CN108023562A - Areflexia lattice filter - Google Patents

Abstract

The invention discloses a reflectionless bridge filter, which comprises four independent single-port circuit sub-networks, input ports and output ports, wherein each single-port circuit sub-network has two endpoints; the four single-port circuit sub-networks The subnetworks are sequentially connected in a ring through their respective endpoints, and one endpoint of the input port is connected to the common endpoint of the first and second single-port circuit subnetworks, and the other endpoint of the input port is connected to the third and fourth A common endpoint of the single-port circuit sub-network; one endpoint of the output port is connected to the common endpoint of the second and third single-port circuit sub-network, and the other endpoint of the output port is connected to the first and fourth single-port circuit sub-network The common endpoint of the network to form a bridge filter circuit. The invention can flexibly realize various filter responses and high-performance filter responses without reflection. The structure is suitable for filter design in various frequency bands and has the advantages of simple structure and excellent performance.

Description

Reflectionless Bridge Filter

technical field

The invention relates to a reflectionless bridge filter, which belongs to the technical field of electronic circuits.

Background technique

A filter is an electronic device that is widely used in various electronic systems. Such devices generally have two ports that allow electrical signals in the passband to pass through without loss or with low loss, while prohibiting electrical signals in the stopband from being transmitted between the two ports.

Most filters are reflective. In this type of filter, according to the law of energy conservation, if the input electrical signal at the input terminal is within the passband, it will be transmitted to the output terminal; if it is within the stop band, it will be totally reflected to the input terminal, and there will be no signal output at the output terminal at this time. If the power of the reflected signal is large, it will have an uncertain impact on the subsequent circuits after returning to the input terminal, especially the stability of the active circuit will be destroyed. In addition, because the reflection between the stages will cause the deterioration of the filter response, the disadvantage of the reflective filter also includes that the response of the filter cannot be enhanced by direct cascading.

No reflection filter, as the name implies, no matter in the passband or stopband, there is no reflection signal or very small at the input end, and it does not affect the transmission response in the passband. The traditional reflectionless filter relies on some special network topology, limited by this, the types of filter response are very limited, which cannot meet the needs of practical use. In addition, a reflectionless filter can also be realized through the combination of an isolator and a filter, but the filter at this time is directional and increases the insertion loss. Like traditional reflective filters, how to realize a non-reflective filter with customized response has great social demand and is also a recognized technical problem in the industry.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide a non-reflection bridge filter, and realize a non-reflection filter with a customizable response, so as to solve the problem of single response and cumbersome design of the existing non-reflection filter And other issues.

The present invention specifically adopts the following technical solutions to solve the above technical problems:

A reflectionless bridge filter comprising independent first to fourth one-port circuit subnetworks, input ports, output ports, wherein each one-port circuit subnetwork has two endpoints; said four one-port circuit subnetworks are sequentially connected in a ring through respective endpoints, and one endpoint of the input port is connected to the common endpoint of the first and second single-port circuit sub-networks, and the other endpoint of the input port is connected to the third and fourth single-port A common endpoint of the circuit subnetwork; one endpoint of the output port is connected to the common endpoint of the second and third single-port circuit subnetworks, and the other endpoint of the output port is connected to the first and fourth single-port circuit subnetwork common terminal to form a bridge filter circuit.

Further, as a preferred technical solution of the present invention: each single-port circuit sub-network includes at least one lossless device and at least one lossy device.

Further, as a preferred technical solution of the present invention: the reference impedances of the input port and the output port are the same and pure resistance.

Further, as a preferred technical solution of the present invention: among the four single-port circuit sub-networks, the network topology of two non-adjacent single-port circuit sub-networks is the same as the value of the corresponding element.

Further, as a preferred technical solution of the present invention: among the four single-port circuit sub-networks, two non-adjacent single-port circuit sub-networks have different network topologies, and have the same input impedance at each frequency.

Further, as a preferred technical solution of the present invention: the lossless device is selected from the group consisting of inductors, capacitors, resonators, varactor diodes, transmission line elements, equivalent distributed devices, Discontinuities, lead parasitics, one-port equivalent lossless devices, and combinations thereof.

Further, as a preferred technical solution of the present invention: the lossy element is selected from the group consisting of: resistors, varistors, single-port non-reflection networks, single-port absorbing networks, single-port matching loads, external circuits A matched input port, a matched antenna and a combination of the above circuits.

