Patent Description:
A branch line coupler is widely used in various kinds of circuits and systems as a basic component, such as a balanced mixer, a balanced amplifier, a power divider, etc..

In some scenarios, for example, in high frequency applications, a size of the branch line coupler is small, and therefore can be integrated onto the surface of a printed circuit board (PCB). Consequently, the branch line coupler can be designed by a single layer PCB or multilayer PCBs.

Further, <CIT> refers to a four-port two branch coupler constructed in stripline or microstrip media having an input port and a pair of output ports.

Further, <CIT> refers to a directional coupler.

The above mentioned problem is solved by the subject matter of the independent claims. Further implementation forms are provided in the dependent claims. In a first aspect, a branch line coupler is provided. The branch line coupler comprises four resonators, i.e., a first resonator, a second resonator, a third resonator, and a fourth resonator. Each of the first resonator, the second resonator, the third resonator, and the fourth resonator comprises an inductor (or an inductor element) and a capacitor (or a capacitor element). The inductor and the capacitor are connected in parallel. The inductor and the capacitor are grounding. The first resonator and the second resonator are coupled by a first coupling, the second resonator and the third resonator are coupled by a second coupling, the third resonator and the fourth resonator are coupled by a third coupling, and the fourth resonator and the first resonator are coupled by a fourth coupling. Thus, the branch line coupler has a better grounding condition, passive intermodulation performance can be improved when a signal is transmitted.

The branch line coupler further comprises four ports, i.e., a first port, a second port, a third port, and a fourth port. The first port is coupled to the first resonator and receives an input signal. The second port is coupled to the second resonator and outputs a direct signal derived from the input signal. The third port is coupled to the third resonator and outputs a coupled signal derived from the input signal. The fourth port is coupled to the fourth resonator and is an isolated port.

In a first possible implementation of the branch line coupler according to the first aspect, each one of the four coupling comprises a capacitive coupling. In an alternative example not covered by the claims, each one of the four coupling may comprises an inductive coupling. The capacitive coupling or the inductive coupling may generate a ninety degree phase difference in a signal passing from a resonator and another resonator which are coupled by the capacitive coupling or the inductive coupling. Accordingly, the direct signal outputted at the second port will be substantially ninety degree phase-shifted with respect to the coupled signal outputted at the third port. Therefore, the branch line coupler can support a beam forming transmission in a wireless communication.

In a second possible implementation of the branch line coupler according to the first aspect and above implementation, each one of the four ports is connected with a port coupling. The port coupling may couple the each port and a corresponding resonator. The port coupling may transform a port impedance of a port to an internal impedance of a transmission line, which is formed by a coupling between two adjacent resonators in the branch line coupler.

In a third possible implementation of the branch line coupler according to the second implementation, the port coupling may comprise an inductive coupling. In an example, a port may be coupled to a corresponding resonator by an inductor. Optionally, each of the four ports may be connected to a grounding capacitor.

Alternatively, the port coupling may comprise a capacitor coupling. In an example, a port may be coupled to a corresponding resonator by an inductor. Optionally, each of the four port may be connected to a grounding inductor.

For the branch line coupler where each port is connected to a grounding capacitor or a grounding inductor, the grounding capacitor and the inductor, or the grounding inductor and the capacitor may form a band pass filter, which can expand the frequency range of the input signal. Therefore, the bandwidth supported by a wireless system can be expanded.

Each of the four resonators comprises a resonator. The four resonators are formed by a body and a grounded element, each one of the four resonators includes a capacitor element, with a first portion of the capacitor element comprising at least a portion of the body and with a second portion comprising at least a portion of the grounded element; an inductor element connected to the capacitor element in parallel, with the inductor element comprising at least a portion of the body and extending to the grounded element. The resonator comprises a metal case, which is grounded, and one or more distributed conductor that can conducting a wireless signal. The inductor in the resonator refers to a distributed inductor, which is formed by one or more distributed conductors. The capacitor in the resonator refers to a distributed capacitor, which is formed by one or more distributed conductors and the metal case. The metal case is grounded. Due to the branch line coupler comprises resonators, particularly, the inductor and capacitor of the resonator are formed by conductors and the metal case, the grounding condition is improved significantly, PIM performance can get more improvements, which causes higher wireless communication quality.

The branch line coupler further comprises isolation component in the metal case. The isolation component has two ends and both the two ends are connected to the metal case. The isolation component may isolate a coupling between the first resonator and the third resonator, and a coupling between the second resonator and the fourth resonator. With the application of the isolation component, the branch line coupler can be avoided to be out of work and the precision of the branch line coupler can be improved.

In a further possible implementation of the branch line coupler according to the first aspect and the above implementations, the first coupling and the third coupling have a first coupling strength, the second coupling and the fourth coupling have a second coupling strength, and the second coupling strength equals the first coupling strength divided by <MAT>.

In a second aspect, an active antenna system is provided. The active antenna system comprises a branch line coupler according to the first aspect and its implementations and a frequency selecting component connected to the branch line coupler. The frequency selecting component input a signal, which is selected by the frequency selecting component, to the branch line coupler at the first port of the branch line coupler. The branch line coupler outputs the direct signal at the second port and the coupled signal at the third port. The active antenna system may be used for advanced beam forming (ABF).

In a first possible implementation of the active antenna system according to the second aspect, the frequency selecting component comprises a filter or a diplexer. In some examples, the frequency selecting component is made to form a metal cavity. Therefore, the frequency selecting component can be connected to the branch line coupler easily because both the frequency selecting component and the branch line coupler are metal cavities. Alternatively, the frequency selecting component and the branch line coupler may be made in a same metal cavity. Therefore, the fabrication cost can be reduced.

In a second possible implementation of the active antenna system according to the second aspect and the first possible implementation of the second aspect, the active antenna system further comprises an antenna. The direct signal and the coupled signal are transmitted to the antenna. Optionally, the branch line coupler may receive a signal from the antenna at an input port, and outputs a direct signal and a coupled signal at two output port to the frequency selecting component. Therefore, high quality can be realized for the signal transmitting and receiving.

In a third aspect, a base station is provided. The base station comprises an active antenna system according to the second aspect and its implementations, and a baseband unit. The baseband unit may comprise a baseband processor. The baseband processor outputs a signal to the active antenna system, and can receive a signal from the active antenna system. With the implementation of the active antenna system, which incorporates the branch line coupler described above, the wireless communication quality of the base station is improved and the fabrication cost can also be reduced accordingly. Moreover, the bandwidth of the system frequency can be expanded and more traffic throughput can be supported.

