A high-isolation waveguide polarization separation structure based on electric field and magnetic field microstrip probes

Abstract

This invention discloses a high-isolation waveguide polarization separation structure based on electric and magnetic field microstrip probes. The structure includes a waveguide for transmitting dual-polarized signals; a first microstrip probe and a second microstrip probe, respectively disposed on opposite sides of the waveguide, both extending into the waveguide and placed face-to-face to form a symmetrical structure; the initial distance between the first and second microstrip probes and the short-circuit surface is one-quarter of the waveguide wavelength; the first microstrip probe is an electric field probe used to extract the first polarization signal via electric field coupling; the second microstrip probe is a magnetic field probe used to extract the second polarization signal via magnetic field coupling; the first and second polarization signals are orthogonal. This invention utilizes the difference in physical mechanisms between electric and magnetic field coupling to achieve high isolation, while simultaneously converting the waveguide TE mode to the microstrip line TEM mode. The output port can be directly integrated with planar circuits, offering advantages such as high isolation, low loss, and easy integration. It can effectively replace traditional orthogonal mode couplers in the terahertz band.

Description

Technical Field

[0001] This invention relates to the field of terahertz passive device technology, and in particular to a high-isolation waveguide polarization separation structure based on electric and magnetic field microstrip probes, which is suitable for terahertz communication, radar detection and radiometer systems. Background Technology

[0002] In microwave, millimeter-wave, and even terahertz communication, radar detection, and radiometer systems, dual-polarized signals contain two orthogonal polarization components. At the system receiver, these two orthogonal components need to be separated for subsequent signal amplification, mixing, and processing. Currently, the core device for achieving dual-polarized signal separation is the orthogonal-mode transducer (OMT). Traditional OMTs achieve separation by setting electric and magnetic field branches in the waveguide structure, utilizing the orthogonality of the electric field distributions of the two orthogonal polarization modes within the waveguide. This technology is relatively mature in the millimeter-wave band, providing good port isolation and low insertion loss.

[0003] However, as operating frequencies extend into the terahertz band, traditional orthogonal mode coupler (GMAC) solutions face numerous challenges. First, the small waveguide size in the terahertz band leads to a significant skin effect on metal surfaces, causing conductor losses to increase dramatically with frequency. Traditional GMACs also have complex internal structures, typically including multiple steps, diaphragms, or tapered sections, resulting in longer electromagnetic wave propagation paths and further increasing insertion loss. Second, regarding isolation, traditional GMACs are highly dependent on structural symmetry and mode orthogonality; even minor fabrication asymmetries or assembly errors can cause cross-coupling between two polarization channels, reducing port isolation. Finally, in terms of system integration, the output of a traditional waveguide GMAC is a waveguide interface, while the back-end active circuitry (such as low-noise amplifiers and mixers) typically uses planar transmission lines. An additional waveguide-microstrip transition structure is required between the two, which not only increases system size and link loss but also hinders the miniaturization and integration of terahertz systems.

[0004] Therefore, there is an urgent need for a new scheme for separating dual-polarized signals with low loss, high isolation, and direct integration with planar circuits in the terahertz band. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a high-isolation waveguide polarization separation structure based on electric and magnetic field microstrip probes, aiming to solve the problems of high loss, easy isolation of traditional orthogonal mode couplers in the terahertz band, and difficulty in integration with planar circuits.

[0006] To achieve the aforementioned objectives of the invention, the technical solution adopted to solve its technical problems is as follows: This invention discloses a highly isolated waveguide polarization separation structure based on an electric and magnetic field microstrip probe, comprising: Waveguide (1) is used to transmit dual-polarized signals; The first microstrip probe (2) and the second microstrip probe (3) are respectively disposed on opposite sides of the waveguide (1), and both extend into the waveguide (1) and are placed face to face to form a symmetrical structure; the initial value of the distance between the first microstrip probe (2) and the second microstrip probe (3) and the short surface is one-quarter of the waveguide wavelength. The first microstrip probe (2) is an electric field probe, which is used to extract the first polarization signal by electric field coupling; The second microstrip probe (3) is a magnetic field probe, which is used to extract the second polarization signal through magnetic field coupling; The first polarization signal is orthogonal to the second polarization signal.

[0007] Preferably, the second microstrip probe (3) is a bipolar dipole structure or a ring structure.

[0008] Furthermore, the dielectric substrates of the first microstrip probe (2) and the second microstrip probe (3) are both thinned and are set in the form of suspended microstrip lines to reduce the transmission loss between the two polarization channels and improve the operating bandwidth.

[0009] Furthermore, the thickness of the dielectric substrate is on the order of micrometers, and its material is a low dielectric constant material. The dielectric substrate is fixed to the cavity by beam leads.

