Signal handling unit

Abstract

The invention provides a signal handling unit for handling signals having a first frequency and signals having a second, lower, frequency. The signal handling unit comprises: a signal divider electronically connected to a first port by a common signal line; a first signal branch electronically connecting the signal divider to a second port, wherein the first signal branch comprises a directional interface adapted to: convey only signals at the first frequency from the signal divider to the second port; and a second signal branch electronically connecting the signal divider to a third port, wherein the second signal branch is adapted to convey signals at the first and second frequency from the signal divider to the third port.

Description

[0001] Signal Handling Unit

[0002] Field of the Invention

[0003] The present invention relates to signal handling units for dividing signals from a common signal pathway onto multiple different signal pathways and / or for combining signals onto a common signal pathway and particularly, although not exclusively, to signal handling units for dividing signals of different frequencies from a common signal pathway onto multiple different signal pathways.

[0004] Background

[0005] It is known to use microwave electromagnetic (EM) radiation for treating biological tissue, for example for coagulating blood or for ablating the tissue itself. Tissue ablation using microwave EM energy is based on the fact that biological tissue is largely composed of water. Human soft organ tissue is typically between 70% and 80% water content. Water molecules have a permanent electric dipole moment, meaning that a charge imbalance exists across the molecule. This charge imbalance causes the molecules to move in response to the forces generated by application of a time varying electric field as the molecules rotate to align their electric dipole moment with the polarity of the applied field. At microwave frequencies, rapid molecular oscillations result in frictional heating and consequential dissipation of the field energy in the form of heat. This is known as dielectric heating.

[0006] This principle is harnessed in microwave ablation therapies, where water molecules in target tissue are rapidly heated by application of a localised electromagnetic field at microwave frequencies, resulting in tissue coagulation and cell death. It is known to use microwave emitting probes to treat various conditions in the lungs and other organs. For example, in the lungs, microwave radiation can be used to treat asthma and ablate tumours or lesions.

[0007] Another application of microwave EM radiation is for sealing vessels. For example, when microwave EM radiation is applied to a vessel that has been clamped, such that the walls of the vessel are in contact with each other, the rapid heating of the vessel tissue causes the vessel walls to fuse together and seal the vessel.

[0008] A complication of vessel sealing is the need to monitor the progress of the vessel sealing in order to determine when the vessel has been properly sealed. If the application of microwave EM radiation is halted too early, then the vessel may not be sufficiently sealed and may rupture or bleed. If the application of microwave EM radiation continues after the vessel has been sufficiently sealed, then unnecessary tissue damage may occur as a result of the procedure.

[0009] In order to monitor the progress of the vessel sealing, a measurement signal that is different from the microwave signal is required. However, different signals will often require different signal pathways in order to be transmitted and delivered properly to and from a target location, such as a biological tissue. As the space is limited in endoscopic applications, it is often not possible to provide two separate signal lines for delivering the microwave EM radiation and the measurement signal to the treatment site; 008856742

[0010] 2 however, providing both signals on a common signal line runs the risk of inaccurate signal delivery or of damaging the measurement equipment with the microwave signals.

[0011] The present invention has been devised in light of the above considerations.

[0012] Summary of the Invention

[0013] At its most general, the present invention provides a signal handling unit for controlling the splitting of incoming signals having different frequencies, and different delivery requirements.

[0014] According to a first aspect of the invention, there is provided a signal handling unit for handling signals having a first frequency and signals having a second frequency, wherein the second frequency is lower than the first frequency, the signal handling unit comprising: a signal divider electronically connected to a first port by a common signal line, wherein the common signal line is adapted to convey signals at the first frequency and signals at the second frequency from the first port to the signal divider; a first signal branch electronically connecting the signal divider to a second port, wherein the first signal branch comprises a directional interface adapted to: convey signals at the first frequency from the signal divider to the second port and substantially prevent the conveyance of signals at the second frequency from the signal divider to the second port; and convey signals at the second frequency from the second port to the first port; and a second signal branch electronically connecting the signal divider to a third port, wherein the second signal branch is adapted to convey signals at the first frequency and signals at the second frequency from the signal divider to the third port.

[0015] The present invention provides a means of splitting signals at the first frequency, for example microwave frequency signals, and signals at the second frequency, for example radiofrequency signals, from a single common signal transmission line to two signal branches such that different combinations of signals at the first frequency and signals at the second frequency arrive at the output ports, i.e., the second and third ports, of the signal handling unit.

[0016] It is to be understood that the term “substantially prevent” as used herein in the context of signal handling may mean attenuate, such that the directional interface attenuates signals at the second frequency travelling from the signal divider towards the second port. Substantially preventing or attenuating may be understood to mean only a negligible component of the signal is conveyed, or passed. It is to be understood that the term substantially prevent as used herein may mean prevent, or entirely prevent, such that the directional interface prevents, e.g., entirely prevents, signals at the second frequency travelling from the signal divider towards the second port. For example, substantially prevent or attenuate may be taken to mean that less than 10% of the signal passes through the directional interface, for example less than 5%, for example less than 1%.

[0017] It is to be understood that the term “convey”, or “pass”, as used herein in the context of signal handling may mean substantially convey, or substantially pass, such that the directional interface provides minimal, insubstantial or negligible attenuation, for example, for signals at the first frequency travelling 008856742

[0018] 3 from the signal divider to the second port. For example, substantially convey or pass may be taken to mean that less than 10% of the signal is attenuated through the directional interface, for example less than 5%, for example less than 1%.

[0019] The signal divider may be adapted to divide, or split, the incoming signals, i.e. , the signals at the first frequency (e.g., microwave frequency signals) and the signals at the second frequency (e.g., radiofrequency signals), into two signal portions. For example, an incoming microwave frequency signal may be divided into a first microwave frequency signal portion and a second microwave frequency signal portion. For example, an incoming radiofrequency signal may be divided into a first radiofrequency signal portion and a second rad io frequency signal portion. In an embodiment, the first and second (microwave and / or radio frequency) portions may be equal (e.g. have equal energy, amplitude or magnitude). That is, the signal may be split into two equal parts. However, in some other embodiments, the first and second (microwave and / or radio frequency) portions may be unequal such that the signal is split into two unequal parts.

[0020] In order for microwave energy to be applied between the second and third ports, or between radiating structures electrically connected to the second and third ports, portions of the microwave frequency signals have to be provided to both of the second and third ports. Put another way, the second port will need to receive a first microwave frequency portion and the third port will need to receive a second microwave frequency portion in order to apply microwave energy between the second and third ports. In order for radiofrequency energy to be applied between the second and third ports, or between radiating structures electrically connected to the second and third ports, the radiofrequency signals have to be provided between the signal lines of the second and third ports, in order to generate a potential difference between the two ports. Put another way, in order to apply radiofrequency energy between the second and third ports, a potential difference between the two ports is required, which means that the first radiofrequency signal portion would need to be isolated from the second radiofrequency signal portion produced by the signal divider.

