Self-biased air waveguide circulator

Abstract

The disclosure is directed at a self-biased air waveguide circulator, in particular for use in a MIMO system, comprising: a guiding chamber having a spherical base shape and at least three ports for inputting and / or outputting electromagnetic signals, and a direction-guiding component disposed along a centre line of the guiding chamber, the centre line having the same distance to any of the ports and the direction-guiding component defining the direction of transmission of an inputted electromagnetic signal.

Description

FIELD

[0001] The present disclosure relates to a self-biased air waveguide circulator.BACKGROUND

[0002] Circulators are essential components in high-frequency and microwave technology, acting as non-reciprocal passive devices that play a crucial role in signal processing. These components enable the directional control of signals, making them indispensable tools in a variety of applications. Circulators are widely used in communication systems, radar technologies, satellite communications, and medical devices such as magnetic resonance imaging (MRI).

[0003] In communication systems, circulators contribute to the efficient use of antennas by separating transmit and receive signals, thereby improving signal quality and efficiency. In radar technology, they facilitate simultaneous transmit and receive functions in radar systems, allowing for more precise detection and processing of target objects. In satellite communications, circulators support isolation and signal separation in complex satellite antenna systems to minimize interference and maximize signal strength.

[0004] Several aspects are important when using circulators. Isolation is a critical aspect of circulator performance, essential for ensuring effective signal separation and minimizing interference. High isolation between the ports of a circulator prevents signals from leaking from one port to another, which is particularly important in applications such as communication systems and radar technology. High isolation allows for the clear separation of transmit and receive paths, thereby enhancing signal clarity and reducing the potential for cross-talk and interference. Moreover, in particular in radar systems, it ensures that the transmitted signal does not interfere with the received signal, which is crucial for accurate target detection and analysis.

[0005] Isolation requirements in radar systems, in particular in radar systems built for automotive applications, are often high and cannot be met by conventional circulators. Moreover, conventional circulators are often bulky and take up a lot of space in such systems.

[0006] Accordingly, there is a need to provide a circulator having improved isolation characteristics and a compact design.

[0007] This need is satisfied by the subject matter of claim 1.SUMMARY

[0008] The present disclosure provides a circulator according to claim 1. are given in the subclaims, the description and the drawings.

[0009] In one aspect, the present disclosure is directed at self-biased air waveguide circulator, in particular for use in a MIMO system, comprising: a guiding chamber having a spherical base shape and at least three ports for inputting and / or outputting electromagnetic signals, and a direction-guiding component disposed along a centre line of the guiding chamber, the centre line having the same distance to any of the ports and the direction-guiding component defining the direction of transmission of an inputted electromagnetic signal.

[0010] The air waveguide circulator is self-biased by using a direction-guiding component disposed within the circulator, wherein the term "self-biased" means that the circulator doesn't need any external component or influence, e.g. an external magnetic bias, in order to be able to set a direction of transmission of an electromagnetic signal, e.g. an electromagnetic wave, inputted at any of the ports. The direction-guiding component may guide the electromagnetic signal from an input port to an output port. In particular, the direction-guiding component may guide the electromagnetic signal in a predetermined direction. The direction-guiding component may solely define to which output port an inputted electromagnetic signal is directed and which port is, in particular simultaneously, isolated. The direction-guiding component may be any kind of magnetically active material generating a magnetic field.

[0011] As the circulator is an air waveguide circulator, i.e. a hollow waveguide circulator, the circulator is configured to transmit electromagnetic signals via the air. Hence, the guiding chamber is essentially hollow. The hollow space inside the circulator may be filled with air or a vacuum which means that the signal transmission essentially takes place in a low-loss medium. The guiding chamber may be made out of any suitable material such as aluminium, copper, silver-plated copper, stainless steel or any other kind of suitable material.

[0012] Usually, an electromagnetic signal provided at an input port of the circulator is directed to an output port of the circulator using the direction-guiding component which sets the direction of transmission, i.e. clockwise or anti-clockwise, wherein the remaining port is for the most part isolated from any signal transmission.

[0013] Directing of electromagnetic signals within a circulator works through the principles of non-reciprocity and magnetically biased operation.

[0014] Circulators are non-reciprocal devices, meaning they allow electromagnetic signals to travel in one direction more effectively than in the opposite direction. This non-reciprocity is crucial for applications like radar systems and communication networks where signal isolation and directionality are required.

