CN104466328B - A kind of balance/unbalance formula filters power splitter - Google Patents

Abstract

The embodiment of the present invention discloses a balanced-unbalanced filter power divider, comprising: a rectangular branch structure (enclosed by 5, 6, 7 and 8), 4 open circuits respectively connected to the 4 vertices of the rectangular branch structure Transmission lines (9, 10, 11 and 12), 2 branch transmission lines (13 and 14) connected to a rectangular branch structure, 1 isolated transmission line (15), 1 isolation resistor (16), 2 balanced input transmission lines (2 and 4) and 2 unbalanced output transmission lines (1 and 3). The invention provides a balanced-unbalanced power splitter, which not only has the filtering function and the common mode suppression function, but also has the characteristics of simple structure, small size, high process tolerance and low cost.

Description

A Balanced-Unbalanced Filter Power Splitter

technical field

The invention relates to the field of radio frequency technology, in particular to a balanced-unbalanced filter power divider.

Background technique

The full name of the power divider is a power divider, which is an energy device that divides the energy of one input signal into two or more outputs that are equal or unequal. According to the number of outputs, the power divider is usually divided into one divided into two, one divided into three and one divided into six. The main technical parameters of the power splitter are power loss (including insertion loss, distribution loss and reflection loss), voltage standing wave ratio of each port, isolation between power distribution ports, amplitude balance, phase balance, power capacity and frequency band width etc.

Nowadays, with the rapid development of radio frequency technology, balanced power splitters are widely used because of their advantages such as convenient connection with other balanced devices and good common-mode rejection. In some radio frequency systems, there are not only balanced ports but also unbalanced ports, that is, single-ended ports. Therefore, a balanced-unbalanced power splitter with a common mode suppression function is urgently needed. So far, there are many balanced-unbalanced duplexer and filter designs, but very few balanced-unbalanced power splitters. Moreover, the existing balanced-unbalanced power splitter needs to process double-sided circuits so that the result is complicated, and the requirements for processing accuracy are relatively high.

On the other hand, integrated design is widely used in radio frequency systems because of its small size and multiple functions. For example, power splitters with integrated filtering functions have been widely used. However, so far there are only single-ended and fully balanced filter power splitters, and there is no balanced-unbalanced filter power splitter. In the prior art, at least one balanced-unbalanced power splitter and two single-ended filters or one balanced-unbalanced power splitter are needed to realize this performance. As a result, the existing technology is not only large in size but also high in cost.

Contents of the invention

The technical problem to be solved by the embodiments of the present invention is that the existing balanced-unbalanced power splitter has no filtering function and has a complex structure and low processing tolerance, and the existing balanced-unbalanced power splitter integrated with the filtering function Due to the defects of large size and high cost, a balanced-unbalanced filter power splitter with simple structure, small size and low cost is provided.

In order to solve the above technical problems, an embodiment of the present invention provides a balanced-unbalanced filter power divider, including: a first input transmission line, a second input transmission line, a first output transmission line, a second output transmission line, First transmission line, second transmission line, third transmission line, fourth transmission line, first open transmission line, second open transmission line, third open transmission line, fourth open transmission line, first branch transmission line, second branch transmission line, isolated transmission line and isolation resistance; where,

The first transmission line, the second transmission line, the third transmission line and the fourth transmission line are sequentially connected end to end to form a rectangular branch line structure, and the electrical lengths of the first transmission line and the third transmission line are both half of the center frequency wavelength, the electrical length and impedance of the second transmission line and the fourth transmission line are the same;

The first open-circuit transmission line, the second open-circuit transmission line, the third open-circuit transmission line and the fourth open-circuit transmission line have the same electrical length and impedance, one end of which is respectively connected to the four vertices of the rectangular branch structure, and the other end is open;

The electrical length and impedance of the first branch transmission line and the second branch transmission line are the same; one end of the first branch transmission line is connected to the midpoint of the second transmission line, and the other end is grounded; the second branch transmission line One end of the branch transmission line is connected to the midpoint of the fourth transmission line, and the other end is grounded; the impedances of the first branch transmission line, the first open transmission line and the second transmission line are the same;

