DE1955888A1 - Microwave window - Google Patents

Description

PATENT LAWYERS
DR. CLAUS REINLÄNDER

DIPL ING. KLAUS BERNHARDT Y 1 F 234 D

D-8 MONKS 60 BXCKERSTRASSE i

VARIAN ASSOCIATES

Palo Alto, California, USA

Microwave window

Priority: -15. Nov. 1968 - U.S.A. - No. 776 088

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Eb will drive a high power microwave window. The window has a waveguide with a dielectric, wave-permeable, gas-tight partition that transversely is inserted tightly over the waveguide to form the window arrangement. The window can be impedance-wise to the waveguide be adapted so that a relatively wide passage, lassband results. In certain windows the passband be as wide as the recommended bandwidth of the waveguide itself. Such windows are created by falling ·· and ghost resonance modes ("trapped" and "ghost" resonant modes) are disturbed, which are stimulated to resonance by slight asymmetries in the window · At their resonance frequencies, these modes couple energy from the main mode of propagation so that there is an impedance mismatch results, and at high power levels overheating and destroying the window itself. Operation at high power levels is therefore usually limited to frequency ranges between two such resonance modes. The frequency spacing

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between the resonance modes is increased to enable a broader range of operation by selectively tuning the resonance frequencies of these modes by, that the electrical path length through the window is selectively changed for one or more of these modes »For example the window is made in the vicinity of the perimeter dioker where one of the resonance modes has the strongest electric fields, and thinner near the center where another mode its, has strongest electric fields to tune one of the modes to a higher frequency and the other mode to a lower frequency. The middle bead of the window is kept roughly constant, so that the passband for the main mode of propagation is not noticeably affected. Instead of this For example, the dielectric constant of different parts of the window can be selected to be different in order to change the electrical path length through the window in the manner described.

State of the leehnik

Conductive arrangements are already provided in dielectric windows in order to selectively short-circuit certain undesired resonance modes or the frequencies of such resonance modes Window out of the passband, or around the To shift the frequencies of the interference modes so that a wider, high-performance operating band is within the pass band for the main reproductive moda results. Such conductive structures are, for example, painted conductive strips one side of the window, or a conductive rod embedded in the window itself. Instead, conductive structures have been placed in the immediate vicinity of the window /, to selectively act on some of the unwanted resonance modes so that their frequencies are detuned without that Passband of the window for the main propagation mode

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heblioh is affected.

The problem with using conductive probes, rods, Painted conductive strips and the like, which are arranged in the immediate vicinity of the window, consists in that this makes the construction of the window very complicated, and thus the manufacturing costs are considerably increased many of these guiding structures also occur other undesirable trap resonance modes near the window, further complicating the design In addition, such probes can cause arcing at high power levels and cause metal to hit the Window is sprayed, so that the operating behavior of the window is adversely affected.

18 there is therefore a desire for a simple facility, with which the special modes of the window can be coordinated, including a higher operating bandwidth for such devices obtain. ■ -

Summary of the Invention

The object of the invention is therefore to provide an improved high-performance Make microwave windows available.

According to the invention, in a high-performance microwave window Variations in the dielectric of the window are provided to avoid certain undesirable modes of resonance associated with the window tune to result in greater high performance operating bandwidth.

According to a special embodiment of the invention, the variations of the dielectric consist in thickness variations of the window element, so that a region of the window has a greater thickness

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than dia average bead of the window to a Reeonanzmodu8, the strong electric field is located in the thick portions of the window to tune to a lower frequency, while the Share can serve the window with less than the average thickness to modes üis your have the highest electric field strength in this range to tune to higher frequencies, and the thinner area of the window can also serve to maintain a constant mean value for the strength of the window so that the passband of the window for the main propagation mode is not changed.

According to another particular embodiment of the invention, the electrical path length through the window is effectively thereby made changed that part of the window is carried out with a first dielectric constant and a second part of the Window with a different dielectric constant in order to electrical path length through the window structure effectively increases change in order to tune the associated resonance modes so that a larger operating bandwidth results.

Further features and advantages of the invention emerge from the following description in conjunction with the drawing; show it:

Fig. 1 is a schematic longitudinal section through a known microwave window}

FIG. 2 shows a section along the line 2 - 2 in FIG. T for illustration purposes the electric field lines for the main mode of propagation;

3 shows a representation corresponding to FIG. 2 with the electrical Field lines a “disturbing orthogonal trap mode;

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Jig. 4 a · Pig.1 corresponding Sar position with a certain » ten, disruptive trap module}

Pig. 5-7

Sections corresponding to Pig. 2 and 3 with the electrical Field line images for certain disturbing ghost modes;

Pig. 8 the dependence of the standing wave ratio on the Frequency for the known window according to Pig. 1 and 2;

Pig. 9 (a) - 9 (g).

