Dual-passband filter with adjustable center frequency and bandwidth

Abstract

The invention discloses a dual-passband filter with all adjustable center frequency and bandwidth, and aims to provide a band-pass filter with low loss and wide tuning range. According to the technical scheme, each part comprises an input port, an output port, a coupled feeder line, a quarter-wavelength resonator with a variable capacitance diode loaded at the tail end, and a branch resonator with a variable capacitance diode loaded. According to the structure, a coupling line connected with a source and a load is adopted to feed a resonator in a slot coupling mode, the capacitance value of a variable capacitance diode is changed, and finally, the bandwidth and the center frequency are tunable. According to simulation verification, the center frequency of a high pass band of the all-tunable filter disclosed by the invention is continuously adjustable within 2.39-2.61 GHz, and at the moment, the center frequency of a low pass band is kept unchanged at 1.61 GHz and the bandwidth of 120 MHz; the center frequency of the low pass band is continuously adjustable within 1.45 GHz-1. 8GHz, and the center frequency of the high pass band is kept unchanged at 2.51 GHz and the bandwidth of 107MHz; the bandwidth of the high pass band is tunable in the range of 83-132MHz, the insertion loss fluctuates in the range of 1.16-1.45 dB, and at the moment, the center frequency of 1.6 GHz and the bandwidth of 122MHz of the low pass band are kept unchanged. The result shows that the microstrip filter with the tunable center frequency and bandwidth has the advantages of low loss, wide tuning range and wide application range.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave devices, and more specifically to a dual-passband filter design for L-band with low loss and wide tuning range and fully adjustable center frequency and bandwidth. Technical Background

[0002] With the rapid development of the communications industry, intelligence is becoming more and more popular, and the demand for communication systems is gradually increasing. However, there are currently fewer spectrum resources available for radio, and the utilization rate of the already divided frequency bands is low, which puts higher requirements on wireless communication equipment. As an important part of the wireless communication system, the filter has a frequency selection function, which plays an important role in allowing useful signals to pass and suppressing interference signals from entering the receiving device. In military communications, the communication frequency band is extremely susceptible to enemy interference, and the filter also has the function of ensuring the safe transmission of signals.

[0003] In current mobile communication systems, filters with tunable functions have become one of the most popular research hotspots due to their flexibility, small size and wide range of applications. In tunable filters, the center frequency is flexibly controllable by affecting the electrical length of the resonator through tunable components, but the bandwidth is difficult to control. Based on this, many experts and scholars have conducted a series of studies on the design of such filters, but more varactor diodes are used in the design, the circuit structure is complex, the tuning difficulty is increased, the tuning range is small, and large losses are easily generated. Therefore, it is expected to provide a fully tunable filter design with a simple circuit structure and a wide tuning range. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the existing tunable filter technology, such as complex circuit structure, narrow tuning range, and large tuning loss, the present invention proposes a dual-passband filter with fully adjustable center frequency and bandwidth. The present invention adopts the method of adding varactor diodes at the end and branches of the resonator and feeding the resonator through slot coupling to design a dual-passband filter with fully adjustable center frequency and bandwidth, which has a wide tuning range, simple circuit structure, and low loss.

[0005] The above-mentioned purpose of the present invention can be achieved through the following measures: a dual-passband filter with fully adjustable center frequency and bandwidth, comprising: an input port, an output port, a coupling feeder of a source and a load, a quarter-wavelength resonator and a bias circuit. The input and output ports are connected to the coupling feeder to feed the resonator through slot coupling, one end of the quarter-wavelength resonator is open and the other end is loaded with a varactor diode to produce a passband with adjustable center frequency; the quarter-wavelength resonator is loaded with a varactor diode at both ends to produce a fully adjustable passband; a low-loss bandpass filter is realized; the structure adopts a symmetrical form to reduce the complexity of the circuit; by adding a varactor diode at the end of the resonator and the resonant branch, and grounding the varactor diode, the tunable functions of the center frequency and bandwidth are realized respectively by changing the capacitance of the varactor diode.

[0006] As described above, the dual-passband filter with fully adjustable center frequency and bandwidth applied for by the present invention has the following beneficial effects: a new resonant branch is added in the resonator to realize a new resonance point, thereby achieving the purpose of increasing the tunable function, and the microstrip line is combined with a varactor diode to realize the tunable function of the filter. The finally designed filter has the advantages of good out-of-band suppression, wide tuning range, and easy integration. It can meet the requirements of modern communication equipment for flexibility, reliability and miniaturization, and has broad application prospects in wireless communication systems, radar systems and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is the structural layout diagram of a dual-passband filter with fully adjustable center frequency and bandwidth.

[0008] Figure 2 This is the structural dimension diagram of a dual-passband filter with fully adjustable center frequency and bandwidth.

[0009] Figure 3 This is the S parameter simulation result diagram when Cv1 and Cv2 are 15pf, Cv3 is 7pf, and Cv4 is 5pf.

[0010] Figure 4 This is the S-parameter simulation result diagram of the tunable high-band center frequency.

[0011] Figure 5 This is the S-parameter simulation result diagram when the low-passband center frequency is tunable.

