JPS6042654B2 - directional coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a directional coupler, and more particularly to a directional coupler constituting an automatic gain control circuit (hereinafter abbreviated as APC circuit) of a radio transmitter.

Figure 1 shows directional coupling to the APC circuit of a radio transmitter.
In the figure, 1 is a circuit that generates a carrier wave circle modulated by a signal at a power level, tentatively called a Younger stage, and 2 is an excitation stage, which inputs the output of Younger stage 1 and raises it to the required level. 3 is a power amplification stage, which inputs the output of the excitation stage 2 and increases it to the transmission power level.

4 is a directional coupler, and the output of the power amplification stage 3 is transmitted from the input terminal a of the directional coupler 4 to its output terminal.

6 is a low-pass filter that removes harmonics of the carrier wave, and 7 is an antenna.

The directional coupler 4 has a reflected wave power detection terminal d) a traveling wave power detection terminal e, and the traveling wave power detection terminal e is grounded by a transmission power setting potentiometer RVI, and the intermediate tap of the potentiometer RVI and the reflected wave power detection terminal e are grounded. Power detection terminal d
and diodes D for backflow prevention.

,D. The signal is input to the feedback amplifier 5 via the . The amplification degree of the excitation stage 2 is feedback-controlled by the output of the feedback amplifier 5. In the circuit shown in FIG. 1, when the antenna 7 is in a normal state, the coupling to the antenna 7 is adjusted so that the output of the reflected wave power detection terminal d is sufficiently small, so the signal input to the feedback amplifier 5 is can be considered to be only the one that passes from the traveling wave power detection terminal e to the potentiometer RV.

In such a state, if the power to the input terminal a of the directional coupler 4 increases for some reason, the gain of the excitation stage 2 is changed by the feedback loop of the terminal e1 potentiometer RVl, the diode D3, and the feedback amplifier 5. This decreases the input power to input terminal a. Conversely, when the input power to input terminal a decreases, terminal e1 potentiometer RV,...
The gain of the excitation stage 2b is increased by the feedback loop of the diode D3 and the feedback amplifier 5, thereby increasing the input power to the input terminal a. In this way the transmission power is kept approximately constant. Next, if an accident such as breakage of the antenna 7 occurs, the input impedance of the antenna 7 will change, the impedance matching seen from the transmitter to the antenna will be impaired, and the reflected wave power will increase, causing the reflected wave power to be detected d. The output of increases and passes through the feedback amplifier 5 to reduce the gain of the excitation stage 2,
This prevents damage to the power amplification stage 3 due to excessive power loss. Since the operation of the directional coupler 5 in the APC circuit of a wireless transmitter is as explained above, the performance required of the directional coupler 5 used in such applications is that it can be adjusted without adjustment over a wide range of frequencies. It does not require high precision, but it is small, inexpensive, and highly reliable.

Conventionally, there has been no directional coupler that fully satisfies these requirements.

FIG. 2 is a perspective view showing an example of a conventional directional coupler, and shows a stop line type directional coupler. In FIG. 2, the same reference numerals as in FIG. 1 indicate the same parts.
a is a transmission line, 4b and 4c are loops each coupled to the transmission line 4a, 4d is a grounding plate, Rl and R2 are terminating resistors, respectively, and Dl and D2 are for detecting and rectifying traveling wave electric power or reflected wave power, respectively. Diode, CPl, CP2
are bypass capacitors. Transmission line 4a
forms a strip line with a characteristic impedance of 4 to the ground plane 4d.

It is well known that when designed to satisfy the following conditions, signals representing forward wave power or reflected wave power are taken out from terminals E and d, respectively.

However, in equation (1), C is the coupling capacitance between the transmission line circuit 4a and the coupling loop 4b or 4c (since the loops 4b and 4c are located symmetrically with respect to the transmission line 4a, the coupling capacitance and mutual impedance are mutually ), M is the mutual inductance between the transmission line 4a and the coupling loop 4b or 4c, and R=R1=R2. The disadvantage of the directional coupler shown in Fig. 2 is that the external dimensions are large, and if C is increased so that small electric power can be detected while keeping the external dimensions constant, R is also changed according to equation (1). It was something that needed to be done.

Figure 3 is a connection diagram showing another example of a conventional directional coupler.
In the figure, the same symbols as in Figure 2 indicate the same or equivalent parts, and 4e is a current transformer in which a single wire is wound around a ring-shaped magnetic core material, and even if the transmission line 4a is short, the necessary mutual inductance M is This device can be made smaller than the device shown in Fig. 2, but the ring-shaped magnetic core material is expensive, the number of parts is large, and the capacitor Cl is used during assembly. , C2, and the current transformer 4e has the disadvantage that if the lead wires of the current transformer 4e are not made sufficiently short, variations in characteristics will occur, and if Cl and C2 are changed, Rl and R2 must be changed. The same is true for .

