Patent Description:
Multiple Input Multiple Output (MIMO) technology dramatically increases data transmission capacity by using multiple antennas. This technology is a spatial multiplexing technique by which a transmitter transmits different data through different transmission antennas, and a receiver distinguishes the transmitted data through proper signal processing. Therefore, as the number of transmission antennas and the number of reception antennas are simultaneously increased, channel capacity may increase, thereby enabling more data to be transmitted. For example, when the number of antennas is increased to <NUM>, a channel capacity of about <NUM> times that of the current single-antenna system is secured in the same frequency band.

The <NUM> LTE-advanced system employs up to <NUM> antennas. , and a product equipped with <NUM> or <NUM> antennas is being developed in the pre-<NUM> stage. Base station equipment with a much larger number of antennas is expected to be employed in the <NUM> system, and the technology therefor is called massive MIMO. Massive MIMO is also referred to as full dimension (FD)-MIMO because massive MIMO enables 3D-beamforming while current cell operation is <NUM>-dimensional.

In massive MIMO, as the number of antenna elements increases, the number of transceivers and filters increases. In <NUM>, more than <NUM>,<NUM> base stations are deployed nationwide. In other words, there is a need for a structure of a cavity filter that minimizes a mounting space and can be mounted easily, and there is also a need for an RF signal line connection structure that provides the same filter characteristics even after individually tuned cavity filters are mounted on the antennas.

In an RF filter having a cavity structure, a resonator including a resonance rod, which is a conductor, is provided inside a box structure formed of a metallic conductor to allow only an electromagnetic field of a natural frequency to be present. Thereby, the RF filter allows only a characteristic frequency component of a very high frequency to pass therethrough by resonance. A bandpass filter with such a cavity structure is widely used as a filter for antennas of a mobile communication base station as it has a low insertion loss and is advantageous for high output power. <CIT> illustrates for example an electronic device, configured to be blindly mated with a printed circuit board, that comprises a housing and at least one RF interconnect. The RF interconnect comprises an outer conductor, an insulator, and an inner conductor that function in a manner similar to the outer conductor, insulator, and inner conductor of a coaxial cable, respectively. The inner conductor comprises a spring-loaded electrical contact such as a POGO pin. An upper end of the outer conductor is electrically coupled to the housing and a lower end of the outer conductor is configured to electrically couple to a ground return path of the printed circuit board. In its normally extended position, the spring-loaded contact extends beyond the lower end of the outer conductor, and the outer conductor limits the compression distance of the spring-loaded contact. <CIT> describes radio frequency unit, comprising a power amplification module, a filtering module, and a signal connector. One end of the signal connector is connected to the filtering module, and the other end is connected to the power amplification module. The power amplification module is provided with a power amplification connector. The end of the signal connector that is connected to the power amplification module forms a guiding structure that guides the power amplification connector to be coaxially aligned with the signal connector, such that the power amplification connector and the signal connector are connected coaxially. <CIT> discloses surface mount electrical interconnect to provide an interface between a PCB and contacts on an integrated circuit device. <CIT> describes a cavity filter with a connector formed with a non-metal layer on the outer peripheral surface of the metal enclosure thereof, which can improve the moisture-proof capability, the salt-mist-proof capability, the mould-proof capability and the reliability of the connector and the cavity filter. <CIT> is related to a contact pin comprising an end tip which is to be brought into contact with a terminal, <CIT> relates to electrical connectors for electrically interconnecting circuits on two parallel surfaces such as printed circuit boards.

It is an object of the present disclosure to provide a cavity filter having a slim and compact structure and an RF connector embedded in a body in a thickness direction thereof.

It is another object of the present disclosure to provide an assembly method capable of minimizing the cumulative amount of assembly tolerances generated at the time of installing a plurality of filters and an RF signal connection structure that is easily mounted and capable of maintaining uniform frequency characteristics of the filters.

Further advantageous embodiments are defined in the dependent claims.

The present disclosure provides a cavity filter with a slim and compact design wherein an RF connector including an elastic connector is embedded in a body thereof in a thickness direction. Thereby, the size of the antenna system may be reduced, and individual cavity filters may be quickly verified with high reproducibility. Further, multiple cavity filters may be easily installed inside the antenna of a mobile communication base station.

It should be noted that, in adding reference numerals to the constituent elements in the respective drawings, like reference numerals designate like elements, although the elements are shown in different drawings. Further, in the following description of the present disclosure, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Additionally, various terms such as first, second, A, B, (a), (b), etc., are used solely for the purpose of differentiating one component from the other but neither imply nor suggest the substances, order or sequence of the components. Throughout this specification, when a part "includes" or "comprises" a component, the part may further include other components, and such other components are not excluded unless there is a particular description contrary thereto. Terms such as "unit," "module," and the like refer to units for processing at least one function or operation, which may be implemented by hardware, software, or a combination thereof.

<FIG> is a diagram illustrating a stack structure of an exemplary massive MIMO antenna.

<FIG> is a perspective view showing an exemplary external shape of an antenna device <NUM> in which an antenna assembly according to the present disclosure is provided. The antenna device <NUM> includes a housing provided with a heat sink <NUM>, and a radome <NUM> coupled to the housing. The antenna assembly is arranged between the housing and the radome <NUM>. A power supply unit (PSU) <NUM> is coupled to a lower portion of the housing through, for example a docking structure. The PSU <NUM> provides operating power for operating electronic components provided in the antenna assembly.

Typically, the antenna assembly includes an antenna board <NUM> having a plurality of antennas <NUM> arranged on the front surface thereof. On the rear surface of the antenna board, cavity filters <NUM> equal in number to the number of the antennas <NUM> are disposed, and subsequently a related PCB board <NUM> is stacked. Before being mounted, the cavity filters <NUM> are individually tuned and verified so as to have a frequency characteristic that meets the specification. The tuning and verification process may be quickly performed in an environment having the same characteristics as the mounted state.

