JP2006121579A - Loop antenna circuit, and transmitter-receiver using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a loop antenna circuit which is suitable for performing two-way simultaneous communication using one loop antenna, and to provide a transmitter-receiver using the loop antenna circuit. <P>SOLUTION: A second capacitor (C2) is connected in parallel to a serial circuit connecting a first capacitor (C1) in series to a loop antenna (2), thereby configuring a loop antenna circuit (1) with both terminals of the second capacitor as signal input and output terminals (3, 4). A transmitting circuit (7) and a receiving circuit (8) are connected in parallel to the input and output terminals. A circuit constant of the loop antenna circuit is determined to incur serial resonance at a transmitting frequency and to incur parallel resonance at a receiving frequency. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a loop antenna circuit suitable for performing bidirectional simultaneous communication with one loop antenna, and a transmission / reception apparatus using the loop antenna circuit.

  Conventionally, there has been an attempt to use a receiving antenna or a transmitting antenna by connecting a capacitor or an inductor to one loop antenna and tuning it at a plurality of frequencies. FIG. 11 shows a loop antenna circuit disclosed in Patent Document 1. In this circuit, a pair of feed points 112 and 113 are provided in the loop antenna 100, and a variable capacitor C11 is connected in series to the loop antenna 100, and a series resonant circuit including an inductor L12 and a capacitor C12 is connected in series to the closed loop. Is configured. Further, a reactance X is connected in parallel to the series resonance circuit.

  The series resonance circuit of the inductor L12 and the capacitor C12 is configured so that the resonance frequency is substantially equal to the first resonance frequency of the antenna that is tuned by the variable capacitor C11. Since the impedance of the series resonant circuit is zero at the first resonance frequency, the reactance X has no influence on the first resonance frequency. Other than the first resonance frequency, the impedance of the series resonance circuit is a value other than zero, so that tuning can be performed at another frequency by adjusting the value of the reactance X. Therefore, it is possible to receive or transmit at two frequencies by connecting a receiving circuit or a transmitting circuit to the feeding points 112 and 113. Further, when a diplexer (frequency divider) is used in combination, transmission and reception can be performed simultaneously at different frequencies.

  However, in the case of the circuit of FIG. 11, the resonance in which the reactance of the loop antenna 100 is mainly involved is a series resonance when viewed from the feeding points 112 and 113. Since the impedance is low in series resonance, the circuit of FIG. 11 is convenient for matching with a transmission circuit having a low output impedance. However, since a voltage input circuit having a high input impedance is generally used for reception, the circuit of FIG. 11 is inconvenient because it is difficult to achieve matching.

  In the circuit of FIG. 11, a series resonant circuit is connected in series to the loop antenna 100. However, when the Q value of the series resonant circuit is high, the resonant frequency tends to shift due to a temperature change or the like. The series resonant circuit in FIG. 11 is also installed outdoors. Therefore, the resonance frequency is shifted due to a temperature change or the like, and the transmission current flowing through the loop antenna 100 may be greatly reduced, which may hinder communication.

Patent Document 2 discloses a circuit that uses a single loop antenna to perform series resonance during transmission and parallel resonance during reception. However, in this circuit, two-way simultaneous communication cannot be performed because series resonance and parallel resonance are performed by switching circuits using a relay.
JP-A-6-177636 Japanese Utility Model Publication No. 63-85931 The Institute of Electronics, Information and Communication Engineers, “Electronic Information Communication Handbook”, published by Ohmsha, 1988, p. 525 EFSartori: “Hybrid Transformers”, IEEE TRANSACTIONS ON PARTS, MATERIALS AND PACKAGING, VOL.PMP-4, NO.3 (Sept. 1968)

  The present invention has been made to solve such problems of the prior art, and the subject thereof is a loop antenna circuit suitable for performing bidirectional simultaneous communication using one loop antenna, and the use thereof. It is to provide a transmission / reception apparatus.

  The invention according to claim 1 for solving the above-mentioned problem is that a second capacitor (C2) is connected in parallel to a series circuit of a loop antenna (2) and a first capacitor (C1). The loop antenna circuit is characterized in that both ends of the capacitor are signal input / output terminals (3, 4).