Further, as a preferred technical solution of the present invention: the filtering response of the bridge filter includes a first-order filter, a second-order filter and a higher-order filter.

Further, as a preferred technical solution of the present invention: the filtering response of the bridge filter includes low-pass, band-pass, high-pass, band-stop, multi-band-pass, multi-band-stop and combinations thereof.

Further, as a preferred technical solution of the present invention: the bridge filter is used to cascade bridge filters with the same port impedance to change the filter response.

The present invention adopts above-mentioned technical scheme, can produce following technical effect:

The present invention can obtain a new type of non-reflection filter by reasonably setting the input impedance value of each single-port circuit sub-network, and can flexibly realize various filter responses, such as Butterworth type, Chebyshev type and elliptic function type Etc., suitable for low-pass, band-pass, high-pass, band-stop, multi-band-pass and multi-band-stop and other filtering occasions. This structure is suitable for filter design in various frequency bands. It has the advantages of simple structure and excellent performance.

The non-reflection bridge filter of the present invention has the characteristics that the reflection coefficient is zero in the whole frequency band. In actual use, there is no need to consider the adverse effect of the filter unit on the overall circuit due to reflection, and it can also be conveniently cascaded to further Improve filter performance. Different from the existing non-reflection filter, the non-reflection filter proposed in the present invention has the advantage that the response can be customized arbitrarily. In theory, all circuit responses that can be physically realized can be realized without reflection by using the bridge structure and subnetwork configuration method in the present invention. In addition, the existing one-port circuit network comprehensive design method and the design data of the traditional two-port reflective filter can be fully utilized to realize the rapid design and manufacture of the non-reflective filter.

Description of drawings

FIG. 1 is a circuit block diagram of a reflection-free bridge filter of the present invention.

FIG. 2 is a structural diagram of a two-port filter network used in the single-port circuit sub-network of the present invention.

FIG. 3( a ) and FIG. 3( b ) are schematic structural diagrams of the single-port circuit sub-networks respectively adopting dual dual ideal LC circuits in Embodiment 1 of the present invention. FIG. 3( c ) is a schematic structural diagram of a reflectionless filter using mutual duality according to Embodiment 1 of the present invention.

FIG. 4 is a simulated response curve of a reflectionless filter realized by an ideal LC circuit in the present invention.

Fig. 5(a) and Fig. 5(b) are respectively the structural schematic diagrams of the dual transmission line sub-network in the second embodiment of the present invention; Fig. 5(c) and Fig. 5(d) are the parallel branches in the second embodiment of the present invention A schematic diagram of the transmission line network structure of the line; FIG. 5( e ) is a schematic structural diagram of a reflectionless filter implemented by a transmission line according to Embodiment 2 of the present invention.

Fig. 6 is a response curve of a reflectionless filter realized by using a transmission line according to the present invention.

Detailed ways

Embodiments of the present invention will be described below in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention has designed a reflectionless bridge filter, including four independent single-port circuit sub-networks, input port 5, and output port 6 of the first to fourth, wherein the first single-port circuit sub-network 1 , the second single-port circuit subnetwork 2, the third single-port circuit subnetwork 3, and the fourth single-port circuit subnetwork 4 all have two endpoints; the four single-port circuit subnetworks are sequentially connected through their respective endpoints to form ring, and one endpoint of the input port 5 is connected to the common endpoint of the first single-port circuit subnetwork 1 and the second single-port circuit subnetwork 2, and the other endpoint of the input port is connected to the third single-port circuit subnetwork 3 and the public endpoint of the fourth single-port circuit subnetwork 4; one endpoint of the output port 6 is connected to the public endpoint of the second single-port circuit subnetwork 2 and the third single-port circuit subnetwork 3, and the output port 6 The other terminal is connected to the common terminal of the first one-port circuit sub-network 1 and the fourth one-port circuit sub-network 4, and the bridge filter circuit is formed according to the above connection method.

