Patent Description:
Practitioners use conventional microwave ablation systems during laparoscopic surgical procedures to treat target tissue, such as a tumor located within the abdomen or pelvis, by using a percutaneous microwave ablation device to deliver microwave energy to the target tissue. An energy source, such as a generator, is coupled to the microwave ablation device via a generator cable. The microwave ablation device typically includes an elongated tubular member that contains a coaxial cable and that has a needle at its distal portion. The tubular member serves as a conduit for the coaxial cable, which guides microwave energy from the generator through an incision in the patient and toward the distal portion, which radiates the microwave energy toward the target tissue. To minimize reflected power and thereby optimize microwave energy delivery from the generator to the distal portion, conventional microwave ablation systems typically include a generator output port, a generator cable, and a microwave ablation device coaxial cable that have respective impedances that are mutually matched to one another within an operational frequency range. In this context, reference is made to document <CIT>.

Recently, to reduce invasiveness and thereby reduce post-surgery healing time and the risk of bleeding or injury, practitioners have expressed a desire for a microwave ablation device having a tubular member that is reduced in outer diameter. One approach to reducing the diameter of the tubular member involves reducing respective outer diameters of a center conductor and a dielectric layer of the coaxial cable housed within the tubular member, to maintain the impedance of the coaxial cable despite its downsizing. This approach, however, results in excess loss in the coaxial cable and thereby decreases the efficiency of microwave energy delivery from the generator to the distal portion. In view of the foregoing, a need exists for a microwave ablation system including a microwave ablation device that has a tubular member that is reduced in diameter and that facilitates efficient delivery of microwave energy from the generator to the distal portion.

In one aspect, this disclosure describes a microwave ablation system comprising a generator, a generator cable, and a microwave ablation device. The generator comprises a generator output port having a generator output port impedance. The generator cable has a generator cable impedance that is matched to the generator output port impedance within a degree of tolerance within a predetermined frequency range. The microwave ablation device comprises a coaxial cable that has a coaxial cable impedance and is coupled to the generator output port by way of the generator cable. Within the predetermined frequency range, the coaxial cable impedance is lower than at least one of the generator output port impedance or the generator cable impedance by at least a predetermined amount that exceeds the degree of tolerance.

In embodiments, the microwave ablation device further comprises a transition waveguide and an electrically conductive element. The transition waveguide comprises a transition waveguide input port, having a transition waveguide input port impedance, and a transition waveguide output port, having a transition waveguide output port impedance. The coaxial cable comprises a coaxial cable input port and a coaxial cable output port, and the coaxial cable input port is coupled to the transition waveguide output port, and the coaxial cable output port is coupled to the electrically conductive element.

In embodiments, at least one of the transition waveguide input port impedance or the transition waveguide output port impedance is matched to the generator output port impedance and the generator cable impedance within the degree of tolerance within the predetermined frequency range.

In embodiments, at least one of the transition waveguide input port impedance or the transition waveguide output port impedance is matched to the coaxial cable impedance within the degree of tolerance within the predetermined frequency range.

In embodiments, the transition waveguide input port impedance, the transition waveguide output port impedance, the generator output port impedance, and the generator cable impedance are in a range from approximately <NUM> ohms (Ω) to <NUM>Ω, and the coaxial cable impedance is in a range from approximately <NUM> S2 to <NUM>Ω.

In embodiments, the coaxial cable comprises a center conductor and a dielectric layer that radially surrounds the center conductor, and an outer diameter of the center conductor is in a range from approximately <NUM> inches to <NUM> inches and an outer diameter of the dielectric layer is in a range from approximately <NUM> inches to <NUM> inches.

In embodiments, the degree of tolerance is approximately <NUM> %.

In embodiments, the transition waveguide output port has a transition waveguide output port impedance that is matched to at least one of the transition waveguide input port impedance or the generator output port impedance within the degree of tolerance.

In embodiments, the microwave ablation system further comprises a balun comprising a balun insulator and a tubing member. The balun insulator has an inner diameter, and the tubing member radially surrounds the balun insulator and has a maximum outer diameter. The balun insulator inner diameter is approximately <NUM> inches, and the tubing member maximum outer diameter is approximately <NUM> inches.

In embodiments, the microwave ablation device further comprises an outer tubular member that houses the coaxial cable, and an outer diameter of the outer tubular member is approximately <NUM> gauge.

In embodiments, the predetermined frequency range includes at least one of <NUM>, <NUM>, or <NUM>.

In another aspect, this disclosure describes a microwave ablation device comprising a transition waveguide, an electrically conductive element, and a coaxial cable. The transition waveguide comprises a transition waveguide input port, having a transition waveguide input port impedance, and a transition waveguide output port, having a transition waveguide output port impedance. The coaxial cable has a coaxial cable impedance and comprises a coaxial cable input port and a coaxial cable output port. The coaxial cable input port is coupled to the transition waveguide output port, and the coaxial cable output port is coupled to the electrically conductive element. Within a predetermined frequency range, the coaxial cable impedance is lower than at least one of the transition waveguide input port impedance or the transition waveguide output port impedance by at least a predetermined amount that exceeds a degree of tolerance.

In embodiments, the transition waveguide input port impedance and the transition waveguide output port impedance are in a range from approximately <NUM> S2 to <NUM>Ω, and the coaxial cable impedance is in a range from approximately <NUM> S2 to <NUM>Ω.

In embodiments, the microwave ablation device further comprises a balun comprising a balun insulator and a tubing member. The balun insulator has an inner diameter, and the tubing member radially surrounds the balun insulator and has a maximum outer diameter. The balun insulator inner diameter is approximately <NUM> inches, and the tubing member maximum outer diameter is approximately <NUM> inches.

In embodiments, the microwave ablation device further comprises an outer tubular member that houses the coaxial cable, and an outer diameter of the outer tubular member is in a range from approximately <NUM> inches to <NUM> inches.

Various aspects and features of the present microwave ablation devices and systems are described herein below with references to the drawings, wherein:.

