JPH04216203A - Compact antenna with matching circuit - Google Patents

Abstract

PURPOSE:To obtain a compact antenna having high efficiency and a wide band by adding an imbalanced transmission line to a resonance type element, which is shorter in comparison with a wavelength, and a 1/4 wavelength matching circuit. CONSTITUTION:As a feeder line, an imbalanced transmission line 3 is directly connected to the side, where no radiator 1 is connected, of a balanced 1/4 wavelength matching circuit 2. This is for obtaining a balance function at the matching circuit 2 itself and transforming transmission from the balanced system of the radiator 1 to the imbalanced system of the feeder line 3 by utilizing a fact that the terminal part not connecting the radiator 1 of the 1/4 wavelength matching circuit 2 becomes the joint of current distribution and the crest of voltage distribution. Therefore, it is not necessary to externally attach a balance, miniaturization and production can be facilitated, and the loss can be reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small antenna with a matching circuit used in a high frequency range.

0002

[Prior Art] Conventionally, commonly used antenna radiating elements, such as half-wavelength dipoles, have a radiation resistance that is sufficiently large compared to the loss resistance of the conductor that constitutes the element. An efficiency value close to 1 is obtained. In addition, since such elements are used in a nearly resonant state, their input impedance becomes a value that is easily matched to the input/output impedance of the transmitter/receiver, that is, the impedance of the power supply system, and the matching circuit is relatively simple and has low loss. It can be used and is sufficient for normal use.

0003

[Problem to be Solved by the Invention] On the other hand, when there are restrictions on the dimensions of the antenna, such as long-wave band antennas or antennas for portable radios, the dimensions of the radiating element are very small compared to the wavelength of the electromagnetic waves. The need arises to use . The radiation resistance of such a so-called micro antenna is
Since it decreases in proportion to the square of the element length, the loss resistance of the conductor that constitutes the element cannot be ignored, and the efficiency of the antenna greatly deteriorates. In addition, as the radiation resistance decreases,
The resistance component of the input impedance of the element, that is, the sum of the radiation resistance and the conductor resistance, is also very small, for example, about 0.1 to 1Ω, making it difficult to match it with the impedance of the power supply system (50Ω).

Furthermore, in non-resonant radiating elements such as micro dipoles and micro loops, the reactance component of the input impedance is extremely large, tens to hundreds of thousands of times as large as the resistance component, making impedance matching even more difficult. . Therefore, conventionally, when using a micro antenna, two lumped constant elements such as capacitors or coils are connected in series and parallel to a radiation resistance element as a circuit to match the input impedance of the radiating element and the impedance of the feeding system. A commonly used method was one in which a stub using a distributed constant line was connected in parallel to the feed line.

However, as mentioned above, since the input impedance of the radiating element and the impedance of the feed system are significantly different, errors in the values of lumped constants in the matching circuit, their dimensions, and their connection positions have a large influence on the characteristics of the matching circuit. It became very large, making it difficult to design and fabricate the matching circuit. For the same reason, the loss of the matching circuit itself is larger than that of a matching circuit of a normal antenna, so the efficiency of the antenna system including the matching circuit is extremely low, at about 0.1 to 0.01. Furthermore, when a non-resonant type element is used as a radiating element, it is necessary to cancel out a very large input reactance with a matching circuit, and the usable frequency bandwidth of the antenna becomes very narrow. Furthermore, when the frequency used is high, above the UHF band, it becomes difficult to realize an ideal lumped constant element due to stray capacitance, etc., and the radiating element itself becomes very small, causing the capacitor or coil to act as a lumped constant element. Therefore, matching circuits are often constructed with stubs, but in this case, the narrowing of the band becomes more noticeable due to the frequency characteristics of the stubs.

