A microstrip dual-band tunable bandpass filter based on folded split ring

Abstract

The present invention discloses a microstrip dual-frequency adjustable bandpass filter based on a folded open ring. The dual-frequency bandpass filter is formed by resonator coupling. Variable capacitance diodes are loaded at the opening of the open ring resonator and the terminal of the step impedance resonator respectively. The capacitance value is changed by changing the external voltage, thereby changing the resonant frequency of the filter, so that the dual frequency bands of the filter are independently adjustable.

Description

Technical Field

[0001] The invention belongs to the technical field of filters, and in particular relates to a microstrip dual-band adjustable bandpass filter based on a folded open ring. Background Art

[0002] As a core component of wireless communication systems, microwave filters play a role in frequency band selection in radio frequency communication systems. With the rapid development of modern wireless communication systems, microwave filters have also ushered in huge challenges. Communication systems are becoming increasingly miniaturized, and the space left for filters is also reduced. In contradiction with miniaturization, the multifunctionality of modern communication systems has enabled communication systems to cover more and more frequency bands, so that the number of filters has increased exponentially. Tunable filters came into being in this context. Tunable filters can effectively solve the contradiction between the large size brought about by the multifunctionality of communication systems and the miniaturization of communication systems. Therefore, the research on tunable filters has become a focus of scientific researchers.

[0003] Since the tunable filter is studied on the basis of the filter, although it developed late, it has progressed rapidly. At the beginning of the research on tunable filters, the attention of scientific research and production personnel was mainly on single-frequency tunable filters. For example, foreign scholar Y.Jeong designed a dual-frequency bandpass filter with a fixed low passband and adjustable high passband through a defective ground structure. However, with the rapid development of modern wireless communication systems, single-band tunable filters have been unable to meet the needs of communication systems to a large extent. Therefore, the research on dual-frequency tunable filters has become increasingly important. Domestic scholars have designed and realized a dual-frequency tunable filter working at 0.8-1.02GHz and 2.02-2.48GHz by means of branch-loaded impedance resonators. However, the designed filter is loaded with more varactor diodes, resulting in a higher insertion loss for the tunable filter designed in the end. The frequency bands of 2.4GHz-2.6GHz and 3.4GHz-3.6GHz are the frequency bands with a wide range of applications. Therefore, designing a tunable filter working in these two frequency bands has great practical application value. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a microstrip dual-frequency tunable bandpass filter based on a folded open ring. The dual-frequency bandpass filter is formed by resonator coupling. Varactor diodes are loaded at the opening of the open ring resonator and the terminal of the stepped impedance resonator respectively. The capacitance value is changed by changing the external voltage, thereby changing the resonant frequency of the filter, thereby completing the design of independent adjustable dual-band filter.

[0005] The technical solution of the present invention to solve the technical problem is to design a microstrip dual-band adjustable bandpass filter based on a folded open ring, the filter covers the frequency band range of 2.4GHz and 3.5GHz, and is characterized in that the filter is composed of a dielectric substrate, a radiation patch located on the front of the dielectric substrate, a varactor diode short-circuit grounding point, a branch short-circuit grounding point, a grounding surface on the back of the dielectric substrate, and a first varactor diode and a second varactor diode loaded on the radiation patch; the grounding surface on the back of the dielectric substrate completely covers the back of the dielectric substrate;

[0006] The radiation patch located on the front of the dielectric substrate comprises three parts, and the overall structure is axisymmetric, wherein the first part is two C-shaped open ring resonators placed in mirror symmetry about the symmetry axis, and the open ends thereof are arranged opposite to each other, and the upper and lower sides of each open end are connected by a No. 1 variable capacitance diode to form two closed frames; a rectangular notch is provided at the lower top corner of the two closed frames on the side close to the symmetry axis, and the upper edge of the rectangular notch is higher than the upper edge of the lower side of the closed frame, and its width is smaller than the width of the vertical side where it is located; a right-angle step is provided along the diagonal of the rectangular notch toward the inside of the closed frame, and the two right-angle sides of the right-angle step are parallel to the right-angle sides of the top angle of the rectangular notch, the bottom of the right-angle step is connected to the terminal end face of the upper edge of the lower side of the closed frame, and the side edge is connected to the inner side face of the lower edge of the vertical side of the closed frame close to the symmetry axis, and the position of the No. 1 variable capacitance diode is higher than the upper end face of the right-angle step; except for the part between the right-angle step and the rectangular notch, the width of the radiation patch constituting the C-shaped open ring resonator is the same;