The present disclosure is directed to a microwave ablation system including a microwave ablation device that has a tubular member that is reduced in outer diameter relative to tubular members of prior microwave ablation devices, and nonetheless facilitates efficient delivery, from the generator to the distal portion, of microwave energy suitable for effective treatment. The microwave ablation system and device of the present disclosure thus reduces invasiveness of microwave ablation procedures and thereby reduces post-surgery healing time and the risk of bleeding or injury. In general, as described in further detail below, the microwave ablation device of the present disclosure includes a coaxial cable (sometimes referred to as a feedline) that has an impedance lower than an impedance of one or more other components of the system, such as, for instance, the generator output port.

In one aspect, the impedance of the coaxial cable is reduced relative to the impedance of the generator output port by decreasing a ratio between an outer diameter of a dielectric layer of the coaxial cable to the outer diameter of the coaxial cable center conductor. In one embodiment, the decreased ratio, relative to a corresponding ratio for a coaxial cable that has an impedance that matches the generator output port impedance, is obtained by decreasing the outer diameter of the dielectric layer while keeping the center conductor outer diameter the same or greater. In another embodiment, the decreased ratio, relative to a corresponding ratio for a coaxial cable that has an impedance that matches the generator output port impedance, is obtained by increasing the center conductor outer diameter while keeping the outer diameter of the dielectric layer the same or lower. Despite the mismatched impedance between the coaxial cable of the present disclosure and the generator output port, the coaxial cable of the present disclosure includes a relatively large center conductor outer diameter, which has an increased thermal mass for absorbing heat and increased surface area for removal of the heat, and has a relatively thin insulating layer (e.g., PTFE), decreasing the amount that the insulating layer mitigates heat removal. The coaxial cable of the present disclosure thus provides performance advantages while minimizing the increase in heat buildup on the center conductor and reduces the risk of overheating the center conductor to the point of sudden and total failure (burnout). The relatively large center conductor also may cause less heat buildup on the center conductor and thereby reduce a risk of overheating the center conductor to the point of sudden and total failure or burnout.

Throughout this description, the term "proximal" refers to the portion of the device or component thereof that is closer to the clinician and the term "distal" refers to the portion of the device or component thereof that is farther from the clinician. The phrases "in an embodiment," "in embodiments," "in some embodiments," or "in other embodiments" may each refer to one or more of the same or different embodiments in accordance with the present disclosure. A phrase in the form "A or B" means "(A), (B), or (A and B). " A phrase in the form "at least one of A, B, or C" means "(A); (B); (C); (A and B); (A and C); (B and C); or (A, B, and C).

With reference to <FIG>, a microwave ablation system <NUM> includes a display <NUM>, a table <NUM> including an electromagnetic (EM) field generator <NUM>, a microwave ablation device <NUM> including an EM sensor <NUM>, an ultrasound sensor <NUM> connected to an ultrasound workstation <NUM>, a peristaltic pump <NUM>, and a computing device <NUM> attached to or in operable communication with a microwave generator <NUM>. The computing device <NUM> may be, for example, a laptop computer, desktop computer, tablet computer, or other similar device. The computing device <NUM> may be configured to control the microwave generator <NUM>, the peristaltic pump <NUM>, a power supply (not shown in <FIG>), and/or any other accessories and peripheral devices relating to, or forming part of, the microwave ablation system <NUM>. The display <NUM> is configured to output instructions, images, and messages relating to the performance of the treatment procedure.

The table <NUM> may be, for example, an operating table or other table that is suitable for use during a treatment procedure and that includes the EM field generator <NUM>. The EM field generator <NUM> is used to generate an EM field during the treatment procedure and forms part of an EM tracking system that is used to track positions of surgical instruments within the body of a patient, such as by tracking a position of the EM sensor <NUM>. The EM field generator <NUM> may include various components, such as a specially designed pad to be placed under, or integrated into, an operating table or patient bed. An example of such an EM tracking system is the AURORA™ system sold by Northern Digital, Inc.

The microwave ablation device <NUM> is a surgical instrument for percutaneously accessing and treating a target location. The microwave ablation device <NUM> may include, or have attached to it, EM sensor <NUM> enabling the EM tracking system to track the location, position, and orientation (also known as the "pose") of the microwave ablation device <NUM> inside the body of the patient.

The microwave generator <NUM> includes a generator output port <NUM> and a generator cable <NUM> couples the generator output port <NUM> to the microwave ablation device <NUM>. The microwave generator <NUM> delivers microwave energy from to the microwave ablation device <NUM> by way of the generator output port <NUM> and the generator cable <NUM>. The generator output port <NUM> has a corresponding generator output port impedance and the generator cable <NUM> has a corresponding generator cable impedance. In some embodiments, to minimize reflected power, the impedance of the generator cable <NUM> is matched, within a degree of tolerance, to the impedance of the generator output port <NUM> within a predetermined frequency range.

In general, the microwave ablation system <NUM> is designed to operate using signals within a predetermined frequency range (sometimes referred to as an operational frequency range). That is, various components of the microwave ablation system <NUM>, such as the microwave generator <NUM>, microwave generator output port <NUM>, generator cable <NUM>, and microwave ablation device <NUM>, are designed to generate, convey, radiate, or otherwise process signals (e.g., microwave signals) having a signal frequency that lies within the predetermined frequency range. The predetermined frequency range may be, for example, sufficiently wide to include a variety of operating frequencies, such as approximately <NUM>, <NUM>, and/or <NUM>, or may be any other suitable frequency range.

Due to inconsistencies and/or imperfections in manufacturing, materials, variations in physical properties of components over signal frequency, and/or other factors, the various impedances of the microwave ablation system <NUM> and its components, such as the respective impedances of the generator output port <NUM> and the generator cable <NUM>, may vary from their nominal impedance values throughout the operational frequency range. The degree of tolerance, in some embodiments, is predetermined in recognition of this fact. The degree of tolerance, as used herein, generally refers to a permissible limit of variation in impedances that would not significantly affect the function of the microwave ablation system <NUM>. The degree of tolerance, for example, may be expressed as a variation in impedance amount relative to a nominal impedance value (such as a maximum number of S2 greater than or less than the nominal impedance value) or as a variation in impedance percentage relative to the nominal impedance value (such as, a maximum percentage greater than or less than the nominal impedance value). In various embodiments, the degree of tolerance may be, for example, approximately ± <NUM>Ω, ± <NUM> %, or any other suitable value.

