Patent Application
20140111285
1. Statement of the Technical Field
The inventive arrangements relate to directional couplers for dividing or splitting an input signal into multiple outputs, or combining multiple input signals into a single output.
2. Description of Related Art
Directional couplers are commonly used in various telecommunications-related applications such as power dividing and combining; combining feeds to and from antennas; antenna beam forming; phase shifting; etc. Commercially available directional couplers are usually categorized as either waveguide-based or thin-film-based. Typical waveguide-based couplers have relatively high power-handling capacity, but possess a relatively large dimensional footprint. Typical thin-film-based couplers have a relatively small dimensional footprint, but possess relatively low power-handling capacity.
The frequency response of directional couplers is usually fixed, e.g., the frequency (or frequency band) at which maximum power transfer will occur cannot be varied. Thus, the performance of such a coupler cannot be optimized or tuned for multiple operating conditions.
Three-dimensional microstructures can be formed by utilizing sequential build processes. For example, U.S. Pat. Nos. 7,012,489 and 7,898,356 describe methods for fabricating coaxial waveguide microstructures. These processes provide an alternative to traditional thinfilm technology, but also present new design challenges pertaining to their effective utilization for advantageous implementation of various devices such as miniaturized switches.
Embodiments of coupler systems include a coupler comprising an electrical conductor and a tuning element. The tuning element has an electrically-conductive first portion in electrical contact with the electrical conductor of the coupler and having a first end face, and an electrically-conductive second portion having a second end face. The tuning element also includes a dielectric element disposed on the first or the second end face, and is spaced apart from the other of the first and second end face by a gap. The second portion is configured to move in relation to the first portion so that the gap is variable.
In accordance with further aspects of the inventive concepts disclosed and claimed herein, embodiments of systems include a coupler comprising an electrically-conductive housing and an electrical conductor. The electrical conductor is suspended within the housing on a plurality of dielectric tabs and is spaced apart from the housing. The coupler systems also include a capacitive element configured to vary the frequency response of the coupler.
In accordance with further aspects of the inventive concepts disclosed and claimed herein, embodiments of systems include a coupler having an electrical conductor that forms a signal path, a capacitive element configured to introduce a reactance in the signal path, and an actuator element operative to vary a capacitance of the capacitive element.
Embodiments will be described with reference to the following drawing figures, in which like numerals represent like items throughout the figures and in which:
The invention is described with reference to the attached figures. The figures are not drawn to scale and they are provided merely to illustrate the instant invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. One having ordinary skill in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operation are not shown in detail to avoid obscuring the invention. The invention is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the invention.
The coupler 12 is configured to split an input signal into two output signals that are equal in power, and differ in phase by 90°. The coupler 12 can also combine two input signals into a single output. Although the coupler 12 is described herein as functioning as a signal splitter, the inventive concepts disclosed and claimed herein can be applied equally to coupler systems in which the coupler 12 functions as a combiner. Moreover, alternative embodiments of the system 10 can include other types of couplers, such as hybrid ring couplers.
The tuning elements 14a, 14b, as discussed below, are capacitive devices that allow the frequency response of the coupler 12 to be varied. This feature permits the response of the coupler 12 to be tuned to a particular frequency or range of frequencies at a given operating condition. The first and second actuators 16a, 16b generate mechanical forces that actuate the respective first and second tuning elements 14a, 14b.
The coupler system 10 has a maximum height (“z” dimension) of approximately 0.5 mm; a maximum width (“y” dimension) of approximately 5.6 mm; and a maximum length (“x” dimension) of approximately 6.9 mm. The coupler system 10 is described as having these particular dimensions for exemplary purposes only. Alternative embodiments of the coupler system 10 can be scaled up or down in accordance with the requirements of a particular application, including size, weight, and power (SWaP) requirements.
The coupler system 10 further comprises a substrate 18, as shown in
The coupler 12 comprises a ground housing 20 disposed on the substrate 18, and an electrical conductor 22. The electrical conductor 22 is accommodated by a series of channels 24 formed in the ground housing 20, as illustrated in
The ground housing 20 is formed from five layers of an electrically-conductive material such as copper (Cu). Each layer can have a thickness of, for example, approximately 50 μm. The number of layers of the electrically-conductive material is application-dependent, and can vary with factors such as the complexity of the design, hybrid or monolithic integration of other devices with the system 10, the overall height (“z” dimension) of the coupler 12, the thickness of each layer, etc.
The first layer of electrically-conductive material is disposed directly on the substrate 18, as shown in
The sides of the ground housing are formed by the second, third, and fourth layers of electrically-conductive material. The fifth layer of electrically-conductive material forms the top of the ground housing 20.
