Abstract:
A microwave oscillator includes at least two active components and a dielectric resonator. The coupling between each active component and the dielectric resonator is of the transmission type and the inputs of neighboring active components are connected to a first point coupled to the resonator and likewise the outputs of the active components are connected to a second point coupled to the resonator. A push-push oscillator of the above kind is simple to produce and its operation is relatively insensitive to adjustments.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a microwave oscillator with dielectric resonator. 
     2. Description of the Prior Art 
     Microwave oscillators with a dielectric resonator are routinely used in the electronics art. They are basic components of many circuits, in particular in the field of television or telecommunications. 
     An oscillator of this kind has an active part with an amplifier or negative impedance and a passive part including the dielectric resonator. 
     The active part and the passive part can be coupled by reflection or by transmission. 
     FIG. 1 shows a prior art set-up using transmission. 
     In this set-up, the active component is an amplifier  10  and the dielectric resonator  12  is in series in a feedback loop connecting the output  11  of the amplifier  10  to its input  13 . 
     The line  14  connected to the output  11  of the amplifier  10  is magnetically coupled to the resonator  12 . Similarly, the input line  16  is magnetically coupled to the resonator  12 . The coupling between the resonator  12  and each of the lines  14 ,  16  therefore increases as the current in the line increases. This is why a line  18  of length λ/4 is generally provided at the input to provide a short circuit and thereby maximize the current. λ is the wavelength corresponding to the frequency of the oscillator. 
     An oscillator of the above kind must conventionally satisfy two conditions, namely, on the one hand, the condition that the gain of the amplifier  10  must be greater than the losses of the feedback circuit between the output  11  and the input  13  and, on the other hand, the condition that there must be zero phase shift (modulo 2π) of the signals across the circuit. To satisfy the second condition, the points at which the conductors  14  and  16  are coupled to the resonator  12  are diametrally opposed relative to the disk-shaped resonator, for example. Under these conditions, the resonator introduces a phase shift of π radians and the amplifier  10  and the associated lines introduce a complementary phase shift of π radians. 
     This type of oscillator has the advantage of being highly reproducible: it therefore lends itself to mass production as it requires few adjustments. On the other hand, it is not always easy to design because two couplings have to be determined: the couplings between the resonator and the lines  14  and  16 . Furthermore, as it is necessary to provide a line  18  whose length is a function of the wavelength in order to produce the short circuit, the bandwidth of the associated circuit is small. 
     FIG. 2 shows a reflection type dielectric resonator oscillator which has two active components  20  and  22  and a dielectric resonator  24 . 
     Each active component is coupled to the resonator  24  by reflection. The resonator reflects a wave emitted by an active component back to the active component, which amplifies it. For oscillation to be obtained it is also necessary to satisfy two conditions: the gain of the active component must be greater than the losses and the reflected waves must be in phase with the emitted waves. The second condition is satisfied by adjusting the distance between the coupling plane of the resonator and the ports of the active components. 
     In the so-called “push-push” set-up shown in FIG. 2, the oscillations produced are in antiphase because the point  23  at which the active component  22  is coupled to the disk-shaped resonator  24  is diametrally opposite the point  21  at which the active component  20  is coupled to the resonator  24 . These waves in antiphase are transferred to an output point  32  by a combiner with lines  28  and  30 . 
     In a set-up of this kind the resonator  24  is between two microstrip lines  23   1  and  23   2 . The function of the resonator is to enable oscillation and to maintain the signals of the two oscillators in antiphase. It has been found that the oscillations are not maintained in antiphase correctly, which degrades performance, if oscillation does not occur at exactly the resonant frequency of the resonator. In fact, the oscillator is intended to supply a frequency 2f 0  which is twice the fundamental frequency f 0  by exploiting the fact that the output waves are in antiphase at the frequency f 0  but cannot be in phase at double the frequency. The combiner with lines  28  and  30  eliminates the waves which are in antiphase and adds the waves which are in phase. However, because the characteristics of the combiner necessarily depend on the frequency f 0 , it is clear that the fundamental frequency will not be completely eliminated if oscillation occurs at a different frequency. 
     Note also that the resonator  24 , having to be exactly symmetrical relative to the lines  23   1  and  23   2 , is not easy to position, which is a particularly serious problem, especially in mass production. Furthermore, it requires manual adjustment, in particular of the impedance  34  connecting an electrode of the active component  20  or  22  to ground. However, the advantage of this set-up is its low phase noise. 
