JPS6093801A - Step variable attenuator - Google Patents

Abstract

PURPOSE:To perform remote control with a small-sized constitution, a low driving power, and a high reliability by moving a by-pass line selecting conductor or an attenuating element selecting conductor with an actuator which performs an alternating operation. CONSTITUTION:Fixed contacts 51a and 71b connected to an input/output connector are provided with attenuator units 5, 6, and 7. The attenuator unit 5 is provided with a by-pass line selecting conductor 52, an attenuating element 57, and attenuating element selecting conductors 53a and 53b and is connected selectively between contacts 51a and 51b. Conductors 52, 53a, and 53b are driven by driving rods 54a, 54b, and 54c. Driving rods 54a, 54b, and 54c are driven alternately by the actuator (which is not shown in a figure), and the driving rod 54b is not driven when driving rods 54a and 54c are driven. Attenuator units 6 and 7 have the same constitution as the attenuator unit 5, and the actuator is controlled remotely to obtain an optional attenuation quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Pertains] The present invention relates to a variable steer knob attenuator that is suitable mainly for high frequency ranges above I Gllz and generally called microwaves. In particular, the present invention relates to a step variable attenuator that changes the amount of attenuation in steps by remote control.

[Description of prior art]

Among conventional step variable attenuators, step variable attenuators using a mechanical variable attenuation method have the following characteristics: ■ Lower insertion loss, ■ Flat frequency characteristics of attenuation, and ■ Larger attenuation than those using semiconductors. It has the excellent advantage of being able to obtain a large amount of attenuation, and is widely used despite its drawbacks such as ■ slow switching speed, and ■ problems with reliability because it has mechanical contacts. There is.

Step variable attenuators using a mechanical variable attenuation mechanism are further divided into two types.

One of them is called the parallel type, in which the attenuation amount is changed by arranging the same number of attenuation elements as the attenuation amount variable steps and switching and selecting them.

The other type is called a series type, in which one attenuator unit is connected in series so that a state in which no attenuation occurs and a state in which attenuation occurs can be alternately switched.

A series type variable step attenuator is characterized by being able to obtain a large number of variable steps with a small number of attenuation elements.For example, if four attenuators are connected in series, it can be One matching step is obtained for the attenuation amount. Therefore, the series type has the advantage of being able to be made smaller because the number of attenuation elements can be reduced compared to the parallel type.

However, since the attenuator units are connected in series, there are many discontinuous points in the line, and the higher the frequency, the lower the V S
W R (voltage standing wave)
There were disadvantages in that the characteristics (voltage standing wave ratio) deteriorated, and that it became difficult to obtain isolation between unconnected terminals due to miniaturization.

In order to solve this problem, the step variable attenuator (Japanese Patent Application No. 58-90938, filed on May 24, 1988) by the same applicant as the present application has a small size and a large attenuation variable range. Moreover, the present invention provides a step variable attenuator with good VSWR characteristics. It also provides a highly reliable step variable attenuator. However, the step variable attenuator of this prior application had the disadvantage that it could not be remotely controlled because the attenuation was manually varied.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks and provides a step variable attenuator that is small, has low driving power, is highly reliable, and has a large attenuation variable range, which allows the attenuation amount to be changed by remote control from a remote location. With the goal.

[Features of the invention]

The present invention includes one movable center conductor for bypass line selection, two movable center conductors for attenuation element selection, and one attenuation element per attenuator unit, and the two types of movable center conductors are It is configured so that the amount of attenuation can be changed by moving the moving drive rod using an actuator that operates alternately like a seesaw, and is characterized by being remote-controlled, compact, low driving power, high reliability, and a wide range of variable attenuation. shall be.

That is, the present invention includes a damping element, two fixed contacts,
A movable central conductor for selecting an attenuating element that connects the attenuating element between these two fixed contacts, and a movable central conductor for selecting a bypass line that is configured to be able to short-circuit between the two fixed contacts. The attenuator Uniso 1- is provided with a signal path, and the movable center conductor for selecting the attenuation element 1 and the movable center conductor for selecting the bypass line are interlocked and set so that their moving directions are opposite to each other. In the step variable attenuator in which one or more step variable attenuators are connected in series, each attenuator unit is provided with a drive rod that moves the two movable center conductors and an actuator that moves the drive rod. Features.