<FIG> is a cross-sectional view illustrating a cavity filter according to an embodiment of the present disclosure, which is stacked between an antenna board and a control board.

Referring to <FIG>, as the conventional RF connector <NUM> is eliminated, connection may be facilitated and an antenna structure <NUM> with a lower height profile may be provided. In addition, RF connectors are provided on both surfaces facing in the vertical direction and are connected with elastic connectors <NUM>, <NUM> and <NUM>. Thereby, even if vibration or thermal deformation occurs in the antenna board <NUM> or the PCB <NUM>, the RF connection may remain the same without change in frequency characteristics.

<FIG> is a perspective plan view of a structure of a cavity filter according to an embodiment of the present disclosure as seen from the bottom side.

<FIG> is a cross-sectional view illustrating a terminal unit structure of a cavity filter employing a push pin type elastic connector according to an embodiment of the present disclosure.

In <FIG> and <FIG>, an internal structure including a resonance element is omitted.

Referring to <FIG> and <FIG>, the cavity filter <NUM> according to an embodiment includes a first case <NUM> including a resonance element (not shown) and having a hollow interior, a second case <NUM> covering the first case <NUM>, a terminal unit <NUM> provided on both longitudinal sides of the first case <NUM> arranged in a vertical direction of the cavity filter <NUM>, and an assembly hole <NUM> provided on both sides of the terminal unit <NUM>. The terminal unit <NUM> is arranged to pass through the first case <NUM> to electrically connect an external member, for example, an electrode pad of the PCB board <NUM> or the antenna board <NUM>, to the resonance element.

Both side assemblies <NUM> including the first case <NUM> and the terminal unit <NUM> of the second case <NUM> may be formed to be thicker than the bottom surface <NUM>, which is an area arranged therebetween, depending on the application. For example, when the bottom surface <NUM> of the first case <NUM> is connected to the PCB board <NUM>, on which various devices are mounted, both side assemblies <NUM> may have a thickness avoiding interference between the first case <NUM> and the mounted devices. The external terminal of the terminal unit <NUM> may be formed such that one side thereof faces the lower end surface <NUM> of the first case <NUM> and the opposite side thereof protrudes from an assembly reference plane of the second case <NUM> as shown in <FIG>. The external terminals of the terminal units <NUM> may be formed to be exposed in the same direction, for example, to the lower end face <NUM> of the first case <NUM> depending on the mounting form of the cavity filter <NUM>.

<FIG> is a side cross-sectional view illustrating a terminal unit structure of a cavity filter employing a push-pin type elastic connector according to an embodiment of the present disclosure.

The terminal unit <NUM> of the cavity filter <NUM> according to an embodiment includes a terminal insertion hole <NUM>, a dielectric bush <NUM>, a pin member <NUM>, an elastic connector <NUM>, a pin spring <NUM>, and a star washer <NUM>.

The terminal insertion hole <NUM> may have a cylindrical shape and may be formed from the lower end surface <NUM> of the first case <NUM> by penetrating the first case <NUM> or formed from the upper end surface of the first case <NUM> by penetrating the first case <NUM>. When the terminal insertion hole <NUM> is formed from the upper end surface of the first case <NUM>, a through hole may also be formed in the second case <NUM>, and the depth of the terminal insertion hole <NUM> may be adjusted in consideration of this hole. The terminal insertion hole <NUM> is formed to have three steps such that the diameter thereof gradually decreases stepwise. In the terminal insertion hole <NUM>, a portion having the smallest diameter is defined as a first insertion hole <NUM>, a portion having the next smallest diameter is defined as a second insertion hole <NUM>, and a portion having the largest diameter is defined as a third insertion hole <NUM>.

The dielectric bush <NUM> has a shape of a two-stage cylinder. The dielectric bush <NUM> is provided with a through hole <NUM> passing through the center of the rotary shaft. The dielectric bush <NUM> has a size as to be inserted and fixed to the first insertion hole <NUM> and the second insertion hole <NUM>. The dielectric bush <NUM> may be formed of Teflon. While it is illustrated in this embodiment that one body has a two-stage cylinder shape, the present disclosure is not limited thereto. Elements having different diameters may be formed and assembled to have a two-stage cylinder shape.

The pin member <NUM> includes a pin portion <NUM> and a terminal body portion <NUM>, which are integrally formed in the longitudinal direction to have a two-stage cylinder shape. In one embodiment, the terminal body portion <NUM> is provided with a socket portion <NUM>. The pin member <NUM> may be prepared by coating a beryllium copper (BeCu) alloy with gold. The pin portion <NUM> is fixedly inserted into the through hole <NUM> of the dielectric bush <NUM>. A wedge-shaped protrusion <NUM> is formed on the outer circumferential surface of the pin portion <NUM> to prevent the pin portion <NUM> from being separated in the opposite direction to insertion of the pin portion <NUM>. An annular step is formed at a boundary between the pin portion <NUM> and the terminal body portion <NUM> and arranged to contact one side surface of the dielectric bush <NUM>. The terminal body portion <NUM> is formed to be shorter than the depth of the third insertion hole <NUM>, and a hollow socket portion <NUM> is formed therein. The terminal body portion <NUM> is provided with a conical opening <NUM> whose diameter decreases from the inlet to the inside. In an embodiment of the present disclosure, the inner wall of the terminal body portion <NUM> in the region where the conical opening <NUM> is formed is inclined at an angle of, for example, <NUM> degrees with respect to the center axis. A first annular groove <NUM> may be formed inside the opening <NUM> to prevent the elastic connector <NUM> inserted thereinto from being separated. A spring <NUM> may be interposed between the innermost side surface of the opening <NUM> and the leading end of the insertion portion of the elastic connector <NUM> to further provide force to push the elastic connector <NUM> outwardly of the opening <NUM>.