[0015] Circulators typically use a magnetic field to induce non-reciprocal behavior. This magnetic field is applied perpendicular to the direction of signal propagation inside the circulator. The interaction between the magnetic field and the electromagnetic waves causes the waves to travel differently depending on their direction of propagation relative to the magnetic field.

[0016] An airwave guide circulator, as disclosed herein, typically has three or more ports. When an electromagnetic signal enters one port, the circulator directs it to the next port in a predetermined sequence, depending on the direction of the magnetic field and the design of the circulator.

[0017] Depending on the strength and direction of the magnetic field the path of the electromagnetic signals can be influenced. This allows them to direct signals from one port to another while isolating signals traveling in the opposite or a different direction. For example, the path of the electromagnetic signal to be transmitted is influenced or determined by adjusting the strength and direction of the magnetic field to the frequency of the transmitted electromagnetic signal. This may be achieved by selecting an appropriate material of the direction-guiding component.

[0018] The electromagnet signals may have a frequency in ranges of 1 GHz to 40 GHz, e.g. in microwave systems, 2 GHz to 30 GHz, e.g. in telecommunication applications, 12-18 GHz (Ku-band) and 26.5-40 GHz (Ka-band), e.g. in satellite communications, 8-12 GHz (X-band), 2-4 GHz (S-band), 4-8 GHz (C-band) and 12-18 GHz (Ku-band) and / or 60 GHz to 90 GHz (E-Band), e.g. in radar systems. The circulator may further be used in an automotive radar system, wherein the frequency of the electromagnetic signal to be transmitted may be between 76 and 81 GHz, in particular between 76 and 77 GHz.

[0019] Achieving high isolation typically involves careful design and material selection to minimize parasitic coupling and to maintain the integrity of the signal pathways. Effective isolation not only improves the performance of the circulator itself but also enhances the overall efficiency and reliability of the system in which it is implemented. In particular, the guiding chamber where the paths of the respective waveguides connected to the circulator are merged is designed to improve the isolation characteristics of the circulator.

[0020] As herein described, the guiding chamber has a spherical base shape, thereby improving isolation characteristic of the circulator. In other words, the guiding chamber has an outer surface wall which runs at least partially along a spherical surface with a predetermined radius. The spherical base shape of the guiding chamber may have a radius of less than 10 mm, less than 5 mm, less than 3 mm or less than 2mm.

[0021] The spherical geometry allows for a more symmetrical distribution of electromagnetic fields within the circulator. This symmetry helps to minimize asymmetrical coupling between ports, thereby improving isolation. The spherical geometry may provide a three-dimensional mirror symmetry in order to enhance the port isolation.

[0022] Unlike circulators with non-spherical geometries that may have sharp edges or corners, a spherical circulator reduces discontinuities in the electric and magnetic fields. This reduction in edge effects lowers the chances of unwanted signal coupling between isolating ports.

[0023] Furthermore, spherical circulators support more uniform propagation of electromagnetic modes compared to non-spherical geometries. This uniform mode distribution helps reduce interactions between different modes traveling through the circulator, contributing to better isolation.

[0024] Moreover, the magnetic field can be more evenly applied and distributed around the spherical path, optimizing its effectiveness in controlling the direction of signal flow and enhancing isolation.

[0025] According to an embodiment, the direction-guiding component is a singly physical unit. I.e. the direction-guiding component has a spatial and physical continuity. The direction-guiding component may be an assembled unit which may comprise physically joined, i.e. connected, components. However, the direction-guiding component does not comprise any external component or bias for inducing a non-reciprocal behavior. In fact, the direction-guiding component itself is capable of providing non-reciprocity without needing any, in particular magnetic, interaction with an external component. Therefore, the need for external components such as external magnet is eliminated resulting in a circulator of reduced size.

[0026] According to an embodiment, the direction-guiding component comprises hard magnetic material, preferably strontium hexagonal ferrite. In particular, the direction-guiding component may comprise any kind of ferrite material. Strontium hexagonal ferrite is a suitable option due to its elevated magnetic anisotropy field ensuring non-reciprocal behavior. However, the direction-guiding component may comprise any kind of ferrite material. The direction-guiding component may additionally comprise hard magnetic materials which are non-ferrite such as SmCo, NdFeB, Aluminium-Nickel-Cobalt or the like.

[0027] In many conventional circulators soft magnetic materials are used which necessitate an external magnet, e.g. a permanent magnet, for inducing non-reciprocity. By using hard magnetic material the need for such external magnets is eliminated. Thus, the size of the circulator can be reduced resulting in a compact design.

