A differential-to-differential filter with broadband differential-mode and common-mode non-reflection characteristics

Abstract

The present invention proposes a double-sided parallel stripline-based differential-to-differential filter with broadband differential-mode and common-mode non-reflection characteristics. The filter comprises two pairs of input or output double-sided parallel stripline transmission lines printed on a dielectric substrate, multiple half-wavelength double-sided parallel stripline resonators, one or more quarter-wavelength double-sided parallel stripline resonators on each side of axis AA′, and resistors connecting the front and back transmission lines of the double-sided parallel stripline transmission lines. Because the resonators can only be excited by differential-mode signals, they exhibit frequency-selective characteristics, but cannot be excited by common-mode energy and therefore lack frequency-selective characteristics. Therefore, common-mode energy is dissipated over a wide bandwidth by matching resistors loaded at the transmission line terminals, effectively broadening the non-reflection bandwidth of common-mode energy. Furthermore, by increasing the number of half-wavelength and quarter-wavelength double-sided parallel stripline resonators, improved passband selectivity can be achieved.

Description

Technical Field

[0001] The present invention belongs to the field of microwave and radio frequency technology, and relates to a filter, specifically to a differential-to-differential filter based on double-sided parallel strip lines with broadband differential mode and common mode non-reflection characteristics, which can be applied to the radio frequency front end of a wireless communication system. Background Art

[0002] In recent years, with the rapid development of wireless technology, demands for communication system performance and quality have become increasingly stringent. Filters are crucial components in modern communication systems, enabling the selection of signals of varying frequencies. Their performance directly determines the effectiveness of wireless transmission systems. Filters can be categorized as single-ended to single-ended, single-ended to differential, differential to single-ended, and differential to differential, depending on the input and output signal types. Differential filters have garnered widespread attention and application due to their significant advantages in resisting ambient noise and improving system dynamic range. Differential filters can be categorized based on how they suppress common-mode energy and stop-band differential-mode signals: filters that reflect common-mode energy and stop-band differential-mode signals, filters that reflect common-mode energy and dissipate stop-band differential-mode signals, filters that dissipate common-mode energy and reflect stop-band differential-mode signals, and filters that dissipate common-mode energy and reflect stop-band differential-mode signals. These filters, which reflect common-mode energy and stop-band differential-mode signals, reflect common-mode energy and dissipate stop-band differential-mode signals, and filters that dissipate common-mode energy and reflect stop-band differential-mode signals, have reflective properties and will reflect common-mode energy or stop-band differential-mode signals back to the source. Because some nonlinear components in the RF front-end, such as mixers and amplifiers, are very sensitive to out-of-band energy, the common-mode energy and stop-band differential-mode signals reflected by these reflective differential filters may introduce additional intermodulation interference and reduce the system's dynamic range.

[0003] Wideband differential-mode and common-mode non-reflection filters are filters that dissipate common-mode signals and stop-band differential-mode signals. By dissipating common-mode energy and differential-mode signals entering the stop-band without causing reflections, they can effectively reduce the impact of reflected energy on the system level and optimize power matching between RF stages, thus eliminating the impact of unpredictable reflected energy.

[0004] At present, how to ensure the reflectionless filtering characteristics of differential-mode signals while achieving the reflectionless characteristics of common-mode energy in a wider bandwidth and improving the passband selectivity is an urgent problem to be solved in differential reflectionless filters. For example, in 2021, scholars such as Xiong Chen published a paper titled "Arbitrary-Order Balanced Filter With Reflectionless Characteristics for Both Common- and Differential-Mode Signals in IEEE Microwave and Wireless Components Letters (Volume 31, No. 6, June 2021). Signals”, a differential-to-differential filter with non-reflection characteristics for both common-mode energy and differential-mode signals is proposed. The filter is mainly composed of two pairs of differential microstrip transmission lines and multiple half-wavelength microstrip resonators. The difference in the frequency response of the half-wavelength resonators to common-mode energy and differential-mode signals is used to achieve common-mode suppression and separate the transmission paths of common-mode energy and differential-mode signals. The common-mode energy and stop-band differential-mode signals are dissipated by the ground resistors loaded at the terminals of the two pairs of differential microstrip transmission lines. The greater the 30dB attenuation rate of the filter's passband, the stronger the passband selectivity of the bandpass filter. The 30dB attenuation rate of the filter's passband is 128.5. Due to the frequency-selective characteristics of its common-mode energy transmission path, the common-mode energy non-reflection bandwidth of the filter is only 0 to 4.5GHz.

