JPH03270403A - Antenna circuit and compact portable radio equipment - Google Patents

Abstract

PURPOSE:To prevent an optimum matching state from being deviated from the resonance frequency of an antenna circuit or a high frequency amplifier circuit by specifying the shape and wiring of a loop antenna. CONSTITUTION:First and second loop antennas 1 and 2 are arranged longitudinally in a lengthwise direction and these opening areas are made almost equal. Then, the first loop antenna 1 is connected to a substrate 3 by a second end part 4 and a first end part 6 and the second loop antenna 2 is connected by a second end part 5 and a first end part 7. The first end parts 6 and 7 are mutually connected and the both loop antennas are connected. Then, the first loop antenna is wound left from the first end part 6 to the second end part 4 or forms the loop from the upside to the downside. On the other hand, the second loop antenna is wound right from the second end part 5 to the first end part 7 or forms the loop from the downside to the upside. Therefore, the first and second loop antennas 1 and 2 are parallelly connected. Thus, the resonance frequency of the resonance circuit is not deviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmitting/receiving antenna for a small portable radio device and its circuit configuration.

"Prior Art 1" Conventionally, loop antennas have been used as antennas for small portable radio devices because they fit inside the main body and can be made smaller.

FIG. 4 is a diagram of a conventional loop antenna viewed from the aperture direction. FIG. 5 is a circuit diagram of an antenna circuit including a conventional loop antenna.

Loop antenna 11 is represented by coil 31.

This coil 31 and the variable capacitance capacitor 32 constitute a resonant circuit, which resonates at the frequency transmitted and received by the antenna circuit. It is connected to terminals 34 and 35 via a capacitor 33, and further connected to a high frequency amplification circuit via the terminal.

Since the conventional loop antenna 11 has a long length,
Inductance increases. Therefore, when a certain amount of variable capacitance capacitor 32 resonates, the resonance frequency becomes a low frequency. Therefore, conventionally, the examples shown in FIGS. 4 and 5 have been widely used as antenna circuits for transmitting and receiving low frequencies.

[Problem to be solved by the invention 1 In a small portable radio device that transmits and receives high-frequency radio signals, in order to increase its transmission and reception sensitivity, it is necessary to
In addition to increasing the purity of the oscillation signal, it is also important to increase the gain of the antenna.

To increase the antenna gain, for loop antennas,
By increasing the aperture area, the radiation resistance increases and that objective is achieved. Increasing the aperture area increases the inductance when the loop antenna is viewed as a coil. In this case, by reducing the capacitance of the capacitor that forms the parallel resonant circuit with the loop antenna,
It can resonate at a target frequency and can transmit and receive radio signals. Alternatively, an optimal matching circuit can be constructed.

However, in a high frequency resonant circuit, the value of the capacitor becomes very small. Then, the capacitance generated between the radio device main body case, the human body, etc. and the loop antenna becomes a value that cannot be ignored, and the resonant frequency of the resonant circuit shifts. Otherwise, the matching state will deviate from the optimum state. As a result, the sensitivity of the radio device will be significantly reduced.

Furthermore, if the capacitance generated between the loop antenna and the mounting board is large, even if the capacitor is removed, it will always be capacitive and it will be impossible to create an inductive impedance.

The purpose of the present invention is to reduce the inductance of a loop antenna used in a small portable radio device and increase the capacitance of a capacitor that constitutes a parallel resonant circuit. or easily match the desired impedance value. The purpose is to provide an antenna circuit. Furthermore, a small portable radio device using the antenna circuit of the present invention provides performance that allows transmission and reception with constant sensitivity at all times.

[Means for Solving the Problems] The antenna circuit of the present invention has a means for receiving a radio wave signal containing an information signal in a small mobile communication device such as a pager or a mobile phone that is always carried and used. a first end of the first loop antenna; and a first end of the second loop antenna having means equivalent to the first loop antenna.
and the end portions are connected to each other at a first connection point, and the first connection point includes a first capacitor that constitutes a resonant circuit.
The terminals were connected, the first and second loop antennas were arranged vertically in the longitudinal direction, and were further connected to each other. The first of the first and second loop antennas
The winding directions of each loop antenna from the end to the second end of each loop antenna are opposite to each other, and the second ends of the first and second loop antennas and a second terminal of the capacitor are connected to each other to form a second connection point, and the first and second loop antennas and the capacitor are connected in parallel at the first and second connection points. Furthermore, a small portable radio device having such an antenna circuit is constructed.

