JPH088442B2 - Step variable high frequency attenuator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a step variable high frequency attenuator capable of high speed switching, use with a large current, and a small phase change.

(Prior Art) Conventionally, fixed resistance attenuation as shown in FIG. 4 was used for adjusting the transmission output of T-CAS (collision prevention system device), mode S (SSR secondary radar), ECM, etc. in the microwave band. A loadable variable attenuator using a PIN diode as shown in FIG. 5 has been used.

The fixed resistance attenuator shown in FIG. 4 is mainly arranged in parallel with a large number of coaxial fixed resistors having a predetermined amount of attenuation, and a predetermined attenuation is obtained by switching the coaxial fixed resistors. Fig. 4 shows an example of this typical configuration. RF provided at the input end and output end (RFin, RFout)
Attenuation resistor including changeover switches 101 and 102 and a plurality of attenuating elements arranged between the RF switches and having different attenuation amounts.
103 and an RF switch driver circuit 104 for switching the RF switch circuit by an external control signal (forward bias).

As the RF switch circuits 101 and 102, a coaxial relay, or a semiconductor element switch that uses the characteristic that the microwave impedance changes with an applied voltage is used.

The attenuation resistor 103 has, for example, a configuration in which the direct connection line 103a, the attenuation resistance element 103b of 1db, the attenuation resistance element 103c of 2db, and the attenuation resistance element 103n of ndb are connected in parallel, and when attenuation is not required. The RF switches 101 and 102 are directly connected to each other with a direct connection line 103a, and an attenuation resistance element 103b is used to obtain 1db of attenuation, and an attenuation resistance element 1 is used to obtain 2db of attenuation.
In the case of 03c, when the attenuation of ndb is obtained, the attenuation resistance elements 103n are selectively switched. These switching operations are performed by the RF switches 101 and 102.

As each of the damping resistance elements 103a to 103n, a coaxial fixed resistor or a strip resistor using a chip resistor is often used.

Fig. 5 shows a commonly used PIN diode-loaded variable attenuator. This PIN diode-loaded variable attenuator shows the characteristics of a PIN diode element whose impedance changes as the applied voltage (forward bias) changes. To use. Capacitors C1 and C2 for shutting off the voltage are arranged at the input and output ends, and each capacitor C1 and C2
Between C2, grounded PIN diodes D1 and D2 are arranged at a required interval, for example, λ / 4 interval, for impedance matching. Variable attenuator PIN diode D1, D
2 is driven by the linear driver circuit 120. The instruction for switching the attenuation amount is given by a control signal from the outside. The choke coil CH and the feedthrough capacitor PC provided on the forward bias line 121 are both for preventing a high frequency signal from being superimposed on the linear driver circuit 120.

In the fixed resistance attenuator and the PIN diode-loaded variable attenuator described above, the paths of the high frequency signals are matched so as to have a predetermined impedance.

However, the conventional fixed resistance attenuator and PIN diode loaded variable attenuator have the following problems, respectively.

First, in a fixed resistance attenuator, switching at high speed is difficult. In the case of a semiconductor switch, the time required for switching is approximately 1 ms or more, depending on the type of element.
Insertion loss occurs due to the structure of the resistance element itself and the length of the connection lead between the arrayed resistors and the RF switch circuit. Since the switching circuit length is relatively long, a phase change occurs due to the influence of the distributed capacitance. Further, since the fixed resistance element generates heat, a large heat dissipation plate is required when used with a large current, resulting in an increase in size and cost.

The PIN diode-loaded variable attenuator can be miniaturized, but due to the characteristics of the element, it cannot be used at large currents, making high-speed switching difficult (switching time of approximately 200 m
s or more). Since the element impedance changes due to the change in the applied voltage, a large phase change occurs, which is not suitable for a system that requires phase stability. The transmission line impedance at the insertion point changes due to the structure of the element, and the loss loss increases. Due to the non-linear characteristics of the element, the amount of attenuation and the phase tend to change with changes in temperature. When the passing power becomes large, it may cause saturation due to self-heating.

(Object of the Invention) The present invention has been made in view of the above, and enables high-speed switching and use of a large amount of power, prevents the occurrence of a phase change, and further significantly reduces the attenuator insertion loss. The present invention provides a step variable high frequency attenuator capable of reducing the attenuation amount of each circuit and finally obtaining the attenuation amount of high power.

