DE1079138B - Waveguide directional coupler - Google Patents

Description

GERMAN

The invention relates to electromagnetic wave transmission systems in which the main form of _{propagation is the circular TE 0n} -WeIIe, in particular waveguide components for such systems, the geometric structure of which is inherently compatible with the circular TE 0n -WeIIe, so that an extremely broadband _{mode of operation is directly in this} Waveform results.

The upper limit of the usable part of the high-frequency spectrum was continuously increased in order to obtain an ever-increasing number of transmission channels. The knowledge that the circular TE ₀₁ wave, which propagates in metallic waveguides with a circular cross-section, has a damping characteristic that is inversely proportional to the frequency, promises a substantial increase in the upper frequency limit. As a result, interest in the theory and components of circular waveguides has increased significantly recently. However, the development of the components has been very uneven. Since the means of transmission most commonly used in the propagation of energy through waveguides are the rectangular waveguide which _{guides the TE 10} basic shape and the circular waveguide which _{guides the TE U} basic shape, most have been designed for these transmission systems required components are adapted to these waveforms. Microwave technology therefore includes directional coupler branches, circulators, isolators, frequency filters and the like, the geometric shape of which is particularly compatible with the electromagnetic field shape of these waveforms.

However, this is not the case with the circular electrical shape. Very few components have been developed that are inherently suitable for the circular electrical waveform. Therefore, in order to perform the various operations required in a transmission system with the circular electrical waveform, it was necessary to _{convert to the TE 1} "waveform in a rectangular tube or the TE ^ waveform in a circular tube. Microwave components have been developed for this purpose. For example, a directional coupler is known to split wave energy in any desired ratio between the circular electrical waveform in a round conductor and the basic shape in a rectangular conductor, both waveguides being parallel to each other and having a common wall in which coupling openings are located. This directional coupler works excellently for its purposes and has a bandwidth of 20%. Also known are channel filters to convert given frequency bands from a round waveguide, which is the waveguide directional coupler

Applicant:

Western Electric Company, Incorporated, New York, N.Y. (V. St. A.)

Representative: Dipl.-Ing. H. Fecht, patent attorney,
Wiesbaden, Hohenlohestr. 21

Claimed priority:
V. St. v. America March 28, 1958

Enrique Alfredo Jose Marcatili, Fair Haven, N. J.

(V. St. Α.),
has been named as the inventor

TE ₀₁ -WeIIe leads into a rectangular waveguide, which leads the TE ₁₀ -WeIIe) without receiving a waveform conversion in this process. In the case of coaxial cables, it is also known to arrange two high-frequency lines coaxially one inside the other.

At this early stage the development of the waveguide technology for the circular electrical Waveform, however, the goal should be to develop microwave components that are suitable for this interesting and highly useful electromagnetic waveform are suitable. It is to be hoped that finally any operation that takes place in a waveguide system for the circular electrical waveform is to be performed directly with the wave energy in the circular electrical form goes on without having to be converted to any other waveform just because that is Performing the function necessary microwave component works in the other waveform. It's closed expect because of the special ISature and geometry the field shape of the circular electric wave known in the art and others Propagation forms applicable methods and designs as a model for the production of such Microwave components that are compatible with the circular electrical shape are insufficient.

A very important operation in any microwave transmission system consists in the transfer of energy from one transmission line to another, either fully or in a different desired ratio, e.g. B. something

909 769 / Ϊ80

Energy To be taken from the main transmission path for investigation or to transfer wave energy from an amplifier station to the main transmission path or from the main transmission path to the amplifier station. _: - ■ - ;; ■ - - - ■ -

The invention aims to create a directional coupling between two transmission lines, which both carry energy only in a circular electrical waveform.

_{In a directional coupler} with multiple openings for electrical wave energy of a circular TE 0n -WeIIe with first and second sections of coaxially aligned waveguides, the ends of which are spaced apart so that a gap is formed, and a third section of a waveguide which is outside the first and second Section and is arranged coaxially to both, according to the invention, the third section is dimensioned so that first and second specific hollow tube waveforms are guided within the operating frequency range in the region of the gap, the second shape being a zero point of the electrical at a distance from the inner surface of the third section Has field strength and the dimensions of the three sections are dimensioned relative to each other so that the conductive boundary surfaces of the first and second sections coincide with the zero point.

