A topology and bandwidth reconfigurable low pass filter
By designing a topology that includes PIN diodes and microstrip lines, the bandwidth reconfigurability of the low-pass filter is realized, solving the problem that existing technologies cannot simultaneously satisfy high selectivity and wide stopband, and possessing the advantages of high selectivity, wide stopband and high isolation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHENZHEN SUNWAY COMM
- Filing Date
- 2024-03-05
- Publication Date
- 2026-07-21
AI Technical Summary
Existing bandwidth-reconfigurable low-pass filters cannot simultaneously satisfy high selectivity and wide stopband, limiting their application in modern wireless communication systems.
A topology consisting of PIN diodes, microstrip lines, open-circuit stubs, etc. is adopted. The bandwidth of the filter is adjusted by controlling the operating state of the PIN diodes, thereby achieving bandwidth reconfigurability.
The designed low-pass filter exhibits high selectivity, wide stopband, and high isolation under different conditions, with reconfigurable bandwidth, meeting the multifunctional requirements of modern wireless communication systems.
Smart Images
Figure CN117937077B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of filter technology, and in particular to a low-pass filter with reconfigurable topology and bandwidth. Background Technology
[0002] With the rapid development of modern 5G technology, miniaturization of multifunctional communication systems has become an inevitable trend. However, the reality is that the radio frequency (RF) filters currently widely used in multifunctional communication systems are characterized by being non-adjustable and having fixed functions. To achieve the multifunctionality of a communication system, a large number of RF filters with different specifications need to be placed inside the system, which undoubtedly increases the complexity and size of the communication system. If the RF filter had reconfigurable characteristics, allowing the same filter to flexibly meet different specifications, it would help simplify the design of wireless communication systems and greatly reduce their size and weight.
[0003] To fully utilize spectrum resources and suppress out-of-band signals, microwave communication systems require low-pass filters with high selectivity and wide stopband. However, existing bandwidth-reconfigurable low-pass filters often cannot simultaneously satisfy both high selectivity and wide stopband, greatly limiting their use in modern wireless communication systems. Summary of the Invention
[0004] In view of the above-mentioned shortcomings of the prior art, the main objective of the present invention is to provide a low-pass filter with reconfigurable topology and bandwidth, which aims to solve the problem that existing bandwidth reconfigurable low-pass filters cannot simultaneously satisfy high selectivity and wide stopband.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:
[0006] A topology includes a first PIN diode, a second PIN diode, a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line, a fifth microstrip line, a sixth microstrip line, a first open-circuit stub, a second open-circuit stub, a third open-circuit stub, a fourth open-circuit stub, a fifth open-circuit stub, an input terminal, and an output terminal.
[0007] One end of the first microstrip line and one end of the second microstrip line are both connected to the input terminal. One end of the fifth microstrip line and one end of the sixth microstrip line are both connected to the output terminal. The other end of the first microstrip line is connected to the first open-circuit stub. The other end of the sixth microstrip line is connected to the fifth open-circuit stub. The other ends of the second microstrip line and the fifth microstrip line are both connected to one end of the third microstrip line. The other end of the third microstrip line is connected to the cathode of the first PIN diode, the cathode of the second PIN diode, and one end of the fourth microstrip line, respectively. The anode of the first PIN diode is connected to the third open-circuit stub. The anode of the second PIN diode is connected to the fourth open-circuit stub. The other end of the fourth microstrip line is connected to the second open-circuit stub.
[0008] Optionally, the third microstrip line and the fourth microstrip line are located on the same vertical line, and the first microstrip line and the sixth microstrip line, the second microstrip line and the fifth microstrip line, the first open-circuit stub and the fifth open-circuit stub, the third open-circuit stub and the fourth open-circuit stub, the first PIN diode and the second PIN diode are all symmetrical about the same vertical line where the third microstrip line and the fourth microstrip line are located.
[0009] Optionally, the first microstrip line, the second microstrip line, the fifth microstrip line, the sixth microstrip line, the second open-circuit stub, the third open-circuit stub, and the fourth open-circuit stub are arranged in parallel and are all perpendicular to the third microstrip line, the fourth microstrip line, the first open-circuit stub, and the fifth open-circuit stub.
