The present invention relates to a tunable waveguide resonator and a method of frequency tuning for the tunable waveguide resonator, wherein the waveguide resonator comprises a tuning element arranged therein.
In wireless communication networks there are various radio equipment that comprise a least some form of a resonator for example used in filters, oscillators such as Voltage Controlled Oscillators (VCOs), or short haul diplexers and similar.
One of the more recent trends calling for special requirements on resonator design, is the millimeter-wave (mmW) domain which is becoming notably popular thus raising the bar for demands on low phase noise for the frequency generation. The phase noise limitations in oscillators are often the bottleneck for more complex modulation in a communication system and for the resolution and range in radar systems.
Tunability is also another important factor being considered in design of resonators for mmW applications, with its practical implementation depending on availability of the tunable resonators with a high Q-factor, which means low losses and low phase noise. It is also important that a tunable resonator is reliable and inexpensive to produce.
Based on the intended application, a resonator can be built from discrete LC components, dielectric resonators, waveguide cavities or variants of these. One common tuning approach is electrical tuning of the cavities. 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.
However, in all existing solutions, the common problem is that as soon as a tuning element is coupled to the waveguide cavity resonator, the losses of the tuning element will lower the Q factor and thereby the phase noise increases. The tighter the coupling between the tuning element and the resonator, the wider bandwidths may be obtained, alongside more losses, which in turn leads to increase in the phase noise.
Several other solutions use mechanical tuning approach for tuning waveguide cavities where e.g. one side is moved and typically is connected to the cavity wall by sliding contacts. Such a design results in relatively high insertion losses, meaning that a high Q factor cannot be achieved.
In a mechanical tuning approach disclosed in WO 2016/058642, the cavity comprises a tuning device comprising an electrically conducting wall part which is mechanically movable, thus making it possible to adjust a distance within the cavity. A support wall by means of a sliding adjustment arrangement is pushed against the movable wall part and this changes the distance inside the cavity which results in change of frequency. However, in this approach a manual knob is used for mechanical adjustment of the distance which may not result in accurate adjustments. Alternatively, moving the sliding adjustment arrangement in a controlled manner, requires using an electrical motor which may lead to increased production complexity, malfunctioning and higher costs.
There is thus a need for a tunable waveguide resonator and an improved tuning of frequencies that delivers a high Q-factor, wide spurious free band and is also compact.
It is an object of the present invention to set forth an apparatus and a method for providing improved and more reliable tunable high Q-factor waveguide cavity resonators. This and other objects of the present invention are defined in the appended set of claims. The dependent claims define several embodiments of the present invention.
The term exemplary in the present disclosure is to be construed as an example, instance or illustration.
According to a first aspect of the present invention there is provided a tunable waveguide resonator comprising a waveguide part having a plurality of walls. One of the plurality of walls at least partly comprises a tuning element, wherein the tuning element has a first main surface, facing toward a first main surface of an inner wall of one other wall of the plurality of walls. The tuning element is caused to, in response to a change in a temperature of the tuning element, be reversibly displaced with respect to a reference plane of the first main surface of the tuning element along an extension perpendicular to the first main surface of the one other inner wall. Whereby, a dimension of a cavity of the tunable waveguide resonator is changed.
According to one exemplary embodiment of the present invention, the tuning element may be configured to be displaced when the temperature of the tuning element is increased. Such that a portion of the tuning element may be caused to bend out of the references plane along the extension perpendicular to the first main surface of the one other inner wall.
In some embodiments, the tunable waveguide resonator may be configured such that a resonance frequency of the tunable waveguide resonator can be tuned corresponding to a distance by which the dimension of the cavity of the tunable waveguide resonator may be changed upon the tuning element being displaced in response to the change in the temperature of the tuning element.
In yet another exemplary embodiment according to the present invention, one of the plurality of the walls may at least partly comprise an opening. Such that the tuning element when mounted on the wall of the waveguide part, may extend along the entire length of the opening whereby sealing the opening.
In some embodiments, the tuning element may be mounted on the waveguide part by means of attachment means. In some embodiments, the attachment means may comprise any one of a screw, a glue portion, or a solder pad. In other embodiments, the attachment means may comprise any combination of screws, glue portions, or solder pads or any other attachment and tightening means.
In yet another embodiment according to the present invention, the tuning element may comprise a membrane comprising a first sheet of a first metal and a first sheet of a second metal. The first sheet of the first metal may be arranged on a surface of the first sheet of the second metal, wherein the first metal may be different from the second metal. According to another exemplary embodiment of the present invention, the membrane may comprise a bi-metallic membrane, wherein the first sheet of the first metal may have a thermal expansion coefficient which is greater than the thermal expansion coefficient of the first sheet of the second metal. According to one exemplary embodiment, the bi-metallic membrane may be a bi-metallic strip. Where, the first metal in the bi-metallic strip may be brass and the second metal in the bi-metallic strip may be steel.
