Patent Publication Number: US-8125752-B2

Title: Coaxial broadband surge protector

Description:
FIELD OF THE INVENTION 
     This invention is directed generally to surge protectors and, more particularly, relates to a coaxial broadband surge protector for use in high frequency communications systems. 
     BACKGROUND OF THE INVENTION 
     In the wireless communication industry, a base station is typically connected to a transmission tower using 50 ohm coaxial cable. Transmission towers are frequently the target of lightning strikes. Despite best efforts to adequately ground the towers, occasionally high voltage surges are transmitted through the coaxial cable. If the high voltage surge is permitted to be picked up by the center conductor of the coaxial cable and transmitted along the distribution network, electrical devices within the interconnects and along the distribution path would become inoperable due to the electrical components essentially melting or otherwise deteriorating as a consequence of the surge. Replacing the components can be expensive, time-consuming, and result in down-time for the cellular tower operator. To mitigate the effect of lightning strikes on the antenna tower, a surge protector is typically installed in line with the coaxial cable to prevent the passage of dangerous surges and spikes that could damage electronic equipment. During normal operation, microwave and radio frequency signals are passed through the surge protector without interruption. In the event of a lightning strike or other surge in voltage and/or current, the surge protector shunts the surge to ground. 
     One type of surge protector used in the coaxial cable for antenna towers is a quarter wave stub device, which has a tee-shaped configuration including a coaxial through-section and a quarter-wave stub connected perpendicular to a middle portion of the coaxial through-section. The coaxial through-section is mated at either end with a standard connector. At the tee-shaped junction between the stub and the coaxial through-section, the center conductor and outer conductor of the stub are connected to the center and outer conductors of the coaxial through-section. At the terminal end of the stub, the center and outer conductors are connected together, thereby creating a short, which is connected to ground. The physical length of the stub is equal to one-quarter of the center frequency wavelength for the band of frequencies passing through the coaxial cable. 
     During normal operation, the quarter wave stub device permits signals within the desired frequency band to pass through the through-section. A portion of the desired signal encounters the stub portion at the tee junction and is scattered down the length of the stub, where it is reflected off the short-circuit and travels back to tee junction. Because the physical length of the stub is equal to one-quarter of the center frequency wavelength for the band of frequencies passing through the coaxial cable, the scattered signal portion adds in phase to the non-scattered signal portion and passes through to the opposite end of the coaxial through-section. 
     When a surge occurs in the transmission line, such as from a lightning strike, the physical length of the stub is much shorter than one-quarter of the center frequency wavelength because the surge is at a much lower frequency than the desired band of operating frequencies. Thus, the surge travels along the inner conductor of the coaxial through-section to the stub, through the stub to the short-circuit, and through the short-circuit to ground. Thus, the surge is diverted to ground by the surge protector. 
     One drawback to the quarter wave stub device is that it has limited capability to pass dc signals. This is a problem for cellular transmission towers that have tower-mounted amplifiers, where it may be necessary to pass up to 90 volts from the base station up to the tower through the coaxial cable. 
     Another drawback the to the quarter wave stub is that it has a limited operating bandwidth, passing only a narrow band of frequency signals. With the growing resistance from communities to add more cellular towers, many cellular carriers are co-locating their operating systems by duplexing or even triplexing their respective frequency bands. In this manner, the different frequency spectrum for each carrier are combined at the top of the tower, sent through a common broadband coaxial cable to the bottom of the tower, and split off to their respective antennas and radios. If a quarter wave stub is installed in the broadband coaxial line, it will pass only a small a small range of frequency signals and filter out the rest, thereby acting as a narrow pass band filter. This is completely undesirable if a particular carrier&#39;s signals are within the filtered range. 
     Co-located carriers may also run their own individual coaxial cable from the tower to the base station, but this approach is wasteful and requires wireless service providers or tower operators to stock a range of quarter wave stub surge protectors to accommodate all the commonly allocated operating bandwidths (e.g., 800-870 MHz, 824-896 MHz, 870-960 MHz, 1425-1535 MHz, 1700-1900 MHz, 1850-1990 MHz, 2110-2170 MHz, 2300-2485 MHz, etc.). 