In addition to outputting microwave energy, the microwave generator <NUM> is configured to control the peristaltic pump <NUM>, which is configured to pump fluid through the microwave ablation device <NUM>, cooling the microwave ablation device <NUM> during operation. While the present disclosure describes the use of the microwave ablation system <NUM> in a surgical environment, it is also envisioned that some or all of the components of the microwave ablation system <NUM> may be used in alternative settings, for example, an imaging laboratory and/or an office setting.

In addition to the EM tracking system, the surgical instruments may also be visualized by using ultrasound imaging. The ultrasound sensor <NUM>, such as an ultrasound wand, may be used to image the patient's body during the treatment procedure to visualize the location of the surgical instruments, such as the microwave ablation device <NUM>, inside the patient's body. The ultrasound sensor <NUM> may have an EM tracking sensor embedded within or attached to the ultrasound wand, for example, a clip-on sensor or a sticker sensor. As described further below, the ultrasound sensor <NUM> may be positioned in relation to the microwave ablation device <NUM> such that the microwave ablation device <NUM> is at an angle to the ultrasound image plane, thereby enabling the clinician to visualize the spatial relationship of the microwave ablation device <NUM> with the ultrasound image plane and with objects being imaged. Further, the EM tracking system may also track the location of the ultrasound sensor <NUM>. In some embodiments, one or more of the ultrasound sensors <NUM> may be placed inside the body of the patient. The EM tracking system may then track the location of such ultrasound sensors <NUM> and the microwave ablation device <NUM> inside the body of the patient. The ultrasound workstation <NUM> may be used to configure, operate, and view images captured by the ultrasound sensor <NUM>. Likewise, the computing device <NUM> may be used to configure, operate, and view images captured by the ultrasound sensor <NUM>, either directly or relayed via the ultrasound workstation <NUM>.

In embodiments, the microwave ablation device <NUM> is used to ablate a lesion or tumor (hereinafter referred to as a "target") by using microwave energy to heat tissue in order to denature or kill cancerous cells. The construction and use of a system including such an ablation probe is more fully described in <CIT>; <CIT>; and <CIT>.

As noted above, the location of the microwave ablation device <NUM> within the body of the patient may be tracked during the treatment procedure. An example method of tracking the location of the microwave ablation device <NUM> is by using the EM tracking system, which tracks the location of the microwave ablation device <NUM> by tracking sensors, such as the EM sensor <NUM>, attached to or incorporated in the microwave ablation device <NUM>. Various types of sensors may be used, such as a printed sensor, the construction and use of which is more fully described in U. Patent Publication No. <CIT> A percutaneous treatment system similar to the above-described microwave ablation system <NUM> is further described in <CIT>.

While the above-described microwave ablation system <NUM> uses a microwave generator <NUM> to provide microwave energy to the microwave ablation device <NUM>, those skilled in the art will appreciate that various other types of generators and tools may be used without departing from the scope of the present disclosure. For example, radio frequency (RF) ablation tools receiving RF energy from RF generators may be substituted for the microwave generators and ablation tools described above. Further, while the above-described microwave ablation system <NUM> is designed for percutaneous access to tissue, those skilled in the art will appreciate that the methods described below may be used with systems and tools designed for endobronchial navigation to access treatment locations via the patient's airways and surrounding parenchyma without departing from the scope of the present disclosure. An example of such an endobronchial navigation system is described in <CIT>.

<FIG> shows a side cross-sectional view of a portion of an example embodiment of the microwave ablation device <NUM> shown in <FIG>. Additional aspects of the microwave ablation device <NUM> shown in <FIG> are described in <CIT> The microwave ablation device <NUM> includes an outer tubular member <NUM>, an inner tubular member <NUM>, a coaxial cable <NUM>, an antenna assembly (shown in <FIG>), and a tip <NUM>, which, when assembled, form a probe assembly <NUM>, or portions thereof. The microwave ablation device <NUM> generally includes two housing halves (not separately shown in <FIG>), which, when assembled, form a handle body <NUM>. The handle body <NUM> defines a handle-body chamber (not separately shown in <FIG>) therein. The microwave ablation device <NUM> includes a hub <NUM> (as well as other components described herein) disposed, at least in part, within the handle-body chamber.

The hub <NUM> includes a hub body <NUM> defining a hub-body chamber (not separately shown in <FIG>) therein. The microwave ablation device <NUM> includes a hub cap <NUM> and a hub divider <NUM>, which are configured to be receivable within the hub-body chamber in sealing engagement with the inner walls of the hub body. The outer tubular member <NUM>, the inner tubular member <NUM>, the hub <NUM>, and the components cooperative therewith (e.g., hub cap <NUM> and hub divider <NUM>) are adapted to maintain fluid flow toward the electrically-conductive element <NUM>. The hub body <NUM> generally includes a first port <NUM> and a second port <NUM> to allow fluid communication with a coolant supply system (for example, the peristaltic pump <NUM> shown in <FIG>) via one or more coolant paths. The first port <NUM> and the second port <NUM> may be of any suitable shape, such as rectangular, cylindrical, and/or the like, and may include a groove adapted to receive an O-ring or other suitable sealing element.

In some embodiments, the hub body <NUM> may include one or more mechanical interfaces, such as a recess <NUM>, adapted to matingly engage with one or more corresponding mechanical interfaces associated with the handle body <NUM> to align the hub <NUM> within the handle body <NUM> and/or to fixedly secure the hub <NUM> within the handle-body chamber. Similarly, each of the housing halves may include a series of mechanical interfacing components, such as alignment pins <NUM>, <NUM>, and <NUM>, configured to matingly engage with a corresponding series of mechanical interfaces (not shown in <FIG>) to align the two housing halves about the components and assemblies of the microwave ablation device <NUM>.

The hub divider <NUM> is configured and utilized to divide the hub-body chamber into a first chamber <NUM> disposed in fluid communication with the first port <NUM>, and a second chamber <NUM> disposed in fluid communication with the second port <NUM>. The first chamber <NUM> generally fluidly connects the first port <NUM> to the inner tubular member <NUM>. The second chamber <NUM> generally fluidly connects the second port <NUM> to the inner tubular member <NUM>.

In some embodiments, the inner walls of the hub body <NUM> may include a configuration of engagement portions adapted to provide sealing engagement with the hub cap <NUM> and/or the hub divider <NUM>. An O-ring <NUM> may be provided for engagement with the hub cap <NUM>. The O-ring <NUM> may provide sealing force that permits flexing and/or other slight movement of the hub cap <NUM> relative to the hub <NUM> under fluid-pressure conditions.