[0012] Figure 6 The S parameter simulation result diagram for high passband bandwidth tunable DETAILED DESCRIPTION

[0013] Certain terms used throughout this specification and claims refer to specific functions, such as the use of terms such as "varicap diode", "DC blocking capacitor" and "bias resistor" to distinguish different devices. This specification uses specific examples to illustrate the implementation methods of the application herein, and those skilled in the art can implement and apply the contents of this specification.

[0014] For those skilled in the art, the specific meanings of the various terms in the present invention can be understood according to relevant circumstances. The term "fully tunable" represents a specific meaning, which means that the tuning function of the center frequency and bandwidth that the filter can achieve can be realized; the term "resonant branch" represents a specific meaning, which means that the resonator part added between the filter resonators can be realized; the terms "left side" and "right side" represent specific meanings, which means that the left structure and right structure of the resonator can be realized.

[0015] See also Figure 1 In the preferred embodiment described below, a dual-passband filter with fully adjustable center frequency and bandwidth includes: an input port 1, an output port 2, feed lines 9-11 and 36-38 connected to the ports, low-frequency quarter-wavelength resonators 3 and 4, high-frequency quarter-wavelength resonators 7 and 8, loaded resonator branches 5 and 6, variable capacitors 28-35, DC blocking capacitors 12-19, bias resistors 20-27, and pads 39-46 for connecting three components of the bias circuit.

[0016] The input and output ports are connected to the coupling lines for feeding through slot coupling, which are coupled with the resonator to produce the filter passband. The best feeding of the filter is achieved by adjusting the size of the coupling feed line, resulting in the lowest insertion loss.

[0017] The center frequency in the fully tunable dual passband filter is tunable.

[0018] A variable capacitance diode is added to the end of the resonator. When the capacitance value changes, it is equivalent to the change of the electrical length of the resonator, thus making the center frequency tunable. Figure 1 By adjusting the varactor diodes 28-31 and 34, 35, the center frequency of the filter can be moved to the low frequency band as the capacitance increases.

[0019] The bandwidth in the fully tunable microstrip filter is tunable.

[0020] By adjusting the capacitance of the variable capacitance diodes 32 and 33 at the branches of the resonator, the even-mode resonance frequency can be changed, thereby making the passband bandwidth of the filter tunable.

[0021] By minimizing the size of the filter's resonant branches, the filter's tunable range can be increased.

[0022] participate Figure 2 The microstrip filter with fully tunable center frequency and bandwidth proposed in the present invention adopts the varactor diode of SMV1273-079LF model. All varactor diodes are connected to a 10pf DC blocking capacitor and a 100 kilo-ohm fixed resistor to prevent the connected large voltage from having a significant impact on the circuit and play a role in protecting the circuit. The radius of all grounding through holes is 0.5mm and runs through the entire circuit board.

[0023] See also Figure 3 The following is the S parameter simulation result diagram of the present invention when Cv1 and Cv2 are 15pf, Cv3 is 7pf, and Cv4 is 5pf. Figure 3 It can be seen that the passband center frequencies are 1.63GHz and 2.41GHz respectively, the -3dB bandwidths are 130MHz and 97MHz, the insertion losses are 0.45dB and 1dB, the return losses are better than 13.3dB and 18.4dB, and a transmission zero point is generated on the left side of the low passband and on the right side of the high passband, for a total of two transmission zero points, achieving better out-of-band suppression.

[0024] See also Figure 4 The S parameter simulation result diagram of the present invention when the high-passband center frequency is tunable. The filter model designed by the present invention is simulated and optimized by electromagnetic simulation software HFSS. Figure 4 It can be seen that by adjusting the variable capacitance diodes Cv1 and Cv2, the center frequency of the high passband can be tuned. When Cv3 is fixed at 10pf and Cv4 is 5pf, and Cv1 and Cv2 are continuously tuned from 3pf to 23pf at the same time, the center frequency of the high passband can be continuously adjusted within 2.39GHz-2.61GHz, and the insertion loss fluctuates within 0.98-1.3dB. At this time, the low passband maintains a center frequency of 1.61GHz and a bandwidth of 120MHz.

[0025] See also Figure 5 The S parameter simulation result diagram of the present invention when the low passband center frequency is tunable. The filter model designed by the present invention is simulated and optimized by electromagnetic simulation software HFSS. Figure 5 It can be seen that by adjusting the variable capacitance diode Cv4, the center frequency of the low passband can be tuned. When Cv1 and Cv2 are fixed to 5pf, Cv3 is 10pf, and Cv4 is continuously tuned from 2.15pf to 30pf, the low passband center frequency can be continuously adjusted within 1.45GHz to 1.8GHz, and the insertion loss fluctuates within 0.3-0.7dB. At this time, the high passband maintains a center frequency of 2.51GHz and a bandwidth of 107MHz.

[0026] By adjusting the capacitance value of Cv3, the odd-mode resonant frequency of the resonator can be fixed, and the even-mode resonant frequency can be changed, thereby realizing the tunable function of the passband bandwidth. In the present invention, in order to fix the position of the center frequency, when adjusting the capacitance value of Cv3, the capacitance values ​​of Cv1 and Cv2 are fine-tuned.

