Patent Application
20170237142
The present disclosure relates generally to wireless telecommunications and, in particular to, tunable filters.
Tunable filters can provide more than one filter response using tuning elements integrated into the filter topology and therefore a single tunable filter can be adapted to multiple frequency bands. The most common tunable parameter in microwave filters is the center frequency. In discrete tuning, finite values of center frequencies are supported by the tuning devices whereas in continuous tuning a continuum range of frequencies is supported. Different tuning methods including mechanical, magnetic, and electrical tuning have been proposed to construct tunable filters with either discrete or continuous tuning. Tuning methods are evaluated in terms of different metrics including their tuning range, quality factor, power handling capability, fabrication complexity, size, and tuning speed. None of the tuning methods is superior in terms of all metrics and, therefore, depending on the application and design constraints, one tuning method might be preferred over the other in a particular application or use.
Mechanical tuning is easy to implement and provide a relatively high power handling capability. However, they have low tuning speed and are usually bulky in size. Micro Electro-Mechanical Systems (MEMS) technology is an attractive approach to realize tunable filters with a compact size. Integration of MEMS devices with three dimensional resonators is a challenge leading to a significant degradation in the resonator Q-factor.
Accordingly, there remains a need in the industry for an improved tunable filter.
The following presents a simplified summary of some aspects or embodiments of the invention in order to provide a basic understanding of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some embodiments of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present specification discloses, in general, a tunable resonator having two or more rods per resonator. Also disclosed herein is a tunable filter that includes two or more such resonators. In each resonator, there are two or more rods which are of different size and/or asymmetrically disposed within the cavity. Each rod can be switched on or off by connecting or disconnecting the rod to a cavity wall or housing. Thus, switching of the rods changes the field distribution and accordingly changes the resonant frequency of the resonator to thereby tune the filter to the desired frequency.
One inventive aspect of the disclosure is a rod-switched tunable resonator having a housing defining a cavity, a first rod disposed within the cavity, a second rod disposed within the cavity, and a switch connected to the first rod and to the second rod to tune the resonator to one of a plurality of frequencies by connecting or disconnecting one or both of the first and second rods to the housing.
Another inventive aspect of the disclosure is a rod-switched tunable filter having a first resonator, a second resonator adjoining the first resonator, wherein each of the first and second resonators includes a housing defining a cavity, a first rod disposed within the cavity, a second rod disposed within the cavity and a switch connected to the first rod and to the second rod to tune the resonator to one of a plurality of frequencies by connecting or disconnecting one or both of the first and second rods to the housing.
Yet another inventive aspect of the disclosure is a method of tuning a resonator. The method entails disposing a first electrically conductive rod inside a cavity of the resonator, disposing a second electrically conductive rod inside the cavity of the resonator, and switching on or off one or both of the first rod and the second rod to tune the resonator.
These and other features of the disclosure will become more apparent from the description in which reference is made to the following appended drawings.
The following detailed description contains, for the purposes of explanation, numerous specific embodiments, implementations, examples and details in order to provide a thorough understanding of the invention. It is apparent, however, that the embodiments may be practiced without these specific details or with an equivalent arrangement. In other instances, some well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention. The description should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.
In general, disclosed herein is a tunable resonator having two or more rods that can be disposed anywhere inside the cavity although some locations will be more sensitive than others. Connecting the rods to the cavity wall (i.e. housing) changes the electromagnetic field distribution inside the cavity and hence changes the resonant frequency, i.e. the frequency at which the electric energy (We) stored in the electric field is equal to the magnetic energy (Wm) stored in magnetic field, i.e. We=Wm. The inventive concept is applicable to any cavity resonator, such as a coaxial resonator, waveguide resonator or dielectric resonator. It is also applicable to a cavity with an electrically conductive post inside (i.e. a combline resonator).
The rods can be switched (i.e. connected to the housing or cavity wall) to define various switch states each exhibiting its own electromagnetic field distribution within the resonator. At each of the different states, the condition We=Wm occurs at a corresponding resonant frequency. Each switch state thus corresponds to a different resonant frequency of the resonator. In a simple implementation, there are two rods inside the cavity, thereby providing four switch states, i.e. four tunable frequencies. However, it is important to note that the number of rods inside the cavity is not restricted to two rods per resonator. The number of tuning states (i.e. frequencies) is equal to 2N where N is the number of rods. Thus, 2 rods provides 4 states, 3 rods provides 8 states, 4 rods provides 16 states, 5 rods provides 32 states, and so on.
The rods may be switched (electrically connected to the cavity walls) using any suitable radio frequency (RF) switch, such as, for example, RF MEMS switches. The rods can alternatively be switched by mechanical relay switches, semiconductor switches, or phase change material type switches or any other suitable switch.
In the embodiments illustrated in the figures, and as will be described below in greater detail, a tunable resonator can be tuned to desired frequencies, e.g. center frequencies (or resonant frequencies) by switching two or more rods inside a cavity within the resonator to change the electromagnetic field distribution inside the resonator.
Some specific embodiments are now described by way of example to further illustrate particular implementations of the technology. These examples are meant solely to further elucidate the inventive concept and to restrict the inventive concept to these particular implementations.
A first example implementation is depicted in
The rods 18, 20 are mounted in this example above the electrically conductive (e.g. metallic) post, as illustrated in
In the embodiment illustrated by way of example in
In another embodiment, the short and long rods 18, 20 are separated by a gap G greater than a diameter D of the post 16. In this embodiment, the short and long rods 18, 20 may extend downwardly to lowest points that are below the plane P defined by the upper surface of the post 16 as shown by way of example in
In the embodiment illustrated in
In the embodiment depicted by way of example in
In the embodiment depicted by way of example in
Two or more resonators 10 may be adjoined to each other to constitute a rod-switched tunable filter 50, an example of which is depicted in
The rod-switched tunable filter 50 shown by way of example in
In the embodiment depicted in
As a proof of concept, an S-band two-pole tunable combline filter with a bandwidth of 30 MHz was constructed using two resonators as shown in
In other embodiments, the rods may be replaced by electrically conductive members having non-cylindrical or non-uniform shapes. In other embodiments, the rods need not be parallel to each other.
Another aspect of the present disclosure is a method of tuning a resonator, or a filter having two such resonators. The tuning method uses an electrical switch to tune the center frequency by switching between the first and second rods with the cavity of the resonator. More specifically, the method entails steps, acts or operations of disposing an electrically conductive post within a cavity of a housing of the resonator, disposing an electrically conductive first rod, disposing an electrically conductive second rod, and switching on or off one or both of the first rod and the second rod to tune the resonator. By connecting the first and second rods to the housing of the resonator, the electromagnetic field distribution changes within the cavity.
It is to be understood that the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a device” includes reference to one or more of such devices, i.e. that there is at least one device. The terms “comprising”, “having”, “including”, “entailing” and “containing”, or verb tense variants thereof, are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of examples or exemplary language (e.g. “such as”) is intended merely to better illustrate or describe embodiments of the invention and is not intended to limit the scope of the invention unless otherwise claimed.
While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. As described above, the cavity resonator could be a combline resonator, coaxial resonator, waveguide resonator, or dielectric resonator. The number of rods in each cavity resonator may be two or greater. It will also be understood that the filter could be composed of two or more resonators.
In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the inventive concept(s) disclosed herein.