[0021] By providing the directional interface connected between the second port and the signal divider, a signal at the second frequency, for example a radiofrequency active signal travelling towards the second port from the signal divider (i.e., a portion of a radiofrequency signal split onto the first signal branch by the signal divider) is removed (or attenuated such that only a negligible signal remains), thereby substantially preventing the conveyance of any portion of signals at the second frequency from the signal divider circuit to the second port. In addition, any return signals at the second frequency, for example radiofrequency return signals, entering the signal handling unit at the second port are isolated from the active signals at the second frequency, for example the radiofrequency active signals.

[0022] Further, by providing the directional interface connected between the second port and the signal divider, a signal at the first frequency, for example a microwave frequency signal travelling towards the second port from the signal divider (i.e., a portion of a microwave frequency signal split onto the first signal branch by the signal divider) is conveyed from the signal divider circuit to the second port. In addition, any signals at 008856742

[0023] 4 the first frequency, for example microwave frequency signals, entering the signal handling unit at the second port may be removed (or attenuated such that only a negligible signal remains).

[0024] Accordingly, whilst the input of the signal handling unit (i.e. , the first port of the signal handling unit) may receive a combination of microwave frequency and radiofrequency signals, both outputs of the signal handling unit (i.e., the second and third ports) will receive a portion of the signals at the first frequency, e.g., the first and second microwave frequency signal portions; whilst signals at the second frequency, e.g., only the first radiofrequency signal portion, will be provided between the signal lines of the second and third ports, in order to generate a potential difference between the two output ports.

[0025] In other words, the invention provides a simplified means of dividing signals having multiple frequencies from a common input line onto two separate signal pathways or branches, wherein each separate signal pathway receives a different combination of signals.

[0026] Put another way, the invention provides a means of selectively delivering / blocking signals that have been split off from a common input signal line to the desired signal outputs.

[0027] The signal handling unit of the present invention may be provided as a consolidated unit, meaning that the only requirements for installing the signal handling unit in an electrical system may be to connect the first port to an input signal line and to connect the second port and the third port to respective output signal lines.

[0028] In an example, the directional interface comprises a first filter for conveying signals at the first frequency from the signal divider to the second port and substantially preventing the conveyance of signals at the second frequency from the signal divider to the second port.

[0029] The first filter may be a high pass filter in order to permit the conveyance of signals at the first frequency, and substantially prevent the conveyance of signals at the second frequency, from the signal divider to the second port.

[0030] The first filter may be a notch filter configured to permit the conveyance of signals at the first frequency, and substantially prevent the conveyance of signals at the second frequency, from the signal divider to the second port.

[0031] A notch filter is a type of band-stop or band-rejection filter, which is a filter that passes most frequencies unaltered but attenuates frequencies in a specific range. A notch filter is an example of a band-stop filter with a narrow attenuation range. In this way, the directional interface may be adapted to remove a specific frequency of interest, such as the second frequency, whilst not attenuating the signals at the first frequency.

[0032] The first filter may be a capacitor (e.g. series connected capacitor) provided along the first signal branch between the signal divider and the second port.

[0033] The capacitor functions as a high pass filter, which permits the signals at the first frequency, e.g., microwave frequency signals, to pass through the directional interface from the signal divider to the second port, whilst attenuating the signals at the second frequency, e.g., rad io frequency signals. A 008856742

[0034] 5 capacitor will provide isolation between radiofrequency active and return signals on either side of the directional interface.

[0035] In an example, the directional interface comprises a second filter for conveying signals at the second frequency from the second port to the first port. The second filter is also configured to allow the conveyance of signals at the first frequency from the second to the first port or in the opposite direction.

[0036] The second filter may be a low pass filter in order to permit the conveyance of signals at the second frequency and signals at the first frequency, from the second port to the first port or in the opposite direction.

[0037] The second filter may be a notch filter configured to permit the conveyance of signals at the second frequency, and at the first frequency, from the second port to the first port or in the opposite direction.

[0038] A notch filter is a type of band-stop or band-rejection filter, which is a filter that passes most frequencies unaltered but attenuates frequencies in a specific range. A notch filter is an example of a band-stop filter with a narrow attenuation range. In this way, the directional interface may be adapted to remove a specific harmonic frequency of interest, such as the second harmonic of the first frequency, whilst not attenuating the signals at the first and second frequency.

[0039] In an example, the second filter is a quarter wavelength stub shorted to ground, wherein the quarter wavelength stub is sized to a quarter of a wavelength of a signal at the first frequency, e.g., a microwave frequency.

[0040] A quarter wavelength stub having a design frequency at the frequency of the microwave signals will act as a quarter wavelength transformer for signals at this frequency of operation. That is, the stub will allow microwave signals received at the second port to travel to the first port. By shorting the quarter wavelength stub to ground, the directional interface provides a return signal pathway for radiofrequency signals. Radiofrequency signals leaving the signal handling unit at the third port, for example radiofrequency active signals on an inner conductor or signal line of the third port, may then return via the second port, for example on an inner conductor or signal line of the second port, and then proceed to ground via the quarter wavelength stub. The signal pathway from the second port to the quarter wavelength stub may form at least part of a return signal pathway for signals at the second frequency, for example radiofrequency return signals. The quarter wavelength stub will appear as a lossless transmission path to the microwave frequency signals.

[0041] The quarter wavelength stub may be provided independently of, or in combination with, the series capacitor described above.

[0042] In some examples, the second filter is provided between the first filter and the second port along the first signal branch. In other words, the first filter may be provided between the signal divider and the second filter along the first signal branch.

[0043] In the example where the capacitor is provided in combination with the quarter wavelength stub, the capacitor may be provided between the signal divider and the quarter wavelength stub along the first 008856742

[0044] 6 signal branch. Put another way, the quarter wavelength stub may be provided between the capacitor and the second port.

[0045] In some examples, the first port is a first coaxial port comprising: a first inner conductor electronically connected to the common signal line; and a first outer conductor electronically connected to ground. In this case, the input line for conveying the signals at the first and second frequencies to the input port may be a coaxial cable.

[0046] In some examples, the second port is a second coaxial port comprising: a second inner conductor electronically connected to the first signal branch; and a second outer conductor electronically connected to ground, wherein the second outer conductor comprises a first capacitive structure.

[0047] By providing a first capacitive structure on the second outer conductor, signals at the second frequency, e.g., radiofrequency signals, such as a radiofrequency return signal, may be substantially prevented from propagating on the second outer conductor. Accordingly, the second outer conductor may be substantially prevented from providing a signal return path for radiofrequency return signals for radiofrequency active signals propagating on the second inner conductor. Put another way, the first capacitive structure may substantially prevent a signal return path being formed between the second inner conductor and the second outer conductor for signals at the second frequency, e.g., radiofrequency signals.

