Ultra-wideband microstrip band-pass filter

Abstract

The ultra-wideband microstrip band-pass filter comprises a dielectric insulating substrate, a plurality of groups of conductive microstrip patches positioned on the front surface of the dielectric insulating substrate, and a conductive grounding plate positioned on the back surface of the dielectric insulating substrate, the plurality of groups of conductive microstrip patches comprise two conductive microstrips which are respectively connected with the input port and the output port, two U-shaped microstrips which are positioned between the two conductive microstrips and are respectively connected in series with the two conductive microstrips, and a plurality of groups of terminal open circuit conductive branch lines which are loaded on the conductive microstrips and the U-shaped microstrips; the cross-shaped conductive micro-strip is located between the two U-shaped micro-strips, the two rectangular micro-strips are transversely connected to the upper end and the lower end of a vertical micro-strip in the cross-shaped conductive micro-strip respectively, and the two triangular micro-strips are loaded on the upper side and the lower side of the output end U-shaped micro-strip. The conductive grounding plate is of a conductive defected ground structure with two symmetrical rectangular gaps. According to the ultra-wideband band-pass filter, low insertion loss, low return loss and wide stop band of the ultra-wideband band-pass filter are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave communications, in particular to an ultra-wideband microstrip bandpass filter for microwave circuits. Background Art

[0002] The ultra-wideband bandpass filter was first designed by Saito A., H. Harada and others in 2002 using hybrid materials. It not only meets the FCC frequency band requirements but also has good stopband suppression performance. However, the insertion loss characteristics within the passband are poor (less than -6.7 dB).

[0003] In the following twenty years, the types of ultra-wideband bandpass filters gradually increased. According to the different structures used, they can be divided into microstrip structure, suspended strip line structure, ridge waveguide, microstrip coplanar waveguide, etc.

[0004] Microstrip structures can be divided into cascade structures and directly designed bandpass structures. Direct design methods include multimode resonators, optimized short-circuit stub lines, microstrip slot lines, composite left-handed and right-handed transmission lines, and various new materials and technologies.

[0005] Cascaded structures typically achieve ultra-wideband characteristics by cascading low-pass and high-pass filters, or band-pass and band-stop filters. While direct cascading is simple, it occupies a large footprint, making it unsuitable for miniaturization. Furthermore, soldering issues can increase insertion loss.

[0006] Compared to using multiple single-mode resonators to construct different resonant modes, multimode resonators reduce the size of the layout, enabling overall miniaturization. Multimode resonator design methods typically rely on parallel coupling structures to achieve strong coupling for energy transmission. Actual simulation and processing techniques reveal that these coupling gaps typically require an accuracy of 0.01 mm. When the coupling lines themselves also require an accuracy of 0.01 mm, this becomes challenging for the microwave dielectric plate processing technology typically used in ultra-wideband bands, making parameter accuracy difficult to guarantee. Furthermore, the design of the multimode resonator structure results in a filter with suboptimal sideband roll-off characteristics.

[0007] The short-circuited stub method was used in the 1970s to propose an optimally distributed ultra-wideband filter. This filter loads a short-circuited stub with a length of λ / 4 onto a λ / 2 microstrip transmission line to form a resonant unit. By connecting multiple units in series according to the requirements of parameter indicators, filters of different orders can be designed. The higher the order, the better the frequency selection characteristics. Adjusting the length of different short-circuited stubs will also affect the resonant characteristics within the passband.

[0008] The microstrip-slotline structure is mainly designed by slotting the microstrip line, which is designed according to the λ / 4 standard of the corresponding frequency and loaded onto the open / short-circuited branch line to strengthen the coupling with the original structure, thereby improving the rectangular coefficient of the filter.