Side views of dielectric window elements with different thicknesses for tuning certain modes to higher frequencies and other modes to lower frequencies j

Figures 10 (a) -10 (e)

a number of! cut through dielectric window doors elements with thickness variations to tune certain unwanted modes to lower frequencies and certain other unwanted modes at higher frequencies; and

Longitudinal sections through a window according to the invention for Illustration of the equivalence of a change in the dielectric constant in certain ranges of a uniform thick window to change the thickness of the window to selectively tune the frequencies of certain associated unwanted resonance modes.

A known microwave window 1 is shown in FIGS (U.S. Patent 2,958,834). In short, the window 1 shows you

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Part 2 of a cylindrical waveguide which is closed off at both ends with conductive transverse walls 3 and 4. ! Two rectangular waveguide pieces 5 and 6 are connected at the ends to the cylindrical waveguide 2 and flow out axially with die-βea. Line disk 7 atm dielectric material is inserted gas-tight across the cross section of the cylindrical waveguide 2, the plane of the disk 7 i * lying essentially in the central plane of the cylindrical waveguide 2. A suitable dielectric for the window 7 is fonerde or beryllium earth, and the electrical length of the window for the main _{propagation module, the TII 1} module according to FIG Window has a thermosetting characteristic, as indicated by line 9 in FIG. It can also be seen that a standing wave ratio of less than 1.10 au 1 can be obtained over the rolling recommended frequencies of the rectangular waveguide.

Within the broad band of discrete points there is a number of discrete points at which points appear. These points are identified in Fig. 8 by vertical lines and with TMq ^ q ₉ Tl ₂ ^ bsw. Tl ₀ ^ designated. It is assumed that the TB - ^ - Modua has a resonance at the low-frequency end of the DurchlaSbandei, which is indicated by the broken vertical line labeled fB | ^ Even though these sea resonance modes are mathematically orthogonal and therefore theoretically dated Main mode of propagation are independent, they are in fact coupled to the main mode of propagation through small asymmetries in the window structure which cannot be avoided. So if the frequency of the operations Hauptfort- ι pflanzungsmodue one of the resonant frequencies of the undesired spurious modes crosses the mode to be resonated. Energy is then stored within this mode, and at high power levels within the window, the energy in window 7

At the frequency of one of these interference modes, the energy consumed leads to damage or failure of the window of the window for the main propagation module. In fact, with the known window according to rig. 1 and 2, the bandwidth that can be used at high power is limited to 10 between the TMq ₁ Q - and the TE ₂₁ - mode and to "between SBp ₁ - and the TE ₀ ^ - mode *

Xs are two undesirable resonance modes The first resonance mode is the trapped mode and is caused by reflections of the oscillation energy between conductive discontinuities of the waveguide on both sides of the window 7, for example by the abrupt transition between the rectangular waveguides 5 and 6 and the cylindrical waveguide 2. Example® of such case modes are the fiL ₁₁ mode and the 3M ₀₁₀ mode, the images of which are shown in ig * 3 and 4, respectively. The second type of disturbance mode is associated with sonars modes in the dielectric window T itself. Examples of such modes are the IEg ₁ mode and the TE ₀ ^ mode. These modes are called mis ghost modes. The electric field images for these gel steroid modes are shown in FIGS. 5-7. a The reason for two TB ₂₁ modes is that any noticeable disturbance of the mode causes its splitting into two modes oriented at 45 ° to one another, which are shown in FIGS. The two TE ₂₁ ghost modes have different resonance frequencies, as indicated in FIG. 8.

From the mode pictures according to Fig.3 -7 it can be seen that some the mode pictures their most powerful electric! Fields in areas of the window 7, while certain other modes have their strongest electric fields in other areas of the window 7

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to have. The electrical PEiD the TE ₂₁ - ^ä eistermodus is strongest near the outer periphery of the window 7, the field of the TE ₀₁ - mode is strongest at an average radius, when viewed from the center of the window 7, the strongest fields of the ^ Mq ₁₀ modes occur in the middle of the window, and the strongest electric field of the TE ₁₁₁ mode occurs in a band that extends diametrically across the window parallel to the wide walls of the waveguides 5 and 6. These differences for the locations of the strongest electric field for the various undesirable modes allow variations in the dielectric properties (parameters) of the window in these ranges to be used to selectively tune the frequencies of these modes in various ways so that a wider usable bandwidth for high performance is available.

