WO2016066227A1

WO2016066227A1 - An electrically tunable oscillator

Info

Publication number: WO2016066227A1
Application number: PCT/EP2014/073490
Authority: WO
Inventors: Mingquan Bao; Per Ligander
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-10-31
Filing date: 2014-10-31
Publication date: 2016-05-06

Abstract

The present invention relates to an oscillator device (1) comprising a first amplifier unit (2) and a waveguide cavity resonator (3) with a cavity (11) and a first tuning device (4) mounted in the cavity (11). The cavity (11) has a first cavity length (a) running between two opposing inner walls (5,6) where a resonance frequency (f_r) of the resonator (3) is dependent on the first cavity length (a). The first tuning device (4) comprises at least one row (13, 14, 15) of switches (16) that are electrically openable and closable. Each row (13, 14, 15) is arranged to constitute an electrically conducting connection between said opposing inner walls (7, 8) when the switches of said row are closed. The first amplifier unit (2) is electrically connected to the waveguide cavity resonator (3) by means of a first (35) and a second connector (36) which are mutually out of phase with each other. The first amplifier unit (2) further comprises a first amplifier arrangement (37) and a tuneable bias connection (38).

Description

TITLE

An electrically tunable oscillator TECHNICAL FIELD

The present invention relates to an oscillator device comprising a first amplifier unit and a waveguide cavity resonator, where the waveguide cavity resonator comprises a cavity and a first tuning device arranged for mounting in the cavity. The cavity has a first cavity length running between two opposing inner walls of the cavity, where a resonance frequency of the waveguide cavity resonator is dependent on the first cavity length. The first tuning device comprises a non-conducting laminate on which at least one row of switches is placed, where said switches are electrically openable and closable and each row is arranged to constitute an electrically conducting connection between said opposing inner walls when the switches of said row are closed.

BACKGROUND

Oscillators are used for delivering a signal with a predetermined frequency, which may be adjustable. However, all oscillators that are set to a certain frequency tend to vary slightly around said frequency. This variation is known as phase noise.

In order to achieve low phase noise in an oscillator, it is well known that one of the main contributing parameters is the losses of the resonator, measured by its so-called Q value, where a high Q means low losses and low phase noise. Especially for a Voltage Controlled Oscillator (VCO) where an electrical tuning element is coupled to the resonator, it is very difficult to acquire a low phase noise. There exist a vast number of different technologies for realizing an oscillator. Basically, an oscillator is formed by an amplifier that is coupled to a resonator, where the resonator normally incorporates the tuning element and where the degree of coupling of the tuning element to the resonator determines the relative tuning bandwidth. Normal ranges for the tuning vary from single percentages to about 30 percentages.

A resonator can be built from microstrip or stripline structures on a substrate. It can also be built from discrete LC components, dielectric resonators, waveguide cavities or variants of these. The tuning element can be a varactor diode, ferroelectric material or some other variable reactance structure. The total Q of a resonator structure depends on the combined resistive losses of the respective components. In all existing resonator structures, the common problem is that as soon as a tuning element is coupled to a resonator such as a cavity, the losses of the tuning element will lower the Q and thereby the phase noise will be increased. The tighter the coupling between the tuning element and the resonator is, the wider bandwidths may be obtained, but also the more losses occur, and then the phase noise is increased.

However, tuning of a waveguide filter which is used as a resonator in oscillators and other waveguide structures using pin diodes, ferroelectrics etc., will affect the general electrical performance of the waveguide filter in a negative way. One of the absolute major problems is the resulting low effective Q-factor when for example using pin diodes or ferroelectric structures in a waveguide filter, which in turn results in high losses. One way to obtain tuning of waveguide E-plane filters is described in WO 2012/016584, where at least one row of switches is used for creating a virtual wall that is possible to turn on and turn off. Such switches may for example be realized by means of MEMS (Micro Electro Mechanical Systems). Such an arrangement provides a far better Q-factor than previous arrangements, and provides a possibility for coarse tuning. However, there is still a desire to obtain a possibility for fine tuning without increasing the losses.

There is thus a need for an enhanced oscillator device, where coarse tuning and fine tuning is obtained with a phase noise that is lower than in previously available arrangements.

SUMMARY

The object of the present invention is to provide an enhanced oscillator device, where coarse tuning and fine tuning is obtained with a phase noise that is lower than in previously available arrangements.

