JP4878304B2 - Trapezoidal element antenna - Google Patents

Description

  The present invention relates to an in-vehicle trapezoidal element antenna, and more particularly to a trapezoidal element antenna for a vehicle capable of receiving terrestrial digital broadcasting.

  FIG. 5 is a structural diagram of a dipole antenna in a conventional configuration. If the element length on one side of the dipole antenna is λ / 4, the total length of the element is λ / 2. In general, a λ / 2 dipole antenna is also called a half-wave dipole antenna. The antenna gain at this time is 2.15 dBi.

  FIG. 6 is a radiation pattern characteristic diagram of a dipole antenna in a conventional configuration. The radiation pattern in the XY plane has a peak in the direction perpendicular to the dipole, and has a shape like “Figure 8” as shown in the figure.

  FIG. 7 is a characteristic diagram showing the amount of reflection (return loss) of the dipole antenna in the conventional configuration. According to the law of conservation of electric charge, the amount of reflection measured electrically indicates an electromagnetic wave radiated into the space. Therefore, assuming that the resonance frequency of the radiated electromagnetic wave is 600 MHz and the target value of the amount of reflection is −10 dB, the bandwidth is 550 MHz to 650 MHz. It becomes. However, in this state, sufficient characteristics cannot be expected for receiving terrestrial digital broadcasts having a bandwidth of 470 MHz to 710 MHz.

  In addition, when a dipole antenna is used in an automobile for receiving terrestrial digital broadcasts, it is difficult to satisfy the bandwidth with one element because the bandwidth is narrow. For example, the bandwidth of the dipole is 17% with respect to the target bandwidth of 40% of the antenna, which cannot satisfy the requirement.

  Patent Document 1 discloses a technique for widening the bandwidth by flattening the element portion of a dipole antenna. In order to widen the bandwidth, using the technique disclosed in Patent Document 1 and studying with a planar antenna, the total length can be reduced when compared with the dipole antenna, but the size of the element portion Becomes larger. If this size is considered for mounting in an automobile, the mountable range becomes narrow and it is difficult to mount.

On the other hand, in Patent Document 2, as shown in FIG. 8, power is supplied to two trapezoidal conductors 2a and 2b formed by opposing long sides and short sides and the trapezoidal conductors 2a and 2b arranged side by side. There is disclosed a trapezoidal two-element antenna 1 including a planar dipole antenna having a feeding point 4 to perform and a parasitic element 6 disposed on the short side of the trapezoidal conductors 2a and 2b.

  FIG. 9 is a characteristic diagram showing the amount of reflection of a trapezoidal element antenna 1 having a conventional configuration as disclosed in Patent Document 2. In FIG. Generally, when a parasitic element is arranged in the vicinity of a rod-shaped dipole antenna, two resonance frequencies of 470 MHz and 710 MHz can be obtained, but a bandwidth in a target reflection amount cannot be obtained. Therefore, it is possible to cover the bandwidth by making the bar-shaped feeding element planar.

  FIG. 10 is a characteristic diagram showing a directivity pattern when the trapezoidal two-element antenna 1 having a conventional configuration is mounted inside a bumper at the rear of the vehicle. As shown in FIG. 10, in the trapezoidal element antenna 1, it can be seen that the gain at the frequency 710 MHz, which is higher than the frequency 470 MHz, is lower than the gain at the frequency 470 MHz.

JP 2003-51708 A JP 2006-186549 A JP 2001-313516 A JP 63-212204 A

  By the way, in order to flatten the function as an antenna in a wide band, it is preferable that the gain at each frequency is also flattened.

  An object of the present invention is to flatten the gain at each frequency in a trapezoidal two-element antenna.

The in-vehicle trapezoidal element antenna according to the present invention is an in-vehicle trapezoidal element antenna, and is arranged symmetrically with respect to the feeding point and the feeding point as a center, and has a long side and a short side facing each other. a planar dipole antenna having two trapezoidal conductor that is, the arranged short side of the trapezoidal conductor and a parasitic element having a long shape in the short side direction, each of said trapezoidal The conductor has a shape obtained by cutting a top end portion on the side close to the feeding point among the top end portions on the parasitic element side, and flattens the frequency characteristics of the gain of the trapezoidal element antenna. .

In one aspect of the in-vehicle trapezoidal element antenna according to the present invention, the cut shape is such that the distance between the trapezoidal conductor and the parasitic element is from the center to the end of the parasitic element. The shape is narrowed.

  According to the present invention, it is possible to flatten the gain at each frequency.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment specifically showing the best mode for carrying out the invention will be described with reference to the drawings.

  FIG. 1 is a pattern diagram of a trapezoidal two-element antenna according to the present embodiment. The trapezoidal two-element antenna 10 includes elements 12 a and 12 b, a feeding point 14, and a parasitic element 16. The element 12a and the element 12b are symmetrical with the feeding point 14 as the central axis.

  The widths of the elements 12a and 12b are H1, including the feeding point, the long side length is L1, and the short side length is L2. Furthermore, these elements 12a and 12b are formed of conductive plates. The parasitic element 16 has a length L3 and a width H3, and is disposed away from the elements 12a and 12b by H2. The parasitic element 16 is a narrow rectangular conductive plate and is not connected to the feeding point 14.

  Furthermore, in the present embodiment, the elements 12a and 12b have the top ends 11a and 11b on the side close to the feeding point 14 among the top ends on the short side (that is, the parasitic element 16 side) L4 in the length direction. The shape is cut diagonally by H4 in the width direction. In the cut portions, the distance between the elements 12a and 12b and the parasitic element 16 is gradually narrowed from the central part of the parasitic element 14 toward both ends. That is, the spacing between the elements 12 a and 12 b at the center of the parasitic element 14 is wider than the spacing between the elements 12 a and 12 b at both ends of the parasitic element 14. By thus cutting the top end portions 11a and 11b, the trapezoidal two-element antenna 10 according to the present embodiment has a current distribution different from the current distribution of the conventional trapezoidal two-element antenna.

