Patent Publication Number: US-2023155278-A1

Title: High frequency adapter for connecting a high frequency antenna with an antenna connector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of European Patent Application No. 21 208 497.4 filed on 16 Nov. 2021, the entire content of which is incorporated herein by reference. 
     FIELD 
     The disclosure relates to a high frequency adapter for connecting a high frequency antenna to an antenna connector. Furthermore, the disclosure relates to a use of the high frequency adapter. 
     BACKGROUND 
     In high-frequency technology, in particular in radar technology, electromagnetic energy, e.g., from a high-frequency generator, is directed to a high-frequency antenna, e.g., to a horn antenna, in order to be able to transmit and/or receive high-frequency waves. This may be implemented by means of a high frequency adapter. In at least some cases, the high frequency waves are conducted from the antenna to the adapter via a waveguide. For example, along this path, moisture can enter the high frequency adapter and cause the adapter to malfunction, e.g., short circuit conductive parts. 
     SUMMARY 
     There may be a desire to reduce moisture penetration into parts of a high-frequency adapter that are susceptible to failure. This desire is met by the subject-matter of the independent patent claims. Further embodiments result from the subclaims and the following description. 
     One aspect relates to a high frequency adapter (for short: adapter) for connecting a high frequency antenna to an antenna connector. The high frequency adapter comprises: 
     CGS:THU 
     a waveguide (for example a hollow cylindrical waveguide), which is arranged for a transmission of high-frequency waves from and to the high-frequency antenna; 
     an impedance matching element disposed within the waveguide and adapted to impedance match the high frequency antenna; 
     a conductive inner conductor electrically and mechanically connected to the impedance matching element, the inner conductor being electrically connected directly or indirectly to the antenna connector; 
     a conductive (for example hollow-cylindrical) sheath adjoining the waveguide; and 
     an electrically insulating hollow cylindrical spacer element disposed between the sheath and the inner conductor, thereby insulating the inner conductor from the sheath and sealing the waveguide in a fluid-tight manner. 
     For instance, the high frequency adapter may be set up for the retransmission of high frequency waves in a range of radar waves. At least some specifics of the adapter can be set up, for example, for a part of the radar frequency range, e.g., for the so-called K-band, which extends over a frequency range from 18 to 27 GHz. At least some of these specifics may also be adaptable—e.g., by minor modifications—to other frequency ranges of the radar frequency range. The adapter may be connected at one side to, for example, a horn antenna and/or other high frequency antenna. The adapter can be connected on another side, for example, to an antenna connector in the form of a coaxial connector. The transmission or forwarding of the high-frequency waves to the antenna can be performed by way of a waveguide, which can have a hollow cylindrical shape. In this case, the antenna may be located in an environment that may, in at least some cases, have moisture. 
     In at least some cases, the high frequency waves are conducted from the antenna to the adapter via a waveguide. In this case, for at least some frequency ranges, an impedance matching element may be arranged within the waveguide that is arranged to impedance match the high frequency antenna. In this case, the impedances at the two ends of the adapter can differ from each other: In the coaxial section, for example, the impedance may be in the range of about 50-75 ohms, and in the waveguide section, for example, the impedance may be in the range of about 700 ohms. For lower frequency radar bands, e.g., for the K-band, the impedance matching element can be designed, for example, in a stepped shape and significantly narrower than an inner through meter of the waveguide. The impedance matching element so designed is sometimes referred to as a fin. The impedance matching element may have a different shape for other frequency ranges. The impedance matching element can have electrical contact with the outer conductor of the coaxial system at at least one point in the area of the transition between the coaxial and the waveguide system as well as at the base surface of the fin in order to realize the matching and/or radiation. 
     The impedance matching element is electrically and mechanically connected to a conductive inner conductor. The inner conductor can be electrically connected directly or indirectly to the antenna connector. In the case of a direct connection, the inner conductor can be routed to the end of the adapter opposite the antenna connector, so that in this case the antenna connector can be plugged onto this end of the inner conductor. In the case of an indirect connection, at least one other conductive component may be arranged on the inner conductor. The inner conductor may extend along a central axis of the waveguide. 