The electrical conductor 22 is formed by a portion of the third layer of electrically-conductive material, and has a substantially rectangular cross section as illustrated in
The input portion 30 of the electrical conductor 22 includes a first leg 40 and a substantially identical second leg 42. The first and second legs 40, 42 are substantially parallel, and extend substantially in the direction of signal propagation, i.e., in the “x” direction. The first and second legs 40, 42 each have a width, or “y” dimension, that is selected so that the characteristic impedance (Zo) of each of the first and second legs 40, 42 matches a desired value, i.e., 50 ohms, at a reference frequency.
The intermediate portion 32 includes a first leg 46 and a substantially identical second leg 48. The first leg 46 adjoins the first leg 40 of the input portion 30, and the second leg 48 adjoins the second leg 42 of the input portion 30. The first and second legs 46, 48 are substantially parallel, and extend substantially in the “x” direction. The first and second legs 46, 48 each have a length denoted by the reference character “d1” in
First and second projections 49a, 49b are formed on the second leg 48 of the intermediate portion 32 thereon, as shown in FIGS. 3 and 5-6B. The first projection 49a is located proximate a first end of the second leg 48. The second projection 49b is located proximate a second end of the second leg 48. The first and second projections 49a, 49b form part of the respective first and second tuning elements 14a, 14b.
Each of the first and second tuning elements 14a, 14b further comprises a thin-film dielectric element 50, as illustrated in FIGS. 3 and 5-6B. The dielectric elements 50 are fixed to the respective end faces of the first and second projections 49a, 49b, by a suitable means such as adhesive. Each dielectric element 50 can have a thickness of, for example, 20 um. The dielectric elements 50 can be formed, for example, from polyethylene, polyester, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide, polyimide, benzocyclobutene, SU8, etc., provided the material will not be attacked by the solvent used to dissolve the sacrificial resist during manufacture of the system 10, as discussed below.
The intermediate portion 32 also includes a third leg 51 and a substantially identical fourth leg 52, as shown in
The length of each of the third and fourth legs 51, 52 is approximately equal to the distance “d1,” as shown in
The output portion 34 includes a first leg 56 and second leg 58, as can be seen in
The electrical conductor 22 is suspended within the channels 24 by a plurality of electrically-insulative tabs 60, as illustrated in
The tabs 60 can each have a thickness of, for example, approximately 15 μm. Each tab 60 spans the width, i.e., y-direction dimension, of the channel 30, as can be seen in
The respective widths, e.g., “x” or “y” dimensions, and the height, e.g., “z” dimension, of the channels 24 are selected so that the electrical conductor 22 is surrounded by, and is spaced apart from the interior surfaces of the ground housing 20 by an air gap, as shown in
Because the coupler 12 is configured as a 90° hybrid coupler, the power of a signal applied to the first leg 40 (or, alternatively, the second leg 42) of the input portion 30 is split evenly between the first and second legs 56, 58 of the output portion 34, and the signals in the first and second legs 56, 58 of the output portion 34 are 90° out of phase. Also, the second leg 42 (or, alternatively, the first leg 40) of the input portion 30 is isolated from the input signal.
The first and second actuators 16a, 16b are substantially identical. The following description of the first actuator 16a, unless otherwise indicated, applies equally to the second actuator 16b.
The first actuator 16a includes a shuttle 102, a control portion 105, a first lead 106a, a second lead 106b, and a portion of the ground plane 26, as can be seen in
The shuttle 102 is formed as part of the third layer of electrically-conductive material. The shuttle 102 has an elongated body 103 that extends substantially in the “y” direction, as shown in
The first tuning element 14a further comprises a movable portion 116 that adjoins an end of the body 103 of the shuttle 102, as depicted in
The first tuning element 14a also includes two posts 120 that extend upwardly from the ground plane 26, as shown in
The shuttle 102 is suspended from the first, second, and third mounts 110a, 110b, 110c, as illustrated in
It should be noted that the configuration of the beam portions 123 is application-dependent, and can vary with factors such as the amount of space available to accommodate the beam portions 123, the required or desired spring constant of the beam portions 123, etc. Accordingly, the configuration of the beam portions 123 is not limited to that depicted in the figures.
