Directional coupler and design method thereof, radio frequency circuit, and electronic device

Abstract

The present invention provides a directional coupler, a design method thereof, and a radio frequency circuit. The directional coupler comprises two parallel microstrip lines, two adjustment units positioned between the parallel microstrip lines, another adjustment unit connected to the second microstrip line, and a matching unit positioned between the second microstrip line and a coupling port. The directional coupler, based on this structural design, can achieve good directivity over a wide operating bandwidth.

Description

Technical Field

[0001] The present application relates to the technical field of radio frequency circuits, and in particular to a directional coupler and a design method thereof, and a radio frequency circuit. Background Art

[0002] As a microwave / millimeter wave device, directional coupler can be used to distribute or synthesize microwave signal power and is often used in power synthesis, frequency and spectrum analyzers, source output power stabilization and transmission, etc. Currently, directional couplers composed of parallel coupled microstrip lines, such as Figure 1 As shown, Term G1 is the input port of the directional coupler, Term G2 is the output port of the directional coupler, Term G3 is the coupled output port of the directional coupler, and R1=50Ω is the isolation resistor. The length of the directional coupling microstrip line is 1 / 4 wavelength, and the wavelength corresponds to the center frequency.

[0003] However, existing directional couplers have a narrow operating bandwidth problem and are usually only applicable to narrowband circuits. Even if they are designed to have a wider bandwidth, they still have the problem of poor directivity. Figure 1 The structure of the directional coupler is shown as an example. By performing ADS simulation on the directional coupler, the following can be obtained: Figure 2 The S-parameter simulation results shown in Figure 2 show that S(2,1) represents the pass coefficient between the output port and the input port; S(3,1) represents the coupling coefficient between the coupled port and the input port; and S(3,2) represents the coupling coefficient between the coupled port and the output port. It can be seen that the center frequency of this directional coupler is 6.372 GHz, and its coupling degree is within the range of 17.8-20.8 dB from 3.181 GHz to 9.579 GHz. However, its directivity is very poor, ranging from -3.7 dB to 6.101 dB. It can be seen that existing directional couplers are difficult to meet the requirements of applications that require both wide bandwidth and high directivity. Summary of the Invention

[0004] The embodiments of the present application provide a directional coupler, a design method thereof, and a radio frequency circuit. The directional coupler can achieve good directivity within a wide operating bandwidth.

[0005] An embodiment of the present application provides a directional coupler, comprising: a first microstrip line, a second microstrip line, a first adjustment unit, a second adjustment unit, a matching unit, a first resistor, a second resistor, and first to third ports;

[0006] The first microstrip line and the second microstrip line are arranged in parallel, two ends of the first microstrip line are connected to the first port and the second port respectively, and the first end of the second microstrip line is connected to the third port;

[0007] The two ends of the first adjustment unit are respectively connected to the first ends of the first microstrip line and the second microstrip line; the two ends of the second adjustment unit are respectively connected to the second ends of the first microstrip line and the second microstrip line; the first end of the third adjustment unit is connected to the first end of the second microstrip line, the second end of the third adjustment unit is respectively connected to the second end of the second microstrip line and the second adjustment unit, and the third end of the third adjustment unit is grounded; the two ends of the matching unit are respectively connected to the first end of the second microstrip line and the third port.

[0008] In one embodiment, the first regulating unit and the second regulating unit each include a regulating resistor and a regulating capacitor connected in series.

[0009] In one embodiment, the third adjustment unit includes a first resistor and a second resistor arranged in series;

[0010] The first end of the first resistor serves as the first end of the third adjustment unit, the second end of the first resistor is connected to the first end of the second resistor, the series connection end of the first resistor and the second resistor serves as the second end of the third adjustment unit, and the second end of the second resistor serves as the third end of the third adjustment unit.

[0011] In one embodiment, the matching unit includes a third resistor, a fourth resistor, and a fifth resistor;

[0012] One end of the third resistor and the fourth resistor are connected to serve as the first end of the matching unit, the other end of the third resistor and one end of the fifth resistor are connected to serve as the second end of the matching unit, and the other ends of the fourth resistor and the fifth resistor are grounded.