One end of the isolated transmission line is connected to the midpoint of the third transmission line, and the other end is open;

One end of the isolation resistor is connected to the midpoint of the third transmission line, and the other end is grounded;

The first input transmission line and the second input transmission line form a balanced input port of the filter power splitter, and are respectively connected to both ends of the first transmission line;

The first output end transmission line and the second output end transmission line are two unbalanced single-ended output ports of the filter power divider, which are respectively connected to both ends of the third transmission line;

The electrical lengths and impedances of the first input transmission line, the second input transmission line, the first output transmission line and the second output transmission line are all the same.

Preferably, the transmission line includes a microstrip transmission line and a coplanar waveguide transmission line;

Preferably, the first open-circuit transmission line, the second open-circuit transmission line, the third open-circuit transmission line and the fourth open-circuit transmission line are accommodated in the rectangular branch structure and are connected by two transmission lines of a diagonal line segment and a horizontal segment transmission line. Into; wherein, the oblique segment transmission line is connected to the apex of the rectangular branch structure, the horizontal segment transmission line is open and parallel to the first transmission line; the first open transmission line, the second open transmission line, the third open transmission line The electrical length of the horizontal segment transmission line is equal to that of the fourth open circuit transmission line.

Preferably, the first input transmission line, the second input transmission line, the first output transmission line and the second output transmission line are arranged outside the rectangular branch structure, and the first output transmission line and the first The input end transmission line extends along the length direction of the second transmission line, and the second output end transmission line and the second input end transmission line extend along the length direction of the fourth transmission line.

Preferably, the first branch transmission line and the second branch transmission line are open transmission lines or short circuit transmission lines and are accommodated in the rectangular branch structure.

Preferably, the electrical lengths of the first open transmission line, the second open transmission line, the third open transmission line and the fourth open transmission line are used to adjust the frequency of the transmission zero of the filter power divider.

Preferably, the electrical lengths of the second transmission line and the first branch transmission line are used to adjust the 1-dB bandwidth and out-of-band rejection of the filter power divider by the following formula:

tanθ ₁ tanθ ₂ (2tanθ ₃ +tanθ ₂ )＝tanθ ₃ +tanθ ₂ -tan ² θ ₂ tanθ ₃

Wherein, Z ₀ is the impedance of the first output transmission line, Z ₃ is the impedance of the second transmission line, θ ₁ is the electrical length of the first open circuit transmission line, and θ ₂ is the electrical length of the second transmission line Half of , θ ₃ is the electrical length of the first branch transmission line.

Preferably, the impedance of the third transmission line and the resistance value of the isolation resistor are selected by the following formula:

Wherein, Z ₀ is the impedance of the first output transmission line, Z ₂ is the impedance of the third transmission line, and R is the resistance of the isolation resistor.

Preferably, the impedance of the first transmission line is used to adjust the common-mode rejection bandwidth of the filter power divider.

Preferably, the width of the third transmission line is used to adjust the isolation amplitude of the filter power divider; the electrical length of the isolated transmission line is used to adjust the isolation frequency of the filter power divider.

Implementing the embodiment of the present invention has the following beneficial effects: the present invention provides a balanced-unbalanced filter power splitter with a filtering function and a common-mode suppression function. The power splitter has a simple structure, small size, and high process tolerance. High and low cost.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a schematic structural diagram of a first embodiment of a balanced-unbalanced filter power splitter provided by the present invention;

Fig. 2 is a schematic structural diagram of a balanced-unbalanced filter power splitter according to a second embodiment of the present invention;

Fig. 3 is a schematic diagram of the principle of the balanced-unbalanced filter power splitter of the first embodiment provided by the present invention;

Fig. 4 is a differential mode response diagram of the balanced-unbalanced filter power splitter of the first embodiment provided by the present invention;

Fig. 5 is a common-mode response diagram of the balanced-unbalanced filter power divider according to the first embodiment of the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to FIG. 1 . FIG. 1 is a schematic structural diagram of a balanced-unbalanced filter power splitter according to a first embodiment of the present invention. As shown in Figure 1, the balanced-unbalanced filter power splitter provided in this embodiment includes: a first input transmission line 2, a second input transmission line 4, a first output transmission line 1, a second output transmission line 3, First transmission line 5, second transmission line 6, third transmission line 7, fourth transmission line 8, first open transmission line 9, second open transmission line 10, third open transmission line 11, fourth open transmission line 12, first branch transmission line 13 , the second branch transmission line 14 , the isolation transmission line 15 and the isolation resistor 16 .

