GB2198302A

GB2198302A - Dielectric resonator oscillator

Info

Publication number: GB2198302A
Application number: GB08628776A
Authority: GB
Inventors: Adrian Nigel Farr
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1986-12-02
Filing date: 1986-12-02
Publication date: 1988-06-08
Anticipated expiration: 2006-12-02
Also published as: GB8628776D0; GB2198302B

Abstract

An injection locked oscillator has its output 12 taken from a third transmission line 9 coupled to the dielectric resonator. The output coupled directly from the resonator has thus already been filtered by the action of the resonator thereby removing unwanted frequencies and eliminating the need for a separate filter at the output. Amplifier 5 provides positive feedback gain for the loop including lines 7, 8 and resonator 8. A reference frequency is injected from oscillator 1 via multiplier 21 which introduces unwanted harmonics. <IMAGE>

Description

A Dielectric Resonator Oscillator This invention relates to a dielectric resonator oscillator hereinafter referred to as a DRO. This comprises an amplifier and a narrow band positive feedback circuit comprising two transmission lines arranged to couple energy into and out of a dielectric resonator. A characteristic advantage of a DRO is that it can have a high fundamental operating frequency and a consequence of this is excellent thermal noise performance. However DROs do not have as good a frequency stability with temperature and age as do bulk crystal oscillators. Neither do they have as good a flicker noise performance at frequency offsets very close to carrier.

In order to benefit from the advantages both of crystal oscillators and DRO1s it has been proposed to use an injection locking technique in which the output of a crystal oscillator is multiplied to the same frequency as the DRO and then injected into the loop of the DRO. The best place to inject the signal from an efficiency point of view is at the input of the loop amplifier of the DRO.

However this means that unwanted harmonics of the crystal oscillator/multiplier arrangement are also amplified and appear at the output. This gives rise to the need for a bulky and expensive filtering element at the output. The present invention aims to overcome this problem.

The invention provides a dielectric resonant oscillator comprising an amplifier and narrow band positive feed back arrangement comprising two transmission lines arranged to couple energy into and out of a dielectric resonator; characterised by a third transmission line arranged to couple energy out of the resonator to provide an output signal.

By employing the invention it is possible to overcome the aforementioned problem because the output has been filtered by the action of the resonant element. Thus the need for a separate filtering element at the output can be eliminated.

One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a schematic illustration of an injection locked DRO constructed in accordance with the invention the DRO being shown with its housing removed to reveal the interior components; Fig. 2 is a cross section through the line Il-Il of Fig. 1 and shows the housing as well as its interior; Fig. 3 is a diagram illustrating the spectrum of the signal at the output of the frequency multiplier of Fig.

1; and Fig. 4 is a diagram similar to Fig. 3 showing the spectrum of the output of the injection locked DRO shown in Fig. 1.

Referring firstly to figure 1 a bulk crystal oscillator 1 produces a signal of frequency fi. This is processed by a frequency multiplier 2 to produce a signal of a wanted frequency 5fi (for this example) which is a microwave frequency. The action of the frequency multiplier 2 however also produces unwanted other harmonics of the basic frequency fi, the spectrum at the output of frequency multiplier 2 being shown on figure 3.

This is passed to a DRO 3 comprising a substrate 4 carrying an amplifier 5, a dielectric resonant element 6 and three strip lines 7, 8 and 9. A tuning element 10 (Fig. 2) can be adjusted by turning a screw 11 which is threaded into the lid of a housing 12, the latter being shown in figure 2 but omitted from figure 1.

The input to the DRO 3 passes to the amplifier 5 where all the frequency components shown in figure 3 are amplified and then applied to the strip line 7 located adjacent to the dielectric resonator 6. The fi component of the input thus couples into the resonator 6 because the latter is resonant at that frequency. The resonant element 6, in resonating induces a signal in the strip line 8 which is fed back to the input of the amplifier 5 to provide the narrow band positive feedback required to establish DRO oscillation.

Normal practices would lead one to take an output from the right hand end of the strip line 7 and to filter the resulting signal to remove the unwanted harmonics.

Such a filter would however be bulky and add to the expense of the equipment. Instead, in this system the output is taken from a third strip line 9. This is located in the neighbourhood of the dielectric resonator 6, but in such a way as to minimise direct coupling from the other two lines (7 and 8), so that, like strip line 8, it has induced in it a signal of frequency 5fi. There is no need to filter this since the other harmonics have already been alternated by the action of the resonator 6.

This is therefore presented on line 12 as the output of the system.

Claims

1. A dielectric resonator oscillator comprising an amplifier and a narrow band positive feed back arrangement comprising two transmission lines arranged to couple energy into and out of a dielectric resonator; characterised by a third transmission line arranged to couple energy out of the resonator to provide an output signal.

2. An injection locked dielectric resonator oscillator comprising means for generating a first signal having a wanted frequency component and a number of unwanted frequency components; an amplifier for amplifying the first signal; a dielectric resonator; a first transmission line arranged to couple the signal at the output of the amplifier into the dielectric resonator to excite resonance thereof; a second transmission line arranged to couple energy out of the resonator; and means for feeding the energy thus coupled out into the input of the amplifier to provide a narrow band filter passing the wanted but not the unwanted frequencies; characterised by a third transmission line also arranged to couple energy out of the resonator to provide an output signal.

3. An injection locked dielectric resonator oscillator according to claim 1 in which the means for generating the first signal comprises a low frequency oscillator; and means for multiplying the frequency of its output to produce the said wanted and unwanted frequencies.

4. An injection locked dielectric resonator oscillator substantially as described with reference to figures 1 and 2 of the accompanying drawings and substantially as illustrated therein.

5. A dielectric resonant oscillator substantially as described with reference to figures 1 and 2 of the accompanying drawings.