[0048] In some examples, the second outer conductor comprises a first section and a second section, wherein the first section has an inner diameter greater than an outer diameter of the second section, and wherein the first section overlaps the second section in a first overlapping section, and wherein the first overlapping section forms the first capacitive structure. The first overlapping section may be sized to a multiple (e.g. fractional multiple) of a quarter of a wavelength of a signal at the first frequency.

[0049] The first capacitive structure may be formed by a first overlapping section between the first section and the second section of the outer conductor. A capacitive structure may be formed from two conductors positioned in close proximity to each other and separated by a non-conducting region, which may in some examples comprise a dielectric. Therefore, the first capacitive structure may be formed by overlapping two separated portions of the second outer conductor, without requiring any additional components such as a discrete capacitor. In an embodiment the first section and the second section of the second outer conductor are separated by an air gap at the first overlapping section. In an embodiment the first section and the second section of the second outer conductor are separated by a first dielectric layer at the first overlapping section.

[0050] The first section of the second outer conductor may comprise a hollow elongate body connected to a hollow elongate end portion, the hollow elongate end portion having a reduced thickness compared to the hollow elongate body, wherein the second section of the second outer conductor comprises a hollow elongate body connected to a hollow elongate end portion, the hollow elongate end portion having a reduced thickness compared to the hollow elongate body, wherein the hollow elongate end portion of the 008856742

[0051] 7 first section of the second outer conductor surrounds the hollow elongate body of the second section of the second outer conductor at the first overlapping section.

[0052] Put another way, the second section of the second outer conductor may be received within the first section of the second outer conductor in the overlapping region forming the first capacitive structure. In an alternative arrangement, the first section may be received within the second section to form the first overlapping region and so form the first capacitive structure.

[0053] The length of the first overlapping section may be between 2mm and 4mm, for example 3.2mm.

[0054] By making the length of the first overlap a multiple (e.g. fractional multiple) of the microwave signal quarter wavelength , the first overlapping section between the first and second sections of the second outer conductor behaves as a capacitor despite essentially being open-circuited lines with no direct electrical connection to each other. In particular, the use of a quarter wavelength overlap means that the first overlapping section becomes a lossless, or low loss, transmission line for the signals at the first frequency, e.g., microwave frequency signals, whilst blocking signals at the second frequency, e.g., radiofrequency signals.

[0055] In some examples, the third port is a third coaxial port comprising: a third inner conductor electronically connected to the second signal branch; and a third outer conductor electronically connected to ground, wherein the third outer conductor comprises a second capacitive structure.

[0056] By providing a second capacitive structure on the third outer conductor, signals at the second frequency, e.g., radiofrequency signals, such as a radiofrequency return signal, may be substantially prevented from propagating on the third outer conductor. Accordingly, the third outer conductor may be substantially prevented from providing a signal return path for radiofrequency return signals for radiofrequency active signals propagating on the third inner conductor. Put another way, the second capacitive structure may substantially prevent a signal return path being formed between the third inner conductor and the third outer conductor for signals at the second frequency, e.g., radiofrequency signals.

[0057] In some examples, the third outer conductor comprises a third section and a fourth section, wherein the third section has an inner diameter greater than an outer diameter of the fourth section, and wherein the third section overlaps the fourth section in a second overlapping section, and wherein the second overlapping section forms the second capacitive structure. The second overlapping section may be sized to a multiple (e.g. fractional multiple) of the quarter of a wavelength of a signal at the first frequency.

[0058] The second capacitive structure may be formed by a second overlapping section between the third section and the fourth section of the outer conductor. A capacitive structure may be formed from two conductors positioned in close proximity to each other and separated by a non-conducting region, which may in some examples comprise a dielectric. Therefore, the second capacitive structure may be formed by overlapping two separated portions of the third outer conductor, without requiring any additional components such as a discrete capacitor. In an embodiment the third section and the fourth section of the second outer conductor are separated by an air gap at the second overlapping section. In an embodiment 008856742

[0059] 8 the third section and the fourth section of the third outer conductor are separated by a second dielectric layer at the second overlapping section.

[0060] The third section of the third outer conductor may comprise a hollow elongate body connected to a hollow elongate end portion, the hollow elongate end portion having a reduced thickness compared to the hollow elongate body, wherein the fourth section of the third outer conductor comprises a hollow elongate body connected to a hollow elongate end portion, the hollow elongate end portion having a reduced thickness compared to the hollow elongate body, wherein the hollow elongate end portion of the third section of the third outer conductor surrounds the hollow elongate body of the fourth section of the third outer conductor at the second overlapping section.

[0061] Put another way, the fourth section of the third outer conductor may be received within the third section of the third outer conductor in the overlapping region forming the second capacitive structure. In an alternative arrangement, the third section may be received within the fourth section to form the second overlapping region and so form the second capacitive structure.

[0062] The length of the first overlapping section may be between 2mm and 4mm, for example 3.2mm.

[0063] By making the length of the second overlap a multiple (e.g. fractional multiple) of the microwave signal quarter wavelength , the second overlapping section between the third and fourth sections of the third outer conductor behaves as a capacitor despite essentially being open-circuited lines with no direct electrical connection to each other. In particular, the use of a quarter wavelength overlap means that the second overlapping section becomes a lossless, or low loss, transmission line for the signals at the first frequency, e.g., microwave frequency signals, whilst blocking signals at the second frequency, e.g., radiofrequency signals.

[0064] The first port, the second port and the third port may comprise or be QMA connectors.

[0065] In some examples, the signal handling unit comprises a microstrip structure comprising: a first conductor layer, wherein the signal divider, the first signal branch, the second signal branch and the directional interface are provided on the first conductor layer; a second conductor layer; and a dielectric layer provided between the first conductor layer and the second conductor layer.

[0066] The first conductor layer may comprise conductive tracks surrounded by an insulator material. The conductive tracks may define the signal divider, the first signal branch, the second signal branch and the directional interface.

[0067] The second conductor layer may form a common ground layer, or ground plane. The second conductor layer may be a planar metallic sheet. The second conductor layer may be connected to the first outer conductor of the first port, the second outer conductor of the second port and / or the third outer conductor of the third port.

[0068] The signals at the first frequency, e.g., microwave frequency signals, may be travel through the signal handling unit between the first conductor layer and the second conductor layer. The signals at the second frequency, e.g., radiofrequency active signals, may travel along the first conductor layer. The second 008856742

[0069] 9 conductor layer may provide a return path for radiofrequency signals travelling along the first conductor layer. Put another way, the second conductor layer may provide a signal pathway for radiofrequency return signals.