[0005] Another example is the paper “High-Performance Common-and Differential-Mode Reflectionless Balanced Band-Pass Filter Using Coupled Ring Transformer” published by Yifan Zhang et al. in IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—Ⅱ: EXPRESS BRIEFS (Volume.69,No.3,MARCH 2022). In the paper "Resonator", a differential-to-differential filter with non-reflection characteristics for both common-mode energy and differential-mode signals is proposed. The filter mainly consists of two pairs of differential microstrip transmission lines, non-reflection branches, and ring resonators. By leveraging the difference in equivalent circuits under differential-mode and common-mode energy excitation, it can achieve common-mode energy non-reflection characteristics over a wider frequency range. Due to the fixed number of resonators in the filter, its differential-mode signal passband selectivity is poor, with a 30dB passband attenuation rate of only 33.8. Because each branch of the filter uses two resistors in parallel to dissipate common-mode energy and stop-band differential-mode signals, the parallel resistor values ​​are always mismatched to achieve the non-reflection effect for both common-mode energy and stop-band differential-mode signals. As a result, the common-mode energy non-reflection bandwidth of the filter is only extended to 0 to 8 GHz. Summary of the Invention

[0006] The purpose of the present invention is to address the defects of the above-mentioned technology and propose a differential-to-differential filter based on double-sided parallel strip lines with broadband differential mode and common mode non-reflection characteristics. The filter aims to ensure the non-reflection filtering characteristics of the differential mode signal while widening the non-reflection bandwidth of the common mode energy and improving the passband selectivity.

[0007] To achieve the above objectives, the present invention comprises a dielectric substrate 1 and a pair of transmission lines 2 for differential input or output printed on either side of its longitudinal axis AA′, one or more first resonators 4 for frequency selection of stopband differential-mode signals printed on either side of the longitudinal axis AA′, and a plurality of second resonators 3 for passband transmission of differential-mode signals.

[0008] The pair of transmission lines 2 is composed of a pair of double-sided parallel stripline transmission lines 2 distributed on both sides of an axis parallel to the horizontal axis BB′ of the dielectric substrate 1; the plurality of second resonators 3 are half-wavelength double-sided parallel stripline resonators distributed between the two pairs of transmission lines 2; the first resonator 4 is a quarter-wavelength double-sided parallel stripline resonator distributed between the upper and lower branches of the pair of double-sided parallel stripline transmission lines 2; the front transmission line and the back transmission line of each branch of the pair of double-sided parallel stripline transmission lines 2 are connected via metallized vias 5 and resistors 6;

[0009] By exciting the half-wavelength double-sided parallel strip line second resonator 3 and the quarter-wavelength double-sided parallel strip line first resonator 4 through two pairs of double-sided parallel strip line transmission lines 2, the reflection-free filtering characteristics of the differential mode signal and the broadband reflection-free characteristics of the common mode signal are achieved.

[0010] Preferably, the resistor 6 is connected to the metallized via 5 via a metal floating island 7 .

[0011] Preferably, for each pair of transmission lines 2 distributed on both sides of the longitudinal axis AA′, the upper branch front transmission line and the lower branch back transmission line, as well as the upper branch back transmission line and the lower branch front transmission line are mirror-symmetrical about an axis parallel to the transverse axis BB′.

[0012] Preferably, the upper branch of the transmission line 2 distributed on one side of the longitudinal axis AA′ and the lower branch of the transmission line 2 distributed on the other side of the longitudinal axis AA′ are rotationally symmetric about the central normal line OO′ of the dielectric substrate 1 .

