Patent Description:
RF MEMS devices are a technology that, in its most general form, can be defined as miniature devices that use an electrically actuated mechanical movement to achieve an open circuit or a closed circuit in a RF transmission line. When the RF MEMS device is in an on-position, the RF transmission line is "closed" and the RF MEMS device can be used to conduct a high-frequency RF signal. It is recognized that RF MEMS devices are ideal for providing such switching capability between open and closed circuits due to their desirable RF properties, including low radiative loss, low capacitive open state coupling (300fFd), and very small mechanical geometry (<NUM>), resulting in minimal inductive parasitics and relatively low contact resistance (1ohm).

One application of RF MEMS devices is for use in electronically steered antenna (ESA) systems, which are systems that combine the signals from multiple stationary antenna elements to point a beam of radio waves at a certain angle in space. The characteristics and angle of the beam may be controlled via an electronic steering of the beam in different directions without physically moving the antennas, with true time delay (TTD) being one known technique for doing so. Beam steering via TTD is accomplished by changing the path length or transmission time of each antenna element, which may be achieved by providing a TTD module that includes a plurality of RF MEMS devices coupled to RF transmission lines of various lengths. The amount of time it takes for a signal to be transmitted between the common feed point and the antenna is controlled by selecting a particular combination of transmission lines via switching of the RF MEMS devices, which imparts a desired amount of phase or time delay on the RF signal to each element.

It is recognized, however, that the use of RF MEMS devices and accompanying RF transmission lines for existing RF transmission systems (including ESA systems that utilize TTD) has numerous limitations and challenges associated therewith. One primary challenge is achieving a desired characteristic impedance of <NUM> Ohms in the system - which is the standard characteristic impedance utilized in most RF transmission systems. That is, due to the size of the RF MEMS devices and RF transmission lines in such systems, it is often difficult to achieve a characteristic
impedance of <NUM> Ohms due to challenges associated with the miniaturization of the system. For example, characteristic impedance may be desirably altered by changing the width of the RF transmission lines or a spacing between the RF transmission lines, but such altering would result in increased resistance in the system (if the RF transmission lines are narrowed) or an increased size of the system (if spacing between the RF transmission lines is increased). As another example, characteristic impedance may be desirably altered by reducing a thickness of the insulating substrate (e.g., glass) upon which the RF transmission lines are formed in the system, but such thinning of the substrate may lead to poorer yields during fabrication due to the fragility of the substrate and potential breakage thereof that might occur with such reduced thickness.

Therefore, it would be desirable to provide an RF MEMS transmission system that provides a desirable characteristic impedance while addressing yield issues during fabrication. It would further be desirable to provide an RF MEMS transmission system with low RF insertion loss (<4dB) that enables passive beamformer assemblies and maintains good signal transmission for broadband frequency signal processing applications. United States Patent Application No. <CIT> discloses a phase shifter having at least one phase shift section. The phase shift section includes an input port for receiving an incoming radio frequency signal, an output port for transmitting an outgoing radio frequency signal, an input junction coupled to the input port, an output junction coupled to the output port, and a plurality of transmission lines. The input junction includes a first plurality of cantilever type switches, and the output junction includes a second plurality of cantilever type switches. Each transmission line connects one of the first plurality of cantilever type switches to a corresponding one of the second plurality of cantilever type switches. The first plurality of cantilever type switches, the second plurality of cantilever type switches, and the plurality of transmission lines are formed in a coplanar waveguide. United States Patent Application No. <CIT> describes a witch module which comprises N MEM switches fabricated on a common substrate, each of which has input and output contacts and a movable contact which bridges the input and output contacts when the switch is actuated. The input contacts are connected to a common input node, and the output contacts are connected to respective output lines. Each output line has an associated inductance and effective capacitance, and is arranged such that its inductance is matched to its effective capacitance. The switches are preferably arranged symmetrically about the terminus point of the signal input line. A phase shifter employs at least two switch modules connected together with N transmission lines having different lengths, operated such that an input signal is routed via one of the transmission lines to effect a desired phase-shift. United States Patent Application No. <CIT> teaches an impedance matching structure for a RF MEMS switch having at least one closeable RF contact in an RF line, the impedance matching structure comprising a protuberance in the RF line immediately adj acent the RF contact that forms one element of a capacitor, the other element of which is formed by the switch's ground plane.