[0010] Optionally, the electrical lengths of the second microstrip line, the third microstrip line, the fifth microstrip line, the third open-circuit stub, and the fourth open-circuit stub are all quarter wavelengths corresponding to the stopband center frequency; the sum of the electrical lengths of the first microstrip line and the first open-circuit stub, the sum of the electrical lengths of the fourth microstrip line and the second open-circuit stub, and the sum of the electrical lengths of the sixth microstrip line and the fifth open-circuit stub are all quarter wavelengths corresponding to the stopband center frequency.
[0011] Optionally, the characteristic impedances of the first microstrip line, the sixth microstrip line, the first open-circuit stub, and the fifth open-circuit stub are the same; the characteristic impedances of the second microstrip line and the fifth microstrip line are the same; the characteristic impedances of the third open-circuit stub and the fourth open-circuit stub are the same; and the characteristic impedances of the fourth microstrip line and the second open-circuit stub are the same.
[0012] Optionally, the topology includes two odd-mode transmission poles, one even-mode transmission pole, and three transmission zeros.
[0013] Another technical solution adopted in this invention is:
[0014] A bandwidth-reconfigurable low-pass filter, comprising the topology described above.
[0015] Optionally, the system also includes a circuit board, on which the topology is disposed. The lengths of the first microstrip line and the sixth microstrip line are the same, the lengths of the first open-circuit stub and the fifth open-circuit stub are the same, the lengths of the second microstrip line and the fifth microstrip line are the same, the lengths of the third open-circuit stub and the fourth open-circuit stub are the same, the widths of the first microstrip line and the sixth microstrip line are the same, the widths of the second microstrip line and the fifth microstrip line are the same, the widths of the fourth microstrip line and the second open-circuit stub are the same, and the widths of the third open-circuit stub and the fourth open-circuit stub are the same.
[0016] Optionally, the circuit board has a dielectric loss of 0.0022, a thickness of 0.813 mm, and dimensions of 25.5 mm * 16.2 mm.
[0017] Optionally, the lengths of the first microstrip line and the sixth microstrip line are both set to 8.1 mm; the lengths of the first open-circuit stub and the fifth open-circuit stub are both set to 1.8 mm; the lengths of the second microstrip line and the fifth microstrip line are both set to 9.6 mm; the length of the third microstrip line is set to 10.8 mm; the length of the fourth microstrip line is set to 1.7 mm; the length of the second open-circuit stub is set to 8.5 mm; the lengths of the third open-circuit stub and the fourth open-circuit stub are both set to 10.2 mm; the widths of the first microstrip line, the sixth microstrip line, the first open-circuit stub, and the fifth open-circuit stub are all set to 0.7 mm; the widths of the second microstrip line and the fifth microstrip line are both set to 0.1 mm; the width of the third microstrip line is set to 1.7 mm; the width of the fourth microstrip line and the width of the second open-circuit stub are both set to 0.6 mm; and the widths of the third open-circuit stub and the fourth open-circuit stub are both set to 0.9 mm.
[0018] The beneficial effects of this invention are as follows: a new topology is proposed, which can be used to design bandwidth reconfigurable low-pass filters. The bandwidth reconfigurable low-pass filters based on this topology have the advantages of high selectivity, wide stopband and high isolation. Attached Figure Description
[0019] Figure 1The diagram shown is a topological structure diagram of an embodiment of the present invention;
[0020] Figure 2 The diagram shown is an equivalent passive topology of an embodiment of the present invention.
[0021] Figure 3 The diagram shown is a schematic representation of the odd-mode form of the equivalent passive topology in an embodiment of the present invention.
[0022] Figure 4 The diagram shown is a schematic diagram of the even-mode form of the equivalent passive topology of an embodiment of the present invention;
[0023] Figure 5 and Figure 6 The diagram shown is a layout diagram of a low-pass filter according to an embodiment of the present invention;
[0024] Figure 7 The figure shows the S-parameter simulation results of the low-pass filter in State 1 according to an embodiment of the present invention;
[0025] Figure 8 The figure shows the S-parameter simulation results of the low-pass filter in State 2 according to an embodiment of the present invention;
[0026] Figure 9 The figure shows the S-parameter simulation results of the low-pass filter in State 3 according to an embodiment of the present invention;
[0027] Figure 10 The figure shows the S-values of the low-pass filter in different operating states according to an embodiment of the present invention. 21 Parameter simulation results. Detailed Implementation
[0028] To better understand the technical content, objectives, and effects of this invention, the following detailed description, in conjunction with specific embodiments and accompanying drawings, is provided. It should be noted that, unless otherwise specified, the embodiments and features of this invention can be combined with each other. Numerous specific details are set forth in the following description to provide a thorough understanding of this invention. The described embodiments are merely a part of, and not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.