[0013] Preferably, a port of the upper branch front transmission line and a port of the lower branch back transmission line of a pair of transmission lines 2 distributed on one side of the longitudinal axis AA′, as well as a port of the upper branch back transmission line and a port of the lower branch front transmission line of another pair of transmission lines 2 distributed on the other side of the longitudinal axis AA′, are each connected to a rectangular metal extension patch.

[0014] Preferably, when the number of the first resonator 4 is one, it is distributed in the middle of the upper and lower branches of a pair of double-sided parallel strip transmission lines; when the number of the first resonator 4 is multiple, it is linearly arranged in the middle of the upper and lower branches of a pair of double-sided parallel strip transmission lines.

[0015] Preferably, the plurality of second resonators 3 are distributed in parallel between the two pairs of transmission lines 2, and adjacent resonators cross each other in the length direction.

[0016] Preferably, one end of the parallel strip lines on two surfaces of the first resonator 4 is connected through a metal via 5 ; and both ends of the parallel strip lines on two surfaces of the second resonator 3 are connected through a metal via 5 .

[0017] Preferably, the front transmission line and the back transmission line of each branch of the double-sided parallel strip line transmission line 2 adopt a broken line structure consisting of a first transmission strip line parallel to the horizontal axis BB′ and a second transmission strip line connected thereto and with its port away from the vertical axis AA′.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The present invention has two pairs of double-sided parallel strip line transmission lines that can simultaneously excite a half-wavelength double-sided parallel strip line resonator and a quarter-wavelength double-sided parallel strip line resonator. The resonator can only be excited by a differential mode signal so that it has a frequency selective characteristic, but cannot be excited by common mode energy and has no frequency selective characteristic. Therefore, the common mode energy is dissipated by the matching resistor loaded at the transmission line terminal within a wide bandwidth, thereby avoiding the defect of the prior art that the common mode energy transmission path has a frequency selective characteristic and the loading resistor mismatch can only achieve the common mode energy non-reflection characteristic within a narrow band, thereby effectively widening the non-reflection bandwidth of the common mode energy.

[0020] (2) The present invention can achieve better passband selectivity by increasing the number of half-wavelength double-sided parallel strip line resonators and quarter-wavelength double-sided parallel strip line resonators, thereby avoiding the limitation of passband selectivity in existing work due to the difficulty in changing the number of resonators. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the overall structure of an embodiment of the present invention.

[0022] Figure 2 2 is a top view of an embodiment of the present invention.

[0023] Figure 3 It is a bottom view of an embodiment of the present invention.

[0024] Figure 4 This is a diagram showing the relationship between components from the upper surface to the lower surface of a rectangular dielectric substrate according to an embodiment of the present invention.

[0025] Figure 5 This is a simulation diagram of the common-mode energy transmission characteristics of an embodiment of the present invention.

[0026] Figure 6 This is a simulation diagram of the differential mode signal transmission characteristics of an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0028] Reference Figure 1 The present invention includes a metal layer printed on the front of a dielectric substrate 1 and a metal layer at the back of the dielectric substrate 1 at the projection position. The dielectric substrate is made of F4BM-2 material with a relative dielectric constant of 2.2, a size of 167.60mm×83.40mm, and a thickness of 0.80mm. AA' is the central longitudinal axis of the dielectric plate 1, BB' is the central transverse axis of the dielectric plate 1, and OO' is the central normal of the dielectric plate 1. Resonator

