Microwave branch filter device for NV color center ODMR readout and its spurious suppression method

Abstract

The application relates to a microwave branch filtering device for NV color center ODMR reading and a stray suppression method thereof. The microwave branch filtering device comprises a dielectric substrate, the lower surface of the dielectric substrate is provided with a metal grounding layer, and the upper surface of the dielectric substrate is provided with a metal pattern layer. The metal pattern layer comprises filtering resonance units and shaping resonance units. The filtering resonance units comprise two groups, the two groups of filtering resonance units are symmetrically arranged along a symmetry axis, each group of filtering resonance units comprises two filtering resonance units which are symmetrically arranged with each other, the shaping resonance units comprise two, the two shaping resonance units are arranged between the two groups of filtering resonance units, the four filtering resonance units and the two shaping resonance units form a six-order band-pass filter, strong out-of-band suppression is realized on the upper and lower sides of the passband through six-order filtering, spectrum distortion and measurement noise caused by harmonics and stray are effectively reduced, and the advantages of good impedance matching in the passband and enhanced out-of-band reflection are achieved.

Description

Technical Field

[0001] This application relates to the field of quantum measurement technology, and in particular to a microwave branch filter device for NV color center ODMR readout and its stray suppression method. Background Technology

[0002] With the further development of fields such as accelerator physics and power systems, higher requirements are being placed on the precision measurement and reliability of electrical measurements. One of the core technologies for precision electrical measurement and reliability is precision magnetic field measurement technology. Diamond NV color centers, due to their characteristics of room temperature operation, optical readout, and high sensitivity to external magnetic fields, have become an important technical route for current-induced magnetic field measurement, weak magnetic field detection, and vector magnetic field reconstruction.

[0003] In a typical CW-ODMR (continuous wave-optical-probe magnetic resonance) magnetic measurement system, in addition to the optical excitation and fluorescence readout links, a stable microwave link is also required to drive NV electron spin resonance and extract spectral line shift / splitting information related to the magnetic field. However, existing microwave excitation links are often accompanied by high-order harmonics, parasitic components, and reflected standing waves caused by impedance mismatch, which can easily lead to ODMR baseline fluctuations, increased noise, and spectral line distortion, thereby reducing the stability and signal-to-noise ratio of magnetic measurements. Summary of the Invention

[0004] Therefore, it is necessary to address the problem in existing diamond NV center continuous wave-optical detection magnetic resonance (CW-ODMR) magnetic measurement systems, where microwave sources and links are often accompanied by high-order harmonics, parasitic components, and reflected standing waves caused by impedance mismatch, which easily lead to ODMR baseline fluctuations, noise increases, and spectral distortion, thereby reducing the stability of magnetic measurement and signal-to-noise ratio. To address this issue, a microwave branch filtering device and its spurious suppression method for NV center ODMR readout should be provided.

[0005] A microwave branch filter device includes a dielectric substrate, a metal ground layer is disposed on the lower surface of the dielectric substrate, and a metal pattern layer is disposed on the upper surface of the dielectric substrate.

[0006] The metal pattern layer includes a filtering resonant unit and a shaping resonant unit. The filtering resonant unit includes two sets, which are symmetrically arranged along the axis of symmetry. Each set of filtering resonant units includes two mutually symmetrically arranged filtering resonant units. The two filtering resonant units in each set are coupled to each other through a first gap. One of the resonant units in one set is provided with an input port, and one of the resonant units in the other set is provided with an output port.

[0007] The shaping resonant unit includes two units, which are disposed between the two sets of filtering resonant units. The two shaping resonant units are symmetrically arranged along the axis of symmetry and are coupled to each other through a second gap. The two shaping resonant units are respectively coupled to the filtering resonant unit closest to them through a third gap.

[0008] In one embodiment, the filter resonant unit is a quarter-wavelength stepped impedance resonator.

[0009] In one embodiment, the shaping resonant unit is a half-wavelength stepped impedance resonator.

[0010] In one embodiment, each of the filter resonant units includes a first impedance line and a second impedance line connected to each other, the impedance of the first impedance line being less than that of the second impedance line, and each of the shaping resonant units includes a third impedance line and two fourth impedance lines, the impedance of the third impedance line being greater than that of the fourth impedance lines, and the third impedance line being connected to the two fourth impedance lines at its opposite ends.

[0011] In one embodiment, the filter resonant unit includes four units: a first filter resonant unit, a second filter resonant unit, a third filter resonant unit, and a fourth filter resonant unit. The first filter resonant unit has an input port on its first impedance line, and the second impedance line of the first filter resonant unit is coupled to the second impedance line of the second filter resonant unit through the first gap. The first impedance line of the second filter resonant unit is coupled to the third impedance line of one of the shaping resonant units through the third gap.

[0012] The fourth filter resonant unit has an input port on its first impedance line, and the second impedance line of the fourth filter resonant unit is coupled to the second impedance line of the third filter resonant unit through the first gap. The first impedance line of the third filter resonant unit is coupled to the third impedance line of another shaping resonant unit through the third gap.