     Another type of surge protector installed in-line with coaxial cable for antenna towers is the gas tube arrestor. A gas tube arrestor typically contains a gas capsule placed in between the center conductor and the outer conductor in the coaxial line. The gas in the tube is normally inert, but ionizes and becomes conductive when a threshold voltage potential is applied across it. The gas tube arrestor allows the operating signals to pass through the device under normal operation but, in the event of a surge, the gas ionizes and creates a current path from the center conductor to the outer conductor, thus shunting the surge to ground. When the voltage potential across the tube decreases below the threshold, the gas in the tube becomes inert again. 
     One drawback with gas tube arrestors is that the response time of the device allows a voltage spike to pass through the device in the time period before the gas ionizes and becomes conductive. Although this time period is only milliseconds, voltages as high as 1 kV may be passed through to equipment at the base station, which may be detrimental to the equipment. 
     Another drawback to gas tube arrestors is that, over time and with multiple surge events, the gas in the tube remains somewhat conductive and may “leak” current to ground. Also, there is no way of determining if the condition of the device is deteriorated until it fails to work during a surge event. Therefore, manufacturers recommend periodic replacement of the gas tube arrestors regardless of their condition, which wastes time, manpower, and money. 
     SUMMARY OF THE INVENTION 
     In view of the background, it is therefore an object of the present invention to provide a surge protector that will protect coaxial transmission lines from large voltage and current spikes and pass dc power in normal usage. Briefly stated, a high voltage surge protection device having a characteristic impedance includes a center conductor defining an axis, an electrically conductive outer body disposed in surrounding relation to the inner conductor, and a dielectric layer disposed between the center conductor and the outer body. An electrically conductive surge protective element having a first value of effective impedance is disposed in electrical contact with the outer body and in spaced-apart relationship with the center conductor. The spaced-apart relationship forms a gap between the surge protective element and the center conductor. An insulative tuning element having a second value of effective impedance larger than the first value of effective impedance is coupled to the surge protective element in impedance-restorative relationship. The combination of the first value of effective impedance and the second value of effective impedance effectively equals the characteristic impedance of the high voltage surge protection device. 
     According to an embodiment of the invention, a surge protector is provided wherein the gap is configured to discharge a voltage of greater than 500 volts. 
     According to another embodiment of the invention, the surge protection device includes a plurality of n electrically conductive surge protective elements having n values of effective impedance. The first value of effective impedance includes a combination of the n values of effective impedance. 
     According to another embodiment of the invention, the surge protection device includes a plurality of m insulative tuning elements having m effective impedance values. The second effective impedance value comprises a combination of the m values of effective impedance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features that are characteristic of the preferred embodiment of the invention are set forth with particularity in the claims. The invention itself may be best be understood, with respect to its organization and method of operation, with reference to the following description taken in connection with the accompanying drawings in which: 
         FIG. 1  is a perspective exploded view of a surge protector according to an embodiment of the invention; 
         FIG. 2  is a cross sectional view of the surge protector shown in  FIG. 1 ; 
         FIG. 3  is a cross sectional view of an alternate embodiment of the surge protective element shown in  FIG. 2 ; 
         FIG. 4A  is a cross sectional view of an alternate embodiment of the surge protective element; 
         FIG. 4B  is a cross sectional view of an alternate embodiment of the surge protective element; 
         FIG. 4C  is a cross sectional view of an alternate embodiment of the surge protective element; 
         FIG. 5  is a perspective exploded view of a surge protector according to another embodiment of the invention; 
         FIG. 6  is a cross sectional view of the surge protector shown in  FIG. 4 ; 
         FIG. 7  is a perspective exploded view of a surge protector according to another embodiment of the invention; 
         FIG. 8  is a cross sectional view of the surge protector shown in  FIG. 6 ; 
         FIG. 9  is a block diagram of a method for providing a high voltage surge protector in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An air gap surge arrestor for 75 ohm coaxial cable has been disclosed that dissipates an electrical surge up to 6,000 volts at 3,000 amps for a period of 50 microseconds, in accordance with IEEE Specification 62.41. Although the disclosed surge arrestor can be useful and may be advantageous for certain applications, it suffers from drawbacks. 
