Patent Description:
With the rapid developments of medical technologies and aerospace technologies, radio frequency (RF) applications in cryogenic environments have received more attention than ever before. Therefore, testing/verifying the performance of RF devices accurately and effectively in the cryogenic environments is particularly necessary.

In general, testing and characterization of the RF devices are extremely sensitive to ambient parameters. Temperature variation, magnetic influence, and/or signal stability may affect testing results. Accordingly, it is an object of the present disclosure to provide a testing probe design with improved thermal and electrical isolation and stability, improved signal loss, and improved magnetic shielding. In addition, there is also a need for the probe to accommodate a cryogenic testing chamber to form a sealed/closed environment, which could separate the probe with the RF devices from the atmospheric environment.

<NPL>) discloses a cryogenic probe and cryostat system for testing active and passive superconducting devices and circuits up to microwave frequencies.

<NPL>) discloses a probe including a cross coil and variable capacitors that are operational at cryogenic temperatures.

<NPL>) discloses a liquid <NUM>He immersion cell.

<CIT> discloses a magnetic flux microscope that measures the magnetic field about a sample surface. The magnetic flux microscope uses a thin-film superconducting quantum interference device as the scanning device.

<CIT> (also published as <CIT>) discloses a cryogen free cooling apparatus.

<CIT> (also published as <CIT>) discloses cryogenic NMR probes that employ cryogenic probe coils.

<CIT> discloses a superconducting magnetic resonance RF probe coil.

<NPL>) discloses a gaseous <NUM>He nuclear magnetic resonance probe for cryogenic environments.

<CIT> discloses a cryogenic medical device for delivery of subcooled liquid cryogen to various configurations of cryoprobes. The device is designed for the treatment of damaged, diseased, cancerous or other unwanted tissues, particularly as utilized for the ablation of cardiac tissue in the treatment of atrial fibrillation.

The present invention provides a radio frequency (RF) functional probe according to claim <NUM>, for testing an RF device in a cryogenic environment. The RF functional probe includes a probe head configured to receive the RF device, a flange structure, an isolation structure coupled between the probe head and the flange structure, and an RF cable structure extending from the flange structure, through the isolation structure, and to the probe head. The isolation structure is configured to provide thermal and electrical isolation to reduce heat leak from the RF cable structure to the RF device. The isolation structure includes multiple baffle structures, each of which includes cable guides. The cable guides of each baffle structure are configured to guide routing paths for the RF cable structure. The RF cable structure is configured to transmit signals to and from the RF device. Each baffle structures further includes a baffle with baffle slots and a center baffle hole. The center baffle hole is located at the center of the baffle, while each baffle slot extends from a periphery of the baffle towards the center baffle hole. Each baffle slot is configured to adapt a corresponding cable guide. Each cable guide includes multiple separate guide holes that are aligned with a corresponding baffle slot.

In one embodiment of the RF functional probe, the cable guides are formed of Teflon, and the baffle is formed of polished stainless steel.

In one embodiment of the RF functional probe, the RF cable structure includes multiple RF cable groups, each of which includes multiple RF cable lines. Herein, each RF cable group extends through a corresponding cable guide of each baffle structure. Each RF cable line extends through a corresponding hole of the corresponding cable guide at each baffle structure.

In one embodiment of the RF functional probe, each RF cable group forms a different routing path through the baffle structures.

In one embodiment of the RF functional probe, each baffle structure further includes two baffle holders, which are put on opposite sides of one baffle to hold the baffle in place.

In one embodiment of the RF functional probe, the isolation structure further includes a Teflon isolator, a first G10 isolator, a support rod, and a second G10 isolator. The Teflon isolator is coupled between the probe head and the first G10 isolator. The support rod is coupled between the first G10 isolator and the second G10 isolator, and extends through each baffle structure via the center baffle hole of the baffle. The Teflon isolator, the first G10 isolator, and the second G10 isolator provide thermal and electrical isolation to reduce heat leak from the RF cable structure to the RF device. The support rod is formed of stainless steel.

In one embodiment of the RF functional probe, the isolation structure further includes a shield ring and a shield mount within the shield ring. Herein, the shield mount includes a connection tube and a splitter coupled to the connection tube. The connection tube covers a junction of the Teflon isolator and the first G10 isolator. The splitter includes a plurality of separation arms, which provide structural support to the shield ring and divide inner space of the shield ring into multiple of equal portions.

