IE42514B1 - Improvements in or relating to micro-wave filters - Google Patents

Description

The invention relates to microwave filters consisting of a plurality of resonators which are mutually coupled and operated in the dual-mode, the first and last resonator in the signal path being pro5 vided with connection lines for the supply and discharge of electromagnetic'energy, and wherein an additional bridge coupling is provided at least two resonators which do not. directly follow one another In the electrical signal path, the individual resonators being arranged in mutually adjacent rows.

Filters in micro-wave technology consist, in known manner, of a plurality of microwave resonators which are coupled to one another, and which can be coupled either capacitively or inductively. The resonators themselves can consist, for example of so-called coaxial line resonators or Of wave-guide resonators.

In contrast to filters constructed using lumped circuit elements, the geometrically predetermined configurations of the resonators means that it is not possible to readily construct any lumped circuit filter as a filter using microwave resonators. This difficulty occurs in particular when it is necessary to produce attenuation poles in the attenuation characteristic of the filter, and/or to produce a levelling of transit time.in the pass band of the filter by means of additional 4SS14 - 3 bridge-arm couplings of filter circuits, and in arrangement described in the German Patent Specification No. 1,942,867, these problems are avoided by adopting a construction having resonators in neighbouring rows with additional over-couplings in at least one common dividing wail between the two resonators of different rows.

The possibility of constructing microwave filters with cavity resonators operated simultaneously in more than one mode is described for example, in the article 'Microwave Filters Employing a Single Cavity Excited in More than One Mode' published in the 'Journal of Applied Physics', Vol. 22, No. 8, August 1951, by Wei-Guan Lin; and in an article Ά Four Cavity Elliptic Waveguide Filter' published in 'IEEE Transactions on Microwave Theory and Techniques', Vol - MTT. 18, No. 12, December 1970 by A.E. Williams. Preferably with this type of construction, two identical but orthogonal modes are employed in H1O1 or ^111 resonat:or:;f and are coupled together by a coupling screw in each case arranged at 45° to the direction of the E-vectors relevant to the dual mode. It is thus possible to realise two electric oscillating circuits of a filter in one single cavity resonator in a technically effective fashion. On account of the possible reductions in weight and volume of up to 50¾ which can be obtained with dualmode operation, an important field of application is in satellite technology, particularly as the filters employed therein are subject to high electric requirements, which becomes manifest in the need for a relatively large number of electrical oscillatory circuits.

As these filters likewise require attenuation poles and/or a levelling of the transist time in the pass band, it is obviously desirable to find suitable filter circuits in the dual-mode technique for these filters. One construction proposal has been made in an article entitled 'Nonminimum-Phase Optimum Amplitude Bandpass Waveguide - 4 Filters' published in 'IEEE Transactions on Microwave Theory and Techniques’, Vol. MTT-22, No. 4 April 1974 by A.E. Atia and A.E. Williams. However, this article is limited to filter circuits which are symmetrical both in terms of structure and in element values, and which also exhibit frequently overlapping bridge-arm couplings, the number and geometric position of which within the filter arrangements cannot be preselected, and whose number of electric oscillating circuits must amount to a multiple of 4, which means that this proposal is frequently impracticable.

One obj ect of the present invention is to provide a construction which overcomes the aforementioned difficulties in a simple fashion, and in particular provides filter circuits which are asymmetrical in terms of element values, yet are to be operated in the dualmode, and whose number of electrical oscillatory circuits amounts to a multiple of 2, and wherein it is possible to achieve bridge-arm couplings as used in corresponding lumped filter circuits, which can be purposively preselected**in respect of their position within the filter arrangement, and in respect of their sign.

The invention consists in a microwave filter in which a plurality of resonators are coupled to one another and operated in the dual-mode, at least a first and last resonator being provided to form a signal path with respective connection lines tor the input and output of electromagnetic energy, and wherein additional bridge coupling is provided between at least two resonators which do not directly follow one another in the signal path, individual resonators being arranged in adjacent rows and the number of resonators in at least one row being different from the number of resonators in the other rows.

A particular advantage of a filter constructed in - 5 accordance with the invention consists in that the limitations regarding the circuit structure which are necessary in the known prior art are dispensed with and that it is thus possible to considerably increase the number of filter circuits which can be constructed to operate in the dual-mode.