     The high frequency adapter further comprises a conductive hollow cylindrical sheath that connects to the waveguide. The sheath may connect to the waveguide without gaps and/or tightly. The sheath may comprise a different material than the waveguide; for example, the sheath may comprise or consist of stainless steel, and the waveguide may comprise or consist of copper. Both the waveguide and the cladding may advantageously be conductive to provide electrical shielding and/or contribute to a defined impedance of the adapter. The sheath may be arranged parallel to the center axis of the waveguide. 
     The high frequency adapter further comprises an electrically insulating hollow cylindrical spacer element disposed between the sheath and the inner conductor, thereby insulating the inner conductor from the sheath and sealing the waveguide in a fluid-tight manner. 
     In one variation, the waveguide and/or the cladding may have a rectangular shape, particularly a square shape. The rectangular shape may involve the outer contour and/or the inner walls. The inner and/or outer corners may be rounded. 
     With this design, in particular due to the spacer element, the high-frequency adapter not only has a defined impedance in the area of the coaxial system, but is also robust against moisture that diffuses in and then condenses, because the spacer element can reduce or even prevent moisture from penetrating into parts of a high frequency adapter that are susceptible to interference, and in particular can prevent a short circuit between the sheath and the inner conductor. A possible condensation point can thus be shifted to an area less sensitive to high-frequency waves. In addition, the spacer element can simplify the assembly of the high-frequency adapter, e.g., serve as an insertion aid during assembly and thus contribute to preventing incorrect assembly. Furthermore, the adapter has proven to be particularly robust in experiments, especially with regard to vibrations, and has an increased longevity, e.g., due to the additional support of the inner conductor of the coaxial system. 
     In some embodiments, a first inner diameter of the cladding is smaller than a second inner diameter of the waveguide such that a step is formed in the region of the connection between the waveguide and the cladding. In addition, the spacer element is at least partially disposed within the waveguide and forms a collar within the waveguide. This can contribute both to a better mechanical cohesion of the adapter and to a better tightness against diffused moisture. In addition, this collar can prevent condensate from accumulating in the cavity. 
     In some embodiments, the spacer element has or consists of materials such as polytetrafluoroethylene, PTFE, polyetheretherketone, PEEK, polyethylene, PE, or polyvinylidene fluoride, PVDF, which are suitable for RF applications. These materials not only have dielectric properties, but also a certain toughness and elasticity, so that the spacer element fits particularly tightly between the adjacent components of the adapter and in this way fills the technically necessary gap between the fin and the coaxial feed. The hole for the inner conductor additionally provides a guide for assembly in manufacturing, to which the relatively low friction—also during assembly—may also contribute. In addition, at least some of the usable materials may be temperature resistant and/or hydrophobic. 
     In an embodiment, the spacer element may be implemented as a plastic turned part. PTFE, for example, can be used as the plastic. This type of production allows the spacer element to be manufactured with particular precision. 
     In some embodiments, the high frequency adapter further comprises a process separation disposed within the sheath and having a conductive element passing therethrough that is electrically connected to the inner conductor. The process separation may be configured, for example, as a glass feedthrough. It should be noted that—due to the spacer element—moisture can also no longer condense on the process separation, in particular because the spacer element realizes a seal against the waveguide and other parts of the adapter. 
     In an embodiment, the conductive element is made in one piece with the inner conductor. This can contribute to a particularly simple manufacturing process. This embodiment can be—realized with or without process separation. 
     In an embodiment, the conductive element has a similar coefficient of expansion as the process separation. Advantageously, this means that the conductive element remains robust and arranged in the process separation over the long term, even in the event of large fluctuations in temperature. 
     In some embodiments, the process separation comprises glass and/or ceramic, and/or the conductive element comprises a nickel alloy, or these elements may comprise these materials. 
