Patent Publication Number: US-8976500-B2

Title: DC block RF coaxial devices

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit and priority of U.S. Provisional Application No. 61/348,659, filed on May 26, 2010, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     The present invention generally relates to DC blocking devices and improvements thereof. More particularly, the invention relates to DC block RF coaxial devices with surge protection and improvements thereof. 
     2. Description of the Related Art 
     DC block filters for use in electric circuits or between systems or devices are known and used in the art. Oftentimes in electrical systems, it is desirable to control input signal frequencies to a desired range of frequency values by blocking low frequency or DC signals from transmitting to a connected system or electrical component. Such signals can interfere with the designed operation of the connected system or damage the electrical components if not blocked along the transmission line. Devices, such as DC block filters, may be connected in-line along the transmission line to prevent the DC signals from encountering any connected equipment downstream from the filter. 
     Currently available DC block filters are commonly two-terminal devices and utilize a single capacitor connected in series between the two terminals. An input source is connected to one terminal and the hardware to be protected is connected to the other terminal. Depending upon the capacitor value of the DC block filter, certain voltage or current frequencies encounter a low impedance and are allowed to pass through the filter while other, lower frequency signals (e.g. DC signals) are blocked by the high impedance of the capacitor. Significant problems can arise if the capacitor of the DC block filter is damaged or otherwise fails and no longer operates to block the DC signals from reaching the connected hardware or equipment. 
     One particularly problematic cause of capacitor failure is the presence of a power surge on the transmission line utilizing the DC block filter. Power surges can originate from a variety of possible causes. One such cause is radio frequency (RF) interference that can couple to power or transmission lines from a multitude of sources. The power or transmission lines act as large antennas that may extend over several miles, thereby collecting a significant amount of RF noise from such sources as radio broadcast antennas. Another source of RF interference stems from equipment connected to the power or transmission lines that conducts along those lines to the equipment to be protected. In particular, older computer hardware may emit significant amounts of RF interference. A further cause of harmful electrical energy surges is conductive noise generated by equipment connected to the power or transmission lines which conducts along the lines to the equipment to be protected. Still another cause of disruptive electrical energy is lightning and typically arises when a lightning bolt strikes a component or transmission line that is coupled to the protected hardware or equipment. Lightning surges generally include DC electrical energy and AC electrical energy up to approximately 1 MHz in frequency and are complex electromagnetic energy sources having potentials estimated from 5 million to 20 million volts and currents reaching thousands of amperes. 
     Such electrical energy surges are often unpredictable and can significantly damage hardware or equipment either directly by entering the hardware or equipment via the transmission line or indirectly by damaging signal conditioning devices (e.g., DC block filters) connected in-line along the transmission line. Currently available DC block filters are particularly susceptible to such power surges since the incorporated capacitor is often not rated for high RF power and has a low breakdown voltage, for example of about 2 kV to 3 kV. The power surge, which can reach voltage levels of 20 kV or higher, will permanently damage the traditional DC block capacitor, often by shoot-through or punch-through of the capacitor dielectric or via carbon shorts. The surge will then continue to propagate down the transmission line towards any connected equipment. Incorporating a DC block capacitor with a much higher breakdown voltage to withstand the power surge is often not a viable solution since the use of such capacitors deteriorates the RF performance of the filter. 
     Even if the surge is mitigated by other surge suppression devices before reaching the connected equipment, the DC block filter will require replacement due to the permanent damage to the DC blocking capacitor. In certain cases, the failure of the DC block filter may not be readily apparent until the connected equipment begins to malfunction or fail due to the presence of unanticipated DC signal bias at its input. Contributing to the problem, communications equipment, computers, home stereo amplifiers, televisions and other electronic devices are increasingly manufactured using small electronic components that are increasingly vulnerable to damage from even small electrical signal variations outside the designed operating parameters. These signal variations can cost significant amounts in both damaged equipment or in maintenance costs to ensure filtering devices have not failed during their operation. 
     Therefore, a cost effective DC block device is needed to ensure hardware or equipment is adequately protected from undesirable DC signals even after a surge condition has propagated through the DC block device. Ideally, such a DC block device would have a compact size, a high return loss for passed RF signals, a low insertion loss for passed RF signals and a low voltage standing wave ratio (VSWR). In addition, the DC block device should be capable of continued operation to protect any connected equipment despite the occurrence of an electrical surge at the DC block device. 