Accordingly, it has been realized by the inventors that it is advantageous to provide the cavity of the tunable waveguide resonator with a tuning element which is in the form of a bi-metallic membrane configured to be displaced and change shape i.e. bend out of its initial shape and position in response to a change in the temperature of the bi-metallic membrane. This way it is possible to tune the frequency of the waveguide resonator in a simple, controllable, accurate and cost-effective manner while maintaining a high Q-factor of the cavity. Furthermore, low phase noise values can also be achieved by such a resonator.
According to an embodiment of the present invention, the tuning element may be electrically conducting. The tuning element may be configured such that when an electric current passes through the tuning element, the temperature of the tuning element may be caused to change.
In some other exemplary embodiments, a thermo-element may be arranged at a predetermined distance (D) from the reference plane of the tuning element, wherein in response to a change in a temperature of the thermo-element, the temperature of the tuning element may be caused to change.
According to some other embodiments of the present invention, the waveguide resonator may further comprise processing circuitry for determining a deviation in a selected working frequency of the waveguide resonator. Where the processing circuitry may be further configured to change the temperature of the tuning element by means of a temperature adjusting means based on the determining and compensate for the deviation by tuning the selected working frequency of the waveguide resonator.
According to a second aspect of the present invention, there is provided a method for tuning a frequency of a tunable waveguide resonator comprising a waveguide part having a plurality of walls. One of the plurality of walls at least partly comprises a tuning element. Wherein the tuning element has a first main surface, facing toward a first main surface of an inner wall of one other wall of the plurality of walls. Wherein the method comprises:
According to one exemplary embodiment, the method may further comprise:
According to yet another exemplary embodiment of the present invention, the method may further comprise:
In some embodiments, the tunable element may be electrically conducting and wherein the method may further comprise:
In some other exemplary embodiments of the present invention, a thermo-element may be arranged at a predetermined distance from the reference plane of the tuning element, wherein the method may further comprise:
Aspects and various embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The different devices, systems, computer programs and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects and embodiments set forth herein. Like numbers in the drawings refer to like elements throughout.
The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.
Each inner wall 101a′, 101b′, 101c′, 101d′ has a first main surface 104 which faces toward a first main surface 104 of one other inner wall. As an example, inner wall 101b′ and 101d′ face each other i.e. each of the two inner walls 101b′ and 101d′ arranged to be substantially parallel to each other, has a first main surface 104 which faces toward the first main surface 104 of the other inner wall.
The waveguide resonator 10 further comprises a tuning element 102. The tuning element 102 in this embodiment is comprised in the waveguide part 100 of the tunable waveguide resonator 10. In the embodiment of
The first main surface 103a of the tuning element 102 comprised in wall 101a′ in this embodiment is arranged to face toward the first main surface 104 of one other inner wall e.g. the third inner wall 101c′.
The tuning element 102 comprises a bi-metallic membrane. the bi-metallic membrane 102 is for example a strip of metal made of at least two sheets of different metals. As shown as a matter of example in
The tuning element 102 can in other embodiments be a metallic foil which is suitable for reversibly changing its shape when exposed to temperature changes and thus result in a change in a dimension of the cavity of the resonator. In other embodiments the tuning element 102 may comprise a plurality of stacks of a bi-metallic membranes, e.g. a second or a third sheet of the first and second metals arranged in stacks.
In the following the tuning element 102 may also frequently be referred to as the bi-metallic membrane 102.
The tuning element 102 is, in response to a change in a temperature of the tuning element 102, caused to be reversibly displaced with respect to a reference plane 106 of the first main surface 103a of the tuning element 102 such that a portion 102a (see
The second length d2 of the waveguide part 100 is to be understood as the distance between the two inner walls, the first 101a′ and the third 101c′ inner wall. In other words, the dimension d2 of the cavity 107 which is changed when the tuning element is caused to be displaced is the same as changing the second length d2 i.e. the distance between the two parallel inner walls 101a′ and 101c′.
When in use, by changing temperature of the tuning element 102 using a temperature adjusting means, the portion 102a of the tuning element 102 is moved towards the first main surface 104 of the opposite inner wall 101c′ by projecting out of the reference plane 106 of the first main surface 103a of the tuning element 102. In some embodiments the portion 102a forms only a part of the tuning element 102. In other embodiments the portion 102a extends along and forms the entire length of the tuning element 102.