[0010] Furthermore, the probe direction of the first microstrip probe (2) is parallel to the electric field distribution direction of the first polarized signal within the waveguide (1), so that it couples only the electric field component of the first polarized signal; the probe direction of the second microstrip probe (3) is parallel to the magnetic field distribution direction of the second polarized signal within the waveguide (1), so that it couples only the magnetic field component of the second polarized signal.

[0011] Furthermore, the structure is also used to realize the conversion from waveguide TE mode to microstrip line TEM mode and the separation of dual-polarized signals; the output ports of the first microstrip probe (2) and the second microstrip probe (3) are in the form of planar microstrip lines, which are used for direct integration with the back-end planar circuit.

[0012] Furthermore, the output ports of the first microstrip probe (2) and the second microstrip probe (3) are oriented in opposite directions, so that the two polarization signals are naturally separated in space.

[0013] Furthermore, the first microstrip probe (2) is connected to a 50Ω microstrip line via a high-impedance line to achieve impedance transformation between the probe and the 50Ω microstrip line and to increase bandwidth.

[0014] Furthermore, the resonant stubs of the second microstrip probe (3) are serrated.

[0015] The present invention also discloses a terahertz receiving system, including the high-isolation waveguide polarization separation structure based on electric and magnetic field microstrip probes as described above.

[0016] Because the present invention adopts the above technical solution, it has the following advantages and positive effects compared with the prior art: 1. High Functional Integration: This invention integrates polarization separation and mode conversion functions into a single device. Traditional solutions require cascading orthogonal mode couplers and waveguide-microstrip transition structures, resulting in long transmission paths and high losses. This invention directly outputs planar microstrip line signals, which can be directly connected to back-end planar circuits such as Schottky diodes or low-noise amplifier chips, eliminating the need for additional transition structures, significantly improving system integration, and reducing link losses.

[0017] 2. High Isolation: This invention utilizes two completely different physical mechanisms—electric field coupling and magnetic field coupling—to extract two orthogonally polarized signals. The electric field probe responds only to the horizontally polarized electric field component, and the magnetic field probe responds only to the vertically polarized magnetic field component. The two coupling methods do not interfere with each other, fundamentally suppressing cross-coupling between channels at the physical mechanism level. Compared with traditional schemes that rely on structural symmetry, this invention can maintain high isolation even with certain processing and assembly errors.

[0018] 3. Low transmission loss: The dielectric substrate of the two probes is thinned and suspended microstrip line, which effectively reduces dielectric loss and conductor loss, while improving the operating bandwidth, making it suitable for high-performance receiving systems in the terahertz band. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 A schematic diagram of the overall structure of a high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe provided in an embodiment of the present invention; Figure 2 This is a side view schematic diagram of a highly isolated waveguide polarization separation structure based on an electric and magnetic field microstrip probe provided in an embodiment of the present invention; Figure 3 The simulation results of the reflection coefficient and isolation of the electric field probe port provided in the embodiments of the present invention are shown in the figure. Figure 4The simulation results of transmission loss are shown in the figure provided for the embodiments of the present invention.

[0020] [Explanation of Key Symbols] 1-Waveguide; 2-First microstrip probe; 3-Second microstrip probe. Detailed Implementation

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] Example 1 Please see Figure 1 and Figure 2 This embodiment provides a high-isolation waveguide polarization separation structure based on electric and magnetic field microstrip probes. The structure includes a waveguide 1, a first microstrip probe 2, and a second microstrip probe 3, wherein: Waveguide 1 is used to transmit dual-polarized signals. In this embodiment, waveguide 1 is preferably a circular waveguide to support two orthogonal polarization modes (such as horizontal polarization and vertical polarization). One end of waveguide 1 is a signal input port, and the other end is a short-circuit surface (i.e., a short-circuit termination).

[0025] The first microstrip probe 2 and the second microstrip probe 3 are respectively disposed on opposite sides of waveguide 1 (e.g., arranged 180° opposite each other on the circumference of a circular waveguide). Both probes extend into the internal cavity of waveguide 1 and are placed face-to-face, forming a completely symmetrical geometry. This symmetrical layout helps ensure the performance consistency of the two polarization channels and lays the foundation for high isolation in terms of physical structure. Preferably, the initial distance between the center position of the two probes and the short-circuit surface of waveguide 1 is one-quarter of the waveguide wavelength (e.g., approximately 460 μm in the 243 GHz band), so that the probes are located in the region with strong standing wave field inside the waveguide, thereby obtaining higher coupling efficiency. The phrase "approximately one-quarter of the waveguide wavelength" refers to the allowable deviation range based on the one-quarter wavelength, taking into account processing tolerances and impedance matching requirements, preferably with a deviation not exceeding ±10%.