  If circuit constants are determined so that such a loop antenna circuit resonates in series at the transmission frequency, a large current can flow through the loop antenna by the transmission circuit having a low output impedance, and radio waves can be radiated efficiently. . In addition, if a circuit constant is determined so as to perform parallel resonance at the reception frequency, a large reception voltage is generated at the input / output terminals, so that a high reception sensitivity can be ensured by a reception circuit having a high input impedance. By connecting such a transmission circuit and a reception circuit in parallel to the input / output terminals, bidirectional simultaneous communication can be efficiently performed.

According to the second aspect of the present invention, the fourth capacitor (C6) is connected in series to the parallel circuit of the loop antenna (2) and the third capacitor (C5), and both ends of the series-connected circuit are connected. It is a loop antenna circuit characterized by having signal input / output terminals (3, 4).
Such a loop antenna circuit also achieves the same effect as that of the first aspect of the invention by determining circuit constants so that series resonance occurs at the transmission frequency and parallel resonance occurs at the reception frequency.

Further, the invention according to claim 3 is the loop antenna circuit according to claim 1 or 2, wherein the circuit causes a series resonance at a transmission frequency and a parallel resonance at a reception frequency of a transmission / reception apparatus using the circuit. It is characterized by a fixed constant.
If series resonance occurs at the transmission frequency, a large current can be passed through the loop antenna by the transmission circuit having a low output impedance, and radio waves can be radiated efficiently. In addition, if parallel resonance is performed at the reception frequency, a large reception voltage is generated at the input / output terminals. Therefore, high reception sensitivity can be ensured by using a reception circuit with high input impedance. By connecting such a transmission circuit and a reception circuit in parallel to the input / output terminals, bidirectional simultaneous communication can be efficiently performed.

According to a fourth aspect of the present invention, in the loop antenna circuit according to any one of the first to third aspects, a resistor (R2) is additionally connected in series to one end of the input / output terminals (3, 4). It is characterized by.
When a series resonance circuit is excited with a transmission frequency that matches the resonance frequency, if the circuit constant changes even slightly due to a temperature change or the like, the resonance frequency shifts and the circuit impedance changes at a large rate. If a resistor is connected in series as in this configuration, the Q value of the circuit is lowered and the transmission efficiency is slightly lowered, but the change rate of the circuit impedance is conversely reduced. Therefore, there is an effect that a change in transmission output can be reduced.

  According to a fifth aspect of the present invention, there is provided a low output impedance transmission circuit (7) and a high input impedance reception circuit (between the input / output terminals of the loop antenna circuit according to any one of the first to fourth aspects). 8) is connected in parallel.

  According to the transmission / reception apparatus having such a configuration, at the transmission frequency, the loop antenna circuit resonates in series and the circuit impedance becomes low. For this reason, a large current can flow from the transmission circuit having a low output impedance to the loop antenna, and radio waves can be radiated efficiently. At the reception frequency, the loop antenna circuit resonates in parallel and a large reception voltage is generated between the input and output terminals. For this reason, if a receiving circuit with high input impedance is used, radio waves can be received with high receiving sensitivity. Further, since the loop antenna circuit is a linear circuit and can operate simultaneously at different frequencies, bidirectional simultaneous communication can be efficiently performed using different transmission frequencies and reception frequencies.

  According to a sixth aspect of the present invention, in the transmission / reception device according to the fifth aspect, a two-wire four-wire conversion circuit (32) using a hybrid transformer (31) instead of connecting the transmission circuit and the reception circuit in parallel. ) And the loop antenna circuit is connected to the two-wire side, and the transmitting circuit and the receiving circuit are connected to the four-wire side.

  In such a configuration, it is possible to achieve isolation between the transmission circuit and the reception circuit, and it is possible to prevent a signal having a transmission frequency from the transmission circuit from reaching the reception circuit. By doing so, only the signal of the reception frequency received by the loop antenna is input to the reception circuit, so that signal reception becomes easy. Further, the signal of the reception frequency received by the loop antenna is distributed to both the transmission circuit and the reception circuit, but more power can be distributed to the transmission circuit by changing the winding ratio of the hybrid transformer. Therefore, the reception sensitivity can be improved by doing so.

The invention according to claim 7 is characterized in that, in the transmitter / receiver according to claim 5 or 6, an impedance matching transformer (11) is provided near an input / output terminal of the loop antenna circuit. To do.
By providing such impedance matching transformer and impedance matching between the loop antenna circuit at the transmission frequency and the parallel connection of the transmission circuit and the reception circuit, the output of the transmission circuit can be efficiently transmitted to the loop antenna. Can lead to.