[0009] In order to further eliminate the accuracy limitation of the filter and reduce the cost, the present invention starts from the microstrip distributed branch line, designs a central symmetrical branch line structure coupled with an interdigitated structure, and then proposes an ultra-wideband microstrip bandpass filter. Summary of the Invention

[0010] The purpose of the present invention is to propose an ultra-wideband microstrip bandpass filter, which obtains good low-frequency stopband characteristics by coupling symmetrical branch resonators with input and output ports. Then, by loading open-circuit branch lines and triangular microstrip patches on the port coupling lines, the sideband roll-off and return loss are optimized respectively, thereby achieving low insertion loss, low return loss and wide stopband of the ultra-wideband bandpass filter.

[0011] To achieve the above object, the technical solution of the present invention is: an ultra-wideband microstrip bandpass filter, comprising a dielectric insulating substrate, a plurality of groups of conductive microstrip patches located on the front surface of the dielectric insulating substrate, and a conductive ground plane located on the back surface of the dielectric insulating substrate; The multiple groups of conductive microstrip patches include two conductive microstrips respectively connected to the input port and the output port, two U-shaped microstrips located between the two conductive microstrips and respectively connected in series to the two conductive microstrips, multiple groups of conductive branch lines with open terminals loaded on the conductive microstrips and the U-shaped microstrips, a cross-shaped conductive microstrip located between the two U-shaped microstrips, two rectangular microstrips respectively connected transversely to the upper and lower ends of the vertical microstrip in the cross-shaped conductive microstrip, and two triangular microstrips loaded on the upper and lower sides of the U-shaped microstrip at the output end; The conductive ground plate is a conductive defect ground structure with two symmetrical rectangular gaps.

[0012] Preferably, the dielectric insulating substrate is a Rogers RO4350B dielectric substrate.

[0013] Preferably, the two conductive microstrips have equal widths.

[0014] Preferably, the two conductive microstrips are loaded with three groups of conductive branch lines with open terminals; wherein, the conductive microstrip connected to the input port is loaded with one group of conductive branch lines, and the conductive microstrip connected to the output port and the U-shaped conductive microstrip are loaded with two groups of conductive branch lines.

[0015] Preferably, the widths and lengths of the three groups of open-ended conductive branch lines are different, and each group of conductive branch lines includes symmetrical branch lines symmetrically connected to the upper and lower sides of the conductive microstrip.

[0016] Preferably, the conductive branch line loaded on the conductive microstrip connected to the input port is a quarter-wavelength conductive branch line.

[0017] Preferably, the two U-shaped microstrips have the same size.

[0018] Preferably, the horizontal microstrips of the cross-shaped conductive microstrip are finger-coupled with two U-shaped microstrips respectively.

[0019] Preferably, the two rectangular microstrips have the same size.

[0020] Preferably, the two rectangular gaps are located on the back sides of the horizontal microstrips on the left and right sides of the cross-shaped conductive microstrip.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The filter of the present invention obtains good low-frequency stopband characteristics by coupling the symmetrical branch resonator with the input and output ends, and then optimizes the sideband roll-off and return loss by loading the open branch line and the triangular microstrip patch on the port coupling line, thereby realizing low insertion loss, low return loss and wide stopband of the ultra-wideband bandpass filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the top structure of the ultra-wideband microstrip bandpass filter of the present invention; Figure 2 Schematic diagram of the underlying structure of the ultra-wideband microstrip bandpass filter of the present invention; Figure 3 Schematic diagram of the side view of the ultra-wideband microstrip bandpass filter of the present invention; Figure 4 Schematic diagram of top-layer structural parameters of the ultra-wideband microstrip bandpass filter of the present invention; Figure 5 Schematic diagram of the underlying structural parameters of the ultra-wideband microstrip bandpass filter of the present invention; Figure 6 Schematic diagram of the side view structural parameters of the ultra-wideband microstrip bandpass filter of the present invention; Figure 7 is the resonance curve of the ultra-wideband microstrip bandpass filter of the present invention; Figure 8 is the Smith impedance curve of the ultra-wideband microstrip bandpass filter of the present invention; Figure 9 is the group delay characteristic curve of the ultra-wideband microstrip bandpass filter of the present invention; Figure 10 This is the phase characteristic curve of the ultra-wideband microstrip bandpass filter of the present invention.