[0013] In one embodiment, each filter resonant unit satisfies: , The electrical length of the first impedance line is... Let be the electrical length of the second impedance line, and , For the corresponding physical length of the first impedance line or the second impedance line, For the effective dielectric constant, The speed of light in a vacuum. The target center frequency of the filtering device is [the frequency of the filter device]. The wavelength of the filter resonant unit is denoted as .

[0014] In one embodiment, the target center frequency of the microwave branch filter is... It is 2.87GHz.

[0015] In one embodiment, each shaping resonant unit satisfies ,in The electrical length of the fourth impedance line. The electrical length of the third impedance line.

[0016] In one embodiment, the width of the first impedance wire W1 = 0.09mm-0.11mm, the length of the first impedance wire L2 = 1.78mm-2.42mm, the length of the second impedance wire L1 = 3.61mm-4.89mm, the width of the second impedance wire W2 = 0.09mm-0.11mm, the width of the third impedance wire W4 = 0.34mm-46mm, the length of the third impedance wire L4 = 4.76mm-6.44mm, the width of the fourth impedance wire W3 = 1.02mm-1.38mm, the length of the fourth impedance wire L3 = 1.78mm-2.42mm, the width of the first gap S1 = 0.19mm-0.25mm, the width of the second gap S3 = 0.24mm-0.32mm, and the width of the third gap S2 = 0.24mm-0.32mm.

[0017] A spurious emission suppression method for a microwave branch filter, applied to the magnetic measurement system described above, includes the following steps:

[0018] By setting the impedance step ratio of the filter resonant unit and the shaping resonant unit, as well as the width and length of the first slit, the second slit, and the third slit, the microwave branch filter device forms a passband near the target center frequency f0 and a stopband on both sides of the passband, thereby suppressing microwave source harmonics and spurious components outside the band and enhancing out-of-band reflection isolation to reduce ODMR baseline fluctuations, measurement noise, and spectral distortion.

[0019] The aforementioned microwave branch filtering device employs four filter resonant units to filter the input microwave signal and form the main passband near f. Simultaneously, two shaping resonant units located in the middle of the dielectric substrate are used for passband shaping and stopband zero generation. The four filter resonant units and two shaping resonant units form a sixth-order bandpass filter. This sixth-order filtering achieves strong out-of-band suppression at both the upper and lower sides of the passband, effectively reducing spectral distortion and measurement noise caused by harmonics / spurious emissions. It also features good impedance matching within the passband and enhanced out-of-band reflection.

[0020] When the aforementioned microwave branch filtering device is applied to the magnetic measurement system of diamond NV color center continuous wave-optical detection magnetic resonance (CW-ODMR), the microwave branch filtering device can achieve low insertion loss transmission in the vicinity of the target frequency band of CW-ODMR, and improve the isolation between the microwave source and the subsequent link in the magnetic measurement system through sixth-order filtering, reduce amplitude fluctuations and link instability caused by reflected standing waves, thereby reducing the impact of out-of-band energy on the ODMR baseline and noise. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a microwave branch filter device in some embodiments of this application.

[0022] Figure 2 for Figure 1 A schematic diagram of the structure of the metal pattern layer in the embodiment.

[0023] Figure 3 for Figure 2 A schematic diagram of the dimensions of the metal pattern layer in the embodiment.

[0024] Figure 4 The following are simulation results of the S-parameters of the microwave branch filter device in some embodiments of this application.

[0025] Figure 5 The input reflection coefficient S of the microwave branch filter device in some embodiments of this application 11 The simulation results are shown in the figure.

[0026] Explanation of reference numerals in the attached figures:

[0027] Dielectric substrate 10; Metal ground layer 11; Metal pattern layer 12;

[0028] Filter resonant unit 20; Input port 21; Output port 22; First impedance line 23; Second impedance line 24; First filter resonant unit 25; Second filter resonant unit 26; Third filter resonant unit 27; Fourth filter resonant unit 28;

[0029] Shaping resonant unit 30; third impedance line 31; fourth impedance line 32;

[0030] First gap 40; second gap 41; third gap 42; axis of symmetry 43. Detailed Implementation

[0031] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0032] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and 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, and therefore should not be construed as a limitation of this application.

[0033] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0034] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0035] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0036] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0037] In diamond NV center continuous wave-optical-detected magnetic resonance (CW-ODMR) magnetic measurement systems, to ensure the stability and high signal-to-noise ratio of magnetic measurements, the microwave link must not only achieve low-loss transmission in the target frequency band but also effectively suppress out-of-band frequency components and link-level interference to avoid introducing spectral distortion, power fluctuations, and measurement noise. However, for miniaturized NV magnetic measurement systems, due to equipment size limitations, the microwave signal source can typically only be a single-tone signal source or an integrated RF module. Such signal sources are prone to significant high-order harmonics and spurious components.

[0038] Therefore, filters with "frequency selection + suppression" functions have become key components in microwave branches. Considering the NV resonant frequency band and its frequency shift / splitting characteristics caused by changes in magnetic field, NV magnetic measurement systems are usually more suitable for using bandpass filters to achieve low insertion loss and good passband flatness within the target passband, as well as provide sufficient out-of-band suppression on both sides of the passband, thereby reducing the impact of harmonics and spurious signals on the ODMR (optical probed magnetic resonance) readout curve (baseline, noise, linewidth, etc.).