[0029] Please refer to Figure 1-4 As shown, Embodiment 1 of the present invention is as follows:
[0030] A topology primarily composed of two PIN diodes, five open-circuit stubs, and six microstrip lines. Please refer to [reference needed]. Figure 1Specifically, it includes a first PIN diode D1, a second PIN diode D2, a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line, a fifth microstrip line, a sixth microstrip line, a first open-circuit stub, a second open-circuit stub, a third open-circuit stub, a fourth open-circuit stub, a fifth open-circuit stub, an input terminal, and an output terminal.
[0031] One end of the first microstrip line and one end of the second microstrip line are both connected to the input terminal. One end of the fifth microstrip line and one end of the sixth microstrip line are both connected to the output terminal. The other end of the first microstrip line is connected to the first open-circuit stub. The other end of the sixth microstrip line is connected to the fifth open-circuit stub. The other ends of the second microstrip line and the fifth microstrip line are both connected to one end of the third microstrip line. The other end of the third microstrip line is connected to the cathode of the first PIN diode D1, the cathode of the second PIN diode D2, and one end of the fourth microstrip line, respectively. The anode of the first PIN diode D1 is connected to the third open-circuit stub. The anode of the second PIN diode D2 is connected to the fourth open-circuit stub. The other end of the fourth microstrip line is connected to the second open-circuit stub.
[0032] The fifth microstrip line and the fourth microstrip line are located on the same vertical line. The first microstrip line and the sixth microstrip line, the second microstrip line and the fifth microstrip line, the first open-circuit stub and the fifth open-circuit stub, the third open-circuit stub and the fourth open-circuit stub, the first PIN diode D1 and the second PIN diode D2 are all symmetrical about the same vertical line where the third microstrip line and the fourth microstrip line are located.
[0033] The first microstrip line, the second microstrip line, the fifth microstrip line, the sixth microstrip line, the second open-circuit stub, the third open-circuit stub, and the fourth open-circuit stub are arranged in parallel and are all perpendicular to the third microstrip line, the fourth microstrip line, the first open-circuit stub, and the fifth open-circuit stub.
[0034] The electrical lengths of the second microstrip line, the third microstrip line, the fifth microstrip line, the third open-circuit stub, and the fourth open-circuit stub are all quarter wavelengths corresponding to the stopband center frequency; the sum of the electrical lengths of the first microstrip line and the first open-circuit stub, the sum of the electrical lengths of the fourth microstrip line and the second open-circuit stub, and the sum of the electrical lengths of the sixth microstrip line and the fifth open-circuit stub are all quarter wavelengths corresponding to the stopband center frequency.
[0035] The characteristic impedances of the first microstrip line, the sixth microstrip line, the first open-circuit stub, and the fifth open-circuit stub are the same, both being Z1; the characteristic impedances of the second microstrip line and the fifth microstrip line are the same, both being Z2; the characteristic impedances of the third open-circuit stub and the fourth open-circuit stub are the same, both being Z4; and the characteristic impedances of the fourth microstrip line and the second open-circuit stub are the same, both being Z5.
[0036] The topology includes two odd-mode transmission poles, one even-mode transmission pole, and three transmission zeros.
[0037] In the above topology, since the characteristic impedance of the fourth microstrip line is the same as that of the second open-circuit stub, and the sum of the electrical lengths of the fourth microstrip line and the second open-circuit stub is a quarter wavelength corresponding to the stopband center frequency, these two can be equivalent to a single open-circuit stub. For ease of explanation, this equivalent open-circuit stub is called the sixth open-circuit stub. The electrical length of the sixth open-circuit stub is a quarter wavelength corresponding to the stopband center frequency, and the characteristic impedance of the sixth open-circuit stub is equal to the characteristic impedances of the four microstrip lines and the second open-circuit stub, i.e., Z5.
[0038] Furthermore, the electrical lengths of the third, fourth, and sixth open-circuit stubs are the same, and they are connected in parallel with respect to the third microstrip line. Therefore, these three can be considered as a single open-circuit stub, hereinafter referred to as the seventh open-circuit stub. In this case, the electrical length of the seventh open-circuit stub is one-quarter of the wavelength corresponding to the stopband center frequency, and the characteristic impedance of the seventh open-circuit stub is the same as the characteristic impedances of the third, fourth, and sixth open-circuit stubs during actual operation. Depending on the operating states of the first PIN diode D1 and the second PIN diode D2, the characteristic impedance of the seventh open-circuit stub has the following three possibilities.
