DE2244838C2 - Inductive coupler for resonator fundamental wave excitation - is effected at several points on resonator front side, distributed along field line of azimuth E-field - Google Patents

Abstract

A TE fundamental wave is selectively energised in a screened dielectric resonator. The excitation of the TE fundamental wave takes place at several points on the resonator front side, the points being uniformly distributed along a field line of an azimuth E-field. The mean dia. of the circle, on which the coupling loops are arranged, corresponds approximately to the nodal circle dia. of the H component of the first harmonic radial TE wave. For decoupling of the TM oscillations in radial and axial direction the electric length of the coupling loop is pref. selected such that the centre of the loops approximately coincide with a voltage node. The coupler may have a coaxial feed, e.g. in strip technique. If a dielectric disc resonator is used, the coupler is accommodated inside a coaxial line. The arrangement may be used in a bandpass filter.

Description

f> 5

The invention relates to a coupling system for the selective excitation of the PD fundamental wave in shielded dielectric resonators.

The in the course of the general trend after implementation of the microwave communication devices in strip line or. Hybrid technology, miniaturization of antenna filters that has become necessary In connection with the postulate of high circular qualities of at least 2500 to 3000, the use of resonators made of ceramic substances with a high dielectric constant comes to the fore (e.g. TiO ₂ , also known as »rutile«, with c / ^ 90und / 5 Å-53-10- ^first

In the case of dielectric resonators, in principle numerous embodiments possible. Discs, punches, cylinders, prisms, spheres were theoretical and in some cases already variously investigated experimentally. There were already bandpass filters with Free-swinging discs arranged between Strelfenleltungen or housed in a tube Discs realized.

With regard to filter optimization, however different points of view have to be taken into account, which leave room for the construction and shape of the resonators constrict considerably. Optimal Q-Wene result from ζ. B. only if the dielectric resonator in a Shielding is operated. Free-running resonators have relatively high radiation losses. and also practically the entire circuit is contaminated by the stray field. Furthermore κ-uli between the metal wall and the dielectric body a minimum gap must be provided on all sides, because otherwise the attenuation inequalities the shielding is too important. The resonator should be in the vicinity of the useful resonance show no secondary resonances. Such Slörresonanzen are z. B. possible due to anisotropies in the resonator material as well as with regard to the vibration types assigned to the respective resonator shape. The oppression or avoidance of such nonsonan / s is primarily a problem of the resonance shape. of the excited Lyps of oscillation and the formation of the coupling element. Regarding Schwioijungs. ·. · Ρ becomes with advantage the fundamental wave of the resonator is excited, as this is usually the largest among the higher natural resonances Has distance.

With the shielded dielectric resonator, if the shield rests directly on the resonator surface, the fundamental oscillation is always of the T M-type (electric dipole field), the next higher, however, of the TE-type (H-WcIIe). As has been proven by calculations on the spherical model, increase with increasing air-filled Space between the resonator and the shield, the frequencies of the TM oscillation types are initially strong at. especially for resonator materials with high dielectric constants. while those of the Tt vibrational types decrease. With an optimally dimensioned dielectric The resonator of the TE basic type is therefore the deepest, making the coupling of this type special Importance.

The basic TE type is characterized by a circular E field that is zero in the center of the resonator. increases approximately sinusoidally with increasing distance from the center and decreases again to zero at the metal jacket of the shield. The associated magnetic field lines enclose those of the electric field, so to speak, in a loroid shape. In the H field, the H. component therefore has its maximum in the resonator center, while the H _r component, as a function of r, follows the same function as Εφ (see also Fig. 2a).

With the filter systems known so far

the resonator coupling is partly capacitive, partly inductive or in a mixed form (capacitive-inductive). An example of a capacitive coupling is in the journal "IEEE Transactions MTT", Vol. MTT-19, -No. 7, July 197KrS.:643 to -652. The resonar - ₅ ■ for gates of the three loop filter explained there are freely oscillating dielectric disks of square shape whose side length is electrically λ / 2. They are excited at the front by two capacitive coupling elements that are fed in phase opposition. As a closer examination of this arrangement shows, in addition to the TM basic wave, at least the somewhat deeper TE basic wave is also excited. In another arrangement, namely the above-mentioned band-pass filter consisting of a metal tube insulated from a metal tube, the coupling takes place through a ring section open at the end and extending over a circular sector of about 135 °, the radius of this ring piece being somewhat is chosen to be larger than that of the dielectric disks (see "IEEE Transactions MTT", Vol. MTT-16, No. 4, April 1968, pp. 210 to 218). The electrical length of this circular connector is about A _o / 4, where A _{0 means} the resonance wavelength of the resonator. In principle, the PD fundamental wave, which has the lowest resonance frequency here, is excited . ._ capacitive coupling exists.