According to a first aspect, the invention provides an RF transmission system in accordance with claim <NUM>. According to a second aspect the invention provides a method of manufacturing a radio frequency (RF) microelectromechanical system (MEMS) transmission device in accordance with claim <NUM>. Further aspects of the invention are set forth in the dependent claims, the drawings and the following description of embodiments.

These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.

The drawings illustrate embodiments presently contemplated for carrying out the invention.

Embodiments of the invention are directed to an RF MEMS transmission system having a selectively increased characteristic impedance that reduces insertion losses, with one or more features of the RF transmission lines being formed to provide the increased characteristic impedance. The RF transmission line may be further structured to increase the durability thereof so as to provide for improved yields during fabrication thereof.

Embodiments of the invention are shown and described here below for use in an RF MEMS transmission system in the form of a radar system that includes radiating antenna elements that receive RF inputs from a true time delay (TTD) beam former or module. However, it is recognized that embodiments of the invention may be implemented with other RF transmission systems other than those specifically shown and described herein. Accordingly, embodiments of the invention are not meant to be limited only to the specific RF MEMS transmission system described herein, but may be utilized in other RF MEMS transmission systems. Furthermore, while a TTD beam former is specifically disclosed here below are being utilized in the radar system, it is recognized that other RF MEMS transmission device that utilize MEMS switches and RFT transmission lines are recognized as being within the scope of the invention.

Referring first to <FIG>, a simplified schematic diagram of a radar system <NUM> (or alternatively an "RF transmission system") is illustrated. The radar system <NUM> includes an antenna <NUM> constructed of multiple radiating elements <NUM> for transmitting and receiving signals. These radiating antenna elements <NUM> are fed by a source <NUM> that provides an RF input such as RF modulated signal having a predetermined wavelength. This RF input is transmitted by a transmit/receive switch <NUM> through a splitter/combiner <NUM> to a true time delay (TTD) beam former or module <NUM> corresponding to each antenna element <NUM>. A controller <NUM> provides drive signals to a driver die <NUM>, which selectively controls switching elements within the TTD module <NUM> in a manner that generates a time delayed signal. These TTD modules <NUM> output the time delayed signal to a respective antenna element <NUM>. Signals received by antenna elements <NUM> are transmitted through splitter/combiner <NUM> to a receiver <NUM>. While not specifically illustrated in <FIG>, it is contemplated that embodiments of the invention may be configured for independent beam control of the vertical, horizontal, and circular polarizations and include separate beam controlling circuitry for each polarization.

<FIG> is a schematic top view of a TTD module <NUM> incorporated in the radar system or RF transmission system <NUM> of <FIG>, according to one embodiment of the invention. The TTD module <NUM> includes a micro-strip transmission line <NUM> or signal line patterned on a base substrate <NUM> to include four (<NUM>) sets of time delay stages <NUM>, <NUM>, <NUM>, <NUM>. Micro-strip transmission line <NUM> is formed using a deposition, patterning, and/or etching technique as known in the art. In a preferred embodiment, base substrate <NUM> is formed of fused silica, which provides reduced current leakage and improved switch channel isolation. According to alternative embodiments, base substrate <NUM> may be an insulating, semi-insulating material, or semi-conductive material such as, but not limited to glass, alumina, ceramic, LTCC, HTCC, quartz, polyimide, gallium arsenide, silicon, or germanium. Alternatively, base substrate <NUM> may be a semiconductor wafer processed to include switching elements or switches <NUM>, <NUM> and micro-strip transmission line <NUM>.

