DE1165109B - Changeable high frequency attenuator - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school KL: HOIp;

H 03 h

German class: 21 a4 - 74

Number: 1 165 109

File number: S 76560 IX d / 21 a4

Filing date: November 4, 1961

Opening day: March 12, 1964

The invention relates to a variable high frequency attenuator in the form of a strip transmission line with an inner conductor and an outer conductor, which is a variable resistance element contains. These are in particular attenuators of the T or π type, in which the series and parallel resistances are set synchronously with each other. The attenuator in A strip transmission line is incorporated has a substantially constant impedance across the Adjustment range, and its mode of operation is essentially independent of the frequency.

Generally, an attenuator is used to measure the conduction level of an electromagnetic To decrease the signal. It does this by inserting an impedance in the signal path between the Source and the load to which the signal is being delivered. Changeable attenuators, which the Making it easier to change the attenuation introduced into the signal path is, for example, part of the development work and particularly when testing and adjusting communications equipment useful. In many applications it is desirable that the input impedance and the output impedance of a variable attenuator of the Attenuation setting are independent. This can be done at low frequencies by using Series and parallel impedances can be achieved, which are set synchronously in a known manner.

A known, variable high frequency attenuator is a waveguide section, the below its cut-off frequency is operated. The attenuation is changed by increasing the length of the section is varied. A disadvantage of this type of attenuator is that the attenuation also increases with the frequency changes, especially when the wavelength of the signal is the cutoff wavelength of the Waveguide approximates. In addition, waveguide devices are generally bulky, except for Microwave frequencies.

Another known high frequency attenuator includes a waveguide section which is a resistive material to absorb energy encloses. In this device, the attenuation is adjusted in that the position or amount of the Resistance material is changed in the waveguide. Change in attenuation with frequency and proportionally considerable size of the waveguide devices are also in this attenuator Disadvantages.

Known variable resistance damping networks usually operate at low frequencies Changeable high frequency attenuator

Applicant:

Sanders Associates, Inc., Nashua, N. H.

(V. St. A.)

Representative:

Dr.-Ing. H. Ruschke, patent attorney,

Berlin 33, Auguste-Viktoria-Str. 65

Named as inventor:

Donald Rodner Ayer, Nashua, N. H.,

Arnold Neil McDowell, Amherst, N. H. (V. St. A.)

Claimed priority:

V. St. v. America November 17, 1960

(No. 69 863)

type used have become for broadband operation Proven to be unsuitable at high frequencies. One reason for this is that the holding elements and the means for adjusting the various resistances result in a construction which is highly reactive or has a large reactance and is therefore very sensitive to frequency.

Attenuators are also known in which attenuation by inducing currents in a lossy element is achieved. The degree of damping will change the duoroh Coupling between this element and the stripline of the transmission line changed, and the damping is caused exclusively by the induced currents in the element, as this is not connected to the outer and plane-parallel conductor of the line. With such attenuators there is no adjustment of the resistance.

The object of the invention is to create a small and easily manufactured variable high-frequency attenuator of the above type, in which the disadvantages mentioned are largely eliminated and its mode of operation depends on the frequency a large range of attenuation and frequency is relatively independent and in which the input and Output impedances remain constant regardless of the damping setting.

409 538/349

According to the invention, this is achieved in the case of an attenuator of the design mentioned in the introduction through first and second adjustable resistor sections, one end of the second adjustable resistance section is connected to the outer conductor by connecting elements, by a movable section which is in sliding contact with the first and second sections, and by movable members to move the movable portion so that the effective Length of the first section with respect to the distance between the movable section and the The end of the second section is reversed.

In general, an attenuator incorporating the features of the invention operates schematically in FIG the same way as a common low frequency T or ^ resistor network. So it includes series and parallel resistors, which are adjusted synchronously in order to reduce the attenuation change while keeping the input and output impedances constant.

The attenuator is preferably built into a strip transmission line of the type at which the band-shaped inner conductor is arranged enclosed between two parallel earth conductors.