This object is achieved by means of an oscillator device comprising a first amplifier unit and a waveguide cavity resonator, where the waveguide cavity resonator comprises a cavity and a first tuning device arranged for mounting in the cavity. The cavity has a first cavity length running between two opposing inner walls of the cavity, where a resonance frequency of the waveguide cavity resonator is dependent on the first cavity length. The first tuning device comprises a non-conducting laminate on which at least one row of switches is placed, where said switches are electrically openable and closable and each row is arranged to constitute an electrically conducting connection between said opposing inner walls when the switches of said row are closed. The first amplifier unit is arranged to be electrically connected to the waveguide cavity resonator by means of a first connector and a second connector, where said connectors are mutually out of phase with each other. The first amplifier unit further comprises a first amplifier arrangement and a tuneable bias connection, and the first amplifier unit is comprised in a second tuning device.

According to an example, the first tuning device is arranged for altering the first cavity length between at least two values such that the resonance frequency of the waveguide cavity resonator is adjustable between at least two corresponding magnitudes. The tuneable bias connection is arranged for adjusting the resonance frequency of the waveguide cavity resonator within a certain frequency span.

According to another example, the waveguide cavity resonator comprises a first inner wall, a second inner wall, a third inner wall and a fourth inner wall. The first inner wall and the second inner wall are facing each other and are separated by a first cavity length, and the third inner wall and the fourth inner wall are facing each other and are separated by a second cavity length. A fifth inner wall and a sixth inner wall are mounted to at least one of said first inner wall, second inner wall, third inner wall and fourth inner wall. The fifth inner wall and the sixth inner wall are facing each other and are separated by a third cavity length such that the cavity is formed and is limited by the inner walls which are constituted by respective main surfaces and are electrically conducting.

According to another example, the waveguide cavity resonator is in the form of a surface-mountable waveguide cavity resonator that is arranged to be mounted to a printed circuit board (PCB) such that a metallization on the PCB constitutes the first inner wall.

According to another example, the first tuning device is placed on the second inner wall and is arranged to alter the distance between the first inner wall and the second inner wall. The first tuning device may comprise switches of the type Micro Electro Mechanical Systems (MEMS). According to another example, each amplifier arrangement comprises a differential amplifier where a differential output is electrically connected to the corresponding connectors. For example, each differential amplifier may comprise a first transistor and a second transistor. The transistors are arranged to amplify signals received from the waveguide cavity resonator, and to reflect the amplified signals back to the waveguide cavity resonator. Other examples are evident from the dependent claims.

A number of advantages are obtained by means of the present invention, for example:

high Q-factor,

- low loss,

low phase noise for an electrically tunable oscillator, increased dynamic range,

lowered sensitivity to external and internal noise,

common-mode noise, e.g. from a DC power supply, is suppressed, and signal power is doubled,

balanced topology, and

boosted signal power.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail with reference to the appended drawings, where:

Figure 1 shows a schematic perspective view of an oscillator according to the present invention; Figure 2 shows a schematic bottom view of an oscillator according to a first example of the present invention;

Figure 3 shows a schematic cut-open side view of the oscillator device in

Figure 2:

Figure 4 shows a schematic circuit diagram of a first example of a differential amplifier; Figure 5 shows a schematic circuit diagram of a second example of a differential amplifier;

Figure 6 shows a schematic bottom view of an oscillator according to a second example of the present invention;

Figure 7 shows a simplified view of a substrate with a MEMS structure as used in the present invention;

Figure 8 shows the different states of each switch of a MEMS structure as used in the present invention;

Figure 9 shows a schematic top view, side view and sectional view of a waveguide cavity resonator with MEMS structures in a first open state; and

Figure 10 shows a schematic top view, side view and sectional view of a waveguide cavity resonator with MEMS structures in a second closed state. DETAILED DESCRIPTION With reference to Figure 1 , showing a perspective view of an oscillator device, there is an oscillator device 1 which comprises an amplifier unit 2 and a waveguide cavity resonator 3. The waveguide cavity resonator 3 comprises a first inner wall 5, a second inner wall 6, a third inner wall 7 a fourth inner wall 8, a fifth inner wall 9 and a sixth inner wall 10.