(Summary of the Invention) In order to achieve the above object, a high-frequency attenuator having a plurality of power absorption / attenuation circuits arranged along a high-frequency power transmission line, wherein each of the power absorption / attenuation circuits is connected to a transmission line. Through a detection line that is arranged in parallel with the transmission line to obtain a predetermined amount of attenuation and that forms a distributed constant circuit with a predetermined degree of coupling, and a resistor that has a predetermined resistance value at each end of the detection line. And a switching means for connecting and disconnecting the detection line and the ground, each of which controls the action of each power absorption and attenuation circuit on the high frequency power transmission line by connecting and disconnecting the switching element, and the high frequency attenuator. The total attenuation is operated by combining the same power absorption / attenuation circuits or by combining the power absorption / attenuation circuits having different degrees of coupling between the transmission line and the detection line. The feature is that it is changed hierarchically.

A high-frequency attenuator having a plurality of power absorption / attenuation circuits arranged along the high-frequency power transmission line, wherein each power absorption / attenuation circuit obtains a predetermined amount of attenuation with the transmission line. Between the detection line and the ground, which are arranged in parallel with the transmission line to form a distributed constant circuit with a predetermined degree of coupling, and which are arranged at both ends of the detection line through resistors having predetermined resistance values. And a semiconductor switching element that connects and disconnects the semiconductor switching element, and a gallium arsenide type FET is used for the semiconductor switching element, the detection line end is connected to the drain of the FET, the ground is connected to the source, and the gate is connected to the forward direction. A bias is applied to control the action of each power absorption and attenuation circuit on the high frequency power transmission line by connecting and disconnecting the switching element, and the attenuation amount of the entire high frequency attenuator. Characterized in that the graduated by the same degree of coupling between the power absorbing damping circuit in combination or the transmission line and the detection line actuates a combination of different respective power absorbing attenuation circuit.

A high-frequency attenuator having a plurality of power absorption / attenuation circuits arranged along the high-frequency power transmission line, wherein each power absorption / attenuation circuit obtains a predetermined amount of attenuation with the transmission line. Between the detection line and the ground, which are arranged in parallel with the transmission line to form a distributed constant circuit with a predetermined degree of coupling, and which are arranged at both ends of the detection line through resistors having predetermined resistance values. And a semiconductor switching element that connects and disconnects the semiconductor switching element.A PIN type diode is used as the semiconductor switching element, the anode of the PIN type diode is connected to the detection line end, and the cathode is connected to the ground, respectively, and a forward bias is applied to the anode. Applied to control the action of each power absorption and attenuation circuit on the high frequency power transmission line by connecting and disconnecting the switching element,
The attenuation of the entire high frequency attenuator is changed stepwise by operating the same power absorption and attenuation circuit in combination or each power absorption and attenuation circuit in which the degree of coupling between the transmission line and the detection line is different. Is characterized by.

(Example) Hereinafter, the step variable high frequency attenuator of the present invention will be described in detail.

FIG. 1 is a structural explanatory view of an embodiment of the present invention in which a GaAs FET is used as a switching element, and this step variable high frequency attenuator has a radio wave absorption having a coupling degree of −6.8 dbB with respect to the transmission line 1. The variable attenuating circuit 2, a radio wave absorption variable attenuating circuit 3 having a coupling degree of -4.3db, and radio wave absorbing variable attenuating circuits 4 and 5 having a coupling degree of -3db are roughly configured. The coupling value (digibell) of each radio wave absorption variable attenuation circuit 2, 3, 4, 5 is the coupling degree of the detection lines 21, 31, 41, 51 of the directional coupler coupled along the central conductor of the transmission line 1. Is variable. The length of each detection line was set to λ / 4 so as to resonate with the radio wave propagating through the central conductor of the transmission line 1.

The radio wave absorption variable attenuation circuit 2 includes a detection line 21 and non-reflective termination resistors 2Ra and 2Rb connected to both ends of the detection line 21, respectively.
And GaAs FET switching elements 2Ta and 2Tb in which a drain is connected to the other ends of the non-reflective termination resistors 2Ra and 2Rb,
The sources of the switching elements 2Ta and 2Tb are grounded, and the gates are connected to the application terminal No. 1 of the control circuit 6 which sends out the forward bias.

The other radio wave absorption variable attenuating circuits 3, 4, 5 also have the same configuration as the radio wave absorption variable attenuating circuit 2, but the detection lines 31, 41 of the radio wave absorbing variable attenuators 3, 4, 5 for the transmission line 1 are the same. , 51 have different degrees of coupling.

The degree of coupling of the detection line 31 of the radio wave absorption variable attenuation circuit 3 is −
The degree of coupling between the detection lines of the radio wave absorption variable attenuation circuits 4 and 5 and the transmission line 1 is −3 dB.