[0039] Meanwhile, from the perspective of the microwave link, the spectral purity, amplitude stability, and impedance matching of microwave excitation directly affect the contrast, linewidth, and baseline stability of the ODMR fluorescence "dimple" signal. Furthermore, non-ideal factors such as source harmonics and spurious sidebands, out-of-band leakage, and standing waves caused by reflections can manifest as spurious responses, baseline fluctuations, or linewidth broadening, thereby increasing the uncertainty in frequency estimation. Therefore, introducing bandpass filtering in the microwave branch to achieve in-band selection and out-of-band suppression is one of the key methods to improve the repeatability and engineering robustness of NV magnetic measurement systems.

[0040] Currently, there are various forms of microwave filtering implementations. Among them, microstrip filters are very suitable for monolithic integration in compact microwave branches due to their low cost, ease of fabrication, ease of integration, and high engineering maturity. Coupled-line microstrip bandpass filters, a typical narrowband microstrip topology, can be constructed by cascading multiple coupled microstrip lines. The passband response is formed through multi-resonant unit coupling, which is more advantageous than single-segment coupled structures in improving passband performance and enhancing out-of-band suppression, making them suitable for suppressing spurious and harmonic waves in complex electromagnetic environments. However, for coupled-line microstrip bandpass filters, the coupling gap is highly sensitive to coupling strength and frequency response shape. Therefore, reasonable structural parameter design and optimization are necessary to balance low loss, good matching, and wideband out-of-band suppression in the target frequency band.

[0041] Therefore, this application provides a microwave branch filtering device, see reference. Figure 1 When this microwave branch filter is applied to a diamond NV color center continuous wave optical detection magnetic resonance (CW-ODMR) vector magnetic measurement system, the microwave branch filter is positioned between the output of the microwave source of the magnetic measurement system and the microwave radiation structure, which can be an antenna or a microstrip radiator. The magnetic measurement system achieves low insertion loss transmission at the target center frequency f0, preferably around 2.87 GHz, through the microwave branch filter, and strongly suppresses harmonics and spurious components on the upper and lower sides of the passband of the microwave branch filter, thereby reducing the impact of out-of-band energy on the ODMR baseline and noise.

[0042] The microwave branch filter includes a dielectric substrate 10. A metal ground layer 11 is disposed on the lower surface of the dielectric substrate 10, and a metal pattern layer 12 is disposed on the upper surface of the dielectric substrate 10. The metal ground layer 11 is used to ground the circuit and provide electromagnetic shielding. On the one hand, it can provide a stable reference ground potential for the microstrip filter structure, ensuring the consistency of filtering characteristics. On the other hand, it can isolate electromagnetic interference below the dielectric substrate 10, preventing stray signal leakage from affecting the detection sensitivity of the magnetic measurement system. The dielectric substrate 10 supports the metal pattern layer 12 and the metal ground layer 11, providing an insulating support foundation for the metal structure of the metal pattern layer 12. At the same time, the appropriate dielectric constant and substrate thickness can be selected according to the filtering performance requirements to adjust the transmission characteristics of the filtering structure, ensuring the structural stability and filtering performance reliability of the overall microwave branch filter.

[0043] The metal pattern layer 12 consists of input and output feeding structures and a multi-resonant coupling network. The multi-resonant coupling network consists of four filter resonant units 20 and two shaping resonant units 30. The wavelength of the filter resonant units 20 is smaller than the wavelength of the shaping resonant units 30. The filter resonant units 20 include two sets, which are symmetrically arranged along the axis of symmetry 43. Each set of filter resonant units 20 includes two mutually symmetrically arranged filter resonant units 20. The two resonant units of each set of filter resonant units 20 are coupled to each other through the first gap 40.

[0044] Furthermore, the shaping resonant unit 30 includes two units, which are disposed on two sets of filter resonant units 20. The two shaping resonant units 30 are symmetrically arranged along the axis of symmetry 43, and the two shaping resonant units 30 are coupled to each other through the second gap 41. The two shaping resonant units 30 are respectively coupled to the filter resonant unit 20 closest to them through the third gap 42.

[0045] The aforementioned microwave branch filtering device employs four filter resonant units 20 to filter the input microwave signal and form the main passband near f0. Simultaneously, two shaping resonant units 30 located in the middle of the dielectric substrate 10 are used for passband shaping and stopband zero generation. The four filter resonant units 20 and two shaping resonant units 30 form a sixth-order bandpass filter. This sixth-order filtering achieves strong out-of-band suppression at the top and bottom of the passband, effectively reducing spectral distortion and measurement noise caused by harmonics / spurious emissions. It also features good impedance matching within the passband and enhanced out-of-band reflection.

[0046] When the aforementioned microwave branch filtering device is applied to the magnetic measurement system of diamond NV color center continuous wave-optical detection magnetic resonance (CW-ODMR), the microwave branch filtering device can achieve low insertion loss transmission in the CW-ODMR target frequency band, preferably around 2.87 GHz. Furthermore, through sixth-order filtering, it can improve the isolation between the microwave source and the subsequent link in the magnetic measurement system, reduce amplitude fluctuations and link instability caused by reflected standing waves, thereby reducing the impact of out-of-band energy on the ODMR baseline and noise.