For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:.

The embodiments of <FIG> are compatible with the invention, but do not show all claimed technical features. The embodiments of <FIG> fall under the scope of the claims.

The structure, manufacture and use of the presently embodiments are discussed in detail below. The specific embodiments discussed are merely illustrative of specific ways to make and use the disclosure, and do not limit the scope of the disclosure.

<FIG> is a diagram of prior art a branch line coupler <NUM>. The prior art branch line coupler <NUM> comprises four transmission lines, i.e., two main transmission lines (also known as horizontal parallel transmission lines) L1 and L2, and two branch lines (also known as vertical parallel lines) L3 and L4. The two main transmission lines L1 and L2 are connected by the two branch lines L3 and L4. The four transmission lines L1-L4 are also known as the four arms of the branch line coupler <NUM>. Each one of the two branch lines L3 and L4 has a characteristic impedance equal to Z<NUM>. Each one of the two main transmission lines L1 and L2 has a characteristic impedance equals to <MAT>. Each line of the four transmission lines L1-L4 has a length equal to a quarter-wavelength λ/<NUM>, where λ represents a wavelength.

The branch line coupler <NUM> has four ports, i.e., a first port (port <NUM>), a second port (port <NUM>), a third port (port <NUM>), and a fourth port (port <NUM>). The four ports L5-L8 can be connected to electrical transmission lines, cables, or other electrical conductor elements. One port is an input port, two ports are output ports, and the remaining one port is an isolated port. The branch line coupler <NUM> may split a signal inputted from the input port into two output ports. A power of the signal inputted from the input port may be equally divided between the output ports, and the signals at the two outputs have a <NUM> degree phase difference (or phase shift) with respect to each other. For example, as shown in <FIG>, the port <NUM> may be an input port, the ports <NUM> and <NUM> are output ports, and the port <NUM> is an isolated port. A power signal is inputted to port <NUM> and is split into the two output ports <NUM> and <NUM>. In an example of the port <NUM> is an input port, the port <NUM> receives an input signal, a signal derived from the input signal is outputted from the port <NUM>, and a signal derived from the input signal is outputted from the port <NUM>. The signal outputted from the port <NUM> is transmitted through the main transmission line L1 directly, thus, the signal outputted from the port <NUM> is also referred to a direct signal. The signal outputted from the port <NUM> is transmitted through the branch transmission line L4, the signal outputted from the port <NUM> is also referred to a coupled signal.

Each port may be coupled to a transmission line of a characteristic impedance Z<NUM>. The transmission lines L5, L6, L7, and L8 have a same characteristic impedance as the characteristic impedance of the branch lines L3 and L4.

The branch line coupler in the present disclosure also refers to a branch line hybrid, a ninety degree (<NUM>°) hybrid coupler, a hybrid, and so on.

<FIG> is a diagram of a branch line coupler <NUM> according to an embodiment. The branch line coupler <NUM> comprises four resonators R1-R4, i.e., a first resonator R1 <NUM>, a second resonator R2 <NUM>, a third resonator R3 <NUM>, and a fourth resonator R4 <NUM>. A pair of adjacent resonators are coupled by a coupling, the coupling between two resonators can produce a ninety degree phase difference between the two resonators. Four resonators are coupled to realize a branch line coupler in embodiments of the present disclosure.

A branch line coupler <NUM> may be widely used in various kinds of circuits and systems as a basic component. As an important component of an active antenna system (AAS), the branch line coupler <NUM> may substantially affect the performance of the AAS. The present application discloses embodiments of a branch line coupler <NUM> that has a high performance and that with less fabrication complexity.

The branch line coupler <NUM> further comprises port <NUM><NUM>, port <NUM><NUM>, port <NUM><NUM>, and port <NUM><NUM>. The branch line coupler <NUM> can advantageously spilt an input signal into signals at two output ports. The branch line coupler <NUM> can advantageously spilt the input signal equally between the two output ports. The signal at the second output port will be substantially ninety degree phase-shifted with respect to the signal at the first output port. Any of the four ports <NUM>-<NUM><NUM>-<NUM> can be an input port, and the other two ports are output ports. The remaining one is termed an isolated port. Port <NUM><NUM> is coupled to the first resonator R1 <NUM> by a first port coupling kp1 <NUM>. Port <NUM><NUM> is coupled to the second resonator R1 <NUM> by a second port coupling kp2 <NUM>. Port <NUM><NUM> is coupled to the third resonator R3 <NUM> by a third port coupling kp3 <NUM>. Port <NUM><NUM> is coupled to the fourth resonator R4 <NUM> by a fourth port coupling kp4 <NUM>.

The first resonator R1 <NUM> is coupled to the second resonator R2 <NUM> by a first coupling k12 <NUM>. The second resonator R2 <NUM> is coupled to the third resonator R3 <NUM> by a second coupling k23 <NUM>. The third resonator R3 <NUM> is coupled to the fourth resonator R4 <NUM> by a third coupling k34 <NUM>. The fourth resonator R4 <NUM> is coupled to the first resonator R1 <NUM> by a fourth coupling k41 <NUM>.

In one example, a port impedance Z<NUM> of the ports <NUM>-<NUM><NUM>-<NUM> may be 50Ω because this value is the most commonly used in industry. Z<NUM> is not limited to a specific value and may also be set to other values based on the actual requirements. The coupling k23 <NUM> and the coupling k41 <NUM> have a characteristic impedance equal to the internal impedance Zi, and the coupling k12 <NUM> and the coupling k34 <NUM> have a characteristic impedance equal to <MAT>. The port couplings kp1-kp4 <NUM>-<NUM> may generate an impedance match between the port impedance Z<NUM> and an internal impedance Zi of the branch line coupler <NUM>, such as transforming the internal impedance Zi to the port impedance Z<NUM>. Zi may be equal to or less than Z<NUM>.

The port <NUM><NUM> receives an input signal. A direct signal is outputted from the port <NUM><NUM>, with the direct signal derived from the input signal. A coupled signal is derived from the input signal and is outputted form the port <NUM><NUM>.

In embodiments of the present disclosure, each one of the resonators R1-R4 <NUM>-<NUM> resonates at a particular frequency or frequency band when an electromagnetic signal at the frequency or frequency band is inputted to the resonator. In the branch line coupler <NUM>, each of the four resonators R1-R4 <NUM>-<NUM> may resonate at substantially the same frequency or frequency band. Through proper design of the four resonators R1-R4 <NUM>-<NUM>, the branch line coupler <NUM> can be constructed to operate at a desired frequency or frequency range.