These radio wave absorption variable attenuation circuits 2, 3, 4, and 5 are
As FET switching element 2Ta, 2Tb, 3Ta, 3Tb, 4Ta, 4T
A threshold value voltage (forward bias) is applied to each source of b, 5Ta, and 6Tb to make the GaAs FET switching element conductively grounded, thereby absorbing and attenuating radio waves of a predetermined value. In each radio wave absorption variable attenuator circuit, in order to realize impedance matching between the detection line and the FET switching element, a non-reflective terminating resistor was connected to each end of the detection line to connect the FET switching element to the conductive ground. At this time, the non-reflective terminating resistor supplies all the electric wave absorbed from the transmission line 1 to the detection line to the FET switching element without reflecting the electric wave.
It enables the absorption and attenuation of radio waves in accordance with the degree of coupling between each of the detection lines.

The forward bias to each source of each GaAs FET switching element is performed by the control circuit 6,
The combination between the radio wave absorption variable attenuation circuits that operate to obtain a desired attenuation amount between RFin and RFout is determined by a control signal that is input to the control circuit 6 and indicates a combination from the outside.

FIG. 2 shows the amount of attenuation of transmitter output power obtained by the combination of the radio wave absorption variable attenuation circuits 2, 3, 4, and 5.

In the figure, 20 is the transmitter output power attenuation amount, 21 is the segment number of the variable absorption circuit for electromagnetic absorption, and 22 is the GaAs FET.
Switching element 2Ta, 2Tb, 3Ta, 3Tb, 4Ta, 4Tb, 5Ta
The applied voltage (forward bias) of each source is shown. -V
Indicates a value at which these elements become non-conductive, and + V indicates a value at which they become conductive at the threshold level.
Therefore, all GaAs FEs of all radio wave absorption variable attenuation circuits
When a forward bias of the control circuit threshold level is applied to the source of the T switching element, the maximum attenuation is 9db, and when a voltage (-V) that makes each GaAs FET switching element non-conductive is applied. , Its attenuation is 0db.

In the above embodiment, the maximum attenuation value is 9d.
Although b is exemplified, the maximum attenuation amount is not limited to this value, and it is possible to freely set a desired attenuation amount value. That is, the radio wave absorption variable attenuation circuits 2, 3, 4,
The degree of coupling of the detection lines 21, 31, 41, 51 of No. 5 with the transmission line 1 may be set according to the desired maximum attenuation.

The gist of the present invention is to combine attenuating elements that operate in order to obtain a desired amount of attenuation within a predetermined range by arranging the attenuating elements in parallel without connecting the attenuating element to the center conductor of the transmission line. Is to make variable. Therefore, a switching element other than GaAs FET can be used. For example, it can be replaced with a PIN diode or the like. However, the PIN diode has a propagation delay time in response speed as compared with the GaAs FET.

FIG. 3 shows a circuit using a PIN diode as a second embodiment. Since the operation of each component is the same as that of the first embodiment, the description thereof will be omitted.

As described above, in the present invention, four transmission lines are arranged in the center conductor of the transmission line at required detection line intervals having different degrees of coupling, and switching elements (GaAs FETs) are connected to both ends of each detection line to reduce the attenuation amount of each. Different attenuation circuits are formed. This GaAs FET is driven (ON-OFF) by applying a forward bias signal sent from the control circuit to the gate, but the total attenuation of all attenuation circuits is set by the combination of each attenuation circuit. It

As described above, in the present invention, a plurality of detection lines having different degrees of coupling with the transmission line are arranged on the transmission line, and switching elements are connected to both ends of each detection line. A resistor having a value close to the resistance of the transmission line is connected in series between the detection line end and the switching element. Therefore, by appropriately combining the degree of coupling between the transmission line and the detection line and the number of radio wave absorption variable attenuation circuits, it is possible to set an arbitrary amount of attenuation and the number of attenuation steps. Furthermore, since the load fluctuations at both ends of each detection line are the same, the desired attenuation level can be adjusted without partially affecting the transmission line and without causing a phase change.

(Effects of the Invention) As described above, the step variable high frequency attenuator of the present invention has the following effects.

(1) Since a GaAs FET is used as a switching element, microwave band power absorption attenuation can be performed at high speed (5ns). Moreover, the output can be freely changed by a slight phase change. Therefore, the output of the transmitter is variable, and the phase of the variable output is important in T-CA.
It can also be applied to systems such as S, mode S, and ECM.