[0006] In order to improve the efficiency of small antennas, there are some examples in which antenna elements and matching circuits are made of superconducting materials, but in conventional examples, micro dipoles, micro loops, lumped constant elements, and stubs have been used. Most of them are combined with a matching circuit, and there remain problems such as the band being narrow, the loss of the matching circuit not being sufficiently low, and the efficiency not being very high. Furthermore, in many cases, the feed line is a transmission line with an unbalanced transmission mode, so when a minute dipole or a minute loop is used, it is necessary to convert the balanced transmission mode to the unbalanced transmission mode. Therefore, in the conventional example, a normally conducting balun is attached externally, which has disadvantages such as the loss further reduces the efficiency and the combined size of the antenna element, matching circuit, and balun cannot necessarily be made small. . An object of the present invention is to realize a small antenna with high efficiency and a wide band using a small radiating element and a simple impedance matching circuit.

[0007]

[Means for Solving the Problems] In order to solve these problems, the present invention uses a resonant element that is shorter than the wavelength, and a quarter wavelength matching circuit or a tapered line matching circuit in one stage or in multiple stages. one with an unbalanced transmission line, and the other with an unbalanced transmission line.

[0008]

[Operation] Matching is achieved between the resonant element and the quarter-wavelength matching circuit output, and by adding an unbalanced transmission line, a balun is no longer necessary.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a small antenna according to the present invention. 1 is a radiating element, 2 is a balanced quarter wavelength matching circuit, 21
22 is a conductor that forms a matching circuit; 22 is a dielectric that forms a matching circuit; 3 is an unbalanced transmission line that is a feed line; 31 is a conductor that forms an unbalanced transmission line; and 32 is a dielectric that forms an unbalanced transmission line. Showing body. If you want to maximize the efficiency of the antenna system, radiating element 1, conductor 21, and conductor 3
At least one of 1 may be made of a superconducting material. When using superconducting materials, it is necessary to cool the antenna system in order to transform the material into a superconducting state. If superconducting material is used, Figure 5
A simple cooling system using liquid nitrogen as the refrigerant can be used. In FIG. 5, 6 is an antenna made of superconducting material, 7 is a feeder line, 8a and 8b are glass Dewar bottles, and 9 is liquid nitrogen.

As mentioned in the section on the prior art, the input impedance of the radiating element, which is very small compared to the wavelength of the electromagnetic wave, differs greatly from the impedance of the feed system, so how to match these impedances depends on the antenna configuration. This is an important point. Hereinafter, the operation of the antenna including the matching circuit will be explained based on the first example.

First, a stub matching circuit that can match any impedance in principle can be considered as a matching circuit, but this uses the reactance of the stub, and this reactance itself has large frequency-dependent characteristics. , the position where the stub should be connected on the feeder line also changes depending on the frequency, so this circuit has a very narrow band. Therefore, the present application proposes that the matching circuit 2 has a wider band than a stub matching circuit, operates ideally even at high frequencies because it is a distributed constant circuit, and has a simple structure and is easy to design and manufacture. Only the characteristic balanced quarter-wavelength matching circuit is used, and no other stubs or lumped constant elements are used. As a result, the matching circuit of the present application can operate in a wider band than a matching circuit using a stub. For example, input resistance O. When connecting a 1Ω radiating element and a feed system with an impedance of 50Ω, the dielectric constant is 2.6, the line width is 2mm, the distance between the two conductors is 50μm, and the length is 1/6 of the wavelength in free space. If parallel lines are used, a matching circuit can be easily realized. Note that it is important to select a dielectric material with low dielectric loss as the dielectric material used at this time.

In the present invention, an unbalanced transmission line 3 is directly connected as a feed line to the end of the balanced quarter-wavelength matching circuit 2 on the side to which the radiating element is not connected. This is 4
Taking advantage of the fact that the end of the half-wavelength matching circuit on which the radiating element is not connected becomes a node of the current distribution and an antinode of the voltage distribution, the matching circuit itself has a balun function, and the balanced system of the radiating element This is to change the transmission mode from the feed line to the unbalanced system. In general, the input/output terminals and feed lines of transmitters and receivers often use unbalanced systems, so using this type of configuration eliminates the need for an external balun, resulting in miniaturization and ease of manufacturing. , it is also advantageous in terms of low loss. FIG. 1A shows an example in which a coaxial line is used as the unbalanced transmission line 3, and FIG. 1B shows an example in which microstrip lines 31a and 32a are used in the unbalanced transmission line 3a.