A resonator in some examples can comprise a hollow region in an electrically conductive material. For example, the hollow region can be filled with air, a specific gas, or a substantial vacuum. Alternatively, the resonator may comprise a hollow region filled with a dielectric or non-conductive material. It should be understood, however, that the resonant frequency of a resonator can be adjusted or varied to some degree, such as by varying the size and/or shape of the cavity. For example, a cavity may include movable or adjustable walls, wherein the cavity size or shape can be varied in order to affect the resonant frequency.

<FIG> is a diagram of a resonator <NUM> in an embodiment. Each of the resonators R1-R4 <NUM>-<NUM> may be represented by an equivalent electrical circuit comprising an inductor (or an inductor element) <NUM> and a capacitor (or a capacitor element) <NUM>, wherein the inductor and capacitor elements form an electronic resonator circuit. The resonator R1 <NUM> may be represented as an inductor <NUM> and a capacitor <NUM>, connected in parallel. Each of the inductor and the capacitor has two ends and one of the two ends is a grounding end, i.e., the end is connected to a ground. For instance, both the inductor <NUM> and the capacitor <NUM> have a grounding end. In an example, the ground is a reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct or indirect physical connection to the earth. An inductor having a grounding end may be referred to a grounding inductor, and a capacitor having a grounding end may be referred to a grounding capacitor. This grounding aspect beneficially reduces passive intermodulation (PIM) in the branch line coupler <NUM>, and will be discussed in more detail below. In an example, a resonance frequency f of the resonators R1-R4 <NUM>-<NUM> may be set according to an equation: <MAT>, where L represents a value of inductance of the inductor <NUM> in Henrys and C represents a value of capacitance of the capacitors <NUM> in Farads.

In some examples, the four resonators R1-R4 <NUM>-<NUM> are formed by a body and a grounded element. Each of the resonators R1-R4 <NUM>-<NUM> comprise a capacitor element, a first portion of the capacitor element comprises at least a portion of the body and a second portion comprises at least a portion of the grounded element. Each of the resonators R1-R4 <NUM>-<NUM> further comprises an inductor element connected to the capacitor element in parallel, the inductor element comprises at least a portion of the body and extends to the grounded element. In an example, the grounded element may include a metal case (or electrically conductive case or cavity), or a conductor connected to the metal case. The body includes an integral component in the metal case, or multiple components connected with each other, or discrete components inside the metal case.

In embodiments of the present disclosure, an inductor is a passive electrical component that stores energy in a magnetic field when electric current flows through the inductor, wherein the amount of energy stored by the magnetic field is quantified as inductance. An inductor opposes changes in electrical current. The inductance measure is the ratio of the voltage to the rate of change in current. It should be understood that the component may comprise multiple distributed elements or components, wherein the distributed elements or components may combined together to work as the inductor <NUM>. For example, each of two metal conductors possesses inductance, where the two metal conductors are connected to each other as a whole and work as an inductor <NUM>. The inductor <NUM> formed by multiple components may be referred to a distributed inductor <NUM>. In some embodiments, the inductor <NUM> may therefore comprise a metal conductor that may possess inductance when a signal passes through, such as a metal wire, a metal piece, or a coil. The metal conductor generates self-inductance in the presence of a signal. In an example, the signal may comprise a high frequency signal, such as a signal with a frequency above <NUM>. It should be noted that the frequency is not limited to the example.

A capacitor <NUM> in the embodiments refers to a passive electrical component that stores energy in an electric field when a voltage potential exists across the capacitor <NUM>, wherein the amount of energy stored by the electric field is quantified as capacitance. The capacitor <NUM> will conduct a current through itself when a time-varying voltage is applied. The capacitive coupling is the transfer of a signal between the two conductors by means of displacement current induced by an electric field. The capacitor <NUM> may comprise a pair of conductors separated by a gap or by an electrical insulator material. The insulator may be air or any other electrical insulating material. The capacitor <NUM> may comprise distributed elements or components, namely, multiple distributed elements or components may be additive and may generate a desired capacitance value. In the embodiments of the present disclosure, the capacitor <NUM> is formed by distributed components or elements, and can be referred to as a distributed capacitor <NUM>.

In some examples, the components forming the inductor <NUM> and the capacitor <NUM> include an electrically conductive case and multiple electrically conductive components. The electrically conductive components are placed inside the electrically conductive case, wherein some of the electrically conductive components connect to the electrically conductive case and some of the electrically conductive components are not connected to the electrically conductive case. The electrically conductive components may form one or more inductors <NUM>. There is a gap or space between the electrically conductive components and the electrically conductive case, or between the electrically conductive components and an electrically conductive component that is connected to the electrically conductive case. A resonator formed by such inductor(s) and capacitor(s), within the cavity of the metal case <NUM>, may be referred to as a cavity resonator (see <FIG>).

In one example, the resonators R1-R4 <NUM>-<NUM> may be constructed from a quarter-wave coaxial resonator, with one end of the center conductor coupled to ground.

Referring again to <FIG>, the first resonator R1 <NUM> and the second resonator R2 <NUM> are coupled by a coupling k12 <NUM>, the second resonator R2 <NUM> and the third resonator R3 <NUM> are coupled by a coupling k23 <NUM>, the third resonator R3 <NUM> and the fourth resonator R4 <NUM> are coupled by a coupling k34 <NUM>, and the forth resonator R4 <NUM> and the first resonator R1 <NUM> are coupled by a coupling k41 <NUM>.

The couplings k12 <NUM>, k23 <NUM>, k34 <NUM>, and k41 <NUM> can successively introduce <NUM> degree phase shifts between the successive connected resonators. Namely, the coupling k12 <NUM> can introduce a <NUM> degree phase difference between the resonators R1 <NUM> and R2 <NUM>, the coupling k23 <NUM> can introduce a <NUM> degree phase difference between the resonators R2 <NUM> and R3 <NUM>, the coupling k34 <NUM> can introduce a <NUM> degree phase difference between the resonators R3 <NUM> and R4 <NUM>, and the coupling k41 <NUM> can introduce a <NUM> degree phase difference between the resonators R4 <NUM> and R1 <NUM>. Thus, the coupling k12 <NUM> causes a ninety degree phase difference in a signal flowing from the resonator R1 <NUM> and the resonator R2 <NUM>. The coupling k23 <NUM> causes a ninety degree phase difference in a signal flowing from the resonator R2 <NUM> and the resonator R3 <NUM>. The coupling k34 <NUM> causes a ninety degree phase difference in a signal flowing from the resonator R2 <NUM> and the resonator R3 <NUM>. The coupling k41 <NUM> causes a ninety degree phase difference in a signal flowing from the resonator R4 <NUM> and the resonator R1 <NUM>.