[0026] The first microstrip probe 2 is an electric field probe. Its probe orientation should be parallel to the electric field distribution direction of the first polarized signal (horizontal polarized signal) within waveguide 1. According to electromagnetic field theory, the electric field probe primarily couples to the electric field components parallel to it. Therefore, the first microstrip probe 2 can efficiently extract the horizontally polarized signal through electric field coupling, while showing almost no response to the electric field components of the vertically polarized signal orthogonal to it.

[0027] The second microstrip probe 3 is a magnetic field probe. It is used to extract the second polarization signal (vertical polarization signal) through magnetic field coupling. To achieve magnetic field coupling, the second microstrip probe 3 is preferably a double-line dipole structure (i.e., a dipole composed of two parallel microstrip lines) or a toroidal structure. The double-line dipole or toroidal structure has a symmetrical geometry, which can form a more ideal and completely symmetrical layout with the electric field probe, further reducing the mutual coupling between the two polarization channels. This structure can be equivalent to a magnetic dipole, mainly coupling the magnetic field component perpendicular to its plane. Therefore, the second microstrip probe 3 can effectively extract the magnetic field component of the vertical polarization signal, while being almost unaffected by the horizontal polarization signal.

[0028] Since the first microstrip probe 2 and the second microstrip probe 3 respond to different physical quantities (electric field and magnetic field) respectively, and the polarization components they respond to are orthogonal to each other, the two coupling mechanisms do not interfere with each other. This suppresses the cross-coupling between the two polarization channels at the physical mechanism level, thereby achieving high isolation. This means that even if there is some structural asymmetry or assembly error, the cross-coupling between the two channels is very weak, thus achieving a port isolation level far higher than that of traditional OMT.

[0029] Please continue reading. Figure 1 and Figure 2To further reduce losses and improve performance, the dielectric substrates of both the first microstrip probe 2 and the second microstrip probe 3 are thinned. In the terahertz band, the substrate thickness is typically on the order of micrometers; for example, a substrate with a thickness of 50 μm is used in this embodiment, and the typical range is 100 μm or less. A thin substrate can effectively reduce parasitic coupling between probes and facilitate wideband matching, while also considering mechanical strength and fabrication feasibility. The substrate can be made of low-loss, low-dielectric-constant materials such as quartz, aluminum nitride, or diamond. Both probes are suspended microstrip lines with a metal layer thickness of 3 μm, meaning the dielectric substrate is not directly in contact with the metal ground but is suspended (e.g., an air cavity below). The dielectric substrate is press-bonded to the cavity using beam leads, and the substrate edge size is slightly smaller than the transmission window by about 10 μm to facilitate assembly and reduce contact stress with the cavity wall. This suspended structure significantly reduces electromagnetic wave transmission loss in the dielectric substrate and reduces parasitic effects caused by substrate modes, thereby further improving the operating bandwidth.

[0030] The probe portion of the first microstrip probe 2 is connected to a 50Ω microstrip line via a high-impedance line with a width of 70μm and a length of 350μm. This high-impedance line facilitates impedance transformation between the probe and the 50Ω microstrip line, improving transmission efficiency and operating bandwidth. These parameters can be adaptively adjusted according to the operating frequency band. The resonant stub of the second microstrip probe 3 (bilinear dipole) is designed in a sawtooth shape. This structure increases the resonant electrical length, optimizes current distribution, thereby improving coupling characteristics and extending bandwidth. The substrates of both probes can be irregularly shaped, retaining only the necessary microstrip line area to minimize the impact on the waveguide's internal field distribution and facilitate assembly.

[0031] like Figure 1 and Figure 2 As shown, the output ports of the first microstrip probe 2 and the second microstrip probe 3 face opposite directions (e.g., extending outwards from the left and right sides of waveguide 1). Since the two probes are located on opposite sides of waveguide 1, their output microstrip lines naturally extend outwards, allowing the two polarization signals to be naturally separated in physical space. This layout eliminates the need for a complex isolation network at the microstrip end, facilitating direct connection to the front end of a dual-channel receiver (such as two low-noise amplifiers or mixer chips). The output ports are planar microstrip lines, allowing for low-loss interconnection with downstream planar circuits such as Schottky diodes and low-noise amplifier chips via gold wire bonding or conductive adhesive. This structure achieves polarization separation and mode conversion simultaneously with a single device, replacing orthogonal mode couplers in the terahertz band.

[0032] In application, the dual-polarized signal is fed into the aperture of waveguide 1. Upon reaching the probe position, the first microstrip probe 2 extracts the horizontal polarization signal through electric field coupling, while the second microstrip probe 3 extracts the vertical polarization signal through magnetic field coupling. The two signals are output through their respective microstrip lines, simultaneously completing the two functions of waveguide TE mode to microstrip line TEM mode conversion and polarization separation.