[Example] FIG. 1 is a diagram of a loop antenna used in the antenna circuit of the present invention, viewed from the aperture direction.

As shown in the figure, the first loop antenna 1 and the second loop antenna 2 are arranged vertically in the longitudinal direction, and the opening areas of the first loop antenna 1 and the second loop antenna 2 are They are almost equal. Each loop antenna is connected to the board 3 at two locations. The first loop antenna 1 is connected at a second end 4 and a first end 6, and the second loop antenna 2 is connected at a second end 5 and a first end 7. Each end is soldered. The first ends 6 and 7 are also connected to each other, connecting both loop antennas.

The first loop antenna extends from the first end 6 to the second end. A loop is formed to the end 4 either left-handed or from top to bottom.

On the other hand, the second loop antenna has a right-handed winding from the second end 5 to the first end 7, or a loop is formed from the bottom to the top.

The second end 4.5 is grounded or has the same potential in terms of high frequency, and when combined with the fact that the first end 6.7 is connected, the first loop antenna 1 and the second loop antenna 2 are
They are connected in parallel.

One of the features of the present invention is that both loop antennas are arranged and wired in this manner.

FIG. 2 is a diagram of the loop antenna viewed diagonally from above. Maxwell's equations are well-known laws of electromagnetic induction. To show one of them, E represents the electric field and B represents the magnetic flux, but when applied to this case, the left side of the equation is the electromotive force of the loop antenna, and the right side is the magnetic field component of the radio signal existing in space. It is a change over time.

In Fig. 2, the magnetic flux 8 and the current 9 flowing through the loop antenna according to the electromotive force at that time are shown.
It is shown. According to Maxwell's equations, the second
As shown in the figure, when the magnetic flux 8 crosses the loop antenna 1.2, the side with the higher potential of the electromotive force is the second end 4 side in the first loop antenna 1, and the second end in the second loop antenna 2. 5 side and the lower side respectively becomes the first end 6.7. Since the second ends 4.5 are designed to have the same potential in terms of high frequency, the potential is maximum between them and the first end 6.7, and a wave signal of 1 can be extracted. .

6. However, if both loop antennas are wound in the same direction, the electromotive forces will cancel each other out,
Radio signals cannot be retrieved. A feature of the present invention is that the winding direction is reversed.

FIG. 3 is a circuit diagram of the antenna circuit of the present invention. 1st
The first loop antenna 1 in the figure is connected to the coil 21, and the second loop antenna 1 is connected to the coil 21.
A loop antenna corresponds to the coil 22. The connection point of the first end 6.7 also corresponds to the contact point 27. The second end 4.5 corresponds to the contacts 28, and a variable capacitance capacitor 23 is inserted between these contacts. This variable capacitance capacitor 23 and coils 21 and 22 constitute a resonant circuit. Furthermore, a capacitor 24 is connected in series with this.
are connected, and the received signal is sent to the high frequency amplifier circuit at terminals 25 and 26. The terminal 26 is grounded in terms of high frequency.

Assuming that the inductance values of coils 21 and 22 are the same, L
Then, the combined inductance Lt of both is: Lt=L/2 The inductance is half of that in the case of one coil. If the variable capacitance capacitor 23 constituting the resonant circuit is tuned to the same frequency, the value of the variable capacitance capacitor 23 can be doubled. This is a feature of the present invention. This effect is shown below.

FIG. 4 is a diagram of a conventional loop antenna viewed from the aperture direction. Compared to FIG. 1, the aperture area of the loop antenna 11 is almost the same. Therefore, the gain of the loop antenna is the same.

FIG. 5 is a circuit diagram of an antenna circuit including a conventional loop antenna. The difference from FIG. 3 is that there is only one coil. Loop antenna 1 in Figure 4
1 is approximately twice the size of one of the two loop antennas 1.2 of FIG.

Therefore, the inductance La of the coil 31 representing the loop antenna 11 is as follows using the inductance L of the coil 21: La=2L. The relationship between the inductance La of the resonant circuit in FIG. 5 and the inductance Lt in FIG. 3 is L t = L
/ 2 = L a / 4 This means that the inductance value of the loop antenna of the antenna circuit of the present invention is 1/4 that of a conventional loop antenna of the same size. Since the inductance is reduced to 1/4,
The variable capacitance capacitor 23 can take a value four times that of the variable capacitance capacitor 32. This will be very significant.

