Broadband frequency reconfigurable non-reflection filter loaded with inductance lumped element

Abstract

The invention discloses a broadband frequency reconfigurable non-reflection filter loaded with an inductance lumped element, a filter main circuit is formed by connecting a high-impedance structure of series inductors and a coupling microstrip line, one end of the coupling microstrip line is grounded, the other end of the coupling microstrip line is loaded with a varactor, and an auxiliary absorption channel absorption circuit is mainly formed by coupling microstrip lines with unequal line widths. Through synchronous tuning of the complementary branches, resonant frequencies of the filtering main circuit and the auxiliary channel absorption circuit are kept in synchronous matching, passbands of the two circuits are complementary, and the broadband non-reflection characteristic is achieved. The broadband frequency reconfigurable non-reflection filter is large in tuning range, simple in overall circuit structure, small in size, good in absorption effect, wide in tunable bandwidth and suitable for multi-band wireless application such as 5G / 6G communication, radar and cognitive radio.

Description

Technical Field

[0001] The present invention relates to a microstrip band - pass filter, and more particularly to a broadband frequency - reconfigurable reflectionless filter. Background Art

[0002] In a wireless communication system, a band - pass filter (BPF) is a key device for selective signal transmission, and is widely used in radio - frequency front - end modules to suppress out - of - band interference and optimize signal quality. However, traditional band - pass filters with fixed center frequencies cannot adapt to changing communication requirements. Especially in dynamic spectrum allocation technologies such as cognitive radio, frequency flexibility has become a key factor determining system performance. In addition, application scenarios such as radar systems and wireless power transfer also pose higher requirements for the tunability of filters. Therefore, in recent years, frequency - reconfigurable filters have become a research hotspot, aiming to meet diverse application needs by dynamically adjusting the center frequency.

[0003] Currently, there are various tunable filter design schemes. The more common methods include varactor loading, MEMS tunable technology, liquid - crystal dielectric tuning, and mechanical adjustment structures. The varactor - loading method realizes the change of the resonant frequency by adjusting the capacitance value. The circuit structure is simple and the control is flexible, but there are large insertion losses and possible harmonic distortions. MEMS (Micro - Electro - Mechanical Systems) tunes by micro - mechanically adjusting the geometric dimensions of the microstrip structure. Although it has the advantages of high Q - value and low power consumption, its manufacturing complexity is high and its reliability is limited. Liquid - crystal dielectric tuning uses a variable dielectric constant to change electromagnetic characteristics, which is suitable for millimeter - wave and terahertz frequency bands, but its response speed is slow and it is significantly affected by temperature. Generally speaking, the existing technologies still have many limitations in terms of tuning range, loss control, manufacturing cost, and system matching, and it is difficult to fully meet the development needs of wireless communication systems.

[0004] On the other hand, there are often large signal reflections at the input port of traditional filters, resulting in an increase in return loss, which affects the efficiency of power amplifiers and reduces the overall system matching characteristics. The research goal of reflectionless filters is to reduce signal reflections at the input port to improve signal integrity and the energy utilization efficiency of the system. Currently, the mainstream reflectionless filter design methods include matching network optimization, absorbing stub design, and coupling structure optimization. Matching network optimization reduces the reflection at the input port through an additional matching circuit, but usually increases the circuit complexity; absorbing stubs consume the reflected signal through resistive loads or coupling structures. However, their reflectionless characteristics are limited to a fixed frequency range and it is difficult to achieve wide - band tuning; coupling structure optimization attempts to adjust the internal coupling network of the filter to reduce the reflected signal, but it is difficult to simultaneously achieve a wide tuning range and reflectionless characteristics. Therefore, how to achieve efficient reconfigurable reflectionless filtering in a wide frequency range remains an important challenge in current research. Summary of the Invention

[0005] Objective of the Invention: Aiming at the above-mentioned existing technologies, a broadband frequency-reconfigurable reflectionless filter with lumped inductance elements is proposed to achieve synchronous tuning of the main and auxiliary channel filters, and to achieve reflectionless filtering tuning in a wide frequency band while ensuring the performance of the filter.

[0006] Technical Solution: A broadband frequency-reconfigurable reflectionless filter with lumped inductance elements includes a broadband reconfigurable main filtering circuit and an auxiliary channel absorption circuit.