9 shows a window structure according to the invention, with which the usable bandwidth of the window can be increased at high power between TM _n10 and TE _{? 1} mode. More specifically, the strongest electric field of the ^ Ep1 "" ^ ^ol ^ ^us occurs near the outer periphery of the window, while the strongest electric field of the TM mode occurs in the central area of the window. The known window 7 according to FIG. 9 (a) is therefore modified in such a way that the thickness in the central region is increased and on. Outer circumference is reduced. In this way, the TMq ^ ₀ mode is tuned lower in terms of frequency, and the TE ₂₁ -MODUS is tuned higher in terms of frequency in order to obtain a wider width for the window that can be used at high power. 9 (b) - 9 (g) are examples of window designs that are thicker in the middle and thinner on the outer circumference to accommodate the wider, high-performance groove bandwidth. In fact, these windows show an improvement in usable bandwidth from $ 16 to $ 25. In a ;, special embodiment of a window element 7 'of the type shown in Fig. 9 (g) for a window 1 with a pass band according to Fig. 8,

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had the custody resulting window 7 ¹ "* ^ while a thickness of about 7.4 now (0.290 of the center portion on the outer circumference had a thickness of 3.7 mm (0.145)"). The outside diameter of the window 7 'was 98.5 mm (3.980 "), the outside diameter of the thicker central portion of the window was 32.7 mm (1.289"), and the window was made of beryllium. The thickness variations can be achieved by milling or otherwise processing the window element a 7 '. Instead, one or more dielectric elements, for example a disk, a ring or a block, can be attached to the surfaces of the flat window element 7 or otherwise attached to it in order to obtain the desired thickness variation for the assembled window.

In FIG. 10 window constructions for increasing the usable high performance operating bandwidth between the TE ₂₁ mode and the TE ^ mode are shown. In this case, the TE ₂₁ mode has its highest electric field strength at the outer circumference of the window, while the TE mode has the greatest field strength at an intermediate radius from the center of the window. Accordingly, the known window element 7 according to Fig. 10 (a) has been modified, as shown in Fig. 10 (b) - 10 (e), in order to increase the thickness of the window in the vicinity of the outer circumference and to decrease it at an intermediate radius, to decrease the frequency of the TE ₂₁ mode and increase the frequency of the TE ₂₁ mode.

Another embodiment of the invention is shown in FIG. in which the dielectric constant of the window is changed instead of the thickness of the window 2 being varied, to get the same result as changing the thickness. More specifically, Fig. 11 (a) shows a window 7 ", at which the center area marked 22 consists of a dielectric, for example alumina, with a dielectric con-

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constant E from. about 9, which is higher than the dielectric constant S of the outer peripheral part of the window "which is made of beryllium earth, which has a dielectric constant τοη about 6.4. This is the equivalent of the window of FIG. 11 (b) which corresponds to the window of FIG. 9 (g), and it results in a high performance bandwidth between the TB «-j mode and the TMq.Q mode by increasing the Frequency of TEp. · Mode and lowering of the frequency of TM ₀₁₀ mode. Instead, the outer periphery of the window 7 "can be made of a material having a higher dielectric constant than the central region of the window, as shown in Fig. 11 (c), in order to obtain a window equivalent to that of Fig. 11 (d). is the ^f the window 7 of Figure corresponds to 10 (b), and this results in an increase of the high-Futzbandbreite between the TE ₂₁ -. mode and the TE ₀₁ - mode, as described in connection with Fig.10.

With all window constructions according to Fig. 9, 10 and 11 remains the mean electrical length through the window element preferably essentially unchanged due to the dielectric variations, so that the passband for the main operating modme is not appreciably changed by the dielectric variations for tuning the disturbance modes.

The window element has been described in connection with a special window construction according to FIGS. However, this is not necessary, since it is also advantageously used in other window constructions, for example in conventional half-wave windows, in which a block of ceramic material half a wavelength thick is placed tightly across a waveguide. >

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Claims (1)

VI P 234 D. Claims Microwave window in which a dielectric window is gas-tight mounted across a hollow transmission line is and bei.dem at least one interfering microwave energy resonance mode occurs, the resonance frequency of which falls in the pass band of the microwave window, thereby characterized in that the dielectric parameters of the pen "etere are dimensioned so that the electrical path length in Direction of the power flow through the window for vibrational energy a frequency within the passband of the window is perpendicular to the direction of the power flow through the window changes to the frequency of the certain interfering resonance mode relative to the essentially unchanged Kitten frequency of the passband of the window for selectively shift the main reproductive mode to to increase the usable free bandwidth for high performances of the main propagation mode of the window. 2 «Window according to claim 1, characterized in that the j Thickness of the dielectric material of the window transverse to the direction of energy flow is changed to a different to get electrical shelter through the window. 3 · Window according to claim 1 or 2, characterized in that the dielectric constant of the window is transverse to the direction the power flow is changed to changeable electrical Path lengths through .the window. ... / 12 009825/1240 4. Window according to claim 1, 2 or 3, characterized in that that the dielectric parameters of the window are dimensioned so that the mean electrical path length through the window for the vibrational energy of the main mode of propagation essentially through the variations of the electrical Path length for the interference mode remains unchanged, so that the center frequency; The Dur chi ate tied it for the main mode of reproduction remains practically unchanged. 5. Window according to one of claims 1 to 4, characterized in that that the window is tightly inserted into a piece of cylindrical waveguide essentially in its longitudinal center is, and at both ends of the same rectangular waveguides are attached. 5 /,. 12AO BAD ORtGlNAL Blank page