The first transmission line 5 , the second transmission line 6 , the third transmission line 7 and the fourth transmission line 8 are sequentially connected end to end to form a rectangular branch line structure. The electrical lengths of the first transmission line 5 and the third transmission line 7 are both half the wavelength of the center frequency. The electrical length and impedance of the second transmission line 6 and the fourth transmission line 8 are the same.

The first open-circuit transmission line 9, the second open-circuit transmission line 10, the third open-circuit transmission line 11 and the fourth open-circuit transmission line 12 are accommodated inside the rectangular branch line structure, and one end of the four open-circuit transmission lines is respectively connected to four vertices of the rectangular branch structure, Open the other end. The electrical lengths and impedances of the four open transmission lines are the same. Accommodating the four open-circuit transmission lines inside the rectangular branch structure is conducive to making full use of the space and reducing the volume and size of the balanced-unbalanced filter power splitter.

The first branch transmission line 13 and the second branch transmission line 14 are accommodated inside the rectangular branch structure and have the same electrical length and impedance. Wherein, one end of the first branch transmission line 13 is connected to the midpoint of the second transmission line 6 and the other end is grounded; one end of the second branch transmission line 14 is connected to the midpoint of the fourth transmission line 8 and the other end is grounded. In addition, the impedances of the first branch transmission line 13 , the first open transmission line 9 and the second transmission line 6 are also the same.

The isolated transmission line 15 is housed inside the rectangular branch structure and one end thereof is connected to the midpoint of the third transmission line 7 , and the other end is open.

One end of the isolation resistor 16 is connected to the midpoint of the third transmission line 7, and the other end is grounded. In this embodiment, for a more compact structure and a smaller size, the isolation resistor 16 is arranged outside the rectangular branch structure. In another preferred embodiment provided by the present invention, the isolation resistor 16 can be arranged inside the rectangular branch structure according to actual needs.

The first input transmission line 2 and the second input transmission line 4 form a balanced input port of the filter power divider, and are respectively connected to two ends of the first transmission line 5 .

The transmission line 1 at the first output end and the transmission line 3 at the second output end are two unbalanced single-ended output ports of the filter power divider, which are respectively connected to two ends of the third transmission line 7 .

The electrical lengths and impedances of the first input transmission line 2 , the second input transmission line 4 , the first output transmission line 1 and the second output transmission line 3 are the same.

In this embodiment, the transmission line includes a microstrip transmission line and a coplanar waveguide transmission line.

As shown in FIG. 1 , preferably, the first open transmission line 9 , the second open transmission line 10 , the third open transmission line 11 and the fourth open transmission line 12 are all formed by connecting two sections of a transmission line with an oblique line and a horizontal section. Among them, the four open-circuit transmission lines are all connected to the corresponding vertices of the rectangular branch structure through their respective oblique transmission lines, and the horizontal transmission lines are open and parallel to the first transmission line 5. The electrical lengths of the horizontal transmission lines of the four open transmission lines are equal. In another preferred embodiment of the present invention, the structures of the four open-circuit transmission lines can also be appropriately changed, as long as the electrical lengths and impedances of the four open-circuit transmission lines are equal. For example, properly adjust the length ratio of the oblique section transmission line and the horizontal section transmission line or connect two or three oblique section transmission lines with one horizontal section transmission line to form an open circuit transmission line.