(2) Do not connect the switching element directly to the transmission line,
Electric power is absorbed by a detection line arranged in parallel with the central conductor in the coaxial structure. The variable attenuator circuit has a detection line length of λ / 4, and the switching element of
Connected to GaAs FET. The resistor acts as a non-reflective terminating resistor when the switching element is activated, and when it is not activated, the GaAs FET has a high impedance, so that it has very little electrical influence on the transmission line. Therefore, no loss occurs due to the insertion of the attenuator, the change in the distributed capacitance on the transmission line is small, and the phase change is unlikely to occur. These advantages make it possible to use in systems such as T-CAS, mode S, and ECM, which emphasize the phase change when the output is changed.

(3) A desired amount of attenuation can be obtained by combining and operating a plurality of attenuation circuits having different combinations of detection lines and transmission lines and having different amounts of attenuation. Therefore, the desired amount of damping can be obtained by the sum of the damping circuits that have been activated. In other words,
Although the power absorption attenuation amounts of the individual attenuation circuits are small, they can be combined to obtain a large current power absorption attenuation amount.

[Brief description of drawings]

FIG. 1 is an explanatory view of the configuration of a variable attenuator using a GaAs FET according to an embodiment of the present invention, and FIG. 2 is a diagram showing the amount of attenuation of transmitter output power obtained by combining a radio wave absorption variable attenuator circuit, FIG. 3 is an explanatory view of the configuration of an embodiment of the present invention using a PIN diode, FIG. 4 is an explanatory view showing a conventional variable attenuator, and FIG. 5 is a configuration of a conventional variable attenuator using a PIN diode. Explanatory drawing. 1 ... Transmission line, 2, 3, 4, 5 ... Radio wave absorption variable attenuation circuit, 6 ... Control circuit, 21, 31, 41, 51 ... Detection line, 2Ra, 2Rb ... Non-reflection termination resistance, 2Ta , 2Tb, 3T
a, 3Tb, 4Ta, 4Tb, 5Ta, 6Tb ... GaAs FET switching element

Claims (3)

[Claims] 1. A high-frequency attenuator having a plurality of power absorption / attenuation circuits arranged along a high-frequency power transmission line, wherein each power absorption / attenuation circuit has a predetermined attenuation with a transmission line. A detection line which is arranged in parallel with the transmission line to form a distributed constant circuit having a predetermined degree of coupling, and detection lines which are arranged at both ends of the detection line through resistors having predetermined resistance values, respectively. And a switching means for connecting / disconnecting to / from the ground. By connecting / disconnecting the switching element, the action of each power absorption / attenuation circuit on the high-frequency power transmission line is controlled, and the attenuation amount of the entire high-frequency attenuator is the same. It is characterized in that the power absorption / attenuation circuit is changed stepwise by operating the power absorption / attenuation circuit in combination or each power absorption / attenuation circuit in which the degree of coupling between the transmission line and the detection line is different. Step variable frequency attenuator to. 2. A high-frequency attenuator having a plurality of power absorption / attenuation circuits arranged along a high-frequency power transmission line, wherein each of the power absorption / attenuation circuits has a predetermined amount of attenuation with the transmission line. In order to obtain a detection line which is arranged in parallel with the transmission line and constitutes a distributed constant circuit with a predetermined degree of coupling, and the detection line and the ground which are arranged at both ends of the detection line through resistors having respective predetermined resistance values. And a semiconductor switching element that connects and disconnects between the semiconductor switching element and a gallium arsenide type FET for the semiconductor switching element, the drain of the FET is connected to the detection line end, and the source is connected to the ground, respectively. A forward bias is applied to each of the high-frequency attenuators to control the action of each power absorption / attenuation circuit on the high-frequency power transmission line by connecting and disconnecting the switching element. Stepwise changing the amount of attenuation by operating the same power absorption / attenuation circuit in combination or each power absorption / attenuation circuit in which the degree of coupling between the transmission line and the detection line is different. Variable high frequency attenuator. 3. A high-frequency attenuator having a plurality of power absorption / attenuation circuits arranged along a high-frequency power transmission line, wherein each power absorption / attenuation circuit has a predetermined amount of attenuation with respect to the transmission line. In order to obtain a detection line which is arranged in parallel with the transmission line and constitutes a distributed constant circuit with a predetermined degree of coupling, and the detection line and the ground which are arranged at both ends of the detection line through resistors having respective predetermined resistance values. And a semiconductor switching element that connects and disconnects between the semiconductor switching element and a PIN diode, the anode of the PIN diode is a detection line end,
The cathode is connected to the ground, a forward bias is applied to the anode, and the switching element is connected / disconnected to control the action of each power absorption / attenuation circuit on the high-frequency power transmission line. Stepwise variable high-frequency attenuation characterized by operating the same power absorption and attenuation circuit in combination or each power absorption and attenuation circuit in which the degree of coupling between the transmission line and the detection line is different. vessel.