Wherein, the reference impedances of the input port 5 and the output port 6 are the same, and both are pure resistances, denoted as R ₀ ; the input impedances of the four single-port circuit sub-networks 1, 2, 3 and 4 are sequentially denoted as: Z ₁ , Z ₂ , Z ₃ and Z ₄ . In order to realize the filtering function, each of the single-port circuit sub-networks 1, 2, 3 and 4 contains at least one lossless device and at least one lossy device. Therefore, Z ₁ , Z ₂ , Z ₃ and Z ₄ are complex numbers whose real part is always greater than zero, and are functions of frequency. By reasonably setting the network topology and component values of each sub-network, it is possible to:

Ideally, at any frequency f:

In general, it only needs to be within the required operating frequency, including passband and stopband:

The design of reflectionless filter can be realized. At this time, when the output port 6 is connected to a load with a resistance value of R ₀ and the internal resistance of the excitation terminal 5 is also R ₀ , the modulus |S ₁₁ | of the filter reflection coefficient is zero or close to zero, that is, the Non-reflective design. And the transmission coefficient S ₂₁ is numerically equal or approximately equal to the reflection coefficient Γ ₂ of the load of the second one-port circuit subnetwork 2 or the fourth one-port circuit subnetwork 4 to the resistance value R ₀ , that is:

According to the above restrictions, under the premise that the port reference impedance is determined, the transmission response of the filter is completely determined by the input impedance Z ₂ of the second single-port circuit sub-network 2 . Z ₂ is a function of frequency, and its characteristics are determined by the network topology and component values of the second single-port circuit sub-network 2 . According to the circuit network synthesis theory, the topology structure and component values of the second single-port circuit sub-network 2 can be obtained through the comprehensive design of the target response function, as long as the function to be synthesized satisfies the properties of a physically achievable circuit network , the specific comprehensive design method will not be discussed in depth here. When the independent reflection coefficient of the second single-port circuit sub-network 2 is a certain filter response, the transmission response of the overall network is also the same filter response, and the reflection coefficient of the overall network is zero.

In order to satisfy that Z ₁ and Z ₃ are completely or substantially equal at all frequencies, the network topology adopted by the two non-adjacent single-port circuit sub-networks may be the same as the value of the corresponding component. The following technical means can be adopted: the first single-port circuit sub-network 1 and the third single-port circuit sub-network 3 adopt exactly the same network topology and the types, types, values, implementation methods and selections of corresponding components are exactly the same. Or the network topology of two non-adjacent one-port circuit subnetworks is different, and the input impedance at each frequency is the same, the following technical means can be adopted: the first single-port circuit subnetwork 1 and the third single-port circuit subnetwork 3 Different network topologies are adopted, and after network equivalence, the input impedances of the first single-port circuit sub-network 1 and the third single-port circuit sub-network 3 can be completely the same at each frequency. Considering the individual differences and various uncertainties of the components in the specific implementation, the input impedances of the first single-port circuit sub-network 1 and the third single-port circuit sub-network 3 can be roughly the same, and the reflection of the filter at this time The coefficient is close to zero.

In order to satisfy that Z ₂ and Z ₄ are completely or substantially equal at all frequencies, the network topology adopted by the two non-adjacent single-port circuit sub-networks may be the same as the value of the corresponding component. The following technical means can be adopted: the second single-port circuit sub-network 2 and the fourth single-port circuit sub-network 4 adopt exactly the same network topology and the types, types, values, implementation methods and selections of corresponding components are completely the same; or The network topology of two non-adjacent single-port circuit sub-networks is different, and the input impedance at each frequency is the same, the following technical means can be adopted: the second single-port circuit sub-network 2 and the fourth single-port circuit sub-network 4 adopt different For the same network topology, after network equivalence, the input impedances of the second single-port circuit sub-network 2 and the fourth single-port circuit sub-network 4 can be completely the same at each frequency. Considering the individual differences and various uncertainties of the components during the specific implementation, the input impedances of the second single-port circuit sub-network 2 and the fourth single-port circuit sub-network 4 can be roughly the same, and the reflection of the filter at this time The coefficient is close to zero.

In order to satisfy the product of Z ₁ and Z ₂ at all frequencies and the square of R ₀ is completely equal or roughly equal, the following technical means can be used:

The first single-port circuit sub-network 1 and the second single-port circuit sub-network 2 adopt a dual network topology, for example: series and parallel interchange; at the same time, the types of corresponding components are interchanged: that is, the inductance and capacitance are interchanged, and the resistance and conductance are interchanged; At the same time, the component values are reciprocals of each other after normalization to R ₀ .