As shown in Figure 1, preferably, the first input transmission line 2, the second input transmission line 4, the first output transmission line 1 and the second output transmission line 3 are arranged outside the rectangular branch structure, and the first output transmission line 1 and the first input transmission line 2 extend along the length direction of the second transmission line 6 , and the second output transmission line 3 and the second input transmission line 4 extend along the length direction of the fourth transmission line 8 . It should be understood that, for the convenience of wiring, generally, the transmission lines of the input end and the output end are arranged outside the rectangular branch structure. In another preferred embodiment provided by the present invention, the input transmission lines 2 and 4 can also extend along the length direction of the first transmission line 5 , while the output transmission lines 1 and 3 can also extend along the length direction of the third transmission line 7 . Those skilled in the art can design the output and the extension direction of the transmission line at the output end according to the actual needs of the circuit.

As shown in FIG. 1 , preferably, the first branch transmission line 13 and the second branch transmission line 14 are parallel to the first transmission line 5 . Arranging the branch transmission lines 13 and 14 parallel to the first transmission line 5 can make the structure of the filter power divider more compact, which is beneficial to reduce the size. In another preferred embodiment provided by the present invention, the branch transmission lines 13 and 14 can also be accommodated in a rectangular branch structure in other ways.

As shown in FIG. 1 , preferably, the isolated transmission line 15 is parallel to the second transmission line 6 , so that the structure of the filter power divider can be made more compact, which is beneficial to reduce the size. In another preferred embodiment provided by the present invention, the isolated transmission line 15 can also be accommodated in a rectangular branch structure in other ways.

By implementing this embodiment, a balanced-unbalanced power splitter with filtering function can be provided. The power divider has the advantages of simple structure, small size, high process tolerance and low cost.

In this embodiment, the first branch transmission line 13 and the second branch transmission line 14 are short-circuit transmission lines. It should be understood that in the present invention, the first branch transmission line 13 and the second branch transmission line 14 may be designed as open transmission lines according to actual needs. The electrical length of an open transmission line is increased by a quarter wavelength of the center frequency compared to a short circuit transmission line. Therefore, the balanced-unbalanced filter power divider using the open transmission line scheme requires a larger size, but also has a larger bandwidth. In addition, because the electrical length of the open-circuit transmission line is long, in a small-sized circuit, signal interference with the open-circuit transmission lines 9, 10, 11, and 12 is easy to occur, thereby affecting the performance of the power divider.

Please refer to FIG. 2 . FIG. 2 is a schematic structural diagram of a balanced-unbalanced filter power splitter according to a second embodiment of the present invention. As shown in Figure 2, the difference between the structure of the filter power divider in this embodiment and the structure of the filter power divider in the first embodiment is: the first open transmission line 9, the second open transmission line 10, the third open transmission line 11 and the fourth open transmission line 12 is arranged outside the rectangular branch structure and is a horizontal line segment, and the first branch transmission line 13 and the second branch transmission line 14 are also arranged outside the rectangular branch structure.

It should be understood that, according to the actual design requirements, in the present invention, any transmission line connected to the rectangular branch structure can be selectively arranged inside or outside it. Similarly, the isolation resistor 16 can also be selectively arranged inside or outside the rectangular branch structure. external.

In this embodiment, compared with the first embodiment, disposing the first open transmission line 9, the second open transmission line 10, the third open transmission line 11 and the fourth open transmission line 12 outside the rectangular branch structure will increase the filter work. The size of the splitter, but also simplified the structure of the four open transmission lines. Moreover, there will no longer be an interference phenomenon between the open transmission line and the first branch transmission line 13 and the second branch transmission line 14, which is more conducive to designing the first branch transmission line 13 and the second branch transmission line 14 as open transmission lines, thereby Make the filter power divider have better bandwidth.

Please refer to FIGS. 3-5. FIG. 3 is a schematic diagram of the principle of the balanced-unbalanced filter power splitter according to the first embodiment of the present invention. As shown in Figure 3, this embodiment will illustrate the principle of the balanced-unbalanced filter power divider provided by the present invention from the circuit. It is arranged outside the rectangular branch structure, because whether the open circuit transmission lines 9, 10, 11 and 12 are inside the rectangular branch structure does not affect the electrical performance of the filter power divider, but only affects the structure and size.