  The invention according to claim 8 is the transmitter / receiver according to any one of claims 5 to 7, wherein the transmitting circuit includes a resonance circuit (26) that resonates in series at a transmission frequency in series with the output side, The receiving circuit is characterized in that a resonance circuit (27) that resonates in series at the reception frequency is additionally connected in series to the input side.

  In such a configuration, since the impedance of the series resonant circuit connected to the output terminal of the transmission circuit is zero at the transmission frequency, the output from the transmission circuit is not hindered. On the other hand, at this transmission frequency, the series resonant circuit connected to the input terminal of the receiving circuit exhibits high impedance, so that the output power from the transmitting circuit is prevented from being consumed by the receiving circuit. For this reason, there is an effect that the efficiency of the output power from the transmission circuit is improved. At the reception frequency, the series resonant circuit connected to the input terminal of the reception circuit has zero impedance, and does not hinder reception. On the other hand, at this reception frequency, the series resonant circuit connected to the output terminal of the transmission circuit exhibits high impedance, so that power received by the antenna is prevented from being consumed by the transmission circuit. As a result, the reception power of the reception circuit is increased, so that the reception sensitivity is improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a circuit configuration of a first embodiment of a loop antenna circuit according to the present invention. The loop antenna circuit 1 includes a loop antenna 2, a first capacitor C1, and a second capacitor C2. The capacitor C1 is connected in series with the loop antenna 2, and the capacitor C2 is connected in parallel with the series circuit. Both ends of the capacitor C2 are connected to the input / output terminals 3 and 4.

An equivalent circuit of the loop antenna 2 is represented by a series circuit of a resistance r1 with an inductance L1. The resistance r1 is a resistance of the loop antenna 2 and has a small value. The impedance Z of the loop antenna circuit 1 viewed from the input / output terminals 3 and 4 is expressed as follows.
Z = {(1 / ωC2) · (ωL1-1 / ωC1) −jr1 / ωC2}
/ {J (ωL1-1 / ωC1-1 / ωC2) + r1} (1)

The value of the impedance Z is equal to the resistance r1 when ω ² = 1 / (L1 · C1) and r1 << 1 / (ωC2) are satisfied. That is, the loop antenna circuit 1 of FIG.
ω ² = 1 / (L1 · C1) Series resonance occurs at an angular frequency ω1 satisfying the equation (2), and the impedance Z at that time becomes equal to a small resistance value r1. In this state, the capacitor C2 connected in parallel hardly affects the operation of the circuit.

Further, according to equation (1), when r1 << 1 / (ωC2) is satisfied at an angular frequency ω that satisfies ωL1 = 1 / ωC1 + 1 / ωC2 (3), the value of impedance Z is very high. Large value. That is, the loop antenna circuit 1 of FIG. 1 causes parallel resonance at an angular frequency ω2 that satisfies the expression (3), and the impedance becomes a very large value.
Thus, the loop antenna circuit 1 that causes series resonance at the angular frequency ω1 and parallel resonance at the angular frequency ω2 exhibits its effect when used as an antenna circuit of a transmission / reception device that performs bidirectional simultaneous communication. Next, it will be described.

FIG. 2 is a configuration diagram of the first embodiment of the transmission / reception apparatus. In the transmission / reception apparatus 6 of this embodiment, a transmission circuit 7 and a reception circuit 8 are connected in parallel to input / output terminals 3 and 4 of the loop antenna circuit 1. The output impedance of the transmission circuit 7 is Z1, and an AC voltage E1 having a transmission frequency f1 (angular frequency is ω1 = 2πf1) is output. The input impedance of the receiving circuit 8 is Z2.
The output impedance Z1 of the transmission circuit 7 is generally designed to be a low value in order to increase power efficiency. On the other hand, the receiving circuit 8 is often a voltage input that is easy to design, and its input impedance Z2 is designed to a very high value.

  Considering the operation at the transmission frequency f1 (angular frequency ω1), the impedance of the loop antenna 2 viewed from the input / output terminals 3 and 4 is equal to the resistance r1 due to series resonance. Therefore, a large current of E1 / | Z1 + r1 | flows through the loop antenna 2. The current when the capacitors C1 and C2 are not attached is a value represented by E1 / | Z1 + r1 + jωL1 |, which is very small as compared with the case where the capacitors C1 and C2 are attached. That is, by attaching the capacitors C1 and C2 and causing series resonance at the transmission frequency f1, a large current flows through the loop antenna 2 and an effect of emitting strong radio waves is produced.