[0070] In examples wherein the directional interface comprises a quarter wavelength stub as described above, the quarter wavelength stub may be connected to the second conductor layer by way of a via extending through the dielectric layer in order to short the quarter wavelength stub to ground. For example, the first conductor layer may be electrically isolated from the second conductor layer by the dielectric layer and the via may provide an (e.g. the only) electrical pathway between the first conductor layer and the second conductor layer. That is, the via may provide an (e.g. the only) electrical pathway for signals at the second frequency to travel from first conductor layer to the second conductor layer.

[0071] In an example, the signal divider circuit is a Wilkinson power divider. The Wilkinson power divider may comprise a first arm electrically connecting the first port to the first signal branch and a second arm electrically connecting the first port to the second signal branch, wherein the first arm and the second arm are identical quarter wavelength transformers for the microwave frequency signals.

[0072] As a Wilkinson power divider is constructed from passive components it is reciprocal, meaning that the signal divider can be operated in either direction to either divide the signals received at the first port to the second and third ports or to combine signals received at the second and third ports onto the first port. By providing identical first and second arms, the signals at the first frequency and the signals at the second frequency will arrive at the second and third ports in phase with each other, meaning that no potential difference will exist between the first and second signal branches. The use of quarter wavelength transformers as the first and second arms improves the impedance matching across the signal divider, thereby reducing signal attenuation through the signal handling unit.

[0073] In a specific example, the first frequency is a microwave frequency, the second frequency is a radiofrequency and the directional interface comprises a quarter wavelength stub provided between a capacitor and the second port along the first signal branch. The signal divider is a Wilkinson power divider. Further, the first, second and third ports are coaxial ports as described above, with the outer conductors of the second and third ports comprising capacitive structures. The signal handling unit is a microstrip structure as described above, with the second conductor layer being electronically connected to the outer conductors of each port. The quarter wavelength stub is shorted to ground by way of a via passing from the first conductor layer to the second conductor layer through the dielectric layer. The second and third ports are connected to each other by way of a biological tissue to be treated by the signals at the first and / or second frequency.

[0074] Working through the specific example above, focusing on the signals at the second frequency, i.e., the radiofrequency signals, a radiofrequency active signal enters the signal handling unit at the first inner conductor of the first port and is conveyed to the signal divider along the first conductor layer. The radiofrequency active signal is substantially prevented from travelling along the first signal branch towards the second inner conductor of the second port by the capacitor of the directional interface. The 008856742

[0075] 10 radiofrequency active signal travels along the second signal branch towards the third inner conductor of the third port to be delivered to the biological tissue.

[0076] A radiofrequency return signal is received at the second inner conductor of the second port because the first signal branch is isolated from the radiofrequency active signal by the capacitor of the directional interface, and so can form part of a return signal pathway for radiofrequency signals received from across the biological tissue. The radiofrequency return signal is received at the second inner conductor of the second port rather than the second outer conductor of the second port or the third outer conductor of the third port due to the first and second capacitive structures, respectively.

[0077] The radiofrequency return signal travels along the first signal branch from the second inner conductor of the second port to the quarter wavelength stub of the directional interface, at which point the radiofrequency return signal is shorted to the second conductor, or ground, layer of the signal handling unit by way of a via through the dielectric layer.

[0078] The radiofrequency return signal travels through the second conductor layer to the first outer conductor of the first port to leave the signal handling unit. The radiofrequency return signal leaves the signal handling unit via the first outer conductor rather than the second outer conductor of the second port or the third outer conductor of the third port due to the first and second capacitive structure, respectively.

[0079] Working through the specific example above, focusing on the signals at the first frequency, i.e., the microwave signals, a microwave signal enters the signal handling unit between the first inner conductor and the first outer conductor of the first port and is conveyed to the signal divider between the first conductive layer and the second conductive layer. The microwave signal is divided equally between the first and second signal branches and the equal divisions of the microwave signal are provided to the second and third ports to leave the signal handling unit. The divided portions of the microwave signal are then provided to the biological tissue by suitable radiating structures.

[0080] According to a second aspect of the invention, there is provided an electrosurgical instrument for treating biological tissue comprising: a first conductive element; and a second conductive element, separated from the first conductive element so as to emit energy at the first frequency and second frequency into biological tissue; and the signal handling unit according to the first aspect, wherein: the first conductive element is electrically connected to the third port to convey signals at the first frequency and signals at the second frequency to the first conductive element; and the second conductive element is electrically connected to the second port to convey signals at the first frequency to the second conductive element and to form at least part of a signal return path for signals at the second frequency received at the second conductive element.

[0081] In an example, the first conductive element is separated from the second conductive element by a dielectric element. In another example, the first conductive element is separated from the second conductive element by an air gap.

[0082] Vessel sealing and blood coagulation may be achieved through the application of microwave frequency signals to the treatment area in question. For example, by locating a biological tissue to be treated 008856742

[0083] 11 between the first and second conductive elements, the biological tissue may be exposed to microwave frequency radiation, thereby causing dielectric heating in the tissue. Radiofrequency signals may be used to measure the progress of the treatment of the biological tissue as outlined below.

[0084] As discussed above, in order for microwave energy to be applied between the second and third ports, and so between the first and second conductive elements, portions of the microwave frequency signals have to be provided to both of the second and third ports. In order for radiofrequency energy to be applied between the second and third ports, and so between the first and second conductive elements, the radiofrequency signals have to be provided between the signal lines, e.g., the inner conductors, of the second and third ports,

[0085] By incorporating the signal handling unit described above into the electrosurgical instrument, the mixture of signals received by electrosurgical instrument from a common signal line may be divided and distributed to the first and second conductive elements as required for delivering the signals without also requiring multiple input signal lines.

[0086] In an example, the electrosurgical instrument further comprises: a pair of jaw elements pivotable relative to each other to open and close a gap there between, wherein the first conductive element is mounted in one of the pair of jaw elements adjacent to the gap, and wherein the second conductive element is mounted in the other one of the pair of jaw elements adjacent to the gap opposite the first conductive element.

[0087] An example apparatus for providing microwave frequency signals to a vessel may include a set of forceps, or jaws, comprising a pair of radiating structures to be provided on opposing sides of the vessel to be sealed. The jaw elements may be provided about the vessel when the gap between the jaw elements is open. The jaw elements may then pivot towards the closed position in order to clamp the vessel between the jaw elements. Once the vessel is clamped between the jaw elements, the microwave and radiofrequency signals may be delivered to the electrosurgical device, and so to the first and second conductive elements in the jaws by way of the signal handling unit described above, in order to seal the vessel clamped between the jaws. The jaw elements may then pivot to the open position in order to release the vessel after the sealing process has been completed.

