JPH0488702A - Matching device for antenna - Google Patents

Abstract

PURPOSE:To attain miniaturization with simple structure by connecting a 2nd low impedance line of a 2nd prescribed length in series with a feeder of a high impedance line. CONSTITUTION:A feeding point 14 is provided to a radiation element 13 of a microstrip antenna 10 with an offset by a prescribed distance rf only from the center and excited in the TM 21 mode. Widths W43, W47 are set to line conductors 43, 47 at both ends so that the characteristic impedance is 50ohms, and widths W44, W46 are set to line conductors 44, 46 at intermediate section so that the characteristic impedance is considerably lower than 50ohms. Then the width W45 is set narrow to the line conductor 45 so that the characteristic impedance is considerably higher than 50ohms. Thus, the return loss of the line conductor 46 at the other PIN is formed to be U-shape and the microstrip antenna 10 and the feeder are matched over a comparatively broader frequency band such as nearly 50MHz.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is suitable for microstrip antennas, etc.
The present invention relates to an antenna matching device.

[Summary of the Invention] The present invention provides an antenna matching device which is inserted between a narrowband antenna and a feed line to perform wideband matching. 2 low impedance line of a predetermined length, and a third low impedance line of a predetermined length.
By sequentially connecting a high impedance line of a predetermined length in series, and connecting a second low impedance line of a second predetermined length in series to the feeder side of this high impedance line, the structure can be made smaller with a simple structure. This is how it was done.

[Prior Art] Conventionally, as shown in FIG. 8, a microstrip antenna (10) has a radiating element (13) disposed on a ground conductor (11) via a dielectric layer (12). Since the desired unidirectionality can be obtained with a simple structure and low height, it is used for wireless communication in aircraft, automobiles, etc., especially in the UHF/SHF band.

[Problems to be Solved by the Invention] By the way, the above-mentioned microstrip antenna has a high Q value and a narrow C frequency bandwidth, so it has the disadvantage that it cannot be used in common for two-frequency transmitting/receiving wireless communication, for example. Ta.

A known technique to overcome this drawback is, for example, to load a parasitic element in front of the radiating element to widen the band by creating a two-resonance state. A problem arises in that the density increases.

On the other hand, as shown in FIG.
It is known from the publication No. 2-279704.

That is, in FIG. 8, the matching box (20) is connected to the ground conductor (2
1) A line conductor (23) is placed on top of the dielectric layer (22).
) to (25) are arranged in series, an L-shaped stub (26) is branched from the intermediate point PM, and the load side and input side connectors (27) and (28) are connected to the line conductor (23).
) and (25) respectively.

The feed point (14) of the antenna (10) is connected to the coaxial feed line (1
5) and a connector (16), it is connected to one connector (27) of the matching box (20). A power supply line (not shown) is connected to the other connector (28).

At two desired frequencies fl and f2 (fl< f2), from the midpoint PM of the matching box (20) to the antenna (10
) side become equal, and the susceptance components Bl, B2 (l Bl l > IB2
The distance 11 between the power feeding point (14) and the intermediate point PM is set so that 1 ) have opposite signs.

Furthermore, the length β2 and characteristic impedance of the stub (26) are such that the susceptance component of the stub (26) viewed from the midpoint PM is -B at frequencies fl and f2, respectively.
It is set so that L - B2.

As a result, two desired frequencies f1. At f2, the combined admittances of the stub (26) and the antenna (10) as seen from the intermediate point PM become equal.

The line conductor (24) in the middle part is a well-known λ/4 impedance converter, and the composite admittance seen from the midpoint PM is equal to the standard value [11] seen from the connector (28) at the input end.
is converted to become .

In this way, by using the matching box (20), two desired frequencies f1. At f2, the impedance of the antenna (10) is matched and a wide band is achieved.