[0007] Furthermore, the broadband reconfigurable main filtering circuit has a left-right symmetric structure. In the middle of the structure is an equal-width parallel-coupled microstrip line, and the two microstrip lines of the equal-width parallel-coupled microstrip line are respectively denoted as line a1 and line b1. One side of the left-right symmetric structure includes a feeder, microstrip line one, inductor, and microstrip line two connected in series in sequence. The other end of the microstrip line two is connected to the upper end of the a1 line, and the upper end of the a1 line is also connected to a grounded varactor, and the lower end of the a1 line is grounded.

[0008] Furthermore, in the broadband reconfigurable main filtering circuit, the two symmetric feeders serve as the input feeder and the output feeder respectively; the auxiliary channel absorption circuit includes two unequal-width parallel-coupled microstrip lines, two stub lines with one end loaded with varactors, and one stub line with one end loaded with a resistor. Among them, the two microstrip lines of the unequal-width parallel-coupled microstrip line one are respectively denoted as line a2 and line b2, and the two microstrip lines of the unequal-width parallel-coupled microstrip line two are respectively denoted as line a3 and line b3.

[0009] The upper end of the a2 line is connected to the input feeder, the lower end is connected to the left end of the a3 line, and the right end of the a3 line is connected to one end of the stub line with the load resistor; the upper end of the b2 line is open, and the lower end is connected to the first stub line with the load varactor; the left end of the b3 line is open, and the right end is connected to the second stub line with the load varactor. Among them, the varactors and resistors in the stub lines are all grounded.

[0010] Furthermore, by tuning the capacitance value of the varactor in the broadband reconfigurable main filtering circuit, the electrical length of the equal-width parallel-coupled microstrip line is adjusted, so as to realize the tuning of the center frequency of the reflectionless filter; by tuning the capacitance value of the varactor in the auxiliary channel absorption circuit, synchronous matching with the center frequency of the main filtering circuit is achieved, so that the passbands of the two circuits are complementary, thereby realizing the wideband reflectionless characteristic of the reflectionless filter.

[0011] Beneficial effects: Existing tunable filters have problems such as increased insertion loss, aggravated harmonic distortion, and decreased out-of-band rejection ability during the tuning process. At the same time, there are reflected signals at the input port, affecting the overall stability of the system. In the design of a few existing tunable reflectionless bandpass filters, the reflectionless characteristic is limited to a fixed frequency range, making it difficult to achieve wideband tuning; while optimizing and adjusting the internal coupling network of the filter to reduce the reflected signal, it is difficult to simultaneously take into account the wide tuning range and the reflectionless characteristic. In addition, there are also disadvantages such as complex circuit structure, large size, and limited tuning range, making it difficult to meet the requirements of modern wireless communication systems.

[0012] The present invention proposes a broadband frequency-reconfigurable reflectionless filter based on an inductance-loaded high-impedance structure. By combining the inductance-loaded high-impedance structure with varactor loading, broadband reconfigurable tuning is achieved. Without significantly increasing the insertion loss, the frequency tuning ability of the system is improved, which is applicable to multi-band wireless communication systems. In addition, a structure combining unequal-width coupled microstrip lines and absorption stubs is adopted to effectively dissipate the input signal in the out-of-band range, suppress reflection, and expand the reflectionless coverage band through synchronous tuning. Specifically,

[0013] 1. A bandpass filtering response is achieved by using a coupled microstrip line shorted at one end, a grounded varactor connected at the other end, and a section of high-impedance structure. The shorted coupled microstrip line can generate a transmission zero and two transmission poles, ensuring a high stopband rejection level while tuning.

[0014] 2. By introducing inductance elements into the microstrip structure, the effective impedance is increased, thereby optimizing the tuning ability without increasing the loss and reducing the electrical length of the microstrip line to reduce the circuit size.

[0015] 3. A main and auxiliary channel synchronous tuning strategy is adopted to keep the resonant frequencies of the main filtering path and the absorption stub in synchronous tuning and complementarity, realizing broadband reflectionless characteristics at the input end and improving the stability of the system.

[0016] 4. By adopting the structure of unequal-width coupled microstrip lines, multiple reflection zeros are formed while expanding the tuning range to enhance the out-of-band rejection ability and maintain high-quality signal transmission in the band. And the unequal-width coupled microstrip lines can enhance the matching with the main channel, further expanding the tuning range.