[0039] State 1: When both the first PIN diode D1 and the second PIN diode D2 are open-circuited, the third and fourth open-circuit stubs are disconnected from the third microstrip line, and only the sixth open-circuit stub is connected to the third microstrip line. At this time, the characteristic impedance Z6 of the seventh open-circuit stub is equal to the characteristic impedance of the sixth microstrip line, i.e.:
[0040] Z6 = Z5
[0041] State 2: When the first PIN diode D1 is in the connected state and the second PIN diode D2 is in the open-circuit state, only the third and sixth open-circuit stubs are connected to the third microstrip line, while the fourth open-circuit stub is in the open state; when the first PIN diode D1 is in the open-circuit state and the second PIN diode D2 is in the connected state, only the fourth and sixth open-circuit stubs are connected to the third microstrip line, while the third open-circuit stub is in the open state. Considering that the characteristic impedance of the third open-circuit stub is equal to that of the fourth open-circuit stub, the seventh characteristic impedance in both cases is:
[0042]
[0043] State 3: When both the first PIN diode D1 and the second PIN diode D2 are connected, the third, fourth, and sixth open-circuit stubs are all connected to the third microstrip line. At this time, the characteristic impedance of the seventh open-circuit stub is:
[0044]
[0045] From the above analysis, it can be seen that the first PIN diode D1, the second PIN diode D2, the fourth microstrip line, the second open-circuit stub, the third open-circuit stub, and the fourth open-circuit stub can be equivalent to the seventh open-circuit stub. The electrical length of the seventh open-circuit stub is one-quarter wavelength corresponding to the stopband center frequency, and the characteristic impedance of the seventh open-circuit stub changes with the operating states of the first PIN diode D1 and the second PIN diode D2. Therefore, the above topology can be transformed into... Figure 2 The equivalent passive topology is shown to facilitate further analysis of its transmission zeros and poles.
[0046] because Figure 2 The equivalent topology shown is a symmetrical structure, and its transmission zeros and poles can be analyzed using parity modes.
[0047] like Figure 3 The figure shows the odd-mode form of the equivalent topology.
[0048] When Y ino When =∞, it can be concluded that this topology has two odd-mode transmission poles, and the frequencies corresponding to the two odd-mode transmission poles are:
[0049] f op1 =0
[0050] f op2 =f0
[0051] Where f0 is the center frequency of the band-stop filter.
[0052] like Figure 4The figure shows the even-mode form of the equivalent topology.
[0053] The electrical lengths of the seventh microstrip line and the eighth open-circuit stub are both quarter wavelengths corresponding to the stopband center frequency. The characteristic impedance of the seventh microstrip line is twice that of the third microstrip line, and the characteristic impedance of the eighth open-circuit stub is twice that of the seventh open-circuit stub.
[0054] When Y ine When =∞, it can be concluded that this topology has an even-mode transmission pole, the corresponding frequency of which is:
[0055]
[0056] For this topology, its transmission zeros can be calculated as follows: multiply the ABCD matrices of the cascaded resonators that make up the topology sequentially to obtain the corresponding ABCD matrix of the topology; then transform the ABCD matrix of the topology into the corresponding S matrix. When |S 21 When | = 0, it can be concluded that this topology has three transmission zeros, and the frequencies corresponding to the three transmission zeros are as follows:
[0057]
[0058] f z2 =f0
[0059]
[0060] From the above analysis, it can be seen that this topology has two odd-mode transmission poles, one even-mode transmission pole, and three transmission zeros. Regardless of how the values of parameters Z1, Z2, Z3, and Z6 change, the relative positions of these transmission poles and zeros, i.e., f... op1 <f ep1 <f z1 <f op2 =f0=f z2 <f z3 The characteristics of a transmission zero and a transmission pole will not change. Furthermore, based on the characteristics of RF filters, when the positions of the transmission zero and transmission pole coincide, only the characteristics of the transmission zero are displayed. Therefore, RF filters designed based on this topology can only be low-pass filters, with two transmission poles in the passband to ensure flatness, and three transmission zeros in the stopband to ensure high selectivity, wide stopband, and high isolation.
