An adjustable band reject filter

Abstract

The application discloses a kind of adjustable band elimination filters, belongs to band elimination filter technical field, including 3dB bridge and adjustable band pass filter, 3dB bridge has first road quadrature signal output end and second road quadrature signal output end, first road quadrature signal output end is connected to the input end of adjustable band pass filter, the output end of adjustable band pass filter is connected to second road quadrature signal output end, two-port signal converges to the isolation end output of bridge, input signal is acted together with adjustable band pass filter by 3dB bridge, the first road quadrature signal phase and amplitude are made to be opposite phase and equal amplitude with second road quadrature signal in output port, constitute output band elimination filter signal.The application can use one 3dB bridge and one adjustable band pass filter to realize the preparation of adjustable band elimination filter, the scheme structure is simpler, size is smaller, cost is lower, and it is convenient to cascade.

Description

Technical Field

[0001] This invention relates to the field of adjustable bandstop filter technology, and specifically to an adjustable bandstop filter. Background Technology

[0002] An adjustable bandstop filter is a filter that allows the center frequency, stopband width, and notch depth to dynamically vary within a specific range. It plays an irreplaceable role in applications requiring flexible suppression of specific interference signals where the interference frequency may change. In communication and radio systems, adjustable bandstop filters can dynamically suppress strong interference signals from nearby transmitters, radar, or other wireless communications, prevent receiver front-end overload, and are used for channel segmentation and anti-blocking. In electronic warfare and military communications, they can provide anti-jamming communication by quickly adjusting the stopband center frequency to the interference frequency, thereby filtering out interference and ensuring the passage of useful signals.

[0003] Currently, tunable bandpass filters are widely used in communication countermeasures equipment. These are passive anti-interference technologies and cannot actively filter signals at specific frequencies. However, with technological advancements, electromagnetic interference and other problems in the communications field are becoming increasingly prominent. Consequently, the demand for active anti-interference applications using tunable bandstop filters is also growing. However, in engineering applications, tunable bandstop filters are difficult to implement, troubleshoot, and have poor technical specifications. Therefore, this invention designs a method for implementing a tunable bandstop filter, featuring miniaturization, integration, low cost, no debugging required, and easy cascading.

[0004] Traditional implementation schemes for tunable band-stop filters mainly fall into two categories. One is a frequency-hopping filter based on band-stop technology, such as the one described in Chinese patent application (publication number CN116683890A). This frequency-hopping filter mainly utilizes impedance matching networks, impedance transformation unit groups, and basic band-stop filter unit groups to realize a tunable band-stop filter. However, this scheme requires multiple basic band-stop filters and impedance transformation unit groups, thus requiring the custom design of multiple basic band-stop filters to form a band-stop filter bank, which is characterized by complex design and high debugging difficulty. The other is a method for implementing a frequency-hopping band-stop filter, such as the one described in Chinese patent application (publication number CNCN109904569A). This method mainly utilizes a 3dB bridge, two tunable pass filters, and two 50Ω matched loads to realize a tunable band-stop filter. However, this scheme requires two tunable band-pass filters and matched loads, and the performance indicators of the two tunable band-pass filters must be similar; otherwise, mismatch will occur. Therefore, the product is characterized by large size, high debugging difficulty, and high cost. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide an adjustable bandstop filter that enables miniaturization, eliminates the need for debugging, reduces cost, and facilitates easy cascading.

[0006] To solve the above-mentioned technical problems of the present invention, the technical solution adopted by the present invention is as follows: An adjustable band-stop filter, comprising a 3dB bridge and an adjustable bandpass filter, wherein the 3dB bridge has a first quadrature signal output terminal and a second quadrature signal output terminal, the first quadrature signal output terminal is connected to the input terminal of the adjustable bandpass filter, and the output terminal of the adjustable bandpass filter is connected to the second quadrature signal output terminal. The signals at the two ports are combined and output to the isolation terminal of the 3dB bridge. The input signal, after passing through the 3dB bridge and the adjustable bandpass filter, works together to make the phase and amplitude of the first quadrature signal out of phase and equal in amplitude with the second quadrature signal at the output port, thereby forming the output band-stop filter signal.

[0007] Furthermore, the above uses two or more sets of 3dB bridges and adjustable bandpass filters connected in series.

[0008] Furthermore, the aforementioned 3dB bridge is implemented using a transmission line parallel coupling method.

[0009] Furthermore, the aforementioned 3dB bridge and the inductor of the adjustable bandpass filter are integrated into the LTCC substrate, and the LTCC substrate has surface-mount varactor diodes, resistors, and variable capacitors.

[0010] Furthermore, the aforementioned LTCC substrate is a seven-layer board, comprising, from bottom to top, layers L1, L2 and L3, a ground layer L4, layers L5 and L6, and layer L7. Layer L1 is provided with bottom ground and input / output surface mount pads; layers L2 and L3 are coupled to form a 3dB 90° bridge; the ground layer L4 is used for impedance control and isolation; layers L5 and L6 integrate filter inductors; layer L7 is the top layer, containing surface mount varactor diodes, resistors, and variable capacitors.