[0047] In some embodiments of this application, the filter resonant unit 20 is based on a quarter-wavelength stepped impedance resonator, that is, the filter resonant unit 20 is a quarter-wavelength stepped impedance resonator, and the shaping resonant unit 30 is based on a half-wavelength stepped impedance resonator, that is, the shaping resonant unit is a half-wavelength stepped impedance resonator. Thus, four quarter-wavelength stepped impedance resonators serve as four filter resonant units 20, utilizing the filtering capability of the quarter-wavelength stepped impedance resonator to form the main passband near the target center frequency f0. Furthermore, by using two half-wavelength stepped impedance resonators as two shaping resonant units 30, utilizing the channel shaping capability of the half-wavelength stepped impedance resonator itself, the two symmetrically arranged shaping resonant units 30 can achieve passband shaping and stopband zero generation.

[0048] In some embodiments of this application, each filter resonant unit 20 includes a first impedance line 23 and a second impedance line 24 that are interconnected and extend in the same direction. The impedance of the first impedance line 23 is greater than that of the second impedance line 24, thereby forming a stepped impedance structure on the filter resonant unit 20 through the first impedance end and the second impedance line 24 with different impedances. Further, each shaping resonant unit 30 includes a third impedance line 31 and two fourth impedance lines 32 that extend in the same direction. The impedance of the third impedance line 31 is greater than that of the fourth impedance line 32. The third impedance line 31 is connected to the two fourth impedance lines 32 at its opposite ends, so as to form a stepped impedance structure on the shaping resonant unit 30 through one third impedance line 31 and two fourth impedance lines 32 with different impedances.

[0049] In practical use, by adjusting the equivalent electrical lengths of the first impedance line 23 and the second impedance line 24 of each filter resonant unit 20, as well as the physical lengths of the first impedance line 23 and the second impedance line 24, and the equivalent electrical lengths of the third impedance line 31 and the fourth impedance line 32 of each shaping resonant unit 30, as well as the physical lengths of the third impedance line 31 and the fourth impedance line 32, the center frequency f0 of the entire microwave branch filter device can be adjusted.

[0050] To achieve mutual coupling between the various filter resonant units 20 and the shaping resonant units 30, four filter resonant units 20 are defined as the first filter resonant unit 25, the second filter resonant unit 26, the third filter resonant unit 27, and the fourth filter resonant unit 28. The first filter resonant unit 25 has an input port 21 on its first impedance line 23, and its second impedance line 24 is coupled to the second impedance line 24 of the second filter resonant unit 26 through a first gap 40. The second impedance line 24 of the second filter resonant unit 26 is coupled to the third impedance line 31 of one of the shaping resonant units 30 through a third gap 42. Similarly, the fourth filter resonant unit 28 has an input port 21 on its first impedance line 23, and its second impedance line 24 is coupled to the second impedance line 24 of the third filter resonant unit 27 through a first gap 40. The second impedance line 24 of the third filter resonant unit 27 is coupled to the third impedance line 31 of another shaping resonant unit 30 through a third gap 42.

[0051] Thus, the first filter resonant unit 25 and the second filter resonant unit 26 constitute a frequency band. The first filter resonant unit 25 and the second filter resonant unit 26 are coupled to each other through the first gap 40, so that the microwave input from the input port 21 resonates in the first filter resonant unit 25 and the second filter resonant unit 26. This makes the microwave exhibit a low impedance and high transmission state near the designed resonant frequency of the first filter resonant unit 25 and the second filter resonant unit 26. Microwaves at non-resonant frequencies will be reflected or attenuated due to impedance mismatch, and finally the filtered microwave is output.

[0052] The filtered microwave output from the second filter resonant unit 26 enters one of the shaping resonant units 30. The second filter resonant unit 26 and the shaping resonant unit 30 are coupled to each other through the third gap 42, that is, through a quarter-wavelength stepped impedance resonator and a half-wavelength stepped impedance resonator. The microwave will split into two output paths. At a specific frequency point, the signals of these two paths just satisfy a 180-degree phase difference. At this time, the signals completely cancel each other out at the output port 22, thus generating a transmission zero.

[0053] After the two shaping resonant units 30 are coupled to each other through the second slit 41, by adjusting the size of the second slit 41, a transmission zero can be formed on the left and right sides of the channel, thereby achieving strong out-of-band suppression on the upper and lower sides of the passband, effectively reducing spectral distortion and measurement noise caused by harmonics and spurious emissions.

[0054] Furthermore, after the microwave signal passes through the first filter resonant unit 25, the second filter resonant unit 26, and the two shaping resonant units 30, although it has undergone multiple filtering processes, it will generate a relatively serious return loss. At this time, the third filter resonant unit 27 and the fourth filter resonant unit 28 form a gradually changing impedance matching network, which smoothly outputs the microwave signal in the microwave branch filter device from the output port 22.