For reasons of clarity, only the inner walls are indicated in Figure 1 although, in practice, the walls have a certain thickness with an outer side and an inner side and may be referred to as walls as well as inner walls in the description. It should be understood that in this context, it is electrically conducting surfaces of the inner walls that define the cavities in question as will be discussed below.

The first inner wall 5 and the second inner wall 6 are facing each other and are separated by a first cavity length a. The third inner wall 7 and the fourth inner wall 8 are facing each other and are separated by a second cavity length b. The fifth inner wall 9 is mounted to the second inner wall 6, the third inner wall 7 and the fourth inner wall 8, while the sixth inner wall 10 is mounted to the first inner wall 5, the second inner wall 6, third inner wall 7 and fourth inner wall 8.

The fifth inner wall 9 and the sixth inner 10 wall are facing each other and are separated by a third cavity length L such that a cavity 1 1 is formed and is limited by the inner walls 5, 6, 7, 8, 9, 10. These inner walls 5, 6, 7, 8, 9, 10 are constituted by respective main surfaces and are electrically conducting. In this example, the waveguide cavity resonator 3 is in the form of a surface- mounted waveguide cavity resonator 3 that is mounted to a printed circuit board (PCB) 17 such that a first metallization 18 on a first side 52 of the PCB 17 comprises the first inner wall 5. The PCB comprises a second metallization 53 on a second side 54 of the PCB 17, where the second metallization 53 constitutes a ground plane.

In the following, reference is also made to Figure 7 that shows a simplified view of a substrate with a MEMS structure as used in the present invention, Figure 8 that shows the different states of each switch of a MEMS structure as used in the present invention, Figure 9 that shows a schematic top view, side view and sectional view of a waveguide cavity resonator with MEMS structures in a first open state and Figure 10 that shows a schematic top view, side view and sectional view of a waveguide cavity resonator with MEMS structures in a second closed state.

The waveguide cavity resonator 3 further comprises a first tuning element 4 which is arranged for altering the second cavity length a between a first value aeffi and a second value a_eff2 such that a resonance frequency f_r of the waveguide cavity resonator 3 is adjustable between two corresponding magnitudes.

The size of the waveguide cavity resonator 3 is thus altered in steps between two values, which results in different resonance frequencies. In order to achieve this, the first tuning element 4 comprises three rows 13, 14, 15 of switches 16. The switches 16 are electrically openable and closable and are arranged to constitute an electrically conducting connection between the third inner wall 7 and the fourth inner wall 8.

The switches 16 are of the type Micro Electro Mechanical Systems (MEMS), the switches being cantilever switches 16 and are positioned on a MEMS substrate 12. The MEMS substrate 12 serves as a carrier material, and is mounted on the second inner wall 6. A magnification 31 of a part of the first tuning element 4 with the MEMS switches 16 is shown in a magnifying circle in Figure 1 .

In Figure 7, one MEMS structure forming the first tuning element 4 is shown with the 3 rows 13, 14, 15 of switches 16. The switches 16 are electrically controlled by means of bias voltages, which are applied at certain bias inputs 48. A common ground pad 32 is used. When no bias voltage is applied, the switches 16 in a corresponding row 13, 14, 15 are open, and when voltage is applied, the switches 16 in a corresponding row 13, 14, 15 will be closed.

This is illustrated in detail in Figure 8, where, in a first state where bias voltage is applied, one shown switch 16 is closed, and can be regarded as equivalent to a resistor R. In a second state where no bias voltage is applied, the shown switch 16 is open, and can be regarded as equivalent to a capacitor C.

How the tuning is performed by means of the MEMS structure 1 will now be explained more in detail with reference to Figure 9 and Figure 10, where each of these Figures shows a simplified top view, side view and sectional view of the waveguide cavity resonator 3.

As shown, the first tuning element 4 is mounted to the first inner wall. The substrate 8 comprises a conducting frame 33 with vias 34. In this way, a good electrical connection between the rows 13, 14, 15 of switches 16 and the surrounding third inner wall 7 and fourth inner wall 8 is ensured. In Figure 9, the switches 16 are opened, and in this state the first tuning element 4 does not affect the original electrical dimension of the waveguide cavity resonator 3, the first length a having the first value a_eff i -

In Figure 10, the switches 16 are closed such that each row 13, 14, 15 constitutes a electrically conducting connection between the third inner wall 7 and the fourth inner wall 8 via the conducting frame 33. In this way, the electrical dimension of the second length a is altered from the first value a_em to the second value a_eff2, which here is a minimum value.