The area and volumetric thermal expansion of the bi-metallic membrane 102 can be isotropic in some embodiments. In other embodiments the thermal expansion may be anisotropic.
The membrane may be manufactured by any customary production technologies in the field such as 3D printing.
By reversibly here it is meant to be understood that when the temperature of the tuning element is increased with the amount ΔT from an initial temperature T e.g. ambient temperature to T+ΔT, the tuning element 102 is accordingly displaced as described above. However, when the temperature of the tuning element 102 returns to T, the tuning element 102 is moved in the opposite direction and returns to its initial position.
As shown in
Alternatively or additionally, the wall 101a of the waveguide part 100 completely comprises the tuning element 102 as shown in
In some embodiments, the bi-metallic membrane 102 is attached to the end portions 108 of the walls as shown in
The bi-metallic membrane 102 is attached to the waveguide part 100 at its end portions 110 by means of attachment means 111. As shown in
In some embodiment the bi-metallic membrane 102 is attached to a portion of the inner walls adjacent the wall comprising the bi-metallic membrane 102. For example, as shown in
Moving on, the bi-metallic membrane 102 in some embodiments is attached to the bottom part of waveguide part 100 i.e. to the bottom portion of the walls of the waveguide part 100. For example, as shown in
The end portions 114 of the other sides of the bi-metallic membrane 102 are attached in the same way to the bottom portions of the other remaining walls of the waveguide part 100 (not shown). This means that the waveguide part 100 is physically as well as electrically sealed by the bi-metallic membrane 102.
The attachment means 111 in the above discussed embodiments may be screws, glue portions/pads, solder pads/bumps or some other tightening or attachment means.
In some embodiments, the tunable element 102 may be partly or fully comprised in multiple walls e.g. in two or in three or in four walls of the waveguide part 100. (not shown)
In the embodiment of
In some embodiments the distance “D” may be varied during operation e.g. by being mounted on an adjustable stage or platform controlled by a user or processing circuitry 116. This provides for several advantages such as calibration of the thermo-element, maintenance, test measurements, or adjustment of the distance during a tuning session based on the frequency readout.
When the bi-metallic membrane 102 is in its initial position, the first main surface 103a and the second main surface 103b are substantially parallel with the reference plane 106. In the initial position, the dimension d2 of the cavity 107 which is changed when the tuning element is caused to be displaced from the initial position to the tuning position is the same as the second length d2 of the waveguide part 100 i.e. the distance between the two parallel inner walls 101a′ and 101c′.
By using the thermo-element 115, the temperature of the bi-metallic membrane 102 is changed indirectly e.g. the membrane 102 is heated up or cooled down indirectly. The thermo-element can for example be a Peltier element.
When the temperature of the thermo-element changes e.g. when a temperature increase from T to T+ΔT is applied to the thermo-element, the bi-metallic membrane 102 is caused to be displaced corresponding to this increase. This means that the bi-metallic membrane 102 moves along the extension 105 perpendicular to the first main surface 104 of the inner wall 101c′. In this embodiment the temperature increase of ΔT causes the bi-metallic membrane 102 to move towards the inner wall 101c′. More specifically, when saying the bi-metallic membrane 102 is caused to be displaced, it is meant that the first main surface 103a of the bi-metallic membrane 102 moves towards the first main surface 104 of the inner wall 101c′. For example, the portion 102a of the bi-metallic membrane 102 is caused to be displaced towards the first main surface 104 of the inner wall 101c′ such that the highest point 102b of the portion 102a of the bi-metallic membrane 102, when forming an arc shape, is displaced a corresponding distance of Δd, with respect to the reference plane 106, along the extension 105. Highest point of the arc shape is to be construed with respect to a chord of a circle comprising the arc, wherein the chord connects the two endpoints of the arc.
This movement of the bi-metallic membrane 102 cause the dimension d2 of the cavity 107 to decrease to d2-Δd at the highest point 102b of the portion 102a.
If the temperature of the thermo-element 115 is then decreased from T+ΔT to T, the tuning element 102 and more specifically the highest point 102b of the portion 102a of the tuning element 102 is moved in the opposite direction along the extension 105 away from the first main surface 104 and towards its initial position. This causes the dimension d2-Δd of the cavity 107 to increase and ultimately return to the initial value of d2.
It must be clear to the skilled person that the other portions of the bi-metallic membrane 102 other than the portion 102a as well as other points than the highest point 102b of the portion 102a will experience a slightly different thermal expansion and distance alteration than Δd and thus the dimension change over the entire length of the bi-metallic membrane 102 will graduate between d2 and d2-Δd. Stating differently, the bi-metallic membrane 102 forms the arc shape between the two attachment points.