Since the inner conductor in the listed stripline through the outer conductor only on two sides are limited, they can easily be arranged for externally controlled movement with respect to one another without adversely affecting the field distribution. Since the changeable resistances are effective If the inner conductors are parts of, they still do not form discontinuities causing large reactance in the transmission line. As a result, the attenuation and the input and output impedances are essentially independent of frequency over a broad frequency band.

For a better understanding of the nature and the object of the invention, reference is now made to the following detailed description in connection with the drawing reference. It shows

F i g. 1 is a simplified perspective view of a section of a strip transmission line;

Fig. 2A is a horizontal section of a changeable T-attenuator according to the invention, wherein the inner conductors are shown in plan view,

2B is a schematic representation of a T resistor network,

F i g. 3 shows a vertical section of the variable attenuator of FIG. 2A,

F i g. 4 is a plan view of the inner conductors of another T-attenuator according to the invention;

Fig. 5A is a horizontal section of a variable π-attenuator according to the invention, wherein the inner conductors are shown in plan view,

Fig. 5B is a schematic representation of the π resistor network and

F i g. 6 shows a vertical section of the changeable π network.

In Fig. 1 illustrates the field distribution in a typical strip transmission line. The line has an inner conductor 10 which is located between a pair of outer or ground conductors 12 and 14. The conductors 10, 12 and 14 are flat and can be very thin. For example, they can be made from foil bonded or glued to dielectric material (not shown) that fills the space between the conductors. At a point in time when the conductor 10 is positive to the ground conductors 12 and 14 and the current in the conductor 10 is flowing in the direction of the arrow 15, the field distribution in the transmission line is as shown in FIG. 1, the solid arrows representing the electrical field and the dashed lines representing the magnetic field H.

The field design of the F i g. 1 indicates the

ίο TEM propagation mode. However, others can Types of vibration are transmitted on the line under certain conditions. If for example the inner conductor 10 is displaced from its position midway between the earth conductors 12 and 14 they get slightly different potentials. This voltage difference supports a plane-parallel one Mode. As a result, the earth conductors are "short-circuited" by a number of pins 16 running lengthways both edges of the inner conductor are arranged at a distance. The pins press one of the earth conductors Equipotential state and thereby suppress this type of oscillation. For effective suppression the distance between the pins in the longitudinal direction of the cable must be less than half a wavelength. Usually this distance is on the order of an eighth wavelength or less.

Another limitation of the pin spacing results from the requirement to have a resonance state in avoid any loop defined by the ground conductors and a pair of adjacent pins. A resonance loop distorts the transmission characteristics of the line and facilitates the radiation of energy from the line. Resonance occurs when the length of the loop is an integer number of wavelengths and as a result the spacing between adjacent pins must be considerably less than be the distance that forms a wavelength loop. If one of the transverse dimensions, i.e. H. the distance between the grounded planes or the distance from pin to pin greater than half a wavelength an electrical transverse waveguide mode can be excited. Hence these two are supposed to Dimensions to be less than half a wavelength. The circumferential path around the inner conductor 10 in FIG Center between the inner conductor and the earth conductors 12 and 14 and the pins 16 must be less than one Be wavelength. Otherwise the line is carrying a higher order transverse transmission line mode.

As shown in Fig. 2A, is a T-attenuator according to the invention contained in a strip transmission line unit having an inner conductor 17 has. The conductor 17 contains, in the order given, an end section 18, a series resistor section 19, a bridging section 20, a parallel resistor section 21, a series resistor section 22 and an end section 23. The end sections 18 and 23 and the Bridging section 20 consist of a substantially non-resistive metal foil, while the resistor sections 19, 21 and 22 are made of conventional resistor materials suitable for use at high frequencies.