Next, consider the operation at the reception frequency f2 (angular frequency is ω2 = 2πf2). The received radio wave generates a voltage E2 in series with the inductance L1 of the loop antenna 2. Impedance of the transmission circuit 7 and the reception circuit 8 viewed from the parallel connection points 12 and 13 between the transmission circuit 7 and the reception circuit 8, that is, the parallel connection impedance of the input impedance Z1 of the transmission circuit 7 and the input impedance Z2 of the reception circuit 8 Is Z3, and the reception voltage of the reception circuit 8 is V2. If the expression (3) is satisfied at the reception frequency f2, that is, if the circuit constant is set so that the loop antenna circuit 1 causes parallel resonance at the reception frequency f2, the reception voltage V2 at that time is It is expressed by a formula.
V2 = E2 · | Z3 | / {1 / (ω2 · C2)} (4)

On the other hand, the reception voltage V2 when the capacitors C1 and C2 are not attached is as follows.
V2 = E2 · | Z3 | / | Z3 + jω2 · L1 | (5) Expression From the expression (3),
ω2 · L1-1 / (ω2 · C1) = 1 / (ω2 · C2)> 0
Than this,
ω2 ・ L1> 1 / (ω2 ・ C1)

  Since the impedance Z3 may be considered as a resistance, the value of the denominator of the equation (4) is considerably smaller than the value of the denominator of the equation (5). Therefore, the value of the reception voltage V2 calculated by the equation (4) is considerably larger than the value of the reception voltage V2 calculated by the equation (5). That is, by attaching the capacitors C1 and C2 and causing parallel resonance at the reception frequency f2, an effect that a large voltage can be obtained in the reception voltage V2 of the transmission circuit 7 is produced.

  Thus, the capacitors C1 and C2 are added to the loop antenna 2 as shown in FIG. The capacitances of the capacitors C1 and C2 are determined so that the expression (2) is satisfied at the transmission frequency f1 to cause series resonance, and the expression (3) is satisfied at the reception frequency f2 to cause parallel resonance. A transmission / reception apparatus 6 as shown in FIG. 2 is configured using the loop antenna circuit 1 in which circuit constants are determined in this way. With such a configuration, a large transmission current of the transmission frequency f1 flows through the loop antenna 2 and a strong radio wave is radiated, and the reception circuit 8 has an effect of obtaining a reception voltage V2 of a large reception frequency f2.

  FIG. 3 is a modified embodiment of the loop antenna circuit 1 of the first embodiment shown in FIG. This loop antenna circuit 1a is obtained by adding a resistor R2 between a terminal 3 which is one end of input / output terminals 3 and 4 and one end of a capacitor C2. The capacitances of the capacitors C1 and C2 are determined so as to cause series resonance at the transmission frequency f1 and parallel resonance at the reception frequency f2, as in the loop antenna circuit 1 of FIG.

  When a transmission voltage having a transmission frequency f1 is applied to the input / output terminals 3 and 4 of the loop antenna circuit 1 of FIG. 1, the impedance Z seen from the input / output terminals 3 and 4 due to series resonance is zero and has a resistance value. Becomes r1. However, when the values of the inductance L1 and the capacitor C1 change due to a temperature change or the like, the reactance of the impedance Z calculated in (1) does not become zero, and | Z |> r1.

  If the input impedance Z2 of the receiving circuit is sufficiently large, the current flowing through the loop antenna 2 is expressed by E1 / | Z1 + Z |. Therefore, when the reactance appears and | Z |> r1, the current decreases. When the Q (Quality factor) value of the series resonance is large, the impedance | Z | changes greatly only by causing a slight difference between the resonance frequency and the transmission frequency f1. If the rate of change of the impedance | Z | is large, the rate of change of the current flowing through the loop antenna 2 is also large, and the intensity of the transmission radio wave changes greatly.