  FIG. 2 shows the gain for each frequency of the trapezoidal two-element antenna in this embodiment and the gain for each frequency of the conventional trapezoidal two-element antenna (that is, the antenna in which the top ends 11a and 11b are not cut). FIG. In FIG. 2, the solid line indicates the gain in the present embodiment, and the broken line indicates the conventional gain. As shown in FIG. 2, by cutting the top end portions 11a and 11b, the gain at each frequency is flattened as compared with the conventional case.

  Here, the dimensions of L4 and H4 are determined by experiments so that the gain at each frequency is flattened. For example, L4 and H4 are each about 3/4 of H1. Note that L4 and H4 do not necessarily have the same dimensions.

  FIG. 3 is a characteristic diagram showing the amount of reflection of the trapezoidal two-element antenna in the present embodiment. There are resonance frequencies 470 MHz and 710 MHz within the target value of the reflection amount, the resonance frequency 470 MHz is experimentally determined by the relationship of λ / 2 = (L1 + L2) / 2, and the bandwidth BW1 at the target value of the reflection amount is determined by H1.

  Further, the resonance frequency 710 MHz is experimentally determined by λ / 2 = L3 and H2, and the bandwidth BW2 is determined by H3, and the element size of the trapezoidal two-element antenna is determined.

  Subsequently, the operation will be described. First, a current flows from the feeding point 14 to the elements 12a and 12b, which are feeding elements, and resonates at a resonance frequency of 470 MHz. Next, a current is induced in the parasitic element 16 from the short side of the elements 12a and 12b, which are feeding elements, and resonates at a resonance frequency of 710 MHz. And each resonance overlaps and the broadband is realized.

  4A and 4B show a directivity pattern when the trapezoidal two-element antenna 10 is built in the rear bumper portion of the vehicle and a directivity pattern when a conventional trapezoidal two-element antenna is built in the same position. FIG. 4A and 4B, a solid line is a directivity pattern in the present embodiment, and a broken line is a conventional directivity pattern. Further, FIG. 4A shows a directivity pattern at a resonance frequency of 470 MHz, and FIG. 4B shows a directivity pattern at a resonance frequency of 710 MHz.

  A person skilled in the art can suitably adjust the frequency and bandwidth suitable for the conditions by changing the dimensional ratio of L1 to H4 in the present embodiment.

  Further, the material of the element is flexible, and a conductive material, for example, conductive rubber, conductive paint, etc. may be used, and it can also be realized by a method of forming a conductive pattern on an insulating film. Furthermore, even if the material of the element is not a plate shape but a net shape, it is possible to suitably obtain the same performance as the current state.

  In addition, in the present embodiment, the interior of the rear bumper of the vehicle is illustrated as the installation location of the trapezoidal two-element antenna. However, the installation location is not limited to the interior of the rear bumper, and may be installed at other positions such as on a door, roof, or bonnet as long as a metal body (GND plate) is disposed near the antenna.

  Furthermore, the frequency band is not limited to the above-described band, and the present embodiment is effective for other media such as analog TV, digital TV, and FM radio that require wideband frequency characteristics.

It is a pattern figure of the trapezoid type 2 element antenna in this embodiment. It is a figure for demonstrating the gain with respect to each frequency of the trapezoid type 2 element antenna in this embodiment compared with the conventional antenna. It is the characteristic view which showed the reflection amount of the trapezoid type | mold 2 element antenna in this embodiment. It is a figure which compares the directivity pattern of resonance frequency 470MHz when trapezoid type 2 element antenna 10 is built in the back bumper part of vehicles with the directivity pattern of the conventional antenna. It is a figure which compares the directivity pattern of the resonant frequency of 710 MHz when the trapezoid type | mold 2 element antenna 10 is incorporated in the back bumper part of a vehicle with the directivity pattern of the conventional antenna. It is a structural diagram of a dipole antenna in a conventional configuration. It is a characteristic view of the radiation pattern of the dipole antenna in a conventional structure. It is the characteristic view which showed the reflection amount of the dipole antenna in a conventional structure. It is a pattern diagram of a trapezoidal two-element antenna in a conventional configuration. It is the characteristic view which showed the reflection amount of the trapezoid type | mold 2 element antenna in a conventional structure. It is a characteristic view which shows the directivity pattern at the time of mounting the trapezoid type | mold 2 element antenna of a conventional structure in the bumper of vehicle rear.

Explanation of symbols

  10 trapezoidal two-element antenna, 11a, 11b top end, 12a, 12b element, 14 feeding point, 16 parasitic element.

Claims (2)

A trapezoidal element antenna for in-vehicle use,
Feeding point, symmetrically disposed around the feed point, and planar dipole antenna having opposed long sides and two to the short sides are formed trapezoidal conductor,
A parasitic element that is disposed on the short side of the trapezoidal conductor and has a shape that is long in the short side direction;
With
Each of the trapezoidal conductors has a shape obtained by cutting a top end portion on the side close to the feeding point among the top end portions on the parasitic element side, and flattens the frequency characteristics of the gain of the trapezoidal element antenna. A trapezoidal element antenna. The trapezoidal element antenna according to claim 1,
The cut shape is a shape in which the gap between the trapezoidal conductor and the parasitic element becomes narrower from the central part toward the end of the parasitic element.
A trapezoidal element antenna.

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