In one embodiment of the RF functional probe, the RF cable structure includes multiple RF cable groups, each of which includes multiple RF cable lines. Herein, each RF cable group extends from the flange structure, through each baffle structure, through a corresponding portion of the inner space of the shield ring, and toward the probe head.

According to another embodiment, the RF functional probe further includes a magnetic shield. The shield ring is configured to adapt the magnetic shield. The magnetic shield fully covers the probe head, and partially covers the isolation structure.

In one embodiment of the RF functional probe, the shield ring is formed of aluminum, the shield mount is formed of aluminum, and the magnetic shield is formed of mu-metal.

In one embodiment of the RF functional probe, the probe head includes a chuck and a mount stud inserted into the chuck. Herein, a printed circuit board (PCB) is coupled to the chuck and located on an opposite side of the chuck from the mount stud. The chuck is configured to receive the RF device through the PCB. The chuck includes a plurality of chuck notches. The chuck and the mount stud are formed of copper.

In one embodiment of the RF functional probe, the flange structure includes a seal ring, a flange with multiple flange notches, and a flange mount ring. Herein, the seal ring faces the isolation structure and is formed at a periphery of the flange. The flange mount ring faces the isolation structure and is formed at a center of the flange to adapt to the isolation structure.

In one embodiment of the RF functional probe, the chuck and the mount stud are formed of copper, the seal ring is formed of buna or viton, the flange mount ring is formed of aluminum, and the flange is formed of Stainless steel.

In one embodiment of the RF functional probe, the RF cable structure includes multiple RF cable groups, multiple cable connectors, and multiple hermetic RF connectors. Herein, each RF cable group includes multiple RF cable lines. Each cable connector goes through a corresponding chuck notch. Each hermetic RF connector goes through a corresponding flange notch and hermetically seals the corresponding flange notch. Each RF cable group extends from a corresponding hermetic RF connector, through each baffle structure, and to a corresponding cable connector.

In one embodiment of the RF functional probe, the RF cable structure includes multiple RF cable groups, each of which includes multiple RF cable lines. Herein, each RF cable group forms a loop between two adjacent baffle structures so as to absorb cable shrinkage due to temperature changes.

According to another embodiment, the RF functional probe further includes a temperature control structure, which is configured to sense and change temperature of the RF device.

In one embodiment of the RF functional probe, the temperature control structure includes a hermetic DC connector, a temperature sensor, a DC cable group, and a heater. Herein, the hermetic DC connector extends through the flange structure via a flange hole, and a portion of the hermetic DC connector hermetically covers the flange hole. The temperature sensor and the heater are located at the probe head. The temperature sensor is configured to sense the temperature of the RF device, and the heater is configured to change temperature of the RF device. The DC cable group extends from the hermetic DC connector, along the isolation structure, and toward to the temperature sensor and the heater.

According to another embodiment, the RF functional probe further includes a handle structure with a handle and a handle mount bar. Herein, the handle mount bar connects the handle to the flange structure. The handle structure and the isolation structure are located at opposite sides of the flange structure.

It will be understood that for clear illustrations, <FIG> may not be drawn to scale.

Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts without departing from the scope of the invention, as defined in the appended claims.

A radio frequency (RF) functional probe is described for RF devices testing in a cryogenic environment, e.g., in a hermetically sealed vacuum environment below <NUM>. <FIG> shows an isometric view of an RF functional probe <NUM> without a magnetic shield, <FIG> shows an isometric view of the RF functional probe <NUM> with a magnetic shield <NUM>, and <FIG> shows a cross-section view of the RF functional probe <NUM> along dashed line A-A' in <FIG> (from bottom to top).

In the exemplary embodiment, the RF functional probe <NUM> includes a probe head <NUM>, an isolation structure <NUM>, a handle structure <NUM>, and a flange structure <NUM> between the isolation structure <NUM> and the handle structure <NUM>. Herein, a printed circuit board (PCB) <NUM> with a to-be-tested RF device <NUM> is attached to the probe head <NUM>. The magnetic shield <NUM> fully covers the probe head <NUM> and partially covers the isolation structure <NUM>. In addition, the RF functional probe <NUM> also includes an RF cable structure <NUM> for transmitting signals from/to the RF device <NUM> (from/to the PCB board <NUM>). The RF cable structure <NUM> extends through the flange structure <NUM>, along the isolation structure <NUM>, and towards the probe head <NUM>. The isolation structure is configured to provide thermal and electrical isolation to reduce radiant and conductive heat leak from the RF cable structure <NUM> to the RF device <NUM> (details are described in the following paragraphs).