[0013] In one embodiment, the electrical lengths of the first microstrip line and the second microstrip line range from 48 degrees to 56 degrees.

[0014] In one embodiment, the value range of the adjustment capacitors in the first adjustment unit and the second adjustment unit is 0.1 pF to 1 pF.

[0015] In one embodiment, the adjustment resistors in the first adjustment unit and the second adjustment unit both have a value range of 500Ω to 700Ω.

[0016] An embodiment of the present application further provides a bidirectional directional coupler, comprising a first coupling unit and a second coupling unit arranged back to back, wherein each of the coupling units is the above-mentioned directional coupler.

[0017] An embodiment of the present application further provides a radio frequency circuit, comprising the above-mentioned directional coupler or bidirectional directional coupler.

[0018] An embodiment of the present application further provides an electronic device, comprising the above-mentioned radio frequency circuit.

[0019] An embodiment of the present application further provides a method for designing a directional coupler, the structure of which adopts the above-mentioned directional coupler. The method for designing a directional coupler includes:

[0020] Determining the physical lengths of the first microstrip line and the second microstrip line according to a target operating frequency band of the directional coupler and a value range of the electrical lengths of the first microstrip line and the second microstrip line;

[0021] Determining the gap and line width of the first microstrip line and the second microstrip line respectively according to the target coupling degree and characteristic impedance of the directional coupler;

[0022] Determining device values ​​in the first adjustment unit and the second adjustment unit according to the target directivity of the directional coupler;

[0023] Determining device values ​​in the third adjustment unit according to the target flatness of the directional coupler;

[0024] The component values ​​in the matching unit are determined according to the target reflection value of the directional coupler.

[0025] In one embodiment, the electrical lengths of the first microstrip line and the second microstrip line range from 48 degrees to 56 degrees.

[0026] The embodiments of the present application have the following beneficial effects:

[0027] The directional coupler of the embodiment of the present application provides an adjustment unit at each end of a parallel microstrip line, another adjustment unit at each end of a second microstrip line, and a matching circuit between the coupled port and the second microstrip line. By designing corresponding circuits and selecting appropriate device values ​​at corresponding positions, the directional coupler based on the above-mentioned structural design can effectively improve the narrow operating bandwidth and poor directivity problems of existing directional couplers. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the drawings shown below are only certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 Shown is a simulation structure diagram of an existing directional coupler;

[0030] Figure 2 Shown Figure 1 S-parameter simulation test results of directional coupler;

[0031] Figure 3 FIG2 is a schematic diagram of a simulation structure of a directional coupler according to an embodiment of the present application;

[0032] Figure 4 Shown is another simulation structure schematic diagram of the directional coupler according to an embodiment of the present application;

[0033] Figure 5 The figure shows an S-parameter simulation test result of a directional coupler according to an embodiment of the present application;

[0034] Figure 6 FIG2 is a flow chart of a design method for a directional coupler according to an embodiment of the present application.

[0035] Description of main component symbols:

[0036] Directional coupler; 110 - first microstrip line; 120 - second microstrip line; 130 - first adjustment unit; 140 - second adjustment unit; 150 - third adjustment unit; 160 - matching unit. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0038] The components of the embodiments of the present application generally described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but rather merely represents selected embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort are within the scope of protection of the present application.

[0039] Hereinafter, the terms "including", "having" and their cognates, which may be used in various embodiments of the present application, are intended only to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be understood as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0040] Furthermore, the terms “first,” “second,” “third,” etc., are merely used for distinguishing descriptions and are not to be understood as indicating or implying relative importance.

[0041] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which the various embodiments of the present application belong. The terms (such as those defined in generally used dictionaries) will be interpreted as having the same meaning as in the context of the relevant technical field and will not be interpreted as having an idealized meaning or an overly formal meaning unless clearly defined in the various embodiments of the present application.

[0042] Because existing directional couplers cannot effectively meet the requirements of maintaining good directivity over a wide operating bandwidth, embodiments of the present application propose a directional coupler and a general design method thereof. This directional coupler improves parallel coupled microstrip lines and provides various devices at corresponding locations along the parallel coupled microstrip lines for adjustment and matching, thereby achieving high directivity over a wide operating frequency band. This will be described below with reference to specific embodiments.