     One such problem noted with the surge arrestor configured for 75 ohm coaxial service is that it was designed for relatively small surges, such as a surge in an indoor line in the vicinity of a lightning strike. In such an application, only a small portion of the surge impulse is carried through the coaxial cable. A surge arrestor adapted for 50 ohm service in an outdoor transmission tower, however, may be very close to a lightning strike, or experience a direct hit. The energy impulse surging through the coaxial line may be orders of magnitude greater than the energy impulse in an indoor 75 ohm coaxial connector during the same surge event. Thus, the design of the disclosed 75 ohm surge protector is not scalable for use in 50 ohm service in transmission towers, for example. In accordance with IEEE Standard 62.41, a surge protector for use in a transmission tower (e.g., Location C with high exposure) may need to trip at 500 volts and dissipate up to 20,000 volts and 10,000 amps in 50 microseconds. The device disclosed for 75 ohm usage would surely melt during the energy surge present during a direct lightning strike because the device is typically very thin, on the order of 0.02 inches (0.51 millimeters). One possible solution is to stack the disclosed air gap surge arrestors in series to build up enough thickness to survive the energy surge, but stacking the devices negatively affects the characteristic impedance of the surge arrestor. Deviations as little as 1 or 2 ohms from the characteristic impedance of 50 ohms may cause unacceptable return losses in the coaxial line. 
     There is described herein one embodiment of a coaxial surge protector to dissipate the large energy surges in a lightning strike. The surge protector also mitigates the negative impact on characteristic impedance by incorporating tuning elements, as described below. 
     Referring to  FIG. 1  of the drawings, a coaxial surge protector  10  incorporating the voltage surge protection device of the subject invention is illustrated. The surge protector  10  may be generally cylindrical in shape and include a center conductor  12  defining a central longitudinal axis  14 . The center conductor  12  is adapted to mate with the center conductor of a coaxial connector. Depending on the particular application, the center conductor  12  may be metallic, such as copper, and further may be solid or hollow. In one example, the center conductor  12  includes a collet at each end configured to accept the male pin of a 7/16 DIN connector. The surge protector  10  further includes an electrically conductive outer body  16  concentrically surrounding the center conductor  12 , and a dielectric layer  18  disposed between the center conductor  12  and the outer body  16 . In the example illustrated in  FIG. 1 , the dielectric layer  18  is air, but other dielectric materials may be used, for example polycarbonate. The conductive outer body  16  may be rigid, as shown, or alternatively may include a flexible metal sheath surrounded by a protective outer jacket. 
     In one example, the surge protector  10  includes a connector interface to mate with a coaxial connector. The example connector interface shown in  FIG. 1  is a female-female 7/16 DIN connector including a sleeve  28  adapted to guide a male 7/16 DIN connector (not shown). The connector interface may be selected from the group of connector interfaces consisting of a BNC connector, a TNC connector, an F-type connector, an RCA-type connector, a 7/16 DIN male connector, a 7/16 DIN female connector, an N male connector, an N female connector, an SMA male connector and an SMA female connector. 
     As mentioned above, the dielectric layer  18  in one example may be air, as shown in  FIG. 1 . The center conductor  12  must then be supported within the surge protector  10 . In this configuration, the surge protector  10  further includes a center conductor support insulator  30  disposed in between and in contact with the center conductor  12  and the outer body  16 . The support insulator includes a bore  38  centrally disposed therethrough for receiving the center conductor  12 . The support insulator  30  may be fabricated from a non-conducting material, such as plastic, and concentrically aligns the center conductor  12  within the outer body  16  about axis  14 . In the disclosed embodiment the support insulator  30  is a washer, but other configurations are possible. For example, the support insulator  30  may comprise an inner ring, an outer ring, and support arms joining the inner ring to the outer ring. Further, the inner ring and outer ring may be solid or segmented. The support insulator  30  is optional if the dielectric layer  18  layer is a solid, such as polycarbonate, because the dielectric layer  18  may provide the supporting function. 
     The surge protector  10  further includes a surge protective element  20  disposed concentrically about the axis  14  and in electrical contact with the outer body  16 . The surge protective element  20  is composed of a conductive material, such as bronze, and is of a predetermined width W. In the disclosed embodiment, the outer diameter of the surge protective element  20  is press-fit into the outer body  16 . 