As shown in FIG. 3, the T-attenuator includes metal housing members 24 and 26, which are arranged one above the other so that between their opposite surfaces 24 α and 26 a

5 6

There is sliding contact. The housing elements have changes in the resistance values of the various Recesses 28 and 30, the surfaces of which produce 28 a resistor sections, which the input and 30 a the grounded flat conductor for the internal and output impedance of the attenuator conductors 17 of the strip transmission line are. Keeping the setting range constant. For reducing sliding contact between the surfaces 24 a and 26 a 5 tion of the reflection to a minimum, which by performs the same function as the shorting pins short-circuiting the parallel resistor section 21 16 in Fig. 1 is introduced to the earth plan ladders, "must the Ab-

A pair of thin dielectric flaps or foils stood from conductor 36 to the bridging gap.

32 and 34, which are arranged in the recesses 28 and 30 at 20 substantially smaller than a quarter-wave have to be at a close distance from each other in length over the damping setting range. In

overlying surfaces 32a and 34a. As in every case, reflected signals in the

2A and 3, the end sections 18 are largely separated from individual resistor sections.

and 23 and the parallel resistor portion 21 of FIG. 3, a spring 48 is between the

Inner conductor 17 is bonded or glued to the surface 34 α of the thin surface 28 α and the thin dielectric plate dielectric plate 34. The 15 32 arranged to be between the inner conductor section

Series resistor sections 19 and 22 and the th to get reliable contact while

Bridging portion 20 are at the surface of contact between the housing members 24 and

32 a bound or glued. Which is maintained at the dielectric 26.

It is useful if the spring 48 does not have any in sliding contact with the changes in the electrical distance between

those sections, d. h., The resistance sections the inner conductor 17 and the earth plane conductor in the

19 and 22 touch the end sections 18 and 23, respectively, recess 28 introduces. Hence the spring exists

while the bridging portion 20 has the resistor preferably made of a dielectric material

Stand section 21 touched. to avoid such changes. It can also be a

As in Fig. 3, the parallel is a thin plate or sheet of conductive material

Stand section 21 with the grounded flat conductors (not shown) between the spring and the dielectric

connected by conductor 36. A coaxial verge plate 32 can be inserted to serve as a ground conductor

binding element 42 allows the manufacture of to serve.

external connections to the end section 18. As shown in FIG. 4 is shown, has another T-damper

Connecting element 42 comprises an inner conductor 49 attached to the connection member according to the invention,

cut 18 connected inner conductor 44 and one of the one end section 50, a series resistor

directly on the housing element 26 arranged ko-section 52, a bridging section 54, a

axial outer conductor 46. A similar connection parallel resistor section 56, a bridging

The connection element (not shown) has an inner conductor, kung section 58, a series resistor section

which is connected to the end section 23. One at 35 60 and one end section 62. The interior

The button 47 attached to the housing element 24 is connected to the earth conductors (not shown) in one

allows its movement along the housing element construction assigned in the same way as

tes 26 to adjust the attenuator to the construction according to F i g. 3 is formed. the

cause. Resistor sections 52, 56 and 60 are connected to one of the

In particular, the various sections 40 are bonded or glued to thin dielectric sheets,

of the inner conductor 17 in Fig. 2A schematically as and the conductor sections are tied to one another

arranged in Fig. 2B, with the resistors 19 ', or -glued.

21 'and 22' in the last-mentioned figure form a conventional bridging sections 54 and 58 according to the T-attenuator. When element 24 F i g. 4 are preferably moved as a continuous line to the right (Fig. 3), the rows of 45 tender strips are formed which extend across all three resistor sections 19 and 22 of Fig. 2A effectively resistor sections in sliding contact with these tiv, and the parallel resistor section runs. The parallel resistor section 56 is effectively shortened at 21. In this way, the earth conductors are connected by a conductor 63, resistance values of the resistors 19 'and 22' that of the conductor 36 in FIG. 3 corresponds.
Fig. 2B is enlarged, and the resistance value of the 50. The operation of the variable damping resistor 21 'is reduced. In itself it is part of FIG. 4 is easy to understand, if one knows this results in an increased attenuation. B. to the right directed movement of the conductor (reduced amplitude) of through the unit strip 64 along the individual resistance depending signals, but assumes in the section. The series resistor sections have essentially constant wave impedance. By 55, 52 and 60 are lengthened and the parking space is reduced. A left-facing ball resistance section 56 is shortened, whereby the movement of the housing element 24 reduces the damping. the damping between the end sections