For the purpose of this illustration, the RF cable structure <NUM> includes four hermetic RF connectors <NUM> (a first hermetic RF connector <NUM>-<NUM>, a second hermetic RF connector <NUM>-<NUM>, a third hermetic RF connector <NUM>-<NUM>, and a fourth hermetic RF connector <NUM>-<NUM>), and four RF cable groups <NUM> (a first RF cable group <NUM>-<NUM>, a second RF cable group <NUM>-<NUM>, a third RF cable group <NUM>-<NUM>, and a fourth RF cable group <NUM>-<NUM>), each of which includes multiple RF cable lines. Each hermetic RF connector <NUM> extends through the flange structure <NUM> and corresponds to a different RF cable group <NUM>. In different applications, there might be fewer or more hermetic RF connectors <NUM> and fewer or more RF cable groups <NUM>, respectively, included in the RF cable structure <NUM> for signal transmission.

<FIG> show architecture details of the RF functional probe <NUM> without the magnetic shield <NUM> and the RF cable structure <NUM>. In detail, the probe head <NUM> includes a chuck <NUM> (zoom-in view as shown in <FIG>) and a mount stud <NUM> inserted into the chuck <NUM>. For the purpose of this illustration, the chuck <NUM> includes four chuck notches <NUM> formed in a squared layout to accommodate the RF cable structure <NUM> (details are described in the following paragraphs). The chuck <NUM> and the mount stud <NUM> might be formed of copper.

The PCB board <NUM> is in contact with the chuck <NUM> and is opposite to the mount stud <NUM>. Herein, the PCB board <NUM> has four jack sets <NUM> (only one jack set is labeled with a reference number for clarity), each of which is aligned with a corresponding chuck notch <NUM> of the chuck <NUM>, respectively. The RF device <NUM> is mounted at a center of the PCB board <NUM> and into the chuck <NUM>. Note that the PCB board <NUM> is not permanently attached to the chuck <NUM> and the RF device <NUM> is not permanently mounted to the PCB board <NUM>. It is easy to replace the existing PCB board <NUM> with another PCB board and/or replace the existing RF device <NUM> with another RF device that needs to be tested.

In different applications, if the RF cable structure <NUM> includes fewer or more RF cable groups, the chuck <NUM> will have fewer or more chuck notches <NUM> accordingly and the PCB board <NUM> will have fewer or more jack sets <NUM> accordingly. In addition, the chuck <NUM> may have different layouts of the chuck notch <NUM> and the PCB board <NUM> may have different layouts of the jack sets <NUM> to accommodate different RF cable structures. The RF device <NUM> might be mounted to a different portion of the PCB board <NUM>.

The isolation structure <NUM> includes a Teflon isolator <NUM> (formed of Teflon), a shield ring <NUM>, a shield mount <NUM> within the shield ring <NUM>, a first G10 isolator <NUM> (formed of a G10 material), a support rod <NUM>, multiple baffle structures <NUM> (a first baffle structure <NUM>-<NUM>, a second baffle structure <NUM>-<NUM>, a third baffle structure <NUM>-<NUM>, a fourth baffle structure <NUM>-<NUM>, a fifth baffle structure <NUM>-<NUM>, and a sixth baffle structure <NUM>-<NUM>), and a second G10 isolator <NUM> (formed of a G10 material). The Teflon isolator <NUM>, the first G10 isolator <NUM>, the baffle structures <NUM>, and the second G10 isolator <NUM> are configured to provide thermal and electrical isolation to reduce heat leak (from the flange structure <NUM>, the RF cable structure <NUM>, and/or the isolation structure <NUM> itself) to the RF device <NUM> to be tested. Therefore, reliable and rapid (in seconds) temperature change, e.g., between room temperature and <NUM> cryogenic temperature, can be achieved for the RF device <NUM>.

The mount stud <NUM> of the probe head <NUM> is inserted into a first side of the Teflon isolator <NUM> (cross-section view as shown in <FIG>). A protrusion at a second side of the Teflon isolator <NUM>, opposite to the first side of the Teflon isolator <NUM>, is inserted into the first G10 isolator <NUM> (cross section view as shown in <FIG>).