     SUMMARY 
     A device for blocking DC signals and capable of continued operation without replacement after a surge condition is disclosed. In one embodiment, a DC block RF device includes a housing defining a cavity with a first conductor, a second conductor, a first capacitor, a second capacitor and a coil positioned within the cavity. The first capacitor has a first terminal electrically connected to the first conductor and a second terminal. The first capacitor is configured to pass a surge signal from the first terminal to the second terminal without damaging the first capacitor. The second capacitor has a first terminal electrically connected to the second conductor and a second terminal electrically connected to the second terminal of the first capacitor. The coil has an inner radius electrically connected to the second terminal of the first capacitor and an outer radius electrically connected to the housing. 
     In another embodiment, a DC block RF device includes a housing defining a cavity having a central axis, an input conductor disposed in the cavity of the housing and extending substantially along the central axis of the cavity and an output conductor disposed in the cavity of the housing and extending substantially along the central axis of the cavity. The DC block RF device further includes two N-Type end connectors, an N-Type input connector electrically connected to the input conductor and an N-Type output connector electrically connected to the output conductor. A first capacitor is connected to the input conductor and is configured to arc a predetermined level of surge voltage across the first capacitor without impairing the first capacitor. A second capacitor is connected to the output conductor and an inductor is disposed within the cavity, the inductor having an outer edge connected to the housing and an inner edge connected to the first capacitor and to the second capacitor. 
     In still another embodiment, a DC block RF device includes a housing defining a cavity having a central axis and an input conductor and an output conductor positioned substantially along a portion of the central axis within the cavity. A DIN input end connector is attached to the housing and coupled with the input conductor and a DIN output end connector is attached to the housing and coupled with the output conductor. A first capacitor is connected to the input conductor and is configured to arc a predetermined level of surge voltage across the first capacitor without damaging the first capacitor. A second capacitor is connected to the output conductor. A spiral inductor, positioned along a plane substantially perpendicular to the central axis, has an outer radius connected to the housing and an inner radius connected to the first capacitor and to the second capacitor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other systems, methods, features, and advantages of the present invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. Component parts shown in the drawings are not necessarily to scale, and may be exaggerated to better illustrate the important features of the present invention. In the drawings, like reference numerals designate like parts throughout the different views, wherein: 
         FIG. 1  is a schematic circuit diagram of a DC block RF coaxial device according to an embodiment of the invention; 
         FIG. 2  is a cross-sectional view of the DC block RF coaxial device having the schematic circuit diagram shown in  FIG. 1  according to an embodiment of the invention; 
         FIG. 3  is a perspective view of the DC block RF coaxial device having the schematic circuit diagram shown in  FIG. 1  and having N-type female-female press-fit end connectors according to an embodiment of the invention; 
         FIG. 4  is a disassembled perspective view of the DC block RF coaxial device of  FIG. 3  having N-type female-female press-fit end connectors according to an embodiment of the invention; 
         FIG. 5  is a perspective view of the DC block RF coaxial device having the schematic circuit diagram of  FIG. 1  and having DIN male-female end connectors according to an embodiment of the invention; 
         FIG. 6  is a disassembled perspective view of the DC block RF coaxial device of  FIG. 5  having DIN male-female end connectors according to an embodiment of the invention; 
         FIG. 7  is a graph of the input in-band return loss of the DC block RF coaxial device having the schematic circuit diagram shown in  FIG. 1  according to an embodiment of the invention; 
         FIG. 8  is a graph of the input in-band insertion loss of the DC block RF coaxial device having the schematic circuit diagram shown in  FIG. 1  according to an embodiment of the invention; and 
         FIG. 9  is a graph of the standing wave ratio of the DC block RF coaxial device having the schematic circuit diagram shown in  FIG. 1  according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , a schematic circuit diagram of a DC block RF coaxial device  100  is shown. The device  100  blocks DC voltage or current from propagating to protected hardware or equipment  125  that is connected to the device  100 . The device  100  also helps protect the hardware or equipment  125  from an electrical surge  120  that could damage, destroy or interfere with the hardware or equipment  125 . The device  100  includes various electrical components, including capacitors and an inductor. For illustrative purposes, the schematic circuit diagram of the device  100  will be described with reference to specific capacitor and inductor values to achieve specific DC block and surge protection capabilities. However, other specific capacitor or inductor values or configurations may be used to achieve other performance characteristics. Similarly, although the embodiments are shown with particular capacitive devices, inductors and terminal connection elements, it is not required that the exact components described be used in the present invention. Thus, the capacitive devices, inductors and terminal connection elements are to illustrate the various embodiments and not to limit the present invention. 