In addition, as shown in FIG. 9, the above-mentioned matching box can be integrated with the antenna by making both ground conductors common. In this FIG. 9, (17) is a connecting conductor, (29
) is a non-grounded conductor, and the non-grounded conductor (29) is the feeder line (15) and line conductor (23) to Stabk 26) in Figure 8.
represent.

However, in the matching box (20) described above, the stub (26)
is branched from the line conductor (23), so the stub (
Even if the matching box (26) is L-shaped, there is a problem that the size of the matching box (20) becomes relatively large.

Furthermore, when constructed using coaxial lines, there is a problem that the structure becomes complicated.

In view of the above, an object of the present invention is to provide an antenna matching device that is small in size and has a simple structure.

[Means for Solving the Problems] The present invention provides an antenna matching device which is inserted between a narrow band antenna (10) and a feed line to match the antenna and the feed line over a wide band. 1 standard impedance line (43) of a predetermined length is arranged on the antenna side,
a second predetermined length of low impedance line (44);
A high impedance line (45) of a predetermined length is sequentially connected in series to a standard impedance line, and '! An antenna matching device in which two second low impedance lines (46) of a predetermined length are connected in series! ! ! (40).

[Function] According to the present invention, the structure is simplified and the shape is reduced.

[Embodiment] Hereinafter, an embodiment of an antenna matching device according to the present invention will be described with reference to FIGS. 1 to 7.

FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, parts corresponding to those in FIG. 8 described above are given the same reference numerals, and some explanations will be omitted.

In Figure 1, a microstrip antenna (10)
The radiating element (13) is provided with a feed point (14) offset from the center by a predetermined distance rf, and is excited in the TM21 mode.

For example, in the 2.5 GHz frequency band, a dielectric layer (12
) thickness and permittivity are d12 = 3.2 mm! = 2.6, the radius ra of the radiating element (13) and the feeding point (14
) are set as follows.

ra -35,5mm rf = 17.5 m
m (40) is a matching box and a ground conductor (not shown)
On top, a low-loss dielectric layer (e.g. fluororesin)
42), 5B worth of line conductors (43), (44
).

(45), (46), and (47) are arranged in series to form a microstrip line configuration.

Incidentally, as in the case shown in FIG. 9 above, in this embodiment as well, the matching box (40) and the antenna (10) can be integrated by using a common ground conductor.

The line conductors (43) and (47) at both ends have a width W4 so that the characteristic impedance is the standard 500.
3W47 is set, and this line conductor (43), (47
) respectively adjacent intermediate line conductors (44);
(46) has a width W44. so that the characteristic impedance is much lower than 500. W46 is set wide.

The line conductor (45) in the center has a width W4 such that the characteristic impedance is considerably higher than 50Ω.
5 is set narrowly.

In addition, the length L43 of the line conductor (43) at the end is set to a little less than 274, and the line conductor (44), (46) is wide.
Length L44. L46 are all set to approximately λ/4, and the length L45 of the central line conductor (45) is approximately λ/4.
/2.

One line conductor (43) at the end is connected to the feed point (14>) of the antenna (10), and the other line conductor (47) is connected to a connector (48). A power supply line (not shown) having a characteristic impedance of 500 is connected.

Next, the operation of an embodiment of the present invention will be described with reference to FIGS. 2 to 7.

In this example, the frequency bandwidth of the antenna (10) alone is extremely narrow, and the frequency bandwidth of the antenna (10) alone is extremely narrow, as can be easily seen from the sharp figure 7 shape of the reflection loss (return loss) shown by the broken line in FIG. 43) The load impedance ZLD viewed from the PL port at one end to the antenna side is as shown in FIG. 2 on the Smith chart.

Such a load impedance ZLD is a line "conductor (43)" with a characteristic impedance of 50Ω and a length of just under 274Ω.
], the intermediate impedance ZMI as seen from the antenna side from the connection midpoint PMI with the wide line conductor (44) is rotated on the Smith chart by the predetermined two frequencies fl, as shown in FIG. , f2 becomes symmetric with respect to the real axis.