The second and third mounts 110b, 110c are substantially identical to the first mount 110a, with the following exception. The second and third mounts 110b, 110c each include an arm 130 having a first end that adjoins the beam portion 123, as illustrated in
Alternative embodiments can be constructed without the second and third mounts 110b, 110c, as depicted in
The control portion 105 of the first actuator 16a includes two legs 130, and an adjoining top portion 132, as depicted in
The top portion 132 of the control portion 105 includes a first half 134a and a second half 134b, as depicted in
The shuttle 102 and the first and second halves 134a, 134b of the control portion 105 are configured so that the fingers 138 of the first and second halves 134a, 134b and the fingers 104 of the shuttle 102 are interleaved or interdigitated, i.e., the fingers 138, 104 are arranged in an alternating fashion along the “y” direction, as illustrated in
The first and second leads 106a, 106b of the first actuator 16a are disposed on the substrate 18 as shown in
The first actuator 16a is configured to cause movement of its shuttle 102. In particular, subjecting the first and second leads 106a, 106b to a voltage causes the shuttle 102 to move from its first position and toward its second position due to the resulting electrostatic attraction between the shuttle 102 and the top portion 132 of the control portion 105, as follows. As discussed above, the shuttle 102 adjoins the beam portions 123 of the first, second, and third mounts 110a, 110b, 110c, so that the shuttle 102 is suspended from the mounts 110a, 110b, 110c. The beam portions 123 are in their neutral or un-deflected positions when the shuttle 102 is in its first position, as depicted in
Subjecting the first and second leads 106a, 106b of the first actuator 16a to a voltage potential results in energization of the fingers 138, as discussed above. The energized fingers 138 act as electrodes, e.g., an electric field is formed around each finger 138 due the voltage potential to which the finger 138 is being subjected. Each of the energized fingers 138 is positioned sufficiently close to its associated finger 104 on the grounded shuttle 102 so as to subject the associated finger 104 to the electrostatic force resulting from the electric field around the finger 138. The electrostatic force attracts the finger 104 to its corresponding finger 138.
The net electrostatic force acting on the six fingers 104 urges the shuttle 102 in the +y direction, toward its second or defected position. The beam portions 123 of the first, second, and third mounts 110a, 110b, 110c, which were in their neutral or un-deflected state prior to energization of the fingers 138, are configured to deflect in response to the net force acting on the shuttle 102, thereby permitting the suspended shuttle 102 to move in the +y direction toward, or to its second position. The beam portion of the first mount 110a is depicted in a deflected condition in
The shuttle 102 will remain in a partially or fully deflected condition while the first actuator 16a remains subject to a voltage potential. The resilience of the beam portions 123 and the posts 120 will cause the shuttle 102 to return toward, or to its first or un-deflected position when the voltage potential is reduced or eliminated.
The relationship between the amount of deflection of the beam portions 123 and the voltage applied to the first actuator 16a is dependent upon the stiffness of the beam portions 123, which in turn is dependent upon factors that include the shape, length, and thickness of the beam portions 123, and the properties, e.g., Young's modulus, of the material from which the beam portions 123 are formed. These factors can be tailored to a particular application so as to minimize the required actuation voltage, while providing the beam portions 123 with sufficient strength for the particular application; with sufficient stiffness to tolerate the anticipated levels of shock and vibration; and with sufficient resilience to facilitate the return of the shuttle 102 to its first position when the voltage potential to the first actuator portion 16a is removed.
The first and second actuators 16a, 16b can be configured in a manner other than that described above in alternative embodiments. For example, suitable comb, plate, or other types of electrostatic actuators can be used in the alternative. Moreover, actuators other than electrostatic actuators, such as thermal, magnetic, and piezoelectric actuators, can be used in the alternative. In other alternative embodiments, a single actuator can be connected to, and can actuate both of the tuning elements 14a, 14b.
The first and second actuators tuning elements 14a, 14b are substantially identical. The following description of the functional characteristics of the first tuning element 14a, unless otherwise indicated, applies equally to the second tuning element 14b.
The movable portion 116 of the first tuning element 14a is disposed at an end of the body 103 of the shuttle 102, as discussed above. Movement of the shuttle 102 in the “y” direction thus imparts a corresponding movement to the movable portion 116. In particular, the movable portion 116 is movable in the “y” direction between a first or un-deflected position that corresponds to the first position of the shuttle 102, as depicted in
The first tuning element 14a comprises the projection 49a, the dielectric element 50, and the movable portion 116, as discussed above. The projection 49a adjoins the second leg 48 of the intermediate portion 32 of the coupler 12, and is thus subjected to the voltage potential associated with the input signal being transmitted through the coupler 12. The movable portion 116 adjoins the body 103 of the shuttle 102 of the first actuator 14a, and is thus maintained at a grounded, or zero-potential state.