The first single-port circuit sub-network 1 and the second single-port circuit sub-network 2 adopt a non-dual network topology. After the network is equivalent, it can be achieved that at each frequency, the first single-port circuit sub-network 1 and the second The product of the input impedances of the one-port circuit subnetwork 2 is equal to the square of R ₀ .

In the implementation of a reflectionless bridge filter, the lossless elements are selected from the group consisting of: inductors, capacitors, resonators, varactors, transmission line elements, one-port equivalent lossless devices, and A combination thereof; wherein the lossy element is selected from the set consisting of: resistors, varistors, one-port nonreflective networks, one-port snubbing networks, one-port matched loads, matched input ports of external circuits, matched antennas and combinations of the above circuits. Each component can be fixed value or adjustable, so as to facilitate the later debugging of the filter or change the working mode. The device combination here refers to the formation of a new equivalent device by connecting multiple different devices in parallel, series and cascade.

According to the above description, the transmission response of the reflectionless bridge filter is completely determined by the reflection response of the second single-port circuit sub-network 2 or the fourth single-port circuit sub-network 4 . Therefore, in particular, when the second single-port circuit sub-network 2 is implemented as a traditional two-port pure reactive filter network 7 connected to a load, as shown in FIG. 2, the response of the two-port filter network 7 is the same as the synthesized The transmission responses of the reflectionless bridge filter have a one-to-one correspondence, which is a simplified design method for the reflectionless filter involved in the present invention. Specifically, when the transmission responses of the two-port filter network 7 are low-pass, band-pass, high-pass, band-stop, multi-band-pass, and multi-band-stop respectively, after the matching load is connected at the end, according to the law of energy conservation, the other end The reflection coefficients are high-pass, band-stop, low-pass, band-pass, multi-band-stop and multi-band-pass respectively. At this time, if the two-port filter network 7 connected to the load is used as the second single-port circuit sub-network 2 or the fourth single-port circuit sub-network 4, correspondingly, the first single-port circuit sub-network 1 or the third single-port circuit sub-network The circuit sub-network 3 is the dual network of the two-port filter network 7, and the transmission responses of the reflectionless bridge filter are also high-pass, band-stop, low-pass, band-pass, multi-band-stop and multi-band-pass respectively. Based on the above considerations, the design of the non-reflection bridge filter can refer to the existing and mature reflective two-port filter design. More generally, the design of the second single-port circuit sub-network 2 can be free from the limitations of the existing reflective two-port filter design, and is more flexible and free. Therefore, the reflection-free bridge filter is more flexible than the traditional reflective two-port filter The transmission response of the device is richer and the design is more flexible.

Preferably, the overall filter response of the reflection-free bridge filter can be a first-order, second-order and higher-order filter, where the order refers to the minimum value among the orders of the single-port circuit sub-network.

The non-reflection bridge filters with exactly the same response can be connected in parallel or in series for power expansion. After changing the load resistance of the port accordingly, the non-reflection property will not be affected, and the filter response is the same as before. For example, after two filters of the same type with a reference impedance of 50Ohm are connected in parallel, the reference impedance becomes 25Ohm, and the filter response remains unchanged.

The non-reflection bridge filters with the same port impedance can be cascaded to improve the filter response or produce a more complex filter response, and the non-reflection property remains unchanged. For example, by cascading two reflection-free filters with exactly the same port impedance, steeper and deeper out-of-band rejection can be produced, and the insertion loss is correspondingly higher. As another example, a band-pass filter can be realized by cascading low-pass and high-pass reflection-free filters. In the above two cases the non-reflection property remains unchanged.

The non-reflection filter of the present invention has the characteristic that the reflection coefficient is zero in the whole frequency band. In actual use, there is no need to consider the adverse effect of the filter unit on the overall circuit due to reflection, and it can also be conveniently cascaded to further improve the filter. device performance.

In order to verify that the present invention can realize a reflectionless filter with a customizable response, two examples are given for illustration.

Embodiment one,

In this embodiment, as shown in FIG. 2 , each single-port circuit sub-network is realized by using a two-port reflective filter network 7 connected to a load, which is not limited by the present invention.

In this embodiment, a port reference impedance of 50 Ohm is adopted, that is, R ₀ =50Ω, which is not limited in the present invention.

In this embodiment, an elliptic function bandpass filter design based on lumped elements is adopted, which is not limited in the present invention.