In addition, by providing the actuator with a contact that interrupts the excitation current during the movement stroke of the drive rod, it is possible to reduce back-off power, simplify the attenuation amount selection circuit, and improve reliability.

[Explanation based on examples]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an external view of a step variable attenuator for a microwave band according to an embodiment of the present invention. Fig. 1 (A> is a plan view thereof, Fig. 1 (B) is a front view thereof, and Fig. 1 (C) is a side view thereof. In Fig. 1, 1a and 1b are input/output connectors,
2a and 2b are cases whose surfaces are made of a conductor, and 3 is a control terminal for changing the amount of attenuation by remote control.

FIG. 2 is an enlarged sectional view taken along line II--II in FIG. 1(B), showing the microwave circuit portion of the step variable attenuator. In FIG. 2, a case 2a whose surface is made of a conductive material also serves as a substrate on which a step variable attenuator is constructed.

Reference numeral 4 denotes a groove provided in the case, which forms the outer conductor of the strip line. 5 to 7 each constitute an attenuator unit, for example, attenuator unit 5 is 10d
B, the attenuator unit 6 is set to 20 dB, and the attenuator unit 7 is set to 40 dB.

The attenuator unit 5 includes fixed contacts 51a and 51b, a movable central conductor 52 for bypass line selection, movable central conductors 53a and 53b for attenuation element selection, a movable central conductor 53a,
52.53b drive rods 54a, 54b, 54c
, a steady rest 55, a damping element 56, and the like. Further, the damping element 56 includes a damping body 57 formed on a substrate of porcelain, glass, plastic, etc., and center conductors 58a and 58b connected to both ends of the damping body 57. movable central conductor 53a,
The drive rods 54a, 54b, 54c of the movable center conductors 53a, 52.53b are fitted onto the respective movable center conductors 53a, 52.53b, as will be described later.
．． 53b.

As will be described later, when the movable center conductor 52 is pushed by a lever, it short-circuits the fixed contact 51a and the fixed contact 51b to form a bypass line, and when it is not pushed, it short-circuits the fixed contact Ijλ51a and the fixed contact 51b. Disconnected. Furthermore, the movable center conductors 53a and 53b also connect the damping element 56 and the fixed contact 51a or the fixed contact 511 by the same operation.
) to connect or disconnect.

In addition, the steady rest 55 includes each movable center conductor 52, 53a, 53
b is correctly fixed contacts 51a, 51b or center conductor 58
I am guiding it so that it makes contact with a158b. Further, the movable center conductors 53a and 53b are moved simultaneously in the same direction by an actuator and a lever that will be described later, but the operating position of the movable center conductors 53a and 53b is
It is configured to be in a position opposite to the operating position of No. 2.

The attenuator unit 6.7 is constructed from the same parts as the attenuator unit 5. However, in order to facilitate identification of individual parts, the reference numerals are different from those of the attenuator unit 5.

Note that 8.9 is a center conductor that connects each attenuator unit 5.6.7 and is supported in a fixed position by a dielectric IO, and both ends of the center conductor 8 are fixed contacts 51b and 61a1 are both ends of the center conductor 9. are fixed contacts 61b and 71a.

Further, the fixed contact 51a is connected to the center conductor of the input/output connector 1a, and the fixed contact 71b is connected to the center conductor of the input/output connector b.
connected to the center conductor of

The embodiment shown in FIG. 2 shows a step variable attenuator in which three variable attenuator units are connected in series, and the planar configuration of the microwave circuit section has been explained.

FIG. 3 is an enlarged sectional view taken along line 11-1 [[ of FIG. 1(A), and shows the microwave circuit portion of the step variable attenuator. FIG. 3 shows a cross section passing through the central axis of the input/output connector a, and 13 is a cover that also serves as an external field body for the strip line in order to shield the microwave circuit section from the outside world;
14 is a coil spring for pressing the movable central conductor 53a against the inner wall of the cover 13.

As shown in FIG. 3, when the drive rod 54a is not pushed, the movable center conductor 53a is in close contact with the inner wall of the cover 13 without contacting the fixed contact 51a.

15a is a lever for moving the drive rod 54a, which rotates around a lever shaft 18a, and a leaf spring 19 for pressing the drive rod 54a with a constant pressure and the pressed lever 15a It is provided with a leaf spring 20 that returns to the original position when the pressure is released.