[0088] Providing the signal transmission lines necessary for providing both the microwave frequency signals for treatment and the radiofrequency signals for measurement to a pair of radiating structures would conventionally require numerous signal transmission lines. However, in space limited applications, such as in electrosurgical instruments for endoscopic insertion, the use of multiple different signal transmission lines may not be possible. By incorporating the signal handling unit described above into the electrosurgical instrument, the treatment and measurement signals may be provided to the electrosurgical instrument along a single common signal line and divided and filtered in order to deliver the desired portions of the incoming signals to the radiating structures of the electrosurgical instrument for delivery to the tissue. 008856742

[0089] 12

[0090] According to a third aspect of the invention, there is provided an electrosurgical apparatus for treating biological tissue, the apparatus comprising: a first signal generator for generating a first signal having a first frequency; a second signal generator for generating a second signal having a second frequency that is lower than the first frequency; an electrosurgical instrument according to the second aspect; and a feed structure for conveying the first signal and the second signal to the electrosurgical instrument..

[0091] In an example, the apparatus further comprises a control circuit adapted to monitor the operation of the first signal generator and the second signal generator, and wherein the control circuit is further adapted to: monitor a current and / or a voltage drawn by the second signal generator to generate the second signal; determine a tissue impedance based on the monitored current and / or voltage; and control the first signal generator based on the determined tissue impedance.

[0092] The combined return signal may comprise a reflected radiofrequency signal, wherein the reflected radiofrequency signal is obtained from an interface between the first and second conductive element with the biological tissue wedged between the two conductive elements.

[0093] In an example, controlling the first signal generator based on the determined tissue impedance comprises: determining whether the determined tissue impedance is greater than or equal to a predetermined threshold; and if the determined tissue impedance is greater than or equal to the predetermined threshold, deactivate the first signal generator; or if the determined tissue impedance is less than the predetermined threshold, maintain an activation of the first signal generator.

[0094] In order to ensure accurate and complete vessel sealing, and in order to substantially prevent insufficient vessel sealing or overexposure to microwave energy, it may be desirable to measure / monitor the state of the vessel during the sealing process. An example method of measuring the state of the vessel during the sealing process is to measure the impedance of the tissue using a radiofrequency signal. The impedance of the vessel tissue is linked to the water content of the tissue, which will change as the vessel is sealed, thereby changing the impedance of the tissue. Once a target impedance is reached, or an impedance threshold crossed, the vessel may be determined to be sealed sufficiently and the provision of microwave frequency signals to the vessel tissue stopped automatically. Alternatively, or in addition, the clinician may be informed that the vessel is sealed sufficiently, for example by way of an alert generated at a user interface of the electrosurgical apparatus. The alert may comprise a visual signal, an audible signal, a haptic signal and the like.

[0095] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0096] Summary of the Figures

[0097] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which: 008856742

[0098] 13

[0099] Figure 1A shows a schematic representation of a signal handling unit according to an aspect of the invention.

[0100] Figure 1B shows a detailed schematic representation of the signal handling unit shown in Figure 1A.

[0101] Figure 1C shows a schematic elevation view of the signal handling unit shown in Figure 1B.

[0102] Figure 2 shows a schematic representation of a signal handling unit according to an aspect of the invention.

[0103] Figure 3 shows a circuit representation of the signal handling unit shown in Figure 2.

[0104] Figures 4A to 4C show graphs of the microwave performance of a signal handling unit according to an aspect of the invention.

[0105] Figure 5 shows a schematic representation of an electrosurgical apparatus according to an aspect of the invention.

[0106] Figure 6 shows a method for controlling a microwave signal generator according to an aspect of the invention.

[0107] Detailed Description of the Invention

[0108] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0109] Figure 1A shows a schematic representation of a signal handling unit 100 according to an aspect of the invention.

[0110] The signal handling unit 100 comprises a signal divider 110 connected to a first port 120 for receiving a microwave signal 130 as the signal having the first frequency and a radiofrequency active signal 140 as the signal having the second frequency. In the examples described herein the first frequency is a microwave frequency, for example 2.45GHz, and the second frequency is a radiofrequency, for example between 300kHz to 500kHz. 008856742

[0111] 14

[0112] The signal divider 110 is connected between the first port 120 and a second port 150 along a first signal branch 160. The signal divider is connected between the first port 120 and a third port 170 along a second signal branch 180.

[0113] The signal divider 110 would split the radiofrequency active signal 140 onto both the first signal branch 160 and the second signal branch 180. However, the signal handling unit 100 comprises a directional interface 190 provided along the first signal branch 160 between the signal divider 110 and the second port 150. The directional interface 190 is adapted to convey signals at the first frequency, i.e. , microwave signal 130, from the signal divider 110 to the second port 150 and substantially prevent the conveyance of signals at the second frequency, i.e., radiofrequency active signal 140, from the signal divider 110 to the second port 150. The directional interface 190 therefore isolates the second port 150 from the signal divider 110 for signals at the second frequency, i.e., radiofrequency active signal 140.

[0114] Accordingly, the radiofrequency active signal 140 is conveyed only to the third port 170 along the second signal branch 180.

[0115] The signal divider 110 splits the microwave signal 130 into a first microwave frequency signal portion 132 to be received at the second port 150 and a second microwave frequency signal portion 134 to be received at the third port 170.

[0116] Therefore, the third port 170 of the signal handling unit 100 receives the radiofrequency active signal 140 and the second microwave frequency signal portion 134 and the second port 150 of the signal handling unit 100 receives only the first microwave frequency signal portion 132.

[0117] In addition to conveying the first microwave frequency signal portion 132 to the second port 150 and substantially preventing the conveyance of the radiofrequency active signal 140 to the second port 150, the directional interface 190 is further adapted to convey signals at the second frequency, e.g., a radiofrequency return signal 145 as shown in Figure 1A, from the second port 150 to the first port 120.

[0118] The arrangement shown in Figure 1A, provides a signal handling unit 100 for supplying radiofrequency electromagnetic energy and microwave electromagnetic energy from a single common signal pathway to two isolated output branches / ports, i.e., the second port 150 and the third port 170. As shown in Figure 1A, the signal handling unit splits the microwave frequency signals onto the two output ports and the radiofrequency signal is split between the two output ports.

[0119] Figure 1 B shows a detailed schematic representation of the signal handling unit 100 shown in Figure 1A. Figure 1C shows a schematic elevation view of the signal handling unit 100 shown in Figure 1 B. Features in common between Figures 1A, 1B and 1C share the same reference numerals.

[0120] In practice, the microwave signal 130 and the radiofrequency active signal 140 are both applied to a common input transmission line, between a signal line and a nominal ground line, and delivered to the input port 120 of the signal handling unit 100.