[0028] Moreover, the direction-guiding component may be adjusted to the frequency bandwidth of the electromagnetic signals to be transmitted. For example the material of the direction-guiding component may be selected based on the frequency and / or the frequency bandwidth of the electromagnetic signals in order to obtain desired signal transmission and / or isolation characteristics. Hard magnetic materials have specific magnetic properties that can be strongly influenced by the frequency of the passing signals. These materials often have a characteristic resonance frequency at which they work most effectively. The effectiveness of the generated magnetic field depends on the resonance frequency of the material. Outside of this resonance frequency, the magnetic properties of the material can diminish, which can impair the performance of the circulator.

[0029] According to an embodiment, the direction-guiding component has a cylindrical shape and comprises at least two ferrite disks. For example, the direction-guiding component penetrates the guiding chamber at least partially along the centre line of the guiding chamber. The surface of the direction-guiding component may seamlessly transition into the surface of the guiding chamber resulting in a smooth surface structure. Furthermore, a first ferrite disk may be disposed at first end of the cylindrical shaped direction-guiding component and a second ferrite disk may be disposed at a second end of the direction-guiding component. The ferrite disks may induce a magnetic field in order to ensure the desired non-reciprocal behavior of the circulator.

[0030] According to an embodiment, the direction-guiding component may further comprise a polymer base structure. The polymer base structure may comprise Teflon. For example, the base structure of the direction-guiding component may consist of a polymer like Teflon wherein the ferrite disks may be arranged at the ends of the base structure or at predetermined positions along the base structure. The ferrite disks may have a smaller diameter than the diameter of the polymer base structure. Additionally, the height of the ferrite disks, i.e. their expansion in an axial direction, may be significantly smaller than the height of the direction-guiding component. More particular, the height and / or volume of a respective ferrite disk may be three times, 5 times or 8 times smaller than the height and / or volume of the overall direction-guiding component.

[0031] Using a polymer as a base structure provides mechanical stability and support for the ferrite disks to ensure their structural integrity. Furthermore, polymers such as Teflon have high thermal stability and may help manage heat efficiently, protecting the ferrite material from thermal stress. Moreover, they have a very low dielectric loss tangent, leading to minimal signal loss at high frequencies, thereby supporting the efficient transmission of high-frequency signals. Polymers are chemically inert and protect the ferrite material from environmental influences and chemical degradation, extending the circulator's lifespan. Lastly, a polymer may aid in impedance matching to minimize reflections and losses, ensuring efficient signal transmission.

[0032] According to an embodiment, the guiding chamber comprises at least one recess between two adjacent ports. A recess may be a groove in the surface of the guiding chamber extending from an upper section of the guiding chamber to a lower section of the guiding chamber. In other words, the recess may be a deepening, in particular any kind of deepening, within the surface of the guiding chamber. In a cross section of a top view of the circulator such a recess may extend radially inwards, thereby interrupting the circular shape of the guiding chamber.

[0033] Implementing recesses between adjacent ports may improve the isolation characteristics of the circulator. In particular, recesses increase the surface area between two ports, enhancing the scattering of electromagnetic waves. This leads to a reduction in signal transmission between the input port and the isolated port.

[0034] Moreover, electromagnetic bandgap (EBG) structure energy may be reflected in a specified band gap. This effect is based on the EBG phenomenon.

[0035] The EBG phenomenon refers to a property of certain structures or materials that inhibit the propagation of electromagnetic waves within specific frequency ranges. These structures utilize periodic variations in material properties or geometry to block particular wavelengths or frequencies of electromagnetic waves. Such a structure is implemented between adjacent ports by using the prescribed recesses. The structures may be characterized by a periodic arrangement of recesses, e.g. with differing dielectric or magnetic properties. These periodic arrangements, for instance, may create band gaps, where the propagation of electromagnetic waves is prohibited or prevented. The arrangement of recesses may therefore be adjusted to the transmitted electromagnetic signals, i.e. to the specified frequency range of the electromagnetic signals. The periodic nature of the structure may further cause constructive and destructive interference of electromagnetic waves. For specific frequencies, the waves reflected within the structure interfere destructively, preventing the propagation of those frequencies. Similar to semiconductors, where electrons cannot exist in certain energy bands (band gaps), EBG structures may feature frequency ranges (electromagnetic band gaps) where no electromagnetic wave propagation occurs. This may reduce undesired propagation of signals between ports, in particular between ports which are meant to be isolated from each other. What is more, recesses may increase the electrical length between adjacent ports, improving impedance matching and minimizing reflections. This is critical in high-frequency applications to reduce losses and reflections.