     The frequency range of operation for the device  100  described by the schematic circuit diagram is between about 680 MHz and about 2.5 GHz. In one embodiment, the frequency range of operation is 680 MHz to 1 GHz, within which the insertion loss is specified less than 0.1 dB and the voltage standing wave ratio (VSWR) is specified less than 1.1:1. In another embodiment, the frequency range of operation is 1.0 MHz to 3.0 MHz (a telemetry band), within which the insertion loss is similarly specified less than 0.1 dB and the VSWR is specified less than 1.1:1. The values produced above can vary depending upon the tuning of the circuit for a particular frequency range, the degree of surge protection or the desired RF performance. The device  100  is designed for blocking DC signals and has a breakdown voltage of about 6 kV. In another embodiment, a different breakdown voltage (e.g., 10 kV or higher) may be achieved. 
     The device  100  has two connection terminals including an input port  102  having an input center conductor  109  and an output port  104  having an output center conductor  110 . The connection at the input port  102  or the output port  104  may be a coaxial line with center pins as the input center conductor  109  or the output center conductor  110  for propagating RF signals and an outer shield that surrounds the center pins. The input port  102  or output port  104  may be of either gender (male or female) and of various connector types (e.g., N-Type, P-Type, DIN, etc.). Moreover, the device  100  is bidirectional, hence the input port  102  may function as an output port and the output port  104  may function as an input port. By electrically connecting the device  100  along a conductive path or transmission line between an input signal or power source and the connecting hardware or equipment  125 , an undesirable DC signal or electrical surge  120  present at the input port  102  will be blocked by the device  100  or propagated to ground through the device  100 , as described in greater detail herein. The protected hardware can be any communications equipment, cell tower, base station, PC computer, server, network component or equipment, network connector or any other type of surge or DC sensitive electronic equipment. 
     The device  100  has various components coupled between the input center conductor  109  and the output center conductor  110 , the components structured to form a desired impedance (e.g., 50Ω) and for providing an RF signal path  155  through the device  100 . This RF path  155  blocks DC voltage or current from propagating between the input port  102  and the output port  104 . The RF path  155  includes the input center conductor  109 , a first DC blocking capacitor  131 , a second DC blocking capacitor  132  and an output center conductor  110  coupled to the protected hardware and equipment  125 . During normal operation, RF signals travel across the RF path  155  from the input center conductor  109  through the first and second capacitors  131  and  132  to the output center conductor  110 . As stated above, the device  100  can operate in a bidirectional RF manner, thus the protected hardware or equipment  125  can receive or transmit RF signals along the RF path  155 . 
     The first capacitor  131  and the second capacitor  132  are positioned in series between the input center conductor  109  and the output center conductor  110  in order to block DC signals and undesirable surge transients. The first and second capacitors  131  and  132  each have a value between about 3 picoFarads (pF) and about 15 pF wherein higher capacitance values allow for better low frequency performance. Preferably, the first and second capacitors  131  and  132  each have a value of about 4.5 pF. The first or second capacitors  131  or  132  may be realized in either lumped or distributed form or may be realized by parallel rods, coupling devices, conductive plates or any other device or combination of elements which produces a capacitive effect. The first and second capacitors  131  and  132  can have the same capacitance value or different capacitance values. The capacitance of the first or second capacitors  131  or  132  can vary depending upon the frequency of operation desired and will block the flow of DC signals while permitting the flow of AC signals along the RF path  155  depending on the chosen capacitance or frequency values. At certain frequencies, the first or second capacitors  131  or  132  may operate to attenuate the AC signals. 