[0043] Example 1

[0044] Please refer to Figure 3 This embodiment proposes a directional coupler 100, which can be applied to scenarios where a coupler is needed, such as mobile phone communications, radar communications, and instrument testing. The directional coupler 100 can achieve broadband and high-directivity directional signal coupling.

[0045] For example, Figure 3 As shown, the directional coupler 100 includes a first microstrip line 110, a second microstrip line 120, a first adjustment unit 130, a second adjustment unit 140, a third adjustment unit 150, a matching unit 160, and a first port Term G1, a second port Term G2, and a third port Term G3; wherein the first microstrip line 110 as a main line and the second microstrip line 120 as a secondary line are arranged in parallel to form a pair of parallel coupled microstrip lines.

[0046] Based on this parallel coupled microstrip line, the two ends of the first adjustment unit 130 are respectively connected to the first end of the first microstrip line 110 and the second microstrip line 120, and the two ends of the second adjustment unit 140 are respectively connected to the second ends of the first microstrip line 110 and the second microstrip line 120. In other words, the two adjustment units 130 and 140 are respectively located at the two ends of the parallel microstrip line. The third adjustment unit 150 has a three-terminal structure, with its first end connected to the first end of the second microstrip line 120, its second end connected to the second end of the second microstrip line 120 and the second adjustment unit 140, and its third end grounded. The two ends of the matching unit 160 are respectively connected to the first end of the second microstrip line 120 and the third port Term G3.

[0047] The directional coupler 100 of this embodiment is a three-port device, wherein the two ends of the first microstrip line 110 are connected to the first port Term G1 and the second port Term G2, respectively. The first port Term G1 and the second port Term G2 serve as the signal input port and output port of the directional coupler 100, respectively. The first end of the second microstrip line 120 is connected to the third port Term G3 via the matching unit 160, which serves as the coupling port of the directional coupler 100.

[0048] Based on the aforementioned parallel coupled microstrip line structure, to ensure that the directional coupler 100 meets the expected performance indicators such as operating frequency band, directivity, and coupling, this embodiment will combine the inherent parameters of the parallel microstrip line and the values ​​of other components to select and explain. The operating frequency band refers to the operating frequency range of the directional coupler 100; the coupling degree is the ratio of the input power at the input port of the directional coupler 100 to the output power at the coupled port; and the directivity is the ratio of the output power at the coupled port of the directional coupler 100 to the output power at the isolated port (grounded).

[0049] Regarding the first microstrip line 110 and the second microstrip line 120 described above, this section primarily discusses parameters such as the physical length and line width of the microstrip lines, as well as the gap between the two microstrip lines. This physical length, also known as line length, can be adjusted to adjust the center frequency band and operating bandwidth of the directional coupler 100. Setting an appropriate line width can adjust the characteristic impedance of the microstrip lines. Setting an appropriate gap size can adjust the coupling degree of the directional coupler 100.

[0050] During the actual design process, the length of the microstrip line can be calculated based on the target operating bandwidth of the desired directional coupler 100. For example, the center frequency of the microstrip line can be determined from the target operating bandwidth of the directional coupler 100, and the wavelength of the transmitted electromagnetic wave can be calculated. Based on the relationship between the wavelength of the electromagnetic wave and the physical length, the theoretical required length of the microstrip line can be calculated.

[0051] The ratio of the physical length of a microstrip line to the wavelength of the electromagnetic wave it transmits is called the electrical length. It's worth noting that the microstrip lines in conventional directional couplers 100 all have a physical length of 1 / 4 wavelength, where the electrical length is 90 degrees. However, in this embodiment, the physical lengths of the first and second microstrip lines 110 and 120 are no longer determined based on the 90-degree electrical length rule. Instead, the lengths of the parallel coupled microstrip lines are less than 90 degrees, meaning that the physical lengths no longer correspond to 1 / 4 wavelength.