FIG. 4 is an enlarged sectional view taken along line rV-rV in FIG. 1(A), showing the microwave circuit portion of the step variable attenuator. Figure 4 shows two incoming and outgoing crab knits la.

1b represents a cross section including the center conductor. As in the case of FIG.
b, 64b, and 74b are not pressed, they are in close contact with the inner wall of the cover 13 due to the force of the coil spring 14. Next, when the drive rods 54b, 64b, 74b are pressed by an armature described later, each of the drive rods 54b, 64b.

The movable center conductor 52, 62, 72 supported by 74b has fixed contacts 51a, 51b;
, 61b; contacts 71a and 71b, and a bypass line is connected thereto.

FIG. 5(A) is an internal view when the case 2b is removed in FIG. 1(B). In FIG. 5(A), 2+
a, 21b, 21c are attenuators knee'-soto 5.6.
It is an actuator that drives 7, and 23a, 23b,
23c is the armature and actuator 218121b
, 21c. It is difficult to explain the configuration using only Fig. 5 (A), so Fig. 5 (B), Fig. 6,
FIG. 7(A) will be explained first.

First, FIG. 5(B) is a sectional view taken along the line Xia-■ in FIG. 5(A), and is a view of the microwave circuit portion.

Here, the attenuator unit 5 will be explained. Lever 1
5a, 15b, 15c are variable attenuator units 5
The levers 15a, 15c rotate around the lever shaft 18a, and the lever 15b rotates around the lever shaft 18b.

Next, the configuration related to the drive rods 54, 64, 74 and actuators 21a, 21b, and 21c of the microwave circuit section will be explained. FIG. 6 is a right side view of FIG. 5(A), and a sectional view of the microwave circuit portion is omitted. Levers 15a, 15b, 15c are provided so as to cover the drive rods 54a, 54b, 54c, and the armature 23a of the actuator 21a is shown pushing the lever 15b. When the armature 23a switches between the two polar states around its central axis, the protrusion at the tip of the armature 23a pushes the levers 15a, 15c, and when the levers 15a, 15c are pushed, they are attached to the levers 15a, +5c. The drive rods 54a, 54c are pushed through the plate springs 19, so that the movable center conductors 53a, 53b carried by the drive rods 54a, 54c move between the fixed contact 51a and the center conductor 58a, and between the fixed contact 51b and the center conductor 58b. connect between

Since the pressure to press the drive rods 54a, 54c is determined by the displacement of the leaf spring 19, the contact pressure between the movable center conductors 53a, 53b and the center conductors 58a, 58b is a constant value. The leaf spring 20 is a leaf spring for returning the lever. 42 is a coil of the actuator 21a; 40
is its magnetic pole. Further, 41 is a magnet of the actuator 21a.

As shown in FIG. 5(B), each attenuator unit consists of two levers on one side and one lever on the opposite side. Two pieces on each side must be pressed at the same time. Figure 7 (A) is Figure 5 (A) V-
In the cross-sectional view taken along the V line, actuators 21a, 21b,
It is a view looking at the 21c side, and shows the actuators 21a,
21b, 21c armature 23a123b, 2
3c is visible. 24a, 24b, and 24c are armature members that push the levers 15, 16, and 17, and are integrally attached to the armatures 23a, 23b, and 23c. 25.26.27 are the armature protrusions that contact the lever 15.16.17. Reference numeral 28 denotes an armature shaft around which the armatures 23a, 23b, and 23c rotate. Armatures 23a, 23b,
23c is attracted to the magnetic pole 40 in a steady state. The reason for this is that the magnetic flux generated by the magnet 41 forms a magnetic path passing through the armature armature, and when the armature 23 is attracted to the magnetic pole 40, the magnetic resistance takes a low extreme value. In order to reverse the operation of the armature 23, the coil 42 is energized to break the balance of the magnetic circuit and the armature is attracted from one magnetic pole to the other magnetic pole.

Now that the configuration of the step variable attenuator of the present invention has been explained above, the basic attenuation variable operation will be described next. In this example, a three-stage series step variable attenuator consisting of three attenuator units 5.6.7 is shown.
In this case, eight combinations are obtained. For example, if the attenuation step is 10 dB, the attenuation element will be 10 dB, 20 dB,
It consists of three combinations of dB and 40 dB, and a variable range of attenuation from no attenuation to a maximum of 70 dB is obtained.