[0007] The second part is a stepped impedance resonator with an approximately U-shaped structure in which two C-shaped open ring resonators are mounted; a boss-shaped branch extends upward from the middle of the bottom of the stepped impedance resonator, and the top surface of the boss-shaped branch is connected to the branch short-circuit grounding point; the boss-shaped branch and the branch short-circuit grounding point are located between two rectangular notches, and the top of the branch short-circuit grounding point is lower than the upper edge of the rectangular notch; the top surface of the boss-shaped branch is higher than the lower edge of the rectangular notch, and its bottom surface is lower than the lower edge of the lower part of the C-shaped open ring resonator; the left and right sides of the stepped impedance resonator are all at right angles to the bottom The tops of the left and right sides are connected with "n"-shaped branches; one vertical side of the two "n"-shaped branches is the top extension of the left and right sides respectively, and the other vertical sides are located outside the left and right sides and the middle of the outer side of the vertical side is connected to a second varactor diode, and the other end of the second varactor diode is connected to the short-circuit grounding point of the varactor diode; the short-circuit grounding point of the varactor diode is connected to the grounding surface on the back of the dielectric substrate; the radiating patch constituting the step impedance resonator has the same width except for the vertical side of the outer side of the "n"-shaped branches;

[0008] The third part is two symmetrical feeding ports arranged on both sides of the stepped impedance resonator. The feeding ports are composed of two three-section feeding microstrip lines connected at right angles. The first section is horizontally arranged below the stepped impedance resonator; the second section is located outside the left and right sides of the stepped impedance resonator and arranged parallel to each other; the third section is horizontally connected to the top of the second section and extends to the edges of both sides of the dielectric substrate.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] 1. By coupling the stepped impedance resonator loaded with short-circuit branches with the split ring resonator, the filter can operate in two frequency bands (2.4 GHz and 3.5 GHz) simultaneously.

[0011] 2. By folding the split ring resonator and the stepped impedance resonator, the volume of the filter is effectively reduced and the S of the filter is improved. 11 With S 21 parameter.

[0012] 3. By loading the second varactor diode at the terminal of the step impedance resonator, the center frequency of the filter can be adjusted in the frequency band of 2.4GHz-2.6GHz.

[0013] 4. Loading a variable capacitance diode No. 1 at the opening of the split ring resonator makes the center frequency of the filter adjustable within the frequency band of 3.4 GHz-3.6 GHz.

[0014] 5. The center frequencies of the two working passbands of the filter are independently adjustable and do not affect each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a front structural schematic diagram of an embodiment of the filter of the present invention.

[0016] Figure 2 It is a schematic diagram of the first part of the structure of a radiation patch of an embodiment of the filter of the present invention.

[0017] Figure 3 It is a schematic diagram of the second part of the structure of the radiation patch of an embodiment of the filter of the present invention.

[0018] Figure 4 It is a schematic diagram of the third part of the structure of the radiation patch of an embodiment of the filter of the present invention.

[0019] Figure 5 It is a schematic diagram of the back structure of an embodiment of the filter of the present invention.

[0020] Figure 6 It is a simulation curve diagram of return loss and insertion loss of an embodiment of the filter of the present invention.

[0021] Figure 7 It is a first frequency band tuning curve diagram of an embodiment of the filter of the present invention.

[0022] Figure 8 It is a second frequency band tuning curve diagram of an embodiment of the filter of the present invention. DETAILED DESCRIPTION

[0023] The specific embodiments of the present invention are given below and described in detail with reference to the accompanying drawings. The specific embodiments are only used to further describe the present invention in detail and do not limit the protection scope of the claims of this application.