  Although the voltage E1 generated by the transmission circuit 7 and the transmission frequency f1 are constant, the series resonance frequency of the loop antenna circuit 1 changes due to a temperature change or the like, so that the intensity of the transmission radio wave greatly changes. It becomes an obstacle. Therefore, in the loop antenna circuit 1a of FIG. 3, a resistance R2 is added in series to lower the Q value at the time of series resonance. If the resistor R2 is added, the value of Q decreases and the intensity of the transmitted radio wave decreases. On the other hand, when the series resonance frequency deviates from the transmission frequency f1, the rate of change of the impedance Z as viewed from the input / output terminals 3 and 4 is small, so the rate of change of the intensity of the transmission radio wave is conversely small. That is, the loop antenna circuit 1a shown in FIG. 3 stabilizes the intensity of the transmission radio wave at the expense of the intensity of the transmission radio wave. Therefore, when importance is attached to the stability of the intensity of the transmission radio wave, it is preferable to employ the loop antenna circuit 1a of FIG. 3 instead of the loop antenna circuit 1 of FIG.

  FIG. 4 is a modified embodiment of the transmission / reception device 6 shown in FIG. Although the loop antenna circuit 1a of FIG. 3 is adopted as the loop antenna circuit, the loop antenna circuit 1 of FIG. 1 may be used. The transmission / reception apparatus 10 according to this embodiment is suitable for a case where the distance between the parallel connection points 12 and 13 of the transmission circuit 7 and the reception circuit 8 and the loop antenna circuit 1a is long, and it is necessary to connect the cable 17 between them. It is a form.

The difference from the transmission / reception apparatus 6 of FIG. 2 is that an impedance matching transformer 11 is added near the loop antenna circuit 1a. The characteristic impedance of the cable 17 is assumed to be Z0. The ratio of the number of primary windings n1 and the number of secondary windings n2 of the transformer 11 is determined so that the impedance when the loop antenna 2 side is viewed from the primary side is equal to the characteristic impedance Z0. That is,
Z0 = (n1 / n2) ² · (R2 + r1) It is determined so as to satisfy the equation (6).

  Further, the impedance Z3 is the impedance Z3 as seen from the side of the transmission circuit 7 and the reception circuit 8 connected in parallel from the parallel connection points 12 and 13, and the value is made equal to the characteristic impedance Z0. Since the input impedance Z2 of the receiving circuit 8 is sufficiently higher than the output impedance Z1 of the transmitting circuit 7, the impedance Z3 is equal to the impedance Z1. Therefore, the value of the output impedance Z1 of the transmission circuit 7 is designed to be equal to the characteristic impedance Z0. By doing so, impedance matching is achieved, and the loop antenna circuit 1a is supplied with the maximum power that the transmission circuit 7 can supply to the outside.

FIG. 5 shows another modified embodiment of the transmission / reception apparatus 10 shown in FIG. The transmission / reception apparatus 20 of this embodiment is obtained by additionally attaching an impedance matching transformer 14 between the output of the transmission circuit 7 and the parallel connection points 12 and 13. This circuit configuration is suitable when the output impedance Z1 of the transmission circuit 7 is lower than the characteristic impedance Z0 of the cable 17 and matching is not possible. The winding ratio is determined so that the impedance of the transmission circuit 7 viewed from the secondary side (cable 17 side) of the added transformer 14 is equal to the characteristic impedance Z0 of the cable 17. That is, the ratio of the number of primary windings n3 and the number of secondary windings n4 of the transformer 14 is determined so as to satisfy the following expression.
Z0 = (n4 / n3) ² · Z1 (7) Formula

  When the winding ratio is set in this way, the maximum power is supplied from the transmission circuit 7, and all the power is supplied to the loop antenna circuit 1a to radiate strong transmission radio waves. In the case of this circuit configuration, since the impedance of the transmission circuit 7 viewed from the secondary terminal of the transformer 14 is higher than the output impedance Z1 of the transmission circuit 7, the reception voltage V2 of the reception circuit 8 is not attached to the transformer 14. There is also an effect that becomes larger than.

  FIG. 6 shows still another modified embodiment of the transmission / reception apparatus 10 shown in FIG. The transmission / reception device 25 of this embodiment includes a series resonance circuit 26 including a capacitor C3 and an inductance L2 in series with the output of the transmission circuit 7 of the transmission / reception device 10 shown in FIG. 4, and a capacitor C4 in series with the input of the reception circuit 8. And a series resonance circuit 27 including an inductance L3. The circuit constants are set so that the resonance frequency of the series resonance circuit 26 coincides with the transmission frequency f1, and the resonance frequency of the series resonance circuit 27 coincides with the reception frequency f2.