The elastic connector <NUM> includes a truncated conical pin socket contact <NUM> inserted into the socket portion <NUM> so as to correspond to the conical opening <NUM> having a cylindrical structure, and an impedance matching portion <NUM> extending from the pin socket contact <NUM>, wherein the pin socket contact and the impedance matching portion are integrated with each other in the longitudinal direction. The elastic connector <NUM> may be formed by coating a BeCu alloy with gold. A wedge-shaped annular protrusion <NUM> protruding from the outer circumferential surface is formed in the longitudinal middle of the cylindrical structure. When the elastic connector <NUM> is inserted into the socket portion <NUM>, the annular protrusion <NUM> is accommodated in the first annular groove <NUM> to prevent the elastic connector <NUM> from being separated from the socket portion <NUM>.

The angle of the pin socket contact portion <NUM> with respect to the central axis is formed to be larger than the angle of the conical opening <NUM> of the socket portion <NUM> by <NUM> degrees to <NUM> degrees. In addition, the elastic connector <NUM> is provided with a cross-shaped cutoff part <NUM> that is locally formed along the central axis from the outer side surface of the elastic connector that is exposed to the outside after the elastic connector <NUM> is inserted into the socket portion <NUM>. The depth of the cutoff part <NUM> extends up to the cylindrical structure of the elastic connector <NUM>, passing through the truncated conical shape. While the cutoff part <NUM> is illustrated as having a cross shape in this embodiment, the present disclosure is not limited thereto. The cutoff part <NUM> may have a flat-head shape or a shape with a plurality of slots.

When the elastic connector <NUM> is inserted into the socket portion <NUM> and brought into contact with the conical opening <NUM> of the socket portion <NUM> without the cross-shaped cut-open part <NUM> being contracted, the elastic connector <NUM> may protrude from the lower end surface <NUM> of the first case <NUM>. When the cavity filter <NUM> is mounted, the elastic connector <NUM> may press the opening <NUM> of the socket portion <NUM> to have an inserted length.

The outer edge of the outer surface of the elastic connector <NUM> is an area that is electrically connected to an electrode pad formed on the PCB <NUM>, on which the cavity filter <NUM> is mounted, as the elastic connector <NUM> is contracted. This outer edge is defined as an electrode edge <NUM>. In one embodiment, the electrode edge <NUM> may be formed in a round shape in the range of R0. <NUM> to R0. Thus, even if the elastic connector <NUM> is contracted to form a shallow conical recessed outer surface with respect to a plane, the electrode edge <NUM> may have a uniform area of contact with the electrode pad formed on the PCB <NUM>. The cavity filter <NUM> is substantially connected with the PCB <NUM> and may have various height deviations. By forming the electrode edge <NUM> in a round shape, the elastic connector <NUM> may have a uniform contact area even if there is a variation in degree of contraction of the elastic connector <NUM>.

The angle of the opening <NUM>, the angle of the pin socket contact portion <NUM>, the length of the elastic connector <NUM>, and the degree of roundness of the electrode edge <NUM> are preferably selected based on the state in which one side surface of the first case <NUM> or the assembly reference surface of the second case <NUM> is coupled with the PCB <NUM>. More specifically, when the PCB <NUM> is coupled, the elastic connector <NUM> is pushed up to slide along the opening <NUM> of the socket portion <NUM> to contract the cross-shaped cut-open part <NUM>. When the cut-open part <NUM> is contracted, the angle of the pin socket contact portion <NUM> of the elastic connector <NUM> is reduced, and the contact area of the opening <NUM> and the pin socket contact portion <NUM> is changed. In addition, as the outer surface of the elastic connector <NUM> is retracted in a shallow conical shape, the area of the electrode edge <NUM> that contacts the electrode pad of the PCB <NUM> is also changed. As the force by which the spring <NUM> inserted into the socket portion <NUM> urges the elastic connector <NUM> toward the PCB <NUM> and force including the reaction force from the pin socket contact portion <NUM> act on the respective contact points, the respective contact surfaces are elastically deformed.

The design specifications of the socket portion <NUM>, the elastic connector <NUM>, and the spring <NUM>, which determine the contact area, are preferably selected in consideration of the impedance of the terminal unit <NUM>. That is, design specifications that minimize the change in impedance along a signal path of the terminal unit <NUM> including the contact resistance determined by the contact area and the contact pressure is preferably determined. In particular, for a mobile communication antenna signal, which is transmitted at a high frequency, the signal quality may be degraded if the characteristic impedance of the signal line is not constant. For signals of a few gigahertz, impedance mismatching of the signal path may increase the voltage standing wave ratio (VSWR), thereby degrading signal quality due to signal reflection and distortion.

Considerations for maintaining uniform impedance of the terminal unit <NUM> are also necessary in determining the sizes of the first insertion hole <NUM> to the third insertion hole <NUM> and the size of the terminal body portion <NUM>. The third insertion hole <NUM> and the outer circumferential surface of the terminal body portion <NUM> are spaced apart from each other by a predetermined air gap, and the dielectric bush <NUM> formed of, for example, PTFE is interposed between the first and second insertion holes <NUM> and <NUM> and the pin portion <NUM>. The pin portion <NUM> and the terminal body portion <NUM> of the pin member <NUM> form a radial step, and the diameter and depth of the second insertion hole <NUM> are preferably determined in consideration of the step such that the impedance between the pin member <NUM> and the terminal insertion hole <NUM> is kept constant.