[0029] Each pair of transmission lines 2 distributed on both sides of the longitudinal axis AA′ serves as the input or output port of the differential signal, and their specific dimensions and mutual relationships are as follows: Figure 2 and Figure 3 As shown, the upper branch front transmission line and the lower branch back transmission line, as well as the upper branch back transmission line and the lower branch front transmission line, are mirror-symmetrical about an axis parallel to the horizontal axis BB′ and 2.10 mm away. The upper branch of the transmission line 2 distributed on one side of the longitudinal axis AA′ and the lower branch of the transmission line 2 distributed on the other side of the longitudinal axis AA′ are rotationally symmetrical about the central normal OO′ of the dielectric substrate 1. The port of the upper branch front transmission line and the port of the lower branch back transmission line of the pair of transmission lines 2 distributed on one side of the longitudinal axis AA′, as well as the port of the upper branch back transmission line and the port of the lower branch front transmission line of the other pair of transmission lines 2 distributed on the other side of the longitudinal axis AA′ , each connected to a 17.29mm×10.00mm rectangular metal extension patch to achieve better input and output impedance matching. The excitation method of each pair of double-sided parallel strip transmission lines 2 is to perform reverse phase feeding on the basis of differential signals. The double-sided parallel strip transmission line 2 includes a first transmission strip line parallel to the horizontal axis BB′ and a second transmission strip line connected thereto with a port away from the vertical axis AA′. The folded line structure ensures that there is sufficient distance between the differential input and output ports. The width of the second transmission line adopts a 50Ω impedance line width. The length of the folded line structure of each branch of the second transmission line should be consistent to ensure the integrity of the input and output differential signals. The first transmission strip line of the transmission line 2 is divided into three sections, which are coupled with a second resonator 3 and two first resonators 4 respectively. The width of each section is W 2_4 =2.60mm, W 2_5 =3.00mm and W 2_6 =2.70mm, lengths are L 2_3 =12.24mm, L 2_4 =22.86mm and L 2_5=20.73mm. The front and back transmission lines of each pair of double-sided parallel strip transmission lines 2 are connected via 50Ω resistors 6 on metal floating islands 7 and metal vias 5. Two quarter-wavelength first resonators 4 are linearly arranged in the center of the upper and lower branches of the pair of double-sided parallel strip transmission lines, parallel to the horizontal axis BB′. The width and length of the first resonators 4 are W4 = 1.30mm and L4 = 17.86mm, respectively. The ends of the parallel strip lines on both sides, away from the vertical axis AA′, are connected via metal vias 5. The first resonators 4 are simultaneously excited by the transmission lines 2 on both sides through coupling. The coupling spacings between the quarter-wavelength double-sided parallel strip first resonators 4 and the double-sided parallel strip transmission lines 2 on both sides are g3 = 0.10mm and g4 = 0.30mm, respectively. The width and length of the three cascaded half-wavelength double-sided parallel strip line second resonators 3 are W3 = 2.00 mm and L3 = 35.88 mm. They are printed rotationally symmetrically about the center normal OO' of the dielectric substrate 1 and are parallel to the horizontal axis BB'. The two ends of the parallel strip lines on the two surfaces are connected by metal vias 5. Adjacent second resonators 3 intersect each other in the length direction. The projected length of the intersection on the horizontal axis BB' is 16.94 mm. The ends of the two second resonators 3 at the two ends away from the longitudinal axis AA' are distributed on the pair of transmission lines 2. In the middle of the upper and lower branches, the length of the overlapping part with the projection of the transmission line 2 on the horizontal axis BB′ is 16.94 mm, the coupling spacing with the double-sided parallel strip transmission line 2 is g2 = 0.10 mm, and the coupling spacing between adjacent second resonators 3 is g1 = 0.65 mm, to ensure low-loss transmission of differential-mode signals within the filter passband. On the basis of the embodiment, the same number of half-wavelength resonators and quarter-wavelength resonators on each side of the vertical axis AA′ are added at the same time, which can improve the differential-mode passband selectivity of the filter and increase the passband attenuation rate by 30 dB.