  At the transmission frequency f1, the series resonance circuit 26 is short-circuited. Therefore, the series resonance circuit 26 does not interfere with the output of the transmission circuit 7. The other series resonant circuit 27 exhibits a high impedance at the transmission frequency f1. Therefore, the impedance of the receiving circuit 8 viewed from the parallel connection points 12 and 13 becomes higher than before the addition due to the addition of the series resonance circuit 27. As a result, of the output power of the transmission circuit 7, the power consumed by the reception circuit 8 is reduced, and the power supplied to the loop antenna circuit 1a is increased accordingly.

  Further, since the series resonant circuit 27 is short-circuited at the reception frequency f2, the presence of the series resonant circuit 27 does not interfere with reception by the receiving circuit 8. On the other hand, the series resonant circuit 26 exhibits high impedance at the reception frequency f2. Therefore, the impedance of the transmission circuit 7 viewed from the parallel connection points 12 and 13 is significantly higher than before the addition due to the addition of the series resonance circuit 26. As a result, of the received power, the power flowing through the transmission circuit 7 decreases, the power flowing through the reception circuit 8 increases accordingly, and the reception voltage V2 increases.

  By adding the series resonant circuits 26 and 27 in this way, the transmission power efficiency is increased and the reception sensitivity is also increased. In the case of the transmitting / receiving apparatus 20 shown in FIG. 5, the same effect can be obtained by adding the series resonant circuits 26 and 27 as in FIG.

  FIG. 7 shows still another modified embodiment of the transmission / reception apparatus 10 shown in FIG. The transmission / reception device 30 of this embodiment is obtained by additionally attaching a 2-wire / four-wire conversion circuit 32 using a hybrid transformer 31 to the transmission circuit 7 and reception circuit 8 sides of the transmission / reception device 10 shown in FIG.

  The 2-wire 4-wire conversion circuit is a circuit that is often used in public telephone networks, and it connects a 2-wire section that shares uplink / downlink lines with a 4-wire section that uses separate two lines for uplink and downlink. Attached to the part. A transmitter / receiver is connected to the two-wire line, a transmitter circuit is connected to two of the four-wire lines, and a receiver circuit is connected to the other two lines. The 2-wire 4-wire conversion circuit is characterized in that there is no mutual interference between the 2-wire line to which the transmission circuit is connected and the 2-wire line to which the reception circuit is connected. .

  Various circuit configurations have been proposed for the 2-wire 4-wire conversion circuit having such characteristics. The 2-wire 4-wire conversion circuit 32 shown in FIG. 7 is an example thereof, and has a circuit configuration introduced in Non-Patent Documents 1 and 2 described in “Background Art”. The two-wire / four-wire conversion circuit 32 includes a hybrid transformer 31 and a resistor R3. The hybrid transformer 31 is an insulating transformer having a primary winding and a secondary winding. The primary winding is on the two-wire circuit side, and the cable 17 is connected to both end terminals 33 and 34 thereof.

  An intermediate tap is provided on the 4-wire circuit side of the secondary winding. A resistor R3 is connected to the intermediate tap, and the other end of the resistor R3 is connected to commonly connected terminals 36 and 38. The output signal line of the transmission circuit 7 is connected between one end 35 of the secondary winding and the terminal 36, and the input signal line of the reception circuit 8 is connected between the other end 37 of the secondary winding and the terminal 38. The

The number of turns of the primary winding is n5, the number of turns between the terminal 35 and the intermediate tap of the secondary winding is n6, the number of turns between the terminal 37 and the intermediate tap is n7, and the cable 17 side is viewed from both ends 33 and 34 of the primary winding. The impedance is regarded as a resistance and its value is R4. The output impedance Z1 of the transmission circuit 7 and the input impedance Z2 of the reception circuit 8 are both resistors. When the circuit constants are set so that the following relationship is established between the resistors and the windings of the two-wire / four-wire conversion circuit 32, mutual interference does not occur between the transmission circuit 7 and the reception circuit 8 (for example, Non-patent document 1).
p = n6 / n5
q = n7 / n5
Z1 = p (p + q) · R4
Z2 = q (p + q) .R4
R3 = pq · R4

  That is, when the value of the resistor R3 and the number of turns n5, n6, and n7 of the hybrid transformer 31 are determined so that the above equation 5 is established, the transmission signal output from the transmission circuit 7 does not appear in the reception voltage V2 of the reception circuit 8. The power output from the transmission circuit 7 is consumed by the resistors r1 and R2 in the loop antenna circuit 1a and the resistor R3 in the 2-wire 4-wire conversion circuit 32. On the other hand, the power received by the loop antenna 2 and input to the primary winding of the hybrid transformer 31 is distributed to the transmission circuit 7 side and the reception circuit 8 side at a winding ratio n6: n7.