A particular advantage in comparison to the prior art consists in that it is possible to preselect the arrangement within the filter arrangement of the coupling elements and the elements provided for additional bridge couplings actually during the design stage of the filter, and that generally speaking this produces designs of filter arrangements which can always be actually realised as a construction.

The possibility of producing filter circuits whose additional couplings do not frequently overlap provides the additional advantage that these additional couplings assume values which at least in part can be more easily realised, and that in addition the tunability of the filter is improved and the sensitivity to fine-tuning is reduced.

The invention will now be described with reference to the accompanying drawings, in which:Figure 1 is an equivalent circuit diagram of one exemplary embodiment of the invention with a fourteencircuit filter circuit having four additional bridge couplings; Figure 2 shows a first exemplary filter arrangement of the circuit in Figure 1, constructed in accordance with the invention; Figure 3 shows a second exemplary embodiment of a filter arrangement in accordance with the invention; Figure 4 shows a more advantageous arrangement of the embodiment of a filter shown in Figure 3; and 43514 - 6 Figure 5 is the electric equivalent circuit diagram of the filter corresponding to Figure 3 or Figure 4.

Figure 1 illustrates a fourteen-circuit filter 5 circuit which is asymmetrical in terms Of structure and element values with four additional bridge couplings, as an electric equivalent circuit diagram of the physical arrangement shown in Figure 2. This is a four-pole circuit, in the shunt arms of which are arranged parallel oscillatory circuits SI to S14, and which are coupled via coupling inductances 1/2, 2/3, 3/4 to 13/14 arranged in respective series arms. By way of additional bridge couplings, a coupling inductance 4/13 is introduced between the parallel oscillatory circuits S4 and S13, a coupling inductance 5/12 is introduced between the parallel oscillatory circuits S5 and S12, a coupling inductance 6/11 is introduced between the parallel oscillatory circuits S6 and Sil and a coupling inductance 7/10 is introduced between the parallel oscillatory circuits S7 and S1O.

In the exemplary embodiment in Figure 2 a filter arrangement in accordance with the invention is shown which consists of seven cavity resonators 1 to 7, and is the physical equivalent to the circuit diagram represented in Figure 1. The resonators 1 to 7 are divided between two rows A and B arranged above one another, in such manner that the row A contains the resonators 1 to 4, row B contains the resonators 5 to 7, and the resonators arranged next to one another or above one another in the two rows each possess a respective common dividing wall.

In the present example, the resonators 1, 2 and 2, 3 and 3, 4 arranged next to one another in row A, the resonators 5,6 and 6,7 arranged next to one another in row B and the resonators 2,7 and 3,6 and 4,5 arranged above one another each possess a respective common dividing wall. The coupling elements which serve to couple the - 7 resonators operated in the dual-mode aie here in the form of slot couplings, and are arranged in such manner that the electromagnetic energy supplied to the resonator 1 of the filter passes in turn through the resonators 1 to 4 of row A and 5 to 7 of row B.

In the illustrated exemplary embodiment, two adjacent parallel oscillatory circuits of the equivalent circuit diagram in Figure 1 are each realised by a resonator which, like all the resonators being used here, is operated in the dual-mode with two orthogonal modes. The E-vectors assigned to the individual modes are, correspondingly, likewise orthogonal within a resonator, and in the Figure are designated El to E14 in accordance with the associated parallel oscillating circuits SI to S14. Here the parallel oscillatory circuits SI and S2 are realised by the resonator 1, the parallel oscillatory circuits S3 and S4 are realised by the resonator 2, and the parallel oscillatory circuits S5 to S14 are realised by the resonators 3 to 7 correspondingly.

Each of the resonators is provided with a coupling screw Kl/2 to K13/14 which is arranged at an angle of 45° between its associated E-vector El, E2 to E13, E14, and which serves to set the coupling between the orthogonal modes operated within it. These coupling screws each produce the coupling inductance between two adjacent parallel oscillatory circuits, realised in one resonator, of the equivalent circuit in Figure 1. For tuning purposes each resonator is also provided on two orthogonal outer walls with tuning screws, for example, the resonator 1 is provided with the tuning Screws Al and A2 for the modes assigned to the parallel oscillatory circuits SI and S2. The tuning screws with which the remaining resonators 2 to 7 are provided in like manner have not been shown for clarity of lay-out.