[0036] According to an embodiment, the recesses are evenly distributed between two adjacent ports. In particular, the arrangement of recesses between two adjacent port may be symmetrical. For example, two adjacent recesses have a predetermined distance to each other which is the same for any adjacent recesses. The guiding chamber may have two or three recesses between two adjacent ports. However, the guiding chamber may also have more than 3 recesses between two adjacent ports. The guiding chamber may have at least three per physical wavelength of the electromagnetic signal. The guiding chamber may also have a different amount of recesses between different ports. E.g. the guiding chamber may have a first number of recesses between a first port and a second port, the guiding chamber may further have a second number of recesses between the second port and a third port and the guiding chamber may have a third number of recesses between the third port and the first port. However, preferably the guiding chamber has the same amount of recesses between two adjacent ports for any of the ports of the guiding chamber. I.e. the guiding chamber has the same number of recesses between the first and second port, the second and third port as well as the first and third port. In other words, the arrangement of recesses of the guiding chamber may be symmetrical.

[0037] According to an embodiment, the recesses have a corrugated shape. The guiding chamber may have corrugations as electromagnetically soft surfaces. The recesses may also form a corrugated shape. A recess may extend from an upper section of the guiding chamber to a lower section of the guiding chamber wherein the terms "upper" and "lower" may be defined by the two ends of the central line or by the two ends of the direction-guiding component, wherein one end may be an "upper end" and the other end may be a "lower end". Upper may also mean above a middle plane comprising the middle point of the spherical shape wherein the middle plane is perpendicular to the centre line. Accordingly, the term "lower" may mean below said middle plane. In a top view the recesses may appear rectangular, wherein the recesses extend radially inwards. Though the recesses are described to have a corrugated shape, the recesses may comprise any suitable shape.

[0038] According to an embodiment, a depth of the recess is at least 1 / 10, in particular at least 1 / 5, in particular at least 1 / 3 of the radius of the spherical base shape. The term "depth" used herein relates to the radial extension of the recesses. By increasing the depth of the recesses the isolation effect can be maximized. In particular, undesired reflection of the electromagnetic signals can be prevented. The depth of the recesses may also be adjusted to the desired isolation characteristics of the circulator. However, the depth of the recesses should be designed to provide an S-parameter-value of the isolated port corresponding to the isolation of the isolated port which is lower than -30 dB or lower than -35 dB.

[0039] According to an embodiment, the width of the recess is smaller than the minimal distance between two adjacent recesses, in particular two times smaller than the minimal distance between two adjacent recesses or four times smaller than the minimal distance between two adjacent recesses. The term "width" used herein relates to the extension of the recesses in circumferential direction. By reducing the width of the recesses the isolation effect can be maximized. In particular, undesired reflection of the electromagnetic signals can be prevented. The width of the recesses may also be adjusted to the desired isolation characteristics of the circulator. However, the width of the recesses should be designed to provide an S-parameter-value of the isolated port which is lower than -30 dB or lower than -35 dB. It is also possible to have recesses having differing depths and / or widths.

[0040] According to an embodiment, the guiding chamber has a holding section for holding the direction-guiding component, wherein the direction-guiding component is disposed in the holding section. The holding section may be adjusted to the design and / or shape of the direction-guiding component. I.e. the guiding chamber comprises a cavity or a passage running through the guiding chamber for holding or mounting the direction-guiding component.

[0041] According to an embodiment, the guiding chamber comprises holding structures for holding the direction-guiding component within the holding section. The guiding chamber and / or holding section may comprise clips or other connection components to attach the direction-guiding component to the guiding chamber. During a production process the direction-guiding component may therefor be easily attached to the guiding chamber in a safe and reliable manner. Hence, the efficiency of production may be enhanced.

[0042] According to an embodiment, impedance matching is performed using a quarter-wavelength matching technique, wherein the distance between two adjacent ports is designed to be a quarter of a wavelength of the transmitted electromagnetic signal. The quarter wavelength technique may be used for matching the circulator port impedance to the connected waveguide impedance. Impedance matching is crucial in order to ensure that the maximum amount of power is transferred between the ports with minimal loss and to prevent signal reflections that can lead to inefficiencies and potential interference in the system. Proper matching maintains the signal quality by preventing distortion and ensuring that the signal travels as intended through the circulator. Hence, the circulator dimensions may be chosen to ensure that the characteristic impedance matches that of the connected components.