     The object of the invention is to provide a microwave oscillator which delivers a wave at the frequency 2f 0  using a resonator which resonates at the frequency f 0 , which is easy to manufacture and whose operating parameters are relatively insensitive to adjustments. 
     The oscillator according to the invention includes at least two active components and a dielectric resonator and the coupling between each active component and the dielectric resonator is of the transmission type, the set-up being such that the input and the output of each active component are in antiphase at the resonant frequency of the resonator and the inputs of neighboring active components are connected to a first point coupled to the resonator and likewise the outputs of the active components are connected to a second point coupled to the resonator, the coupling of the ports to the resonator being such that they are practically short circuited. 
     In other words, it is the simultaneous presence of the active components that enables oscillation and the oscillations of two neighboring oscillators are synchronized with a phase difference of 180°. Accordingly, compared to the “push-push” structure shown in FIG. 2, the resonator enables one or other of the basic oscillators to oscillate but is not required to maintain a phase difference of 180° between the signals from the two oscillators. In other words, in the oscillator according to the invention, the two basic oscillators are synchronized independently of the resonator. 
     This makes the oscillator less sensitive to the parameters of the resonator. 
     Because the resonator of the oscillator according to the invention does not have to provide the phase difference of 180° between the oscillations produced by each of the basic oscillators, it is not necessary for the resonator to be exactly symmetrical relative to the first and second ports, whereas in the “push-push” circuit oscillator shown in FIG. 2 the resonator  24  must be symmetrical relative to the lines  23   1  and  23   2 . The invention therefore enables different decouplings between the resonator and, on the one hand, the first port and, on the other hand, the second port. 
     Note also that, to obtain the antiphase relationship between the waves supplied by each of the active components, it is not necessary to provide a combiner hose line lengths depend on λ, as is the case in the “push-push” set-up of FIG.  2 . he associated circuit can therefore have a greater bandwidth than prior art set-ups like those shown in FIGS. 1 and 2. 
     Furthermore, note that, compared to an oscillator having a single active component and coupled to a dielectric resonator by transmission (FIG.  1 ), the short circuit is obtained without it being necessary to provide a line having a length of a quarter-wavelength. 
     Over and above this, compared to the “push-push” set-up, the fact that a combiner is not necessary simplifies designing the oscillator. 
     SUMMARY OF THE INVENTION 
     The invention provides a microwave oscillator including at least two active components and a dielectric resonator and wherein the coupling between each active component and the dielectric resonator is of the transmission type and inputs of neighboring active components are connected to a first point coupled to the resonator and likewise outputs of the active component are connected to a second point coupled to the resonator. 
     In one embodiment waves in the lines terminating at the first coupling point are in antiphase and likewise waves in the lines terminating at the second coupling point are in antiphase. 
     The active components can be practically identical, the length of the lines connecting the first coupling point to the inputs of the active components can be practically equal and the lengths of the lines connecting the second coupling point to the outputs of the active components can be substantially equal. 
     The oscillator preferably includes an even number of active components associated with a single resonator. 
     The active components each include an amplifier, for example. 
     In one embodiment the resonator is circular and the coupling points are at diametrally opposite positions relative to the resonator. 
     The dielectric resonator has a resonant frequency chosen so that the oscillator has a frequency in the band from 10 GHz to 15 GHz, for example. 
     The invention also provides a method of producing an oscillator as defined above starting from an active component and a resonator, in which method a line of length λ/4 is connected to the first and second coupling points to provide short circuits, the distance of the coupling points from the resonator is adjusted to minimize feedback whilst maintaining the oscillation obtained with the active component, the lines of length λ/4 are removed and at least one other active component is installed at the coupling point(s). 
     Other features and advantages of the invention will become apparent from the description of embodiments of the invention which is given with reference to the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIGS. 1 and 2, already described, show prior art oscillators. 
     FIG. 3 is a block diagram of an oscillator according to the invention which has two active components. 
     FIG. 4 is a block diagram of another embodiment of an oscillator according to the invention, which has four active components. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The oscillator shown in FIG. 3 has two active components  40  and  42  and a dielectric resonator  44 . In this embodiment the active components  40  and  42  are amplifiers. The dielectric resonator  44  is mounted in transmission in the feedback loop of each of the amplifiers  40  and  42  so that the coupling ports  46  and  48  practically constitute virtual grounds or short circuits. In this embodiment the resonator  44  is in the form of a disk and the ports  46  and  48  are at diametrally opposite positions relative to the disk. 