[0017] 5. Through the combined regulation of unequal-width coupled microstrip lines and varactors, the reflected signal at the input port is effectively dissipated, the return loss is reduced, the interference of the reflected signal is reduced, and the power transmission efficiency is improved.

[0018] The present invention's inductively loaded broadband frequency-reconfigurable reflectionless filter can be widely used in 5G / 6G communication systems, satellite communications and radar systems, cognitive radio, and other fields to achieve multi-band coverage, dynamic spectrum management, and efficient power utilization. In summary, the present invention overcomes the limitations of traditional filters in tunability and reflectionlessness, providing an efficient, compact, and reconfigurable filtering solution for the next generation of wireless communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of a broadband frequency reconfigurable non-reflection filter loaded with lumped inductor elements according to the present invention;

[0020] Figure 2 This is a schematic diagram of the circuit dimensions of an embodiment of the present invention with an operating center frequency of 2 GHz;

[0021] Figure 3 A side view of an embodiment of the present invention;

[0022] Figure 4 The following is a comparison of the frequency responses of the main filter channel before and after the inductor is loaded in the embodiment, where (a) is the frequency response of the lumped component without the inductor loading, and (b) is the frequency response of the lumped component with the inductor loading;

[0023] Figure 5 For example, a broadband frequency reconfigurable reflectionless filter with C t (pF) and C t1 Frequency response curve of (pF) change;

[0024] Figure 6 For example, a broadband frequency reconfigurable reflectionless filter with C t (pF) and C t1 Signal absorbance curve with changes in (pF). DETAILED DESCRIPTION

[0025] The present invention will be further explained below with reference to the accompanying drawings.

[0026] A broadband, frequency-reconfigurable, non-reflective filter loaded with lumped inductive elements is fabricated using microstrip PCB technology. The microstrip structure comprises three layers: an upper microstrip structure, a middle dielectric substrate, and a lower metal ground structure. The upper microstrip structure includes an input feeder, an output feeder, a parallel coupled microstrip line of equal width shorted at one end, a pair of microstrip lines connected in series with an inductor, two parallel coupled microstrip lines of unequal width, two branch lines loaded with varactors at one end, and a branch line loaded with a resistor at one end.

[0027] The broadband frequency reconfigurable reflectionless filter consists of a broadband reconfigurable filtering main circuit and an auxiliary channel absorption circuit structure.

[0028] As Figure 1 shown, the broadband reconfigurable filtering main circuit has a left - right symmetric structure. The left - hand side structure of this symmetric structure is: an inductor 102 is connected in series between microstrip lines 101 and 103. The right end of microstrip line 103 is connected to the upper end of line a1 of the equal - width parallel - coupled microstrip line 105. The left end of microstrip line 101 is connected to the input feeder 121. The lower end of line a1 of the equal - width parallel - coupled microstrip line 105 is grounded through a metallized via, and the upper end is connected to the grounded varactor C t . For the right - hand side structure of this symmetric structure, the lower end of line b1 of the equal - width parallel - coupled microstrip line 105 is grounded through a metallized via, and the upper end is connected to the grounded varactor C t ', then connected to the left end of microstrip line 103'. Microstrip line 103' is successively connected in series with inductor 102', microstrip line 101' and output feeder 122. The input feeder 121 is connected to port 1, and the output feeder 122 is connected to port 2.

[0029] The auxiliary - channel absorption circuit structure is connected in parallel at the connection between the input feeder 121 and the microstrip line 101. Among them, the upper end of line a2 of the unequal - width parallel - coupled microstrip line 106 is connected to the input feeder 121, and the lower end is connected to the left end of line a3 of the unequal - width parallel - coupled microstrip line 109. The right end of line a3 of the unequal - width parallel - coupled microstrip line 109 is connected to the left end of microstrip line 112d. The right end of microstrip line 112 is connected to the grounded resistor 113. The upper end of line b2 of the unequal - width parallel - coupled microstrip line 106 is open - circuited, and the lower end is connected to the upper end of microstrip line 107. The lower end of microstrip line 107 is connected to the grounded varactor C t1 . The upper end of line b3 of the unequal - width parallel - coupled microstrip line 109 is open - circuited, and the right end is connected to the upper end of microstrip line 110. The lower end of microstrip line 110 is connected to the grounded varactor C t1 '. Among them, one end of the resistor 113 and the cathodes of each varactor are respectively connected to the lower - layer metal ground structure through each grounding pad 104 and metallized vias to achieve grounding.