Micro-strip transmission line <NUM> may be any conductive material such as, for example, copper, gold, a tungsten/nickel/gold stack, or another common packaging material. As shown, micro-strip transmission line <NUM> is patterned such that the delay stages <NUM>, <NUM>, <NUM>, <NUM> are serially connected, with the first delay stage <NUM> coupled to an RF signal input <NUM> of the TTD module <NUM> and the fourth delay stage <NUM> coupled to the RF signal output <NUM> of the TTD module <NUM>. Each of the delay stages <NUM>, <NUM>, <NUM>, <NUM> includes an input electronic switching element <NUM> and an output electronic switching element <NUM> that are selectively controlled in either their on or off positions to insert a cumulative time delay in a transmission signal sent to the respective antenna element <NUM> (<FIG>), as described in additional detail below. While elements <NUM> and <NUM> are described herein as input and output, respectively, it is contemplated that the functionality of elements <NUM>, <NUM> might be reversed such that element <NUM> is an RF signal output and element <NUM> is an RF signal input. Similarly, it is to be understood that switching elements <NUM> and <NUM> function as respective "input" and "output" switching elements of respective delay lines <NUM>, <NUM>, <NUM>, <NUM> when an RF signal travels through TTD module <NUM> from RF signal element <NUM> to RF signal element <NUM> and as "output" and "input" switching elements, respectively, when the signal travels in the reverse direction.

The first delay stage <NUM> includes four micro-strip delay lines <NUM>, <NUM>, <NUM>, <NUM> patterned on the base substrate <NUM> of the TTD module <NUM>. Delay lines <NUM>, <NUM>, <NUM>, <NUM> have different lengths that impart different time delays to the RF input signal. Delay line <NUM> has a length L1, delay line <NUM> has a length L2, delay line <NUM> has a length L3, and delay line <NUM> has a length L4, with L1<L2<L3<L4. The phase of the transmission signal is shifted in proportion to the time delay imparted by the delay line <NUM>, <NUM>, <NUM>, <NUM>, with the longest delay line <NUM> imparting the greatest time delay.

The second, third, and fourth delay stages <NUM>, <NUM>, <NUM> are formed in a similar manner as the first delay stage <NUM>, with each delay stage <NUM>, <NUM>, <NUM> including four micro-strip delay lines <NUM>-<NUM> of varying lengths patterned on the base substrate <NUM>. Line segments <NUM>, <NUM>, <NUM> interconnect the delay stages <NUM>-<NUM>. Additional phase shift is imparted to the input signal by each subsequent delay stage <NUM>-<NUM> by selectively closing a given pair of switches <NUM>, <NUM> on one of the four micro-strip delay lines <NUM>-<NUM> while the remaining pairs of switches are maintained in an open position a similar manner as described above.

Switching devices <NUM>, <NUM> are positioned on base substrate <NUM> at the terminal input and terminal output, respectively, of each micro-strip delay line <NUM>-<NUM>. In the illustrated embodiment, the micro-strip delay lines <NUM>-<NUM> of the first delay stage <NUM> and the third delay stage <NUM> are constructed having a star or fan out configuration and the micro-strip delay lines <NUM>-<NUM> of the second delay stage <NUM> and the fourth delay stage <NUM> are constructed having a linear configuration. However, it is contemplated that the delay stages may be constructed having any number alternative configurations based on design specifications of a particular application.

The TTD module <NUM> disclosed herein is designed as a <NUM> state beam former, with four (<NUM>) delay stages, and a <NUM> degree delay/phase-shift range. TTD module <NUM> is operable over the entire Ku-band or over a <NUM>-<NUM> bandwidth. However, it is contemplated that the concepts disclosed herein may be extended to TTD modules having any number of delay stages, with the number of delay stages and the length of the individual delay lines within those stages determined based on the desired amount of delay and resulting beam steering resolution for a particular application. Likewise, while the dimensions of TTD module <NUM> disclosed herein are approximately <NUM> by <NUM>, a skilled artisan will recognize that the dimensions of TTD module may be altered based on the design specifications of a particular application.