[0055] Specifically, in some embodiments, in order for the four filter resonant units 20 to form a main passband near f0, each filter resonant unit 20 satisfies the following: , The electrical length of the first impedance line 23. The electrical length of the second impedance line 24 is given. , For the corresponding physical length of the first impedance line 23 or the second impedance line 24, For the effective dielectric constant, The speed of light in a vacuum. The target center frequency of the filtering device is preferably 2.87 GHz. λ is the wavelength of the filter resonant unit.

[0056] At least one filter resonant unit 20 has an open-circuit end and a short-circuit end. The short-circuit end is connected to the metal grounding layer 11 via a grounding via. Preferably, the first filter resonant unit 25 and the fourth filter resonant unit 28 adopt a resonance configuration of "one end short-circuited and one end open-circuited" for the open-circuit end and the short-circuit end, that is, the two filter resonant units 20 with input port 21 and output port 22. The short-circuit end is the end of the first filter resonant unit 25 near the input port 21 and the end of the fourth filter resonant unit 28 near the input port. They are connected to the grounding metal layer through the metal grounding via to form an equivalent short circuit. The open-circuit end refers to the end of the first filter resonant unit 25 away from the input port 21 and the end of the fourth filter resonant unit 28 away from the output port 22. This improves the stopband suppression capability while ensuring a compact size. The second filter resonant unit 26 and the third filter resonant unit 27 can adopt a configuration where both ends are short-circuited. Here, "both ends" refers to the two ends of the second filter resonant unit 26 and the third filter resonant unit 27 in their own extension direction.

[0057] Specifically, in some embodiments, in order to enable the two shaping resonant units 30 located in the middle to form controllable deep attenuation regions for transmission zeros / quasi-zeros on both sides of the passband, and to improve the upper and lower stopband suppression depth and effective suppression bandwidth, improve passband flatness and port matching, and reduce passband echo, each shaping resonant unit 30 satisfies the equivalent electrical length constraint at the center frequency: ,in The electrical length of the fourth impedance line 32. The electrical length of the third impedance line 31.

[0058] In this design, each shaping resonant unit 30 has two open-circuit ends, meaning that the shaping resonant unit 30 is a "two-end open-circuit" resonant form. This gives the shaping resonant unit 30 the characteristics of constant impedance and symmetrical standing wave, thus enabling the two shaping resonant units 30 to achieve stable transmission of microwave signals.

[0059] In some embodiments, for the first impedance line 23 with lower impedance, the low impedance can be achieved by a rectangular patch of a wide-line microstrip, while for the second impedance line 24 with higher impedance, the high impedance can be achieved by a rectangular patch of a narrow-line microstrip.

[0060] For microstrip lines, a unit length of microstrip line can be considered as a network composed of a series inductor L and a parallel capacitor C. The characteristic impedance Z0 of the microstrip is approximately equal to... When the microstrip line is wide, the distance between the microstrip and the metal step ground layer below the dielectric substrate 10 remains unchanged, that is, the thickness of the dielectric substrate 10 remains unchanged. The microstrip line becomes wider, that is, the bottom area of ​​the microstrip becomes larger, which makes the parallel capacitance C formed by the microstrip and the metal ground layer 11 larger, so that the impedance Z0 of the microstrip is significantly reduced.

[0061] When the microstrip line is very thin, the microstrip's resistance to current increases, resulting in a larger series inductance L. At the same time, the smaller area of ​​the microstrip also leads to a smaller parallel capacitance C formed by the microstrip and the metal ground layer 11. The combination of these two factors results in a significant increase in the impedance Z0 of the microstrip.

[0062] Thus, by controlling the trace width of the microstrip, the impedance of the microstrip can be controlled. Therefore, for the filter resonant unit 20, the impedance of the first impedance line 23 is less than that of the second impedance line 24, that is, the trace width of the first impedance line 23 is less than the trace width of the second impedance line 24. Specifically... Figure 3 In this embodiment, the linewidth of the first impedance line 23 is W1, the linewidth of the second impedance line 24 is W2, W1 is less than W2, and the characteristic impedance corresponding to the first impedance line 23 is Z. H The characteristic impedance corresponding to the second impedance line 24 is Z. L .

[0063] For a stepped impedance resonator (SIR), Z is defined as follows: H / Z L=K, which is the ratio of high impedance characteristics to low impedance characteristics. By changing the value of K, the parasitic resonance position can be controlled and the out-of-band suppression can be enhanced. Choosing a larger value of K can push the undesired parasitic passband away from the target frequency band and improve the stopband roll-off and suppression depth.

[0064] Specifically, in some embodiments, the width W1 of the first impedance line 23, the length L2 of the first impedance line 23, the length L1 of the second impedance line 24, the width W2 of the second impedance line 24, the width W4 of the third impedance line 31, the length L4 of the third impedance line 31, the width W3 of the fourth impedance line 32, the length L3 of the fourth impedance line 32, the width S1 of the first gap 40, the width S3 of the second gap 41, and the width S2 of the third gap 42 are defined.

[0065] The length L1 of the second impedance line 24 of the first filter resonant unit 25 serves as the effective coupling length of the main coupling channel on the input side. It determines the port energy injection efficiency and fine-tunes the center frequency. Specifically, increasing L1 increases the equivalent electrical length of the second impedance line 24, thus decreasing the center frequency. The lengths L2 and L3 of the first impedance line 23 and the fourth impedance line 32, respectively, are used for port matching and impedance gradation, suppressing parasitic reflections at the port and improving passband echo.