This is because, in the high frequency range, there is a capacitance between the loop antenna and objects that are close to it, such as the exterior case of the radio or the human body, which shifts the frequency of the resonant circuit and reduces reception sensitivity. It may be stored away. This capacitance is small, a few pF, but if the value of the capacitor included in the resonant circuit is small, this effect cannot be ignored, causing the resonant frequency to shift or the matching state to shift.

However, if the value of the capacitor in the resonant circuit can be increased, this effect can be almost ignored, and stable receiving sensitivity can be maintained.

The antenna circuit of the present invention can solve the above-mentioned problems. That is, the influence of several pF of capacitance due to the case and the human body can be reduced to 1/4 compared to the case where a conventional loop antenna is used.

For radio equipment that transmits and receives high frequencies, and when such radio equipment is always carried and used,
Although the above-mentioned problems inevitably occur, the antenna circuit of the present invention is very effective as a means for solving these problems.

FIG. 6 is a diagram showing a case where two loop antennas used in the antenna circuit of the present invention have different aperture areas. Further, FIG. 7 is a circuit diagram of the same, in which case the second loop antenna 2 with a large aperture area has a large gain, the first loop antenna 1 has a small gain,
Moreover, as in the case of FIG. 1, the inductance value is not 1/4 of the conventional value of 6, so the influence of the human body etc. becomes somewhat large. However, it is effective for the following uses.7 In high frequency receiving circuits, when a loop antenna is attached to a board, there is a capacitance between the loop antenna and the board,
In addition to the value of the variable capacitance capacitor 23 of the resonant circuit, the capacitance increases, and sometimes the characteristics of the resonant circuit become capacitive, with the value of the variable capacitor 23 being minimized.

However, the input impedance of the high-frequency amplifier circuit connected to terminals 25 and 26 is mostly capacitive, so if you want to improve the gain and NF by impedance matching, the antenna The impedance on the circuit side must be inductive.

In such a case, the value of the inductance of the resonant circuit of the antenna circuit may be reduced.

If the antenna circuit side of the main second loop antenna 2 becomes capacitive as in the present invention, by attaching the first loop antenna 1, the coil 21 can be inserted in parallel to the resonant circuit of the antenna circuit. Therefore, the antenna circuit can be made inductive.

Further, in the embodiment shown in FIG. 6, the tap 36 is provided from the middle of the second loop antenna 2.

By doing so, impedance can be lowered and matching can be optimized.

Furthermore, unlike a chip coil or a wound coil, the fill 21 formed by the first loop antenna is expected to have a high value of Q in a high frequency range, and therefore, a coil is inserted therein. There is almost no increase in antenna circuit loss.

From this 6, it is clear that the antenna circuit of the present invention is suitable for high frequency transmission and reception.

FIG. 8 is a diagram showing a case where two loop antennas used in the antenna circuit of the present invention are integrated and the number of end portions is reduced.

Since the first end 6.7 in FIG. 1 is eliminated and fixed integrally, it can be expected that the loss will be reduced accordingly and the receiving sensitivity will be improved.

FIG. 9 shows another embodiment of the loop antenna used in the antenna circuit of the present invention, similar to the example shown in FIG. 1, and is an enlarged view of the ends of the first loop antenna and the second loop antenna. be.

Beyond the first end 6.7 of each loop antenna,
The claws 45 and 46 are inserted into holes in the board when attaching the loop antenna to the board.

The pawls 45 are inserted from the top of the board, and the pawls 46 are inserted from the bottom of the board and fixed. The substrate has two holes for this purpose, and if they are electrically connected to each other, the first loop antenna 1 and the second loop antenna 2 will be connected to each other. This structure is similar to that shown in FIG. 8 when viewed from the direction of the aperture of the loop antenna.

By dividing the loop antenna into two parts and attaching them in this way, the manufacturing process of the loop antenna can be simplified.

Section 10 is an embodiment of the loop antenna used in the antenna circuit of the present invention, viewed diagonally from above.

Compared to FIG. 2, the width and length of the first loop antenna 51 are different. The inductance of the loop antenna is
It increases as the width becomes smaller, and decreases as the length becomes shorter.

Using this fact, in Fig. 6, the opening area of the first loop antenna l is small, that is, the length is short, and the inductance value is small. By making it small, it is possible to match the inductance component of the second loop antenna 2. In this way, the inductance of the antenna circuit can be further reduced.

FIG. 11 is an embodiment of the loop antenna used in the antenna circuit of the present invention, viewed obliquely from above. In this embodiment, the width of the first loop antenna 61 is not constant.