[0052] Exemplarily, the electrical length of the microstrip line can range from 48 to 56 degrees, which can be selected according to actual needs and is not limited here. For example, when the operating frequency is 0.6-7.1G and the center frequency is 3.85G, the electrical length is 54 degrees, and the corresponding line length L = 7mm. Alternatively, when the operating frequency is 0.8-8.2G and the center frequency is 4.3G, the electrical length is 51 degrees, and the corresponding line length L = 6mm; or, when the operating frequency is 0.96-9.9G and the center frequency is 5.5G, the electrical length is 52 degrees, and the corresponding line length L = 5mm.

[0053] By changing the value of the electrical length instead of the existing 90-degree electrical length, the directional coupler 100 can have a wider operating bandwidth, meeting the needs of operating in an extremely wide operating frequency band. By further combining the comprehensive adjustment of various adjustment units and matching unit 160 and other components, the directional coupler 100 can achieve good directivity while meeting the wide bandwidth.

[0054] Similarly, the microstrip line width and the gap size between the two microstrip lines can be determined based on the characteristic impedance of the microstrip line and the target coupling degree. For two coupled microstrip lines, the smaller the gap, the greater the coupling degree; conversely, the smaller the gap, the smaller the coupling degree. Therefore, in the actual design process, the appropriate gap size can be continuously adjusted based on the above principles and actual simulation results.

[0055] Since the characteristic impedance of the microstrip line is mainly related to the line width, plate thickness and dielectric constant of the microstrip line, is the characteristic impedance of the microstrip line; W and H are the line width and plate thickness of the microstrip line respectively; is the dielectric constant of the plate, and they satisfy the following relationship:

[0056] .

[0057] Therefore, for microstrip line width design, after preliminarily determining the board thickness and dielectric constant, the line width of the microstrip line can be preliminarily estimated based on the above relationship. It should be understood that in actual design, adjustments should be made based on simulation test results to obtain a line width that meets impedance requirements.

[0058] In this embodiment, the first adjustment unit 130 and the second adjustment unit 140 can be used to adjust the directivity of the directional coupler 100 to generate two maximum points of the directivity. For example, in one embodiment, the first adjustment unit 130 and the second adjustment unit 140 have the same structure. For example, for the two adjustment units 130 and 140, as shown in FIG. Figure 4 As shown, each adjustment unit may include an adjustment resistor and an adjustment capacitor, and the adjustment resistor and the adjustment capacitor are arranged in series. Figure 4In the example, R11 is connected in series with C11 and R12 is connected in series with C12.

[0059] For example, the value range of the adjustment capacitors in the adjustment units 130 and 140 can be 0.1 pF to 1 pF. The value range of the adjustment resistors in the adjustment units 130 and 140 can be 500Ω to 700Ω, etc. It is understood that the values ​​of the adjustment resistors and adjustment capacitors in the adjustment units 130 and 140 can be selected based on the target directionality, target location of the maximum point, and other requirements of the actual scene. The values ​​of the two adjustment resistors can be the same or different, and the same applies to the values ​​of the two adjustment capacitors.

[0060] Considering that poor flatness will also affect the directivity of the directional coupler 100, in this embodiment, the third adjustment unit 150 can be used to adjust the flatness of the directivity of the directional coupler 100 to ensure the required high directivity.

[0061] In one embodiment, Figure 4 As shown, the third adjustment unit 150 may include a first resistor R1 and a second resistor R2 arranged in series. By adjusting the values ​​of the two resistors R1 and R2, the flatness can be adjusted. Figure 4 As shown, the non-series connection end of the first resistor R1 (i.e., the end not connected to the second resistor R2) serves as the first end of the third adjustment unit 150, the series connection end of the first resistor R1 and the second resistor R2 serves as the second end of the third adjustment unit 150, and the non-series connection end of the second resistor R2 serves as the third end of the third adjustment unit 150. It can be understood that the first resistor R1 is connected in parallel to both ends of the second microstrip line 120, and the second end of the second microstrip line 120 connected to the second adjustment unit 140 is also grounded through the second resistor R2.