[0121] In the example shown in Figure 1 B, the input port 120 is a coaxial connector, such as a QMA connector, having a first inner conductor 122 electronically connected to the signal line of the common input 008856742

[0122] 15 transmission line carrying the radiofrequency signal. The input port 120 further comprises an outer conductor 124 connected to the nominal ground line of the common input transmission line.

[0123] In the example shown in Figures 1B and 1C, the signal handling unit 100 is provided on a microstrip structure comprising a first conductor layer 102, a second conductor layer 104 and a dielectric layer 106 provided between the first conductor layer 102 and the second conductor layer 104. The signal divider 110, the first signal branch 160, the second signal branch 180 and the directional interface 190 are provided on the first conductor layer 102.

[0124] The directional interface 190 comprises a first filter 192, such as a series capacitor, and a second filter 194, such as a quarter wavelength stub, provided between the signal divider 110 and the second port 150. The first filter 192 is provided between the signal divider 110 and the second filter 194. The second filter 194 is provided between the first filter 192 and the second port 150. In the example where the second filter 194 is a quarter wavelength stub, the quarter wavelength stub is shorted to the second conductor layer 104 by way of a via 195 in the dielectric layer 106. The functions of a series capacitor as a first filter 192 and a quarter wavelength stub as a second filter 194 within the directional interface are discussed in further detail below with reference to Figures 2 and 3.

[0125] The second port 150 and the third port 170 are both coaxial connectors, such as QMA connectors, in the example shown in Figures 1B and 1C.

[0126] The second port 150 comprises a second inner conductor 152electronically connected to the first signal branch 160 on the first conductor layer 102. The second port 150 also comprises a second outer conductor 154 electronically connected to the second conductor layer 104, which functions as a ground plane. The second outer conductor 154 comprises a first capacitive structure 156.

[0127] The first capacitive structure 156 comprises a first section 155 and a second section 157. The first section 155 has an inner diameter greater than an outer diameter of the second section 157. The first section 155 overlaps the second section 157 in a first overlapping section to form the first capacitive structure 156.

[0128] The third port 170 comprises a third inner conductor 172 electronically connected to the second signal branch 180 on the first conductor layer 102. The third port 170 also comprises a third outer conductor 174 electronically connected to the second conductor layer 104, which functions as a ground plane. The third outer conductor 174 comprises a second capacitive structure 176.

[0129] The second capacitive structure 176 comprises a third section 175 and a fourth section 177. The third section 175 has an inner diameter greater than an outer diameter of the fourth section 177. The third section 175 overlaps the fourth section 177 in a second overlapping section to form the second capacitive structure 176.

[0130] In use, the microwave frequency signals 130 are split into two parts 132, 134 and delivered from two output ports (the second port 150 and the third port 170) onto two output signal lines, each with their own signal lines, connected to the inner conductors of the ports, and a nominal ground line, connected to the outer conductors of the ports. The radiofrequency signals have to be applied between the two output signal lines, which is not possible if the radiofrequency signals are split in the same way as the microwave 008856742

[0131] 16 frequency signals using an ordinary reactive splitter or a conventional power divider as both output signal lines are joined to the single input line by a direct conducting path.

[0132] In order to achieve the desired, uneven splitting of the radiofrequency signals, whilst still maintaining the even splitting of the microwave frequency signals, the directional interface 190 is configured to act as a short circuit to a radiofrequency return path through the quarter wavelength stub for radiofrequency signals, whilst appearing as an open circuit to microwave frequency signals as described in further detail below with reference to Figure 2.

[0133] Figure 2 shows a schematic representation of a signal handling unit 200 according to an aspect of the invention. Reference numerals in common with Figures 1A to 1C refer to the same components and function as described above. The electronic characteristics of the components illustrated in Figure 2 are described below with reference to Figures 3 and 4A to 4C.

[0134] In the example shown in Figure 2, the signal divider 110 is a Wilkinson power divider 210. The Wilkinson power divider 210 comprises a second arm 230 electrically connecting the first port 120 to the third port 170 and a first arm 220 electrically connecting the first port 120 to the directional interface 190. The first arm 220 and the arm branch 230 are identical quarter wavelength transformers for the microwave frequency signals.

[0135] A Wilkinson power divider 210 is a class of power divider circuit that can achieve isolation between the output ports while maintaining a matched condition on all ports. The Wilkinson power divider can also be used as a power combiner because it is made up of passive components and hence is reciprocal.

[0136] Wilkinson power dividers are used to divide or combine power in power distribution networks. They have the advantages of being matched at all three ports and lossless when the powers at ports are as designed. In particular, a 3-dB Wilkinson power divider is able to evenly distribute the power from the first port 120 to the second port 150 and the third port 170 and combine even, i.e. , signals that have the same amplitudes and are in-phase, incident signals at the second port 150 and the third port 170 at the first port 120, whilst odd, i.e., signals having the same amplitudes but being anti-phase to each other, incident signals is all dissipated in the shunt resistor 235, according to the even and odd mode analysis.

[0137] The directional interface 190 shown in Figure 2 comprises a quarter wavelength stub 240 configured to allow the conveyance of microwave frequency signals with negligible transmission loss and permit the conveyance of radiofrequency return signals to the inner conductor 152 of the second port 150. The quarter wavelength stub is sized to a quarter of a wavelength of the microwave signals.

[0138] In addition, the directional interface comprises a series capacitor 250, which may also be referred to as a DC break to substantially prevent conveyance of radiofrequency active signal 140 to the second port 150, such that the quarter wavelength stub 240 is provided between the series capacitor 250 and the second port 150.

[0139] Figure 3 shows a circuit representation 300 of the signal handling unit 200 shown in Figure 2. 008856742

[0140] 17

[0141] The signal handling unit 300 is a bi-directional device which splits a common input signal received at the first port 120 into two equal phase output signals, or combines two equal-phase signal into a common signal in the opposite direction. The signal handling unit 300 relies on quarter wavelength transformers 320 and 330, which correspond to the first 220 and second 230 arms of the Wilkinson divider 210 respectively, to match the split ports, i.e. , the second port 150 and the third port 170, to the common port, i.e. , the first port 120.

[0142] The terminations of the first 220 and second 230 arms of the Wilkinson divider 210 will add in parallel at the first port 120. Therefore, for a first port 120 having a resistance Z0, for example which may be 50Q, the terminations of the first 220 and second 230 arms of the Wilkinson divider 210 must be transformed to 2xZ0 each at the input port 120 to combine to Z0. In this case, each quarter wave transformer 320, 330, i.e., the first 220 and second 230 arms of the Wilkinson divider 210, has an impedance of 1.414 x Zo. The shunt resistor 235 has a resistance of 2xZ0.