In another arrangement, which is published in the journal jo for applied physics ", Vol. 24, Issue 3, 1968, pp. 142 to 147, are two parallel, open at the end Coaxial lines λ / 4 connected in front of their ends by a cross tube, and in the two connection levels slide disks are attached. The coupling takes place at the disc periphery; waves are excited vom TErJyp ^ namely the TE fundamental as well as Vibrations of the 'first,.' Second, third, fourth, '' Order.

Finally, filter arrangements are still known where the resonator coupling takes place via waveguide sections. However, such systems have the disadvantage of large Dimensions.

In the case of the coupling arrangements discussed, it is disturbing that, in addition to the useful resonance, also the neighboring vibration types can be excited. With the TE fundamental wave these are the next higher vibration types, with the TM fundamental wave Ist another one deeper lying TE waves possible. In fact, practically all published T'lier curves in the vicinity of the Useful resonance z. T. considerable attenuation drops, which suggest such phenomena.

The invention is based on the object of creating a coupling system for shielded dielectric resonators by means of which only the TE fundamental wave is excited, while there is practically no coupling with any of the neighboring oscillation types. In this case, the possibility of a feed should be provided both coaxially and using stripline technology. According to the invention, the object is achieved in that the excitation of the TE fundamental wave takes place purely inductively and at several / points on the front side of the resonator, that the coupling points are evenly distributed along a field line of the azimuthal E-field and that the mean diameter of the Circle on which the coupling elements are arranged, at least approximately corresponds to the knot diameter of the M, component of the first higher radial TE wave.

The invention will now be explained in more detail with reference to the figures. In Figs. 1 and 2, the operation of the according to the invention proposed coupling system on Example of a dielectric disk resonator in the sense of a function synthesis "schematically illustrates; FIG. 1 showing the decoupling process with respect to azimuthal oscillations and FIG. 2 with respect to it makes radial vibrations understandable. S is a disk resonator with a high DK, e.g. B. consisting of rutile. According to FI g. 1 a there is only one coupling loop. It can be the PD fundamental wave as well as oscillations of the first, second, third, fourth, order are excited. Fig. Ib shows two each other opposite, in the same direction fed coupling loop. Resonances are still possible here for the fundamental wave and the wave types of the second, fourth,

Order. Finally, in c) four coupling loops fed uniformly and in the same direction are in quadrature arranged. In addition to the fundamental, higher wave types are only possible from the fourth order onwards. Already with four coupling loops Unn there is thus an oscillation t> p decoupling in the azimuthal direction to achieve very high order. In addition, higher resonances can also occur in the radial direction.

FIG. 2 shows the distribution of the E and Η fields of the first two radial TE waves in a shielded dielectric disk, namely in FIG. 2 a (right). the. radial course of the field strength components E / ,,. H _: and H _{r are shown} for the TE fundamental wave, while FIG. 2 b (right) illustrates the radial course of the first higher TE oscillation. As can be seen from the H, diagram, there is a circle concentric with the disk, along the periphery of which the ^ component passes through zero, ie has nodes. The diameter of this "knot circle" is denoted by D ₀ . Accordingly, the diameter of the circle on which the coupling loops are arranged; be chosen so that it at least approximately coincides with O ₀ , ie the diameter of said nodal circle of the Η, field of the first higher radial TE oscillation type. This also suppresses the excitation of this type of oscillation. In addition to the fundamental wave, the PD vibration types of the third, fourth, fifth, etc. order are then possible in the radial direction, with those of the third order usually already having a large, practically hardly disturbing distance from the fundamental resonance.

The node circle diameter of the radial TE oscillation type of the second order can be calculated for simple resonator farms, but can be determined experimentally in each case. For example, with a "full" disk resonator (resonator diameter D equal to the tube width of the shielding, the node circle diameter is 0.546Z), on the other hand the maximum of the Hv component of the PD fundamental is 0.485 D. Both extreme values are therefore very close to each other. At the point of decoupling from the radial TE oscillation type of the second order, a practically optimal coupling to the TE fundamental wave is required.