First, to achieve a non-attenuated state, connect a pair of input/output connectors 1
a, two fixed contacts 51 shown in FIG. 2 connected to 111;
The three movable center conductors 52.a and 71b are on the line connecting them.
Fixed contacts 51a, 51b corresponding to 62.72; 61
a, 6N+; 71a, 71b,
A total of 6 other movable center conductors 53a, 53b, 6
3a, 63b, 73a, and 73b may be left unconnected.

Next, to set the attenuation amount to 10 dB, attenuator unit 5
You only need to select. To do this, 4. Three movable center conductors 52 included in the attenuator unit 5.
53a53b, the center conductor 58a15 of the damping element 56
By pushing the drive rods 54a, 54c on the two movable center conductors 53a, 53b that are in contact with the fixed contacts 51a, 51
b. As a result, for example, input/output connector 1a
The microwave signal passes through the fixed contact 51a, passes through the movable center conductor 53a, enters the damping element 56, and after receiving a certain amount of attenuation, passes through the movable center conductor 53b, and then passes through the movable center conductor 53a of the attenuator unit 6.7. It is output from the input/output connector 1b via 62 and 72.

In this manner, the step variable attenuator of the present invention can obtain a combination of fixed attenuation amounts by connecting in series attenuator units each consisting of three movable center conductors and one attenuation element. When there is one attenuator unit, 2 steps, 2
When there are 1, the amount of attenuation can be changed in 4 steps, when there are 3, it is 8 steps, and when there are 4, the amount of attenuation can be changed in 16 steps.

As mentioned above, the step variable attenuator of the present invention is an attenuator unit consisting of three movable center conductors and one damping element connected in series, and one of the three movable center conductors is connected to the damping element. The two movable center conductors in contact and the remaining movable center conductor for forming an undamped bypass line must operate in opposition to each other, that is, in a complementary manner. Furthermore, a plurality of these attenuators Uniso I• are connected in series, and two-state t! In order to make multiple attenuation amounts greater than or equal to i variable, a mechanism for this purpose is required. 5, 6 and 7 show the method and structure. The amount of attenuation is determined by the actuators 21a and 21b.
, 21c can be changed to obtain a predetermined value each time one of two states is selected. The armatures 23a, 23b, 23c of the actuators 218321b, 21c are a pair of levers 53a, 53c on the damping element selection side;
3a, 63c i 73a, 73c is pressed, the movable center conductor 53a, 53c; 63
a, 63c; 73a, 73c are attenuation elements 57
．． 67. Form a circuit passing through 77. Armature 23
When a, 23b, and 23c are in the opposite state, the movable center conductor 52.62.7 on the bypass line forming side
2 are fixed contacts 51a, 51b; 61a, 6
]b H71a.

5 71b and produces almost no attenuation. As mentioned above, in a steady state, the armature blade is attracted to either one of the pair of magnetic poles 40 and is stable. This is because, in this state, the magnetic circuit of the magnet 17 that passes through the armature blade has minimal magnetic resistance. As just mentioned, by providing one actuator for each attenuator unit, each actuator can select one of the two stable states, so by connecting the attenuator units in series, step variable Various attenuation amounts can be obtained by combining them as an attenuator.

The basic configuration, variable attenuation mechanism, and operation of the step variable attenuator for the microwave band according to the present invention have been described above.

The step variable attenuator of the present invention is characterized in that it is small, provides a large attenuation variable range, and can be remotely controlled. A major constraint on miniaturization is the amount of attenuation caused by the presence of signals that leak directly between the terminals rather than passing through the attenuation element when selecting an attenuation element in the attenuator unit. This is a substantial decline in If this leakage signal is large, even if a damping element having a large amount of attenuation is used, the expected amount of attenuation cannot actually be obtained.

However, the step variable attenuator of the present invention can obtain large isolation between unconnected terminals.

The reason for this is that the movable center conductor for forming the bypass line is pressed against the inner wall of the case when selecting the attenuation element. As shown in FIG. 4, when selecting a damping element, the movable center conductor 52, 62, 7 for bypass element selection
2 is pressed against the inner wall of the case by a coil spring 14. In this state, the line in this portion can be considered to be a ridge waveguide in a cutoff state. Further, the cross-sectional dimensions are selected so that the cut-off frequency is sufficiently higher than the frequency used. Electromagnetic waves propagating in a cutoff waveguide are attenuated exponentially.