[0024] The present invention provides a microstrip dual-band tunable bandpass filter based on a folded split ring (referred to as filter, see Figure 1-5 ), the filter covers the frequency band range of 2.4GHz and 3.5GHz, and the filter is composed of a dielectric substrate 1, a radiation patch located on the front of the dielectric substrate 1, a varactor diode short-circuit grounding point 8, a branch short-circuit grounding point 501, a ground plane 9 on the back of the dielectric substrate, and a first varactor diode 6 and a second varactor diode 7 loaded on the radiation patch. The ground plane 9 on the back of the dielectric substrate completely covers the back of the dielectric substrate 1;

[0025] The radiation patch located on the front of the dielectric substrate 1 includes three parts, and its overall structure is axisymmetric, wherein the first part is two C-shaped open ring resonators 2 placed in mirror symmetry about the symmetry axis, and the open ends are arranged opposite to each other, and the upper and lower sides of each open end are connected by a No. 1 varactor diode 6 to form two closed frames; a rectangular notch 201 is provided at the lower top corner of the side close to the symmetry axis of the two closed frames, and the upper edge of the rectangular notch 201 is higher than the upper edge of the lower side of the closed frame, and its width is smaller than the width of the vertical side where it is located; a right-angle step is provided along the diagonal of the rectangular notch 201 toward the inside of the closed frame, and the two right-angle sides of the right-angle step are parallel to the right-angle sides of the top angle of the rectangular notch, the bottom of the right-angle step is connected to the terminal end face of the upper edge of the lower side of the closed frame, and its side is connected to the inner side face of the lower edge of the vertical side of the closed frame close to the symmetry axis, and the position of the No. 1 varactor diode 6 is higher than the upper end face of the right-angle step. Except for the portion between the right-angle step and the rectangular notch 201 , the widths of the radiation patches constituting the C-shaped split ring resonator 2 are all the same.

[0026] The second part is a U-shaped stepped impedance resonator 3 in which two C-shaped split ring resonators 2 are mounted. A boss-shaped branch 5 extends upward from the middle of the bottom of the stepped impedance resonator 3, and the top surface of the boss-shaped branch 5 is connected to the branch short-circuit grounding point 501; the boss-shaped branch 5 and the branch short-circuit grounding point 501 are located between the two rectangular notches 201, and the top of the branch short-circuit grounding point 501 is lower than the upper edge of the rectangular notch 201; the top surface of the boss-shaped branch 5 is higher than the lower edge of the rectangular notch 201, and its bottom surface is lower than the lower edge of the lower part of the C-shaped split ring resonator 2; the left and right sides of the stepped impedance resonator 3 The sides and bottom are connected at right angles, and the tops of the left and right sides are connected with "n"-shaped branches 301; one vertical side of the two "n"-shaped branches 301 is the top extension of the left and right sides respectively, and their other vertical sides are located outside the left and right sides and the middle of the outer side of the vertical side is connected to a second varactor diode 7, and the other end of the second varactor diode 7 is connected to a varactor diode short-circuit grounding point 8; the varactor diode short-circuit grounding point 8 is connected to the grounding surface 9 on the back of the dielectric substrate 1. The radiation patch constituting the stepped impedance resonator 3 has the same width except for the vertical side of the outer side of the "n"-shaped branches 301 (with the side close to the symmetry axis as the inner side).

[0027] The third part is two symmetrical feeding ports 4 arranged on both sides of the stepped impedance resonator 3. The feeding port 4 is composed of two three-section feeding microstrip lines 401 connected at right angles. The first section is horizontally arranged below the stepped impedance resonator 3; the second section is located outside the left and right sides of the stepped impedance resonator 3 and arranged parallel to each other; the third section is horizontally connected to the top of the second section and extends to the edges of both sides of the dielectric substrate 1.