However, at the present stage of development of the circular electric waveform technique, it is very likely that the transmitted energy in the basic shape in a rectangular waveguide must be converted in order to be used effectively, i.e. H. demodulated, amplified, filtered or the like. However, this conversion can be done in a known manner, it will be more detailed described below.

The directional coupler according to the invention is expediently dimensioned in such a way that the first waveform is the circular TE ₀₁ shape and the second waveform is the circular TE ₀₂ shape, and that the third section is dimensioned so that its cutoff frequency is slightly below that for the circular TE ₀₃ Waveform is in the operating frequency range. This allows it to operate at frequencies that are considerably removed from the cutoff frequency. Since a directional coupler becomes less frequency-dependent with the distance of the working range from the cut-off frequency, it is clear that this device is very broadband. Indeed, in this way, theoretically frequency bands of up to 40% can be transmitted between transmission lines. It has not yet been possible to determine whether this theoretical band limit can actually be reached, since there is no known microwave generator which is sufficiently broadband to test the limits of the device at the frequencies of interest, ie in the millimeter wave region.

It is particularly advantageous that no matching elements are required to eliminate reflections in the area where the energy is shared between the inner and outer coaxial conductor, because the geometric structure of the energy divider inherently with the geometric shape of the electric field TE ₀₁ and TE ₀₂ waveforms in round waveguides match.

Exemplary embodiments of the invention are shown in the drawings.

Fig. 1 shows a perspective cut-away view of an embodiment of an inventive Directional Coupler for Circular Electrical Waveforms ·; Figs. 2 A, 2 B, 3 A, 3 B show explanatory notes Curves and models of certain field shapes necessary for understanding how the execution works of Fig. 1 are useful;

Figures 4A to 4E show sequential cross-sectional views a waveform transmitter used in the embodiment of FIG.

Fig. 1 shows a perspective view of a Directional coupler according to the invention, the geometric structure of which with the field shape of the circular electrical waveforms is compatible. Fig. 1 can expediently consist of two larger parts to be viewed as. The first part is the directional coupler itself, the second is a transformer, to take wave energy from an opening of the directional coupler and convert it into wave energy of the Convert basic shape into a rectangular conductor.

If you now look at the first part, namely the directional coupler itself, you can see that there are shown two lengths 11 and 12 of a waveguide with a circular cross-section, each of which is dimensioned so that it has the circular electrical TE ₀₁ waveform to the exclusion of all Lead higher numbered waveforms. The conductors 11 and 12 have the same transverse dimensions and are aligned with the same axis, the adjacent ends being spaced apart from one another by a distance d , so that a coupling gap 10 is formed. Arranged coaxially with the conductors 11 and 12 is a waveguide 13 with a circular cross-section, which surrounds the conductors 11 and 12 and which constitutes a conductive boundary around the said waveguides 11 and 12 and around the gap 10. The conductor 13 is dimensioned in the area of the gap 10 in such a way that it leads the circular electrical waveforms TE ₀₁ and TE _{02 to the} exclusion of all waveforms of higher numbers, with its radius r _{e corresponding} to the radii r, - the conductors 11 and 12 in a special one Manner, which will be described in more detail later. Hollow dielectric cylinders or disks 14 and 15 hold conductors 11 and 12 in their coaxial position, respectively, within conductor 13, surrounding conductors 11 and 12 and filling conductor 13 in a manner known in the coaxial conductor art is. The discs 14 and 15 are preferably made of a dielectric material with a very low dielectric constant, e.g. B. from a foam material to keep the reflection of incident wave energy very small. For ease of reference, the four openings of the directional coupler are designated as follows: opening 1 is delimited by conductor 11, opening 2 is the annular area between conductor 12 and the inner boundary of conductor 13; the opening 3 is delimited by the conductor 12 and the opening 4 is the annular area between the conductor 11 and the inner boundary of the conductor 13. The mode of operation of the directional coupler described and certain other structural relationships of this device can be more easily understood if certain properties of the circular electrical waveforms are considered, which will now be briefly discussed, but only to the extent necessary to facilitate understanding of the arrangement of FIG.