[0062] In this embodiment, matching unit 160 is located between second microstrip line 120 and the coupled port, and is used to improve the port reflectivity of directional coupler 100, thereby minimizing the signal reflection coefficient at the coupled port and ensuring signal transmission efficiency. Furthermore, in addition to adjusting the coupling degree based on the gap between the two microstrip lines, for example, when the coupled port is mismatched, which may result in poor coupling, matching unit 160 can be used to further fine-tune the coupling degree of directional coupler 100.

[0063] Exemplarily, the matching unit 160 is mainly composed of components such as resistors. For example, in one embodiment, Figure 4As shown, the matching unit 160 includes a third resistor, a fourth resistor and a fifth resistor, wherein one end of each of the third resistor and the fifth resistor is connected to serve as the first end of the matching unit 160, which is used to connect to the first end of the second microstrip line 120; the other end of the third resistor and one end of the fourth resistor are connected to serve as the second end of the matching unit 160, which is used to connect to the coupling port; and the other ends of the fourth resistor and the fifth resistor are both grounded.

[0064] The directional coupler 100 obtained by combining the above structure design is simulated and tested. Figure 4 For the directional coupler 100 shown, if its target operating frequency band is 0.6 GHz to 7.1 GHz, the microstrip line length L of the directional coupler 100 is designed to be 7 mm, the line width is 0.08 mm, and the gap is 0.08 mm. The adjustment resistor R11 and the adjustment capacitor C11 in the first adjustment unit 130 are designed to be 620 Ω and 0.5 pF, respectively. The adjustment resistor R12 and the adjustment capacitor C12 in the second adjustment unit 140 are designed to be 540 Ω and 0.6 pF, respectively. The first resistor R1 and the second resistor R2 in the third adjustment unit 150 are designed to be 10 Ω and 7 Ω, respectively. The third resistor R3, the fourth resistor R4, and the fifth resistor R5 in the matching unit 160 are designed to be 36 Ω, 1000 Ω, and 500 Ω, respectively. It should be understood that the above values ​​for each component are merely examples.

[0065] Therefore, by performing ADS simulation on the above-mentioned directional coupler 100, the following can be obtained: Figure 5 The test results are shown. Figure 5 As can be seen, the operating bandwidth of the directional coupler 100 is measured to be 597MHz-7.171GHz, covering the entire frequency band of mobile terminals. The coupling degree (S3,1) of the coupler is between 30-33dB, and the directivity D is above 20dB throughout the entire operating bandwidth, with two extreme points within the band. It can be understood that the directional coupler 100 can achieve high directivity performance across a wide bandwidth.

[0066] The directional coupler of this embodiment comprises an adjustment unit comprising a capacitor and a resistor connected in series, disposed at each end of a parallel microstrip line, another adjustment unit comprising a plurality of resistors, disposed at each end of a second microstrip line, and a matching circuit comprising a plurality of resistors disposed between the coupled port and the second microstrip line. By providing appropriate circuits and device values ​​at appropriate locations, the problems of narrow operating bandwidth and poor directivity of existing directional couplers based on parallel coupled microstrip lines can be effectively addressed.

[0067] Example 2

[0068] Please refer to Figure 6This embodiment further provides a general design method for a directional coupler 100. Based on the structure of the directional coupler 100 of the first embodiment, the design method exemplarily includes:

[0069] Step S10 : determining the physical lengths of the first microstrip line 110 and the second microstrip line 120 according to the target operating frequency band of the directional coupler 100 and the electrical length value ranges of the first microstrip line 110 and the second microstrip line 120 .

[0070] In step S20 , the gap and line width of the first microstrip line 110 and the second microstrip line 120 are determined respectively according to the target coupling degree and characteristic impedance of the directional coupler 100 .

[0071] Step S30 : determining component values ​​in the first adjustment unit 130 and the second adjustment unit 140 according to the target directivity of the directional coupler 100 .

[0072] Step S40 : determining component values ​​in the third adjustment unit 150 according to the target flatness of the directional coupler 100 .

[0073] Step S50 : determining the component values ​​in the matching unit 160 according to the target reflection value of the directional coupler 100 .