The diameter of the third insertion hole <NUM> is formed to be larger than the diameter of the first and second insertion holes <NUM> and <NUM> in consideration of the dielectric constant of PTFE, which is about twice that of air. For example, if the dielectric bush <NUM> is made of PEEK, whose dielectric constant is about three times that of air, instead of PTFE, the diameter of the third insertion hole <NUM> is formed to be larger than in the case of PTFE.

<FIG> illustrate various shapes of the electrode edge <NUM> and the impedance matching portion <NUM> of the elastic connector <NUM> which is in contact with the electrode pad of the PCB <NUM>. These shapes and sizes may be selected by performing numerical analysis in consideration of a gap with the third insertion hole <NUM> or by evaluating the VSWR of the terminal unit <NUM> using, for example, a network analyzer.

In the example of <FIG>, the impedance matching portion <NUM> has a shape vertically protruding at a position deviating from the pin socket contact portion <NUM>, and the electrode edge <NUM> is formed with fine roundness of R0. In the example of <FIG>, the impedance matching portion extends to the electrode edge <NUM> while the pin socket contact portion <NUM> of the elastic connector <NUM> maintains the inclination angle thereof. In the example of <FIG>, the impedance matching portion <NUM> has an inclined surface whose diameter decreases at a position deviating from the pin socket contact portion <NUM>. In the example of <FIG>, the impedance matching portion has an inclined surface whose diameter decreases at a position deviating from the pin socket contact portion <NUM>, and the electrode edge <NUM> has relatively high roundness of R0. <FIG> shows a case where the spring <NUM> is omitted. In this example, the force (contact pressure) to push the elastic connector <NUM> and the electrode pad of the PCB <NUM> in contact therewith is formed by the reaction force from the pin socket contact portion <NUM> as the cross-shaped cut-open part <NUM> is contracted.

A second annular groove <NUM> may be formed on the outer side of the third insertion hole <NUM> to surround the signal line and accommodate the star washer <NUM>, which surrounds the cylindrical portion and is inserted so as to secure the ground connection.

<FIG> is a partial cross-sectional view of a terminal unit structure of a cavity filter employing a push ring type elastic connector according to an embodiment of the present disclosure.

Referring to <FIG>, the terminal unit <NUM> according to another embodiment of the present disclosure includes a terminal insertion hole <NUM>, a dielectric bush <NUM>, a pin member <NUM>, a push ring-type elastic connector <NUM>, and a star washer <NUM>. In the embodiment of <FIG>, which illustrates a case in which impedance matching is performed more strictly, it is illustrated that the dielectric bush <NUM> is formed to be separable, the through hole <NUM> of the dielectric bush <NUM> having two stages are formed to have different diameters, and the pin portion <NUM> of the pin member <NUM> is formed to have two steps corresponding to the dielectric bush <NUM>. However, the terminal insertion hole <NUM>, the dielectric bush <NUM>, the pin portion <NUM> and the star washers <NUM> may be formed to have the same shapes as in the embodiment of <FIG>.

The pin member <NUM> according to one embodiment includes a pin portion <NUM> and a terminal body portion <NUM> provided with a socket portion <NUM>. The pin member <NUM> may be formed of a BeCu material plated with gold. The pin portion <NUM> is fixedly inserted into the through hole <NUM> of the dielectric bush <NUM>. A wedge-shaped protrusion <NUM> is formed on the outer circumferential surface of the pin portion <NUM> to prevent the pin member <NUM> from being separated in the opposite direction to insertion of the pin member <NUM>. An annular step formed at the boundary between the pin <NUM> and the terminal body portion <NUM> is disposed to contact one side surface of the dielectric bush <NUM>. The terminal body portion <NUM> is formed to be shorter than the depth of the third insertion hole <NUM>, and the inside thereof is hollow. The terminal body portion is provided with a conical opening <NUM> whose diameter is reduced inward from the inlet. In an embodiment of the present disclosure, the conical opening <NUM> is formed to be inclined at, for example, <NUM> degrees with respect to the central axis such that a circular spring portion <NUM> of the push ring-type elastic connector <NUM> is circumscribed about the opening.

The pushing-type elastic connector <NUM> according to the embodiment is formed of a spring plate having a constant width over most of the length thereof except both ends thereof. The elastic connector <NUM> includes a circular spring portion <NUM> provided on one side and two plate-shaped protrusions <NUM> protruding from two adjacent points <NUM> on the circumference of the circular spring portion <NUM> perpendicularly with respect to the circumference. The elastic connector <NUM> is formed to have a width allowing the plate-shaped protrusions <NUM> to be inserted into the socket portion <NUM>. The elastic connector <NUM> may be formed of a BeCu material plated with gold. The two plate-shaped protrusions <NUM> are stretched away from each other, and the circular spring portion <NUM> operates as a leaf spring so as to be deformed into an ellipse when an external force acts thereon toward the center thereof.

That is, when the two plate-shaped protrusions <NUM> of the elastic connector <NUM> are inserted into the socket portion <NUM>, the two plate-shaped protrusions <NUM> may be stretched away from each other, and thus the end portions of the two plate-shaped protrusions <NUM> may come into close contact with the inner circumferential surface of the socket portion <NUM>, thereby maintaining the inserted state. The circular spring portion <NUM> is brought into close contact with the conical opening <NUM> in a circumscribing manner, and the opposite side positions of the plate-shaped protrusions <NUM> protrude from the lower end surface <NUM> of the first case <NUM> by a predetermined distance. Thus, when the cavity filter <NUM> is mounted, the electrode pad presses the circular spring portion <NUM>, and thus the circular spring portion is elastically deformed into an elliptical shape to electrically connect the pin member <NUM> and the electrode pad to each other. Here, sufficient contact pressure is applied to the contact portions such that the contact state remains unchanged even if external vibration is applied.