[0030] The RF signal is fed into from port 1, successively passes through the high - impedance structure in series composed of the input feeder 12, microstrip line 101, inductor 102 and microstrip line 103, then passes through the combination of the equal - width parallel - coupled microstrip line 105 and the grounded varactors C t , C t ', and then is transmitted by the right - hand side microstrip line 103', inductor 102', microstrip line 101' to the output feeder 122 to form a band - pass filtering response, and then output from port 2. The RF signal adjusts the electrical length of the coupled line 105 under the action of the variable capacitors C t , C t ' to achieve the tuning of the center frequency, and the capacitance values satisfy C t = C t'. In the ideal mode, the high-impedance structure on one side (microstrip line 101, inductor 102, and microstrip line 103) can be regarded as a microstrip line with an impedance of Z x connected to the connection point of the coupled microstrip line 105 and the varactor C t . At this time, the expressions of the odd- and even-mode resonance points f e and f o of this filter are:

[0031]

[0032] where Y e , Y o and Y x are the even-mode admittance, odd-mode admittance of the coupled microstrip line 105, and the admittance of the high-impedance structure respectively. The electrical length θ2 of the coupled line is less than 90°.

[0033] The stopband signal reflected back to port 1 will be successively transmitted to the unequal-width parallel coupled microstrip line 106, unequal-width parallel coupled microstrip line 109, and microstrip line 112 and then dissipated through the resistor 113. By simultaneously tuning the capacitance values of C t1 , C t1 ' to achieve synchronous matching with the center frequency of the main filtering channel, and keep the passband of the auxiliary channel complementary to that of the main filter, realizing the synchronous reflectionless tuning characteristic, where the capacitance values satisfy C t1 = C t1 ', that is, these two capacitance values remain consistent during the tuning process.

[0034] To better illustrate the technical effects of the present invention, this embodiment designs a broadband frequency-reconfigurable reflectionless filter based on loaded inductor lumped elements with a center frequency of 2 GHz and conducts simulation verification. Figure 2 This is the size schematic diagram of the upper-layer microstrip structure of the broadband frequency-reconfigurable reflectionless filter in this embodiment. As Figure 2 shown, the overall size is 52 mm × 29.7 mm, and the specific parameters are as follows: input / output feeder Wport = 3.38 mm, Lport = 6 mm; coupled microstrip line 105: W CL1 = 2.81 mm, S1 = 3.9 mm, L CL1 = 8.8 mm; microstrip lines 101, 103, 101', 103' have the same size: W1 = 0.18 mm, L1 = 6.1 mm; inductors 102, 102' have the same inductance value: L n = 8.2 nH; unequal-width parallel coupled microstrip line 106: W CL2 = 2.38 mm, W CL21 = 2.55 mm, S2 = 0.15 mm, L CL2 = 11.6 mm; unequal-width parallel coupled microstrip line 109: WCL3 = 2.06 mm, W CL31 = 2.22 mm, S3 = 0.42 mm, L CL3 = 12.5 mm; The microstrip line 107 has the same dimensions as the microstrip line 110: W4 = 0.3 mm, L4 = 7.44 mm; Microstrip line 112: W5 = 2.2 mm, L5 = 7 mm; Resistor 113: R1 = 91 Ω; The radius of the metallized via R via = 0.2 mm, the radius of the pad W pad = 1 mm; The varactor diodes C t 、C t ' both range from 0.23 - 2.1 pF, and the varactor diodes C t1 、C t1 ' both range from 0.23 - 2.1 pF.

[0035] Figure 3 This is the side view of the broadband frequency - reconfigurable reflectionless filter of this embodiment. As Figure 3 shown, the overall structure mainly includes the upper - layer microstrip structure 10, the lower - layer metal - ground structure 30, the middle - layer dielectric substrate 20, and the metallized via Via. Among them, the middle - layer dielectric substrate 20 uses RO4003C board material, with a relative dielectric constant ε r of 3.55 and a thickness H of 1.524 mm; The thicknesses of both the upper - layer microstrip structure 10 and the lower - layer metal - ground structure 30 are 0.017 mm. The center - frequency - tunable band - pass filters of other frequency bands can be obtained by scaling in this embodiment.