     Referring to  FIG. 2  of the drawings, in one example surge protective element  20  comprises a ring-shaped outer body  22  and at least one prong  24  extending radially inwardly therefrom. 
     Although surge protective element  20  as illustrated in the drawings includes three, equally spaced apart prongs  24 , it has been found that four prongs  24  work just as well. In fact, the number of prongs  24  is not critical to the present embodiment; as one or more prongs  24  would suffice. Also, the prongs  24  do need not be equally spaced apart. 
     Depending on the particular usage and application, the surge protector  10  may include a single surge protective element  20  or a plurality of elements  20  spaced along the axis  14 . In general, multiple surge protective elements  20  having multiple prongs  24  will enhance the useful life of the surge protector  10 , but these benefits must be carefully weighed against impedance considerations, as will be discussed below. 
     The prongs  24  are disposed in spaced-apart relationship with the center conductor  12 , meaning no portion of the surge protective element  20  physically contacts the center conductor  12 . The combination of the surge protective element  20 , the center conductor  12 , and the spaced-apart relationship forms a spark gap  26  adapted to shunt to ground high voltage surges in the center conductor  12 . In the disclosed embodiment, the spark gap  26  is comprised of air, which has a dielectric strength of 3,000,000 volts/meter. The size of the spark gap  26  dictates the threshold voltage level at which the electric current will arc from the center conductor  12  to the outer body  16 . In one example, the spark gap  26  is adapted to arc when the center conductor voltage reaches 500 volts. The spark gap  26  would be approximately 0.007 inches (0.18 millimeters). 
     The 50 ohm coaxial transmission lines utilized in wireless communication towers may experience surges exceeding 100,000 volts during a lightning strike. Although the spark gap  26  may be configured to arc at voltages well below this value, for example 500 volts, the structure of the surge protective element  20  must be designed such that it can repeatedly withstand not only the high voltages but also the prolonged current density and high temperatures reached in the plasma phase during the arcing event. The width W and material composition of the surge protective element  20  are adapted to withstand these extremes. 
     Referring to  FIG. 3  of the drawings, an alternate embodiment of the present invention is shown wherein the spark gaps  26  are different sizes to accommodate different conditions. In one example, gap  26 A is 0.007 inches (0.18 millimeters), which would arc at approximately 500 volts. Gap  26 B is 0.026 inches (0.66 millimeters), which would arc at approximately 2,000 volts. Finally, gap  26 C is sized at 0.079 inches (2.0 millimeters), which would arc at 6,000 volts. The corresponding prongs  24 A- 24 C may also have differing widths, allowing for more robust configuration at higher voltages. In this manner, the surge protective element  20  provides a measure of insurance that, in the event of a very large surge, the larger-gap prongs would carry some the load. Further, if the smaller gaps  26 A and/or  26 B were to be consumed or damaged, an undamaged gap  26 C may still be available. 
     Referring to  FIGS. 4A-4C  of the drawings, different configurations for the prong  24  of the surge protective element  20  are shown. In  FIG. 4A , a tip  25  of one prong  24  is shown to include rounded off corners. In  FIG. 4B , the tip  25  has a semi-cylindrical contour, thereby creating a parallel plate arrangement with the circular contour of the center conductor  12 .  FIG. 4C  shows the tip  25  being notched. This configuration has the advantage of minimizing the capacitive effect of the prong-to-center conductor arrangement without losing the proximity of the gap or the majority of the current carrying capacity of the tip  25 . Depending upon the particular requirements of the design, a configuration for the tip  25  may be selected that is most suitable. 