<FIG> is a cross-sectional view illustrating a process of assembling a pin assembly employing a push ring-type elastic connector according to an embodiment of the present disclosure.

<FIG> is a plan view and partial cross-sectional view showing the pin assembly employing a push ring-type elastic connector according to an embodiment of the present disclosure.

Referring to <FIG>, the push ring-type elastic connector <NUM> is inserted into the socket portion <NUM>. Preferably, the two plate-shaped protrusions <NUM> inserted into the cylindrical holes in the socket portion <NUM> are connected by soldering and joined to the pin assembly <NUM>. A preferred embodiment of joining the elastic connector <NUM> and the pin member <NUM> according to one embodiment is disclosed below.

When multiple pin members <NUM> are prepared such that the openings <NUM> of the socket portions <NUM> of the pin members <NUM> are positioned on the upper side, a certain amount of solder is inserted into the socket portions <NUM> and the pin members <NUM> are heated such that the solder is melted. Then, the elastic connector <NUM> is inserted. The elastic connector <NUM> inserted into the socket portion <NUM> is held in position until the solder cools and solidifies. When the solder is hardened, joining of the elastic connector <NUM> and the pin member <NUM> is completed. The cavity filter <NUM> handles high frequency signals at the gigahertz level. It is preferable to minimize portions which may make incomplete mechanical contact in transmitting signals of such a frequency band.

It is important for antennas of a mobile communication base station in which the cavity filter <NUM> is used to secure extremely low noise in the operating frequency band. Accordingly, it is necessary to minimize the passive intermodulation distortion (PIMD) caused not only at the mechanical connection portions of various RF connection elements, but also at portions where metal contact is made and inside parts coated with different kinds of metal. Particularly, a radio signal having a high frequency and a high energy may cause an intermediate frequency by mixing of multiple frequencies due to nonlinearity of voltage and current at such contact portions. Signal quality of the antennas may be greatly degraded by an intermediate frequency which is closer to the frequency of a main signal than the other intermediate frequencies. The PIMD may be minimized by firmly joining the plate-shaped protrusions <NUM> inserted into the socket portion <NUM> by soldering.

The pin assembly <NUM> employing the push ring-type elastic connector according to the embodiment of the present disclosure is electrically and physically connected by soldering as described above. The pin assembly is connected to the electrode pad of the PCB substrate on which the cavity filter <NUM> is installed in the form of a circular leaf spring. Particularly, the circular spring portion <NUM> provides stable mechanical connection with the electrode pad, and the signal line undergoes a small change in impedance. Accordingly, performance of low signal reflection is implemented with a simple component structure.

<FIG> is a conceptual view illustrating a method of manufacturing a push ring-type elastic connector according to an embodiment of the present disclosure.

Referring to <FIG>, the elastic connector <NUM> according to an embodiment may be formed by press-forming a sheet metal from a spring plate material and subjecting the press-formed metal to heat treatment such that a plurality of elastic connectors <NUM> is connected to each other on one side so as to be easily separated from each other by bending. Since the circular spring portion <NUM> is a part that contacts the opening <NUM> of the socket portion <NUM> and the electrode pad, the circular spring portion is preferably processed such that the burr of the edge portion can be generated only inwardly of the circular portion by fine blanking.

The diameter of the circular spring portion <NUM> is determined based on the outer diameter of the terminal body portion <NUM>. The circular spring portion <NUM> is brought into close contact with the conical opening <NUM> of the socket portion <NUM> at two points, and is spaced apart from the inner circumferential surface of the third insertion hole <NUM> to have a predetermined characteristic impedance. The diameter of the circular spring portion <NUM> is preferably formed such that the impedance is equal or similar to the characteristic impedance between the outer diameter of the terminal body portion <NUM> and the third insertion hole <NUM>. For signals of a few gigahertz, impedance mismatch of the signal path may increase the voltage standing wave ratio (VSWR), thereby degrading signal quality due to signal reflection and distortion. Accordingly, change in impedance is preferably minimized.

The circular spring portion <NUM> contacts the electrode pad at the circular portion side thereof and is bifurcated to be electrically connected to the opening <NUM> of the socket portion <NUM>. The circular spring portion <NUM> may have a diameter determined to be greater than or equal to the width thereof and less than or equal to twice the width thereof, it may be seen as electrical extension of one cylindrical electrode, when viewed from the inner circumferential surface of the third insertion hole <NUM> corresponding to the ground electrode. In other words, even if the circular spring portion <NUM> is connected to the socket portion <NUM> in the band of a high frequency signal transmitted from the cavity filter <NUM> according to the present disclosure, variation of the impedance may be small.

<FIG> illustrate RF characteristics and electric field shapes of various types of contact type RF terminal units <NUM> which are compared with each other through computer simulation. The right side of the analysis model is the terminal unit <NUM>, and the left side is a cylindrical terminal corresponding to an electrode pad. A cylindrical ground terminal is disposed to surround the terminal unit and the electrode pad.

<FIG> is an analytical model of a typical plunger type terminal unit for comparison.

<FIG> shows a result of electric field analysis of the typical plunger-type terminal unit of <FIG>.

Referring to <FIG>, it can be seen that the terminal unit of the conventional typical plunger structure has a disconnected portion in the middle of the electric field distribution due to structural limitations. The pin portion supported by the spring may have a considerably smaller diameter than the pin housing for accommodating the pin due to the structure thereof and inevitably have a section where the gap becomes abruptly wide with respect to the inner circumferential surface of the cylindrical ground end. As a result, the diameter of the protruding pin portion is smaller than the outer diameter of the plunger body, which results in a sudden change in impedance. Thereby, the terminal unit of the typical plunger structure has a high insertion loss S21 and a high reflection loss S11.