The outer tubular member <NUM> and the inner tubular member <NUM> may be formed of any suitable non-electrically-conductive material, such as, for example, polymeric or ceramic materials. In some embodiments, as shown in <FIG>, the inner tubular member <NUM> is coaxially disposed around the coaxial cable <NUM> and defines a first lumen <NUM> therebetween, and the outer tubular member <NUM> is coaxially disposed around the inner tubular member <NUM> and defines a second lumen <NUM> therebetween.

The probe assembly <NUM> generally includes an antenna assembly <NUM> (shown in <FIG> but not separately shown in <FIG>) having a first radiating portion (e.g., distal radiating section <NUM> shown in <FIG>) and a second radiating portion (e.g., proximal radiating section <NUM> shown in <FIG>). The antenna assembly <NUM>, which is described in more detail below, is operably coupled by the coaxial cable <NUM> to a transition waveguide <NUM> shown in <FIG>, which is adapted to transmit microwave energy from the cable assembly <NUM> to the coaxial cable <NUM>. The transition waveguide <NUM> has a transition waveguide input port <NUM> having a transition waveguide input port impedance, and a transition waveguide output port <NUM> having a transition waveguide output port impedance. The coaxial cable <NUM> has a coaxial cable impedance and includes a coaxial cable input port <NUM>, and a coaxial cable output port <NUM>. The coaxial cable input port <NUM> is coupled to the transition waveguide output port <NUM>, and the coaxial cable output port <NUM> is coupled to the electrically-conductive element <NUM>.

The coaxial cable <NUM> may be any suitable transmission line, e.g., a coaxial cable. In some embodiments, as shown in <FIG>, the coaxial cable <NUM> includes an inner conductor <NUM>, an outer conductor <NUM> coaxially disposed around the inner conductor <NUM>, and a dielectric material <NUM> disposed therebetween. The dielectric material <NUM> may be formed from any suitable dielectric material, e.g., polyethylene, polyethylene terephthalate, polyimide, or polytetrafluoroethylene (PTFE). The inner conductor <NUM> and the outer conductor <NUM> may be formed from any suitable electrically-conductive material. In some embodiments, the inner conductor <NUM> is formed from a first electrically-conductive material (e.g., stainless steel) and the outer conductor <NUM> is formed from a second electrically-conductive material (e.g., copper). Electrically-conductive materials used to form the coaxial cable <NUM> may be plated with other materials, e.g., other conductive materials, such as gold or silver, to improve their properties, e.g., to improve conductivity, decrease energy loss. The coaxial cable <NUM> may have any suitable length defined between its proximal and distal ends. In accordance with various embodiments of the present disclosure, the coaxial cable <NUM> is coupled at its proximal end to the transition waveguide <NUM> and coupled at its distal end to the antenna assembly <NUM>. The coaxial cable <NUM> is disposed at least in part within the inner tubular member <NUM>.

As shown in <FIG>, the probe assembly <NUM> is disposed in part within the hub <NUM>, wherein the hub cap <NUM> and the hub divider <NUM> are disposed in sealing engagement with the inner walls of the hub body, and a proximal portion of the probe assembly <NUM> is disposed in association with the hub cap <NUM> and hub divider <NUM>. The hub divider <NUM> generally divides the hub-body chamber (not separately shown in <FIG>) into the first chamber <NUM> and the second chamber <NUM>. The first chamber <NUM> is disposed in fluid communication with the first port <NUM>. The second chamber <NUM> is disposed in fluid communication with the second port <NUM>. In some embodiments, as shown in <FIG>, the proximal end of the inner tubular member <NUM> is disposed within the first chamber <NUM>, wherein the first lumen <NUM> is disposed in fluid communication with the first port <NUM>, and the proximal end of the outer tubular member <NUM> is disposed within the second chamber <NUM>, wherein the second lumen <NUM> is disposed in fluid communication with the second port <NUM>.

In some embodiments, as shown in <FIG> and <FIG>, the inner tubular member <NUM> is coaxially disposed around a coaxial cable <NUM> and defines the first lumen <NUM> therebetween, and the outer tubular member <NUM> is coaxially disposed around the inner tubular member <NUM> and defines the second lumen <NUM> therebetween. As shown in <FIG>, the proximal end of the inner tubular member <NUM> is disposed within the first chamber <NUM>, the first lumen <NUM> is disposed in fluid communication with the first port <NUM>, the proximal end of the outer tubular member <NUM> is disposed within the second chamber <NUM>, and the second lumen <NUM> is disposed in fluid communication with the second port <NUM>.

In some embodiments, as shown in <FIG>, the inner tubular member <NUM> includes a first portion having a first outer diameter, a second portion having a second outer diameter greater than the first outer diameter, and a neck portion <NUM> disposed therebetween. In some embodiments, the opening in the hub divider <NUM> is configured for sealing engagement with the second portion of the inner tubular member <NUM> having the second outer diameter. In some embodiments, located within the interior of the second portion of the inner tubular member <NUM> is a high hoop strength metal cylinder <NUM>. The metal cylinder <NUM> engages the inner diameter of the inner tubular member <NUM>. The hub divider <NUM> is formed of an elastomeric material and when forced into place within the hub <NUM>, as shown in <FIG>, the elastomeric material of the hub divider <NUM> creates an improved water tight seal separating the first hub chamber <NUM> from the second hub chamber <NUM>. The metal cylinder <NUM> improves this seal by ensuring better contact between the elastomeric material of the hub divider <NUM> and the inner tubular member <NUM> upon application of lateral forces to the hub divider <NUM>.

The hub body <NUM> may be configured to sealingly engage the coolant supply lines forming coolant paths to fluid inlet port <NUM> and fluid outlet port <NUM>. The fluid inlet port <NUM> and the fluid outlet port <NUM> may have any suitable configuration, including without limitation nipple-type inlet fittings, compression fittings, and recesses, and may include an O-ring type elastomeric seal.