[0030] The working principle of the present invention is:

[0031] When a pair of transmission lines distributed on the left side of the longitudinal axis AA′ of the dielectric substrate 1 serves as a differential input end, and a pair of transmission lines distributed on the right side of the longitudinal axis AA′ of the dielectric substrate 1 serves as a differential output end, the signal input form is to perform reverse phase feeding on the basis of the differential signal. When the differential signal enters the first transmission line portion of a pair of double-sided parallel stripline transmission lines 2 and is coupled with a half-wavelength double-sided parallel stripline second resonator 3 and two quarter-wavelength double-sided parallel stripline first resonators 4, the quarter-wavelength double-sided parallel stripline first resonator 4 is simultaneously excited by the double-sided parallel stripline transmission lines 2 on both sides through coupling, and resonates under the excitation of the differential mode signal to achieve the frequency selection characteristics of the double-sided parallel stripline transmission lines 2 on both sides for reflecting the differential mode signal within the filter passband and transmitting the differential mode signal outside the filter passband and being dissipated by the terminal 50Ω matching resistor. The common mode energy is transmitted to the terminal 50Ω matching resistor through the double-sided parallel stripline transmission lines 2 on both sides and dissipated without causing the half-wavelength double-sided parallel stripline second resonator 3 and the quarter-wavelength double-sided parallel stripline first resonator 4 to resonate, so as to ensure the differential mode Under the premise of signal frequency selection characteristics, the common-mode energy non-reflection effect in a wide bandwidth is achieved. The half-wavelength double-sided parallel stripline second resonator 3 located at both ends on each side of the axis AA′, the overlapping part of its projection on the axis BB′ and the projection of the double-sided parallel stripline transmission line 2 on the axis BB′ is excited by a pair of transmission lines 2 on both sides, and it resonates under the excitation of the differential mode signal. The differential mode signal within the filter passband is transmitted from the differential input port to the differential output port through the coupling between the three series-connected half-wavelength double-sided parallel stripline second resonators 3. It cannot resonate under the excitation of common-mode energy. Therefore, the common-mode energy cannot be transmitted between the differential input and differential output ports of the invented differential filter, and the terminal 50Ω matching resistor entering the double-sided parallel stripline transmission line 2 is dissipated to achieve common-mode suppression and broadband common-mode energy non-reflection characteristics.

[0032] The following is a further explanation of the technical effects of the present invention in conjunction with simulation experiments:

[0033] 1. Experimental conditions and content:

[0034] The relevant performance indicators of the present invention are simulated using the three-dimensional structural electromagnetic field simulation software ANSYS Electronics Desktop v.18.2:

[0035] Experiment 1: Simulate the common-mode energy transmission characteristics of the present invention, including the common-mode energy return loss and the insertion loss of common mode energy from port one to port two The simulation results are shown in Figure 5 ;

[0036] Experiment 2: Simulate the differential mode signal transmission characteristics of the present invention, including the differential mode signal return loss. And the insertion loss of the differential mode signal from port 1 to port 2 The simulation results are shown in Figure 6 ;

[0037] 2. Analysis of experimental results:

[0038] Reference Figure 5 , the minimum insertion loss of common mode energy from port one to port two in this embodiment is is 26.67dB, of which the insertion loss This directly reflects the common-mode rejection effect of the differential non-reflective filter, and the minimum return loss of common-mode energy in the range of DC to 4.5 GHz. The minimum return loss is 11.89dB from DC to 10GHz. is 5.51dB, where the return loss The frequency range directly reflects the effective width of the non-reflection characteristic of the common mode energy. Figure 5 It can be seen that compared with the work in the first article, the common-mode signal non-reflection bandwidth is widened by 5.50 GHz, and compared with the work in the second article, the common-mode signal non-reflection bandwidth is widened by 2.00 GHz.

[0039] Reference Figure 6 In this embodiment, the center frequency of the differential mode signal passband from port 1 to port 2 is 3.03 GHz, and the minimum differential mode signal insertion loss from port 1 to port 2 is The minimum return loss of the differential mode signal is 0.50dB in the range of DC to 5.02GHz The minimum return loss of differential mode signal is 10.00dB in the range of DC to 9GHz is 6.13dB, the passband 30dB attenuation rate is 225, from Figure 6 It can be seen that compared with the work in the first article, the passband 30dB attenuation rate is increased by 96.5%, and compared with the work in the second article, the passband 30dB attenuation rate is increased by 191.2. The differential reflectionless filter has good passband selectivity for differential mode signals.