The analysis result shows that the insertion loss is -<NUM> dB and the reflection loss is -<NUM> dB at <NUM>. This result may be interpreted as meaning that reflection of the signal is large due to the impedance variation area in the middle of the signal path.

<FIG> is an analytical model of a terminal unit employing a push-pin type elastic connector according to an embodiment of the present disclosure.

<FIG> shows a result of electric field analysis of a terminal employing a push-pin type elastic connector according to an embodiment of the present disclosure.

Referring to <FIG>, in the case of the terminal unit <NUM> employing a push pin-type elastic connector according to the embodiment of the present disclosure, the distribution of the electric field is relatively uniform. The push pin-type elastic connector can maintain the gap of the impedance discontinuity section to be relatively narrow as to, for example, <NUM> or less, and be formed to be similar to the outer diameter of the terminal body portion <NUM> with reference to the inner circumferential surface of the third insertion hole <NUM>, which is advantageous for minimization of variation in impedance. According to the analysis result, the insertion loss is -<NUM> dB and the reflection loss is -<NUM> dB at <NUM>.

<FIG> is an analytical model of a terminal unit employing a push ring-type elastic connector according to an embodiment of the present disclosure.

<FIG> shows a result of electric field analysis of a terminal unit employing a push ring-type elastic connector according to an embodiment of the present disclosure.

Referring to <FIG>, in the case of the terminal unit <NUM> employing a push ring-type elastic connector according to the embodiment of the present disclosure, the pin assembly <NUM> may form a relatively uniform electric field together with the inner circumferential surface of the third insertion hole <NUM>. It can also be seen that while a different magnetic field is formed inside the spring portion <NUM>, the distribution of the electric field is formed at the outer periphery of the circular spring portion <NUM> and change of the electric field continuously occurs with respect to the inner circumferential surface of the third insertion hole <NUM>. In other words, there is no section in which the impedance of the signal line changes discontinuously, and accordingly the insertion loss and the reflection loss may be kept low. The circular spring portion <NUM> may be designed to have various sizes because it has a simple structure while securing a sufficient contact pressure. Thereby, impedance matching may be facilitated. According to the analysis result, the insertion loss is -<NUM> dB and the reflection loss is - <NUM> dB at <NUM>.

<FIG> is a graph showing and comparing the results of analysis of insertion losses of the contact-type RF terminal units disclosed in <FIG>, <FIG> and <FIG>.

<FIG> is a graph showing and comparing the results of analysis of reflection losses of the contact-type RF terminal units disclosed in <FIG>, <FIG> and <FIG>.

Referring to <FIG> and <FIG>, the above-described three types of terminal units may be compared with each other in terms of insertion loss and reflection loss. It can be seen that the terminal unit <NUM> having the push pin structure exhibits the best signal quality and the terminal unit <NUM> having the push ring structure exhibits sufficient performance in practical use.

In the above-mentioned comparison, the influence of PIMD generated due to incomplete inner contact between the typical plunger type pin portion and the pin housing is not considered in the analysis. Considering this fact, the signal transmission quality may be further degraded in the typical plunger structure. On the other hand, both contact portions of the terminal unit <NUM> having the push pin structure are brought into annular surface contact by the elastic connector <NUM> and is made to make firm contact by elasticity. The terminal unit <NUM> having the push ring structure is directly joined to the socket portion <NUM> by soldering, and stable contact with the PCB <NUM> is secured by the elasticity of the circular spring portion <NUM>. Accordingly, in both cases, a uniform signal quality may be maintained without increasing the PIMD even when external vibration is applied.

<FIG> is a conceptual diagram showing a terminal unit structure of a cavity filter employing a leaf spring-type elastic connector according to an embodiment of the present disclosure.

<FIG> shows a pin member structure, which is inserted into the terminal insertion hole <NUM> of the cavity filter <NUM>, and a leaf spring, and <FIG> is a plan view showing a plate spring contact portion, and <FIG> is a side view showing the leaf spring contact portion.

Referring to <FIG>, a leaf spring-type terminal unit <NUM> according to another embodiment of the present disclosure includes a terminal insertion hole <NUM>, a dielectric bush <NUM>, a pin member <NUM>, and a leaf spring-type elastic connector <NUM>.

The terminal insertion hole <NUM> of the embodiment includes a fourth insertion hole <NUM> and a fifth insertion hole <NUM>. The fourth insertion hole has an elongated cross section extending from the lower end surface of the first case <NUM> to accommodate the leaf spring-type elastic connector <NUM>, and the fifth insertion hole <NUM> is formed a cylindrical shape at the central position of one side of the elongated shape of the fourth insertion hole <NUM>. The fourth insertion hole <NUM> is shown as a rectangular area in <FIG>.

The dielectric bush <NUM> has a two-stage cylindrical shape and has a through hole formed through the center of the axis of rotation. The first stage of the dielectric bush <NUM> is formed to have a diameter allowing the first stage to be inserted into the fifth insertion hole <NUM>, and the second stage, which has a diameter larger than that of the first stage of the dielectric bush <NUM>, is formed to be at least partially inserted into one side of the fourth insertion hole <NUM>. The height of the second stage of the dielectric bush <NUM> is set to form a predetermined gap between the dielectric bush and one side surface or ground electrode surface of the PCB <NUM>, to which the cavity filter <NUM> is coupled after the elastic connector <NUM> and the pin member <NUM> are disposed, such that the terminal unit <NUM> has a constant impedance. The dielectric bush <NUM> may be formed of PTFE. The outer diameter of the first stage of the dielectric bush <NUM> and the size of the through hole are determined in consideration of the dielectric constant of the dielectric bush <NUM> such that the terminal unit <NUM> has a predetermined characteristic impedance.