[0066] As for the length L4 of the third impedance line 31, L4 is the effective length of the key horizontal transmission / coupling section of the two shaping resonant units 30, used to adjust the equivalent electrical length and phase matching condition of the lower coupling network of the microwave branch filter device. It also synergistically affects the position of the lower stopband zero and the deep attenuation bandwidth with the width S3 of the second slot 41. By changing L4, the passband flatness, passband ripple, and lower stopband suppression characteristics can be jointly shaped without significantly changing the port structure.

[0067] To simultaneously meet the three requirements of "center frequency, bandwidth, and out-of-band rejection", this application adopts the following parameter tuning strategy:

[0068] Adjusting the center frequency f0: Prioritize adjusting the equivalent electrical length of each filter resonant unit 20 and shaping resonant unit 30, as well as the channel length parameters related to the phase condition, including L1 and L4;

[0069] Adjusting passband bandwidth and passband ripple: Prioritize adjusting external coupling S1 and its corresponding coupling length L1, and refine the middle coupling strength through S3 and S2;

[0070] Adjusting out-of-band suppression and parasitic response: Prioritize adjusting the impedance step ratios ZH / ZLW2 / W1 and W4 / W3 to change the parasitic passband and zero position, and then use S3, S2 and L4 to fine-tune the upper and lower stopband suppression regions and the suppression bandwidth.

[0071] In one specific embodiment, based on a set of typical structural dimension parameters of the microwave branch filter device at the target center frequency f0 = 2.87 GHz, such as... Figure 3 As indicated, this embodiment uses a dielectric substrate with a dielectric constant εr=3.66, a loss tangent tanδ=0.004, and a thickness h=0.508mm. Both the metal ground layer and the microstrip metal pattern layer are 1oz copper thick (approximately 35μm), and the characteristic impedance of the input / output ports is 50Ω.

[0072] See Figure 2 The key geometric parameters are as follows:

[0073] Width parameters (unit: mm): Width of first impedance line 23 W1=0.10 (wide line width in low impedance section), width of second impedance line 24 W2=0.10 (narrow line width in high impedance section, corresponding to a quarter-wavelength stepped impedance resonator), width of fourth impedance line 32 W3=1.20 (wide line width in the middle low impedance section, corresponding to a half-wavelength stepped impedance resonator), width of third impedance line 31 W4=0.40 (narrow line width in the middle high impedance section, corresponding to a half-wavelength stepped impedance resonator).

[0074] Length parameters (unit: mm): The length of the second impedance line 24 is L1=4.25 (effective coupling length of the main coupling channel on the input side), the length of the first impedance line 23 is L2=2.10 (length of the input transition section), the length of the fourth impedance line 32 is L3=2.10 (length of the output transition section), and the length of the third impedance line 31 is L4=5.60 (length of the horizontal coupling section of the main channel in the lower middle part).

[0075] Coupling gap parameters (unit: mm): the width of the first gap 40 is S1=0.22, the width of the second gap 41 is S3=0.28, and the width of the third gap 42 is S2=0.28.

[0076] It should be noted that the above dimensional parameters are optimized based on a specific dielectric substrate and target frequency band. In practical applications, the length and gap parameters can be adjusted proportionally within ±15% according to the material, thickness, and center frequency of the dielectric substrate used. That is, W1=0.09mm-0.11mm, L2=1.78mm-2.42mm, L1=3.61mm-4.89mm, W2=0.09mm-0.11mm, W4=0.34mm-0.46mm, L4=4.76mm-6.44mm, W3=1.02mm-1.38mm, L3=1.78mm-2.42mm, S1=0.19mm-0.25mm, S3=0.24mm-0.32mm, S2=0.24mm-0.32mm.

[0077] After selecting the various length and gap parameters, L1, L4, L1, S3, and S2 can be fine-tuned through electromagnetic simulation to restore the best matching and suppression performance. However, the six-resonator SIR topology and impedance step relationship of this application should remain unchanged. This embodiment does not constitute the sole limitation on the scope of protection of this application.

[0078] In terms of electromagnetic verification, this embodiment uses COMSOL Multiphysics to perform finite element simulation analysis on the filter, and uses S-parameters as the main verification indicator. Figure 4 The figure shows the frequency response curve of the scattering parameter S-parameter of the microwave branch filter device of the present invention, where S11 represents the reflection characteristics at the input end and S21 represents the transmission characteristics. Figure 4 The simulation curves for FDmode and discrete frequency points are presented simultaneously. The two show good consistency in passband location, stopband attenuation trend, and key inflection points, indicating the reliability and repeatability of the established electromagnetic model and structural parameter settings. As shown in the figure, the filter forms a narrow passband around the target operating frequency of approximately 2.87 GHz. Within the passband, S21 is close to 0 dB, indicating that the signal can pass through the filter with low insertion loss in this frequency band, thus meeting the requirements of the NV color center CW-ODMR microwave excitation link for effective power transmission and spectral purity maintenance. Meanwhile, S11 shows a significant dip within the passband, with return loss reaching approximately −20 dB and deepening locally, indicating good port impedance matching within the passband and minimal reflection between the microwave source and the filter, which can reduce amplitude fluctuations and power instability caused by link standing waves.