Therefore, also for the step variable attenuator of the present invention,
Signal leakage between unconnected terminals is small, and the amount of attenuation is determined by the selected attenuation element itself, resulting in a large amount of attenuation. Further, since the above-described structure is adopted, it is not necessary to increase the size in order to increase the amount of attenuation, and a small step variable attenuator can be obtained.

Further, as explained in the embodiments, the step variable attenuator of the present invention has a simple structure and has few sliding parts. This is extremely useful in achieving high reliability. The mechanism that transmits the movement of the armature of the actuator to the drive rod has few sliding parts, and the force pushing the drive rod is stable, so that the amount of attenuation can be switched stably.

Furthermore, the step variable attenuator of the present invention also has the advantage that the driving power required for switching the attenuation amount is small. This is basically due to the fact that the actuator only requires a small amount of momentum, and as mentioned earlier, the sliding movement of the movable part is small.

As explained above, the step variable attenuator of the present invention is
It can be remotely controlled and has a small size and a large variable range of attenuation. It also has high reliability and low driving power, making it suitable for use in communication equipment that requires high reliability.

Here, an additional mechanism for further reducing power consumption will be described. The actuator of the step variable attenuator described in detail of the present invention is a polarized actuator using magnets 71, and the armature is in a stable state when one side of the armature is attracted to two magnetic poles. Therefore, there are two stable states. In steady state,
The armature attempts to maintain this stable state, but it does not consume any energy, so there is no need to energize the coil. Therefore, it is conceivable to cut off the excitation current of the coil after changing the amount of attenuation of the step variable attenuator. One method for this purpose is to excite the coil with a pulsed current and supply power only during switching operations. Although this method does not require any additional mechanism on the step variable attenuator side, it does have some drawbacks. One drawback occurs when noise from other sources enters the control line of the step variable attenuator. It may happen that the actuator of the step variable attenuator is incompletely excited by the short pulse, such as when a short pulse is introduced as noise. In that case, the armature would not be supplied with sufficient energy to transition from one stable state to the other. In that case, the attenuation amount selection mechanism of the step variable attenuator may not work completely, and the step variable attenuator circuit may remain open. For the above-mentioned reasons, the drive circuit of a step variable attenuator tends to be complicated, which makes it difficult for users to use and also unfavorable in terms of reliability.

Therefore, it is conceivable to incorporate the coil excitation current breaker inside the step variable attenuator. Figure 7 (A), (B
) and (C) illustrate one embodiment. Figure 7 (B)
is a cross-sectional view taken along line VI-VI in FIG. 5(A). Figure 7 (
In B), 29a, 29b, 29c are excitation current breakers attached to each of the actuators 21a-21b, 21c. This is the actuator 21a,
21b, 21c armatures 23a, 23b,
It is a kind of switch mechanism 1 0 operated by 23c. FIG. 7(C) is a cross-sectional view taken along line 7--7 in FIG. 7(B), and is a diagram illustrating a method of interlocking the armature 23a and this switch mechanism. In FIG. 7(C), a cross-sectional view of the microwave circuit portion is omitted. Figure 7 (A
), an armature overhang 33 is provided at the tip of the armature armature. In FIG. 7 CO,), an interlocking pin 31 for interlocking the excitation current breaker is provided at a position corresponding to the armature overhang 33. When the interlocking pin 31 is pushed by the armature 23a, the contacts 32 are opened.

Next, the operation of the contact 32 will be described. In FIG. 7(C), the armature 23a is attracted to the lower magnetic pole 40. At this time, since the lever 15b is pressed, the attenuator uni-nod 5 of the step variable attenuator is selected to be on the bypass line side where almost no attenuation occurs. In order to switch from this state to the side where the damping element 56 is selected, the armature 23a is reversed and the levers 15a and 15c are pressed.
All you have to do is press .