[0061] Furthermore, further research on the equivalent topology reveals that the bandwidth of the low-pass filter designed based on this topology is primarily determined by the ratio of Z6 to Z3, and the larger the ratio of Z6 to Z3, the larger the bandwidth of the low-pass filter. Therefore, based on the topology proposed in this invention, the bandwidth of the low-pass filter can be reconfigured by controlling the value of Z6 through the operating states of the first PIN diode D1 and the second PIN diode D2.
[0062] Due to the different operating states of the topology proposed in this invention, the characteristic impedance corresponding to the seventh open-circuit stub exhibits the following relationship:
[0063]
[0064] Therefore, the bandwidth-reconfigurable low-pass filter designed based on this topology has the maximum bandwidth in State 1 and the minimum bandwidth in State 3.
[0065] Please refer to Figure 5-10 As shown, Embodiment 2 of the present invention is as follows:
[0066] A bandwidth-reconfigurable low-pass filter includes a circuit board and the topology described in Embodiment 1, wherein the topology is disposed on the circuit board, as shown below. Figure 5 and Figure 6The layout diagram of the low-pass filter 100 is shown, where D1 is the first PIN diode, D2 is the second PIN diode, 10 is the input terminal, 20 is the first microstrip line, 21 is the second microstrip line, 22 is the third microstrip line, 24 is the fifth microstrip line, 25 is the sixth microstrip line, 30 is the first open-circuit stub, 31 is the second open-circuit stub, 32 is the third open-circuit stub, 33 is the fourth open-circuit stub, 34 is the fifth open-circuit stub, and 70 is the output terminal. The low-pass filter also includes inductors L1, L2, and L3, resistors R1 and R2, pads 40, 41, 50, and 51, a grounding hole 60, a first DC source P1, and a second DC source P2 (not shown in the figure). The first DC source P1 supplies power to the first PIN diode D1, and the second DC source P2 supplies power to the second PIN diode D2. The end of the third open-circuit stub 32 furthest from the first PIN diode D1 is connected to inductor L1 and resistor R1 in sequence. Pad 40 is located at the connection between inductor L1 and resistor R1. The end of the fourth open-circuit stub 32 furthest from the second PIN diode D2 is connected to inductor L2 and resistor R2 in sequence. Pad 50 is located at the connection between inductor L2 and resistor R2. The end of resistor R1 furthest from inductor L1 is connected to pad 41, and the end of resistor R2 furthest from inductor L2 is connected to pad 51. Pad 50 is the pad for the first DC power supply P1, and pad 51 is the pad for the second DC power supply P2. The connection point of the third microstrip line 22, the second microstrip line 21 and the fifth microstrip line 24 is connected to an inductor L3. The inductor L3 is connected to a grounding hole 60. By loading the grounding hole, the function of DC ground is realized.
[0067] As shown above, the first PIN diode D1 and the second PIN diode D2 control the operating states of the third open-circuit stub 32 and the fourth open-circuit stub 33 through two independent DC power supplies. The switching on and off of the first PIN diode D1 and the second PIN diode D2 controls whether the first open-circuit stub 30 and the second open-circuit stub 31 are in operation; the switching on and off of the first PIN diode D1 and the second PIN diode D2 can be controlled by whether or not power is supplied to them. Resistors R1 and R2 are protective resistors, designed to protect the first PIN diode D1 and the second PIN diode D2; inductors L1, L2, and L3 are RF blocking inductors, designed to prevent the power supply circuit and grounding circuit from participating in the RF circuit operation, and to prevent RF signals from interfering with the voltage source; pads 40 and 41 provide soldering points for the resistors and inductors.
[0068] The circuit board has a dielectric loss of 0.0022, a thickness of 0.813 mm, and dimensions of 25.5 mm * 16.2 mm.
[0069] like Figure 6 As shown, the specific parameters on the circuit board are set as follows:
[0070] The lengths of the first and sixth microstrip lines are denoted as l. 1H , l 1H = 8.1mm; the lengths of the first open branch and the fifth open branch are denoted as l. 1V , l 1V =1.8mm; the lengths of the second and fifth microstrip lines are denoted as l2, l2 = 9.6mm; the length of the third microstrip line is denoted as l3, l3 = 10.8mm; the length of the fourth microstrip line is denoted as l 4V , l 4V =1.7mm; the length of the second open branch is denoted as l 4H , l 4H =8.5mm; the lengths of the third and fourth open-circuit branches are denoted as l5, l5 = 10.2mm; the widths of the first, sixth, first, and fifth microstrip lines are denoted as w1, w1 = 0.7mm; the widths of the second and fifth microstrip lines are denoted as w2, w2 = 0.1mm; the width of the third microstrip line is denoted as w3, w3 = 1.7mm; the width of the fourth microstrip line and the width of the second open-circuit branch are denoted as w4, w4 = 0.6mm; the widths of the third and fourth open-circuit branches are denoted as w5, w5 = 0.9mm.