<FIG> illustrate details of the shield ring <NUM> and the shield mount <NUM>. The shield ring <NUM> is configured to adapt the magnetic shield <NUM> (as shown in <FIG>). The shield mount <NUM> includes a connection tube <NUM> and a splitter <NUM> coupled to the connection tube <NUM>. For the purpose of this illustration, the splitter <NUM> has four separation arms <NUM>, which are orthogonal to each other. Herein, the separation arms <NUM> of the splitter <NUM> provide structural support to the shield ring <NUM> and the magnetic shield <NUM>, and also divide the inner space of the shield ring <NUM> into four equal portions. Therefore, each RF cable group <NUM> of the RF cable structure <NUM> could extend through a corresponding portion of the inner space of the shield ring <NUM>, respectively (details are described in the following paragraphs). In different applications, if the RF cable structure <NUM> includes fewer or more RF cable groups, the splitter <NUM> of the shield mount <NUM> will include fewer or more separation arms <NUM>. The splitter <NUM> is configured to enable each RF cable group <NUM> extending through a separate inner portion of the shield ring <NUM>. In addition, the junction of the Teflon isolator <NUM> and the first G10 isolator <NUM> may be covered by the connection tube <NUM> of the shield mount <NUM>. The shield ring may be formed of aluminum, the shield mount may be formed of aluminum, and the magnetic shield may be formed of mu-metal.

The support rod <NUM> might be a hollow rod and formed of stainless steel. In one exemplary embodiment, the support rod <NUM> is formed between the first G10 isolator <NUM> and the second G10 isolator <NUM>, and extends through the second to sixth baffle structures <NUM>-<NUM>~<NUM>-<NUM>. The second G10 isolator <NUM> extends from the flange structure <NUM>, through the first baffle structure <NUM>-<NUM> and inserts into the support rod <NUM>.

<FIG> show details of one baffle structure <NUM>. Each baffle structure <NUM> includes a baffle <NUM>, four cable guides <NUM> (including a first cable guide <NUM>-<NUM>, a second cable guide <NUM>-<NUM>, a third cable guide <NUM>-<NUM>, and a fourth cable guide <NUM>-<NUM>), and two baffle holders <NUM>. Herein, the baffle <NUM> may be formed of polished stainless steel, and the cable guides <NUM> may be formed of Teflon. Each baffle structure <NUM>, especially the baffle <NUM>, is configured to limit radiant heat transmitting from the RF cable structure <NUM> to the probe head <NUM>.

For the purpose of this illustration, the baffle <NUM> includes four baffle slots <NUM> to adapt the four cable guides <NUM>, a center baffle hole <NUM> to adapt the support rod <NUM>, and a side baffle hole <NUM> to route a DC cable group (not shown herein, details are described in the following paragraphs). Each baffle slot <NUM> extends from the periphery of the baffle <NUM> towards the center baffle hole <NUM> and is orthogonal to another. Each cable guide <NUM> includes multiple guide holes <NUM> (only one guide hole is labeled with a reference number for clarity) to guide a corresponding RF cable group <NUM> to route through the baffle structure <NUM> (via a corresponding baffle slot <NUM> of the baffle <NUM>). The size of each guide hole <NUM> is designed on the diameter size of one RF cable line of the RF cable group <NUM> (details are described in the following paragraphs). In different applications, if the RF cable structure <NUM> includes fewer or more RF cable groups <NUM>, the baffle <NUM> will include fewer or more baffle slots <NUM> and the baffle structure <NUM> will include fewer or more cable guides <NUM> accordingly. In addition, the cable guides <NUM> and the baffle slots <NUM> may have different layouts. The two baffle holders <NUM> are put on opposite sides of one baffle <NUM> (through the support rod <NUM>) to hold the baffle <NUM> in place.