[0023] In the picture: 1-dielectric insulating substrate; 2-conductive microstrip; 3-first conductive branch line; 4-U-shaped microstrip; 5-horizontal microstrip; 6-vertical microstrip; 7-rectangular microstrip; 8-multiple groups of conductive microstrip patches; 9-triangular microstrip; 10-second conductive branch line; 11-third conductive branch line; 12-conductive ground plane; 13-rectangular gap. DETAILED DESCRIPTION

[0024] The following is combined with Figure 1-10 , the technical solution of the present invention is described in detail.

[0025] The present invention provides an ultra-wideband microstrip bandpass filter operating at 10.5 GHz to 19.52 GHz, comprising a dielectric insulating substrate 1, a conductive microstrip pattern formed by a plurality of conductive microstrip patches 8 located on the front surface of the dielectric insulating substrate 1, and a conductive ground plane 12 located on the back surface of the dielectric insulating substrate 1; The multiple groups of conductive microstrip patches 8 include two conductive microstrips 2 respectively connected to the input port and the output port, two U-shaped microstrips 4 located between the two conductive microstrips 2 and connected in series to the two conductive microstrips 2, multiple groups of open-ended conductive branch lines loaded on the conductive microstrips 2 and the U-shaped microstrips 4, a cross-shaped conductive microstrip located between the two U-shaped microstrips 4, two rectangular microstrips 7 respectively connected to the upper and lower ends of the vertical microstrip 6 in the cross-shaped conductive microstrip, and two triangular microstrips 9 loaded on the upper and lower sides of the U-shaped microstrip 4 at the output end; The conductive ground plate 12 is a conductive defect ground structure with two symmetrical rectangular gaps 13; The specific structure diagram of the bandpass filter is shown in the attached Figure 1-3 , Figure 1-2 In the figure, the horizontal direction is the length direction and the vertical direction is the width direction.

[0026] In this embodiment, the dielectric insulating substrate 1 is a Rogers RO4350B dielectric substrate. Its relative permittivity is 3.66, and its loss tangent is 0.009. The dielectric substrate thickness can be set to 0.508 mm, and the patterned copper thickness is 0.035 mm. The overall dimensions of the filter are 15.4 mm (length) × 10 mm (width) × 0.578 mm (thickness).

[0027] In this embodiment, the widths of the two conductive microstrips 2 are equal.

[0028] In this embodiment, three sets of open-ended conductive stubs are loaded onto the two conductive microstrips 2. The conductive microstrip 2 connected to the input port is loaded with one set of conductive stubs, specifically first conductive stubs 3. The conductive microstrip 2 connected to the output port and the U-shaped conductive microstrip 4 are loaded with two sets of conductive stubs, namely second conductive stubs 10 and third conductive stubs 11. The open-ended stubs at the output introduce two zeros into the filter's high-frequency stopband, optimizing the stopband rejection and improving the roll-off rate at the high-frequency edge of the passband.

[0029] In this embodiment, the three groups of open-ended conductive branch lines have different widths and lengths, and each group includes symmetrical branch lines symmetrically connected to the upper and lower sides of the conductive microstrip 2. By loading three groups of microstrip distributed branch lines of different lengths and widths on the conductive microstrip 2, low-frequency and high-frequency harmonics are suppressed and the roll-off rate of the passband edge is improved.

[0030] In this embodiment, the conductive stubs loaded on the conductive microstrip 2 connected to the input port are quarter-wavelength conductive stubs for frequency selection. By optimizing and adjusting the parameters of the two sets of open-circuit stubs at the output, the filter's high-frequency stopband rejection characteristics can be improved, avoiding the generation of additional parasitic passbands caused by the coupled structure. The use of stubs of varying widths provides a certain degree of suppression of higher-frequency stopband harmonics, preventing overcrowding at the output end that could lead to unnecessary resonances that affect the passband characteristics, while also reducing energy loss at the input end.