<FIG>, and <FIG>, which show respective views of various portions of the microwave ablation device <NUM> of <FIG> and <FIG>, illustrate exemplary dimensions of components of the microwave ablation device <NUM>, in accordance with embodiments of the present disclosure. In particular, <FIG> shows an assembly including the coaxial cable <NUM> having the transition waveguide <NUM> coupled to its proximal end, having the electrically conductive element <NUM> coupled to its distal end, and having a balun <NUM> disposed adjacent to, and on a proximal side of, the electrically-conductive element <NUM>. <FIG> shows an enlarged view of a distal portion of the assembly shown in <FIG>. <FIG> shows an enlarged cross-sectional view of a proximal portion of the balun <NUM> identified in <FIG>.

As shown in <FIG>, a tubular member <NUM>, which in some embodiments may be a stainless steel tube, is coaxially disposed around the coaxial cable <NUM> and is partially disposed within the transition waveguide <NUM>. A tubing member <NUM>, which, in some embodiments is a heat-shrink tubing member (described below in connection with <FIG>) is coaxially disposed around the coaxial cable <NUM> in a position that is distal to that of the tubular member <NUM>. The balun <NUM> is coaxially disposed around the coaxial cable <NUM> in a position that is distal to that of the heat-shrink tubing member <NUM>. And the electrically conductive element <NUM> is coupled to the coaxial cable <NUM> at its distal end.

In general, various dimensions of the microwave ablation device <NUM> may vary in various embodiments. The view in <FIG> illustrates various exemplary dimensions of the microwave ablation device <NUM> and corresponding degrees of tolerance for those dimensions. In particular, a dimension <NUM> from a proximal end portion of the center conductor <NUM> to a distal end portion of the center conductor <NUM> may be, for example, approximately <NUM> inches in one embodiment or approximately <NUM> inches in another embodiment. A dimension <NUM> from the proximal end portion of the center conductor <NUM> to a distal end portion of the balun <NUM> may be, for example, approximately <NUM> inches in one embodiment or approximately <NUM> inches in another embodiment. A dimension <NUM> from a proximal portion of the transition waveguide <NUM> to a distal end portion of the electrically-conductive element <NUM> may be, for example, approximately <NUM> inches in one embodiment or approximately <NUM> inches in another embodiment. An outer diameter <NUM> of the tubular member <NUM> may be, for example, approximately <NUM> inches. An outer diameter <NUM> of the tubular member <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from the proximal portion of the transition waveguide <NUM> to a distal end portion of the balun <NUM> may be, for example, approximately <NUM> inches in one embodiment or approximately <NUM> inches in another embodiment. A dimension <NUM> from a distal end portion of the tubular member <NUM> to the proximal end portion of the balun <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from a distal end portion of the heat-shrink tubing member <NUM> to a distal end portion of the heat-shrink tubing member <NUM> may be, for example, approximately <NUM> inches. An outer diameter <NUM> of a middle portion of the balun <NUM> may be, for example, approximately <NUM> inches. An outer diameter <NUM> of a distal portion of the balun <NUM>, more particularly, of a dielectric layer <NUM> (described below in connection with <FIG>) of the balun <NUM> exposed at its distal portion, may be, for example, approximately <NUM> inches. An outer diameter <NUM> of the outer conductor <NUM> of the coaxial cable <NUM> may be, for example, approximately <NUM> inches. An outer diameter <NUM> of exposed dielectric material <NUM> of the coaxial cable <NUM> may be, for example, approximately <NUM> inches.

Referring now to <FIG>, a dimension <NUM> from the proximal end portion of the balun <NUM> to a distal end portion of the center conductor <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from the proximal end portion of the balun <NUM> to a distal end portion of a tubing member <NUM> of the balun <NUM> may be, for example, approximately <NUM> inches. In various embodiments, the tubing member <NUM> may be a heat-shrink tubing member, a metal (e.g., copper) tubing member crimped in place, and/or the like. A dimension <NUM> from the proximal end portion of the tubing member <NUM> of the balun <NUM> to the distal end portion of the tubing member <NUM> of the balun <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from a proximal end portion of the dielectric layer <NUM> of the balun <NUM> to the distal end portion of the tubing member <NUM> of the balun <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from a proximal end portion of the dielectric layer <NUM> of the balun <NUM> to a distal end portion of the dielectric layer <NUM> of the balun <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from a proximal end of an exposed portion of the dielectric layer <NUM> to a distal end portion of the exposed portion of the dielectric layer <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from the proximal end of the exposed portion of the dielectric layer <NUM> to a distal end portion of the outer conductor <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from a distal end of the exposed portion of the dielectric layer <NUM> to the distal end portion of the outer conductor <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from the distal end portion of the outer conductor <NUM> to a distal end portion of the exposed dielectric material <NUM> of the coaxial cable <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from the distal end portion of the exposed dielectric material <NUM> of the coaxial cable <NUM> to the distal end portion of the center conductor <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from the distal end portion of the center conductor <NUM> to the distal end portion of the electrically-conductive element <NUM> may be, for example, approximately <NUM> inches.

Referring now to <FIG>, an outer diameter <NUM> of the balun at its proximal end portion may be, for example, approximately <NUM> inches. A dimension <NUM> from a proximal end portion of the balun short <NUM> to the proximal end portion of the tubing member <NUM> may be, for example, approximately <NUM> inches. A dimension <NUM> from the proximal end portion of the balun short <NUM> to a distal end portion of balun short <NUM> may be, for example, approximately <NUM> inches.

As mentioned above, in some embodiments, the microwave ablation device <NUM> has an outer tubular member <NUM> (not shown in <FIG>) that is reduced in outer diameter relative to outer tubular members of prior microwave ablation devices. In some examples, for instance, the outer tubular member <NUM> is approximately <NUM> gauge in diameter, or has an outer diameter in a range from approximately <NUM> inches +/-<NUM> inches or from approximately <NUM> inches +/-<NUM> inches. The microwave ablation system <NUM> and device <NUM> thus reduces invasiveness of microwave ablation procedures and thereby reduces post-surgery healing time and the risk of bleeding or injury. Despite the reduction in size of the outer tubular member <NUM>, however, the microwave ablation system <NUM> and microwave ablation device <NUM> facilitate the efficient delivery of microwave energy from the generator <NUM> to the antenna assembly <NUM> for effective treatment. In particular, the microwave ablation system <NUM> and device <NUM> are designed such that the coaxial cable <NUM> includes a relatively large outer diameter <NUM> of the center conductor <NUM>, even though maintaining a relatively large outer diameter <NUM> of the center conductor <NUM> while downsizing the outer tubular member <NUM>, in at least some instances, gives rise to an impedance mismatch along a signal path from the generator <NUM> to the coaxial cable <NUM>. Nonetheless, even with an impedance mismatch located at a particular portion along the signal path from the generator <NUM> to the coaxial cable <NUM>, the microwave ablation system <NUM> and device <NUM> of the present disclosure yields performance advantages while minimizing the increase in energy loss to the antenna assembly <NUM> relative to that that would result by using a coaxial cable that has a impedance that is matched to the impedance of the generator output port <NUM> but that has a reduced outer diameter of its center conductor, in part because the coaxial cable <NUM> of the present disclosure maintains a relatively large outer diameter <NUM> of the center conductor <NUM>.