In this case, the first end 6 side which is the hot end side of the first loop antenna 61 is thicker, and the second end which is the ground side is thicker.
The end 4 side is made thinner. Thereby, the gain of the first loop antenna 61 can be increased and the inductance can also be increased.

[Effects of the Invention] As described above, the antenna circuit of the present invention particularly has the following advantages:
By configuring the shape and wiring of the loop antenna as described above, the inductance of the loop antenna can be reduced to 1/4 of that of a conventional loop antenna of the same size.

■ As a result, it is less affected by the capacitance between the loop antenna and the loop antenna that occurs when the radio is attached to an external case or worn on the human body. There is almost no difference in the condition.

■ @ Since the Q is higher than that of a linear coil, there is almost no loss. If the inductance component is insufficient when using a conventional loop antenna, by changing to the antenna circuit of the present invention, the impedance of the circuit can be induced. can be made into a sex.

(2) Due to the shape of the loop antenna in the antenna circuit of the present invention, the aperture area is almost the same as that of a conventional loop antenna of the same size, so the gain of the antenna can be made the same.

There are effects as described above. Moreover, these effects are very large and very effective, especially when used in a small portable radio device that transmits and receives high frequencies.

A small portable radio device using the antenna circuit of the present invention can stably perform transmission and reception at high frequencies, and can always transmit and receive with constant sensitivity even when it is in close proximity to a human body, that is, when it is being carried, and even when it is not.

[Brief explanation of drawings]

FIG. 1 is a diagram of a loop antenna used in the antenna circuit of the present invention, viewed from the direction of the aperture. Figure 2 is a diagram of the loop antenna viewed diagonally from above. FIG. 3 is a circuit diagram of the antenna circuit of the present invention. FIG. 4 is a diagram of a conventional loop antenna viewed from the aperture direction. FIG. 5 is a circuit diagram of an antenna circuit including a conventional loop antenna. FIG. 6 is a diagram in which two loop antennas used in the antenna circuit of the present invention have different aperture areas. FIG. 7 is a circuit diagram of the antenna circuit shown in FIG. 6. FIG. 8 is a diagram showing a case where two loop antennas of the loop antennas used in the antenna circuit of the present invention are integrated and the number of end portions is reduced. FIG. 9 shows another embodiment of the loop antenna used in the antenna circuit of the present invention, similar to the example shown in FIG. 1, and is an enlarged view of the ends of the first loop antenna and the second loop antenna. FIG. 10 is an embodiment of the loop antenna used in the antenna circuit of the present invention, viewed obliquely from above. FIG. 11 is an embodiment of the loop antenna used in the antenna circuit of the present invention, viewed obliquely from above. 1 . . . . . 2 . l , 22 ・ 23 ・ ・ ・ 24 ・ ・ ・ ・ ・First loop antenna・Second loop antenna・Substrate・Second end・First end・Magnetic flux・Current・Loop antenna・Substrate・End・Coil・Variable capacitor/capacitor 25, 26 ・ 27, 28 ・ 29 ・ ・ 3 l ・ ・ ・ 32 ・ ・ ・ 33 ・ ・ ・ 34, 35 ・ 36 ・ ・ ・ 37 ・ ・ ・ 41 ・ ・・ ・ 42 ・ ・ ・ ・ 45, 46 ・ 51, 61 Terminal, contact, tap contact, coil capacitance variable capacitor, capacitor, terminal, tap, end, loop antenna, integral stop contact, pawl, first loop antenna and above Figure 1 Figure 2

Claims (2)

[Claims] (1) In a small mobile communication device such as a pager or a mobile phone that is always carried and used, the first end of the first loop antenna has a means for receiving a radio wave signal containing an information signal; A second loop antenna having means equivalent to the first loop antenna.
and a first end of the loop antenna are connected to each other at a first connection point, and a first terminal of a capacitor constituting a resonant circuit is connected to the first connection point, and the first end of the loop antenna is connected to the first end of the loop antenna.
, the second loop antenna is arranged vertically in the longitudinal direction, and the first and second loop antennas are connected to each other.
The winding directions of the respective loop antennas from the first end of the loop antenna to the second end of the respective loop antennas are arranged to be opposite to each other, and
, the second ends of the second loop antenna and the second terminal of the capacitor are connected to each other to form a second connection point;
An antenna circuit, wherein the first and second loop antennas and the capacitor are connected in parallel at the first and second connection points. (2) A small portable radio device characterized by having the antenna circuit according to item 1.