[0143] A signal entering the signal handling unit 300 at the first port 120 reaches the physical split and passes to the two quarter wavelength transformers 320, 330 of the signal divider 110. As the two quarter wavelength transformers 320, 330 are identical, the signals appearing at the outputs of the quarter wavelength transformers 320, 330 will have the same phase. This means that the outputs of the quarter wavelength transformers 320, 330 will be at the same potential and no current will flow in the shunt resistor 235.

[0144] The portions of the signals flowing from the first port 120, along quarter wavelength transformer 320 (the first branch 220 of the Wilkinson power divider 210) and to the third port 170, which will be the radiofrequency active signal and the first microwave signal portion, continue uninterrupted.

[0145] The portions of the signals flowing from the first port 120, along quarter wavelength transformer 330 (the second branch 230 of the Wilkinson power divider 210) and to the second port 150 will encounter a series capacitor 250. A capacitor used in series will act as a high pass filter on the first signal branch 160 to allow the second microwave signal to pass through, and impede any radiofrequency active signals from passing through to the second port 150 of the signal handling unit 300. The series capacitor 350 provides radiofrequency signal isolation between the active and return radiofrequency poles of the radiofrequency signal.

[0146] The quarter wavelength stub 240 connects the transmission path 340 between the series capacitor 250 and the second port 150 to short the first signal branch 160 to a radiofrequency signal return path. The short-circuited quarter wavelength stub 240 is virtually invisible to the transmission path for the second microwave signal and offers minimum through loss for the second microwave signal.

[0147] When the signal handling unit 300 functions as a signal combiner, a signal entering the divider circuit at an output of one of the quarter wavelength transformers 320, 330, half the power would pass through the shunt resistor 235 and the other half would pass through the given quarter wave transformer 320, 330. The signal then appears at the junction connecting the first port 120 to the outputs of the quarter wavelength transformers 320, 330. Any power passing from the junction through the other quarter wave 008856742

[0148] 18 transformer 330, 320 to the output port of said other quarter wave transformer 330, 320 will be out of phase with the signal appearing via the shunt resistor 235 as it will have passed through two quarter wave lines. As a result there is isolation between the outputs of the quarter wavelength transformers 320, 330, with half the incident power being dissipated within the shunt resistor 235 and the remaining half appearing at the first port 120.

[0149] Figures 4A to 4C show graphs of the performance of a signal handling unit according to an aspect of the invention. Each graph is a graph of transmission loss (dB) against frequency (GHz).

[0150] Figure 4A shows a graph 400 of the signal losses between the first port 120 and the third port 170.

[0151] Plot 410 shows the losses for signals travelling between the first port 120 and the third port 170, or between the third port 170 and the first port 120 as the plots are identical. As plot 410 shows, the losses between the first port 120 and the third port 170 are low around the mark 405 of 2.45GHz.

[0152] Plot 420 shows the return loss, i.e., the port match at the third port 170. Plot 430 shows the port match at the first port 120.

[0153] Figure 4B shows a graph 500 of the signal losses between the first port 120 and the second port 150.

[0154] Plot 510 shows the losses for signals travelling between the first port 120 and the second port 150, or between the second port 150 and the first port 120 as the plots are identical. As plot 510 shows, the losses between the first port 120 and the second port 150 are low around the mark 505 of 2.45GHz. ,.

[0155] Plot 530 shows the return loss, i.e., the port match at the second port 150. Plot 520 shows the port match at the first port 120.

[0156] Figure 4C shows a graph 600 of the signal losses between the third port 170 and the second port 150.

[0157] Plot 610 shows the losses for signals travelling between the third port 170 and the second port 150, or between the second port 150 and the third port 170 as the plots are identical. As plot 610 shows, the losses between the third port 170 and the second port 150 are high around the mark 605 of 2.45GHz due to the signal isolation between the third port 170 and the second port 150 described above.

[0158] Plot 620 shows the return loss, i.e., the port match at the third port 170. Plot 630 shows the port match at the second port 150.

[0159] Figure 5 shows a schematic representation of an electrosurgical apparatus 700 according to an aspect of the invention.

[0160] In the example shown in Figure 5, the electrosurgical apparatus 700 comprises an electrosurgical instrument 710 for treating biological tissue, the electrosurgical apparatus comprising the signal handling unit 100, 200, 300 described above. The electrosurgical instrument 710 comprises a pair of jaw elements 711 , 714 pivotable relative to each other to open and close a gap therebetween.

[0161] A first conductive element 713 is mounted in one of the pair of jaw elements adjacent to the gap and wherein a second conductive element 712 is mounted in the other one of the pair of jaw elements adjacent to the gap opposite the first conductive element 713. The first conductive element 713 is 008856742

[0162] 19 electrically connected to the third port 170 to convey the radiofrequency active signal and the first microwave frequency signal portion to the first conductive element 713 contacting biological tissue. The second conductive element 712 is electrically connected to the second port 150 to convey the second microwave frequency signal portion to the second conductive element 712 and to return the radiofrequency return signal from the second conductive element contacting biological tissue to the second port 150.

[0163] The electrosurgical apparatus 700 further comprises a signal generator 730, which includes a radiofrequency signal generator for generating radiofrequency electromagnetic radiation having a first frequency and a microwave signal generator for generating microwave electromagnetic radiation having a second frequency that is higher than the first frequency. The signal generator 730 is connected to the electrosurgical instrument by a feed structure 735 for conveying the radiofrequency electromagnetic radiation and the microwave electromagnetic radiation to the electrosurgical instrument 710.

[0164] In the example shown in Figure 5, the electrosurgical apparatus further comprises a control circuit 740 adapted to control the operation of the radiofrequency signal generator and the microwave signal generator according to the method described below with reference to Figure 6.

[0165] Figure 6 shows a method 800 for controlling the signal generator 730, and in particular the microwave signal generator, of the electrosurgical apparatus 700.

[0166] The method 800 begins in step 810 by monitoring the current and / or voltage of the radiofrequency signals at the tissue site. This is sensed by the corresponding voltage and current sensors at the radiofrequency signal generator that are a scaled ratio of the actual voltage and current measurement. The tissue impedance is a measure of the resistive component (V / l) of the instrument tip.

[0167] The tissue impedance computation uses the below formula:

[0168] Output admittance, Youtis comprised of cable admittance (estimated at 1 / (ZcaBi£. Ohms) in phase quadrature with tip REAL admittance, which is Ytip= 1 / Rtip). Knowing two of these values allows a third value (the resistive tissue load, Rtip) to be calculated.

[0169] In step 820, a tissue impedance is determined from the combined return signal and in step 830 the microwave signal generator is then controlled based on the determined tissue impedance.