[0013] Next, when using the matching circuit, the input reactance of the radiating element must be zero, so the input reactance of the radiating element 1 can be made zero without adding a stub or a lumped constant element. A self-resonant element is used. If a self-resonant element is used, there is no need to use a stub or the like, so broadband operation can be expected. Figure 1 shows an example using a small helical element. ), the resonance state, that is, the input reactance becomes 0, and the radiation resistance becomes approximately 0.1Ω.

Furthermore, in the antenna having the above configuration, in order to maximize the efficiency of the antenna system including the matching circuit, etc., the radiating element 1, the conductor 21 forming the matching circuit, and the conductor 31 forming the unbalanced transmission line. At least one of them is made of a superconducting material. As mentioned above, since the radiation resistance of a minute radiating element is very small, even a small loss resistance of the element conductor significantly degrades the efficiency of the antenna. Further, since the input resistance of the radiating element and the impedance of the feeding system are significantly different, a large standing wave is generated on the matching circuit, and even a small loss resistance of the conductor forming the matching circuit significantly degrades the efficiency of the matching circuit.

[0015] Furthermore, when it is necessary to route the feed line for a considerable length, such as in a feed circuit for an array antenna,
Even a small loss resistance of the conductor forming the feed line significantly degrades the efficiency of the feed circuit. Therefore, if at least one of the radiating elements, the conductors that make up the matching circuit, and the conductors that make up the unbalanced transmission line become superconducting, the loss resistance will be much smaller than that of ordinary metals, making this antenna highly efficient. will be obtained.

For example, FIGS. 2A and 2B show actual measured values of the absolute gain of an antenna with the configuration shown in FIG. 1(b) with an element length of 1/50 wavelength. A is the absolute gain at room temperature when the radiating element 1, the conductor 21 constituting the matching circuit, and the conductor 31 constituting the unbalanced line are all made of copper material, and -8.
9 dBi was obtained. B is approximately 80 mm when the radiating element 1, the conductor 21 forming the matching circuit, and the conductor 31 forming the unbalanced line are all made of yttrium-based superconducting material.
The absolute gain at °K is -1.5 dBi. Further, symbols C and D indicate the absolute gain of a loop antenna with a diameter of 1/30 wavelength using a stub matching circuit as an example of a conventional micro antenna. Symbol C is the absolute gain at room temperature when the radiating element is made of copper material, and symbol D, where -17.5 dBi is obtained, is the absolute gain at room temperature when the radiating element is made of copper material. , -17
．． 5 dBi was obtained. Comparing the conventional antenna and the antenna of the present application, the antenna of the present application has a gain of 8.6 dB in the case of a normal conduction antenna and 3.5 dB in the case of a superconducting antenna, even though the dimensions of the antenna of the present application are 3/5 times smaller. A high value is obtained. Furthermore, in the case of a superconducting antenna, the frequency band of the antenna of the present application is approximately 1.8 times wider than that of the conventional antenna. This shows that the antenna of the present application is very effective.

FIG. 3(a) is an example of a small antenna having the configuration of FIG. 1(a) with a different shape of the radiating element. 1a is a self-common type small meander-shaped radiating element, 2 is a balanced quarter-wavelength matching circuit, 21 is a conductor that makes up the matching circuit, 22 is a dielectric that makes up the matching circuit, and 3 is a coaxial type feeding line. An unbalanced transmission line, 31 is a conductor constituting the unbalanced transmission line, and 32 is a dielectric body constituting the unbalanced transmission line. If it is desired to maximize the efficiency of the antenna system, at least one of the radiating element 1 and the conductor 31 may be made of a superconducting material. For example, if the shape of the radiating element is as shown in Fig. 2(b), the length and width are each 1/15 wavelength,
If the conductor line spacing outside the element center is 1/300 wavelength, and the conductor line spacing at the element center is 1/150 wavelength, then
The resonance state, that is, the input reactance becomes zero, and the radiation resistance becomes 2Ω. The operation of each part of the antenna is the same as in the case of FIG.