As noted above, the impedance mismatch may be located between the coaxial cable <NUM> and one or more other components of the microwave ablation system <NUM>. For example, the impedance mismatch may be located (<NUM>) at a junction where the coaxial cable <NUM> is coupled to the transition waveguide <NUM>, (<NUM>) at a portion internal to the transition waveguide <NUM>, or (<NUM>) at a junction where the transition waveguide <NUM> is coupled to the generator cable <NUM>. In this manner, the impedance of the coaxial cable <NUM> may be mismatched with (for example, by being at least a predetermined amount lower than) at least one of the impedances of the generator <NUM>, the generator output port <NUM>, the transition waveguide input port <NUM>, and/or the transition waveguide output port <NUM>.

In some embodiments, for example, the impedance mismatch is located at a junction where the coaxial cable <NUM> is coupled to the transition waveguide <NUM>, or, more particularly, where the input port <NUM> of the coaxial cable <NUM> is coupled to the output port <NUM> of the transition waveguide <NUM>. For instance, the respective impedances of the transition waveguide output port <NUM>, the transition waveguide input port <NUM>, the generator cable <NUM>, and the generator output port <NUM> may be matched to one another within the degree of tolerance and within the predetermined frequency range, and the impedance of the coaxial cable <NUM> may be lower than the respective impedances of the transition waveguide output port <NUM>, the transition waveguide input port <NUM>, the generator cable <NUM>, and the generator output port <NUM> by at least a predetermined amount, which exceeds the degree of tolerance. In particular, in one embodiment, the impedance of the coaxial cable <NUM> is in a range from approximately <NUM>Ω to <NUM>Ω, and the respective impedances of the transition waveguide output port <NUM>, the transition waveguide input port <NUM>, the generator output port <NUM>, and the generator cable <NUM> are in a range from approximately <NUM> S2 to <NUM>Ω, although each of these ranges may be smaller or larger in other embodiments.

In another embodiment, the impedance mismatch is located at a portion of the transition waveguide <NUM> between the transition waveguide input port <NUM> and the transition waveguide output port <NUM>. For instance, within the predetermined frequency range, the impedance of the coaxial cable <NUM> may be matched to the impedance of the transition waveguide output port <NUM>, and the respective impedances of the transition waveguide input port <NUM>, the generator cable <NUM>, and the generator output port <NUM> may be matched to one another within the degree of tolerance. In particular, in one illustrative embodiment, the respective impedances of the coaxial cable <NUM> and the transition waveguide output port <NUM> may be in a range from approximately <NUM>Ω to <NUM>Ω, and the respective impedances of the transition waveguide input port <NUM>, the generator cable <NUM>, and the generator output port <NUM> may be in a range from approximately <NUM> S2 to <NUM>Ω.

In yet another embodiment, the impedance mismatch is located at a junction where the transition waveguide <NUM> is coupled to the generator cable <NUM>, or, more particularly, where the transition waveguide input port <NUM> is coupled to the generator cable <NUM>. For instance, within the predetermined frequency range, the impedance of the coaxial cable <NUM> may be matched to the respective impedances of the transition waveguide output port <NUM> and the transition waveguide input port <NUM>, and the respective impedances of the generator cable <NUM> and the generator output port <NUM> may be matched to one another within the degree of tolerance. In particular, in one embodiment, the respective impedances of the coaxial cable <NUM>, the transition waveguide output port <NUM>, and the transition waveguide input port <NUM> may be in a range from approximately <NUM>Ω to <NUM>Ω, and the respective impedances of the generator cable <NUM> and the generator output port <NUM> may be in a range from approximately <NUM> S2 to <NUM>Ω.

Referring now to the coaxial cable <NUM>, which may be solid conductor or a hollow conductor, the approximate characteristic impedance Z<NUM> of the coaxial cable <NUM> can be computed according to equation (<NUM>), shown below, where ODcenter conductor represents the outer diameter <NUM> of the center conductor <NUM> of the coaxial cable <NUM>, ODdielectric represents the outer diameter <NUM> of the dielectric layer <NUM> of the coaxial cable <NUM>, and εr represents the dielectric constant of the dielectric layer <NUM>. <MAT> In some embodiments, the impedance of the coaxial cable <NUM> is reduced relative to one or more other components of the microwave ablation system <NUM> by decreasing the ratio of the outer diameter <NUM> of the dielectric layer <NUM> to the outer diameter of the center conductor <NUM> of the coaxial cable <NUM>. For example, the decreased ratio (relative to a corresponding ratio for a coaxial cable that has an impedance that matches the impedance of the generator output port <NUM>) is obtained by decreasing the outer diameter <NUM> of the dielectric layer <NUM> while (<NUM>) keeping the outer diameter <NUM> of the center conductor <NUM> constant or (<NUM>) increasing the outer diameter <NUM> of the center conductor <NUM>. In another embodiment, the decreased ratio is obtained by increasing the outer diameter <NUM> of the center conductor <NUM> while (<NUM>) keeping the outer diameter <NUM> of the dielectric layer <NUM> constant or (<NUM>) decreasing the outer diameter <NUM> of the dielectric layer <NUM>. In some embodiments, the outer diameter <NUM> of the center conductor <NUM> is in a range from approximately <NUM> inches to <NUM> inches, the outer diameter <NUM> of the dielectric layer <NUM> is in a range from approximately <NUM> inches to <NUM> inches, and the dielectric constant εr of the dielectric layer <NUM> is <NUM>, thereby causing the coaxial cable <NUM> to have an impedance in a range from approximately <NUM>Ω to <NUM>Ω.