As shown in FIG. 3 , the characteristic impedance of the first transmission line 5 is Z ₁ , and the electrical length is half the wavelength of the center frequency. The characteristic impedance of the second transmission line 6 and the third transmission line 7 is Z ₃ , and the electrical length is 2θ ₂ . The characteristic impedance of the fourth transmission line 8 is Z ₂ , and the electrical length is half the wavelength of the central frequency. The characteristic impedance of the open transmission lines 9, 10, 11 and 12 is Z ₃ and the electrical length is θ ₁ . The characteristic impedance of the branch transmission lines 13 and 14 is Z ₃ , and the electrical length is θ ₃ . The characteristic impedance of the isolated transmission line 15 is Z ₄ , and the electrical length is θ ₄ . The resistance value of the isolation resistor 16 is R. Balanced input port A includes input transmission lines 2 and 4 . The whole structure is a symmetrical structure, and the symmetric line is shown by the dotted line in Fig. 2 . The output transmission lines 1 and 3 constitute two unbalanced single-ended output ports of the filter power divider.

During operation, by adding a half-wavelength first transmission line 5 between the input ports 2 and 4, a differential signal can be fed into the balanced input port A; and then by adding θ ₁ , θ ₂ and θ ₃ The transmission line stub makes the differential signal fed by the balanced input port A evenly distributed to the unbalanced single-ended output ports 1 and 3, thereby realizing the power distribution function and generating the filtering function at the same time. Simultaneously, the isolation between the single-ended output ports 1 and 3 can be realized by adding a third transmission line 7 of 1/2 wavelength, an isolation transmission line 15 and a grounded isolation resistor 16 between the unbalanced single-ended output ports 1 and 3 .

For a power splitter, it is usually necessary to consider some specific performance indicators, such as port matching, power equalization, and transmission port isolation. These three performance indicators can be expressed by S parameters: S _ddAA <-20dB; S _dsA1 =S _dsA3 =-3dB; S _ss31 <-20dB. According to these S parameters, it can be further determined:

tanθ ₁ tanθ ₂ (2tanθ ₃ +tanθ ₂ )＝tanθ ₃ +tanθ ₂ -tan ² θ ₂ tanθ ₃ (3)

Among them, Z ₀ is the characteristic impedance of the input/output transmission lines 1, 2, 3 and 4, usually 50Ω. For the convenience of calculation, the values of Z ₃ and R are usually 50Ω.

Preferably, the electrical length _θ1 of the open transmission lines 9, 10, 11 and 12 can adjust the frequency of the transmission zero of the filter power divider. In the present invention, θ ₁ is a quarter of the wavelength at the frequency where the transmission zero is located. Therefore, θ ₁ can be determined by the known transmission zero frequency, and the transmission zero frequency of the power divider can also be controlled by selecting the value of θ ₁ . On this basis, through formulas (1) and (3), adjusting θ ₂ and θ ₃ can control the 1-dB bandwidth and out-of-band rejection of the filter power divider. In the present invention, the bandwidth increases with the increase of θ ₃ until _SddAA reaches -20dB at the center frequency.

Preferably, the characteristic impedance Z1 of the _first transmission line 5 can adjust the common-mode rejection bandwidth of the filter power divider. That is to say, the value of Z ₁ can be determined by the requirement of the suppressed common-mode rejection bandwidth, or a filter power divider with a specific common-mode rejection bandwidth can be designed by adjusting the value of Z ₁ . In the present invention, as Z ₁ increases, the bandwidth of common mode rejection of the circuit will decrease accordingly.

Preferably, the isolation amplitude and isolation frequency of the filter power divider provided by the present invention can be adjusted through the width of the third transmission line 7 and the electrical length of the isolation transmission line 15 respectively.