The flange structure <NUM> includes a seal ring <NUM>, a flange <NUM> with four flange notches <NUM> (only one flange notch is labeled with a reference number for clarity) and a flange hole <NUM>, and a flange mount ring <NUM>. The seal ring <NUM> faces the baffle structures <NUM> and is formed at the periphery of a first surface of the flange <NUM>. The flange <NUM> with the seal ring <NUM> is configured to seal the probe head <NUM> with the RF device <NUM>, the isolation structure <NUM>, and major portions of the RF cable structure <NUM> in a cryogenic environment (details are described in the following paragraphs). In different applications, if the RF cable structure <NUM> includes fewer or more hermetic RF connectors <NUM> (fewer or more RF cable groups <NUM>), the flange <NUM> will include fewer or more flange notches <NUM> accordingly. Also, the flange notches <NUM> may have different layouts. The flange hole <NUM> is configured to hold a hermetic direct-current (DC) connector (not shown herein, details are described in the following paragraphs). The four flange notches <NUM> and the flange hole on the flange <NUM> are exposed through the seal ring <NUM>. The flange mount ring <NUM> is mounted at a center of the first surface of the flange <NUM> and is configured to hold the second G10 isolator <NUM>. The seal ring <NUM> may be formed of buna or viton, the flange <NUM> may be formed of stainless steel, and the flange mount ring <NUM> may be formed of aluminum. In one exemplary embodiment, the RF device <NUM> is about <NUM> (<NUM> inches) (with -/+<NUM> % margin) away from the flange structure <NUM>. In addition, the handle structure <NUM> includes a handle <NUM> and a handle mount bar <NUM> connecting the handle <NUM> to a second surface of the flange <NUM>, which is opposite to the first surface of the flange <NUM>.

<FIG> and <FIG> show details of the RF cable structure <NUM>. In one exemplary embodiment, each RF cable group <NUM> has eight RF cable lines, and each RF cable line might have a <NUM> (<NUM> inch) diameter. Each RF cable line may be formed from three portions (not shown): an inner portion formed of a first conductive material (such as copper or copper nickel), an intermediate portion formed of Teflon, and an outer portion, which is for RF shielding, formed of a second conductive material (such as copper or copper nickel). In different applications, each RF cable group may have fewer or more RF cable lines, and each RF cable line may have a smaller or larger diameter size.

Besides the four hermetic RF connectors <NUM> and the four RF cable groups <NUM>, the RF cable structure <NUM> also includes four cable holders <NUM> (a first cable holder <NUM>-<NUM>, a second cable holder <NUM>-<NUM>, a third cable holder <NUM>-<NUM>, and a fourth cable holder <NUM>-<NUM>), and four cable connectors <NUM> (a first cable connector <NUM>-<NUM>, a second cable connector <NUM>-<NUM>, a third cable connector <NUM>-<NUM>, and a fourth cable connector <NUM>-<NUM>). Each RF cable group <NUM>, a corresponding cable holder <NUM>, a corresponding cable connector <NUM>, and a corresponding hermetic RF connector <NUM> form one cable assembly, which has a high density of cabling. Herein, the high density of cabling refers to numerous compact RF connections in a small footprint to limit the diameter of the probe to reduce the heat and radiation load. The high density of cabling leads to high density RF capacity and low signal loss at GHz frequency. Both the cable connectors <NUM> and the hermetic RF connectors <NUM> are spring loaded so as to compensate some cable shrinkage due to the temperature change, e.g., between the room temperature and the cryogenic temperature <NUM>. As such, the cable assembly can be kept in place and will be reliable. In different applications, there might be fewer or more numbers of RF cable groups <NUM> included in the RF cable structure <NUM>, and in consequence, there will be fewer or more cable holders <NUM>, cable connectors <NUM>, and hermetic RF connectors <NUM>, accordingly.

In one exemplary embodiment, a first side of the first RF cable group <NUM>-<NUM> is attached to the first cable connector <NUM>-<NUM> that is electrically connected to the PCB board <NUM> and the first cable holder <NUM>-<NUM>, while a second side of the first RF cable group <NUM>-<NUM> is attached to the first hermetic RF connector <NUM>-<NUM> that extends through the flange structure <NUM>. A same connection configuration is applied to each of the second RF cable group <NUM>-<NUM>, the third RF cable group <NUM>-<NUM>, and the fourth RF cable group <NUM>-<NUM>. Each RF cable group <NUM> extends continuously from the corresponding cable connector <NUM> to the corresponding hermetic RF connector <NUM>. Herein, the four cable holders <NUM> and the RF device <NUM> are located at a same side of the PCB board <NUM>, while the four cable connectors <NUM> and the RF device <NUM> are located at opposite sides of the PCB board <NUM>. The cable holders <NUM> might be sockets or solder structures attached to the PCB board <NUM>.

The first RF cable group <NUM>-<NUM>, the second RF cable group <NUM>-<NUM>, the third RF cable group <NUM>-<NUM>, and the fourth RF cable group <NUM>-<NUM> may have different routing paths so as to reduce electrical interference with each other, and consequently, to reduce or eliminate thermal addition from the electrical interference. In each routing path of the RF cable group <NUM>, there might be multiple loops formed to absorb cable shrinkage due to the temperature change, e.g., between the room temperature and the cryogenic temperature below <NUM>.