[0033] Please see Figure 3 and Figure 4 The results are simulations based on the aforementioned structure in the 243 GHz band. Figure 3 The reflection coefficient (S11) and isolation (S21) curves of the electric field probe port are shown. Figure 4 The transmission loss curve is shown. The simulation of this structure mainly focuses on the transmission and reflection parts. Because the waveguide transmitting dual-polarized signals cannot excite perfectly orthogonal signals in full-wave electromagnetic simulation software, the reflection part is simulated using a horn antenna to excite the orthogonal signals, while the transmission part is simulated using a back-to-back structure, resulting in half the loss of a back-to-back structure. The simulation results show that in the 240-250 GHz frequency band, the reflection coefficients of both polarization ports are better than -20 dB, and the transmission loss is less than 0.5 dB. This indicates that the structure of this invention has excellent impedance matching characteristics and low insertion loss, making it fully suitable for high-performance receiving systems in the terahertz band. Those skilled in the art can use other three-dimensional full-wave electromagnetic simulation software (such as CST Microwave Studio) for equivalent verification according to actual needs.

[0034] Example 2 This embodiment provides a terahertz receiving system, including a high-isolation waveguide polarization separation structure based on electric and magnetic field microstrip probes as described in Embodiment 1. After the dual-polarized signal is separated by this structure, the two polarized signals are respectively connected to the low-noise amplifier chip and mixer chip at the back end via gold wire bonding through the planar microstrip line output port to complete signal amplification and down-conversion processing. Since this structure has completed the conversion from waveguide TE mode to microstrip line TEM mode, no additional OMT is required in the system. Its low-noise amplifier or mixer module can be directly used as the RF front-end input module, significantly reducing link loss and system size. The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-isolation waveguide polarization separation structure based on electric and magnetic field microstrip probes, characterized in that, include: Waveguide (1) is used to transmit dual-polarized signals; The first microstrip probe (2) and the second microstrip probe (3) are respectively disposed on opposite sides of the waveguide (1), and both extend into the waveguide (1) and are placed face to face to form a symmetrical structure; the initial value of the distance between the first microstrip probe (2) and the second microstrip probe (3) and the short surface is one-quarter of the waveguide wavelength. The first microstrip probe (2) is an electric field probe, which is used to extract the first polarization signal by electric field coupling; The second microstrip probe (3) is a magnetic field probe, which is used to extract the second polarization signal through magnetic field coupling; The first polarization signal is orthogonal to the second polarization signal.

2. The high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe according to claim 1, characterized in that, The second microstrip probe (3) is a bilinear dipole structure or a ring structure.

3. The high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe according to claim 1, characterized in that, The dielectric substrates of the first microstrip probe (2) and the second microstrip probe (3) are both thinned and are set in the form of suspended microstrip lines to reduce the transmission loss between the two polarization channels and improve the operating bandwidth.

4. The high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe according to claim 3, characterized in that, The thickness of the dielectric substrate is on the order of micrometers, and its material is a low dielectric constant material. The dielectric substrate is fixed to the cavity by beam leads.

5. The high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe according to claim 1, characterized in that, The probe direction of the first microstrip probe (2) is parallel to the electric field distribution direction of the first polarized signal in the waveguide (1) so that it only couples the electric field component of the first polarized signal; the probe direction of the second microstrip probe (3) is parallel to the magnetic field distribution direction of the second polarized signal in the waveguide (1) so that it only couples the magnetic field component of the second polarized signal.

6. The high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe according to claim 1, characterized in that, The structure is used to realize the conversion from waveguide TE mode to microstrip line TEM mode and the separation of dual-polarized signals; the output ports of the first microstrip probe (2) and the second microstrip probe (3) are in the form of planar microstrip lines, which are used to directly integrate with the back-end planar circuit.

7. The high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe according to claim 6, characterized in that, The output ports of the first microstrip probe (2) and the second microstrip probe (3) are oriented in opposite directions, so that the two polarization signals are naturally separated in space.

8. The high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe according to claim 1, characterized in that, The first microstrip probe (2) is connected to a 50Ω microstrip line via a high-impedance line to achieve impedance transformation between the probe and the 50Ω microstrip line and to increase bandwidth.

9. The high-isolation waveguide polarization separation structure based on an electric and magnetic field microstrip probe according to claim 1, characterized in that, The resonant stubs of the second microstrip probe (3) are serrated.

10. A terahertz receiving system, characterized in that, Including the high-isolation waveguide polarization separation structure based on electric and magnetic field microstrip probes as described in any one of claims 1 to 9.

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