     Thus it can be seen that the output of the amplifier  40  is connected by a conductor  50  to the port  46 . Similarly, a line  52  connects the output of the amplifier  42  to the port  46 . 
     In an analogous manner, a line  54  connects the input of the amplifier  40  to the port  48  and a line  56  connects the input of the amplifier  42  to the port  48 . 
     As already mentioned, to obtain a zero phase shift (module 2π) for a wave passing through an amplifier and the resonator  44  and returning to the input of the same amplifier, the amplifier and the associated lines must introduce a phase shift of π if the resonator introduces a phase shift of π. If the resonator introduces a phase shift other than π, the remainder of the circuit must introduce a phase shift that is its 2π&#39;s complement. 
     To obtain short circuits at the ports  46  and  48  the active components  40  and  42  are preferably identical and the lengths of the lines  50  and  52  are preferably equal. Likewise, the lengths of the lines  54  and  56  are also preferably equal. However, the antiphase relationship at the ports  46  and  48  between the oscillations of the two basic oscillators (and therefore the aforementioned short circuits) is obtained even if the components  40  and  42  are not identical and/or the lengths of the lines are not equal, because of the action of one basic oscillator on the other one. 
     One of the oscillators shown in FIG. 3 can be designed in the following manner: 
     The design process starts with an active component, for example the active component  40 , of the resonator  44 , the port  46  and the line  50  and the port  48  and the line  54 . The active component  42  and the lines  52  and  56  are initially not provided. 
     A line of length λ/4 (not shown) analogous to the line  18  from FIG. 1 is fitted at the ports  46  and  48  to obtain short circuits at those ports. 
     The distances of the ports  46  and  48  from the resonator are then adjusted to optimize the feedback. 
     After this operation the lines of length λ/4 are removed. Under these conditions oscillation is no longer obtained. 
     The active component  42  with the lines  52  and  56  is then installed. The signals from the two basic oscillators with active components  40  and  42  then automatically assume an antiphase relationship. The two oscillators are synchronized to 180°, i.e. practically form short circuits at the ports  46  and  48 , independently of the characteristics of the resonator. 
     The oscillator operates at twice the resonant frequency of the resonator  44 . It is highly stable and has low phase noise. It does not require manual adjustment. It can therefore easily be mass produced by automated plant. Also, as already mentioned, the associated circuits can have a relatively large bandwidth. Furthermore, it is not necessary to provide a combiner as in a standard “push-push” set-up. 
     The output signal of the oscillator is obtained with the aid of an antenna (not shown) coupled to the housing containing the components  40 ,  42  and  44 , for example. 
     It can operate throughout the microwave range, i.e. from 500 MHz to 60 GHz. It gives particularly good results in the Ku band from 10 GHz to 15 GHz. It is useful in particular in the field of telecommunications and/or digital television signal transmission. 
     In the embodiment shown in FIG. 4 the oscillator includes a resonator  44  associated with four basic oscillators, i.e. four active components,  60 ,  62 ,  64  and  66 . The active components are amplifiers which are arranged so that the input of one amplifier is connected to the input of a neighboring amplifier via a corresponding port  70 ,  72  and the output of each amplifier is connected to the output of another neighboring amplifier via respective ports  74  and  76 . 
     Thus the port  70  is connected to the inputs of the amplifiers  60  and  62  and the port  72  is connected to the inputs of the amplifiers  64  and  66 . The port  74  is connected to the outputs of the amplifiers  60  and  66  and the port  76  is connected to the outputs of the amplifiers  62  and  64 . 
     As in the FIG. 3 set-up, positions of the ports are chosen so that the input and the output of each amplifier are practically in antiphase. 
     Moreover, each basic oscillator operates in antiphase with the neighboring basic oscillator, i.e. the ports  70 ,  72 ,  74 ,  76  practically constitute short circuits or virtual grounds. Thus, for example, the basic oscillator with the active element  60  produces oscillations in antiphase with the oscillations of the basic oscillator with the active component  62  and in antiphase with the oscillations of the basic oscillator with the active component  66 . 
     As in the embodiment described with reference to FIG. 3, the oscillator with four active components oscillates at twice the frequency of the resonator. Note that in this embodiment two non-adjacent oscillators are in phase. 
     The advantage of the FIG. 4 set-up over that shown in FIG. 3 is that it delivers a higher power and its phase noise is even lower. 
     Generally speaking, the set-up can include an even number of active components.