 12 is connected to the metal
Such antennas are usually too long. Accordingly, short- conductor 20.
ening devices such as coils are put in the antenna. How- 25 A parallel conductor 30 is provided also substantially
ever the shortening of the length results in sacrificing parallel to the metal conductor 20, and one end 31 of
some gain. Thus, the shortening of antenna length in- this Parallel conductor 30 is connected to the metal
volves some limitations. conductor 20.
Plate form antennas are occasionally used as electro- uAn amplifier 40 amplifies signals which are sent
static antennas. However, in order to obtain a sufficient 30 '^J 'he Paral el conductor 30 and the outer sheath
gain, metal plates of as large surface area as 300 cm' are " of th^Oax'al llne 10' The, S1SnaIs thus TMPM«* ^
• , the amplifier 40 are outputted to the central core 11 of
required. , . . ,. ,„
i, , . ..... r . the coaxial line 10.
Furthermore, in automobiles it ^referred not to Jn icul the ,ifier 40 is an FET (field effcct
have any projected objects on the vehicle body m view transistor) Other amplifying means can be used as the of design preference and in order to avoid noises which amplifler 40. An end 32 of the parallel conductor 30 is they would make when the car is in motion. No conven- connected to a gate 41 of the amplifier or FET 40. A tional antennas could have met these demands. Anten- source 42 of the FET 40 is connected to the end 14 of nas for indoor equipment and those incorporated in the outer sheath 12, and a drain 43 of the FET 40 is receivers, on the other hand, are formed fiat so that they ^ connected to the central core 11. lay against the attached surface of the equipment, and The distance between the end 31 of the parallel conreceivers are required to be as unobtrusive as possible ductor 30 and the end 13 of the outer sheath 12 of the for esthetic reasons and harmony of indoor environ- coaxial line 10 is set approximately at X/4 in this emments. However conventional antennas are not satisfac- bodiment.
tory in this area, either. 45 FIG. 2 shows electromotive force with respect to the
line length of the above-described embodiment, and
SUMMARY OF THE INVENTION FIG 3 is a perspective view of the antenna of FIG. 1.
Accordingly, it is a primary object of the present Operation of the embodiment will be described be
invention to provide an FM wave antenna which does lownot project from surfaces of receivers and automobiles 50 First of all, when a conductor is set parallel to a metal and stays low on such surfaces. Plate and one end of the conductor is grounded, the
According to the FM wave antenna of the present impedance of the other end of the conductor usually invention, a coaxial line comprising a central core and rePeats cycles of hi8h and low volta8es at every X/4 an inductive outer sheath is installed substantially paral- lenSth as thfe le"^h of .the conductor is changed^ Aclel to the surface of a metal conductor, and one end of 55 TM*TM&l> if a high point of this cycle ,s selected an .... L i_ • j i. i induced voltage from the high frequency electrical field
the inductive outer sheath is connected to the metal m a ^ ... if ends
conductor. A parallel conductor is installed also sub- Qf {wo conductors are set face to face on a metal lat
stantially parallel to the metal conductor, and one end the potentials between the open ends can be doubled.
of the parallel conductor is connected to the metal con- ^ The reason for such potentiais to be doubled between
ductor. An amplifier is provided between the coaxial the open ends of two conduct0rs can be described such
line and the parallel conductor. Thus, the signal from that a signal from the paranei conductor 30 in the above the parallel conductor and the inductive outer sheath of embodiment and a signal from the outer sheath 12 are in
the coaxial line are amplified by the amplifier and out- a reverse voltage relationship. For example, when the
putted to the central core of the coaxial line. Thus, the 65 gate signal is positive with respect to the ground which
FM wave antenna mounted on an intended surface does is the metal conductor 20, the source signal with respect
not project and stay flat on the metal conductor which to the ground or the metal conductor 20 becomes nega
can be an automobile body. live.