[0043] In order to improve impedance matching, matching stubs may be used. These are short sections of waveguide or resonant structures added to the circulator to adjust the impedance. They can be capacitive or inductive, depending on the nature of the mismatch. Furthermore, the material of the direction defining component, e.g. of the ferrite material, may be selected in order to adjust the magnetic bias field, to achieve proper impedance matching. The ferrite's properties may affect the propagation constants and thus the impedance characteristics of the circulator.

[0044] Furthermore, when an electromagnetic signal travels through the ferrite, it experiences a phase shift proportional to the wavelength and the magnetic field strength. By designing the circulator such that the total phase shift for a round trip (forward and backward) is approximately a quarter wavelength (π / 2 radians or 90 degrees), the circulator ensures that forward and reverse waves interfere constructively in one direction and destructively in the opposite direction.

[0045] The dimensions of the air waveguide, including its cross-sectional dimensions and length, in particular the distance between two adjacent ports, may therefore be determined in such a manner that ensures the correct phase relationship over the operating frequency range.

[0046] According to an embodiment, an S-parameter-value corresponding to the isolation of a respective isolated port is lower than -30 dB, preferably less than -35 dB, for a specified frequency range of the transmitted electromagnetic signals, wherein the S-parameter value S iso is calculated based on the following equation: S iso = − 10 log 10 P leak P in wherein P in is an input power at the port where the electromagnetic signal enters the circulator and P leak is the power that leaks into an unintended port.

[0047] According to an embodiment, an S-parameter-value of the insertion loss corresponding to the amount of signal power lost as the signal passes from one port to the next intended port is higher than -0.25 dB, wherein the S-parameter-value S IL is calculated based on the following equation: S IL = − 10 log 10 P out P in wherein P in is the input power at the port where the electromagnetic signal enters the circulator and P out is the output power at the port where the signal exits the circulator.

[0048] According to an embodiment, the three ports are offset by 120 degrees to each other. The 120-degree offset ensures that each port interacts with the adjacent ports in a specific manner. The physical arrangement of the circulator's ports is designed to maintain precise angular spacing to achieve the desired phase relationships. This spacing is critical for controlling the interference patterns and ensuring proper operation across the circulator's frequency range.

[0049] According to an embodiment, the circulator further comprises connection elements which are connected to the guiding chamber via the at least three ports, wherein the connection elements are configured to connect the ports of the guiding chamber to respective waveguides. The connection elements may be also designed as part of the guiding chamber. For example, the connection elements and the guiding chamber may be formed in one-piece. The connection elements may be made out of the same material as the guiding chamber in order to enhance transmission of the electromagnetic signal. Furthermore, the connection elements may be configured to guide the electromagnetic signals into the guiding chamber via the ports. The connection element may further taper in a peripheral direction, i.e. the cross-sectional surface of the connection elements may shrink in a peripheral, i.e. a radially outwards, direction.

[0050] Another aspect of the invention relates to a MIMO system, in particular a radar system, comprising: at least one transmitter for transmitting an electromagnetic signal, at least one receiver for receiving an electromagnetic signal, at least one transceiver antenna for radiating an electromagnetic signal into an environment and / or receiving an electromagnetic signal from the environment, at least one self-biased air waveguide circulator according to any of the preceding embodiments connected to the at least one transmitter, to the at least one receiver and to the at least one transceiver antenna.

[0051] The foregoing components may be attached to a printed circuit board, e.g. a radar sensor board, of the MIMO system and connected to each other by respective air waveguide channels. The MIMO system may further comprise a processing unit for performing various operations, including filtering, amplification, and digital signal processing, to interpret the received electromagnetic signals accurately. The MIMO system may be configured to determine a distance between the MIMO system and an object in the environment based on the reflected electromagnetic signal. The distance may be determined based on a TOF-method (Time-of-Flight), an FMCW-method (frequency modulated continuous wave) or any other suitable method.