By employing the above mechanism, the inventors have found that the dimension or volume of the cavity 107 can be accurately adjusted which results in a change in frequency of the waveguide resonator 10. For example, when the bi-metallic membrane 102 is heated up, the volume of the cavity will be reduced as discussed above in detail and this will lead to an increase in the frequency of the waveguide resonator, thus a convenient frequency tuning is achieved. This way, the variations of the ambient or working temperature of the tunable waveguide resonator 10 is advantageously compensated for. The present invention advantageously makes possible to tune the resonance frequency of the cavity 107 of the waveguide resonator 10 without sacrificing the high Q-factor of the cavity 107. Further, the present invention eliminates the need for installing a varactor diode inside the waveguide cavity 107 which when installed in the cavity 107, negatively affects the high Q-factor of the cavity 107 of the waveguide resonator 10. The waveguide resonator 10 according to the present invention can also achieve considerably low phase noise values compared to standard available solutions. For instance, a standard VCO available on the market today can deliver a −114 dBc phase noise at a central frequency of 10 GHz. As an example, in comparison, the VCO comprising a waveguide cavity resonator 10 according to the present invention can deliver an improvement of at least 19 dB at the same working frequency over the above standard VCO.
In some embodiments the dimensions of the cavity 107 may e.g. be d1=21 mm×d2=18 mm for a central frequency of 10 GHZ. Other arrangements and dimension are clearly conceivable to the skilled person based on the working frequency of the waveguide resonator 10.
In some exemplary embodiments, the displacement (Δd) of the bi-metallic membrane 102 is in the range of 10 μm to 20 μm for a central frequency of 10 GHz. It is however conceivable that for several other working frequencies , waveguide cavities and corresponding bi-metallic membranes could be designed for achieving desired frequency tuning ranges without departing from the scope of the appended claims.
The thermo-element 115 is arranged to be accurately controllable by means of control and processing circuitry 116. This way the temperature of the thermo-element 115 can be adjusted with high precision. In some embodiments the control circuitry 116 may execute an algorithm to regulate the temperature of the thermo-element 115 such that a certain tuning position of the membrane 102 i.e. a certain frequency tuning target is constantly maintained and fluctuation in the ambient temperature, and/or working temperature of the waveguide resonator 10 are compensated for.
In another embodiment according to the present invention illustrated in
Furthermore, in some other embodiments, the bi-metallic membrane 102 is configured to operate in the ambient temperature and compensate only for temperature variations in the working environment of the waveguide resonator 10. In such embodiments no direct and/or indirect temperature regulating means are installed. Instead, it is the fluctuations of the ambient temperature which control the displacement of the bi-metallic membrane 102 and in such way control the volume of the cavity 107 and the changes in the frequency of the waveguide resonator 10. It is however required that a suitable combination of metals or alloys be used to construct the bi-metallic membrane 102 when it is controlled by the ambient temperature.
In some embodiments the method further comprises providing S11 a temperature adjusting means 115, 117 for changing a temperature of the tuning element 102, and changing S12 the temperature of the tuning element 102 by the temperature adjusting means.
In other embodiments the bi-metallic membrane 102 may be configured to operate in the ambient temperature and compensate only for temperature variations in the working environment of the waveguide resonator 10. In such embodiments, temperature adjusting means are not required. Instead, it is the fluctuations of the ambient temperature which control the displacement of the bi-metallic membrane 102 and in such way control the volume of the cavity 107 and the cause the tuning of the frequency of the waveguide resonator 10. It is however noted that a suitable combination of metals or alloys is to be used to construct the bi-metallic membrane 102 when it is controlled by the ambient temperature.
The method can be carried out in any desired order, or parts of the method may be performed repeatedly or sequentially in different applications as desired.
In other embodiments, the method may further comprise determining S5, by means of a processing circuitry 116, 203, 204 a deviation in a selected working frequency of the waveguide resonator, and changing S6 the temperature of the tuning element by means of the temperature adjusting means 115, 117 based on the determining. The method may further comprise compensating S7 for the deviation by tuning the selected working frequency of the waveguide resonator corresponding to the change in the dimension d2 of the cavity 107. The deviation may for example be any temperature fluctuations in the working environment leading to a deviation of the frequency of the resonator. The deviation may also be caused due to mechanical vibrations or any other conceivable environmental disturbances such as wind, irradiation, and the like.
Filing Document | Filing Date | Country | Kind |
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PCT/SE2020/050387 | 4/15/2020 | WO |