JPH0460364B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to impedance characteristics when an antenna aperture shortening capacitor plate is attached to a printed dipole antenna in order to reduce the size of an in-vehicle mobile station antenna for a car phone. It is about improving gain.

(Conventional technology) The car phone system uses the 900MHz band.

The element length of the dipole antenna at this time is approximately 12cm.
This makes it possible to mount the antenna inside a passenger car.
However, when a dipole antenna is attached to the center of the car near the windshield, it is attached to the rear part of the car as shown in ["Study of in-vehicle installed antenna for land mobile communication" IEICE Antenna and Propagation Study Group material AP85-30 1985]. It becomes difficult to receive radio waves. Similarly, if you install it in the center near the rear window, it will be difficult for radio waves to be emitted to the front. Therefore, in order to configure an in-vehicle antenna, it is necessary to install two antennas at the front and rear of the vehicle. When the in-vehicle antenna is configured in this way, omnidirectionality in the horizontal plane can be achieved by using directivity for the front and rear antennas that have a beam width of 180 degrees in the horizontal plane centered on the front and rear. here,
An example of an antenna with horizontal directivity having a beam width of 180 degrees is a printed dipole antenna shown in FIG. This antenna has 1 feeding terminal,
It consists of the core wire of the microstrip line (2), the reflective element (3) (the ground plane of the microstrip line), the dielectric (4), and the radiating elements (5, 5'). If it is slightly longer than 5,5', it will act as a reflecting element and will take on the appearance of a two-element Yagi antenna, as shown in Figure 11.
Close to 180 degree beam directivity. However, 5,
5' is H≈approximately 1/2 wavelength.

Although it is extremely effective to use a printed dipole antenna as an in-vehicle antenna in this way, it is necessary to consider the antenna installation position so as not to obstruct the driver's field of view.

Therefore, it may be possible to mount the antenna at the rear of the room mirror and at the rear tray.

How to attach the antenna to the rear of the rearview mirror so that the antenna cannot be seen by the driver 6
It needs to be ~7cm high. Also, when installing it on the rear tray, it needs to be as low as possible.

(Problems to be Solved by the Invention) Therefore, in order to apply the antenna as an in-vehicle antenna, it is necessary to make the antenna smaller and lower its profile while satisfying the required antenna gain and impedance characteristics. As a means for realizing this, a conventionally well-known structure has been used in which a capacitive plate is attached to the end of each element in a T-shape at right angles to a radiating element and a reflecting element, as shown in FIG.

If the antenna configuration shown in Figure 12 is designed on the assumption that the antenna will be almost invisible to the driver when attached to the rear of the rearview mirror, each dimension of the antenna will be Height 6cm, reflective element capacitance plate width 10
cm, the capacitive plate width of the radiating element is 9 cm, and the depth is 6 cm. In this case, the relationship between the radiating element and the reflecting element is that the antenna length H' is the same for both, so the length W' of 6, 6' and the length W of 7, 7' is W'+H'<W+H'. There needs to be. Here, W′+H′ is approximately 1/2 wavelength. The impedance characteristics of the antenna configuration in Fig. 12 are as shown in Fig. 13, with V, S,
The frequency at which W, R (voltage standing wave ratio) = 1.5 or less is
The drawback is that it does not meet the usage band of the car telephone system at 875-925MHz. Furthermore, although FIG. 14 shows an example of measuring the antenna gain, there is also a disadvantage that the gain shifts with respect to frequency and that the gain decreases at 940 MHz.

The purpose of the present invention is to change the shape of the capacitive plate attached to the radiating element to achieve V, S, W, R.
It is an object of the present invention to provide a fixed-position printed dipole antenna that has a wide frequency band (voltage standing wave ratio) of 1.5 or less and further improves gain.

(Means for Solving the Problems) The present invention changes the mounting method of the capacitive plate attached to the radiating element from a T-shape to bring the tip of the capacitive plate closer to the reflecting element, thereby ensuring antenna gain while reducing impedance. The main feature is increased capacitance. Compared to the conventional technology, the antenna has the same external dimensions, has a wide band impedance characteristic, and has a performance that reduces fluctuations in antenna gain due to frequency characteristics.

(Embodiment) Fig. 1 is a diagram explaining the first embodiment of the present invention, in which 1 is a power supply terminal, 3 is a ground plane of a microstrip line, 4 is a dielectric, and 5 and 5' are radiation element,
6, 6' are capacitive plates attached to the radiating element; 7,
7' is a reflective element (ground plane of microstrip line)
This is a capacitor plate attached to the 6 and 6' are bent at an angle of about 130 degrees at the center toward the reflective element. At this time, the antenna external shape is the 12th
It has the same dimensions as the conventional antenna shown in the figure. The relationship between W' and W must be W'<W as described above. Further, α is smaller than 180° and can be set to any angle as long as it does not hit the capacitive plates 7 and 7' of the reflective element, but the smaller α is, the wider the impedance characteristic becomes. However, the amount of deterioration in antenna gain with respect to frequency becomes smaller near α=130°.