Referring now to <FIG>, in some embodiments, the first lumen <NUM> is utilized as a fluid inflow conduit and the second lumen <NUM> is utilized as a fluid outflow conduit. In other embodiments, the first lumen <NUM> may serve as a fluid outflow conduit and the second lumen <NUM> may serve as a fluid inflow conduit. The outer tubular member <NUM> and/or the inner tubular member <NUM> may be adapted to circulate coolant fluid therethrough, and may include baffles, multiple lumens, flow restricting devices, or other structures that may redirect, concentrate, or disperse flow depending on their shape. The size and shape of the inner tubular member <NUM>, the outer tubular member <NUM>, the first lumen <NUM>, and the second lumen <NUM> may be varied from the configuration depicted in <FIG> and <FIG>.

<FIG> shows a portion of the probe assembly <NUM> of the microwave ablation device <NUM> of <FIG> including the first lumen <NUM>, shown disposed between the outer tubular member <NUM> and the inner tubular member <NUM>, the second lumen <NUM>, shown disposed between the inner tubular member <NUM> and the coaxial cable <NUM>, and a transmission line <NUM> extending longitudinally within the second lumen <NUM>. The coaxial cable <NUM> is a coaxial cable that includes a center conductor <NUM>. As indicated by the direction of the arrow-headed lines in <FIG>, the first lumen <NUM> serves as an inflow conduit for coolant fluid "F" and the second lumen <NUM> serves as an outflow conduit for coolant fluid "F," however as noted above these could be reversed without departing from the scope of the present disclosure. In general, the impedance of the coaxial cable <NUM> may be determined by the inner diameter of the outer conductor <NUM>, the outer diameter of the center conductor <NUM>, and the dielectric constant of the dielectric material <NUM>, and reducing the inner diameter of the outer conductor <NUM> causes the impedance of the coaxial cable <NUM> to decrease.

<FIG> shows a portion of the coaxial cable <NUM> including the inner conductor <NUM>, the outer conductor <NUM> coaxially disposed around the inner conductor <NUM>, and the dielectric material <NUM> disposed therebetween, shown with a balun short <NUM> coaxially disposed around a portion of the outer conductor <NUM>. During assembly, the balun short <NUM> is coupled, deposited or otherwise formed onto, or joined to, the outer conductor <NUM>. The balun short <NUM> may be formed as a single structure and electrically coupled to the outer conductor <NUM>, for example, by solder or other suitable electrical connection. The balun short <NUM> may be formed of any suitable electrically-conductive materials, such as copper, gold, silver, or other conductive metals or metal alloys. In some embodiments, the balun short <NUM> has a generally ring-like or truncated tubular shape. The balun short <NUM> is electrically coupled to the outer conductor <NUM> of the coaxial cable <NUM> by any suitable manner of electrical connection, e.g., soldering, welding, or laser welding. The size and shape of the balun short <NUM> may be varied from the configuration depicted in <FIG>.

<FIG> further depicts a dielectric layer <NUM> (also referred to herein as a balun insulator) coaxially disposed around the outer conductor <NUM> and coupled thereto. The balun insulator <NUM> may be formed of any suitable insulative material, including, but not limited to, ceramics, water, mica, polyethylene, polyethylene terephthalate, polyimide, polytetrafluoroethylene (PTFE) (e.g., Teflon®, manufactured by E. du Pont de Nemours and Company of Wilmington, Del. , United States), glass, metal oxides or other suitable insulator, and may be formed in any suitable manner. In some embodiments, as shown in <FIG>, the balun insulator <NUM> is a dielectric sleeve. The balun insulator <NUM> may be grown, deposited or formed by any other suitable technique. In some embodiments, the balun insulator <NUM> is formed from a material with a dielectric constant in the range of about <NUM> to about <NUM>.

<FIG> further depicts a temperature sensor <NUM> disposed in contact with a proximal end of the balun short <NUM>. The temperature sensor <NUM> is coupled to the transmission line <NUM> extending generally along a longitudinal axis of the coaxial cable <NUM>. In some embodiments, the temperature sensor <NUM> is a thermocouple and the transmission line <NUM> is a thermocouple wire. The thermocouple wire may be a two lead wire thermocouple wire, for example it may be comprised of an insulated (anodized) side-by-side constantine wire and a copper wire. The balun short <NUM> may include an engagement element <NUM> adapted to engage with the temperature sensor <NUM>, for example, to facilitate electrical and mechanical coupling of the temperature sensor <NUM> and the balun short <NUM>. In some embodiments, the engagement element <NUM> may be a groove, slot, or recess cut into the balun short <NUM>. Alternatively, the temperature sensor <NUM> may be soldered to balun short <NUM>. Placement of the thermocouple <NUM> directly against the balun short <NUM> improves the sensitivity and thermo-profiling characteristics of the microwave ablation device <NUM>, particularly as compared to traditional thermocouples in microwave ablation devices, which measure the temperature of the cooling fluid. As will be appreciated by those of skill in the art, the temperature of the coolant will lag the temperature of the balun itself, and thus provide only approximate indications of the temperature of the elements which are heated during operation. As a result, in instances where little or no coolant is flowing, the temperature of the balun <NUM> and coaxial cable <NUM> associated therewith can increase faster than that of the coolant and result in damage to the microwave ablation device <NUM> even before triggering a shut-off of the microwave ablation system <NUM> based on the temperature of the coolant. Accordingly, improved safety and performance can be achieved by direct sensing of temperature of the balun <NUM>.

Still further, <FIG> depicts a heat-shrink tubing member <NUM> disposed in a first configuration around the outer conductor <NUM>. During assembly, the heat-shrink tubing member <NUM> is utilized to secure a portion of the transmission line <NUM> to the coaxial cable <NUM>. The heat-shrink tubing member <NUM> may be any suitable tubing material with the capability to respond to heat and bind around an object, and may have any suitable length. In some embodiments, the heat-shrink tubing member <NUM> may be a thermoplastic.

<FIG> shows the coaxial cable <NUM> of <FIG> following application of heat to the heat-shrink tubing member <NUM>. During assembly, securing a portion of the transmission line <NUM> to the coaxial cable <NUM>, as shown in <FIG> keeps the transmission line stable and helps to maintain the electrical and mechanical coupling of the temperature sensor <NUM> and the balun short <NUM> during subsequent assembly operations. <FIG> further shows a second tubing member <NUM> disposed in a first configuration.