Coupling strength of the couplings k12 <NUM>, k23 <NUM>, k34 <NUM>, and k41 <NUM> may be set according to a coupling coefficient. The coupling coefficient is a dimensionless value that characterizes interaction of the two resonators. In one example, the coupling strength of the coupling k12 <NUM> equals the coupling strength of the coupling k34 <NUM>, while the coupling strength of the coupling k23 <NUM> equals to the coupling strength of the coupling k41 <NUM>. In this embodiment, the coupling strength of the coupling k23 <NUM> and k41 <NUM> equals the coupling strength of the couplings k12 <NUM> or k34 <NUM> divided by <MAT>. With stronger coupling strength, a wider operational bandwidth can be achieved. The bandwidth, which can also be referred to as an impedance bandwidth, refers to a range of frequencies over which a given return loss can be maintained. The bandwidth is typically paired with a given return loss or voltage standing wave ratio (VSWR) value.

The coupling between a pair of adjacent resonators may comprise an impedance inverter, which is also known as a K-inverter. Adjacent resonators may be coupled by an inductive coupling, which refers to a coupling through an inductance linked by a common changing magnetic field. The coupling between a pair of resonators optionally may comprise a capacitive coupling. The capacitive coupling refers to a coupling or connection by means of a device that possesses a capacitance effect, such as a capacitor, wherein the electrical interaction between two resonators is caused by a capacitance effect between them.

In this embodiment, the port couplings kp1-kp4 <NUM>-<NUM> may comprise an inductive coupling. Alternatively, the port couplings kp1-kp4 <NUM>-<NUM> may comprise a capacitive coupling. In some examples, in the inductive coupling, a voltage of a signal leads a current of the signal by ninety degrees. Conversely, in a capacitive coupling embodiment, the voltage lags the current by ninety degrees.

The interaction of mechanical components generally causes the nonlinear elements, especially anywhere that two different metals come together. Junctions of dissimilar materials are a prime cause. PIM occurs in antenna elements, coax connectors, coax cable, and grounds. Insufficient grounding is a key factor in causing PIM. A better grounding condition may improve the PIM performance. Conversely, a worse grounding condition may cause more PIM and the transmission performance in a network can drop.

The PIM level may be represented by a specific value with a unit of a decibel-milliwatts (dBm). A lower PIM level means a better PIM performance.

A wireless high speed data network uses tightly grouped channels and complex modulation schemes to enable the transmission of vast amounts of data. Such a wireless high speed data network, in association with ultra-sensitive receivers, may face unanticipated but serious capacity losses if the network is disturbed by PIM. PIM is a form of intermodulation distortion that occurs in components normally thought of as linear components, such as cables, connectors and antennas. PIM is interference resulting from the nonlinear mixing of two or more frequencies in a passive circuit. Modulating such radio frequency signals is necessary to transport information, but arbitrary PIM can significantly impact radio frequency signal performance. Unwanted PIM may desensitize one or more receiving channels to such a degree that it causes a very high bit error rate (BER), which in turn reduces network bandwidth. The existence of more than minor levels of PIM may even lead to communications being disrupted. In a worst case scenario, it can even lead to permanently unusable receiver channels.

Loss of already sparse network capacity, caused by PIM, is unacceptable for high volume, high speed wireless data networks. The PIM can happen whenever more than one signal is channeled through a radio frequency path, such as when two or more signals are present in a passive non-linear device or element. The signals will mix or multiply with each other to generate other unwanted signals, with the unwanted signal being related to the original signals.

In embodiments of the present disclosure, since the branch line coupler <NUM> is designed by incorporating the resonators including grounding inductors and grounding capacitors, the couplings k12-k41 between the resonators are used to realize the branch line coupler <NUM>, which provides a better grounding performance. The branch line coupler <NUM> improves PIM performance of the wireless high speed transmission. Furthermore, the design of the branch line coupler may alleviate design complexity and fabrication cost.

<FIG> is a diagram of a branch line coupler <NUM> in an embodiment. The branch line coupler <NUM> is similar to the branch line coupler <NUM> except for four extra grounding components (GC1-GC4) <NUM>-<NUM>. Each of the grounding components <NUM>-<NUM> has a grounding end and an other end that is connected to a corresponding port of port <NUM><NUM>, port <NUM><NUM>, port <NUM><NUM>, or port <NUM><NUM>.

In one example, for a port whose port coupling kp1-kp4 <NUM>-<NUM> is an inductive coupling, each one of the grounding components <NUM>-<NUM> comprises a grounding capacitor. For a port whose port coupling kp1-kp4 <NUM>-<NUM> is a capacitive coupling, each one of the grounding components <NUM>-<NUM> comprises a grounding inductor.

In this embodiment, the grounding components <NUM>-<NUM>, together with the port couplings <NUM>-<NUM>, may form parallel resonance circuits and work as band pass filters in some embodiments. In other embodiments, in an example where the port couplings <NUM>-<NUM> comprise inductors and the grounding components <NUM>-<NUM> comprise grounding capacitors, low pass filters are therefore formed. In yet other embodiments, in an example where the port couplings <NUM>-<NUM> comprise capacitors and the grounding components <NUM>-<NUM> comprise grounding inductors, high pass filters are therefore formed.

<FIG> are diagrams of a branch line coupler <NUM> according to an embodiment. <FIG> is top view of the branch line coupler <NUM> without a cover <NUM>. <FIG> is a cross-sectional diagram AA of the branch line coupler <NUM> from the front. <FIG> is a diagram of internal components of the branch line coupler <NUM>.

<FIG> is a top view of the branch line coupler <NUM>. The branch line coupler <NUM> in the embodiment shown includes the cover <NUM>, walls <NUM>, and a bottom <NUM>. The cover <NUM>, the walls <NUM>, and the bottom <NUM> are made up of metal material and form a metal case, which is grounded. The branch line coupler <NUM> further comprises a body <NUM> comprising four metal pieces <NUM>-<NUM>, with the body <NUM> being located within the metal case. The four metal pieces <NUM>-<NUM> are surrounded, but do not touch, by the walls <NUM> of the metal case.