     In an embodiment, the conductive element is designed for direct connection to the antenna connector. The conductive element can be particularly robust and/or have a particularly conductive and/or corrosion-resistant coating, such as gold, at the connection points. 
     One aspect relates to a method of manufacturing a high frequency adapter, comprising the steps of: 
     arranging an electrically insulating hollow cylindrical spacer element in a conductive hollow cylindrical jacket; and 
     inserting a conductive inner conductor into the spacer element; and 
     connecting a waveguide with an impedance matching element arranged inside the waveguide, for example by pressing it into an existing hole in the impedance matching element. 
     The spacer element can particularly advantageously serve as an insertion aid during assembly, thereby helping to prevent incorrect assembly. 
     In some embodiments, the method comprises the further step of: 
     arranging a process separation in the sheath, through which process separation a conductive element is led, which is arranged for an electrical connection with the inner conductor. 
     One aspect relates to a use of a high frequency adapter as described above and/or below for connecting a high frequency antenna to an antenna connector. The high-frequency adapter can be particularly suitable in particular for level measurement, for topology determination and/or for level limit determination, because it can be used, for example, to realize a feedthrough between an antenna in a container and a high-frequency generator outside the container. Due to the robust design of the high-frequency adapter, the container can also be, for example, a process tank, which is designed in particular for high temperatures and/or pressures. Furthermore, embodiments with a process separation can further increase the robustness of the high-frequency adapter. 
     For further clarification, the disclosure is described with reference to embodiments illustrated in the figures. These embodiments are to be understood only as examples and not as limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    shows a high frequency adapter in a longitudinal section; 
         FIG.  2    shows a high-frequency adapter according to an embodiment in a longitudinal section; 
         FIG.  3    shows a high-frequency adapter according to an embodiment in a further longitudinal section; 
         FIG.  4    shows a high-frequency adapter according to an embodiment in a perspective external view; 
         FIG.  5    shows a high-frequency adapter according to a further embodiment in a longitudinal section; and 
         FIG.  6    shows a flowchart according of a method according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG.  1    schematically shows a high frequency adapter  12  in longitudinal section. The high-frequency adapter  12  has a hollow cylindrical waveguide  20 , which is set up to transmit high-frequency waves from and to a high-frequency antenna  80  (not shown). Adjacent to the waveguide  20  is a conductive jacket  50 . At least partially disposed within the sheath  50  is a conductive inner conductor  40  that is electrically and mechanically connected to an impedance matching element  30 . The inner conductor  40  is separated from the sheath  50  by a cavity  18 . The cavity  18  may be shaped as a rotationally symmetrical cavity, e.g., in the case of a round high frequency adapter; in the case of other shapes of high frequency adapter—e.g., rectangular, hexagonal, etc.—correspondingly adapted or likewise cylindrical. In at least some cases, moisture may enter the cavity  18 . This can significantly degrade the functionality of the high frequency adapter, up to and including failure of the adapter. 
       FIG.  2    schematically shows a high frequency adapter  10  according to an embodiment in a longitudinal section. The high-frequency adapter  10  is arranged for connecting a high-frequency antenna  80  (left side, not shown) to an antenna connector  90  (right side, not shown). The high-frequency adapter  10  has a hollow cylindrical waveguide  20 , which is arranged to transmit high-frequency waves from and to the high frequency antenna  80 —which is arranged on the left side of the waveguide  20 . Within the waveguide  20 , a step-shaped impedance matching element  30  is arranged, which is arranged for impedance matching to the high frequency antenna  80 . The high frequency adapter  10  further comprises a conductive inner conductor  40  electrically and mechanically connected to the impedance matching element  30 , wherein the inner conductor  40  is electrically indirectly connected—namely via a conductive element  45 —to the antenna connector  90 . A conductive hollow-cylindrical sheath  50  adjoins the waveguide  20 . The joint between the waveguide  20  and the cladding  50  may be sealed, but in at least some cases may also allow moisture intrusion due to defects and/or long-term stresses. In at least some embodiments, the joint may be omitted. The high frequency adapter  10  further comprises an electrically insulative hollow cylindrical spacer element  60  disposed between the cladding  50  and the inner conductor  40 , thereby isolating the inner conductor  40  from the cladding  50  and providing a fluid-tight seal to the waveguide  20 . In at least some embodiments, the spacer element  60  may be configured to be non-fluid-tight. The spacer element  60  may be configured to “occupy” the space where condensate could form, and in this way may displace the condensate or reduce or prevent the formation of condensate. Advantageously, this can also prevent malfunction of the high-frequency adapter  10  in the event that moisture enters. The high-frequency adapter  10  further comprises a process separation  70  to further increase the robustness of the high-frequency adapter. The conductive element  45  is passed through the process separation  70 . 