     In conventional connector design, it is desirable to match the impedance of the connector assembly as closely as possible to the characteristic impedance of the transmission line. As mentioned above, signals in the wireless communication industry may be transmitted between a cellular antenna tower and a base station using coaxial cable with a characteristic impedance of 50 ohms. Therefore, the surge protector  10  in one embodiment may be adapted to match a characteristic impedance of 50 ohms. Typically, each individual component in the connector assembly is designed with an effective impedance value that closely matches the characteristic impedance of the assembly. As used herein, the term “effective impedance” means the impedance value of the individual component in the assembly. In general, the effective impedance value for a coaxial section varies by the logarithm of the ratio of the outer conductor diameter to the center conductor diameter. In other words, for a given dielectric, the greater the distance between the two conductive diameters, the higher the effective impedance value. As can be seen with reference to  FIG. 2 , the diameter of the prong  24  is very close to the diameter of the center conductor  12 , separated only by the spark gap  26 . Thus, the local impedance value becomes very small, that is, the local contribution of the prong&#39;s impedance serves to lower the overall effective impedance value. Thus, the effective impedance value for the surge protective element  20  is negatively impacted by the prong  24 . If the surge protective element  20  includes three or four prongs  24 , the negative impact is exacerbated. 
     Additionally, the thickness W of the surge protective element  20  further affects the effective impedance value in a negative manner. Each of the configurations for the surge protective element  20  discussed above are adapted to withstand very large voltage spikes, in many cases greater than 1000 volts, and in some situations, up to 100,000 volts. Therefore, the width W of each surge protective element  20  may be quite thick in relation to other components in the surge protector  10  in order to carry the current. Whereas the thickness of the device disclosed in the 75 ohm example was approximately 0.020 inches thick, the width of the surge protective element  20  may be much thicker, in some examples more than an order of magnitude thicker. The thickness directly correlates to the cross-sectional surface area of the prong  24  and therefore to the amperage the element  20  may carry. In some examples, the cross-sectional area of the prongs  24  in sum is greater than the cross-sectional area of the center conductor  12 . In this manner, the prongs  24  would be configured to carry at least as much current as the center conductor. In other examples, the width W of the surge protective element  20  may be 0.250 inches (0.64 centimeters) or even as much as three inches (7.6 centimeters), depending on the current capacity required of the design. 
     For simple geometric cross sections, the effective impedance value can be calculated according to known formulae. For complex cross sections, for example as illustrated in  FIG. 2 , commercially available software such as CST Microwave Studio® sold by Computer Simulation Technology is available to determine the effective impedance value. 
     With these considerations in mind and referring now back to  FIG. 1  of the drawings, the surge protector  10  further includes an insulative tuning element  32  coupled to the surge protective element  20  in impedance-restorative relationship. The inventor of the present invention has recognized that the surge protective element  20  in close proximity to the center conductor  12  will not adversely affect the signal response of the surge protector  10  if the local zone of low impedance created by the spark gap  26  is compensated for elsewhere within the surge protector  10 . 
     In general, the tuning element  32  will have a value of effective impedance greater than the value for the surge protective element  20  such that, in combination, the characteristic impedance of the surge protector  10  is restored to the design value. The tuning element  32  may be coupled purely to the surge protective element  20 , or it may take into consideration all of the effective impedance values for each component in the surge protector  10 . In the embodiment shown in  FIG. 1 , a plurality of tuning elements  32  are coupled to a plurality of surge protective elements  20 . The impedance-restorative relationship may be created by arranging the tuning element  32  in physical contact with the surge protective element  20 , as shown in  FIG. 1 , or by arranging the tuning element  32  anywhere along the axis  14  within the outer body  16 . 
     The tuning element  32  may be made of an insulative material such as polycarbonate, DuPont™ Teflon®, or the like. 
     In one example, the impedance-restorative relationship is created by pairing one surge protective element  20  with one tuning element  32 . The restorative impedance Z m  of the tuning element  32  may be calculated generally according to the formula:
 
 Z   m =√{square root over ( Z   0   ×Z   eff )}  (1)
 
     where Z 0  is the characteristic impedance of the surge protector  10 , and Z eff  is the effective impedance of the surge protective element  20 . 
     The particular arrangement and pairing of surge protective elements  20  and tuning elements  32  may vary depending on design considerations. For example, one alternate arrangement calls for a plurality of n electrically conductive surge protective elements  20  paired with a single tuning element  32 . Each surge protective element  20  has an effective impedance value that would be considered in calculating a single effective impedance value Z eff . As the number of elements increases, the individual effective impedances may be combined to a single effective impedance value Z eff  using the aforementioned software CST Microwave Studio®. 