Four ports <NUM>-<NUM> emerge from the metal case <NUM>, with the four ports <NUM>-<NUM> being electrically coupled to four resonators R1-R4 <NUM>-<NUM> inside the branch line coupler <NUM>. The ports <NUM>-<NUM><NUM>-<NUM> are coupled to the body <NUM> (and therefore are coupled to four resonators R1-R4 <NUM>-<NUM> of the body <NUM>), by port coupling kp1-kp4 <NUM>-<NUM>. Each of the ports <NUM>-<NUM><NUM>-<NUM> may be coupled to a metal piece <NUM>-<NUM> by a corresponding port coupling kp1-kp4 <NUM>-<NUM>. The port couplings kp1-kp4 <NUM>-<NUM> in some embodiments comprise metal conductors. The port couplings kp1-kp4 <NUM>-<NUM> in some embodiments comprise metal conductors which function as inductors when a signal passes through the port couplings kp1-kp4 <NUM>-<NUM>. The port <NUM><NUM> and the metal piece <NUM> are coupled by a metal conductor <NUM>, the port <NUM><NUM> and the metal piece <NUM> are coupled by a metal conductor <NUM>, the port <NUM><NUM> and the metal piece <NUM> are coupled by a metal conductor <NUM>, and the port <NUM><NUM> and the metal piece <NUM> are coupled by a metal conductor <NUM>. In the embodiment shown, the ports <NUM>-<NUM><NUM>-<NUM> pass through apertures in the sidewalls <NUM> and may clamp to or be affixed to the sidewalls <NUM>. Further, the affixing of the ports <NUM>-<NUM> to the sidewalls <NUM> can hold the body <NUM> in position within the metal case, including affixing the body <NUM> at predetermined distances from the metal case for the purpose of completing capacitor components of the branch line coupler <NUM>. Alternatively, the ports <NUM>-<NUM><NUM>-<NUM> are located outside of the walls <NUM>, and the metal conductors <NUM>-<NUM> pass through the walls <NUM> and connect to the ports <NUM>-<NUM><NUM>-<NUM>.

The port couplings kp1-kp4 <NUM>-<NUM> are inductive couplings in some embodiments. Optionally, each of the ports <NUM>-<NUM><NUM>-<NUM> is connected to a grounding capacitor.

The four metal pieces <NUM>-<NUM> are connected to a metal base <NUM> which is connected to the bottom <NUM>. Optionally, the four metal pieces <NUM>-<NUM> and the metal base <NUM> can be an integral unit. The four metal pieces <NUM>-<NUM> are spaced a predetermined distance D1 from the cover <NUM>, and a predetermined distance D2 from the bottom <NUM> (see <FIG>). Each metal piece <NUM>-<NUM> is spaced a predetermined distance D3 from the closest wall <NUM>, as shown in <FIG>. When a signal is transmitted to the metal pieces <NUM>-<NUM>, the signal is also transmitted to the bottom <NUM> through the metal base <NUM>. The metal base <NUM> and each of the metal pieces <NUM>-<NUM> form an inductor in some embodiments. Due to the inductor being formed by multiple inductance-contributing components, such an inductor is also referred to a distributed inductor. In embodiments of present disclosure, the cover <NUM>, the walls <NUM>, and the bottom <NUM> are grounded. Since the metal base <NUM> contacts to the bottom <NUM>, i.e., the exterior metal case of the branch line coupler <NUM>, one end of such inductor is a grounding end.

<FIG> is a diagram of an inductor <NUM> in the first resonator <NUM> in an embodiment. A signal S is imputed at the port <NUM><NUM>, and is transmitted to the metal piece <NUM> through the port coupling <NUM>. The signal S then passes from the metal piece <NUM> to the metal base <NUM>, and finally passes to the bottom <NUM>, which is grounded. The metal piece <NUM> and the metal base <NUM> can generate self-inductance in the presence of the signal S1. Therefore, the metal piece <NUM> and the metal base <NUM> may form the inductor <NUM> of the first resonator <NUM>. Since the metal base <NUM> is connected to the bottom <NUM>, thus, the one end of the inductor <NUM> is grounded, the inductor <NUM> is a grounding inductor. When a signal is passed through the metal pieces <NUM>-<NUM> and the metal base <NUM>, grounding inductors of the second to fourth resonators <NUM>-<NUM> can be similarly formed.

The four metal pieces <NUM>-<NUM> and the cover <NUM>, the bottom <NUM>, and/or the walls <NUM> may also form different grounding capacitors. Such a capacitor may be referred to as a distributed capacitor. The metal piece <NUM> can form capacitor elements with respect to the cover <NUM>, the bottom <NUM>, or the wall <NUM> at the left side of <FIG>. The metal piece <NUM> can form a capacitor element by forming a small gap (or air gap) between two conductive plates or bodies, wherein electrical energy is stored and discharged due to electric potential between the two conductive plates or bodies. In some examples, the predetermined distance D1, D2, or D3 may be multiple mils or more than <NUM> mils (a mil is a length unit equal to a thousandth of an inch). It should be noted that embodiments of the present disclosure do not limit the specific length of the predetermined distance D1, D2, or D3. Alternatively, a distance D3 between a metal piece and the wall may be different from another distance D3 between another metal piece and the wall.

Similarly, the metal piece <NUM> can form capacitor elements with respect to the cover <NUM>, the bottom <NUM>, or the wall <NUM> at the back side in the figure. The metal piece <NUM> can form capacitor elements with respect to the cover <NUM>, the bottom <NUM>, or the wall <NUM> at the right side in the figure. The metal piece <NUM> can form capacitor elements with respect to the cover <NUM>, the bottom <NUM>, or the wall <NUM> at the front side in the figure. Each one of the metal pieces <NUM>-<NUM> can therefore comprises one portion or end of a capacitor element, and the cover <NUM>, the bottom <NUM>, or the wall <NUM> comprise another portion or end.

<FIG> is a diagram of a capacitor <NUM> (or a capacitor element) in the first resonator <NUM> in an embodiment. The signal S is inputted at the port <NUM><NUM>, and is transmitted to the metal piece <NUM> through the port coupling <NUM>. The metal piece <NUM> and the cover <NUM> form the capacitor <NUM>, with a gap D1 therebetween. Because the cover <NUM> is grounded, the one (i.e., upper) portion of the capacitor <NUM> is grounded. Thus, the capacitor <NUM> is a grounding capacitor. When a signal is passed through the metal pieces <NUM>-<NUM>, the metal pieces <NUM>-<NUM>, together with the cover <NUM>, may similarly form grounding capacitors of the second to fourth resonators <NUM>-<NUM>. It should be understood that the capacitor <NUM> is just an example, the first resonator <NUM> may comprise more capacitors, such as capacitors formed by the metal piece <NUM> and at least one of the bottom <NUM>, the wall <NUM> at the right side in the figure, or the metal rod <NUM>.