According to embodiments of the invention, switches <NUM>, <NUM> are provided as MEMS devices - such that the TTD module <NUM> may be referred to as an "RF MEMS transmission device. " The MEMS switches <NUM>, <NUM> may be formed using a build-up technique involving multiple deposition, anodization, patterning, and etching steps. In an exemplary embodiment, MEMS switches <NUM>, <NUM> have a construction similar to the MEMS switch <NUM> depicted in <FIG>, which is illustrated as an ohmic contact switch mechanism. MEMS switch <NUM> includes a contact <NUM> and a moveable element <NUM> such as for example, a cantilevered beam. In some embodiments, the moveable element <NUM> can be supported by an anchor, which may be integrated with the moveable element <NUM> and serve to connect the moveable element <NUM> to an underlying support structure such as base substrate <NUM>. In the illustrated embodiment the moveable element <NUM> is a cantilevered beam that includes two cantilever portions connected to a common beam portion. However, it is contemplated that moveable element may be configured having alternative geometries in other embodiments. Contact <NUM>, cantilevered beam <NUM>, and electrode <NUM> are formed at least partially of at least one conductive material such as gold, gold alloy, nickel, nickel alloy, platinum, tantalum, and tungsten, as non-limiting examples. The switch <NUM> also includes an electrode or driving means <NUM> that effects a potential difference between the electrode <NUM> and the cantilevered beam <NUM>.

As shown in <FIG>, the contact <NUM> and moveable element <NUM> of switch <NUM> are formed between two micro-strip lines 72a and 72b patterned on base substrate <NUM>, with the electrode <NUM> positioned between micro-strip lines 72a and 72b. Switch <NUM> may be formed on base substrate <NUM> through a micro fabrication technique, such as, for example, vapor deposition, electroplating, photolithography, wet and dry etching, and the like, such that switch <NUM> constitutes a portion of a microelectromechanical device, nanoelectromechanical device, or MEMS. In such an embodiment, switch <NUM> is fabricating having features on the order of ones or tens of micrometers or nanometers.

When appropriately charged, the electrode <NUM> of MEMS switch <NUM> generates an electrostatic force that pulls the cantilevered beam <NUM> toward the electrode <NUM> and the contact <NUM>. The electrode <NUM> thus acts as a gate with respect to the switch <NUM>, causing the cantilevered moveable element <NUM> to move between a non-contacting or "open" position in which the moveable element <NUM> is separated from the contact <NUM> (shown in <FIG>), and a contacting or "closed" position in which the moveable element <NUM> contacts and establishes electrical communication with the contact <NUM>, thereby closing a circuit between micro-strip lines 72a and 72b.

As further shown in <FIG>, an embedded micro-strip configuration is provided with MEMS switch <NUM> (and overall in TTD module <NUM> of <FIG>) by including a ground layer <NUM> below the base substrate <NUM> along with micro-strip lines 72a and 72b (and micro-strip transmission lines <NUM>, <FIG>) patterned on base substrate <NUM> - with the micro-strip lines and ground plane layer <NUM> interacting with each other to create an electromagnetic wave that travels through dielectric substrate <NUM> to create an RF signal. While a specific grounding configuration is illustrated in <FIG>, it is contemplated that TTD module <NUM> may be fabricated having alternative strip-line and embedded micro-strip grounding configurations, such as, for example a grounded coplanar waveguide configuration wherein two ground lines (not shown) are provided coplanar to the micro-strip transmission line <NUM> on the base substrate <NUM>. In yet another alternative embodiment, TTD module <NUM> is constructed with an inverted ground plane (not shown) that is positioned above the anchor <NUM> and base substrate <NUM>.