[0079] On both sides of the passband, S21 drops rapidly and enters the stopband region, exhibiting a steep roll-off characteristic. Attenuation of tens of dB is achieved in the lower stopband (approximately 2.0–2.6 GHz) and the upper stopband (approximately 3.3 GHz and above), demonstrating strong out-of-band suppression capability. This result indicates that the microwave branch filter device of this application, through a multi-resonant coupling network, can effectively suppress high-order harmonics, spurious components, and link-level interference from the microwave source while ensuring low loss and good matching in the passband. This reduces ODMR baseline fluctuations, noise increases, and spectral distortion caused by out-of-band energy injection into the NV microwave radiation structure, improving the signal-to-noise ratio and measurement stability of the NV color center magnetic measurement / quantum current sensing system. Furthermore, the near-0 dB characteristic of S11 within the stopband indicates that out-of-band signals are mainly reflected back to the source, which is beneficial for improving the isolation between the microwave source and subsequent links, further enhancing robustness in system engineering applications.

[0080] like Figure 5The figure shows a Smith chart of the input reflection coefficient S11 of the filter device of this application. The curve color indicates the frequency variation in GHz. The Smith chart uses normalized impedance as the coordinate, where the center of the circle corresponds to an ideal matching state with a normalized impedance of 1, i.e., 50 Ω matching. The closer the curve is to the center, the smaller the reflection and the better the impedance matching. As can be seen from the figure, in the target operating frequency band of approximately 2.87 GHz, corresponding to the green area in the figure, the S11 trajectory converges and forms a small loop near the center, indicating that the input impedance is close to 50 Ω in this frequency band, and the reflection coefficient is small. This is consistent with the result of deep return loss in the passband in the aforementioned S11 frequency response, indicating that the filter has good port matching characteristics in the passband.

[0081] As the frequency deviates from the passband, the S11 trajectory gradually moves towards the outer edge of the Smith circle, forming a large-scale arc-shaped change along the circumference. This indicates that the input impedance deviates more from 50 Ω, and reflection is enhanced, meaning that out-of-band signals mainly return to the source in the form of reflection. This characteristic is beneficial for "blocking" and isolating out-of-band harmonics and spurious components, reducing their probability of entering the subsequent NV microwave radiation structure. On the other hand, it also reduces the transmission and coupling of out-of-band energy in the link, thereby improving the isolation between the microwave source and the subsequent link and reducing amplitude fluctuations and link instability caused by standing waves. In summary, the Smith chart further verifies the matching optimization effect of the filter in the target frequency band and its strong reflection isolation characteristics in the non-operating frequency band from the perspective of impedance trajectory, making it suitable for engineering applications of NV color center CW-ODMR microwave excitation links.

[0082] In some embodiments of this application, in a magnetic measurement system based on diamond NV center continuous wave-optical detection magnetic resonance (CW-ODMR), when the magnetic measurement system includes a microwave source, a microwave radiation device, and a microwave branch filter as described in any of the above embodiments, the microwave branch filter is connected in series between the microwave source and the microwave radiation device. This microwave branch filter enables the microwave radiation device to accurately output 2.87 GHz microwaves, causing the diamond NV center to resonate. Furthermore, the microwave branch filter improves the isolation between the microwave source and the subsequent link in the magnetic measurement system, reduces amplitude fluctuations and link instability caused by reflected standing waves, thereby reducing the impact of out-of-band energy on the ODMR baseline and noise.

[0083] Furthermore, the magnetic measurement system also includes a power amplifier connected in series between the microwave branch filter and the microwave radiation device. This power amplifier amplifies the clean, low-power microwave signal output from the microwave branch filter to a power level sufficient to manipulate the spins of the NV color center. The microwave source, microwave branch filter, microwave radiation device, and power amplifier are integrated onto the same circuit board to achieve miniaturization and consistent mass production applications.

[0084] This application also provides a spurious suppression method for a microwave branch filter device, based on any of the above embodiments of the microwave branch filter device, and includes the following steps: by setting the impedance step ratio of the filter resonant unit 20 and the shaping resonant unit 30, as well as the width and length of the first slit 40, the second slit 41 and the third slit 42, the microwave branch filter device forms a passband near the target center frequency f0 and a stopband on both sides of the passband, thereby suppressing microwave source harmonics and spurious components outside the band and enhancing out-of-band reflection isolation, so as to reduce ODMR baseline fluctuations, measurement noise and spectral distortion.

[0085] Furthermore, the above method also includes center frequency calibration by using the equivalent electrical length and coupling length parameters of the filter resonant unit 20 and the shaping resonant unit 30, and passband bandwidth and passband ripple control by adjusting the external coupling gap parameter.

[0086] Furthermore, the above method also includes: changing the position of the parasitic passband and deep attenuation region by adjusting the impedance step ratio of the filter resonant unit 20 and the shaping resonant unit 30, and coordinating the adjustment of the middle coupling gap parameter and the middle and lower coupling length parameter to achieve joint shaping of the upper and lower stopband suppression characteristics.

