GB2129226A - Resonator arrangements - Google Patents

Abstract

All dielectric resonators are capable of supporting a number of resonance modes. This may cause difficulties, for example when a resonator is used in a filter circuit and a mode other than that required is present, producing unwanted pass or stop bands at another frequency. These difficulties may be reduced in a filter by employing a plurality of resonators having fundamental modes with the same resonant frequency. Other higher order modes have different frequencies and thus do not reinforce each other to the same extent. Therefore the effect of such spurious modes is reduced.

Description

SPECIFICATION Resonator arrangements This invention relates to resonator arrangements, and more specifically to such arrangements which include a number of individual dielectric resonators. Dielectric resonators are now well known devices and are described in, for example, the article "Application of Dielectric Resonators in Microwave Components" by J. K. Plourde and C. L. Ren, IEEE Transactions on Microwave Theory and Techniques, Vol. MTT. 29, No. 8, August 1981, pages 754 to 770.

All dielectric resonators are capable of supporting a number of resonance modes. This can cause difficulties for example, when a resonator is employed in a filter circuit and a mode other than that required is also present, producing unwanted pass or stop bands at another frequency. This invention seeks to provide an improved resonator arrangement.

According to a first aspect of this invention a resonator arrangement includes a plurality of dielectric resonators, each of the resonators being such as to resonate in a plurality of different modes occurring at mutually different frequencies, one of said resonance frequencies being common for all of the plurality of resonators, and at least some of the remaining resonance frequencies of all of the plurality of resonators having mutually different values.

Thus, since all of the dielectric resonators resonate at a same desired frequency, resonance at this frequency is greatly reinforced whereas this is not the case for the other frequencies. Thus the resultant amplitudes of any other frequencies which occur will be very much less, even if one or two modes at other frequencies happen to have the same or similar frequency value. The desired common frequency may occur at different modes for the different resonators, but preferably each resonator resonates at the desired common frequency in its fundamental mode. The fundamental mode of resonance generally has a greater amplitude than higher order modes and hence when resonances in the fundamental mode coincide and reinforce each other they produce a correspondingly higher effect than if the modes in coincidence were higher order modes.

The dimensions of a resonator are a factor in determining the frequencies at which is resonates and the frequency separation of its modes, in particular in the case of a cylindrical resonator its height to diameter ratio. Conveniently therefore each resonator has different dimensions to the remainder of the said plurality such that it naturally resonates at frequencies different to the remainder of the plurality in modes other than its fundamental mode. In practice it may be necessary to provide a small degree of external tuning to bring the fundamental modes of the different resonators to precisely the required common value.

Alternatively each resonator may be deliberately arranged to have different natural resonance frequency in its fundamental mode from the remainder of the plurality, and means are included for tuning the frequency of each resonator such that its fundamental mode is brought to the desired common frequency. Thus the resonators can be of slightly differing sizes and, by bringing their fundamental modes into coincidence using the said means, their higher order modes are made to remain out of coincidence, since their frequencies are not altered by a similar amount because of the slightly differing sizes. Preferably tuning screws are used for altering the frequency but other means may be employed, such as altering dimensions of a housing within which the resonators are contained.

According to a second aspect of this invention a filter circuit includes a resonator arrangement as described above.

The invention will be further described by way of example with reference to the accompanying drawing in which: Figure 1 illustrates an arrangement of resonators, Figure 2 is an explanatory diagram relating thereto; Figure 3 illustrates schematically a further resonator arrangement; and Figure 4 is an explanatory diagram relating thereto.

With reference to Figures 1 and 2, a resonator arrangement consists of first, second and third dielectric resonators 1, 2 and 3 comprising part of a filter circuit, other elements of which are not shown. In practice the three resonators are mounted in close proximity to each other, within a common enclosure, and are coupled by means of electromagnetic fields to input and output ports.