In operation of TTD module <NUM>, a given delay line, such as delay line <NUM> of the third delay stage <NUM> for example, is activated by closing the input switch <NUM> and output switch <NUM> on the delay line <NUM> while maintaining the switches <NUM>, <NUM> on delay lines <NUM>-<NUM> in an open position. The MEMS switches <NUM>, <NUM> of TTD module <NUM> are controlled to move between their open and closed positions by applying a selective gate voltage to the electrode <NUM> of the MEMS switch <NUM>, <NUM>. This gate voltage is provided through gating lines (not shown) patterned on the base substrate <NUM>, with the gating lines electrically coupling the MEMS switches <NUM>, <NUM> to gate voltage sources or gate drivers (not shown) that receive power from power sources to establish a potential difference between the contact <NUM> and the cantilevered beam <NUM> of the MEMS switches <NUM>, <NUM> when the switch is in the open position.

With regard to the operation of TTD module <NUM>, it is recognized that ideal operation of the module would be at a characteristic impedance of <NUM> Ohms - which would typically match with a <NUM> Ohm source resistance and load resistance found in an RF transmission system. However, it is recognized that it may be difficult to achieve a characteristic impedance of <NUM> Ohms in TTD module <NUM> due to the small size of the RF MEMS devices <NUM>, <NUM> and micro-strip transmission line <NUM> in the module. For example, characteristic impedance may be lowered in TTD module <NUM> by increasing a width of the micro-strip transmission line <NUM>, but such altering would result in an increased size of the module. As another example, characteristic impedance may be lowered by reducing a thickness of the substrate <NUM>, such as by forming the substrate with a thickness of <NUM>, but such thinning of the substrate <NUM> may lead to poorer yields during fabrication due to the fragility of the substrate and potential breakage thereof that might occur with such reduced thickness.

Accordingly, embodiments of the invention are directed to an RF MEMS transmission device (such as TTD module <NUM>) having a selectively increased characteristic impedance. According to an exemplary embodiment, the characteristic impedance in TTD module <NUM> is increased to a level of <NUM> Ohms, which minimizes the impact of resistive losses in the micro-strip transmission line <NUM> and MEMS switches <NUM>, <NUM> and lowers RF insertion loss, so as enable passive beamformer assemblies and maintain good signal transmission. Block schematic diagrams of a prior art RF MEMS transmission system <NUM> and an RF MEMS transmission system <NUM> according to an embodiment of the invention are shown in <FIG>, respectively. As shown therein, each of the RF MEMS transmission systems <NUM>, <NUM> includes an RF source <NUM> and an RF load <NUM> (e.g., radiating antenna element) that have a characteristic impedance of <NUM> Ohms. However, the prior art RF MEMS transmission system <NUM> of <FIG> includes a <NUM>-stage TTD module <NUM> having a characteristic impedance of <NUM> Ohms (based on the construction thereof, as will be explained in greater detail below), whereas the <NUM>-stage TTD module <NUM> of <FIG> has an increased characteristic impedance of <NUM> Ohms (based on the construction thereof, as will be explained in greater detail below).

As further shown in <FIG>, impedance transformers <NUM> are provided at the input and output of TTD module <NUM> to account for differences in the characteristic impedance between the RF source80, the TTD module <NUM>, and the RF load <NUM> - with the impedance transformers <NUM> increasing/decreasing the characteristic impedance as required to transition between these impedance values. Such impedance transformers <NUM> may be of a known construction and function to convert current at one voltage to the same waveform at another voltage, with a balun transformer being one possible device/component to perform the impedance transformation, for example. In another embodiment, the impedance transformers <NUM> may be formed on the same substrate as the TTD module <NUM> to enable a <NUM> Ohm "part" to be created. That is, impedance transformers <NUM> may be formed on base substrate <NUM> (<FIG>) of the TTD module <NUM> as part of the fabrication thereof, so as to be considered an integral part/component of the TTD module - with the TTD module <NUM> functioning as a <NUM> Ohm device.