In a preferred embodiment provided by the present invention, the operating frequency of the balanced-unbalanced filter power divider is 1.88GHz, and there is a transmission zero point near 2.1GHz, and the 1-dB bandwidth is 7.5%, and the matching S _ddAA at the input end is at the center Frequency to -20dB, common mode rejection to 20dB and isolation to 15dB. The first and third transmission line length l ₁ =47.2mm, the first to fourth open transmission line length l ₂ =22mm, the second and fourth transmission line length l ₃ =9mm, the first and second open transmission line length l ₄ =2mm , the isolated transmission line length l ₅ =1.75 mm, the first transmission line width w ₁ =1.4 mm, the first to fourth open transmission line widths w ₂ =1 mm, and the third transmission line width w ₃ =0.5 mm. Figure 4 and Figure 5 are the differential mode response diagram and common mode response diagram of the balanced-unbalanced filter power splitter designed according to this size parameter respectively. The comparison results of measured S-parameters and simulated S-parameters are shown in the figure.

It can be seen from Figure 4 that the amplitudes of single-ended output ports 1 and 3 around the center frequency |S _ds1A |=|S _ds3A |=-3dB, that is to say, the input power is evenly distributed to single-ended output port 1 and 3. Moreover, it shows obvious bandpass characteristics near the center frequency, and the S amplitude drops sharply outward from the center frequency. Therefore, the power divider exhibits very obvious bandpass filtering characteristics. The isolation parameters |S _ss31 | between single-ended output ports 1 and 3 are basically all below -15dB, and the isolation characteristics fully meet the design requirements. While the port matching parameter | _SddAA | is -40dB at the center frequency and below -20dB in the bandpass range. Port matching characteristics are good.

It can be seen from Fig. 5 that the amplitude of the common-mode suppression parameter |S _ccAA | is basically 0dB, and the common-mode signal of the filter power divider is basically completely suppressed. As analyzed in Figure 4, the isolation of the common mode signal in Figure 5 also meets the design requirements.

It can be seen from the above analysis that the balanced-unbalanced filter power divider designed in the present invention can fully meet the design requirements. In addition, it can also be seen from the figure that the measured S-parameters and the simulated S-parameters basically coincide completely. This has fully verified the effectiveness of the structure and performance of the balanced-unbalanced filter power splitter provided by the present invention, and also verified the structure and structure of each transmission line component of the balanced-unbalanced filter power splitter provided by the present invention. Functionality. According to the structure provided by the present invention and the functions of the transmission line components, those skilled in the art can design different balanced-unbalanced filter power splitters that work at various frequencies and satisfy various characteristic parameters.

What is disclosed above is only a preferred embodiment of the present invention, and of course it cannot limit the scope of rights of the present invention. Those of ordinary skill in the art can understand all or part of the process for realizing the above embodiments, and according to the rights of the present invention The equivalent changes required still belong to the scope covered by the invention.

Claims (10)