In the exemplary embodiment in Figure 2, the - 8 coupling elements are in the form of slot couplings, which if required can also at least partially be replaced by hole-couplings, the resonator 1 is coupled to the resonator 2, and the mode corresponding to the parallel oscillatory circuit S2 and possessing the Evcctor E2 is coupled to the mode corresponding to the parallel oscillatory circuit S3 and possessing the Evector E3 through the coupling slot CS2/3 which is provided in the common dividing wall between resonator 1 and 2 at right angles to the E-vectors E2 and E3. The coupling of resonator 2 to the adjoining resonator 3, and of their associated modes with the E-vectors E4 and E5 is effected via the coupling slot CS4/5 arranged in the common dividing wall between these resonators at right angles to the E-vectors E4 and E5.

Precisely the same considerations regarding the arrangement of the coupling slots also apply to the following resonators 4 to 7 with the associated E-vectors E7 to E14, the coupling slot CS6/7 provided for coupling the wave modes with the associated E-vectors E6 and E7 being arranged in the common dividing wall between the resonators 3 and 4, the coupling slot.(’S8/9 provided for coupling the wave modes with the associated E-vectors E8 and E9 being arranged in the common dividing wall between the resonators 4 and 5 the coupling slots CS10/11 provided for coupling the wave modes with the associated E-vectors E10 and Ell being arranged in the common dividing wall between the resonators 5 and 6, and the coupling slot CS12/13 provided for coupling the wave modes with the associated E-vectors E12 and Ξ13 being arranged in the common dividing wall between the resonators 6 and 7.

In the dividing wall which is common to the resonators 2 and 7 is provided an additional coupling slot CS4/13 whioh lies at right angles to the E-vectors E4 and E13 and which corresponds to the coupling 42S14 - 9 inductanco 4/13 of the circuit in Figure 1.. Further additional coupling slots CS5/12, C56/1.J and CS7/1.0 are arranged in the common dividing walls of the resonators 3 and 6, 3 and 6 and 4 and 5 at right angles to the E5 vectors E5 and E12, E6 and Ell, and E7 and E10 and correspond to the additional overcoupling inductances 5/12, 6/11 and 7/10 of the equivalent circuit diagram in Figure 1.

The additional magnetic couplings can be realised with the correct sign by the spatial assignment of the dual-mode coupling screws of two resonators which follow one another in the signal path sequence, by adjustment of respective screws to introduce a phase-shift to select between a coupling that is positively inductive and negatively inductive, whether the additional couplings in the signal path sequence are alternately inductive couplings and capactive couplings, or vice versa, and whether the couplings via common walls are in the form of capacitive couplings or inductive couplings.

Figure 3 schematically illustrates a further filter arrangement constructed in accordance with the invention, whose cavity resonators 1 to 7 operated in the dual-mode are arranged in three rows A, B and C lying above one another, in such manner that the resonators lying above one another in adjacent rows and the resonators arranged next to one another each have a respective common dividing wall. In row A the resonators 1 and 2 are arranged next to one another, in row B the resonators 5, 4 and 3, and in row C the resonators 6 and 7, in such manner that the resonators 1,4 and 2, 3 and , 6 and 4, 7 each lie one above another and possess a respective common dividing wall.

This filter arrangement is of little technical significance, however, as the resonator 4 is not accessible from two orthogonal sides for the provision of tuning screws. - 10 Figure 4 schematically illustrates an improved exemplary embodiment of the filter shown in Figure 3, whose resonators rows A, B and C are not arranged in one plane, as in Figure 3, but in part in orthogonal planes, whereby it is ensured that all the resonators are accessible from two separate orthogonal sides for tuning purposes.

In this filter arrangement the rows A and B are of the same construction as in Figure 3, so that the mutual arrangement of the resonators 1 to 5 is identical to that in Figure 3. The row C, formed by the resonators 6 and 7 in the exemplary embodiment, is arranged now below, but next to the row B, as a result of which the resonators 5, 6 and 4, 7 do not lie above one another as in Figure 3 but next to one another, and each possess a respective common dividing wall, and the resonator 4, like the other resonators, is accessible from two orthogonal sides from the provision of the tuning elements .