The projection 49a, the dielectric element 50, the air with the gap 119, and the movable portion 116 function as a capacitive element when the coupler 12 is energized by the input signal thereto. In particular, the projection 49a and the movable portion 116 acts as the electrically-conductive plates of a capacitor, and the dielectric element 50 and the air within the gap 119 act as a dielectric located between the plates. The first and second tuning elements 14a, 14b thus introduce a source of reactance within the signal path through the coupler 12 when a sinusoidally-varying signal is input to the coupler 12 via the first leg 40 of the input portion 30.
The reactance of the first and second tuning elements 14a, 14b affects the resonance frequency of the coupler 12, which in turn varies the frequency response of the coupler 12. In particular, introducing the noted reactance into the coupler 12 causes the coupler 12 to act as a band-pass filter in which a band of frequencies at and near the resonance frequency of the coupler 12 pass through the coupler 12 with little or no attenuation, while frequencies outside of the pass band are substantially attenuated.
Moreover, the capacitance of the first and second tuning elements 14a, 14b can be varied as follows, which allows the pass band to be altered. Altering the pass band permits the coupler 12 to be “tuned” so as to facilitate the transmission of certain frequencies and the attenuation of others.
As discussed above, the first and second actuators 16a, 16b each operate the movable portion 116 of the first or second actuator 16a, 16b in the “y” direction, which in turn varies the gap 119 between the end face 117 of the movable portion 116 and the dielectric element 50. Increasing the gap 119 increases the amount of air between the end face 117 and the dielectric element 50. Increasing the gap (d) decreases the capacitance (C) of the first and second tuning elements 14a, 14b, which in turn increases the reactance (L/C) introduced into the signal path within the coupler 12 (C=εo*εr*A/d). The increase in reactance produces a corresponding increase in the resonant frequency (fo) of the coupler 12, which in turn increases the frequency of the pass band (fo=sqrt(L/C)). The coupler 12 can thus be tuned to respond maximally to an optimum or otherwise desired frequency or range of frequencies at a particular operating condition.
The optimal number of tuning elements 14a, 14b for the system 10 is application-dependent, and can vary with factors such as the desired or required level of reactance to be introduced into the signal path within the coupler 12; size constraints imposed on tuning elements; etc. Alternative embodiments of the system 10 can be formed with more, or less than two of the tuning elements 14a, 14b.
The system 10 can be equipped with a controller (not shown) configured to control the movement of the movable portions 116 of the first and second tuning elements 14a, 14b so as to produce a desired tuning effect in the coupler 12 at a particular operating condition.
Based on finite element modeling (FEM), it is estimated the system 10 has a tuning range of approximately 3.6 (GHz) with a center frequency of approximately 42.4 GHz, and with very favorable return losses of 42.5 (dB). Moreover, the substantially all-metal construction of the coupler 12 gives the coupler 12 relatively high power-handling capability, while permitting the coupler 12 to be constructed within a relatively small dimensional footprint.
The system 10 and alternative embodiments thereof can be manufactured using known processing techniques for creating three-dimensional microstructures, including coaxial transmission lines. For example, the processing methods described in U.S. Pat. Nos. 7,898,356 and 7,012,489, the disclosure of which is incorporated herein by reference, can be adapted and applied to the manufacture of the switch 10 and alternative embodiments thereof.
The system 10 can be manufactured using the following process. A layer of photoresist material is selectively applied to the upper surface of the substrate 18 so that the only exposed portions of the upper surface correspond to the locations of the various components of the system 10 that are to be disposed directly on the substrate 18. The electrically-conductive material, i.e., Cu, is subsequently deposited on the exposed portions of the substrate 18 to a predetermined thickness, to form the first layer of the electrically-conductive material.
Another photoresist layer is subsequently applied to the partially-constructed system 10 by patterning additional photoresist material over the partially-constructed system 10, and over the previously-applied photoresist layer, so that so that the only exposed areas on the partially-constructed system 10 correspond to the locations at which the various portions of the second layer of the system 10 are to be located. The electrically-conductive material is subsequently deposited on the exposed portions of the system 10 to a predetermined thickness, to form the second layer of the electrically-conductive material. The third through fifth layers are subsequently formed in substantially the same manner. Once the fifth layer has been formed, the photoresist material remaining from each of the masking steps can be released or otherwise removed, using a suitable technique such as exposure to an appropriate solvent that dissolves the photoresist material.
An adaptation of the above process to the manufacture of a microelectromechanical systems (MEMS) switch is described in detail in co-pending U.S. application Ser. No. 13/592,435 filed on Aug. 23, 2012, the contents of which is incorporated by reference herein in its entirety.