     Another alternate arrangement calls for a single surge protective element  20  paired with a plurality of m insulative tuning elements  32 . Each tuning element  32  has an effective impedance value. The individual effective impedances may be combined to a single restorative impedance Z m  using the aforementioned software CST Microwave Studio®. 
     A third alternate arrangement calls for a plurality of n electrically conductive surge protective elements  20  paired with a plurality of m insulative tuning elements  32 . In this arrangement, the individual effective impedances may be combined to a single effective impedance value Z eff  and the individual effective impedances may be combined to a single restorative impedance Z m . 
     As may be appreciated with reference to the above alternate arrangements, a special case arises wherein the spacer  44  may be utilized as at least one of the tuning elements  32 . Prior art spacers typically were designed to match the characteristic impedance of the connector, but as used herein, the spacer may be designed in an impedance-restorative relationship with the surge protective element  20 . 
     The voltage surge in the coaxial transmission line must be shunted to ground. In one example, the surge protector  10  is utilized to accomplish this function by transmitting the voltage spike from the center conductor  12  across the spark gap  26 , to the outer body  16 , and to ground. The surge protector  10  may include a grounding element  36  in electrical communication with the outer body  16 . In the disclosed embodiment, the grounding element  36  is a lug securely fixed to the outer body  16 , for example by welding, to assure proper electrical transmission. Other examples of the grounding element  36  include a grounding stud or strap-type grounding clamps. 
     Referring to  FIGS. 5 and 6  of the drawings, the surge protector  10  includes two surge protective elements  20 A,  20 B and one tuning element  32 . The center conductor  12  has an irregular shape. Section  12 A has essentially the same configuration as disclosed in previous embodiments. The center conductor  12  has an outwardly projecting diameter section  12 B, including a V-notch  40  that serves to enhance the ability of an arc to travel across the spark gap  26  by directing surges to the tip  25  of the prongs  24 . The V-notch  40  also reduces the amount of capacitance that is created between the semi-circular portion of the surge tip  25  and the cylindrical portion  12 B of the center conductor  12 . The reduction in capacitance helps to mitigate the low impedance created by the surge protective element  20 . Section  12 C of the center conductor has a reduced diameter in area of the tuning element  32  to improve the effective impedance value. In the arrangement shown, a higher effective impedance value may be achieved for the tuning element  32  by increasing the radial distance of the dielectric layer comprised of air. 
     The prongs  24  of the surge protective elements  20 A,  20 B do not have to be in the same angular orientation with respect to the axis  14 . As best seen in  FIG. 5 , the prongs on surge protective element  20 B are rotated approximately 60 degrees with respect to the prongs on surge protective element  20 A. 
     Referring to  FIGS. 7 and 8  of the drawings, another embodiment of the surge protector  10  includes one surge protective element  20  and two tuning elements  32 A,  32 B. The center conductor  12  has an irregular shape. Section  12 A has essentially the same configuration as disclosed in previous embodiments. Section  12 B of the center conductor has a reduced diameter in area of the tuning elements  32 A,  32 B to improve the effective impedance value. In the arrangement shown, a higher effective impedance value may be achieved for the tuning element  32 A,  32 B by increasing the radial distance of the dielectric layer comprised of air. Section  12 C of the center conductor has an outwardly projecting diameter greater than the diameter of section  12 A. 
     Although not shown in the accompanying drawings, the center conductor  12  may include protrusions, similar to the prongs  24  of the surge protective element  20 , and the surge protective element  20  may be devoid of protrusions, comprising only the ring-shaped outer body  22 . 
     Referring now to  FIG. 9  of the drawings, a method  200  is shown for providing high voltage surge protection for a coaxial cable. The method  200  comprises a step  210  of determining a threshold voltage for which surge protection is desired. As defined herein, threshold voltage is the value that causes the voltage in the center conductor to jump to the surge protective element  20 . In one example, the threshold voltage is 500 volts, meaning equipment connected to the coaxial cable must be able to withstand 500 volts for a brief period. The method  200  further comprises a step  220  of selecting a surge protective element  20  for use with the threshold voltage. One factor to be considered when selecting the element  20  includes the size of the spark gap  26 . The spark gap  26  will be sized according to (1) the dielectric layer  18  separating the center conductor  12  and the outer body  16  and, (2) the threshold voltage to which surge protection is desired. Other factors to be considered when selecting the surge protective element  20  include the number and cross-sectional area of the prong(s)  24 , which have a bearing on the robustness of the surge protector  10 , its durability, and the number of surges the surge protector  10  will be able to withstand. In one example, the cross-sectional area of the prong is greater than the cross-sectional area of the center conductor. In another example, the selection of the surge protective element  20  includes selecting a plurality of surge protective elements  20  in the arrangement. 