The above example uses a quarter-wavelength matching circuit, but when matching a circuit with a very large impedance ratio, a one-stage matching circuit may be too critical. In this case, a multi-stage matching circuit or a tapered line type matching circuit may be used as in the other embodiment shown in FIG. In these examples, the matching circuit itself does not have a balun function. In FIG. 4, 5 indicates a power feeding position. As the matching circuit 2, Fig. 3(a) uses a one-stage quarter-wavelength matching circuit, and Fig. 3(b) uses a multi-stage quarter-wavelength matching circuit (in this example, a two-stage quarter-wavelength matching circuit). (c) uses a tapered line type matching circuit.

[0019] The multi-stage quarter wavelength matching circuit has one stage quarter wavelength matching circuit.
A tapered line type matching circuit, which consists of two or more wavelength matching circuits connected in a subordinate manner, gradually changes the characteristic impedance of the line, and each has a simple structure and is easy to manufacture, and operates ideally even at high frequencies. It has characteristics such as being easy to use. These circuits have a restriction that the reactance of the matched impedance must be zero, similar to the one-stage quarter-wave matching circuit, but in both of these circuits, the reactance of the matched impedance must be zero.
It is possible to operate in a wider range than a wavelength matching circuit.

For example, using a two-stage quarter-wavelength matching circuit, a radiating element with an input resistance of 0.1Ω and an impedance of 50Ω are used.
When connecting a power supply system of Ω, the permittivity of the dielectric is 2.6,
The line width is 4 mm, and the overall length is 1/1 of the wavelength in free space.
3, and the spacing between the two conductors is 16 μm for the 1/2 length part on the radiating element side, and 0.4 mm for the remaining 1/2 length part.
It is sufficient to use parallel lines. Note that it is important to select a dielectric material with low dielectric loss as the dielectric material used at this time.

Next, as in the previous embodiment, the input reactance of the radiating element needs to be zero in this case as well.
The radiation element 1 has a self-resonant element. As for the shape of the radiating element, the aforementioned small helical element, small meandering element, etc. can be used in exactly the same manner.

[0022]

[Effects of the Invention] As explained above, the present invention uses a resonant element and a one-stage or multi-stage quarter wavelength matching circuit or a tapered line type matching circuit, so matching is easy despite its small size. It has the advantages of high efficiency and wide band.

[Brief explanation of the drawing]

[Fig. 1] A perspective view showing one embodiment of the present invention (using a helical element)

[Figure 2] Graph explaining the characteristics of the device in Figure 1

[Figure 3]
A perspective view showing another embodiment (using a meandering element)

[Fig. 4] A perspective view showing another embodiment (modified example of matching circuit)

[Figure 5] Diagram showing the configuration of an antenna using superconducting material

[Explanation of symbols]

1, 1a element 2 Matching circuit 3,3a Transmission line 6 Antenna 7 Power supply line 8 Dewar bottle 9. Liquid nitrogen 21, 31, 31a Conductor 22, 32, 32a Dielectric

Claims (4)

[Claims] Claim 1. An antenna system that combines an electric dipole antenna element and a matching circuit that matches the element impedance and the feed system impedance. a radiating element whose element length is shorter than the electrical length of a linear half-wavelength dipole element used in a resonant state and which is self-resonant at the center frequency used and connected to one end of the matching circuit; and the other end of the matching circuit. A small antenna with a matching circuit, characterized in that it has a transmission line in an unbalanced transmission mode connected to an end of the antenna. 2. The small antenna with a matching circuit according to claim 1, wherein a superconducting material is used for at least one of the antenna element, the matching circuit, and the transmission line. 3. The small antenna with a matching circuit according to claim 1, wherein the antenna element has a helical shape or a small meander shape. 4. In an antenna system that combines an electric dipole antenna element and a matching circuit that matches the element impedance and the feed system impedance, a one-stage quarter-wave matching circuit or a multi-stage quarter-wave matching circuit in a balanced transmission mode is used. A matching circuit, either a matching circuit or a tapered line type matching circuit, and a device whose electrical element length in the direction of the main polarized electric field is shorter than the electrical length of the linear half-wavelength dipole element used in the resonant state and whose center is used. A small antenna with a matching circuit, characterized in that it has a radiating element that self-resonates at a frequency and is connected to one end of the matching circuit.