[0052] It is to be noted that the foregoing explanations and embodiments with respect to the circulator may apply to the MIMO system accordingly.DRAWINGS

[0053] Exemplary embodiments and functions of the present disclosure are described herein in conjunction with the following drawings, showing schematically: Fig. 1a flow diagram illustrating an operation of a circulator according to an embodiment of the present disclosure Fig. 2a top view of a circulator according to an embodiment of the present disclosure Fig. 3aa perspective view of a circulator according to an embodiment of the present disclosure Fig. 3ba cross-sectional view of a circulator according to an embodiment of the present disclosure Fig. 4a diagram of a return loss, an insertion loss and isolation of a circulator according to an embodiment of the present disclosure DETAILED DESCRIPTION

[0054] Fig. 1 depicts a flow diagram illustrating an operation of a circulator according to an embodiment of the present disclosure. The circulator 12 comprises a first port 14, a second port 16 and a third port 18.

[0055] A transmitter 20 which generates an electromagnetic signal, is connected to the first port 14 of the circulator 12. An antenna 22, responsible for radiating the signal into the environment or receiving signals from it, is connected to the second port 16. A receiver 24, which processes incoming signals, is connected to the third port 18.

[0056] When the transmitter 20 sends out an electromagnetic signal, it enters the circulator 12 at the first port 14. The circulator 12 is designed using a direction-guiding component 28 comprising a hard magnetic material, e.g. strontium hexagonal ferrite, and a induced magnetic field to create non-reciprocal paths for the electromagnetic signal. Due to this design, the signal from the first port 14 is directed to the second port 16 essentially without leaking to the third port 18. As a result, the signal travels through the air waveguide circulator 12 and exits at the second port 16, where it is radiated into the environment by the antenna 22.

[0057] Conversely, when the antenna 22 receives an electromagnetic signal, this incoming signal enters the circulator 12 at the second port 16. The circulator 12 then routes the signal to the third port 18, directing it to the receiver 24. This ensures that the receiver 24 processes only the signals received from the antenna 22 and not the signals directly from the transmitter 20.

[0058] The circulator's 12 non-reciprocal behavior is crucial for maintaining isolation. The design ensures that signals can flow from the transmitter 20 to the antenna 22 and from the antenna 22 to the receiver 24, but not directly from the transmitter 20 to the receiver 24. In particular, the isolation of the isolated port, i.e. the port which shouldn't receive any signal during a transmission process, is less than -30 dB (S-parameter value) at the specified frequency range of the electromagnetic signal to be transmitted. This directional coupling is achieved by the precise arrangement of the circulator's 12 ports 14, 16, 18, which are typically offset by 120 degrees in a three-port circulator. In a four-port circulator the ports may be offset by 90 degrees, respectively. This arrangement, combined with the quarter-wavelength impedance matching technique, creates the necessary phase and impedance shifts to ensure efficient signal routing and minimal reflections.

[0059] By using the air waveguide circulator 12, the system effectively manages the transmission and reception of signals, ensuring that each component - transmitter 20, antenna 22, and receiver 24 - operates optimally without causing or experiencing interference from the other components.

[0060] Fig. 2 illustrates a top view of a circulator 12 according to an embodiment of the present disclosure. The circulator 12 comprises a guiding chamber 26 having a spherical base shape and three ports 14, 16, 18 for inputting and / or outputting electromagnetic signals and a direction-guiding component 28 comprising a Teflon base structure 30 and strontium hexagonal ferrite disks 32. The direction-guiding component 28 is disposed along a centre line 34 of the guiding chamber 26, the centre line 34 having the same distance to any of the ports 14, 16, 18 and the direction-guiding component 28 defining the direction of transmission of an inputted electromagnetic signal, i.e. to which port a signal entering one of the ports 14, 16, 18 of the circulator 12 is directed.

[0061] The guiding chamber 26 further comprises three recesses 36 between two adjacent ports 14, 16, 18, respectively. The recesses 36 have a corrugated shape and are evenly distributed between two adjacent ports 14, 16, 18 of the circulator 12. The ports 14, 16, 18 are connected to respective connection elements 38, 40, 42 which are connected to the guiding chamber via the at least three ports 14, 16, 18, wherein the connection elements 38, 40, 42 are configured to connect the ports 14, 16, 18 of the guiding chamber 26 to respective waveguides transmitting the electromagnetic signal.

[0062] The recesses 36 of the guiding chamber 26 improve the isolation behavior of the circulator 12. In particular, the recesses 36 increase the surface area between two adjacent ports 14, 16, 18, enhancing the scattering of electromagnetic waves. This leads to a reduction in signal transmission between the input port and the isolated port. Moreover, electromagnetic bandgap structure energy may be reflected in a specified band gap. This may reduce undesired propagation of signals between ports 14, 16, 18. What is more, recesses 36 may increase the electrical length between adjacent ports 14, 16, 18, improving impedance matching and minimizing reflections. This is critical in high-frequency applications to reduce losses and reflections.