The pin member <NUM> includes a pin portion <NUM> fixedly inserted into the dielectric bush <NUM> through the elastic connector <NUM>, and a head portion <NUM> with a low height which brings the elastic connector <NUM> into close contact with the dielectric bush <NUM>. A wedge-shaped protrusion <NUM> is formed on the outer circumferential surface of the pin portion <NUM> to prevent the pin member <NUM> from being separated in the direction opposite to the insertion direction thereof. The pin member <NUM> may be formed of a BeCu material plated with gold.

The elastic connector <NUM> of the leaf spring-type according to one embodiment includes an annular portion <NUM> having a through hole <NUM> formed at the center thereof, and a first extension <NUM> extending from one side of the annular portion <NUM> with a narrower width than the annular portion <NUM>, a second extension <NUM> bent from the first extension <NUM> at an obtuse angle (for example, <NUM> to <NUM> degrees) with respect to the first extension <NUM> and extending such that the elastic connector <NUM> protrudes outward from the lower end surface <NUM> of the first case <NUM>, and a bent portion <NUM> formed between the first extension <NUM> and the second extension <NUM>. The leading end of the second extension <NUM> is formed to maintain a predetermined contact area by pressing the electrode pad of the PCB <NUM>, which is configured to contact the leading end.

Both sides of the bent portion <NUM> are provided with notches so as to be bent at a uniform position and angle. The leaf spring-type elastic connector <NUM> may be bent about the bent portion <NUM>, providing elastic force in the bending direction. The through hole <NUM> is formed to have a size allowing only the pin portion <NUM> of the pin member <NUM> to pass therethrough. When the elastic connector <NUM> is connected to the dielectric bush <NUM>, the annular portion <NUM> is arranged between and brought into close contact with the head portion <NUM> and the second stage of the dielectric bush <NUM> such that the elastic connector <NUM> and the pin member <NUM> are electrically connected to each other. A conductive paste may be applied between the elastic connector <NUM> and the pin member <NUM> or soldering may be performed to ensure more firm connection therebetween.

The electrode pad of the PCB <NUM> to which the leaf spring-type terminal unit <NUM> is electrically connected may be formed as a circular electrode pad which contacts the leading end of the second extension <NUM>. In addition, by arranging a plurality of plated through vias passing through the PCB <NUM> in the circular electrode pad at proper intervals and pitches, variation in impedance may be minimized.

<FIG> is a cross-sectional view showing a cavity filter according to an embodiment of the present disclosure, which is attached to a socket on the back surface of an antenna board.

<FIG> is a cross-sectional view showing a cavity filter according to an embodiment of the present disclosure, which is attached to the back surface of an antenna board.

Referring to <FIG>, the cavity filter <NUM> according to an embodiment of the present disclosure may be coupled to a socket <NUM> attached to an antenna board <NUM> as shown in <FIG>, or may be brought into direct contact with the electrode pad formed on the antenna board <NUM> as shown in <FIG>. The cavity filter <NUM> according to the embodiment may be connected to the antenna board <NUM> and the PCB <NUM> at a certain level of contact pressure due to the elastic connector <NUM>, <NUM>, <NUM> to provide RF signal line connections with a constant quality regardless of assembly tolerance.

A plurality of cavity filters <NUM> is used for a base station antenna apparatus <NUM> as the cavity filter <NUM> is mounted on each antenna <NUM>. Precisely and quickly tuning and verifying the cavity filters <NUM> may be an important factor for improving the quality of the base station antenna apparatus <NUM> and reducing the cost.

The cavity filters <NUM> including the terminal units <NUM>, <NUM>, <NUM> with the elastic connectors <NUM>, <NUM>, <NUM> according to with an embodiment of the present disclosure provides a highly reproducible RF signal line connection. It is not necessary to provide a coupling screw or a snap lock member in the RF connection portion, and the elasticity of the elastic connectors <NUM>, <NUM> and <NUM> cause the electrode pad of the PCB board <NUM> to be disposed and the RF connection portion to make close contact with each other so as to be connected to each other and enables quick attachment/detachment thereof.

Next, verification of the cavity filter <NUM> will be described on the assumption that the terminal units <NUM>, <NUM>, <NUM> of the cavity filter <NUM> are arranged in the same direction. Even when the terminal units <NUM>, <NUM>, <NUM> are arranged in the opposite directions, connection of the RF signal lines may be performed quickly and easily. <FIG> illustrate cases of cavity filters <NUM> employing the push pin-type and push ring-type elastic connectors <NUM> and <NUM>, and <FIG> and <FIG> illustrate a case of a cavity filter <NUM> employing the leaf spring-type elastic connector <NUM>.

<FIG> is a plan view showing a test board of a cavity filter according to an embodiment of the present disclosure.

<FIG> is a cross-sectional view showing a test board of a cavity filter according to an embodiment of the present disclosure.

<FIG> and <FIG> illustrate four cavity filters <NUM> mounted on a test board <NUM> of the cavity filter <NUM> and conceptually shows SMA RF connectors <NUM> mounted on the left and right sides. The test board <NUM> of the cavity filter <NUM> is provided with a circular electrode pad that makes an electrical contact with the elastic connectors <NUM> and <NUM>, a plated through via is connected to the rear surface of the test board <NUM> by bypassing the contact areas of the elastic connectors <NUM> and <NUM> of the circular electrode pad, and is then connected to a center terminal of the SMA RF connector <NUM>. A device such as a network analyzer may be connected to the SMA RF connector <NUM> to enable rapid verification of a plurality of cavity filters <NUM>.

<FIG> is a plan view showing a test board of a cavity filter according to an embodiment of the present disclosure, from which a star washer arranged to surround the elastic connector is omitted.

<FIG> is a sectional view showing the test board of the cavity filter of <FIG>.