The procedure for vibration type suppression just outlined only applies to vibrations of the PD types. In addition, vibrations of the TM types are possible, both in radial and azimuthal as well as in axial RN-direction. Azimuthal excitation is not possible because of the large number and the geometry of the coupling loops up to waves of very high order. For EntkoDDlune in the radial and axial direction is In

Further development of the invention, the electrical length of the Koppelschlelfen chosen so that at least approximately In a tension knot occurs in the middle of the loops. There is then no longer an E field in the radial and axial directions present, so that there are no TM vibration types in these directions can be stimulated more.

In Flg. 3 shows an exemplary embodiment of the coupling system proposed according to the invention in connection with the mutual coupling of a dielectric disk resonator. The arrangement is housed inside a coaxial line consisting of the outer conductor 1 and the leads 2 'and 2 "(Fig. 3 a). Isclierträger is distanced Four coupling sockets are provided, ie a swallowing type suppression with and including the third order in the azimuthal direction. When the coupling sockets are formed, the coaxial line is first converted into four parallel single conductors with as much resistance as possible A disc-shaped thickening 4 is attached to the end of the conductor 2 '(and 2 ") and the inner conductor 2' is continued from this in the form of the four conductors 5. The total wave resistance of the four parallel conductors with respect to the outer conductor 1 should be at least approximately equal to the wave resistance of the inner filter 2 '. The disturbance of the disk 4 can be compensated in a known manner, ζ. Β by reducing the diameter of the inner conductor 2 'immediately in front of the disk 4 (not shown in FIG. 3a). In the plane a '± a ". At a slightly greater distance than A / 4 from the disk 4 </. = Operating wavelength), the four conductors are each bent twice at right angles in the same direction, in such a way that each conductor has the shape of a A coupling loop that runs tangentially in a circle and so that each back liner comes to lie approximately in the middle between its two lines and eggs in each of the neighboring coupling lugs.The four back lugs are then bent at right angles in plane b in the radial direction and finally connected to a common node 6 , the electrical length between the center of the loops and node 6 is at least approximately A / 4. All coupling loops are identical and evenly distributed over the inscribed circle of the loops. The diameter of the inscribed circle on which the coupling loops lie, or more precisely the mean loop circle diameter , corresponds roughly to the node circle diameter of the !!, component of the first higher one radi.ilen 1 L oscillation type The eight Schleilenleiier (four outward and four return lines are advantageously embedded in a dielectric 7, which precisely fixes their position and at the same time shortens the mechanical length. Fig. 3b shows a section in the plane a '-? A " in plan view.

Through the node 6 is in the plane a'-? a ". more accurate transformed into the Bügelmitie of the loops, a short-circuit. The loops have don himself towards and against the outer conductor 1, no electric field. The resulting magnetic field is approximately toroidal shape. ⁶ ^ as is required to excite the fundamental TE wave. The implementation of the inductive coupling without the need for a galvanic connection of the coaxial inner conductor to the outer conductor also offers considerable structural and factory-related advantages.

The electrical length of the outward conductor to the. Loop stirrups, ie between disk 4 and plane a '^ a ". Is not critical and can vary between 3 A / 8 and 5 A / 8. The optimal case of the A / 2 length is the coupling system with regard to possible parallel resonances exactly in anti-resonance.

As tests on various dielectric resonators have shown, the number of coupling loops should be be at least four per coupling element. Likewise, the short circuit in the middle of the coupling bracket must be at least are approximately adhered to, so that practically no radial and axial Ε-components arise. With regard to the decoupling of the first higher radial TE oscillation type, the conditions are less spicy. In terms of frequency, the PD fundamental wave usually follows first the TM fundamental wave, then three azimuthal oscillation types and only in the sixth place the first higher radial TE mode. Therefore the possibility that this is disturbing is only as to estimate low. One can therefore consider a possible decoupling of this type of oscillation resulting points of view often apart from oh; Take into account or only consider what causes there may be certain advantages in terms of production.