It is an object of the present invention to eliminate the drawbacks of the conventional devices as described above, and to provide a directional coupler that is small, inexpensive, and simple in structure.

For this purpose, in the present invention, a π-type low-pass filter provided in a radio transmitter to remove its harmonic components is used as a component of a directional coupler, and the drawings will be explained below. . FIG. 4 is a partially perspective connection diagram showing one embodiment of the present invention, and FIG.
The same reference numerals as those in the figure indicate the same or corresponding parts, 6a is a coil constituting the series impedance element of the π-type low-pass filter, and C3 and C4 are respective capacitors constituting the parallel impedance element of the π-type low-pass filter.

The π-type low-pass filter corresponds to the one shown as the low-pass filter 6 in FIG. 1, and since FIG. 1 is a drawing for general explanation, the low-pass filter 6 is limited to the π-type. I haven't, but
In ordinary designs, a π-type low-pass filter is often used as the low-pass filter 6, and the present invention makes use of this. As is well known, the low-pass filter 6 is used to attenuate harmonic components generated by amplification distortion caused by the excitation stage 2, power amplification stage 3, etc. A π-type low-pass filter indicated by c3 and c4 is used, and although C3 and C4 may be variable depending on the frequency, the coil 6a is usually fixed.

4h is a second coil Cl, C which is electromagnetically coupled to the coil 6a.
Coupling capacitors 2 are connected between the ends of the coil 6a and the coil 4h having the same polarity (that is, the ends at the beginning of winding or the ends at the end of winding).

Furthermore, if the terminating resistors Rl and R2 are respectively referred to as a first terminating resistor R1 and a second terminating resistor R2, and the outputs of the terminals E and d are respectively referred to as a first signal and a second signal, the terminating resistors Rl and R2 can be called a diode. D1 and capacitor CPl constitute a first signal detection circuit, and diode D2 and capacitor CP2 constitute a second signal detection circuit. Since the circuit shown in FIG. 4 is similar to the circuit shown in FIG. 3, the first signal representing the traveling wave power is obtained from the terminal e, and the second signal representing the reflected wave power is obtained from the terminal d. it is obvious.

Moreover, unlike the circuit in FIG. 3, the directional coupler 4 and low-pass filter 6 in FIG. 1 can be integrated without the need for a special ring-shaped magnetic core or the like. It has the advantage that the whole can be made sufficiently small.

As described above, according to the present invention, a directional coupler can be configured using a π-type low-pass filter provided in a wireless transmitter for other purposes, so the structure is simple and reliable. Thus, a directional coupler can be obtained which is inexpensive due to its high efficiency and allows the entire device to be miniaturized.

Although the above description has been made as a directional coupler used in the M°C circuit of a wireless transmitter, the directional coupler of the present invention is required to have similar performance, and there is a π-type low-pass filter that can be used. Needless to say, there are similar advantages when used in other cases.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of using a directional coupler in an APC circuit, Fig. 2 is a perspective view showing an example of a conventional directional coupler, and Fig. 3 is a diagram of a conventional directional coupler. Connection diagram showing another example. FIG. 4 is a connection diagram showing one embodiment of the present invention. In the figure, 6a is the coil of the π-type low-pass filter, C3
, C4 are each one capacitor of the π-type low-pass filter, 4h is the second coil, Cl and C2 are each the coupling capacitor, R1 is the first terminating resistor, R2 is the second terminating resistor, D1 and CPl are the first terminating resistor. A signal detection circuit is constructed, and D2 and CP2 constitute a second signal detection circuit.

Claims (1)

[Claims] 1 Consisting of a coil as a series impedance element and a capacitor as a parallel impedance element, its input terminal is connected to the power source side of the high frequency power, and its output terminal is connected to the load side of the high frequency power, and the high frequency component of the high frequency power is transmitted. a π-type low-pass filter provided for attenuation, a second coil electromagnetically coupled to the coil of the π-type low-pass filter, and between ends of the second coil and the coil of the π-type low-pass filter having the same polarity, respectively. each coupling capacitor connected, a first terminating resistor connected between the starting end of the second coil and ground, and a second terminating resistor connected between the ending end of the second coil and grounding. a resistor, a first signal detection circuit that detects the terminal voltage of the first terminating resistor to obtain a first signal, and a second signal detecting circuit that detects the terminal voltage of the second terminating resistor to obtain a second signal. A directional coupler characterized by comprising a signal detection circuit.