The tubing member <NUM> includes an inner layer of an electrically-conductive material <NUM>. The electrically-conductive layer <NUM> may be formed of any suitable electrically-conductive material, such as metallic material. In one embodiment the metallic material of electrically-conductive layer <NUM> is formed of a silver ink deposited or layered on an interior surface of the tubing member <NUM>. The tubing member <NUM> may have a length from approximately <NUM> to <NUM> inches in length. However, the shape and size of the tubing member <NUM> and the balun insulator <NUM> may be varied from the configuration depicted in <FIG> without departing from the scope of the present disclosure. Indeed, though described as one embodiment, the orientation and implementation of the feed line <NUM> as well as other aspects of the present disclosure are not so limited. For example, the feed line <NUM> may incorporate one or more aspects of the ablation system described in <CIT>, entitled "MICROWAVE ABLATION CATHETER AND METHOD OF UTILIZING THE SAME".

<FIG> shows the balun <NUM> after the application of thermal energy or crimping, as the case may be, to the tubing member <NUM> and the resultant shrinkage or deformation. As shown <FIG>, the electrically-conductive material <NUM> is disposed in intimate contact with the balun short <NUM> and a portion of the balun insulator <NUM>. In some embodiments, as shown in <FIG>, a portion of the balun insulator <NUM> may extend distally beyond the distal end of the tubing member <NUM> and electrically conductive layer <NUM>, to create a gap <NUM>. The gap <NUM> improves the microwave performance of the probe assembly <NUM> and can assist in achieving a desired ablation pattern. More specifically, the gap <NUM> ensures adequate coupling of microwave energy from a proximal radiating section <NUM> (<FIG>) into the balun <NUM>, improving the performance of the balun <NUM> over a wide range of tissue dielectric conditions. Further, <FIG> shows the tubing member <NUM> securing the portion of the transmission line <NUM> between the heat-shrink tubing member <NUM> and the balun short <NUM> to the coaxial cable <NUM> preventing its movement and substantially preventing the temperature sensor <NUM> from being removed from physical contact with the balun short <NUM>.

In some embodiments, the balun insulator <NUM> has an inner diameter, and the tubing member <NUM>, which radially surrounds the balun insulator <NUM>, has a maximum outer diameter <NUM>, which is its diameter at its largest portion. For example, the balun insulator <NUM> inner diameter may be approximately <NUM> inches, and the maximum outer diameter of the tubing member <NUM> may match the maximum outer diameter <NUM> of the tubing member <NUM> and may be approximately <NUM> inches. In this manner, despite having an outer diameter of the tubing member <NUM> that is relatively small compared to prior baluns of microwave ablation devices, the balun <NUM> is able to have a relatively large thickness, because the thickness of the outer diameter of the coaxial cable <NUM> has been decreased. This relatively thick size of the balun <NUM> facilitates efficient and concentrated delivery of energy to the antenna assembly <NUM> of the microwave ablation device <NUM>, despite the downsizing of the microwave ablation device <NUM> relative to prior devices.

<FIG> is a cross-sectional view of a portion of the probe assembly <NUM> illustrating the balun <NUM> of <FIG> connected to the antenna assembly <NUM>, in accordance with an embodiment of the present disclosure. In operation, microwave energy having a wavelength, lambda (λ), is transmitted through the antenna assembly <NUM> and radiated into the surrounding medium, e.g., tissue. The length of the antenna assembly <NUM> for efficient radiation may be dependent on the effective wavelength, λeff, which is dependent upon the dielectric properties of the treated medium. The antenna assembly <NUM> through which microwave energy is transmitted at a wavelength λ, may have differing effective wavelengths, λeff, depending upon the surrounding medium, e.g., liver tissue as opposed to breast tissue, lung tissue, kidney tissue, etc..

The antenna assembly <NUM>, according to the embodiment shown in <FIG>, includes a proximal radiating section <NUM> having a length "L1", a distal radiating section <NUM> including an electrically-conductive element <NUM> having a length "L2", and a feed point <NUM> disposed therebetween. In some embodiments, the proximal radiating section <NUM> may have a length "L1" in a range from approximately <NUM> inches to about <NUM> inches. The electrically-conductive element <NUM> may be formed of any suitable electrically-conductive material, e.g., metal such as stainless steel, aluminum, titanium, copper, or the like. In some embodiments, the electrically-conductive element <NUM> may have a length "L2" in a range from about <NUM> inches to about <NUM> inches.

As shown in <FIG>, the electrically-conductive element <NUM> has a stepped configuration, such that the outer diameter of the distal portion <NUM> is less than the outer diameter of the proximal portion <NUM>. Further, the inner conductor <NUM> of the coaxial cable <NUM> is arranged such that it extends past the distal end of the insulator <NUM> and into the proximal portion <NUM> of the electrically-conductive element <NUM>. A hole <NUM> formed in the proximal portion <NUM> approximately at <NUM> degrees to the inner conductor <NUM> allows for solder, a set screw, or other securing mechanisms to physically secure the electrically-conductive element <NUM> to the inner conductor <NUM> and therewith the coaxial cable <NUM> of the microwave ablation device <NUM>.

The embodiments disclosed herein are examples of the disclosure and may be embodied in various forms. For instance, although certain embodiments herein are described as separate embodiments, each of the embodiments herein may be combined with one or more of the other embodiments herein. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure. Like reference numerals may refer to similar or identical elements throughout the description of the figures.

Claim 1:
A microwave ablation system, comprising:
a generator (<NUM>), comprising:
a generator output port (<NUM>) having a generator output port impedance;
a generator cable (<NUM>) having a generator cable impedance,
wherein the generator cable impedance is matched to the generator output port impedance within a degree of tolerance within a predetermined frequency range; and
a microwave ablation device (<NUM>), comprising:
a coaxial cable (<NUM>) that has a coaxial cable impedance and is coupled to the generator output port by way of the generator cable,
wherein, within the predetermined frequencyrange, the coaxial cable impedance is lower than at least one of the generator output port impedance or the generator cable impedance by at least a predetermined amount that exceeds the degree of tolerance,
characterized in that the coaxial cable impedance is in a range from approximately <NUM>Ω to <NUM>Ω.