In Figure 10, the electric dimension of the cavity 1 1 is not defined only by the inner walls 5, 6, 7, 8, 9, 10, but also of an artificial wall which primarily is constituted by the rows 13, 14, 15 of closed switches 16 that constitute electrically conducting connections. The artificial wall confines the electric field and makes the cavity 1 1 electrically smaller which makes the resonance frequency higher than when the switches 16 are opened.

When the switches 16 are opened again, as shown in Figure 9, the field will be confined by the inner walls 5, 6, 7, 8, 9, 10 only. The waveguide cavity resonator 3 will be electrically larger, which makes the resonance frequency lower than when the switches 16 are closed.

The present invention will now be described with reference to Figure 1 , Figure 2, Figure 3 and Figure 4, where Figure 2 shows a bottom view of a first example of the oscillator device 1 , Figure 3 shows a cut-open side view of the oscillator device 1 in Figure 2, and Figure 4 shows a circuit diagram of an amplifier arrangement. According to the present invention, the first amplifier unit 2 is arranged to be electrically connected to the waveguide cavity resonator 3 by means of a first connector 35 and a second connector 36, where the connectors 35, 36 are mutually out of phase with each other, i.e. their mutual phase difference is 180°. The first amplifier unit 2 is comprised in a second tuning device, and further comprises a first amplifier arrangement 37 and a tuneable bias connection 38.

The first amplifier unit 2 is positioned outside the cavity 1 1 and is arranged to be electromagnetically connected to the cavity 1 1 via an opening 21 in the metallization of the first inner wall 5, which opening 21 constitutes a waveguide port and is at least partly surrounded by vias 55 that electrically connect the first metallization 18 and the second metallization 53.

The waveguide port 21 comprises a coupling arrangement 22 that in turn comprises a first coupling patch 23 and a second coupling patch 24, where the first coupling patch 23 is connected to the first connector 35 and the second coupling patch 24 is connected to the first connector 36, the coupling patches having a triangular shape and joining the surrounding first metallization 18 on the PCB 17. A shorting back housing 56 is mounted opposite the waveguide cavity resonator 3, providing a shorting back for the waveguide port 21 .

In this example, the first amplifier arrangement 37 is connected to the first connector 35 and the second connector 36 by means of a corresponding first bond wire 57 and second bond wire 58. With special reference to Figure 4, the first amplifier arrangement 37 comprises a differential amplifier 44 where a differential output 46, 47 is electrically connected to the corresponding first connector 35 and second connector 36 via the bond wires 57, 58. The differential amplifier 44 comprises a first transistor Qi_A and a second transistor Qi _B, where these transistors QIA, QIB are arranged to amplify signals received from the waveguide cavity resonator 3 and to reflect the amplified signals back to the waveguide cavity resonator 3. A first parasitic capacitance Cbc_A is present across the base and collector of the first transistor Q _A, and a second parasitic capacitance Cb_C is present across the base and collector of the second transistor Qi_B. In order to tune the oscillation frequency, the transistor's bias is varied at the tuneable bias connection 38 comprised in a first tuning arrangement 59. The emitters of the first transistor Qi_A and the second transistor Qi_B are connected to a common DC current source which is comprised in the first tuning arrangement 59 and which comprises a first bias transistor Q₂A and a second bias transistor Q₂B- The DC current can be varied by changing the bias voltage, constituting a tuning voltage V_tune, that is connected with the diode configured bias transistors Q₂B via a bias resistor R_c. As the DC current is varied by varying the tuning voltage V_tune, the voltage swing at the respective collector of the first transistor Qi_A and the second transistor Qi_B changes too, and then also an equivalent DC voltage. Thus, the capacitances of Cbc_A and Cbc_B are changed. Those two capacitances will be coupled to the resonator and tune the oscillation frequency.

If bonding wires are used, the bonding wires 57, 58 constitute respective inductances that may have to be taken into account.