In this embodiment, the same single-port circuit sub-network circuit design is adopted, that is, the first single-port circuit sub-network 1 or the third single-port circuit sub-network 3 are completely the same, and the second single-port circuit sub-network 2 or the fourth The single-port circuit sub-network 4 is completely the same, which is not limited in the present invention.

In this embodiment, a design in which adjacent single-port circuit sub-networks are dual to each other is adopted, that is, the first single-port circuit sub-network 1 and the second single-port circuit sub-network 2 are dual to each other, which is not limited in the present invention.

In this embodiment, the design target is a (quasi) elliptic function bandpass filter with lumped parameters, the central operating frequency is 1 GHz, and the relative operating bandwidth is 4%. The reflection response of the second single-port circuit sub-network 2 to the port reference impedance R ₀ =50 Ohm is the transmission response of the overall filter network. Therefore, when the reflection response of the second single-port circuit sub-network 2 is a (quasi) elliptic function bandpass filter, and the circuit elements are all lumped parameter formulas, the design requirements can be met. Considering the simplicity of the design, a mature two-port filter network is used in this example as the specific implementation method of the second single-port circuit sub-network 2, as shown in Figure 2. When the two-port filter network 7 is connected to a 50 Ohm load, a single-port circuit sub-network circuit is formed. When the reflection response of the two-port filter network 7 connected to the load is a (quasi) elliptic function bandpass filter, according to the energy conservation relational expression, it can be drawn that the transmission response of the two-port filter network 7 at this time should be (quasi) ) Elliptic function band-stop filter. Therefore, the design of the second single-port circuit sub-network 2 can be completed only by designing a (quasi) elliptic function band-stop filter that meets the requirements and realizing it with lumped parameter elements.

In order to simplify the overall circuit design, in the specific implementation process, this embodiment adopts the identical and dual single-port circuit subnetwork design, that is, the non-adjacent single-port circuit subnetworks are completely the same, and the adjacent single-port circuit subnetworks are completely identical. Dual, single-port circuit sub-networks 8 and 9 are shown in Figure 3(a) and Figure 3(b) respectively. The final structure of the filter circuit is shown in Fig. 3(c). In this filter circuit, the four single-port circuit subnetworks are simplified into two types, which are dual to each other, that is, the single-port circuit subnetworks 8 and 9 in Fig. 3, where the values of each component are shown in Table 1 shown.

Table 1

Using ADS simulation software, the above-mentioned circuit schematic diagram is simulated and simulated, and the obtained S parameter curve is shown in Figure 4. It can be seen from the transmission coefficient S ₂₁ curve that at 1.0GHz, the filter forms a passband with a bandwidth of about 4%, and also has two out-of-band transmission zeros, which meet the design requirements. The simulated reflection coefficient S ₁₁ of the filter is less than -100dB in the whole frequency band, which verifies the property of no reflection.

Embodiment two,

In the present embodiment, as shown in Fig. 5 (e), utilize ideal transmission line structure, the present invention has designed a kind of reflectionless filter, comprise: input port 5 and output port 6, two single-port transmission line sub-networks 12 and 13 ; Its bridge connection mode is the same as embodiment 1, and will not be described in detail here, as shown in Figure 1. The specific design method of this type of transmission line filter is briefly described below.

The goal of this implementation example is a reflectionless bandpass filter with a transmission line structure. In order to simplify the design process, this implementation example uses a terminal load with a normalized impedance of 1Ohm and an input and output reference port; the adjacent subnetworks are dual , The overall network design in which non-adjacent sub-networks are identical. The present invention is not limited thereto.

As shown in Fig. 5(a), the transmission line sub-network 10 is a transmission line network generated directly by Richard transform, and its prototype is a two-port third-order Chebyshev function low-pass filter connected to a single-ended load. Component values are normalized values. The reflection coefficient curve of the network 10 can be regarded as a bandpass filter. Using the principle of duality, another corresponding transmission line sub-network 11 can be directly generated, which is also a third-order Chebyshev function low-pass filter connected to the load, as shown in Figure 5(b).

Using the Kuroda transformation, the transmission line sub-networks 10 and 11 can be transformed into transmission line networks with only parallel stub lines, respectively forming the transmission line network 12 shown in Figure 5(c) and the transmission line network 13 shown in Figure 5(d). At this time, the reactance elements in the transmission line network have been separated by unit elements, which is beneficial to the realization of microwave.