[0063] Fig. 3a depicts a perspective view of the circulator 12 of Fig. 2, wherein Fig. 3b depicts a cross-sectional view of the corresponding circulator 12.

[0064] As shown in Fig. 3a, the guiding chamber 26 has a spherical base shape which is interrupted by the ports 14, 16, 18, the connection elements 38, 40, 42 and the recesses 36. The recesses 36 extend from an upper section of the guiding chamber to a lower section of the guiding chamber linearly. Herein, the term "upper" means above a middle plane comprising the middle point of the spherical shape wherein the middle plane is perpendicular to the centre line. Accordingly, the term "lower" means below said middle plane. The radius r of the spherical base shape may be smaller than 5 mm, smaller than 3 mm or smaller than 2 mm. In Fig. 3a the radius r of the spherical base shape is 1.76 mm, wherein a length I of the circulator 12 depicted in Fig. 3a is 7 mm and a width of the circulator 12 is 6 mm. As previously described, the recesses 36 enhance isolation characteristics of the circulator 12.

[0065] Fig. 3b illustrates, in particular, the direction-guiding component 28 and its arrangement within the circulator 12. The direction-guiding component 28 has a cylindrical shape and comprises the Teflon base structure 30 which is penetrating the guiding chamber 26 along the centre line 34 and the ferrite disks 32 which are disposed at opposing ends of the cylindrical direction-guiding component 28. In a cross-sectional view the Teflon base structure 30 has an H-shape wherein the ferrite disks 32 are included in the cavities of the H-shaped structure. The direction-guiding component 28 is further fixed and / or hold within a holding section 44 by using holding structures 46, such as clippers or any other suitable holding structure 46, at the ends of the holding section 44. The holding section 44 is adjusted to the shape of the direction-guiding component 28 so that the direction-guiding component 28 can be incorporated in the guiding chamber 26 seamlessly. For example, the holding section 44 may be a cylindrical shaped passage running through the guiding chamber 26. The holding structures 46 ensures that the direction-guiding component 28 is safely fixed within the guiding chamber 26 and the holding section 44.

[0066] Fig. 4 shows a diagram of S-Parameter-values (in dB) mapped to the frequency (in GHz) for different metrics such as return loss, insertion loss and isolation of a circulator 12 according to an embodiment of the present disclosure. In particular, Fig. 4 illustrates the S-Parameter-values for the metrics return loss S11 at an input port, herein the first port 14, insertion loss S21 between the first port 14 and second port 16 and isolation S31 between the first port 14 and the third port 18.

[0067] Insertion loss refers to the amount of signal power lost as the signal passes from one port to the next intended port. It quantifies how much of the original signal power is dissipated within the circulator 12, rather than being transmitted through to the next port. It is calculated as the ratio of the output power to the input power, expressed in a logarithmic scale. A lower insertion loss value indicates better performance because it means less signal power is lost during transmission.

[0068] The insertion loss (IL) may be calculated using the formula: IL = − 10 log 10 P out P in wherein P in is the input power at the port where the signal enters the circulator 12 and P out is the output power at the port where the signal exits the circulator 12.

[0069] Return loss is the measure of the signal power reflected back to the source due to impedance mismatches in the transmission line or at the interface of the apparatus. Return loss in a circulator refers to the measure of signal power that is reflected back towards the source due to impedance mismatches at the ports 14, 16, 18 of the circulator 12. It quantifies how effectively the circulator 12 transmits the signal without reflecting it back. It is calculated as the ratio of the reflected power to the incident power, expressed in a logarithmic scale. A higher return loss value indicates better performance because it means less signal power is reflected back and more is transmitted through the circulator 12.

[0070] The return loss (RL) may be calculated using the formula: RL = − 10 log 10 P ref P in wherein P in is the input power at the port where the signal enters the circulator 12 and P ref is the reflected power at the same port.

[0071] Isolation refers to the degree to which an RF or microwave component prevents unwanted signal leakage between its ports. Isolation in a circulator 12 refers to the measure of how effectively the circulator 12 prevents signal leakage between its ports that are not intended to communicate. It quantifies the degree to which a signal entering one port is isolated from another port, other than the designated output port. Isolation ensures that signals are directed along the intended paths without interfering with other ports. Higher isolation values indicate better performance, meaning less signal leakage between the unintended ports.