<FIG> illustrate how the RF cable structure <NUM> extends through the shield ring <NUM> and illustrate connection details of the RF cable structure <NUM> at the probe head <NUM>. Recall that the splitter <NUM> of the shield mount <NUM> divides the inner space of the shield ring <NUM> into four equal portions, each RF cable group <NUM> of the RF cable structure <NUM> extends through the shield ring <NUM> separately via a corresponding inner space portion of the shield ring <NUM>. The separation of the RF cable groups <NUM> will have reduced electrical interference and reduced thermal effect to each RF cable group <NUM> due to the reduced electrical interference.

The first side of the first RF cable group <NUM>-<NUM> is attached to the first cable connector <NUM>-<NUM> that goes through a corresponding chuck notch <NUM> on the chuck <NUM>, though a corresponding jack set <NUM> on the PCB board <NUM>, and into the first cable holder <NUM>-<NUM>. As such, the first RF cable group <NUM>-<NUM> is electrically connected to the PCB board <NUM>, and of course, the RF device <NUM>, via the first cable connector <NUM>-<NUM> and the first cable holder <NUM>-<NUM>. Similarly, the second RF cable group <NUM>-<NUM>, the second RF cable group <NUM>-<NUM>, and the fourth RF cable group <NUM>-<NUM> are electrically connected to the PCB board <NUM> and the RF device <NUM>. In addition, the connection between each cable holder <NUM> and the corresponding cable connector <NUM> enables the PCB board <NUM> attached to the chuck <NUM> and keeps each RF cable group <NUM> in place.

<FIG> illustrate connection details of the RF cable structure <NUM> at the flange structure <NUM>. The second side of the first RF cable group <NUM>-<NUM> is connected to the first hermetic RF connector <NUM>-<NUM>, which extends through a corresponding flange notch <NUM> on the flange <NUM>. Similarly, the second RF cable group <NUM>-<NUM> is connected to the second hermetic RF connector <NUM>-<NUM>, which extends through a corresponding flange notch <NUM> on the flange <NUM>. The third RF cable group <NUM>-<NUM> is connected to the third hermetic RF connector <NUM>-<NUM>, which extends through a corresponding flange notch <NUM> on the flange <NUM>. The fourth RF cable group <NUM>-<NUM> is connected to the fourth hermetic RF connector <NUM>-<NUM>, which extends through a corresponding flange notch <NUM> on the flange <NUM>. As such, signals can be transmitted from the hermetic RF connectors <NUM>, through the RF cable groups <NUM>, to the RF device <NUM>. Herein, a portion of the first hermetic RF connector <NUM>-<NUM>, a portion of the second hermetic RF connector <NUM>-<NUM>, a portion of the third hermetic RF connector <NUM>-<NUM>, and a portion of the fourth hermetic RF connector <NUM>-<NUM> hermetically cover the corresponding flange notches <NUM>, respectively.

<FIG> illustrates routing details of the RF cable structure <NUM> through the baffle structures <NUM>. Each RF cable group <NUM> extends from a corresponding hermetic RF connector <NUM> and through six baffle structures <NUM> in a different routing path. In different applications, there might be fewer or more baffle structures <NUM> included in the isolation structure <NUM>.