The circular electrical waveforms are generally referred to as TE _0n . The expression TE, from "transverse electrical", indicates that the electrical field components are everywhere exclusively transverse to the longitudinal axis of the waveguide and to the direction of propagation of the wave energy. the

The designation On represents the order and number of this waveform family. The order is zero in each case to indicate the number of whole periods of the electrical transverse component that occur when traversing the circumference of the waveguide cross-section. On the other hand, η represents the number of half periods that occur when passing through the radius of the waveguide cross-section. Examples of the field image of the TE ₀₁ and TE ₀₂ waveforms in the cross section of a round waveguide are intended to explain these designations and to show the electrical field images of the two waveforms which are of interest in the embodiment of FIG.

2A shows the TE ₀₁ shape. Corresponding to the above designations, it can be seen that the polarity of the electric field components (the solid concentric circles) is nowhere reversed when passing through the circumference of the waveguide, and thus no entire period is shown. When running through the radius from the center of the conductor to the circumference, one can see that the polarity remains constant and that only half a period is shown. Figure 2B is another way of displaying the TE ₀₁ shape electric field image as is known in the art. The ordinate represents the strength of the field, while the abscissa represents the distance from the center of the waveguide (this is just another form of representation of the electric field image in FIG. 2A). In Fig. 3 A, the TE ₀₂ shape is shown. It can be seen that when the radius is traversed from the center of the conductor to the circumference, the polarity is reversed. electric field components (and thus a zero point of the electric field strength) is present, so that the designation of this field image as a circular electric waveform of number two is justified. Figure 3B is the alternate way of displaying the electric field image of the TE ₀₂ shape.

As is well known, any electromagnetic waveform at a given frequency requires a waveguide of some minimum transverse dimension if the waveform is to be propagated. Conversely, a round waveguide with a given radius will only carry those frequencies in the particular waveform of interest which are above a certain minimum frequency (the wavelength of which is known as the cutoff wavelength). Lower frequencies with longer wavelengths are not passed through this waveguide. Parameter expressions which relate the cutoff wavelength, the radius of the circular waveguide and a function of the electromagnetic waveform to one another are known. So it is known that the cutoff wavelength for the TE ₀₃ form

A. =

for the TE ₀₂ shape

2no

55

60

and for the TE ₀₁ waveform

7.02

Z.nr

⁶ 3.83

where Xc is the cutoff wavelength, r is the radius of the waveguide and the denominator is in each case the corresponding root of the Bessel function for the respective transverse electrical waveform. For a more complete explanation of the facts, reference is made to any standard textbook, e.g. B. on "Principles and Applications of Waveguide Transmission" by GC Southworth, "D. van Nostrand and Co., 1950, pp. 119 to 129 The radius r _{e of} the outer waveguide 13 can be selected so that the conductor 13 in the region of the gap 10 for the TE ₀₃ shape is just below the cut-off frequency at the highest frequency of the working range The radii r _{t of} the inner conductors 11 and 12 are then easily determined in such a way that the conductive boundaries of the conductors 11 and 12 coincide with the electrical field nucleus of the TE ₀₂ shape (see FIGS. 3A and 3B) that coincides with the outer Conductor 13 is guided along the coupling gap 10, ie if r _{e is} fixed, r _{t is} equal to r _e multiplied by the ratio of the roots of the Bessel function of the TE ₀₁ shape and the TE ₀₂ shape, so is

_ 3.83

In this way, the directional coupler according to FIG. 1 operates in a frequency range which is off the cutoff wavelength is significantly removed, so that he is from the considerable frequency independence of this mode of operation Benefits.