[0036] Figure 4 This is the comparison diagram before and after loading the inductor in the high - impedance structure of the main channel in this embodiment. Among them, the value of the varactor diode C t = C t ' is 0.64 pF. It can be seen that after loading the inductor lumped element, the main - channel circuit achieves good impedance matching within the passband. This is mainly due to the fact that after loading the inductor L n it can greatly improve the characteristic impedance of the transmission line while maintaining the original microstrip - line dimensions.

[0037] Figure 5 This is the frequency - response curve of the broadband frequency - reconfigurable reflectionless filter of this embodiment obtained by the CST MWS 3D simulation software with the variation of C t and C t1 . The tuning range of the center frequency is between 2.06 - 3.52 GHz, and the corresponding relative center - frequency tuning range is 52.3%. The minimum insertion loss within the passband is maintained between 1.14 - 1.47 dB, and both the insertion loss and the return loss can maintain a good level within the center - frequency tuning range. In the range of 0.57 - 4 GHz, the signal of the stopband |S 11are all less than -10 dB.

[0038] Figure 6 is the signal absorption rate curve of the center frequency tunable bandpass filter of this embodiment with respect to C t and C t1 changing, which is calculated by the formula 100×(1 - |S 11 | 2 - |S 21 | 2 ). The out-of-band signal absorption rate is all greater than 82%, and it has good absorption characteristics.

[0039] In summary, compared with the existing tunable non-reflective filter, the present invention has significant advantages in terms of tuning range, input matching, out-of-band rejection, and structural optimization. Through inductive loading of the high-impedance structure and varactor tuning, dynamic tuning in a wider frequency range is achieved. At the same time, synchronous tuning of the main and auxiliary channels and the design of absorption stubs are adopted to effectively reduce the reflection at the input end and improve the system matching characteristics. Combining the unequal line width coupled microstrip line structure enhances the out-of-band rejection ability, reduces harmonic distortion, and optimizes the microstrip circuit layout, making the filter smaller in size, higher in integration, and simpler in structure, suitable for multi-band wireless applications such as 5G / 6G communication, radar, and cognitive radio, and providing a better tunable filtering solution for modern communication systems.

[0040] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A broadband frequency-reconfigurable reflectionless filter loaded with lumped inductance elements, characterized in that It includes a broadband reconfigurable filtering main circuit and an auxiliary channel absorption circuit.

2. The broadband frequency reconfigurable reflectionless filter according to claim 1, characterized in that, The broadband reconfigurable filtering main circuit has a left-right symmetric structure. In the middle of the structure is an equal-width parallel-coupled microstrip line, and the two microstrip lines of the equal-width parallel-coupled microstrip line are respectively denoted as line a1 and line b1; one side of the left-right symmetric structure includes a feeder, a first microstrip line, an inductor, and a second microstrip line connected in series in sequence. The other end of the second microstrip line is connected to the upper end of the a1 line, and the upper end of the a1 line is also connected to a grounded varactor, and the lower end of the a1 line is grounded.

3. The broadband frequency reconfigurable reflectionless filter according to claim 2, characterized in that In the broadband reconfigurable filtering main circuit, the two symmetric feeders are respectively used as the input feeder and the output feeder; the auxiliary channel absorption circuit includes two unequal-width parallel-coupled microstrip lines, two stub lines with one end loaded with a varactor, and one stub line with one end loaded with a resistor; among them, the two microstrip lines of the first unequal-width parallel-coupled microstrip line are respectively denoted as line a2 and line b2, and the two microstrip lines of the second unequal-width parallel-coupled microstrip line are respectively denoted as line a3 and line b3; The upper end of the a2 line is connected to the input feeder, the lower end is connected to the left end of the a3 line, and the right end of the a3 line is connected to one end of the stub line with a load resistor; the upper end of the b2 line is open, and the lower end is connected to the first stub line with a load varactor; the left end of the b3 line is open, and the right end is connected to the second stub line with a load varactor; among them, the varactor and the resistor in the stub line are both grounded.

4. The broadband frequency reconfigurable reflectionless filter according to claim 3, characterized in that, By tuning the capacitance value of the varactor in the broadband reconfigurable filtering main circuit, the electrical length of the equal-width parallel-coupled microstrip line is adjusted, so as to realize the tuning of the center frequency of the reflectionless filter; by tuning the capacitance value of the varactor in the auxiliary channel absorption circuit, synchronous matching with the center frequency of the filtering main circuit is realized, so that the passbands of the two circuits are complementary, thereby realizing the wideband reflectionless characteristic of the reflectionless filter.

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