The first RF cable group <NUM>-<NUM> extends from the first hermetic RF connector <NUM>-<NUM>, forms a first loop before the first baffle structure <NUM>-<NUM>, extends through the first baffle structure <NUM>-<NUM> via the guide holes <NUM> (one guide hole <NUM> for a corresponding cable, only one guide hole is labeled with a reference number for clarity) at the first cable guide <NUM>-<NUM> (through a corresponding baffle slot <NUM> of the baffle <NUM>), forms a second loop between the first baffle structure <NUM>-<NUM> and the second baffle structure <NUM>-<NUM>, extends through the second baffle structure <NUM>-<NUM> via the guide holes <NUM> (one guide hole <NUM> for a corresponding cable) at the first cable guide <NUM>-<NUM> (through the corresponding baffle slot <NUM> of the baffle <NUM>), forms a third loop between the second baffle structure <NUM>-<NUM> and the third baffle structure <NUM>-<NUM>, extends through the third baffle structure <NUM>-<NUM> via the guide holes <NUM> (one guide hole <NUM> for a corresponding cable) at the first cable guide <NUM>-<NUM> (through the corresponding baffle slot <NUM> of the baffle <NUM>), forms a fourth loop between the third baffle structure <NUM>-<NUM> and the fourth baffle structure <NUM>-<NUM>, extends through the fourth baffle structure <NUM>-<NUM> via the guide holes <NUM> (one guide hole <NUM> for a corresponding cable) at the first cable guide <NUM>-<NUM> (through the corresponding baffle slot <NUM> of the baffle <NUM>), forms a fifth loop between the fourth baffle structure <NUM>-<NUM> and the fifth baffle structure <NUM>-<NUM>, extends through the fifth baffle structure <NUM>-<NUM> via the guide holes <NUM> (one guide hole <NUM> for a corresponding cable) at the first cable guide <NUM>-<NUM> (through a corresponding baffle slot <NUM> of the baffle <NUM>), forms a sixth loop between the fifth baffle structure <NUM>-<NUM> and the sixth baffle structure <NUM>-<NUM>, and extends through the sixth baffle structure <NUM>-<NUM> via the guide holes <NUM> (one guide hole <NUM> for a corresponding cable) at the first cable guide <NUM>-<NUM> (through the corresponding baffle slot <NUM> of the baffle <NUM>).

The loops formed between adjacent baffle structures <NUM> are configured to absorb cable shrinkage due to the temperature changes, e.g., between the room temperature and the cryogenic temperature (like below <NUM>). As such, the cable connectors <NUM> and the hermetic RF connectors <NUM> can be kept in place to provide good cable connection for the RF device <NUM>. In addition, these loops provide enough cable material for each thermal stage (between adjacent two baffle structures <NUM>) to maximize thermal gradient of each RF cable line to reduce heat leak. Herein, the guide holes <NUM> of the first cable guide <NUM>-<NUM> of each baffle structure <NUM> are configured to electrically isolate the RF cable lines from each other within the first RF cable group <NUM>-<NUM>. Furthermore, the guide holes <NUM> of the first cable guide <NUM>-<NUM> of each baffle structure <NUM> is also configured to hold each RF cable line of the first RF cable group <NUM>-<NUM> in a fixed place relative to a plane of each baffle <NUM>, when the RF cable lines of the first RF cable group <NUM>-<NUM> slide through the baffle structures <NUM> during thermal expansion and contraction.

Similarly, each of the second RF cable group <NUM>-<NUM>, the third RF cable group <NUM>-<NUM>, and the fourth RF cable group <NUM>-<NUM> forms six loops along the six baffle structures <NUM>, and extends through the baffle structures <NUM> via the guide holes <NUM> of a correspond cable guide <NUM>. Each cable guide <NUM> provides electrical isolation of the RF cable lines within one RF cable group and provides avoidance from movement relative to a plane of each baffle <NUM> during thermal expansion and contraction. Notice that there are no magnetic components from the support rod <NUM> down to the RF device <NUM>.

<FIG> and <FIG> show details of an optional temperature control structure <NUM>, which is configured to sense and change temperature of the RF device <NUM>, in the RF functional probe <NUM>. The temperature control structure <NUM> include a hermetic DC connector <NUM>, a temperature sensor <NUM>, a DC cable group <NUM>, and a heater <NUM>. The hermetic DC connector <NUM> extends through the flange hole <NUM> on the flange <NUM> and a portion of the hermetic DC connector <NUM> hermetically covers the flange hole <NUM>. The temperature sensor <NUM> and the heater <NUM> are located at the probe head <NUM>. The temperature sensor <NUM> is mounted to the PCB board <NUM> and located at a same side of the PCB <NUM> as the RF device <NUM>. The temperature sensor <NUM> is configured to sense the temperature of the RF device <NUM>. The heater <NUM> is mounted on the chuck <NUM> and located at a same side of the chuck <NUM> as the mount stud <NUM>. The heater <NUM> is configured to change temperature to the PCB <NUM> and the RF device <NUM> (via the chuck <NUM>). Note that the temperature sensor <NUM> is not permanently mounted to the PCB board <NUM>, and the heater <NUM> is not permanently attached to the chuck <NUM>. It is easy to replace the existing temperature sensor <NUM> with another temperature sensor and/or replace the existing heater <NUM> with another heater for different applications. The DC cable group <NUM> extends from the hermetic DC connector <NUM>, through the side baffle hole <NUM> (only one side baffle hole is labeled with a reference number for clarity) on each baffle structure <NUM>, through the shield ring <NUM>, and toward the chuck <NUM>. A first cable portion <NUM>-<NUM> of the DC cable group <NUM> is electrically coupled to the temperature sensor <NUM>, and a second cable portion <NUM>-<NUM> of the DC cable group <NUM> is electrically coupled to the heater <NUM>. As such, DC signals can be transferred between the temperature sensor <NUM> and the hermetic DC connector <NUM>, and between the heater <NUM> and the hermetic DC connector <NUM>.