A first differential signal output 60 and a second differential signal output 61 are each arranged to output signals received from the collectors of the first transistor Qi_A and the second transistor Qi_B via a respective relatively small output capacitor C3_A, C3b to avoid loading the resonator from a possible outside load of for example 50Ω (not shown). However, a trade-off between the influence of the outside loading and the available output power has to be made when selecting these output capacitors C3_A, C3b- The differential signal outputs 60, 61 are also schematically indicated in Figure 1 , Figure 2 and Figure 6 as well. The collector of the first transistor Qi_A is connected to a DC collector voltage supply Vcc via a first AC choke inductor L_CIA which prevents the AC signal from being grounded. Correspondingly, the collector of the second transistor QIB is connected to the DC collector voltage supply V_CC via a second AC choke inductor L_CIB-

The base of the first transistor Qi_A is connected to a DC base voltage supply V_b via a first base bias resistor R_bA which should be large enough to block the AC signal. Correspondingly, the base of the second transistor Qi _B is connected to the DC base voltage supply V_b via a second base bias resistor

The collector of the first transistor Qi_A is connected to the base of the second transistor Qi _B via a first decoupling capacitor CIA, and the collector of the second transistor Qi _B is connected to the base of the first transistor Qi_A via a second decoupling capacitor CIB. The first decoupling capacitors CIA and the second decoupling capacitor CIB should have a respective impedance that is much smaller than that of the corresponding first parasitic capacitance CbcA and second parasitic capacitance CbcB-

The first bonding wire 57 is connected in series with a third decoupling capacitor C2A, and the second bonding wire 58 is connected in series with a fourth decoupling capacitor C2B- The third decoupling capacitor C2A and the fourth decoupling capacitor C2B should have a respective impedance that is much smaller than that of the inductance comprised in the respective series connected bonding wire 57, 58.

By choosing the decoupling capacitors C 1A, CIB, C2A C2B according to the above, the contributions of the decoupling capacitors CIA, CIB, C2A C2B to the oscillation frequency can, practically, be ignored. With reference to Figure 5, an alternative amplifier arrangement 49 comprises an alternative differential amplifier 45, where the difference to the previously described differential amplifier 44 lies in that the alternative differential amplifier 45 comprises a second tuning arrangement 62; all other components are identical and have the same reference numbers. Here, the oscillation frequency can be tuned continuously by changing the base bias voltage, constituting a tuning voltage V_tune, of a bias transistor Q₃, which alters a DC bias current l_bi_as- A bias capacitor C_e is connected over the collector of the bias transistor Q₃ and ground, and the emitter of the bias transistor Q₃ is connected to ground.

With reference to Figure 6, that mainly corresponds to Figure 5, a second example of an oscillator device is shown. Here, an oscillator device V comprises a second amplifier unit 39 that is arranged to be electrically connected to the waveguide cavity resonator 3' by means of a third connector 40 and a fourth connector 41 . As for the first amplifier unit 2, the third connector 40 and fourth connector 41 are mutually out of phase with each other. The second amplifier unit 39 further comprises a second amplifier arrangement 42 and a tuneable bias connection 43. The second amplifier unit 39 is also comprised in the second tuning device.

The second amplifier unit 39 is positioned outside the cavity 1 1 and is arranged to be electromagnetically connected to the cavity 1 1 via an opening 21 ' in the metallization of the first inner wall 5', which opening 21 ' constitutes a waveguide port and is at least partly surrounded by vias 55' as in the case with only one amplifier unit 2.

Also for the second amplifier unit 39, the waveguide port 21 ' comprises a coupling arrangement 22' that in turn comprises the first coupling patch 23 and the second coupling patch 24 for the first amplifier unit 2, and also a first coupling patch 50 and a second coupling patch 51 for the second amplifier unit 39. A shorting back housing 56' is mounted as in the first example. The second amplifier arrangement 42 is connected to the third connector 40 and the fourth connector 41 by means of a corresponding third bond wire 65 and fourth bond wire 66. The second amplifier arrangement 42 comprises a differential amplifier that is of the same kind as the differential amplifiers 44, 45 described previously for the first amplifier arrangement 37. Corresponding differential signal outputs 63, 64; 66, 67 are schematically indicated in Figure 6. The present invention is not limited to the examples discussed above, but may vary freely within the scope of the appended claims. For example, more than one of the disclosed first tuning element 4 may be used, a number of tuning elements may be stacked, allowing tuning in several steps. Other types of connections are conceivable between each amplifier unit and the cavity 1 1 , for example by means of bond wires or other types of probes that enter the cavity via an opening in the cavity resonator 3. If a waveguide port is not used, the fifth wall may also be used for mounting of at least one first tuning element.