The mode of operation of the directional coupler of FIG. 1 can now be easily understood with the aid of the field images in FIGS. 2A to 3B. At the left end of the conductor 11, electromagnetic wave energy is only _{excited in the TE 01} form. This energy propagates along the conductor 11 to the right until it reaches the coupling gap 10-. - Immediately after entering the gap 10, in which both the TE ₀₁ and the TE ₀₂ form can be guided, the wave energy consists of both wave forms. The electric field image can therefore be used directly at the left .End of the gap 10 as a superposition of the electric field image TE ₀₁ , as shown in _Fig. 2 A or. 2B can be viewed with the electric field image TE ₀₂ as shown in FIG. 3A or 3B. It should be noted that the electrical vectors of this waveform are in phase within the cross-sectional area corresponding to opening 1 and out of phase in the annular area corresponding to opening 4.

The waveforms TE ₀₁ and TE ₀₂ are known to have different phase constants. They therefore propagate along the gap 10 in the direction of the waveguide 12 at unequal speeds. The phase relationship of the two waveforms along the distance d of the coupling gap 10 must change accordingly. If the distance d is chosen so that the directional coupler produces a complete transition from the opening 1 to the opening 2, the electrical vectors of the two waveforms at the end of the gap in the vicinity of the conductor 12 are within the annular cross-sectional area which the opening 2 corresponds, in phase, but in the cross-sectional area which corresponds to the opening 3, in opposite phase. Accordingly, port 2 is energized by energy which initially entered the conductor Ii. Furthermore, the electric field image which excites the opening 2 and which is propagated along the conductor 13 outside the conductor 12 is the TE ₀₁ shape, but now of course in a coaxial waveguide. In this

Explanation has been given of the phase relationships between the electric field images of the TE ₀₁ and TE ₀₂ forms in the coupling process. However, there are also amplitude relationships. However, this part of the theory of the device of FIG. 1 is not amenable to a simple qualitative explanation. A computation must be made of the contributions of a plurality of waveforms, many of which are below the _{cutoff wavelength, in addition to the TE 01} and TE ₀₂ waveforms in order to obtain a quantitatively accurate description, that is, nothing less than a solution to Maxwell's equation for the boundary conditions of the embodiment of FIG. 1 is necessary. This theoretical examination is not undertaken because it would not make the structure of the invention any more understandable and because it represents an obvious but tedious process for the person skilled in the art.

It should be noted that in the arrangement of the invention in which the energy is completely drawn from the opening 1 is coupled to opening 2, the phase relationship between the two waveforms am right end of gap 10 is exactly 180 ° out of phase with that at the beginning of the coupling area, i.e.

where ß _{t is} the phase constant of the TE ₀₁ form, /? _{2 is} the phase constant of the TE ₀₂ form and η is an integer. If an equal energy division between openings 2 and 3 is desired, the distance d can be changed (to an odd number of quarter-overlapping wavelengths and not to an odd integer number of half-superimposing wavelengths) that the phase targeting between the waveforms at the right end of the gap 10 is exactly 90 ° different from that at the beginning of the coupling area, ie

It can thus be seen that any desired ratio of energy transfer can be achieved by suitable definition of the distance d .

It is clear that the TE ₀₂ shape can easily be adapted to the openings 2 and 3 during operation of the directional coupler, since the conductive boundary of the conductor 12, as explained above, is dimensioned so that it coincides exactly with the zero point of the electrical Field strength of this waveform. However, it is not so obvious that the TE ₀₁ shape is matched as the conductive boundary of conductor 12 appears to coincide with an area where the electric field of that waveform has a finite value. In a waveguide for many waveforms, the amount of wave energy that is scattered forward from an impedance discontinuity is extremely much larger than the amount reflected. In fact, a scattering matrix investigation of the energy splitter, which consists of the _{gap 10 leading the waveforms TE 01} and TE ₀₂ and the openings 2 and 3, shows that the boundary conditions are such that the TE ₀₁ shape is properly adapted to these openings. Accordingly, there is only a negligible reflection at the coupler. The use of a scatter matrix representation for the investigation of waveguides is known. A description of this type of presentation and investigation can be found in standard works, e.g. B. in "Waveguide Handbook" by Marcuvitz, Radiation Laboratory Series, Vol. 10, 1951, pp. 106 to 108, and in "The use of scattering matrices in Microwave Circuits" by Matthews, IRE Transactions on Microwave Theory and Techniques, April 1955, p. 21. That the reflections from the coupler are indeed negligible is confirmed by the results obtained in various successful embodiments of the invention shown in FIG. So is with couplers, which in a frequency range from 50.4 GH ₂ to