  Due to such an operation, in the transmission / reception apparatus 30 shown in FIG. 7, only the signal of the reception frequency f2 appears in the reception voltage V2 of the reception circuit 8. Therefore, there is an effect that signal reception by the receiving circuit 8 is facilitated. Further, the reception voltage V2 can be increased by increasing the turn ratio n7 / n6.

  In the case of the transmission / reception apparatus 30 as well, the transmission power efficiency can be improved if impedance matching is performed by adding an impedance matching transformer 14 on the output side like the transmission circuit 7 in FIG. If the series resonance circuit 26 as shown in FIG. 6 is added to the output side of the transmission circuit 7, the value of the reception voltage V2 can be increased.

  FIG. 8 shows a circuit configuration of a second embodiment of the loop antenna circuit according to the present invention. The loop antenna circuit 1b includes a loop antenna 2, a third capacitor C5, and a fourth C6. The capacitor C5 is connected to the loop antenna 2 in parallel, and the capacitor C6 is connected between one end 3 of the input / output terminals 3 and 4 and one end of the capacitor C5.

The impedance Z of the loop antenna circuit 1b viewed from the input / output terminals 3 and 4 is expressed as follows. However, it is assumed that the value of the resistor r1 is small and ωL1 >> r1.
Z = −j (ωC5 + ωC6-1 / ωL1) / {ωC6 · (ωC5-1 / ωL1)}
(8) Expression The value of the impedance Z becomes zero when the angular frequency ω satisfies the following expression.
ω ² = 1 / {L1 · (C5 + C6)} (9) However, in practice, it is not completely zero, and becomes a small value almost equal to r1. That is, the loop antenna circuit 1b causes series resonance at an angular frequency ω that satisfies the expression (9).

Further, according to the equation (8), the value of the impedance Z becomes a very large value with the denominator being zero when the angular frequency ω satisfies the following equation.
ω ² = 1 / (L1 · C5) Equation (10) In other words, the loop antenna circuit 1b causes parallel resonance at an angular frequency ω that satisfies Equation (10).

  Next, the loop antenna circuit 1b that causes the series resonance at the angular frequency ω satisfying the expression (3) and the parallel resonance at the angular frequency ω satisfying the expression (10) as described above is used for bidirectional simultaneous communication as before. A case where the antenna circuit is used as an antenna circuit of a transmitting / receiving apparatus that performs the above will be described. FIG. 9 is an example of such a transmitting / receiving apparatus according to the second embodiment, and is a circuit corresponding to FIG. 2 described above.

  As the circuit constant of the loop antenna circuit 1b, the values of the capacitors C5 and C6 are set so that series resonance occurs at the transmission frequency f1 of the transmission circuit 7 and parallel resonance occurs at the reception frequency f2. At the transmission frequency f1, because of the series resonance, the impedance of the loop antenna circuit 1b becomes a small value equal to r1, so that the loop antenna 2 does not have capacitors C5 and C6 as in the case of the transmission / reception device 6 of FIG. A large current flows. Therefore, an effect of emitting a strong radio wave is produced.

At the reception frequency f2, the loop antenna circuit 1b causes parallel resonance, and the reception voltage V2 of the reception circuit 8 is as follows.
V2 = E2 · | Z3 / (ω2 · L1) | (11) where Z3 is the impedance when the transmission circuit 7 and the reception circuit 8 are viewed from the parallel connection points 12 and 13. The reception voltage V2 when the capacitors C5 and C6 are not attached is expressed as follows.
V2 = E2 · | Z3 / (Z3 + ω2 · L1) | Equation (12) Since the impedance Z3 is considered to be almost a resistance, the denominator of Equation (11) is clearly smaller than the denominator of Equation (12). Therefore, by connecting the capacitors C5 and C6, there is an effect that the reception voltage V2 becomes a very large value.