[0031] In this embodiment, the two U-shaped microstrips 4 have the same size.

[0032] In this embodiment, the horizontal microstrips 5 of the cross-shaped conductive microstrip are interdigitally coupled with two U-shaped microstrips 4. The parallel coupled line structure formed by the horizontal microstrips 5 optimizes the stopband characteristics and effectively suppresses low-frequency stopband harmonics. Furthermore, a triangular microstrip 9 is introduced along the edge of the U-shaped conductive microstrip 4 connected to the output terminal. This triangular microstrip 9 is connected above the interdigitated coupled line structure, affecting the surface current distribution on the symmetrical branch lines, forming new resonance points, and improving the return loss characteristics within the filter's passband.

[0033] In this embodiment, the two rectangular microstrips 7 have the same size.

[0034] In this embodiment, two rectangular slots 13 are located on the backsides of the horizontal microstrips 5 on the left and right sides of the cross-shaped conductive microstrip. By adjusting the parameters of the defective ground structure directly below the parallel coupling line structure, the filter's passband return loss characteristics can be improved and the coupling of the structure itself can be strengthened.

[0035] Table 1 gives Figure 4-6The designed ultra-wideband bandpass filter structure parameter values. The values ​​in Table 1 are for the best comprehensive characteristics. The patent of this invention protects this structure shape and is not limited to the above specific parameter values.

[0036] Table 1 Optimal filter characteristic parameters (unit: mm) Figure 7 This is the resonance curve of the ultra-wideband microstrip bandpass filter. The overall passband frequency range is 10.4 GHz to 19.52 GHz, with an insertion loss of 0.3 dB at the passband center frequency of 14.96 GHz. The zeros on either side of the passband have losses of 36.88 dB and 48.86 dB at 8.91 GHz and 21.68 GHz, respectively. The reflection level remains below -20 dB in the low-frequency stopband from 0 to 9.36 GHz and the high-frequency stopband from 20.84 to 34.78 GHz, respectively, and below -15 dB from 34.78 to 40 GHz.

[0037] Figure 8 Figure 2 is the impedance curve. The input impedance of the filter is 1.0175-j*0.1342Ω at the center frequency of 14.96 GHz. The normalized input impedance is 0.6536-j*0.3123Ω at 10.4 GHz and 0.4369-j*2.1194Ω at 19.52 GHz. The filter has good impedance matching characteristics within the ultra-wideband 9.12 GHz band.

[0038] Figure 9 This is the filter group delay parameter characteristic curve. The normalized filter group delay within the passband range is less than 1ns, indicating that the filter signal has good stability, extremely low distortion, and guaranteed signal quality. Figure 10 This is the phase distribution characteristic curve of the filter. The filter has good linearity within the passband range.

[0039] In summary, the filter of the present invention adopts a symmetrical first conductive branch line 3, a second conductive branch line 10 and a third conductive branch line 11 to be loaded onto the microstrip 2, and is coupled to the input and output ends through the horizontal microstrip 5 and the U-shaped microstrip 4 to optimize the low-frequency stopband, adjust the distribution of the first conductive branch line 3, the second conductive branch line 10 and the third conductive branch line 11, and load the open-circuit conductive branch line to introduce the transmission zero point, optimize the passband bilateral roll-off and adjust the passband frequency band, the conductive defect ground structure with two rectangular gaps 13 of the conductive ground plate 12 strengthens the coupling, loads the triangular microstrip 9 to adjust the surface current distribution, and optimizes the return loss in the passband. The filter exhibits 0.3 dB insertion loss at a center frequency of 14.96 GHz, better than 20 dB return loss within the passband, a 3 dB relative bandwidth of 60.96% (10.4 GHz to 19.52 GHz), 20 dB low-frequency stopband suppression from 0 GHz to 9.36 GHz, 20 dB high-frequency stopband suppression from 20.84 GHz to 34.78 GHz, and less than 1 ns group delay within the passband. The proposed ultra-wideband microstrip bandpass filter structure has relatively low overall processing costs and is primarily intended for wireless communications, satellite, and radar systems operating in 5G alternative frequency bands. Due to its small size and single-layer planar microstrip structure, the filter is easily integrated, meeting current requirements for miniaturization and integration in electronics and possessing considerable potential for future applications.