According to FIG. 2A, the end sections are 18 and are enlarged. Leftward movement of the

23 of the inner conductor, preferably colinear with the strip 64, reduces the attenuation. It will be

Series resistor sections 19 and 22. Furthermore, 60 notes that in the attenuator according to FIG. 4 all

the ends of the sections 18 and 19 and 22 resistance-exhibiting inner conductor sections are on

and 23 in the overlap area all preferential one dielectric plate and all practically none

wisely rejuvenated. This causes sudden changes in the resisting sections to the other

struggles of the wave impedance are tied to a minimum dielectric plate, whereby the

and thus reflections on a low attenuator are somewhat easier to produce than that

held its worth. These tapers are attenuators according to FIGS. 2A and 3.

together with a taper of the parallel resistor A π-attenuator according to the invention is in

Stand section 21 designed so that they are shown at the same time Fig. 5A and 6. As shown there, to-

an inner conductor 65 summarizes an end section 66, a parallel resistor section 68, a series resistor section 70, a parallel resistor section 72 and an end section 74.

In Fig. 6, the construction of the π-attenuator corresponds to the T-attenuator described above, with conductive housing elements 76 and 78 being arranged one above the other and formed with recesses 77 and 79. Parallel surfaces 77 α and 79 α form ground conductors which form a strip transmission line unit in combination with the inner conductor 65. A spring 80 attached to the lower horizontal surface 76a of the housing member 76 is in sliding contact with the opposite surface 78a.

The resistor sections 68, 70 and 72 are preferably provided as a continuous resistor strip 82 designed, which is bonded to a thin dielectric plate or film 84 arranged in the recess 77 is. The end sections 66 and 74 are connected to a dielectric arranged in the recess 79 Plate or foil 86 bound or glued. As shown, they are angled from one another and are in sliding contact with, intersecting and upon the resistive strip 82 Way into two parallel resistor sections 68 and 72 and the series resistor section 70. The ends 68 a and 72 a of the parallel resistor sections are connected to the grounded flat conductors connected by conductors 88 and 90, respectively. The spring 80 on the housing element 76 makes resilient contact between housing elements 76 and 78 and thus ensures contact between the inner conductor sections as well as between the earth conductors.

According to FIG. 6, a connecting element 96 has an inner conductor connected to the end section 66 98 and an outer conductor 100 connected to the housing element 78. An inner conductor of one Similar connecting element (not visible in the drawing) is connected to the end section 74. A button 102 is attached to the housing member 76 for movement of the member 76 along the housing element 78 to allow adjustment of the π-attenuator.

The operation of the π attenuator can be easily understood in connection with FIG. 5B, which schematically indicates the arrangement of the individual sections that form the inner conductor 65 (Figure 5A). Resistors 68 ', 70' and 72 'form a common.-τ network. When the housing element 76 is displaced by sliding movement directed to the left along the element 78, the resistance strip moves 82 along the end sections 66 and 74, creating the parallel resistor sections 68 and 72 are shortened and the resistance values of the resistors 68 'and 72' are reduced. The series resistor section 70 is lengthened, as a result of which the resistance value of resistor 70 'increases. Consequently the damping between the end sections increases.

According to Fig. 5A, the end portions 66 and 74 as well as the resistance strip 82 are preferably shaped and arranged so that the input and output pulses kept constant when the attenuation is changed. To the effect of the discontinuity to be reduced to a minimum where the parallel resistor sections with the earth conductors are connected, the electrical length of the parallel resistor sections 68 and 72 must be less than one Quarter wavelength over the attenuation adjustment range.