[0170] Controlling 830 the microwave signal generator based on the determined tissue impedance may comprise the steps of determining 832 whether the tissue impedance has exceeded a predetermined impedance threshold. If the tissue impedance has not exceeded the predetermined impedance threshold, the method may progress to step 834 where the microwave signal generator continues to generate the microwave signals for delivery to the biological tissue. The method may then return to step 810 to continue monitoring the progress of the treatment of the biological tissue. If the tissue impedance has exceeded the predetermined impedance threshold in step 832, the method may progress to step 836 and the microwave signal generator may be deactivated. 008856742

[0171] 20

[0172] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0173] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0174] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0175] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0176] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0177] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

00885674221Claims:1 . A signal handling unit for handling signals having a first frequency and signals having a second frequency, wherein the second frequency is lower than the first frequency, the signal handling unit comprising: a signal divider electronically connected to a first port by a common signal line, wherein the common signal line is adapted to convey signals at the first frequency and signals at the second frequency from the first port to the signal divider; a first signal branch electronically connecting the signal divider to a second port, wherein the first signal branch comprises a directional interface adapted to: convey signals at the first frequency from the signal divider to the second port and substantially prevent the conveyance of signals at the second frequency from the signal divider to the second port; and convey signals at the second frequency from the second port to the first port; and a second signal branch electronically connecting the signal divider to a third port, wherein the second signal branch is adapted to convey signals at the first frequency and signals at the second frequency from the signal divider to the third port.

2. The signal handling unit as claimed in claim 1 , wherein the directional interface comprises a first filter for conveying signals at the first frequency from the signal divider to the second port and substantially preventing the conveyance of signals at the second frequency from the signal divider to the second port.

3. The signal handling unit as claimed in claim 2, wherein the first filter is a capacitor provided along the first signal branch between the signal divider and the second port.

4. The signal handling unit as claimed in any of claims 1 to 3, wherein the directional interface comprises a second filter for conveying signals at the second frequency from the second port to the first port.

5. The signal handling unit as claimed in claim 4, wherein the second filter is a quarter wavelength stub shorted to ground, wherein the quarter wavelength stub is sized to a quarter of a wavelength of a signal at the first frequency.

6. The signal handling unit as claimed in any of claims 4 to 5, when dependent directly or indirectly on claim 2, wherein the second filter is provided between the first filter and the second port along the first signal branch.

7. The signal handling unit as claimed in any preceding claim, wherein the first port is a first coaxial port comprising: a first inner conductor electronically connected to the common signal line; and00885674222 a first outer conductor electronically connected to ground.

8. The signal handling unit as claimed in any preceding claim, wherein the second port is a second coaxial port comprising: a second inner conductor electronically coupled to the first signal branch; and a second outer conductor electronically connected to ground, wherein the second outer conductor comprises a first capacitive structure.

9. The signal handling unit as claimed in claim 8, wherein the second outer conductor comprises a first section and a second section, wherein the first section has an inner diameter greater than an outer diameter of the second section, and wherein the first section overlaps the second section in a first overlapping section, and wherein the first overlapping section forms the first capacitive structure.

10. The signal handling unit claimed in claim 9, wherein the first overlapping section is sized to a multiple of a quarter of a wavelength of a signal at the first frequency.

11. The signal handling unit as claimed in any preceding claim, wherein the third port is a third coaxial port comprising: a third inner conductor electronically connected to the second signal branch; and a third outer conductor electronically connected to ground, wherein the third outer conductor comprises a second capacitive structure.

12. The signal handling unit as claimed in claim 11 , wherein the third outer conductor comprises a third section and a fourth section, wherein the third section has an inner diameter greater than an outer diameter of the fourth section, and wherein the third section overlaps the fourth section in a second overlapping section, and wherein the second overlapping section forms the second capacitive structure.

13. The signal handling unit as claimed in claim 12, wherein the second overlapping section is sized to a multiple of a quarter of a wavelength of a signal at the first frequency.

14. The signal handling unit as claimed in any preceding claim, wherein the signal handling unit comprises a microstrip structure comprising: a first conductor layer, wherein the signal divider, the first signal branch, the second signal branch and the directional interface are provided on the first conductor layer; a second conductor layer; and a dielectric layer provided between the first conductor layer and the second conductor layer.

15. The signal handling unit as claimed in claim 14, when dependent directly or indirectly on claim 5, wherein the quarter wavelength stub is connected to the second conductor layer by way of a via extending through the dielectric layer.0088567422316. The signal handling unit as claimed in any preceding claim, wherein the signal divider is a Wilkinson power divider.

17. The signal handling unit as claimed in any preceding claim, wherein the first frequency is a microwave frequency and the second frequency is a radio frequency.

18. An electrosurgical instrument for treating biological tissue comprising: a first conductive element; and a second conductive element, separated from the first conductive element so as to emit energy at the first frequency and second frequency into biological tissue; and the signal handling unit as claimed in any preceding claim, wherein: the first conductive element is electrically connected to the third port to convey signals at the first frequency and signals at the second frequency to the first conductive element; and the second conductive element is electrically connected to the second port to convey signals at the first frequency to the second conductive element and to form at least part of a signal return path for signals at the second frequency received at the second conductive element.

19. The electrosurgical instrument as claimed in claim 18, wherein the first conductive element is separated from the second conductive element by a dielectric element.

20. The electrosurgical instrument claimed in claim 18, wherein the electrosurgical instrument further comprises: a pair of jaw elements pivotable relative to each other to open and close a gap therebetween, wherein the first conductive element is mounted in one of the pair of jaw elements adjacent to the gap, and wherein the second conductive element is mounted in the other one of the pair of jaw elements adjacent to the gap and opposite the first conductive element.

21. An electrosurgical apparatus for treating biological tissue, the apparatus comprising: a first signal generator for generating a first signal having a first frequency; a second signal generator for generating a second signal having a second frequency that is lower than the first frequency; an electrosurgical instrument as claimed in any of claims 18 to 20; and a feed structure for conveying the first signal and the second signal to the electrosurgical instrument.

22. The electrosurgical apparatus as claimed in claim 21 , wherein the apparatus further comprises a control circuit adapted to monitor the operation of the first signal generator and the second signal generator, and wherein the control circuit is further adapted to: monitor a current and / or a voltage drawn by the second signal generator to generate the second00885674224 signal; determine a tissue impedance based on the monitored current and / or voltage; and control the first signal generator based on the determined tissue impedance.

23. The electrosurgical apparatus as claimed in claim 22, wherein controlling the first signal generator based on the determined tissue impedance comprises: determining whether the determined tissue impedance is greater than or equal to a predetermined threshold; and if the determined tissue impedance is greater than or equal to the predetermined threshold, deactivate the first signal generator; or if the determined tissue impedance is less than the predetermined threshold, maintain an activation of the first signal generator.

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