[0074] Regarding how to determine these parameters, please refer to the description in Example 1 above, and this is not intended to be limiting. It will be appreciated that, during the actual design process, simulation tests can be performed based on theoretically calculated values. Considering that some calculated values ​​are estimates, the corresponding parameters can be continuously adjusted based on the test results to ensure that the performance of the directional coupler 100 ultimately meets the requirements. Furthermore, it should be understood that the various steps in this embodiment are primarily described based on the parameters required, and this does not limit the order in which the parameters are calculated in each step.

[0075] An embodiment of the present application further provides a radio frequency circuit. Exemplarily, the radio frequency circuit may include the above-mentioned directional coupler.

[0076] An embodiment of the present application further provides an electronic device, which may include but is not limited to a smart phone, a tablet, a radar communication device, a radio frequency tester, etc. Exemplarily, the electronic device includes the above-mentioned radio frequency circuit.

[0077] The above is only a specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be covered by the scope of protection of the present application.

Claims

1. A directional coupler, characterized in that: include: a first microstrip line, a second microstrip line, a first adjustment unit, a second adjustment unit, a third adjustment unit, a matching unit, and first to third ports; The first microstrip line and the second microstrip line are arranged in parallel, two ends of the first microstrip line are connected to the first port and the second port respectively, and the first end of the second microstrip line is connected to the third port through the matching unit; One end of the first adjustment unit is connected to the first end of the first microstrip line, and the other end of the first adjustment unit is connected to the first end of the second microstrip line; one end of the second adjustment unit is connected to the second end of the first microstrip line, and the other end of the second adjustment unit is connected to the second end of the second microstrip line; a first end of the third adjustment unit is connected to the first end of the second microstrip line, and a second end of the third adjustment unit is respectively connected to the second end of the second microstrip line and the second adjustment unit, and a third end of the third adjustment unit is grounded.

2. The directional coupler according to claim 1, wherein The first regulating unit and the second regulating unit each include a regulating resistor and a regulating capacitor connected in series.

3. The directional coupler according to claim 1, wherein The third adjustment unit includes a first resistor and a second resistor arranged in series; The first end of the first resistor serves as the first end of the third adjustment unit, the second end of the first resistor is connected to the first end of the second resistor, the series connection end of the first resistor and the second resistor serves as the second end of the third adjustment unit, and the second end of the second resistor serves as the third end of the third adjustment unit.

4. The directional coupler according to claim 1, wherein The matching unit includes a third resistor, a fourth resistor and a fifth resistor; One end of the third resistor and the fourth resistor are connected to serve as the first end of the matching unit, the other end of the third resistor and one end of the fifth resistor are connected to serve as the second end of the matching unit, and the other ends of the fourth resistor and the fifth resistor are grounded.

5. The directional coupler according to any one of claims 1 to 4, characterized in that The electrical lengths of the first microstrip line and the second microstrip line range from 48 degrees to 56 degrees.

6. The directional coupler according to claim 2, wherein: The value range of the regulating capacitor in the first regulating unit and the second regulating unit is 0.1 pF to 1 pF.

7. The directional coupler according to claim 2 or 6, characterized in that: The value range of the regulating resistors in the first regulating unit and the second regulating unit is both 500Ω~700Ω.

8. A radio frequency circuit, characterized in that: The directional coupler comprises the directional coupler according to any one of claims 1 to 7.

9. An electronic device, characterized in that: Comprising the radio frequency circuit as claimed in claim 8.

10. A method for designing a directional coupler, characterized in that: The structure adopts the directional coupler according to any one of claims 1 to 7, and the design method of the directional coupler includes: Determining the physical lengths of the first microstrip line and the second microstrip line according to a target operating frequency band of the directional coupler and a value range of the electrical lengths of the first microstrip line and the second microstrip line; Determining the gap and line width of the first microstrip line and the second microstrip line respectively according to the target coupling degree and characteristic impedance of the directional coupler; Determining device values ​​in the first adjustment unit and the second adjustment unit according to the target directivity of the directional coupler; Determining device values ​​in the third adjustment unit according to the target flatness of the directional coupler; The component values ​​in the matching unit are determined according to the target reflection value of the directional coupler.

11. The method for designing a directional coupler according to claim 10, wherein: The electrical lengths of the first microstrip line and the second microstrip line range from 48 degrees to 56 degrees.

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