[0040] The resonance characteristics were analyzed using odd- and even-mode analysis. Under odd-mode excitation, the main resonator's symmetric plane is grounded, resulting in low energy on the horizontal right half of the interdigitated structure. Energy in the remaining right half is transmitted through coupling and reflection from defects in the ground plane. Under even-mode excitation, the horizontal surface current distribution of the interdigitated structure is uniform, and this surface current distribution can be adjusted by adjusting the ratio of the vertical electrical length and dimensions of the interdigitated structure to adjust the resonant frequency and thus the filter's bandwidth. Furthermore, under both odd- and even-mode excitation, the current distribution of the two sets of open-circuited stubs, which introduce transmission zeros, changes significantly.

[0041] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. An ultra-wideband microstrip bandpass filter, characterized in that: It includes a dielectric insulating substrate, a plurality of conductive microstrip patches located on the front surface of the dielectric insulating substrate, and a conductive ground plane located on the back surface of the dielectric insulating substrate; The multiple groups of conductive microstrip patches include two conductive microstrips respectively connected to the input port and the output port, two U-shaped microstrips located between the two conductive microstrips and respectively connected in series to the two conductive microstrips, multiple groups of conductive branch lines with open terminals loaded on the conductive microstrips and the U-shaped microstrips, a cross-shaped conductive microstrip located between the two U-shaped microstrips, two rectangular microstrips respectively connected transversely to the upper and lower ends of the vertical microstrip in the cross-shaped conductive microstrip, and two triangular microstrips loaded on the upper and lower sides of the U-shaped microstrip at the output end; The conductive ground plate is a conductive defect ground structure with two symmetrical rectangular gaps.

2. The ultra-wideband microstrip bandpass filter according to claim 1, wherein: The dielectric insulating substrate adopts Rogers RO4350B dielectric substrate.

3. The ultra-wideband microstrip bandpass filter according to claim 1, wherein: The two conductive microstrips have equal widths.

4. The ultra-wideband microstrip bandpass filter according to claim 1, wherein: The two conductive microstrips are loaded with three groups of conductive branch lines with open terminals. Among them, the conductive microstrip connected to the input port is loaded with one group of conductive branch lines, and the conductive microstrip connected to the output port and the U-shaped conductive microstrip are loaded with two groups of conductive branch lines.

5. The ultra-wideband microstrip bandpass filter according to claim 4, characterized in that: The widths and lengths of the three groups of open-ended conductive branch lines are different, and each group of conductive branch lines includes symmetrical branch lines symmetrically connected to the upper and lower sides of the conductive microstrip.

6. The ultra-wideband microstrip bandpass filter according to claim 4, characterized in that: The conductive branch line loaded on the conductive microstrip connected to the input port is a quarter-wavelength conductive branch line.

7. The ultra-wideband microstrip bandpass filter according to claim 1, wherein: The two U-shaped microstrips have the same size.

8. The ultra-wideband microstrip bandpass filter according to claim 1, wherein: The horizontal microstrips of the cross-shaped conductive microstrip are respectively coupled with the two U-shaped microstrip fingers.

9. The ultra-wideband microstrip bandpass filter according to claim 1, characterized in that: The two rectangular microstrips have the same size.

10. The ultra-wideband microstrip bandpass filter according to claim 1, characterized in that: The two rectangular gaps are located on the back side of the horizontal microstrips on the left and right sides of the cross-shaped conductive microstrip.

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