In one embodiment, the hermetic DC connector <NUM> may be a ten-pin connector, where four pins are for the temperature sensor <NUM>, two pins are for the heater <NUM>, and the remaining four pins are reserved for extra component(s) if applicable. Accordingly, the DC cable group <NUM> includes ten cable wires, where the first cable portion <NUM>-<NUM> for the temperature sensor <NUM> includes four cable wires (each of which may be formed of quad twist Phosphor bronze), and the second cable portion <NUM>-<NUM> for the heater <NUM> includes two cable wires. Furthermore, the heater <NUM> may be mounted on the chuck <NUM> with two aluminum screws. In different applications, the hermetic DC connector <NUM> may have fewer or more pins, the DC cable group <NUM> may include fewer or more cable wires, the temperature sensor <NUM> may accommodate fewer or more cable wires, and the heater <NUM> may accommodate fewer or more cable wires. Herein, the heater <NUM> may be a ceramic heater that produces minimal to no magnetic field.

<FIG> shows an exemplary testing cryostat <NUM>, which provides a cryogenic environment to the RF functional probe <NUM> for RF device testing (simplify the RF functional probe <NUM> for clarity). In the testing cryostat <NUM>, low pressure helium is used to provide cryogenic temperature, e.g., <NUM>. Herein, the probe head <NUM> with the RF device <NUM> (covered by the magnetic shield <NUM>), the isolation structure <NUM>, and the RF cable structure <NUM> (not shown) of the RF functional probe <NUM> are inserted into a chamber <NUM> of the testing cryostat <NUM>. The seal ring <NUM> of the flange structure <NUM> of the RF functional probe <NUM> is directly attached to an opening of the chamber <NUM>. Recall that each flange notch <NUM> is hermetically covered by a corresponding hermetic RF connector <NUM>, and the flange hole <NUM> is hermetically covered by the hermetic DC connector <NUM>, such that a sealed cryogenic vacuum without helium loss can be formed by the chamber <NUM>, the flange structure <NUM>, and the hermetic RF connectors <NUM>. Portions of the hermetic RF connectors <NUM> and the handle structure <NUM> are outside the chamber <NUM>.

Claim 1:
A radio frequency, RF, functional probe (<NUM>) for testing an RF device (<NUM>) in a cryogenic environment, the RF functional probe (<NUM>) comprising:
a probe head (<NUM>) configured to receive the RF device (<NUM>);
a flange structure (<NUM>);
an isolation structure (<NUM>) coupled between the probe head (<NUM>) and the flange structure (<NUM>), wherein the isolation structure (<NUM>) includes a plurality of baffle structures (<NUM>); and
an RF cable structure (<NUM>) extending from the flange structure (<NUM>), through the isolation structure (<NUM>), and to the probe head (<NUM>), wherein:
the RF cable structure (<NUM>) is configured to transmit signals to and from the RF device (<NUM>);
the isolation structure (<NUM>) is configured to provide thermal and electrical isolation to reduce radiant heat leak from the RF cable structure (<NUM>) to the RF device (<NUM>); and
each of the plurality of baffle structures (<NUM>) further comprises a baffle (<NUM>) with a centre baffle hole (<NUM>), the center baffle hole (<NUM>) being located at the center of the baffle (<NUM>);
and characterized in that:
each of the plurality of baffle structures (<NUM>) includes cable guides (<NUM>), the cable guides (<NUM>) of each of the plurality of baffle structures (<NUM>) being configured to guide routing paths for the RF cable structure (<NUM>);
the baffles (<NUM>) of the plurality of baffle structures (<NUM>) have baffle slots (<NUM>);
each baffle slot (<NUM>) extends from a periphery of the baffle (<NUM>) towards the center baffle hole (<NUM>);
each baffle slot (<NUM>) is configured to adapt a corresponding cable guide (<NUM>); and
each cable guide (<NUM>) includes a plurality of separate guide holes (<NUM>) that are aligned with a corresponding baffle slot (<NUM>).