The coil excitation current that causes the reversal operation flows through the upper contact 32 in FIG. 7(C)2. Armature 23a
begins to move, and when the armature protrusion 33 touches the interlocking pin 31 and pushes the interlocking pin 31, when it has passed the center and about 70% of the total stroke, the armature protrusion 33 touches the interlocking pin 31 and pushes the contact 32 to open, thereby cutting off the coil excitation current. The excitation current needs to be cut shortly before the end of the entire stroke of the armature 23a. The timing may vary depending on the excitation power, the magnetic flux density of the magnet, the moment of inertia of the moving part, etc., but a suitable value is 65 to 90% of the total stroke. By incorporating this excitation current breaker, selective control of the amount of attenuation of the step variable attenuator becomes very simple. That is, it is sufficient to select an excitation circuit corresponding to the desired state (attenuation state or no attenuation state!f3) for each damping element. Since the excitation current is cut off by itself when switching is completed, the attenuation amount selection circuit becomes very simple and highly reliable.

The step variable attenuator of the present invention described above using the embodiments may be implemented in various ways other than the embodiments. The levers that push the drive rods carrying the movable center conductor were provided independently for each drive rod, but since the pair of levers that select the damping elements needed to be moved at the same time, they were mechanically connected. May be combined. Specifically, 15a and 15c, 16a and 16c,
17a and 17c may be connected to each other. Also, other types of actuators are possible as long as they have two states.

〔Effect of the invention〕

As explained above, the present invention connects attenuator units in series, and includes a drive rod that moves a movable center conductor to each attenuator unit, and a drive rod that moves the drive rod and connects a damping element to a bypass line. By providing an actuator with two states to select one of, the amount of attenuation can be changed by remote control from a distance, increasing the variable range of attenuation, making it compact, low driving power, and highly reliable. It has excellent effects.

Furthermore, by incorporating an excitation current breaker into the actuator, the attenuation amount selection circuit can be simplified, power consumption can be further reduced, malfunctions due to noise can be prevented, and reliability can be improved.

[Brief explanation of drawings]

FIG. 1 is an external view of a step variable attenuator for a microwave band according to an embodiment of the present invention. FIG. 2 is an enlarged sectional view taken along line II-n in FIG. 1(B). FIG. 3 is an enlarged cross-sectional view taken along line III--III in FIG. 1(A). FIG. 4 is an enlarged sectional view taken along line IV-IV in FIG. 1 (A). FIG. 5(A) is an internal view when the case (2b) of FIG. 1(B) is removed. FIG. 5(B) is a sectional view taken along the if line of FIG. 5(A). FIG. 6 is a right side view of FIG. 5(A). FIG. 7(A) is a sectional view taken along line V-V in FIG. 5(A). FIG. 7(B) is a sectional view taken along line VI-VI in FIG. 5(A). FIG. 7(C) is a sectional view taken along the line ■-■ in FIG. 7(B). DESCRIPTION OF SYMBOLS 1... Input/output connector, 2... Case, 3... Control terminal, 4... Groove part, 5-7... Attenuator unit,
8.9.58.68.78...center conductor, 10...
Dielectric, 13... Cover, 14... Coil spring, 1
5 to 17... Lever, 18... Lever shaft, 5 4 ] 9.20... Leaf spring, 2]... Actuator,
23... Armature, 24... Armature member, 25-27... Armature protrusion, freezing... Armature shaft, 29... Excitation current breaker, 31... Interlocking bin, 32... Contact, 33... Armature overhang, 40... Magnetic pole, 41... Magnet, 42...
...Coil, 51.61.71...Fixed contact, 52.
62.72.53.63.73...Movable center conductor, 5
4.64.74... Drive rod, 55.65.75...
Steady rest, 56.66.76... Damping element, 57.67
．． 77... Attenuation body. Patent Applicant NEC Corporation Agent Patent Attorney Nao Ide Takashi'-・6 JP-A Sho GO-93801 (9) 'n JP-A Sho GO-93801 (11)

Claims (1)

[Scope of Claims] (11 damping elements, two fixed contacts, a movable central conductor for damping element selection that connects the damping element between the two fixed contacts, and a movable center conductor for selecting the damping element between the two fixed contacts) a movable center conductor for bypass line selection configured to short-circuit between In a step variable attenuator in which one or more attenuator units set to be in opposite directions are connected in series in a signal path, driving for moving the two movable center conductors for each attenuator unit. A step variable attenuator comprising a rod and an actuator that moves the drive rod. A step variable attenuator according to range (1).