Figure 5 illustrates the equivalent circuit diagram of the filter arrangements shown in Figure 3 and Figure 4. It shows a structure-symmetrical four-pole circuit which, however, is asymmetrical in respect of the element values and in whose shunt arms are arranged the parallel resonance circuits Si to S14, which are coupled in each case via. the inductances 1/2, 2/3...13/14 arranged in the series arm. In addition, the parallel resonance circuits S2 and S7 are coupled to one another via an inductance 2/7, the parallel resonance circuits S3 and S6 are coupled to one another via an inductance 3/6, the parallel resonance circuits S8 and S13 are coupled to one another via an inductance 8/13, and the parallel resonance circuits S9 and S12 are coupled to one another via a further inductance 9/12.

The parallel oscillatory circuits SI and S2 of the - 11 equivalent circuit diagram have been realised by the resonators 1 of the exemplary embodiments of Figure 3 and Figure 4, the parallel oscillatory circuits S3 and' S4 are realised by the resonators 2 and so on, up to the parallel oscillatory circuits S13 and S14 which are realised by the resonator 7.

Claims (6)

1. CLAIM S;~

1. A microwave filter in which a plurality of resonators are coupled to one another and operated in the dual-mode, at least a first and last resonator 5 being provided to form a signal path with respective connection lines for the input and output of electromagnetic energy, and wherein additional bridge coupling is provided between at least two resonators which do not directly follow one another in the signal path, 10 individual resonators being arranged in adjacent rows and the number of resonators in at least one row being different from the number of resonators in the other rows.

2. A filter as claimed in Claim 1, in which there 15 is an odd number of said resonators.

3. A filter as claimed in Claim 1 or Claim 2, in which each resonator is accessible from at least two orthogonal outer walls for tuning purposes.

4. A filter as claimed in any preceding Claim, in 20 which there are at least two rows arranged in a vertical plane next to one another, and at least two rows arranged in a horizontal plane next to one another, one row of the latter including at least one resonator of said rows in said vertical plane. 25 5. A filter as claimed in any preceding Claim, in which the sign of additional inductive couplings is determined by the mutual spatial arrangement of coupling screws of in each case two resonators which follow one another in the signal path sequence. 3υ 6. A filter as claimed in any preceding Claim, in which said additional couplings include a plurality of inductive couplings, the remainder of the additional couplings being capacitive couplings. 43514 - 13 7. A filter as claimed in any one of Claims 1 to 5, in which the elements provided for the coupling and the additional coupling of resonators are in the form of inductive couplings. 8. A filter as claimed in any one of Claims 1 to 5, in which the elements provided for coupling the resonators are in the form of inductive couplings and the additional couplings in the signal path sequence are alternately in the form of capacitive couplings and inductive couplings. 9. A filter as claimed in any one of Claims 1 to 5, in which the elements provided for coupling the resonators are in the form of inductive couplings and the additional couplings in the signal path sequence are alternately in the form of inductive couplings and capacitive couplings. 10. A filter as claimed in any one of Claims 1 to 5, in which the elements provided for the coupling of the resonators are in the form of capacitive couplings arid the additional couplings in the signal path sequence are alternately inductive couplings and capacitive couplings. 11. A filter as claimed in any one of Claims 1 to 5, in which the elements provided for the coupling of the resonators are in the form of capacitive couplings and the additional couplings in the signal path sequence are alternately in the form of capacitive couplings and inductive couplings. 12. A filter as claimed in any one of Claims 1 to 5, in which the couplings of the resonators and the additional couplings are of like design. 13. A filter as claimed in any one of Claims 1 to 5, in which the elements provided for the additional coupling of the resonators are in the form of coupling slots and/or holed diaphragms. 14. A filter as claimed in Claim 6, in which at least a plurality of individual filter portions are

5. Bridged symmetrically, the additional bridge couplings and the inner-most coupling of the filter portion being alike in respect of the type of coupling whereas the par ticular opposite type of coupling is used for other couplings.

6. 10 15. A microwave filter substantially as described with reference to Figure 2 or Figure 4.