In summary, a new, variable high frequency attenuator has been described, which in a strip transmission line is included. The attenuator can be in the form of a T or π network assume, in which each branch has an inner conductor section made of a resistance material in sliding contact with practically no resistance having section. The attenuation is varied by changing the effective lengths of the resistor sections by sliding the resistance sections along the non-resisting ones Sections are changed. Attenuators formed in this manner are essential less frequency sensitive than known variable high frequency attenuators. Simultaneously they are small and have a relatively simple structure. In the constructions disclosed above the individual resistors can be varied synchronously, and the series resistors can can be changed in inverse proportion to the parallel resistances. That way you can the input impedance and the output impedance of the attenuator are slightly substantially constant held when the attenuation is changed.

Claims (9)

Patent claims: 1. Variable high frequency attenuator in the form of a strip transmission line with an inner conductor and an outer conductor that contains a changeable resistance element, characterized by first and second adjustable resistance sections, one end of the second adjustable resistance section is connected to the outer conductor by connecting elements, by a movable one Portion in sliding contact with the first and second portions, and by movable members to move the movable section so that the effective length of the first section with respect to the distance between the movable section and the The end of the second section is reversed. 2. Attenuator according to claim 1, characterized in that the first adjustable resistance section a first resistance element in series with the line and the second adjustable resistance section a second resistive element parallel to the line, each of the resistive elements a resistive inner conductor portion which is in sliding contact with a substantially non-resistive portion and the movable element is a part of each of the resistance elements touched. 3. Attenuator according to claim 2, characterized in that a third resistance element is provided, which is in series with the line, the second resistance element is arranged between the first and the third resistance element, the third resistance element contains a resistance inner conductor part, which is with a substantially having no resistance part is in sliding contact, the movable member one Touches part of the third element and the third element is arranged so that movement of the Element is the effective length of the resistance portion of the third element inversely to that Change in length of the resistance part of the second element. 4. Attenuator according to claim 2, characterized in that a third resistance element is provided, which is parallel to the line, the first resistance element between the second and third resistance element is arranged, the third resistance element a Contains resistance inner conductor part, which has essentially no resistance Part is in sliding contact, the movable element part of the third element touches and the third element is arranged so that movement of the element the effective ao Length of the resistance part of the third element inversely to the change in length of the Resistance part of the first element changes. 5. Attenuator according to one of claims 2 to 4, characterized in that a first element with one part of each element and a second element with the other part of each element is connected, the elements being movable with respect to one another to to move a part of each element along its other part, so that the effective The length of the resistor parts is changed inversely. 6. Attenuator according to claim 5, characterized in that a second ground conductor is symmetrical to the first ground conductor is arranged above the inner conductor, the one ground conductor structurally shared with the first element and the other earth conductor with the second element are trained. 7. Attenuator according to claim 5, characterized in that the first and second elements are first and second electrically conductive housing members which are superposed and in sliding contact are arranged with one another along first surfaces thereof, the housing members have second surfaces forming the ground conductors of the strip transmission line and the strip transmission inner conductor is arranged between the ground conductors and separated therefrom by dielectric elements. 8. Attenuator according to claim 7, characterized in that each housing element has a recess in its first surface and having first and second dielectric elements formed in the corresponding recesses are arranged that the dielectric elements first and second opposing surfaces have that the second resistance element and none Resistive portions in sliding contact with the first and second third resistive element bonded to the first opposing dielectric surface or glued and the first and third resistance elements and the one having no resistance Section in sliding contact with the second resistance element to the second opposite one dielectric surface are bonded or glued. 9. Attenuator according to claims 4 and 7, characterized in that the inner conductor the strip transmission line has first and second non-parallel end portions, that each end of the first resistance element is connected to the ground conductors, the first resistance element extends across the end portions and is in sliding contact therewith is located, the first resistance element moves transversely to the end portions along these when the first housing element is displaced along the second housing element, so that the length of the part of the first resistance element between the end portions is reversed to the lengths of the parts of the first resistance element between the end sections and changing the ends of the first resistance element. Considered © publications:
U.S. Patent Nos. 2,810,891, 2,909,736. 1 sheet of drawings 409 538/349 3.64 ® Bundesdruckerei Berlin