[0027] See also Figure 6 . This is a diagram of the S parameter simulation result of the present invention when the high passband bandwidth is tunable. Analysis Figure 6 It can be seen that in order to achieve a fixed low passband bandwidth and center frequency, Cv4 is fixed to 5pf. The tunable function of the high passband bandwidth is achieved by adjusting the capacitance values ​​of Cv1, Cv2 and Cv3. The final design realizes that when the high passband fixed center frequency is 2.56GHz, the tuning range of the -3dB passband bandwidth is 83MHz-132MHz, and the insertion loss fluctuates within 1.16dB-1.45dB. At this time, the low passband maintains a center frequency of 1.6GHz and a bandwidth of 122MHz.

[0028] It is easy for a person skilled in the art to know that, under the premise of keeping the teachings of the present invention unchanged, some feasible modifications can be made to the structure and related methods on the basis of improving the performance of the microstrip filter with fully tunable center frequency and bandwidth. Therefore, the above disclosure should be regarded as limited only by the scope of the attached claims. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A dual-passband filter with fully adjustable center frequency and bandwidth, comprising: Input port (1), output port (2), feed lines (9)-(11) and (36)-(38) connected to the ports, quarter-wavelength resonator (3) (4) (7) (8), resonator branch (5) (6), variable capacitor (28)-(35), DC blocking capacitor (12)-(19), bias resistor (20)-(27), and pads (39)-(46) for connecting three components of the bias circuit. By adding resonant branches (5)-(6) in the middle of the resonator, a new resonance point is added, which can increase the tunable function. Finally, by adding varactor diodes at the ends of the resonator and the resonant branches, the tunable functions of the center frequency and bandwidth can be achieved by changing the capacitance of the varactor diode.

2. The dual-passband filter with fully adjustable center frequency and bandwidth according to claim 1, characterized in that: Two identical quarter-wavelength resonators loaded with resonator branches are symmetrically placed in the upper half of the tunable dual-passband filter, and both ends of the resonator and the end of the resonator branch are connected to bias circuits for adjustment; Two quarter-wavelength resonators with bias circuits loaded at one end are symmetrically placed in the lower half of the tunable dual-passband filter.

3. The dual-passband filter with fully adjustable center frequency and bandwidth according to claim 1, characterized in that: The structure is symmetrical, and the structures on the left and right sides of the resonator are exactly the same, which reduces the complexity of the circuit and facilitates tuning when the varactor diode is powered on. The symmetrical structure is coupled to each other through a gap in the middle to form the passband part of the resonant filter.

4. The dual-passband filter with fully adjustable center frequency and bandwidth according to claim 1, characterized in that: The upper and lower resonators are fed by a coupling feed line connected between a source and a load through slot coupling, so that the coupling produces a bandpass filter with low loss.

5. The dual-passband filter with fully adjustable center frequency and bandwidth according to claim 1, characterized in that: The tunable filter is loaded with a bias circuit, which consists of a DC blocking capacitor, a variable capacitor and a bias resistor. The DC blocking capacitor and the bias resistor are used to prevent the circuit from being burned out by a sudden addition of a large voltage to the circuit, and play a protective role in the circuit. The added voltage is used to adjust the capacitance of the variable capacitor, which plays a role in tuning the electrical length of the resonator branch.

6. The dual-passband filter with fully adjustable center frequency and bandwidth according to claim 1, characterized in that: When the center frequency is tunable, the capacitance of the varactor diode at the end of the resonator is mainly adjusted to adjust the electrical length, thereby causing the center frequency of the filter to shift. When the bandwidth is tunable, the capacitance of the varactor diode at the center branch of the resonator is mainly adjusted to achieve the movement of the even-mode resonant frequency by changing the capacitance, and the odd-mode resonant frequency is fixed to achieve the adjustable passband bandwidth.

7. The dual-passband filter with fully adjustable center frequency and bandwidth according to claim 1, characterized in that: Varactors are added to both sides of the ends of the resonator (3) (4), and a variable capacitance diode is added to the end of the resonator branch (5) (6), so as to realize the full adjustable function of the passband. A variable capacitance diode is added at one end of the resonator (7) (8) to realize the tunable function of the center frequency of the passband. The designed tunable filter can select the required signal according to the required frequency band and filter out the interference signal to ensure the safe transmission of the signal.

8. The dual-passband filter with fully adjustable center frequency and bandwidth according to claim 1, characterized in that: The resonator (3)(4)(5)(6) is bent inwardly to reduce the size of the resonator and achieve a reduction in the substrate area.

9. The dual-passband filter with fully adjustable center frequency and bandwidth according to claim 1, characterized in that: The filter of the invention has a characteristic impedance of 50Ω added at its input port (1) and output port (2), and is designed on a high-frequency dielectric substrate with a thickness of 0.508mm, a relative dielectric constant of 3.5, and a dielectric loss tangent of 0.0018. The grounding holes of the upper and lower circuits correspond to each other, and the through holes at the grounding point are set with a radius of 0.5mm, and all grounding structures are connected to the upper and lower circuits through metal through holes.

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