Claims

1. A differential-to-differential filter with broadband differential-mode and common-mode non-reflection characteristics, comprising a dielectric substrate (1) and a pair of transmission lines (2) for differential input or output printed on both sides of its longitudinal axis AA′, one or more first resonators (4) for frequency selection of stopband differential-mode signals, and a plurality of second resonators (3) for passband transmission of differential-mode signals; characterized in that: The pair of transmission lines (2) is composed of a pair of double-sided parallel strip line transmission lines distributed on both sides of an axis parallel to the horizontal axis BB′ of the dielectric substrate (1); the plurality of second resonators (3) are half-wavelength double-sided parallel strip line resonators distributed between the two pairs of transmission lines (2); the first resonator (4) is a quarter-wavelength double-sided parallel strip line resonator distributed between the upper and lower branches of the pair of transmission lines (2); the front transmission line and the back transmission line of each branch constituting the pair of transmission lines (2) are connected via metallized vias (5) and resistors (6); By exciting a half-wavelength double-sided parallel strip line second resonator (3) and a quarter-wavelength double-sided parallel strip line first resonator (4) through two pairs of double-sided parallel strip line transmission lines (2), a reflection-free filtering characteristic of a differential mode signal and a broadband reflection-free characteristic of a common mode signal are achieved.

2. The differential-to-differential filter with broadband differential mode and common mode non-reflection characteristics according to claim 1, characterized in that: The resistor (6) is connected to the metalized via (5) via a metal floating island (7).

3. The differential-to-differential filter with broadband differential mode and common mode non-reflection characteristics according to claim 1, characterized in that: In each pair of transmission lines (2) distributed on both sides of the longitudinal axis AA′, the upper branch front transmission line and the lower branch back transmission line, as well as the upper branch back transmission line and the lower branch front transmission line are mirror-symmetrical about an axis parallel to the transverse axis BB′.

4. The differential-to-differential filter with broadband differential mode and common mode non-reflection characteristics according to claim 3, characterized in that: The upper branch of the transmission line (2) distributed on one side of the longitudinal axis AA' and the lower branch of the transmission line (2) distributed on the other side of the longitudinal axis AA' are rotationally symmetric about the central normal line OO' of the dielectric substrate (1).

5. The differential-to-differential filter with broadband differential mode and common mode non-reflection characteristics according to claim 3, characterized in that: A pair of transmission lines (2) distributed on one side of the longitudinal axis AA′, a port of the upper branch front transmission line and a port of the lower branch back transmission line, and a port of the upper branch back transmission line and a port of the lower branch front transmission line of another pair of transmission lines (2) distributed on the other side of the longitudinal axis AA′, are each connected to a rectangular metal expansion patch.

6. The differential-to-differential filter with broadband differential mode and common mode non-reflection characteristics according to claim 1, characterized in that: When the number of the first resonator (4) is one, it is distributed in the middle of the upper and lower branches of a pair of double-sided parallel strip transmission lines; when the number of the first resonator (4) is multiple, it is linearly arranged in the middle of the upper and lower branches of a pair of double-sided parallel strip transmission lines.

7. The differential-to-differential filter with broadband differential mode and common mode non-reflection characteristics according to claim 1, characterized in that: The plurality of second resonators (3) are distributed in parallel between the two pairs of transmission lines (2), and adjacent resonators cross each other in the length direction.

8. The differential-to-differential filter with broadband differential mode and common mode non-reflection characteristics according to claim 1, characterized in that: The first resonator (4) has parallel strip lines on two surfaces at one end connected via a metallized via (5); the second resonator (3) has parallel strip lines on two surfaces at both ends connected via a metallized via (5).

9. The differential-to-differential filter with broadband differential mode and common mode non-reflection characteristics according to claim 1, characterized in that: The double-sided parallel strip line transmission line (2), the front transmission line and the back transmission line of each branch thereof adopt a broken line structure consisting of a first transmission strip line parallel to the horizontal axis BB' and a second transmission strip line connected thereto and with its port away from the vertical axis AA'.

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