[0072] The isolation (Iso) may be calculated using the formula: Iso = − 10 log 10 P leak P in wherein P in is the input power at the port where the signal enters the circulator 12 and P leak is the power that leaks into the unintended port.

[0073] As illustrated in Fig. 4, for a signal transmission between the first port 14 and the second port 16 the insertion loss S21 between the first port 14 and the second port 16 is almost zero for the specified frequency range of 76 GHz to 77 GHz, wherein the amount of insertion loss is smaller than 0.25 dB. Moreover, the return loss S11 at the first port 14 is smaller than -20 dB for the specified frequency range or in other words the amount of return loss is higher than 20 dB. Lastly, the isolation between the first port 14 and the third port 16 is smaller than -30 dB in the specified frequency range or in other words the amount of isolation is higher than 30 dB with a peak isolation value of around -42 dB. Fig. 4 refers to a signal transmission between the first port 14 and the second port 16 when the third port 18 is to be isolated. However, the same metrics apply to a signal transmission between the second port 16 and the third port 18 when the first port 14 is to be isolated, accordingly.Reference numeral list

[0074] 12circulator 14first port 16second port 18third port 20transmitter 22antenna 24receiver 26guiding chamber 28direction-guiding component 30teflon base structure 32strontium hexagonal ferrite disks 34centre line 36recesses 38-42connection elements 44holding section 46holding structure

Claims

1. Self-biased air waveguide circulator (12), in particular for use in a MIMO system, comprising: a guiding chamber (26) having a spherical base shape and at least three ports (14, 16, 18) for inputting and / or outputting electromagnetic signals, and a direction-guiding component (28) disposed along a centre line (34) of the guiding chamber (26), the centre line (34) having the same distance to any of the ports (14, 16, 18) and the direction-guiding component (28) defining the direction of transmission of an inputted electromagnetic signal.

2. Circulator according to claim 1, wherein the direction-guiding component (28) is a single physical unit.

3. Circulator according to claim 1 or 2, wherein the direction-guiding component (28) comprises hard magnetic material, preferably strontium hexagonal ferrite.

4. Circulator according to any one of the preceding claims, wherein the direction-guiding component (28) has a cylindrical shape and comprises at least two ferrite disks.

5. Circulator according to any one of the preceding claims, wherein the direction defining component further comprises a polymer base structure.

6. Circulator according to any one of the preceding claims, wherein the guiding chamber (26) comprises at least one recess (36) between two adjacent ports (14, 16, 18).

7. Circulator according to claim 6, wherein the recesses (36) are evenly distributed between two adjacent ports (14, 16, 18).

8. Circulator according to any one of claims 6 or 7, wherein the recesses (36) have a corrugated shape.

9. Circulator according to any one of claims 6 to 8, wherein a depth of the recess (36) is at least 1 / 10, preferably at least 1 / 5, more preferably at least 1 / 3 of the radius of the spherical base shape.

10. Circulator according to any one of the preceding claims, wherein the guiding chamber (26) has a holding section (44) for holding the direction-guiding component (28), wherein the direction-guiding component (28) is disposed in the holding section (44).

11. Circulator according to claim 10, wherein the guiding chamber (26) comprises holding structures (46) for holding the direction-guiding component (28) in the holding section (44).

12. Circulator according to any one of the preceding claims, wherein impedance matching is performed using a quarter-wavelength matching technique, wherein the distance between two adjacent ports (14, 16, 18) is designed to be a quarter of a wavelength of the transmitted electromagnetic signal.

13. Circulator according to any one of the preceding claims, wherein an S-parameter-value corresponding to the isolation of a respective isolated port (14, 16, 18) is less than -30 dB, preferably less than -35 dB, for a specified frequency range of the transmitted electromagnetic signals, wherein the S-parameter value S is calculated based on the following equation: S = − 10 log 10 P leak P in wherein Pin is an input power at the port (14, 16, 18) where the electromagnetic signal enters the circulator (12) and Pleak is the power that leaks into an unintended port (14, 16, 18).

14. Circulator according to any one of the preceding claims, wherein the three ports (14, 16, 18) are offset by 120 degrees to each other.

15. Circulator according to any one of the preceding claims, further comprising connection elements (38, 40, 42) which are connected to the guiding chamber (26) via the at least three ports (14, 16, 18), wherein the connection elements (38, 40, 42) are configured to connect the ports (14, 16, 18) of the guiding chamber (26) to respective waveguides.

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