Referring to <FIG> and <FIG>, the second annular groove <NUM> surrounding the third insertion hole <NUM> and the star washer <NUM> accommodated therein are omitted. The illustrated configuration may further reduce the transverse length of the cavity filter <NUM>. The terminal unit <NUM> may be modified to have various shapes as shown in <FIG>.

<FIG> is a plan view showing a test board of a cavity filter employing a leaf spring-type elastic connector according to an embodiment of the present disclosure.

<FIG> is a cross-sectional view showing the test board of the cavity filter of <FIG> employing a leaf spring-type elastic connector.

Referring to <FIG> and <FIG>, the cavity filter <NUM> having a leaf spring-type terminal unit according to the embodiment allows the terminal unit <NUM> to have an outer diameter smaller than that in the embodiment shown in <FIG> or <FIG>, and is advantageous in reducing the transverse length.

Basically, the test board <NUM> of the cavity filter <NUM> has a wide ground electrode surface formed on both sides. In addition, by arranging a plurality of plated through vias, which pass through the test board <NUM> and surround the circular pad to which the center terminal of the SMA RF connector <NUM> and the elastic connector <NUM> are connected, at proper intervals and pitches, variation in impedance may be minimized.

Hereinafter, an annular groove for accommodating a star washer and a configuration for preventing separation of the star washer will be described.

<FIG> is a conceptual view showing a star washer according to an embodiment of the present disclosure.

<FIG> is a conceptual view showing a process of forming a second annular groove of a dovetail shape for accommodating a star washer according to an embodiment of the present disclosure.

The first case <NUM> of the cavity filter <NUM> has a complex inner shape as it includes a resonance element (not shown), while having a hollow interior. The first case spaced is usually formed of a material containing aluminum or a magnesium alloy by press working.

Referring to <FIG>, the second annular groove <NUM> of the first case <NUM> provided with a vertical wall is processed by a dovetail machining tool <NUM> so as to increase the diameter of the inner edge, thereby forming an accommodating portion for the star washer <NUM>. The inlet of the second annular groove <NUM> having a dovetail shape has the minimum diameter that allows the star washer <NUM> to be contracted and inserted thereinto by elasticity.

<FIG> is a conceptual view showing a second annular groove for accommodating a star washer and a press-fit pin for preventing separation of the star washer and according to an embodiment of the present disclosure.

Referring to <FIG>, a plurality of holes into which a press-fit pin <NUM> is inserted is formed outside the second annular groove <NUM>', and at least three press-fit pins <NUM> with thin heads are press-fitted into the holes to prevent the star washer <NUM> from being separated.

<FIG> is a conceptual view illustrating a second annular groove for accommodating a star washer and caulking for preventing separation of the star washer according to an embodiment of the present disclosure.

Referring to <FIG>, a plurality of holes IS formed outside a second annular groove <NUM>", and a sidewall <NUM> of the second annular groove <NUM>" is recessed toward the star washers <NUM> by caulking to prevent the star washer <NUM> from being separated. The surface may locally rise due to caulking. Accordingly, the reference surface to which the PCB <NUM> is coupled may be formed at a higher position, or a shallow counter bore (not shown) may be formed at the upper end of the caulking hole <NUM> such that the height of the sidewall <NUM> of the second annular groove <NUM>" is lower than the reference surface coupled to the PCB <NUM>.

A conductive paste may be applied between the star washer <NUM> and the second annular groove <NUM>" to ensure good electrical contact of the star washer <NUM> at all times.

The cavity filter <NUM> according to an embodiment of the present disclosure includes RF connection terminal units <NUM>, <NUM>, and <NUM> including elastic connectors <NUM>, <NUM>, and <NUM> formed such that terminals are exposed on both sides or one side in the height direction. Thereby, the thickness of the cavity filter <NUM> may be reduced, thereby implementing a massive MIMO antenna system with a slim and compact stack structure.

Claim 1:
A cavity filter (<NUM>) configured to be used in a base station antenna for mobile communication and configured to be installed on an external member, comprising:
a resonance element;
a first case (<NUM>) configured to be disposed on the external member and containing the resonance element therein; and
a terminal unit (<NUM>, <NUM>) configured to be arranged passing through the first case (<NUM>) to electrically connect an electrode pad of the external member and the resonance element, the terminal unit (<NUM>, <NUM>) being electrically insulated from the first case (<NUM>);
wherein the terminal unit (<NUM>, <NUM>) comprises:
a terminal insertion hole (<NUM>) formed in a lower end surface of the first case (<NUM>) by recessing at least a part of the first case (<NUM>);
a pin member (<NUM>, <NUM>) having a two-stage cylinder shape and comprising a pin portion (<NUM>, <NUM>) disposed in the terminal insertion hole (<NUM>) and having one end connected to the resonance element, and a terminal body portion (<NUM>, <NUM>) extending from an opposite end of the pin portion (<NUM>, <NUM>) and having a diameter larger than a diameter of the pin portion (<NUM>, <NUM>) , the terminal body portion (<NUM>, <NUM>) having a cylindrical hollow socket portion (<NUM>, <NUM>) formed therein with an opening (<NUM>, <NUM>) towards the external member; and
an elastic connector (<NUM>, <NUM>) formed of a conductive material having elasticity and configured to be inserted into the hollow socket portion (<NUM>, <NUM>) and to be disposed between the terminal body portion (<NUM>, <NUM>) and the electrode pad to electrically connect the terminal body portion (<NUM>, <NUM>) and the electrode pad, wherein
the elastic connector (<NUM>, <NUM>) is configured to be compressed to provide a contact pressure to an inner wall of the opening (<NUM>, <NUM>) of the hollow socket portion (<NUM>, <NUM>) and to the electrode pad, whereby the respective contact surfaces of the elastic connector (<NUM>, <NUM>) become elastically deformed when the cavity filter is installed on the outer member.