Typical data of a coupling element designed to excite the PD fundamental wave of a rutile spherical resonator are z. B .:

Resonance frequency 8 GlI,

Ball diameter 4.0 mm

Clearance of the shielding 10 mm

ZaM the coupling loops 4

Sehiellcnkrels diameter 5 mm

Clear time of the coupling loops 1.4 mm

Loop conductor diameter 0.5 mm

The short circuits in the middle of the coupling bracket are also for the WelUibsclckiion one with such elements formed filter of importance. With a given bandwidth and number of circles, the Weilabselection is theoretical set. In practice slöre influences are now possible, which can reduce the blocking attenuation of a filter by orders of magnitude. Such a disorder can z. B. through the direct field penetration between coupling and decoupling through the shielding tube be given. The shielding tube behaves for such ! ■ elder, considering the influence of dielectric bodies disregards how one operated below its cut-off frequency Waveguide. The longitudinal attenuation is now in the waveguide below the limit frequency for pipe widths, as they come into consideration here, for the deepest TM vibration type several orders of magnitude smaller than that of the deepest PD vibration type. in terms of optimal If the filter is far away, it is therefore extremely advantageous to operate the resonators in the deepest TE oscillation type. In doing so, however, care must be taken to ensure that the TM components have a good uni / pressure. At the im By the way, the resonator operated in the deepest PD oscillation type has a considerable maximum achievable circular quality higher than the one excited in the TM fundamental oscillation glyph.

Arrangements of the type described are also referred to as vibration-type transformers. In the present Case it is about the mutual transition between the TEM-Schwingungsiyp and the PD fundamental mode.

The invention enables the direct transition from a coaxial or strip line to the TE fundamental mode an insulated mounted dielectric resonator. The system also effects a vibration type selection, by largely decoupling the vibration types adjacent to the useful resonance.

With the coupling system proposed according to the invention dielectric resonators can be excited practically free of spurious waves, an advantage for production of the physical filters of fundamental Meaning is.

It should also be mentioned that the one described above Decoupling system for the TE oscillation types IiV larger types only in radial and azimuthal directions

ment works. The simultaneous decoupling of higher TE oscillation types in the axial direction is in principle not possible. To achieve a sufficiently large frequency spacing these vibrations compared to those of the TE fundamental must be the dimension of the dielectric Body can be kept correspondingly small in the axial direction.

For this purpose 3 sheets of drawings

Claims (6)

Patent claims: 1. Inductive coupling system for the selective excitation of the TE fundamental wave in shielded dielectric resonators, characterized in that the excitation of the TE fundamental wave takes place at several points on the end face of the resonator, which are evenly distributed along a field line of the azimuthal Ε field, and that the mean diameter of the circle on which the coupling _{loops are arranged corresponds at least approximately to the nodal circle diameter of the H r} component of the first higher radial TE wave. 2. Coupling system according to claim 1, characterized in that for decoupling the TM vibration types The electrical length of the coupling loops in the radial and axial direction is selected in this way is that a tension node occurs at least approximately in the middle of the loops. 3. Head system according to claim 1 or 2, characterized through a Koaxiai feed. 4. Coupling system according to claim 1 or 2, characterized in that the feed in strip technology he follows. 5. Coupling system according to one of claims 1 to 4, for the mutual coupling of a dielectric Disc resonator, characterized in that the arrangement is inside a coaxial line is housed. the one from an outer conductor (1, JO Fig. 3) and two coaxial thereto, serving as feed lines Innei ^ itern (2 ', 2 ") consists that the disc-shaped dielectric resonator (3) also coaxial to the outer conductor (1) and the inner conductors (2 ', 2 "), each of which is located on a resonator face It is connected to the fact that the resonator (3) is spaced from the outer conductor (1) by insulating supports is that at the ends of the inner conductor facing the resonator (2 '. 2 "), disc-shaped thickenings (4) are attached from which the inner conductor in the direction of the resonator (3) in the form of four conductors (5) which form the coupling loops form that the total wave resistance of the four parallel Conductor (5) with respect to the outer conductor (1) is at least approximately equal to the wave resistance of the inner vein (2 '. 2 ") is. that at a distance of the disc-shaped thickening (4), which is slightly larger than a quarter of the operating wavelength λ, the four conductors (5) are bent in the same direction twice at right angles so that each conductor has the shape of a / u an incircle tangentially extending bow-like coupling loop e, and that each return conductor approximately in the middle / between its outward conductor and the outward conductor of the respective adjacent coupling loop comes to lie, and that the four return lines in one plane (b). whose distance from the bracket (a) is at least approximately /./4, bent at right angles in the radial direction and connected to a common node (6). 6. Coupling system according to claim 5, characterized »° characterized in that the back and forth the Loop conductor (5) on each cable of the disc transducer (3) are embedded in a dielectric (7).