Adjacent pairs of resonators are coupled to each other by their external electromagnetic fields and each resonator only excites the adjacent one, or ones, in the phase of resonance that allows coupling between them. The resonators 1, 2 and 3 are in cylindrical form and each has a different height and diameter from the others. The dimensions of resonators 1, 2 and 3 are such that they have resonances at frequencies as shown in Figure 2 at lines A, B and C respectively which represent variation in amplitude against frequency. In each case m0 denotes the fundamental mode of resonance, m1 and m2 denote the first and second order modes of resonance respectively and fro to f8 denote the frequencies at which the resonances occur.The dimensions of the resonators are chosen such that the fundamental mode m0 for each of them occurs at the same frequency, i.e. frequencies f0, f3 and f6 are the same. However because each of the resonators has a different height to diameter ratio to that of the others their higher order modes occur at different frequencies. The first order mode m, of resonators 1, 2 and 3 occurs at frequenciesf1, f4 and f7 respectively, these frequencies being different. Similarly their second order modes m2 resonate at frequencies f2, f5 and f8 respectively which are again different and do not coincide with any other resonance frequencies of the resonators 1, 2 and 3.

Hence the fundamental mode of resonance at frequency f0 is reinforced whilst modes resonating at other frequencies are not. The resultant action is an increase in the effect of the resonance frequency f0 in the filter circuit compared to higher order spurious modes.

Referring to Figure 3, an alternative resonator arrangement is shown in which first and second cylindrical dielectric resonators 4 and 5 are of similar, but not identical dimensions and resonate in their natural fundamental modes m0 at frequencies f9 and f10 respectively (as shown in Figure 4 at lines D, E and F in which a notation similar to Figure 2 is used). The higher order modes m, and m2 of the first resonator 4 occur at frequenciesf11 and f12 respectively and the higher order modes m1 and m2 of the second resonator 5 occur at frequencies f13 and f14 respectively.

The first and second resonators 4 and 5 are contained within a housing 6 within which are located two tuning screws 7 and 8. The first screw 7 is arranged to alter the frequencies of the first resonator 4 and the second screw 8 to tune the second resonator 5. The tuning of the resonators 4 and 5 is effected by altering the distance between each screw and the corresponding resonator. In the case of the first resonator 4 this distance is denoted by a and for the second resonator 5 it is denoted byb.

Initially a and b are the same, but because of the dimensions of the resonators 4 and 5 the frequencies f9 and f10 at which they resonate in their fundamental modes m0 are not the same.

The frequencies f11 and f13 differ by a similar amount as do f12 and14.

The resonances in the fundamental mode m0 are then arranged to resonate at the same frequency by adjusting the tuning screw 8 so that a and b are no longer equal. The effect of adjusting the screw 8 on the resonance mode of the second resonator 5 is shown at line F.

After the screw 8 has been adjusted the frequency frO at which the fundamental mode resonates is increased to coincide with the fundamental mode of the first resonator 4, i.e. fg and f10 are equal. However f,3 does not come into coincidence with f,1 ore14 with f.2 because the adjustment of the tuning screw does not affect the modes in a linear fashion, i.e. the frequencies alter by different amounts.

Claims (7)

Claims

1. A resonator arrangement including a plurality of dielectric resonators, each of the resonators being such as to resonate in a plurality of different modes occurring at mutually different frequencies, one of said resonance frequencies being common for all of the plurality of resonators, and at least some of the remaining resonance frequencies of all of the plurality of resonators having mutually different values.

2. Apparatus as claimed in claim 1 and wherein each resonator resonates at the desired frequency in its fundamental mode.

3. Apparatus as claimed in claim 2 and wherein each resonator has different dimensions to the remainder of the said plurality such that it naturally resonates at frequencies different to the remainder of the said plurality in modes other than its fundamental mode.

4. Apparatus as claimed in claim 2 and wherein each resonator is deliberately arranged to have a different natural resonance frequency in its fundamental mode from the remainder of the plurality and including means for tuning the frequency of each resonator such that its fundamental mode is brought to the desired common frequency.

5. Apparatus as claimed in claim 4 and wherein the said means comprises tuning screws.

6. A filter circuit including a resonator arrangement as claimed in any preceding claim.

7. Apparatus substantially as illustrated in and described with reference to Figures 1 and 2 or Figures 3 and 4 of the accompanying drawing.