     When the selection of the surge protective element  20  is complete, the first effective impedance value of the element can be determined at a step  230 . The first effective impedance value may be calculated using CST Microwave Studio®, for example. Due to the geometry of the surge protective element  20 , i.e. the prongs  24  being closely spaced to the center conductor  12 , the first effective impedance value will likely fall below the characteristic impedance of the coaxial transmission line. 
     At a step  240 , the tuning element  32  is selected with a second effective impedance value that is greater than the first effective impedance value for the surge protective element  20 . The second effective impedance value is selected such that when paired with the first effective impedance value, the characteristic impedance of the coaxial connector will essentially equal characteristic impedance of the transmission line. By “essentially equal”, what is meant is that the differences in the impedances will not adversely affect the signal response of the transmission through the connector. The surge protective element  20  and the tuning element  32  are coupled within the connector in impedance-restorative relationship at a step  250 , for example by assembling the two components in physical contact with each other. In some examples, a path to ground from the outer body  16  may be necessary. Therefore, the method  200  further includes a step  260  of providing the grounding element  36 . 
     One advantage of the present invention is that very large surges, for example in excess of 20,000 volts at 10,000 amps for 50 microseconds, may be accommodated in the coaxial line without resort to multiple surge protection devices. Unlike the quarter wave stub, the surge protector of the present invention is able to pass dc power because the center conductor  12  maintains electrical continuity throughout the surge event. Also, the surge protector of the present invention is not subject to “leaking” current to ground when degraded. 
     Another advantage of the disclosed surge protector  10  is that there are virtually no constraints on the width W of the surge protective element  20 . Prior art surge protective elements attempted to minimize the width to minimize the negative impacts on impedance and signal response. Removing the constraint on the width W by coupling a tuning element  32  allows a more robust design, and further allows the surge protective element  20  to be designed for much greater voltages at significantly higher current. 
     Another advantage of the disclosed surge protector  10  is that its effective performance band is not limited to a narrow band of frequencies. Whereas the quarter wave stub may be useful in a very limited range of frequencies about 10 megahertz wide, the present invention does not suffer from such limitations. In other words, the surge protector  10  does not act as a band pass filter in the manner a quarter wave stub does. The surge protector  10  of the present invention is adapted to operate throughout a broad frequency spectrum that includes 470 megahertz (beginning of UHF band) up to 3 gigahertz (cellular frequencies), including the WiMAX frequency spectrum. Moreover, because the tuning element  32  restores the characteristic impedance to that of the line impedance (e.g., 50 ohms), the return losses within the effective performance band are no less than 20 decibels. In fact, for an effective performance band comprised of a discrete frequency range, such as the group consisting of 800-870 MHz, 824-896 MHz, 870-960 MHz, 1425-1535 MHz, 1700-1900 MHz, 1850-1990 MHz, 2110-2170 MHz, and 2300-2485 MHz, the return loss is greater than 30 decibels and, in some cases, greater than 40 decibels. 
     The disclosed surge protector  10  is predicted to last longer than conventional gas tubes. In addition, the surge protector  10  does not leak current when nearing the end of its useful life. Further, when compared to gas tubes, the disclosed surge protector  10  has a faster response time, meaning that less voltage and/or current is allowed to travel down the transmission line before the surge is shunted. 
     The surge protector  10  is of much simpler construction than either the gas tube or quarter wave stub, and therefore more economical to manufacture. 
     Although the surge protector  10  disclosed herein has been described with reference to a 50 ohm coaxial cable, it will be understood by those skilled in the art that the invention is not so limited. For example, the surge protector  10  of the present invention may also be suitable for 75 ohm coaxial cable, such as that utilized with CATV. Other various modifications and the like could be made thereto without departing from the scope of the invention as defined in the following claims.