[0071] Figure 7 The S-parameter simulation results of the low-pass filter in State 1 are presented. State 1 refers to a state where neither the first nor the second DC power supply provides voltage, both the first PIN diode D1 and the second PIN diode D2 are open-circuited, and the third and fourth open-circuit stubs are inactive. In this state, the filter has an impedance bandwidth of DC to 1.571 GHz with a reflection coefficient less than -10 dB, a maximum in-band loss of 0.51 dB, a stopband isolation greater than 18.5 dB from 2.319 GHz to 7 GHz, two transmission poles in the passband to ensure in-band flatness, and three transmission zeros in the stopband to ensure high selectivity, wide stopband, and high isolation.
[0072] Figure 8The S-parameter simulation results of the low-pass filter in State 2 are presented. State 2 has two scenarios: The first scenario is where the first DC power supply provides voltage but the second DC power supply does not, the first PIN diode D1 is connected but the second PIN diode D2 is open, the third open stub is active but the fourth open stub is inactive; the second scenario is where the first DC power supply does not provide voltage but the second DC power supply does, the first PIN diode D1 is open but the second PIN diode D2 is connected, the third open stub is inactive but the fourth open stub is active. In this scenario, the filter's impedance bandwidth (reflection coefficient less than -10dB) ranges from DC to 1.231GHz, with a maximum in-band loss of 0.49dB; the stopband isolation (greater than 18.5dB) ranges from 1.895GHz to 7GHz; the passband has two transmission poles to ensure in-band flatness; and the stopband has three transmission zeros to ensure high selectivity, wide stopband, and high isolation. It should be noted that the third transmission zero in the stopband is greater than 7GHz, therefore it is not included in the calculation. Figure 8 It is displayed in the middle.
[0073] Figure 9 The S-parameter simulation results of the low-pass filter in State 3 are presented. State 3 refers to a state where both the first and second DC power supplies provide voltage, both the first PIN diode D1 and the second PIN diode D2 are connected, and both the third and fourth open-circuit stubs are operational. In this state, the filter has an impedance bandwidth of DC to 1.026 GHz with a reflection coefficient less than -10 dB, a maximum in-band loss of 0.49 dB, a stopband isolation greater than 18.5 dB from 1.655 GHz to 7 GHz, two transmission poles in the passband to ensure in-band flatness, and three transmission zeros in the stopband to ensure high selectivity, wide stopband, and high isolation. It should be noted that the third transmission zero in the stopband is greater than 7 GHz, therefore it is not included in the simulation. Figure 9 It is displayed in the middle.
[0074] from Figure 7-9 Simulation results show that, under the control of two independent DC power supplies, the maximum operating frequency of the low-pass filter in this embodiment decreases from 1.571 GHz to 1.206 GHz. Under different operating conditions, the low-pass filter exhibits high selectivity, wide stopband, and high isolation.
[0075] Figure 10 Simulation results of the S-parameters of the low-pass filter under different operating conditions are presented. Figure 10 It can be seen that the bandwidth of the low-pass filter in this embodiment can be reconfigured under different operating conditions.
[0076] In summary, the low-pass filter with reconfigurable topology and bandwidth proposed in this invention has the advantages of high selectivity, wide stopband, and high isolation, in addition to the reconfigurable bandwidth.
[0077] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Therefore, any modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.
Claims
1. A topological structure, characterized in that, It includes a first PIN diode, a second PIN diode, a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line, a fifth microstrip line, a sixth microstrip line, a first open-circuit stub, a second open-circuit stub, a third open-circuit stub, a fourth open-circuit stub, a fifth open-circuit stub, an input terminal, and an output terminal; One end of the first microstrip line and one end of the second microstrip line are both connected to the input terminal. One end of the fifth microstrip line and one end of the sixth microstrip line are both connected to the output terminal. The other end of the first microstrip line is connected to the first open-circuit stub. The other end of the sixth microstrip line is connected to the fifth open-circuit stub. The other ends of the second microstrip line and the fifth microstrip line are both connected to one end of the third microstrip line. The other end of the third microstrip line is connected to the cathode of the first PIN diode, the cathode of the second PIN diode, and one end of the fourth microstrip line, respectively. The anode of the first PIN diode is connected to the third open-circuit stub. The anode of the second PIN diode is connected to the fourth open-circuit stub. The other end of the fourth microstrip line is connected to the second open-circuit stub.