According to embodiments of the invention, and in order to increase the characteristic impedance in TTD module <NUM>, <NUM>, one or more of a width of the micro-strip transmission lines <NUM> and a thickness of the substrate <NUM> may be selectively controlled relative to one another during fabrication of the TTD module <NUM>, <NUM>. Referring again to <FIG>, a width of the micro-strip transmission lines 72a, 72b, indicated at <NUM>, and a thickness of the substrate <NUM>, indicated at <NUM>, are illustrated. As indicated previously, varying a width <NUM> of the micro-strip transmission lines 72a, 72b (and of lines <NUM> generally, in <FIG>) alters the characteristic impedance in TTD module <NUM> - with a narrowing of the width <NUM> increasing the characteristic impedance. Additionally, varying a thickness <NUM> of the substrate <NUM> alters the characteristic impedance in TTD module <NUM> - with a thickening of the substrate <NUM> increasing the characteristic impedance. Various combinations of substrate thickness <NUM> and micro-strip transmission line width <NUM> - when taken in combination with a length <NUM> and thickness <NUM> of the micro-strip transmission lines 72a, 72b and material properties of the substrate <NUM> and micro-strip transmission lines 72a, 72b (e.g., gallium arsenide (GaAs) substrate and copper lines) - are possible to achieve a desired characteristic impedance in TTD module <NUM> and examples of such combinations are provided here below in Table <NUM>, with such thicknesses/widths being provided for a prior art <NUM> Ohm TTD module and for various <NUM> Ohm TTD modules, according to embodiments of the invention.

While it can be seen in Table <NUM> that each of the TTD modules with a characteristic impedance of approximately <NUM> Ohms (i.e., <NUM> +/- <NUM> to <NUM> Ohms) has an increased resistive loss (dB/mm) as compared to the resistive loss in the TTD module with a characteristic impedance of approximately <NUM> Ohms, it is recognized that the overall resistive loss in the TTD modules is dominated by the contact resistance of the MEMS switches <NUM>, <NUM>. Furthermore, it is recognized that the overall impact of resistive loss in the TTD module is relative to the characteristic impedance of the TTD module - with the impact of resistive loss decreasing as the characteristic impedance of the TTD module increases. Accordingly, for TTD modules with characteristic impedances of <NUM> Ohms and <NUM> Ohms, insertion losses for the <NUM> Ohm TTD module are greatly reduced as compared to the <NUM> Ohm TTD module. Using the TTD modules <NUM>, <NUM> of <FIG> as an example, and assuming that each TTD module has an RF signal path with a minimum of eight (<NUM>) MEMS switches through which an RF signal must pass, the insertion losses would be defined as: <MAT> Thus, it is seen that an approximate <NUM>% reduction in insertion loss can be achieved in TTD module <NUM> by constructing the TTD module to have a characteristic impedance of <NUM> Ohms rather than a characteristic impedance of <NUM> Ohms. This reduction in the insertion loss in the high impedance TTD module <NUM> results in an accompanying decrease in DC power consumed by the TTD module.

While it is recognized that the useage of impedance transformers <NUM> with the TTD module <NUM> (either positioned at inputs/outputs of the TTD module or formed on the same substrate as the TTD module, so as to be a part thereof) serves to reduce the bandwidth of the RF transmission system, this reduction does not have a negative impact on system operation. That is, as the antenna elements <NUM> in the radar system <NUM> (<FIG>) already limit the bandwidth of the system, the inclusion of impedance transformers <NUM> in the RF transmission system do not have any additional negative impact on the system bandwidth.