In particular, after the Kuroda transformation, the transmission line networks 12 and 13 are no longer strictly dual networks in structure, but their input impedances are reciprocals of each other. The values of the components of the above-mentioned circuit networks are shown in Table 2.

Table 2

By bridging the transmission line networks 12 and 13 as shown in Fig. 5(e), and setting the port impedance to 1 Ohm, the prototype design of the transmission line band-pass (high-pass) filter can be completed. In the actual processing and realization of the filter, first, the characteristic impedance of the transmission line of each component needs to be denormalized using the required reference impedance, for example: 50 Ohm, which is not described in detail in the present invention. In physical implementation, transmission lines such as microstrip lines, coaxial lines, slot lines, coplanar waveguides, and double-sided parallel strip lines can be used for design, and mixed designs can also be used, which are not limited by the present invention.

As shown in Figure 6, using ADS software, you can get the complete response of the circuit. There is a passband at 1GHz, and the magnitude S ₁₁ of the reflection coefficient in the whole frequency band is less than -70dB, which is close to no reflection. The non-ideality of the reflection coefficient here is caused by the truncation error when calculating the characteristic impedance of the transmission line. By improving the numerical accuracy of the simulated impedance, the reflection coefficient can be reduced. Similarly, in actual circuit fabrication, the magnitude of the above-mentioned reflection coefficient is related to machining accuracy, but has nothing to do with design.

In summary, the bandpass filter based on the transmission line structure of the present invention can realize a high-performance filter response without reflection, and has the advantages of zero reflection coefficient in the entire frequency band, simple structure, and excellent performance. This invention has wide application prospects.

The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and can also be made without departing from the gist of the present invention within the scope of knowledge possessed by those of ordinary skill in the art. Variations.

Claims (10)

1. No reflection bridge filter, it is characterized in that, comprises independent first to the 4th single-port circuit sub-network, input port, output port, wherein each single-port circuit sub-network all has two endpoints; Said four A single-port circuit subnetwork is sequentially connected in a ring through respective endpoints, and one endpoint of the input port is connected to the common endpoint of the first and second single-port circuit subnetworks, and the other endpoint of the input port is connected to the first and second single-port circuit subnetworks. Common endpoints of the three and fourth single-port circuit subnetworks; one endpoint of the output port is connected to the common endpoint of the second and third single-port circuit subnetworks, and the other endpoint of the output port is connected to the first and fourth The common endpoint of a one-port circuit subnetwork to form a bridge filter circuit. 2 . The non-reflection bridge filter according to claim 1 , wherein each single-port circuit sub-network contains at least one lossless device and at least one lossy device. 3. The non-reflection bridge filter according to claim 1, characterized in that: the reference impedances of the input port and the output port are the same and are pure resistance. 4 . The non-reflection bridge filter according to claim 1 , wherein the network topology of two non-adjacent single-port circuit sub-networks among the four single-port circuit sub-networks is the same as the value of the corresponding element. 5. according to the described non-reflection bridge filter of claim 1, it is characterized in that: the network topology of two non-adjacent one-port circuit sub-networks in the four one-port circuit sub-networks is different, and at each frequency The input impedance is the same. 6. The reflectionless bridge filter of claim 2, wherein said lossless device is selected from the group consisting of inductors, capacitors, resonators, varactors, transmission line elements, etc. Effective distributed devices, discontinuities, lead parasitics, one-port equivalent lossless devices, and combinations thereof. 7. The reflectionless bridge filter according to claim 2, wherein said lossy element is selected from the group consisting of resistors, varistors, single-port non-reflection networks, single-port absorbing networks, single-port The port matches the load, the input port after the external circuit is matched, the antenna after the match and the combination of the above-mentioned circuits. 8. The non-reflection bridge filter according to claim 1, characterized in that: the overall filter response of the bridge filter includes a first-order filter, a second-order filter and a higher-order filter. 9. no reflection bridge filter according to claim 1, is characterized in that: the transmission response of described bridge filter comprises low-pass, band-pass, high-pass, band-stop, multi-band-pass, multi-band-stop and combinations thereof . 10. The non-reflection bridge filter according to claim 1, wherein the bridge filter is used to cascade bridge filters with the same port impedance to change the filter response.