10 is a modified embodiment of the loop antenna circuit 1b of the second embodiment shown in FIG. 8, and is a modified embodiment of the loop antenna circuit 1 of the first embodiment of FIG. This corresponds to the circuit 1a. The loop antenna circuit 1c is obtained by adding a resistor R2 in series with a capacitor C6. The values of the capacitors C5 and C6 are set to cause series resonance at the transmission frequency f1 and parallel resonance at the reception frequency f2 as in the loop antenna circuit 1b of FIG.
The reason for adding the resistor R2 is the same as in the case of the loop antenna circuit 1a of FIG. 3, in order to reduce the intensity change of the transmission radio wave when the resonance frequency deviates from the transmission frequency f1 by reducing the Q value of the series resonance. It is.

  These loop antenna circuits 1b and 1c are used in place of the loop antenna circuits 1 and 1a in the transmission / reception devices 6, 10, 20, 25 and 30 shown in FIG. 2, FIG. 4, FIG. 5, FIG. Can be used. And the same effect as demonstrated previously about the transmission / reception apparatus of each figure is show | played.

It is a circuit structure of the loop antenna circuit 1 which concerns on 1st Embodiment. It is a circuit structure of the transmission / reception apparatus 6 which concerns on 1st Embodiment. 5 is a modified embodiment of the loop antenna circuit 1 according to the first embodiment. It is modification embodiment of the transmission / reception apparatus 6 which concerns on 1st Embodiment. It is other modification embodiment of the transmission / reception apparatus 6 which concerns on 1st Embodiment. It is further another modified embodiment of the transmission / reception device 6 according to the first embodiment. It is further another modified embodiment of the transmission / reception device 6 according to the first embodiment. It is a circuit structure of the loop antenna circuit 1b which concerns on 2nd Embodiment. It is a circuit structure of the transmission / reception apparatus 35 which concerns on 2nd Embodiment. This is a modified embodiment of the loop antenna circuit 1b according to the second embodiment. FIG. 2 is a view corresponding to FIG.

Explanation of symbols

In the drawings, 1, 1a, 1b, 1c are loop antenna circuits, 2 is a loop antenna, 3, 4 is an input / output terminal, 6, 10, 20, 25, 30, 35 are transmission / reception devices, 7 is a transmission circuit, and 8 is Receiving circuit, 11 is a transformer, 26 and 27 are resonance circuits (series resonance circuits), 31 is a hybrid transformer, 32 is a 2-wire 4-wire conversion circuit, C1 is a first capacitor, C2 is a second capacitor, and C5 is a first 3, a capacitor C6 is a fourth capacitor, and R2 and R3 are resistors.

Claims (8)

  A second capacitor (C2) is connected in parallel to a series circuit of the loop antenna (2) and the first capacitor (C1), and both ends of the second capacitor are connected to signal input / output terminals (3, 4). A loop antenna circuit characterized by that.   A fourth capacitor (C6) is connected in series to a parallel circuit of the loop antenna (2) and the third capacitor (C5), and both ends of the series-connected circuit are connected to signal input / output terminals (3, 4). A loop antenna circuit characterized by that.   3. The loop antenna circuit according to claim 1, wherein circuit constants are set so that series resonance occurs at a transmission frequency and parallel resonance occurs at a reception frequency of a transmission / reception device using the circuit. circuit.   The loop antenna circuit according to any one of claims 1 to 3, wherein a resistor (R2) is additionally connected in series to one end of the input / output terminal (3, 4).   A low output impedance transmitter circuit (7) and a high input impedance receiver circuit (8) are connected in parallel between the input and output terminals of the loop antenna circuit according to any one of claims 1 to 4. Transmitting and receiving device.   6. The transmission / reception apparatus according to claim 5, wherein a two-wire four-wire conversion circuit (32) using a hybrid transformer (31) is provided instead of connecting the transmission circuit and the reception circuit in parallel, and the loop antenna is provided on the two-wire side. A transmitter / receiver characterized in that a circuit is connected to the transmitter circuit and receiver circuit on the four-wire side.   7. The transmission / reception device according to claim 5, further comprising an impedance matching transformer (11) provided near an input / output terminal of the loop antenna circuit.   8. The transmission / reception device according to claim 5, wherein a resonance circuit (26) that resonates in series at a transmission frequency is connected to the transmission circuit in series on an output side, and a resonance circuit that resonates in series at a reception frequency on the reception circuit. A transmitter / receiver characterized in that a circuit (27) is additionally connected in series to the input side.

Images