<FIG> is a diagram of a branch line coupler 500b in an embodiment. The branch line coupler 500b is similar to the branch line coupler <NUM> except that each metal piece includes one hole or cavity, i.e., a cavity <NUM> in the metal piece <NUM>, a cavity <NUM> in the metal piece <NUM>, a cavity <NUM> in the metal piece <NUM>, and a cavity <NUM> in the metal piece <NUM>. There may be four metal rods or screws <NUM>-<NUM> connected with cover <NUM> as shown in <FIG>. A diameter of each metal rods <NUM>-<NUM> may be less than a diameter of each cavity <NUM>-<NUM> on the corresponding metal piece <NUM>-<NUM>, so that there is a small space or gap between the metal rod <NUM>-<NUM> and the metal piece <NUM>-<NUM>. Each metal rod <NUM>-<NUM> may be extend at least partially into the cavities <NUM>-<NUM>, but does not contact the sidewall of the cavity. Therefore, a capacitor may be formed by the gap between the metal rods <NUM>-<NUM> and the metal pieces <NUM>-<NUM>. Because the metal rods <NUM>-<NUM> are connected to the cover <NUM>, i.e., one end of the capacitors is a grounding end, such capacitors are therefore grounding capacitors. The metal rods <NUM>-<NUM> may be fixed to the cover <NUM>. Alternatively, the metal rods <NUM>-<NUM> may be adjustable and move up and down with respect to the cover <NUM>, namely, a length of the metal rods <NUM>-<NUM> extending into the cavities <NUM>-<NUM> could be adjusted. It should be understood that the metal rods <NUM>-<NUM> can be used to adjust the resonant frequency of the resonators R1-R4 <NUM>-<NUM>, and therefore affect the operating frequency of the branch line coupler <NUM>. In some embodiments, the metal rods <NUM>-<NUM> include helical threads and can be extended further into or retracted from the cavities <NUM>-<NUM> by rotating the metal rods <NUM>-<NUM>.

<FIG> is a diagram of another capacitor 5012b in the first resonator <NUM> in an embodiment. The signal S is inputted at the port <NUM><NUM>, and is transmitted to the metal piece <NUM> through the port coupling <NUM>. The metal piece <NUM> and the metal rod <NUM> form the capacitor 5012b. Because the metal rod <NUM> is connected to the cover <NUM>, which is grounded, the one portion of the capacitor <NUM> is grounded. Thus, the capacitor 5012b is a grounding capacitor.

It should be understood that the capacitor <NUM> and the capacitor 5012b are two examples. The first resonator <NUM> may comprise more capacitor elements, such as capacitor elements formed by the metal piece <NUM> and at least one of the bottom <NUM>, or the wall <NUM> at the right side in the figure. Each of these capacitor elements may contribute to a desired overall capacitance.

An inductor (or inductors) and a capacitor (capacitors) may form a resonator. Accordingly, four resonators R1-R4 <NUM>-<NUM> of the branch line coupler <NUM> may be formed by the four metal pieces <NUM>-<NUM> and other components. A first resonator R1 <NUM> includes a first distributed inductor (or inductors) and a first distributed capacitor (capacitors) which are connected in parallel. The first distributed inductor comprises the metal piece <NUM> and the metal base <NUM>. The first distributed capacitor comprises the metal piece <NUM>, and at least one of the cover <NUM>, the wall <NUM>, the bottom <NUM>, or the metal rod <NUM>. The first distributed capacitor has one end, i.e., the metal piece <NUM>. At least one of the cover <NUM>, the wall <NUM>, the bottom <NUM>, or the metal rod <NUM> form the other end of the first distributed capacitor. A second resonator R2 <NUM>, a third resonator R3 <NUM>, and a fourth resonator R4 <NUM> can be similarly formed.

<FIG> is a diagram of the first resonator <NUM> in an embodiment. The first resonator <NUM> comprises the inductor <NUM>, which is as shown in <FIG>, and the capacitor <NUM>, which is as shown in <FIG>. The inductor <NUM> and the capacitor <NUM> have a common end, and both the other ends of the inductor <NUM> and the capacitor <NUM> are grounding, namely, the inductor <NUM> and the capacitor <NUM> are connected in parallel and form a parallel LC resonator (or LC circuit, where the letter L represents an inductor, and the letter C represents a capacitor). Optionally, in the case of more capacitors are formed as described above, such as the capacitor 5012b, the multiple capacitors and the inductor <NUM> may form the parallel LC resonator.

It should be noted that for convenience, <FIG> and <FIG> highlight the some components related to the first resonator. It does not mean the branch line coupler <NUM> in <FIG> only comprises these components.

<FIG> is a diagram of an inductive coupling k12 between the first resonator and the second resonator in an embodiment. A signal S is inputted into the metal piece <NUM> through the port coupling <NUM>. A magnetic field is produced when the signal S is flowing through the metal piece <NUM>. The magnetic field crosses the metal piece <NUM>, and the signal can be generated on the metal piece <NUM>. The signal on the metal piece <NUM> can also generate a magnetic field which crosses the magnetic field <NUM>. Therefore, the first resonator <NUM> and the second resonator <NUM> are coupled by inductance. Optionally, a metal conductor <NUM> connects the metal piece <NUM> and the metal piece <NUM>, and can conduct the signal S to the metal pieces <NUM>. The more signals are transmitted to the metal pieces <NUM>, the stronger inductance can be generated. The metal conductor <NUM> also can generate inductance to strength the coupling between the first resonator <NUM> and the second resonator <NUM>. The other two adjacent resonators of the resonators <NUM>-<NUM> can be similarly coupled.