[0087] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A microwave branch filter device for NV color center ODMR readout, characterized in that, The microwave branch filter device includes a dielectric substrate (10), a metal ground layer (11) is provided on the lower surface of the dielectric substrate (10), and a metal pattern layer (12) is provided on the upper surface of the dielectric substrate (10). The metal pattern layer (12) includes a filter resonant unit (20) and a shaping resonant unit (30). The filter resonant unit (20) includes two sets, which are symmetrically arranged along the axis of symmetry (43). Each set of filter resonant units (20) includes two mutually symmetrically arranged filter resonant units (20). The two filter resonant units (20) in each set are coupled to each other through a first gap (40). One of the resonant units in one set of filter resonant units (20) is provided with an input port (21), and one of the resonant units in the other set of filter resonant units (20) is provided with an output port (22). The shaping resonant unit (30) includes two units. The two shaping resonant units (30) are located between the two sets of filter resonant units (20). The two shaping resonant units (30) are symmetrically arranged along the axis of symmetry (43). The two shaping resonant units (30) are coupled to each other through the second gap (41). The two shaping resonant units (30) are coupled to the filter resonant unit (20) closest to them through the third gap (42).

2. The microwave branch filter device according to claim 1, characterized in that, The filter resonant unit (20) is a quarter-wavelength stepped impedance resonator.

3. The microwave branch filter device according to claim 2, characterized in that, The shaping resonant unit (30) is a half-wavelength stepped impedance resonator.

4. The microwave branch filter device according to claim 3, characterized in that, Each of the filter resonant units (20) includes a first impedance line (23) and a second impedance line (24) connected to each other. The impedance of the first impedance line (23) is less than that of the second impedance line (24). Each of the shaping resonant units (30) includes a third impedance line (31) and two fourth impedance lines (32). The impedance of the third impedance line (31) is greater than that of the fourth impedance line (32). The third impedance line (31) is connected to the two fourth impedance lines (32) at its opposite ends.

5. The microwave branch filter device according to claim 4, characterized in that, The filter resonant unit (20) includes four units: a first filter resonant unit (25), a second filter resonant unit (26), a third filter resonant unit (27), and a fourth filter resonant unit (28). The first filter resonant unit (25) has an input port (21) on its first impedance line (23). The second impedance line (24) of the first filter resonant unit (25) and the second impedance line (24) of the second filter resonant unit (26) are coupled to each other through the first gap (40). The first impedance line (23) of the second filter resonant unit (26) is coupled to the third impedance line (31) of one of the shaping resonant units (30) through the third gap (42). The first impedance line (23) of the fourth filter resonant unit (28) is provided with an input port (21), and the second impedance line (24) of the fourth filter resonant unit (28) and the second impedance line (24) of the third filter resonant unit (27) are coupled to each other through the first gap (40). The first impedance line (23) of the third filter resonant unit (27) and the third impedance line (31) of another shaping resonant unit (30) are coupled to each other through the third gap (42).

6. The microwave branch filter device according to claim 4, characterized in that, Each filter resonant unit (20) satisfies: , The electrical length of the first impedance line (23) is... The electrical length of the second impedance line (24) is given by the following formula: , For the physical length corresponding to the first impedance line (23) or the second impedance line (24), For the effective dielectric constant, The speed of light in a vacuum. The target center frequency of the filtering device is [the frequency of the filter device]. The wavelength of the filter resonant unit is denoted as .

7. The microwave branch filter device according to claim 6, characterized in that, The target center frequency of the microwave branch filter device It is 2.87GHz.

8. The microwave branch filter device according to claim 4, characterized in that, Each shaping resonant unit (30) satisfies ,in The electrical length of the fourth impedance line (32) is... The electrical length of the third impedance line (31) is given.

9. The microwave branch filter device according to claim 4, characterized in that, The width W1 of the first impedance line (23) is 0.09 mm - 0.11 mm, the length L2 of the first impedance line (23) is 1.78 mm - 2.42 mm, and the length L1 of the second impedance line (24) is 3.61 mm - 4.89mm, the width of the second impedance line (24) is W2=0.09mm-0.11mm, the width of the third impedance line (31) is W4=0.34mm-46mm, the length of the third impedance line (31) is L4=4.76mm-6.44mm, the width of the fourth impedance line (32) is W3=1.02mm-1.38mm, the length of the fourth impedance line (32) is L3=1.78mm-2.42mm, the width of the first gap (40) is S1=0.19mm-0.25mm, the width of the second gap (41) is S3=0.24mm-0.32mm, and the width of the third gap (42) is S2=0.24mm-0.32mm.

10. A spurious emission suppression method for a microwave branch filter, applied to the microwave branch filter as described in any one of claims 1-9, characterized in that, Includes the following steps: By setting the impedance step ratio of the filter resonant unit (20) and the shaping resonant unit (30), as well as the width and length of the first slit (40), the second slit (41) and the third slit (42), the microwave branch filter device forms a passband near the target center frequency f0 and a stopband on both sides of the passband, thereby suppressing microwave source harmonics and spurious components outside the band and enhancing out-of-band reflection isolation, so as to reduce ODMR baseline fluctuations, measurement noise and spectral distortion.

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