[0011] Furthermore, the circuit structure of the aforementioned adjustable bandpass filter includes inductors L1, L2, L3, L4, L5, and L6. One end of inductor L1 is connected to the output terminal, and the other end is connected to one end of inductors L2 and L3. The other end of inductor L2 is connected to one end of variable capacitor C1. The other end of inductor L3 is connected to the ground terminal and one end of inductor L4. The other end of inductor L4 is connected to one end of inductors L5 and L6. The other end of inductor L5 is connected to one end of variable capacitor C2. The other end of inductor L6 is connected to the first quadrature signal output terminal. The other ends of variable capacitors C1 and C2 are connected to the ground terminal.

[0012] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention has the following advantages: 1) This invention enables the fabrication of an adjustable bandstop filter using a 3dB bridge and an adjustable bandpass filter. This scheme has a simpler structure, smaller size, lower cost, and is easy to cascade. Compared to the reflective balanced structure in publication number CN109904569A, which utilizes the difference in the reflection characteristics of the filter, this application adopts a transmission structure. Utilizing the principle of transmission interference, the bridge first splits the signal into two orthogonal signals. The bandpass filter undergoes the amplitude and phase changes of the two orthogonal signals from the bridge, causing the two signals to converge at the output. This results in the two signals being out of phase and equal in amplitude at the output port, thus completely canceling each other out and forming a bandstop.

[0013] 2) In order to improve band-stop performance and increase notch depth, the above band-stop filter can also be regarded as a module. Two or more modules can be cascaded, and the output of the previous stage can be directly cascaded to the input of the next stage to improve band-stop performance. 2) In order to reduce size, achieve integration, and eliminate debugging, based on the above principle, the LTCC technology is used to integrate the 3dB bridge and the inductor of the bandpass filter inside the LTCC, and surface-mount varactor diodes, resistors and variable capacitors. This solution has a high degree of integration. Since the loss of the bandstop filter is not sensitive to the Q value, the product size can be further reduced according to the requirements. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the principle structure of a single-stage tunable bandstop filter; Figure 2 This is a schematic diagram of the principle structure of a cascaded tunable bandstop filter; Figure 3 This is a schematic diagram of the circuit structure of a cascaded tunable bandstop filter; Figure 4 This is a schematic diagram (transparent) of the integrated 3D structure of a tunable bandstop filter using an LTCC. Figure 5 This is a schematic diagram of the integrated front-view structure of a tunable bandstop filter (LTCC). Figure 6 This is a schematic diagram of the LTCC integrated surface mount layer structure; Figure 7 This is a schematic diagram of the simulation curve. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0016] Example 1: As Figure 1-6As shown, an adjustable band-stop filter includes a 3dB bridge and an adjustable bandpass filter. The 3dB bridge has a first quadrature signal output terminal and a second quadrature signal output terminal. The first quadrature signal output terminal is connected to the input terminal of the adjustable bandpass filter, and the output terminal of the adjustable bandpass filter is connected to the second quadrature signal output terminal. The signals from the two ports are combined and output from the isolation terminal of the 3dB bridge. The input signal, after passing through the 3dB bridge and the adjustable bandpass filter, works together to make the phase and amplitude of the first quadrature signal out of phase and equal in amplitude to the second quadrature signal at the output port, thus forming the output band-stop filter signal.

[0017] Two or more 3dB bridges and adjustable bandpass filters are connected in series.

[0018] Furthermore, the aforementioned 3dB bridge is implemented using a transmission line parallel coupling method.

[0019] Specifically, the aforementioned 3dB bridge and the inductor of the adjustable bandpass filter are integrated into the LTCC substrate. The LTCC substrate has surface-mount varactor diodes, resistors, and variable capacitors. Integrating the 3dB bridge and the inductor of the bandpass filter inside the LTCC, with surface-mount varactor diodes, resistors, and variable capacitors, this solution has a high degree of integration. Since the loss of the bandstop filter is not sensitive to the Q value, the product size can be further reduced according to requirements.

[0020] In summary, the integrated design primarily integrates the bridge and inductor in the vertical direction. Compared to traditional solutions, it reduces surface-mount components, thus reducing size and the cost of the bridge and inductor. It also reduces solder joints, improving reliability.