1. A balanced-unbalanced filter power splitter, characterized in that, comprising: a first input transmission line (2), a second input transmission line (4), a first output transmission line (1), a second output End transmission line (3), first transmission line (5), second transmission line (6), third transmission line (7), fourth transmission line (8), first open transmission line (9), second open transmission line (10), The third open transmission line (11), the fourth open transmission line (12), the first branch transmission line (13), the second branch transmission line (14), the isolation transmission line (15) and the isolation resistance (16); wherein, The first transmission line (5), the second transmission line (6), the third transmission line (7) and the fourth transmission line (8) are sequentially connected end to end to form a rectangular branch line structure, the first transmission line (5) and the The electrical length of the third transmission line (7) is one-half wavelength of the center frequency, and the electrical length and impedance of the second transmission line (6) and the fourth transmission line (8) are the same; The first open-circuit transmission line (9), the second open-circuit transmission line (10), the third open-circuit transmission line (11) and the fourth open-circuit transmission line (12) have the same electrical length and impedance, and one end thereof is connected to the rectangular branch respectively. The 4 vertices of the branch structure are open at the other end; The electrical length and impedance of the first branch transmission line (13) and the second branch transmission line (14) are the same; one end of the first branch transmission line (13) is connected to the second transmission line (6 ), the other end is grounded; one end of the second branch transmission line (14) is connected to the midpoint of the fourth transmission line (8), and the other end is grounded; the first branch transmission line (13), The impedance of the first open-circuit transmission line (9) and the second transmission line (6) are the same; One end of the isolated transmission line (15) is connected to the midpoint of the third transmission line (7), and the other end is open; One end of the isolation resistor (16) is connected to the midpoint of the third transmission line (7), and the other end is grounded; The first input transmission line (2) and the second input transmission line (4) form a balanced input port of the filter power divider, which are respectively connected to both ends of the first transmission line (5); The first output end transmission line (1) and the second output end transmission line (3) are two unbalanced single-ended output ports of the filter power divider, respectively connected to the third transmission line (7 ) at both ends; The electrical lengths and impedances of the first input transmission line (2), the second input transmission line (4), the first output transmission line (1) and the second output transmission line (3) are all the same. 2. The balanced-unbalanced filter power splitter according to claim 1, wherein the transmission line comprises a microstrip transmission line or a coplanar waveguide transmission line. 3. The balanced-unbalanced filter power splitter according to claim 1, characterized in that, the first open transmission line (9), the second open transmission line (10), the third open transmission line (11) and the first open transmission line Four open-circuit transmission lines (12) are accommodated in the rectangular branch line structure and are formed by connecting two transmission lines of a diagonal line segment and a horizontal segment transmission line; wherein, the diagonal line segment transmission line is connected to the rectangular branch line structure The vertex of the horizontal section transmission line is open and parallel to the first transmission line (5); the first open transmission line (9), the second open transmission line (10), the third open transmission line (11) and the fourth open transmission line Said horizontal sections of the transmission line (12) are of equal electrical length. 4. The balanced-unbalanced filter power splitter according to claim 1, characterized in that, the first input transmission line (2), the second input transmission line (4), the first output transmission line (1 ) and the second output transmission line (3) are arranged outside the rectangular branch line structure, the first output transmission line (1) and the first input transmission line (2) are along the second transmission line (6 ), the second output end transmission line (3) and the second input end transmission line (4) extend along the length direction of the fourth transmission line (8). 5. The balanced-unbalanced filter power splitter according to claim 1, characterized in that, the first branch transmission line (13) and the second branch transmission line (14) are short-circuit transmission lines and accommodate within the rectangular branch line structure. 6. The balanced-unbalanced filter power splitter according to claim 1, characterized in that, the first open transmission line (9), the second open transmission line (10), the third open transmission line (11) and the first open transmission line The electrical length of the four open-circuit transmission lines (12) is used to adjust the frequency of the transmission zero point of the filter power divider. 7. The balanced-unbalanced filter power splitter according to claim 6, characterized in that, the electrical length of the second transmission line (6) and the first branch transmission line (13) is used to pass the following formula Adjust the 1-dB bandwidth and out-of-band rejection of the filter splitter: $\begin{array}{c}{\mathrm{<span\; class="notranslate">\; tan\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&lsqb;</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; tan\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; tan\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; tan\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; tan\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; tan\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>\\ <span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; tan\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; tan\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; the\; tan</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\end{array}$ tanθ ₁ tanθ ₂ (2tanθ ₃ +tanθ ₂ )＝tanθ ₃ +tanθ ₂ -tan ² θ ₂ tanθ ₃ Wherein, Z ₀ is the impedance of the first output transmission line (1), Z ₃ is the impedance of the second transmission line (6), θ ₁ is the electrical length of the first open transmission line (9), θ ₂ is half of the electrical length of the second transmission line ( ₆ ), and θ3 is the electrical length of the first branch transmission line (13). 8. The balanced-unbalanced filter power splitter according to claim 1, characterized in that, the impedance of the third transmission line (7) and the resistance value of the isolation resistor (16) are used to select by the following formula : $\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}$ Wherein, Z ₀ is the impedance of the first output transmission line (1), Z ₂ is the impedance of the third transmission line (7), and R is the resistance value of the isolation resistor (16). 9. The balanced-unbalanced filter power splitter according to claim 1, characterized in that the impedance of the first transmission line (5) is used to adjust the common-mode rejection bandwidth of the filter power splitter. 10. The balanced-unbalanced filter power splitter according to claim 1, characterized in that, the width of the third transmission line (7) is used to adjust the isolation amplitude of the filter power splitter; the isolated transmission line The electrical length of (15) is used to adjust the isolation frequency of the filter power divider.