FIG. 2 shows V, S, W, and R (voltage standing wave ratio) in FIG. 1, which satisfies 1.5 or less at 860 to 940 MHz used in car telephones. Furthermore, FIG. 3 shows the results of measuring the antenna gain with respect to the frequency of this embodiment, and it is found that the antenna gain has almost no frequency characteristics and is almost uniform.

FIG. 4 shows a second embodiment of the present invention, in which the tips of the capacitive plates attached to the reflective element are bent at 90 degrees to face each other.

Figure 5 shows the VSWR (voltage standing wave ratio) for the structure shown in Figure 4, which satisfies the requirement of 1.5 or less. Furthermore, FIG. 6 shows the results of measuring the antenna gain with respect to frequency, and it is found that the antenna gain has almost no frequency characteristics and is almost uniform. It can be seen that the antenna has almost the same characteristics as the first embodiment even though the outer shape of the antenna is slightly smaller.

FIG. 7 shows a third embodiment in which a reflecting element and a radiating element are respectively attached, and the tips of the capacitive plates are bent at 90 degrees so as to face each other.

Figure 8 shows that the VSWR (voltage standing wave ratio) satisfies 1.5 or less. Furthermore, Figure 9 shows the results of measuring the antenna gain with respect to frequency.
Despite the smaller antenna size, the first
The conventional antenna gain shown in Figure 3 is maintained.

From this result, it is clear that even though the external shape of the antenna is smaller than that of the conventional technology, improvements have been made in widening the area and making the frequency characteristics of the antenna gain more uniform.

In addition to the above-mentioned radiating elements and reflecting elements, by using a waveguide element with a similar structure (the only difference being the length of the radiating element, etc.), a multi-element antenna can be used as a printed dipole antenna of the Yagi-Uda antenna type. can also be configured.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of the first embodiment of the present invention;
The figure shows VS versus frequency in the first embodiment of the present invention.
WR characteristics, FIG. 3 shows the gain characteristics versus frequency of the first embodiment of the invention, FIG. 4 shows the structure of the second embodiment of the invention, and FIG. 5 shows the structure of the second embodiment of the invention. VSWR characteristics versus frequency, FIG. 6 shows gain characteristics versus frequency of the second embodiment of the present invention, FIG. 7 shows a structure diagram of the third embodiment of the present invention, and FIG. 8 shows the third embodiment of the present invention. VSW for example frequency
R. characteristics, Fig. 9 is the gain characteristic versus frequency of the embodiment of the present invention shown in Fig. 4, Fig. 10 is a structural diagram of a conventional printed dipole antenna that does not shorten the antenna aperture length, and Fig. 11 is a conventional printed dipole antenna in the 900 MHz band. Figure 12 is a structural diagram of a conventional printed dipole antenna with a shortened antenna aperture length. Figure 13 is a conventional printed dipole antenna with a shortened antenna aperture length. Figure 14 shows the gain characteristics versus frequency of a conventional printed dipole antenna with a shortened antenna aperture length. 1...Feeding terminal, 2...Core wire of microstrip line, 3...Reflector of printed dipole antenna, (earth plate of microstrip line),
4... Dielectric material, 5... radiator of the printed dipole antenna, 6, 6'... shortened capacitance plate attached to the radiator of the printed dipole antenna,
7, 7'... Shortened capacitance plate attached to the reflector of the printed dipole antenna.

Claims (1)

[Scope of Claims] 1. Electrical electrical In the printed dipole antenna, which aims to shorten the antenna dimensions by adding capacitance to the antenna, the conductor plate attached to the reflecting element is linear, and the conductor plate attached to the radiating element becomes more reflective toward the tip. A printed dipole tantenna characterized by having a bend in the flat plate so that the distance between the flat plate and the flat conductor plate attached to the element is reduced. 2. A flat reflective element and a radiating element are formed in the plane of a dielectric substrate, and conductive flat plates perpendicular to the dielectric substrate are attached to both ends of the reflective element and the radiating element to make them electrically capacitive. In a printed dipole antenna that aims to shorten the antenna dimensions, at least one tip of the flat conductor plate attached to the reflective element is bent, and the flat conductor plate attached to the radiating element is attached to the reflective element as it goes toward the tip. A printed dipole antenna characterized by having a curve in the flat conductor plate so that the distance between the flat conductor plate and the flat conductor plate is small. 3. The printed dipole antenna according to claim 2, wherein the tip of at least one of the conductor flat plates attached to the radiating element is bent.