2. The topology according to claim 1, characterized in that, The third microstrip line and the fourth microstrip line are located on the same vertical line. The first microstrip line and the sixth microstrip line, the second microstrip line and the fifth microstrip line, the first open-circuit stub and the fifth open-circuit stub, the third open-circuit stub and the fourth open-circuit stub, the first PIN diode and the second PIN diode are all symmetrical about the same vertical line where the third microstrip line and the fourth microstrip line are located.
3. The topology according to claim 1, characterized in that, The first microstrip line, the second microstrip line, the fifth microstrip line, the sixth microstrip line, the second open-circuit stub, the third open-circuit stub, and the fourth open-circuit stub are arranged in parallel and are all perpendicular to the third microstrip line, the fourth microstrip line, the first open-circuit stub, and the fifth open-circuit stub.
4. The topology according to claim 1, characterized in that, The electrical lengths of the second microstrip line, the third microstrip line, the fifth microstrip line, the third open stub, and the fourth open stub are all quarter wavelengths corresponding to the stopband center frequency. The sum of the electrical length of the first microstrip line and the electrical length of the first open stub, the sum of the electrical length of the fourth microstrip line and the electrical length of the second open stub, and the sum of the electrical length of the sixth microstrip line and the electrical length of the fifth open stub are all quarter wavelengths corresponding to the stopband center frequency.
5. The topology according to claim 1, characterized in that, The characteristic impedances of the first microstrip line, the sixth microstrip line, the first open-circuit stub, and the fifth open-circuit stub are the same; the characteristic impedances of the second microstrip line and the fifth microstrip line are the same; the characteristic impedances of the third open-circuit stub and the fourth open-circuit stub are the same; and the characteristic impedances of the fourth microstrip line and the second open-circuit stub are the same.
6. The topology according to claim 1, characterized in that, The topology includes two odd-mode transmission poles, one even-mode transmission pole, and three transmission zeros.
7. A bandwidth-reconfigurable low-pass filter, characterized in that, Includes the topology described in any one of claims 1-6.
8. A bandwidth-reconfigurable low-pass filter according to claim 7, characterized in that, It also includes a circuit board, on which the topology is disposed. The lengths of the first microstrip line and the sixth microstrip line are the same. The lengths of the first open-circuit stub and the fifth open-circuit stub are the same. The lengths of the second microstrip line and the fifth microstrip line are the same. The lengths of the third open-circuit stub and the fourth open-circuit stub are the same. The widths of the first microstrip line and the sixth microstrip line are the same. The widths of the second microstrip line and the fifth microstrip line are the same. The widths of the fourth microstrip line and the second open-circuit stub are the same. The widths of the third open-circuit stub and the fourth open-circuit stub are the same.
9. A bandwidth-reconfigurable low-pass filter according to claim 8, characterized in that, The circuit board has a dielectric loss of 0.0022, a thickness of 0.813 mm, and dimensions of 25.5 mm * 16.2 mm.
10. A bandwidth-reconfigurable low-pass filter according to claim 9, characterized in that, The lengths of the first and sixth microstrip lines are both set to 8.1 mm; the lengths of the first and fifth open-circuit stubs are both set to 1.8 mm; the lengths of the second and fifth microstrip lines are both set to 9.6 mm; the length of the third microstrip line is set to 10.8 mm; the length of the fourth microstrip line is set to 1.7 mm; the length of the second open-circuit stub is set to 8.5 mm; the lengths of the third and fourth open-circuit stubs are both set to 10.2 mm; the widths of the first, sixth, first, and fifth microstrip lines are all set to 0.7 mm; the widths of the second and fifth microstrip lines are all set to 0.1 mm; the width of the third microstrip line is set to 1.7 mm; the width of the fourth microstrip line and the width of the second open-circuit stub are both set to 0.6 mm; and the widths of the third and fourth open-circuit stubs are both set to 0.9 mm.