In another example, a signal is input at port <NUM><NUM>, the signal is transmitted to from the metal piece <NUM> to the metal piece <NUM> through the metal conductor <NUM>. Eddy currents are generated on the two metal pieces <NUM> and <NUM>. The eddy current on the metal pieces <NUM> and <NUM> may generates magnetic fields. The two magnetic fields interact with each other and generate a mutual inductance. Therefore, the first resonator R1 <NUM> and the second resonator R2 <NUM> may be coupled by the mutual inductance. Optionally, the metal conductors <NUM>-<NUM> generate self-inductances when a signal is flowing, and a pair of adjacent resonators are coupled by the self-inductances. For instance, the first resonator R1 <NUM> and the second resonator R2 <NUM> are coupled by an inductance produced by the metal conductor <NUM> when signal is passing through the metal conductor <NUM>. Similarly, the second resonator R2 <NUM> and the third resonator R3 <NUM> are coupled by an inductance produced by the metal conductor <NUM>, the third resonator R3 <NUM> and the fourth resonator R4 <NUM> are coupled by an inductance produced by the metal conductor <NUM>, and the fourth resonator R4 <NUM> and the first resonator R1 <NUM> are coupled by an inductance produced by the metal conductor <NUM>.

Alternatively, in an embodiment, the branch line coupler <NUM> does not include the metal conductors <NUM>-<NUM>, which is not shown in the figure, wherein a pair of adjacent resonators may be coupled by the mutual inductance.

The metal conductors <NUM>-<NUM> may be made in a shape of a slot or wedge as shown in <FIG> and <FIG>. Alternatively, the shape of the metal conductors <NUM>-<NUM> may adjust the coupling strength between a pair of adjacent resonators. For example, a thickness of the T may adjust the amount of the signal transmitted from one metal piece to another, which can affect the strength of the magnetic field. Optionally, the inductance and/or the impedance of the metal conductors <NUM>-<NUM> can be adjusted to change the coupling strengthen between two resonators.

The branch line coupler <NUM> further comprises an isolation component <NUM>, such as a metal pillar <NUM>. The isolation component <NUM> is placed among the four resonators R1-R4 <NUM>-<NUM>, and can isolate and prevent a coupling between the first resonator R1 <NUM> and the third resonator R3 <NUM>, and isolate and prevent a coupling between the second resonator R2 <NUM> and the fourth resonator R4 <NUM>. One end of the isolation component <NUM> connects to the cover <NUM> and the other end of the isolation component <NUM> connects to the bottom <NUM>. Namely, the two ends of the isolation component <NUM> are grounded, wherein no cross-couplings can be formed between the first resonator R1 <NUM> and the third resonator R3 <NUM>, and between the second resonator R2 <NUM> and the fourth resonator R4 <NUM>. The isolation component <NUM> prevents inductance or capacitance from being generated, due to the two ends of the isolation components being grounded, or wherein the inductance or capacitance is weak enough so that the inductance or capacitance can be ignored.

Optionally, the ports <NUM>-<NUM><NUM>-<NUM> are connected to a corresponding grounding component GC1-GC4, e.g. a grounding capacitor. As shown in <FIG> and <FIG>, port <NUM><NUM> in some embodiments is connected to a metal cylinder <NUM>, which is received in a receptacle <NUM> formed in a top of a metal conductor <NUM>, and a predetermined space is existed between the metal cylinder <NUM> and the metal conductor <NUM>. The metal conductor <NUM> is connected to the bottom <NUM>. Therefore, the metal cylinder <NUM> and the metal conductor <NUM> form a capacitor, with the metal cylinder <NUM> comprising one end of the capacitor and the metal conductor <NUM> comprising the other end, i.e., a grounding end of the capacitor. Similarly, the metal cylinders <NUM>-<NUM> and the metal conductors <NUM>-<NUM> can form such capacitors.

Optionally, there may be no space between each of the metal cylinders <NUM>-<NUM> and corresponding metal conductors <NUM>-<NUM>. Namely, each of the metal cylinders <NUM>-<NUM> may contact the corresponding metal conductors <NUM>-<NUM>, the metal cylinders <NUM>-<NUM> may be wrapped with an electrical insulator or dielectric material, or the receptacles <NUM>-<NUM> may be covered with an electrical insulator or dielectric. With the electrical insulator or dielectric, even though the metal cylinders <NUM>-<NUM> are positioned close to the metal conductors <NUM>-<NUM>, the signal cannot be directly transmitted between them by electrical conduction. Therefore, a capacitance effect is generated by the metal cylinders <NUM>-<NUM> and the metal conductors <NUM>-<NUM>, namely, distributed capacitors are formed.

<FIG> are diagrams of a branch line coupler <NUM> in an embodiment. The branch line coupler <NUM> is similar to the branch line coupler 500b as illustrated by <FIG> except that the port couplings <NUM>-<NUM> of the branch line coupler <NUM> are capacitive couplings. The cavities <NUM>-<NUM> in <FIG> may also be optional, namely, the metal pieces <NUM>-<NUM> do not have the cavities <NUM>-<NUM>. Optionally, the four ports <NUM>-<NUM><NUM>-<NUM> are connected with grounding components GC1-GC4, such as grounding inductors <NUM>-<NUM>.

In this embodiment, the inductor <NUM> is received in a receptacle <NUM> in the metal piece <NUM>, and a predetermined space exists between the inductor <NUM> and the receptacle <NUM>. Thus, a capacitor is formed between the inductor <NUM> and the metal piece <NUM>. Similarly, the inductors <NUM>-<NUM> and the metal pieces <NUM>-<NUM> can form such capacitors.

Optionally, there may be no space between each one of the inductors <NUM>-<NUM> and corresponding metal pieces <NUM>-<NUM>. Namely, each one of the inductors <NUM>-<NUM> may contact the corresponding metal pieces <NUM>-<NUM>, the inductors <NUM>-<NUM> may be wrapped with an electrical insulator or dielectric material, or the receptacles <NUM>-<NUM> may be covered with an electrical insulator or dielectric. With the insulating material, even though the inductors <NUM>-<NUM> are positioned close to the metal pieces <NUM>-<NUM>, the signal cannot be directly transmitted between them. Therefore, a capacitance effect is generated between the inductors <NUM>-<NUM> and the metal pieces <NUM>-<NUM>.

More details of the branch line coupler <NUM> and the branch line coupler <NUM> are similar to the branch line couplers <NUM> and <NUM> described above.

It is noted that shapes, positions, and sizes of the metal case and the components comprised in the branch line coupler <NUM> are not limited to what are shown in <FIG>, and shapes, positions, and sizes of the metal case and the components comprised in the branch line coupler <NUM> are not limited to what are shown in <FIG>.

<FIG> is a diagram of an active antenna system (AAS) <NUM> according to an embodiment. The AAS <NUM> may be used for advanced beam forming (ABF) in some embodiments. The AAS <NUM> comprises at least one branch line coupler <NUM>, at least one frequency selecting component <NUM>, and an antenna <NUM>. In an example, the frequency selecting component <NUM> may comprise a filter or a diplexer.