     On one side thereof, the conductive element  45  is electrically connected to the inner conductor  40 . On the other side, the conductive element  45  is arranged for connection to an antenna connector  90  (right side), via the end protruding on the right side from the process separation  70  and from a sheath  55 . 
       FIG.  3    schematically shows a high-frequency adapter  10  according to an embodiment in a further longitudinal section. Here, the same reference signs as in  FIG.  2    denote the same or similar elements. Here,  FIG.  3    shows particularly clearly how the spacer element  60  insulates the inner conductor  40  from the sheath  50  and in particular with the cooperation of a collar  62 —also realizes a seal against the wall  50 . In this embodiment example, the conductive element  45  is realized with pointed ends to further simplify assembly. 
       FIG.  4    schematically shows a high-frequency adapter  10  according to an embodiment in a perspective external view. Here, the same reference signs as in  FIG.  2    denote the same or similar elements. In particular, the design of the impedance matching element  30  becomes clear, which in this embodiment is designed to be step-shaped and significantly narrower than an inner diameter of the waveguide. The impedance matching element  30  designed in this manner is sometimes referred to as a fin. This design may be particularly suitable for lower frequency radar bands, such as the K-band. For other frequency bands, the impedance matching element—and/or other components of the high-frequency adapter  10 —may be designed at least slightly differently. 
       FIG.  5    schematically shows a high-frequency adapter  10  according to a further embodiment in a longitudinal section. The same reference signs as in  FIG.  2    denote the same or similar elements. This embodiment does not have a process separation  70 . Further, the conductive element  45  is integrally formed with the inner conductor ( 40 ) so that an antenna connector  90  (right, not shown) is electrically connected directly to the antenna connector  90 . Furthermore, it is clear that a first inner diameter  52  of the sheath  50  (as also shown, for example, in  FIG.  2   ) is smaller than a second inner diameter  22  of the waveguide  20 , so that a step  25  is formed in the region of the connection between the waveguide and the sheath. 
       FIG.  6    shows a flowchart  100  showing a manufacturing process for a high frequency adapter  10  (see, e.g.,  FIG.  2    to  FIG.  5   ) according to an embodiment form. In an optional step  102 , a process separation  70  is disposed in the shell  50 , wherein a conductive element  45  is passed through the process separation  70  and is adapted for electrical connection to the inner conductor  40 . In a step  104 , an electrically insulating spacer element  60  is disposed in conductive sheath  50 . In a step  106 , a conductive inner conductor  40  is inserted into the spacer element  60 . In a step  108 , a waveguide  20  is connected, with an impedance matching element  30  disposed within the waveguide  20 . 
     List of Reference Signs 
       10  High frequency adapter 
       12  High frequency adapter 
       15  Center axis 
       18  Cavity 
       20  Waveguide 
       22  Internal diameter of the waveguide 
       25  Step 
       30  Impedance matching element 
       40  Inner conductor 
       45  Conductive element 
       50  Sheath 
       52  Inner diameter of the sheath 
       55  Sheath 
       60  Spacer element 
       62  Collar of the spacer element 
       70  Process separation 
       80  Antenna 
       90  Antenna connector 
       100  Flow diagram 
       102 - 108  steps