The coupling to the cavity 1 1 may be performed in any suitable way, either by electrical or magnetically coupled probes to achieve the desired feedback. Instead of the bond wires 57, 58; 65, 66 that connect each amplifier arrangement 37, 42 to the corresponding first connector 35, 40 and second connector 36, 41 , other connecting means or method may be used, for example flip-chip.

The waveguide cavity resonator 3 has been shown to be in the form of a Surface Mountable Waveguide (SMW) part mounted to a PCB 17. Other arrangements are of course conceivable, for example the cavity resonator may be formed by electrically conducting parts that are connected to one or more amplifier units according to the above in any convenient manner, for example by means of bond wires or similar probes as mentioned above.

It is also conceivable that each wall of the cavity resonator 3 that has a first tuning element 4 is constituted by a PCB where the rows of switches are present on a side of the PCB that faces the interior of the cavity 1 1 , and where a ground plane is present on the other side. The ground plane then constitutes the wall itself. Many other ways of obtaining the cavity resonator are of course conceivable, for example one or more plastic parts that have an electrically conducting coating are conceivable.

One or more bias connections (not shown) may be placed in one or more internal layers of the PCB 17. The first tuning element 4 provides a relatively coarse adjustment of the oscillator device 1 , i.e., the oscillation frequency changes discretely with certain frequency steps, ηΔί (n=1 ,2,3...) depending on the number of first tuning elements used, and the second tuning element 2, 39 provides a relatively fine adjustment of the oscillator device 1 , i.e., the oscillation frequency changes continuously within one frequency step, Δί

The waveguide cavity resonator may have other shapes where the present invention still is applicable, for example cylindrical or polygonal. Each tuning element has been described as a MEMS structure based on cantilever switches, but other electrically controllable switch structures that are able to create an electrically conducting connection between two opposing inner walls, such that a virtual wall is created, may be used. Where MEMS structures are used, the number of rows and the general constitution of the MEMS structure are only given as an example and may of course vary. There may be any suitable switch arrangement constituting such a MEMS structure. There does not have to be any vias or conducting frame, but there has to be an electrical connection via the rows 13, 14, 15 of switches 16 and the surrounding third inner wall 7 and fourth inner wall 8 when the switches 16 are closed

Also, a MEMS structure does not have to be mounted against any one of the inner walls, but there may be a distance between each MEMS structure and the corresponding inner wall. It is, however, important that there is an electrical contact between each MEMS structure and the third inner wall 7 and fourth inner wall 8, or other corresponding walls in another configuration, such that an electrical connection is obtained via the rows 13, 14, 15 of switches 16 and the surrounding third inner wall 7 and the fourth inner wall 8 when the switches 16 are closed.

The amplifier unit 2 may be positioned inside the cavity 1 1 as well, and it may even be placed on the MEMS substrate 12 or using the MEMS substrate 12 as a carrier material.

Each amplifier units 2, 39 and the corresponding differential amplifier 44, 45 may be made in many suitable ways, those described are only examples of how amplifier units and differential amplifiers can be formed in order to obtain the desired electrical properties. Generally, each amplifier unit 2, 39 is arranged to be electrically connected to the waveguide cavity resonator 3 by means of a two corresponding connectors 35, 36; 40, 41 which are mutually out of phase with each other. Each amplifier unit 2, 39 is formed on a substrate, either in the form of MMIC or with discrete components mounted to the substrate. The substrate may then be any suitable type of PCB. A MEMS switch is not sensitive to a voltage swing of an RF signal, which makes it possible to use a high supply voltage in the amplifier and thereby increase the dynamic range and further improve the phase noise. For example, the use of GaN, which is an upcoming semiconductor microwave material, could be advantageous because of high breakdown voltages.

As the continuous analog tuning range is relatively small, the sensitivity to externally and internally generated noise is effectively reduced.