Beneficially, embodiments of the invention thus provide an RF MEMS transmission device (such as a TTD module) having selectively increased characteristic impedance that: reduces insertion losses, improves yields of RF transmission lines in the system, and/or minimizes the planar space of the system. An increasing of the characteristic impedance can be achieved via a thickening of the substrate on which the micro-strip transmission lines are formed, such as to thicknesses of between <NUM>-<NUM>, with the thickening of the substrate also providing greater stability during fabrication thereof so as to decrease the risk of wafer breakage and improve line yield (e.g., increase from <NUM>% yield to <NUM>% yield). An increasing of the characteristic impedance can also be achieved via a narrowing of the micro-strip transmission lines, such as to a width of between <NUM>-<NUM>, with the narrowing of the micro-strip transmission lines also allowing for a decrease in the planar space of the RF transmission system. The thickening of the substrate and/or the narrowing of the micro-strip transmission lines can be selectively optimized according to a selection process so as to achieve a desired increased impedance - such as <NUM> Ohms, for example. Impedance transformers can be employed to perform impedance matching between the high impedance RF MEMS transmission system and the lower impedances of the RF source and RF load, with it being recognized that the impedance transformers should not have an adverse affect on the system bandwidth based on antenna elements in the system already limiting the bandwidth of the system.

According to one embodiment of the invention, an RF transmission system includes an RF source that provides an RF input and one or more RF MEMS transmission devices coupled to the RF source to receive the RF input therefrom and generate output signals for transmission to an RF load. Each of the one or more RF MEMS transmission devices comprises a substrate, a conducting line formed on the substrate to provide signal transmission paths between a signal input of the RF MEMS transmission device and a signal output of the RF MEMS transmission device, and a plurality of switching elements positioned along the conducting line and selectively controllable to define the signal transmission paths between the signal input and the signal output. Each of the RF source and the RF load has a first characteristic impedance and the one or more RF MEMS transmission devices have a second characteristic impedance that is greater than the first characteristic impedance.

According to another embodiment of the invention, a method of manufacturing an RF MEMS transmission device includes forming a substrate, forming a signal line on a top surface of the substrate that includes plurality of line portions, and coupling a MEMS switching device to the signal line, the MEMS switching device operable in a closed position and an open position to selectively couple and decouple respective line portions of the signal line to transmit an RF signal therethrough. Forming the substrate and the signal line comprises selectively controlling a thickness of the substrate and a width of the signal line relative to one another such that, when taken in combination with a length and thickness of the signal line and material properties of the substrate and signal line, a characteristic impedance of the RF MEMS transmission device is higher than a <NUM> Ohm characteristic impedance of an RF source and an RF load to which the RF MEMS transmission device is connected.

According to yet another embodiment of the invention, an RF MEMS transmission device includes a substrate having a thickness, a plurality of MEMS devices disposed on a top surface of the substrate, and conductive signal lines formed on the top surface of the substrate, the conductive signal lines each having a length, width, and thickness. The thickness of the substrate and the width of the conductive signal lines is such that, when taken in combination with others of the thickness of the substrate and the length, width, and thickness of the conductive signal lines, a characteristic impedance of the RF MEMS transmission device is approximately <NUM> Ohms.

Claim 1:
A radio frequency,RF, transmission system (<NUM>), comprising:
an RF source (<NUM>) that provides an RF input;
an RF load; one or more RF microelectromechanical system, MEMS, transmission devices (<NUM>) coupled to the RF source (<NUM>) to receive the RF input therefrom and generate output signals for transmission to an RF load, wherein each of the one or more RF MEMS transmission devices (<NUM>) comprises:
a substrate (<NUM>);
a conductive signal line (<NUM>) formed on the substrate (<NUM>) to provide signal transmission paths between a signal input (<NUM>) of the RF MEMS transmission device (<NUM>) and a signal output (<NUM>) of the RF MEMS transmission device (<NUM>); and
a plurality of switching elements (<NUM>, <NUM>) positioned along the conductive signal line (<NUM>) and selectively controllable to define the signal transmission paths between the signal input (<NUM>) and the signal output (<NUM>);
characterized in that each of the RF source (<NUM>) and the RF load has a first characteristic impedance and the one or more RF MEMS transmission devices (<NUM>) have a second characteristic impedance that is greater than the first characteristic impedance,
wherein the first characteristic impedance of the RF source (<NUM>) and the RF load is approximately <NUM> Ohms and the second characteristic impedance of the one or more RF MEMS transmission devices (<NUM>) is approximately <NUM> Ohms.