     When DC signals travel on the input center conductor  109  and reach the first capacitor  131 , the high impedance of the first capacitor  131  at low frequencies blocks the DC signal from propagating through the first capacitor  131 . The connected equipment or hardware  125  is thus protected from such voltages or currents and only encounter the RF signals allowed to pass through the first capacitor  131  and along the RF path  155 . For high-voltage DC signals, such as during a surge condition, rather than damaging or impairing the capacitor for future operation, the surge is allowed to pass over the first capacitor  131  via a designed or controlled spark-over. The voltages or currents are designed to arc over an air gap of the first capacitor  131  and appear on the other side of the first capacitor  131  without causing a failure of the first capacitor  131 , as discussed in greater detail herein. 
     After the spark-over across the first capacitor  131  and instead of continuing along the RF path  155 , the surge  120  is shunted to a ground  170  through a coil or inductor  135 . At low frequencies (e.g., DC signals), the inductor  135  acts as a short and allows these surge voltages or currents to flow with little impedance through the inductor  135 . Hence, the output center conductor  110  coupled to the hardware or equipment  125  is not exposed to the high voltages or currents and thus the connected hardware or equipment  125  is protected. Preferably, the inductor  135  is a spiral inductor having an inner edge or radius connected to the first capacitor  131  and an outer edge or radius connected to the housing. The inductor  135  may be replaced with or used in conjunction with a variety of low impedance elements (e.g., a quarter-wave stub, a diode, a gas tube, etc.). Integrating a low impedance element between the first capacitor  131  and the second capacitor  132  to ground  170  prevents a voltage differential from building up on the second capacitor  132 . 
     Turning now to  FIG. 2 , a cross-sectional view of the DC block RF coaxial device  100  having the schematic circuit diagram shown in  FIG. 1  is shown. The device  100  has a housing  205  that defines a cavity  210 . The cavity  210  is preferably formed in the shape of a cylinder and has an inner radius of approximately 432.5 mils. In an alternative embodiment, the cavity  210  can be formed of any shape and of varying sizes. The input center conductor  109  and the output center conductor  110  are positioned concentric with and located within the cavity  210  of the housing  205 . 
     The first capacitor  131 , the second capacitor  132  and the inductor  135  are also positioned within the cavity  210  of the housing  205 . The input and output center conductors  109  and  110  are positioned along a central axis within the cavity  210 . The first capacitor  131  has a first terminal  201  connected to the input center conductor  109  and a second terminal  202 . Similarly, the second capacitor  132  has a first terminal  203  connected to the output center conductor  110  and a second terminal  204 . The second terminals  202  and  204  of the first and second capacitors  131  and  132  electrically connect with the inductor  135  as described below. Each of the first or second capacitors  131  or  132  may be formed as parallel conductive plates with an insulative material or dielectric positioned between the plates. The inductor  135  is positioned along a plane such that the central axis of the input and output conductors  109  and  110  is positioned substantially perpendicular to the plane. In an alternative embodiment, the inductor  135  may be positioned differently within the housing  205 . 
     A set screw or other fastening element  206  is coupled to the first capacitor  131  and to the second capacitor  132  for positioning the first capacitor  131  and the second capacitor  132  against and in electrical contact with an inner radius of the inductor  135  in order to form a conductive path or node where the first capacitor  131 , the second capacitor  132  and the inductor  135  meet (see  FIG. 1 ). The set screw  206  may be non-conductive and used merely to position the terminals of the first capacitor  131 , the second capacitor  132  and the inductor  135  in contact with each other to form the above-described conductive path or node. In an alternative embodiment, the set screw  206  may itself be conductive and used to propagate electrical signals along its length. 
     Preferably, the inductor  135  is a spiral inductor that has a small footprint and may be formed as a flat, planar design. The inductor  135  has a preferred value of about 3 nH. In an alternative embodiment, other inductance values may be chosen for the inductor  135  to obtain the desired circuit performance. The chosen value for the inductor  135  helps determine the specific RF range of operation for the device  100 . The diameter, surface area, thickness and shape of the inductor  135  can be varied to adjust the operating frequencies and current handling capabilities of the device  100 . In one embodiment, an iterative process may be used to determine the diameter, surface area, thickness and shape of the inductor  135  to meet the requirements of a particular application. In the preferred embodiment, the diameter of the inductor  135  of the device  100  is about 0.865 inches and the thickness of the inductor  135  is about 0.062 inches. Furthermore, the inductor  135  spirals in an outward direction. 