Claims

1 . An oscillator device (1 ) comprising a first amplifier unit (2) and a waveguide cavity resonator (3), the waveguide cavity resonator (3) comprising a cavity (1 1 ) and a first tuning device (4) arranged for mounting in the cavity (1 1 ), the cavity (1 1 ) having a first cavity length (a) running between two opposing inner walls (5, 6) of the cavity (1 1 ), where a resonance frequency (f_r) of the waveguide cavity resonator (3) is dependent on the first cavity length (a), where the first tuning device (4) comprises a non- conducting laminate (12) on which at least one row (13, 14, 15) of switches (16) is placed, the switches (16) being electrically openable and closable and where each row (13, 14, 15) is arranged to constitute an electrically conducting connection between said opposing inner walls (7, 8) when the switches of said row are closed, characterized in that the first amplifier unit (2) is arranged to be electrically connected to the waveguide cavity resonator (3) by means of a first connector (35) and a second connector (36), the connectors (35, 36) being mutually out of phase with each other, where the first amplifier unit (2) further comprises a first amplifier arrangement (37) and a tuneable bias connection (38), the first amplifier unit (2) being comprised in a second tuning device.

2. An oscillator device according to claim 1 , characterized in that the first tuning device (4) is arranged for altering the first cavity length (a) between at least two values (a_effi , a_eff2) such that the resonance frequency (f_r) of the waveguide cavity resonator (3) is adjustable between at least two corresponding magnitudes, and where the tuneable bias connection (38) is arranged for adjusting the resonance frequency (f_r) of the waveguide cavity resonator (3) within a certain frequency span.

3. An oscillator device according to any one of the claims 1 or 2, characterized in that the waveguide cavity resonator (3) comprises a first inner wall (5), a second inner wall (6), a third inner wall (7) and a fourth inner wall (8), where the first inner wall (5) and the second inner wall (6) are facing each other and are separated by a first cavity length (a), and where the third inner wall (7) and the fourth inner wall (8) are facing each other and are separated by a second cavity length (b), a fifth inner wall (9) and a sixth inner wall (10) being mounted to at least one of said first inner wall (5), second inner wall (6), third inner wall (7) and fourth inner wall (8), where the fifth inner wall (9) and the sixth inner wall (10) are facing each other and are separated by a third cavity length (L) such that the cavity (1 1 ) is formed and is limited by the inner walls (5, 6, 7, 8, 9, 10), which inner walls (5, 6, 7, 8, 9, 10) are constituted by respective main surfaces and are electrically conducting.

4. An oscillator device according to claim 3, characterized in that the waveguide cavity resonator is in the form of a surface-mountable waveguide cavity resonator (3), which is arranged to be mounted to a printed circuit board, PCB, (17) such that a metallization (18) on the PCB (17) constitutes the first inner wall (5).

5. An oscillator device according to any one of the claims 3 or 4, characterized in that the first tuning device (4) is placed on the second inner wall (6) and is arranged to alter the distance between the first inner wall (5) and the second inner wall (6).

6. An oscillator device according to any one of the previous claims, characterized in that the oscillator device (1 ) comprises a second amplifier unit (39) that is arranged to be electrically connected to the waveguide cavity resonator (3) by means of a third connector (40) and a fourth connector (41 ), the connectors (40, 41 ) being mutually out of phase with each other, where the second amplifier unit (39) further comprises a second amplifier arrangement (42) and a tuneable bias connection (43), the second amplifier unit (39) being comprised in the second tuning device.

7. An oscillator device according to any one of the previous claims, characterized in that each amplifier arrangement (37, 42) comprises a differential amplifier (44, 45) where a differential output (46, 47) is electrically connected to the corresponding connectors (35, 36; 40, 41 ).

8. An oscillator device according to claim 7, characterized in that each differential amplifier (44, 45) comprises a first transistor (QIA) and a second transistor (QIB), which transistors (QIA, QIB) are arranged to amplify signals received from the waveguide cavity resonator (3) and to reflect the amplified signals back to the waveguide cavity resonator (3).

9. An oscillator device according to any one of the previous claims, characterized in that the first tuning device (4) comprises switches (16) of the type Micro Electro Mechanical Systems, MEMS.

1 0. An oscillator device according to any one of the previous claims, characterized in that each amplifier unit (2, 39) is positioned outside the cavity (1 1 ) and is arranged to be electromagnetically connected to the cavity (1 1 ) via an opening (21 ), said opening constituting a waveguide port.

1 1 . An oscillator device according to claim 1 0, characterized in that the waveguide port comprises a coupling arrangement (22) that for each amplifier unit (2, 39) comprises a corresponding first coupling patch (23, 50) and second coupling patch (24, 51 ), each coupling patch being connected to a respective connector (35, 36; 40, 41 ).