[0021] Specifically, the LTCC substrate uses a seven-layer board, from bottom to top including L1 layer, L2 and L3 layers, L4 ground layer, L5 and L6 layers, and L7 layer. L1 layer houses the bottom ground and input / output surface-mount pads; L2 and L3 layers are coupled to form a 3dB 90° bridge; L4 ground layer is used for impedance control and isolation; L5 and L6 layers integrate filter inductors; L7 layer is the top layer, containing surface-mount varactor diodes, resistors, and variable capacitors, such as... Figure 6 A schematic diagram of the top-level structure design. (See attached diagram.) Figure 6 As shown: RF signals are input and output through the bottom port of the band-stop filter, and the control signal port is connected to the host computer for signal control. Labeled resistors R1 and R2 control the current. Diodes CV1 and CV2 are varactor diodes to achieve frequency adjustment. C1 and C2 are bypass capacitors, which provide a return path for high-frequency models and filter out AC noise.

[0022] The integration effect is as follows: 1. The L1 layer port is located on the bottom surface for easy reflow soldering.

[0023] 2. L2 and L3 use parallel coupled 3dB bridge bend traces to reduce the area.

[0024] 3. The L4 grounding layer controls the impedance and isolates the bridge circuit from the inductor, preventing cross-contamination.

[0025] 4. Inductors are integrated in layers L5 and L6 to achieve three-dimensional integration in the vertical direction.

[0026] 5. Finally, surface mount the few remaining resistors and capacitors that cannot be integrated onto the surface.

[0027] Specifically, the circuit structure of the adjustable bandpass filter includes inductors L1, L2, L3, L4, L5, and L6. One end of inductor L1 is connected to the output terminal, and the other end is connected to one end of inductors L2 and L3. The other end of inductor L2 is connected to one end of variable capacitor C1. The other end of inductor L3 is connected to ground and one end of inductor L4. The other end of inductor L4 is connected to one end of inductors L5 and L6. The other end of inductor L5 is connected to one end of variable capacitor C2. The other end of inductor L6 is connected to the first quadrature signal output terminal. The other ends of variable capacitors C1 and C2 are connected to ground. Figure 6 As shown, the RF signal is input and output through the bottom port of the band-stop filter. The control signal port is connected to the host computer for signal control, and the labeled components R1 and R2 control the current. CV1 and CV2 are varactor diodes to achieve frequency adjustment, and C1 and C2 are bypass capacitors, providing a return path for high-frequency models and filtering out AC noise.

[0028] The method for fabricating an tunable bandstop filter adopts a conventional approach, and the steps are as follows: Step 1: Perform 3D finite element modeling based on design specifications; Step 2: Simulate and optimize the circuit layout and routing performance indicators; Step 3: Output LTCC layout; Step 4: LTCC machining; Step 5: Patch performance test.

[0029] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. An adjustable band-stop filter, characterized in that, It includes a 3dB bridge and an adjustable bandpass filter. The 3dB bridge has a first quadrature signal output terminal and a second quadrature signal output terminal. The first quadrature signal output terminal is connected to the input terminal of the adjustable bandpass filter, and the output terminal of the adjustable bandpass filter is connected to the second quadrature signal output terminal. The signals from the two ports are combined and output to the isolation terminal of the 3dB bridge. The input signal, after passing through the 3dB bridge and the adjustable bandpass filter, works together to make the phase and amplitude of the first quadrature signal out of phase and equal in amplitude with the second quadrature signal at the output port, thus forming the output bandstop filter signal.

2. The adjustable bandstop filter according to claim 1, characterized in that, Two or more 3dB bridges and adjustable bandpass filters are connected in series.

3. The adjustable band-stop filter according to claim 1, characterized in that, The 3dB bridge is implemented using parallel coupling of transmission lines.

4. An adjustable band-stop filter according to claim 1, characterized in that, The 3dB bridge and the inductor of the adjustable bandpass filter are integrated into the LTCC substrate, and the LTCC substrate has surface-mount varactor diodes, resistors and variable capacitors.

5. An adjustable band-stop filter according to claim 1, characterized in that, The LTCC substrate uses a seven-layer board, which includes L1, L2 and L3, L4 ground layer, L5 and L6, and L7 from bottom to top. L1 layer is set with bottom ground and input / output surface mount pads; L2 and L3 layers are coupled to form a 3dB 90° bridge; L4 ground layer is used to control impedance and provide isolation; L5 and L6 layers integrate filter inductors; L7 layer is the top layer, with surface mount varactor diodes, resistors, and variable capacitors.

6. An adjustable band-stop filter according to claim 1, characterized in that, The circuit structure of the adjustable bandpass filter includes inductors L1, L2, L3, L4, L5, and L6. One end of inductor L1 is connected to the output terminal, and the other end is connected to one end of inductors L2 and L3. The other end of inductor L2 is connected to one end of variable capacitor C1. The other end of inductor L3 is connected to the ground terminal and one end of inductor L4. The other end of inductor L4 is connected to one end of inductors L5 and L6. The other end of inductor L5 is connected to one end of variable capacitor C2. The other end of inductor L6 is connected to the first quadrature signal output terminal. The other ends of variable capacitors C1 and C2 are connected to the ground terminal.

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