     The material composition of the inductor  135  helps determine the amount of charge that can be safely dissipated across the inductor  135 . A high tensile strength material allows the inductor  135  to discharge or divert a greater amount of current. In one embodiment, the inductor  135  is made of a 7075-T6 Aluminum material. Alternatively, any material having sufficient tensile strength and conductivity for a given application may be used to manufacture the inductor  135 . Each of the components or the housing  205  may be plated with a silver material or a tri-metal flash plating. This reduces or eliminates the number of dissimilar or different types of metal connections or components in the RF path to improve passive inter-modulation (“PIM”) performance. 
     The inductor  135  is positioned within the cavity  210  between the first and second capacitors  131  and  132  and has an inner edge with an inner radius of approximately 62.5 mils and an outer edge with an outer radius of approximately 432.5 mils. The inner edge or radius of the inductor  135  is coupled to the second terminals  202  and  204  of the first and second capacitors  131  and  132 . The outer edge or radius of the inductor  135  is coupled to the housing  205 . The housing  205  may operate as a ground connection to facilitate the shunting of DC signals or surges out of the RF path  155 . 
     Each spiral of the inductor  135  spirals in an outward direction. In one embodiment, the inductor  135  has three spirals. The number of spirals and thickness of each spiral can be varied depending on the requirements of a particular application. The spirals of the inductor  135  may be of a particular known type such as the Archimedes, Logarithmic, Hyperbolic or any combination of these or other spiral types. 
     With reference to  FIG. 1  and during normal operation, the first and second capacitors  131  and  132  prevent DC signals from traveling along the RF path  155  to the protected hardware or equipment  125 . During a surge condition however, when the surge  120  exceeds the first capacitor  131  breakdown voltage rating, the surge voltage or current is configured to arc across an air gap of the first capacitor  131  via a desired spark-over. The spark-over is configured to occur before the surge  120  permanently damages, impairs or causes a failure (e.g., punch-through of the dielectric, carbon shorts, etc) of the first capacitor  131 . 
     The electrical energy reaches the inner edge of the inductor  135 , travels in an outward direction through the spirals of the inductor  135  towards the outer edge and is dissipated to ground via the housing  205 . By directing the surge voltages or currents to ground, the voltage potential across the second capacitor  132  is kept below its voltage breakdown rating. By keeping the voltage across the second capacitor  132  low, the surge  120  will not make its way to the protected hardware or equipment  125 . Thus, the surge  120  is shunted to ground after bypassing the first capacitor  131  while the second capacitor  132  keeps the surge  120  from encountering the connected hardware or equipment  125 . 
     One embodiment of the device  100  described above for  FIG. 1  is shown in  FIG. 3  and  FIG. 4 .  FIG. 3  shows a perspective view of a device  300  having N-type female-female press-fit end connectors.  FIG. 4  shows the same device  300  but in a disassembled view for easier identification of the components contained within. The input center conductor  109  and the output center conductor  110  are shown on opposite ends of the device  300 . The input center conductor  109  electrically connects with one of the N-type female press-fit end connectors. The output center conductor  110  electrically connects with the other N-type female press-fit end connector. By inserting the device  300  in-line along a transmission line between an input source and any hardware or equipment to be protected, the device  300  can thus shield the hardware or equipment from DC signals that would otherwise be propagated along the transmission line to the hardware or equipment. 
     The input center conductor  109  and the output center conductor  110  are connected via a number of intermediate components, as discussed above for  FIG. 1  and  FIG. 2 . Inserts or insulating members  400  and  401  isolate the input and output conductors  109  and  110  from the housing and are made of Teflon, but may be made of a variety of other materials (e.g., PTFE) in an alternative embodiment. The first and second capacitors  131  and  132  electrically couple to each other and to the inner radius of the inductor  135  within the housing of the device  300 . The set screw or fastening element  206  positions the first and second capacitors  131  and  132  and the inductor  135  together so they make electrical contact as described in greater detail above. A conductive ring  405  electrically connects with the outer radius of the inductor  135  and operates to connect the outer radius to the housing of the device  300 . The housing may be used as a ground for the propagation of surge voltages and currents outside of the RF path  155  (see  FIG. 1 ). 