The branch line couplers <NUM> may include four resonators, as in the branch line couplers described above. As an example, the branch line coupler <NUM> may comprise the branch line couplers <NUM>, <NUM>-<NUM> as described above.

In operation, a signal is input into the branch line coupler <NUM> from the frequency selecting component <NUM>, at port <NUM> of the branch line coupler <NUM>. Two signals are output at port <NUM> and port <NUM> of the branch line coupler <NUM> and transmitted to the antenna <NUM>. Similarly, another signal may also be input from the frequency selecting component <NUM> at port <NUM> of the branch line coupler <NUM>, and two signals are output at port <NUM> and port <NUM> of the branch line coupler <NUM> and transmitted to the antenna <NUM>. Conversely, the branch line coupler <NUM> can receive a signal from the antenna <NUM> at port <NUM> and transmit two signals at port <NUM> and port <NUM> to the frequency selecting component <NUM>. The branch line coupler <NUM> may also receive a signal from the antenna <NUM> at port <NUM> then transmits two signals at port <NUM> and port <NUM> to the frequency selecting component <NUM>. As a result, the signals to be transmitted on the antenna may have a better PIM performance (i.e. lower PIM levels). For example, the PIM could be lower than -120dBm.

Furthermore, compared with the branch line couplers implemented by a single or multiple PCBs, where the branch line coupler <NUM> comprises resonators, an AAS provided by the embodiments of the present disclosure will have less fabrication complexity and will require less fabrication material. Thus, the fabrication cost is reduced accordingly. For example, the cost could be low as <NUM>% of a cost of the branch line coupler made of multilayer PCBs.

If the branch line coupler <NUM> comprises a grounding capacitor or a grounding inductor at each port, for example, as the embodiments illustrated in <FIG>, <FIG>, and <FIG>, the AAS <NUM> may operate over a wider bandwidth. The bandwidth could be improved from <NUM>% to at least <NUM>% of a central frequency, more traffic throughput can be supported.

Furthermore, insertion loss is another important parameter for evaluating the performance of a branch line coupler. With the application of a branch line couple as provided by the embodiments of the present disclosure, the insertion loss, in an example, is smaller than <NUM> decibel (dB).

The AAS <NUM> as illustrated in <FIG> may be configured for different frequency bands and different numbers of transmitters and receivers. In one example, for a system supporting <NUM> and with <NUM> transmitters and <NUM> receivers (8T8R), four branch line couplers may be included in the AAS <NUM>.

In this embodiment, the frequency selecting component <NUM>, such as the filter and the diplexer may be made in a form of a metal cavity in some examples. Since the branch line coupler <NUM> can also be in a form of a metal cavity, the frequency selecting component <NUM> and the branch line coupler <NUM> can be easily connected in the AAS <NUM> from a manufacture perspective. The manufacture difficulty and cost can be reduced accordingly.

<FIG> is a diagram of a base station <NUM> according to an embodiment. The base station <NUM> comprises a baseband unit (BBU) <NUM> and an AAS <NUM> coupled to the BBU <NUM>. It should be understood that additional components can be included in the base station <NUM>, but are not shown for simplicity. The BBU <NUM> outputs a signal to the AAS <NUM>. The BBU <NUM> can also receive a signal from the AAS <NUM>. The BBU <NUM> may comprise a baseband processor that can generate and transmit signals to the AAs <NUM>, and receive and process signals from the AAS <NUM>. The AAS <NUM> may comprise the AAS <NUM> as described in <FIG>. With the implementation of the AAS <NUM>, which incorporates the branch line coupler described in embodiments of the present disclosure, the wireless transmission quality of the base station <NUM> is improved accordingly.

Although the description has been described in detail, it should be understood that various changes, substitutions and alterations can be made without departing from the scope of this disclosure as defined by the appended claims. Moreover, the scope of the disclosure is not intended to be limited to the particular embodiments described herein, as one of ordinary skill in the art will readily appreciate from this disclosure that processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, may perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

The terminology used in the description of the present disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used in the description of the present disclosed and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. In the embodiments of the present disclosure, "at least one" means one or multiple. The term "multiple" means two or more than two. The term "and/or" describes a relationship between the associated items. The term "and/or" may represent three relationships. For example, "A and/or B" may represent situations of A independently, A and B concurrently, and B independently. Where A and B could be singular or plural. The symbol "/" usually means "or" of the associated items. The expression "at least one item of" or similar expressions may mean any combination of the items, including any combination of singular item, or the plural of items. For instance, at least one of a, b, or c may comprise a, b, c, a plus b, a plus c, b plus c, or a plus b plus c, where a, b, c may be singular, or may be plural.

Claim 1:
A branch line coupler (<NUM>) comprising:
• four resonators (<NUM>, <NUM>, <NUM>, <NUM>) formed by a body and a grounded element, wherein each resonator among the four resonators (<NUM>, <NUM>, <NUM>, <NUM>) comprises:
∘ a capacitor element with a first portion of the capacitor element comprising at least a portion of the body and with a second portion comprising at least a portion of the grounded element, and
∘ an inductor element connected to the capacitor element in parallel, with the inductor element comprising at least a portion of the body and extending to the grounded element,
▪ wherein a first resonator (<NUM>) and a second resonator (<NUM>) among the four resonators (<NUM>, <NUM>, <NUM>, <NUM>) are coupled by a first coupling, the second resonator (<NUM>) and a third resonator (<NUM>) among the four resonators (<NUM>, <NUM>, <NUM>, <NUM>) are coupled by a second coupling, the third resonator (<NUM>) and a fourth resonator (<NUM>) among the four resonators (<NUM>, <NUM>, <NUM>, <NUM>) are coupled by a third coupling, and the fourth resonator (<NUM>) and the first resonator (<NUM>) are coupled by a fourth coupling,
wherein each of the first coupling, the second coupling, the third coupling, and the fourth coupling comprises a corresponding capacitive coupling;
the branch line coupler being characterized in that it further comprises:
▪ a metal case formed by a cover (<NUM>), walls (<NUM>) and a bottom (<NUM>),
▪ an isolation component (<NUM>),
∘ wherein a first end of the isolation component (<NUM>) is connected to the cover (<NUM>) and a second end of the isolation component (<NUM>) is connected to the bottom (<NUM>),
∘ wherein the isolation component (<NUM>) is arranged in a central position among the four resonators (<NUM>, <NUM>, <NUM>, (<NUM>).