Then, this intermediate impedance ZMI is converted by a line with a low characteristic impedance and a length of approximately λ/4 [corresponding to the conductor (44)], and the line conductor (45) in the center
The second intermediate impedance ZM2 when looking at the antenna side from the connection midpoint PM2 with
At frequencies fl and f2, small circles overlap on the real axis.

This intermediate impedance ZM2 is a line [conductor (45)
corresponding to the second wide line conductor (4
As shown in FIG. At f2, it becomes a small loop away from the real axis.

Further, this intermediate impedance ZM3 is converted by a line [corresponding to the conductor (46)] having a low characteristic impedance and a length of approximately λ/4.

In this way, four line conductors (43
) to (46), an impedance that is almost conjugate to the load impedance ZLO in the required frequency range is equivalently added to the load impedance ZLO. Human power impedance ZI
As shown in FIG. 6, a considerable portion of N is concentrated in the vicinity of the center on the Smith chart.

As a result, (
The total return loss is U-shaped as shown by the solid line in FIG. 7, and it can be seen that the microstrip antenna (10) and the feed line are matched over a relatively wide frequency range of about 50 MHz.

As mentioned above, this embodiment has a simple configuration in which narrow and wide line conductors each having a predetermined length are connected in series.
The matching box can be downsized.

In the above embodiment, the matching box (40) has an open type microstrip line configuration, but a shielded type, so-called triplet type microstrip in which a dielectric layer and a ground conductor are arranged on both sides of the line conductor is used. If a line configuration is adopted, the width of the line conductor is reduced to approximately half, and the length is reduced to approximately 1/J, making it possible to downsize the - layer.

When the matching box (40) is a triplet type, for example, 2.
56) In the lz frequency band, the thickness and permittivity of the dielectric layer are d = 1,5 mm e = 2.6
Then, the width and length of each line conductor (43) to (46) are set as follows.

W43 = 1.1mm W45 = 0.7mm W
44=W46=4.5mmL43=12mmL
45 = 37.5mm L44 = L46 = 19mm Above, we have described an embodiment in which this invention is applied to a microstrip line, but this invention can be similarly applied to a coaxial line, and the structure is extremely simple in this case as well. It gets easier.

[Effects of the Invention] As detailed above, according to the present invention, a first predetermined length of the standard impedance line on the antenna side, a second predetermined length of the low impedance line, and a third predetermined length of the high impedance line on the east side. In addition to sequentially connecting the lines in series, a second low impedance line of a predetermined length is connected in series to the feed line side of this high impedance line, so it is possible to create a narrowband antenna with a small and simple structure. An antenna matching device that can match the antenna to the feed line over a wide band is obtained.

[Brief explanation of the drawing]

FIG. 1 is a developed diagram showing the configuration of an embodiment of an antenna matching device according to the present invention, FIGS. 2 to 6 are diagrams for explaining the operation of an embodiment of the invention, and FIG. FIG. 8 is a perspective view showing a configuration example of a conventional antenna matching device, and FIG. 9 is a sectional view showing the configuration of another conventional example. (10) is an antenna, (40) is a matching box, (43) is a standard impedance line conductor, (44), (46)
(45) is a low impedance line conductor, and (45) is a high impedance line conductor. Agent Hide Matsukuma Mori f 1
: 2.39G) lz Freight impedance fl : 2.39GHz f2 : 2.59GHz Fig. 4 f "I : 2.390) lz f2 : 2.59GHz fl : 2.39GHz f2 : 2.59GHz Fig. fl 2 .39 GHz side ni T1.

Claims (1)

[Scope of Claims] An antenna matching device interposed between a narrowband antenna and a feed line to match the antenna and the feed line over a wide band, comprising: a standard impedance line of a first predetermined length; is placed on the antenna side, a second predetermined length of low impedance line and a third predetermined length of high impedance line are connected in series to the standard impedance line, and the above is placed on the feed line side of this high impedance line. An antenna matching device characterized in that a second low impedance line of a second predetermined length is connected in series.