     The first capacitor  131  is constructed of a pair of conductive plates with a dielectric there between. The dielectric is preferably made of Teflon. The second capacitor  132  is constructed in the same manner. During normal operation, the first capacitor  131  blocks DC currents present on the input center conductor  109  from reaching the output center conductor  110 . During a surge condition, instead of the high voltage or current values causing a failure or destroying the first capacitor  131 , the first capacitor  131  is designed to arc the surge voltage or current over the dielectric from one conductive plate to the other. In this manner, the dielectric is unharmed and the first capacitor  131  maintains the same operational characteristics both before and after the surge condition. The surge can then be dissipated to ground (e.g., the housing) through the inductor  135  while the second capacitor  132  continues to prevent undesirable signals from reaching the connected hardware or equipment. 
     By designing the first capacitor  131  to arc a predetermined level of surge voltage or current over the terminals of the first capacitor  131  before allowing failure of the first capacitor  131  due to a surge-induced punch-through of the dielectric or via carbon shorts, the device  300  can thus continue to operate as a DC block providing an RF path even after encountering a surge condition that would destroy most DC blocking devices. 
     Another embodiment of the device  100  described above for  FIG. 1  is shown in  FIG. 5  and  FIG. 6 .  FIG. 5  shows a perspective view of a device  500  having DIN male-female end connectors.  FIG. 6  shows the same device  500  but in a disassembled view for easier identification of the components contained within. The device  500  is similar to the device  300  described above, but incorporates different end connectors. The input center conductor  109  electrically connects with the DIN female press-fit end connector. The output center conductor  110  electrically connects with the DIN male press-fit end connector. By connecting the device  500  in-line along a transmission line between an input source and any hardware or equipment to be protected, the device  500  can thus shield the hardware or equipment from DC signals that would otherwise be propagated along the transmission line. 
     Like described above for  FIG. 4 , the input center conductor  109  and the output center conductor  110  are connected via a number of intermediate components. Inserts or insulating members  600  and  601  isolate the input and output conductors  109  and  110  from the housing and are made of Teflon, but may be made of a variety of other materials (e.g., PTFE) in an alternative embodiment. A set screw or fastening element  206  couples the first and the second capacitors  131  and  132  to each other and to the inner radius of the inductor  135  within the housing of the device  500 . A conductive ring  605  electrically connects the outer radius of the inductor  135  to the housing of the device  500  in order to provide a ground for surge voltages or currents. Operation of the device  500  is similar to that described above for  FIG. 4 . 
     Referring now to  FIG. 7  and  FIG. 8  and with reference to  FIG. 1 , graphs are displayed showing in-band operating characteristics of the input of the device  100 . Graph  700  (see  FIG. 7 ) shows the input in-band return loss of the device  100 . For signals operating at frequencies passed through the first capacitor  131  and the second capacitor  132  along the RF path  155 , a high return loss (e.g., at least 20 dB) is desirable. The device  100  has been configured for an operating frequency range of about 680 MHz to about 2.5 GHz as described above for  FIG. 1 . As shown by the graph  700 , the return loss for the device  100  varies between about 25 dB and about 45 dB within that operating frequency range. Thus, the device  100  exhibits desirable circuit performance over the designed operating frequency range. 
     Graph  800  (see  FIG. 8 ) shows the input in-band insertion loss of the device  100 . For signals operating at frequencies passed through the first capacitor  131  and the second capacitor  132  along the RF path  155 , a low insertion loss (e.g., below 0.4 dB) is desirable. The device  100  has been configured for an operating frequency range of about 680 MHz to about 2.5 GHz as described above for  FIG. 1 . As shown by the graph  800 , the insertion loss for the device  100  varies up to a maximum of about 0.1 dB within that operating frequency range. Thus, the device  100  exhibits desirable circuit performance over the designed operating frequency range. 
       FIG. 9  displays a graph  900  showing the in-band voltage standing wave ratio (VSWR) of the device  100 . The device  100  has been configured for an operating frequency range of about 680 MHz to about 2.5 GHz as described above for  FIG. 1 . VSWR denotes a ratio between a maximum standing wave amplitude and a minimum standing wave amplitude and is used as a measure of efficiency for transmission lines that carry RF signals. Within the operating frequency range of the device described above, the VSWR for the device  100  is about 1.1:1. Thus, the device  100  exhibits desirable circuit performance over the designed operating frequency range. 
     Exemplary embodiments of the invention have been disclosed in an illustrative style. Accordingly, the terminology employed throughout should be read in a non-limiting manner. Although minor modifications to the teachings herein will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted, except in light of the appended claims and their equivalents.