ίο 60.0 GH ₀ work, in which the conductor 13 has an inner diameter of 16.48 mm, the conductors 11 and 12 inner diameter of 8.99 mm and the length d of the coupling gap values of 5.74; 11.48 and 23.01 mm had the largest reflected signal in the entire frequency band in all three cases 23 bb below the incoming signal in order to obtain an equal energy division between openings 2 and 3 or a complete energy transfer or no energy transfer. It is of considerable interest to note that there is no heat loss through the directional coupler.

It should now be considered how the energy transmitted to the opening 2 in the embodiment of FIG. 1 made available for subsequent use

as can be. This is done in a known manner, with the help of the second part of the above-mentioned embodiment of FIG. 1. The right device of the directional _{coupler is a transmitter for converting the coaxial TE 01} waveform, which differs from the

Opening 2 from between the conductors 12 and 13 propagates into the basic shape in a rectangular waveguide 16. It is essentially a waveform converter of the type described in the above-mentioned book by GC Southworth on p. 363. The transducer continuously changes its cross-sectional shape of the double-tube coaxial conductor so that the boundary between the conductors 12 and 13 is gradually converted into a rectangular cross-section, as shown by FIGS. 4A to 4E. In this way, the coaxial shape TE _{01 is} gradually reshaped into the basic shape TE ₁₀ , which then propagates to the right along the rectangular conductor 16 so that it can be used with the aid of normal methods.

Such a waveform converter can also be used at the other end of the directional coupler, in the form that energy entering the conductor 12 from the right from the opening 3 to the opening 4 and then picked up by a waveform converter of the type shown in Figures 4A through 4E will. Such an arrangement would also be useful in waveguide systems for long distances be. Wave energy from the long circular waveguide 11 could pass through the opening 2 to the rectangular waveguide 16 are transmitted and from there to a (not shown) amplifier station, to be appropriately amplified, timed, modulated or the like. Then she could go into the waveguide system using the waveform converter (not shown) to the left of the directional coupler described above be reinserted and then transferred from the opening 4 to the opening 3, so that they are propagates along the long waveguide 12 further.

Claims (6)

PATENT APPLICATIONS: 1. Directional coupler with multiple openings for electrical wave energy of a circular TE _0n -WeIIe with first and second sections of coaxially aligned waveguides, whose Ends are spaced from each other so that a gap is formed, and a third section of a waveguide, which is arranged outside of the first and second section and coaxially to both, characterized in that the third section is sized to define first and second ones Hollow tube waveforms guided within the operating frequency range in the area of the gap the second shape being a zero at a distance from the inner surface of the third section the electrical field strength and the dimensions of the three sections relative to each other are dimensioned so that the conductive boundary surfaces of the first and second section coincide with the zero point. 2. Device according to claim 1, characterized in that the first and the second section form first and third openings of the coupling device and the areas between the first and third or second and third sections form ao second and fourth openings of the coupling device. 3. Device according to claim 1 or 2, characterized in that the first and the third Ab- cut are sized so that only the first waveform and the second waveform is excluded, both related to the operating frequency range. 4. Device according to one of the preceding claims, characterized in that the between the first or second and the third section formed free of the rest of the space physical objects is. 5. Device according to one of the preceding claims, characterized in that the first waveform is the circular TE ₀₁ shape and the second waveform is the circular TE ₀₂ shape and that the third section is dimensioned so that its cutoff frequency is slightly below that for circular TE ₀₃ waveform is in the operating frequency range. 6. Device according to one of the preceding claims, characterized in that devices are provided for exciting one of the openings in a circular wave shape. Considered publications:
French patent specification No. 1 034 908. 1 sheet of drawings ; © 90 * 769/380 3.60