[0028] The material of the dielectric substrate 1 is Rogers 5880, with a dielectric constant of 2.2, a width of 27 mm, a length of 22 mm, and a thickness of 0.787 mm.

[0029] The distance d1 between the inner vertical sides of the two C-shaped open ring resonators 2 in the radiation patch is 0.4mm, and the width W1 of the main part is 1.0mm; the outer length L1 of the upper horizontal side of the C-shaped open ring resonator 2 is 5.0mm, the outer length L3 of the lower horizontal side is 4.2mm, the outer length L2 of the outer vertical side is 5.5mm, the length L4 of the rectangular notch 201 is 1.1mm, and the width W2 is 0.8mm; the distance L6 between the upper end of the open end of the C-shaped open ring resonator 2 and the upper horizontal side is 1.1mm, and the distance L5 between the upper end of the lower side of the open end and the upper end of the rectangular notch 201 is 1.3mm; the width of the right-angle step is 0.8mm, and the length is 1.0mm.

[0030] The distance between the upper edge of the bottom of the stepped impedance resonator 3 and the lower edge of the lower horizontal side of the C-shaped open ring resonator 2 is 0.4mm, and the width W3 of its main part is 0.6mm; the length L11 of the boss-type branch 5 extending upward from the middle of the bottom of the stepped impedance resonator 3 is 1.2mm, and its width W4 is 0.6mm; the length L7 of half the outer length of the bottom of the stepped impedance resonator 3 is 6.1mm, and the length L8 of the left and right sides connected at right angles to the bottom is 6.5mm; the distance L9 between the left and right sides of the "n"-shaped branch 301 is 2.5mm, the distance between the upper and lower sides is 2.0mm, the length L10 of the outer vertical side is 1.5mm, and the distance W5 between the upper and lower edges of the internal notch of the "n"-shaped branch 301 is 1.4mm.

[0031] The horizontal distance d2 between the two feeding ports 4 is 0.4 mm, and the distance between the upper edge of the first section of the feeding microstrip line 401 and the lower edge of the bottom of the stepped impedance resonator 3 is 0.4 mm; the outer length L12 of the first section of the feeding microstrip line 401 is 6.7 mm, and its width W6 is 0.5 mm; the distance L13 from the upper end of the second section to the bottom of the first section is 2.5 mm, and the width of the second section is equal to the width of the first section; the width W7 of the third section is 3 mm, and the distance L14 from the outer side of the third section to the outer side of the second section is 6.6 mm;

[0032] The initial capacitance of the first varactor diode 6 and the second varactor diode 7 are both 0.4 pf, and the varactor diode short-circuit grounding point 8 and the branch short-circuit grounding point 501 are both circles with a radius of 0.25 mm.

[0033] Figure 6 is the simulation curve diagram of this embodiment, from Figure 6 It can be seen that the filter of the present invention can accurately operate in the 2.4 GHz and 3.5 GHz frequency bands when the varactor diode does not change the capacitance, and the return loss in these two frequency bands is better than 20 dB, and the insertion loss is less than 2 dB, which well meets the frequency band requirements of the radio application band. Figure 7 This is a first frequency band tuning curve diagram of this embodiment. As the C1 varactor (varactor diode No. 1 6) changes between 0.2pf and 0.6pf, the center frequency of the filter of the present invention changes stably between 2.25GHz and 2.84GHz, and has no frequency influence on the second working frequency band. Figure 8 This is the second frequency band tuning curve diagram of the present embodiment. As the C2 varactor (varactor diode No. 2 7) changes between 0.4pf and 0.6pf, the center frequency of the filter changes stably between 3.05GHz and 3.52GHz and has no frequency influence on the first working frequency band. The filter of the present invention can independently adjust the working frequency in the dual passband and has good performance.

[0034] The above embodiment is a preferred implementation mode of the present invention. In addition, based on this embodiment, changing the size and position of the open ring resonator and the stepped impedance resonator, as well as the folding length of the open ring resonator, and changing the initial capacitance of the varactor diode should all be included in the protection scope of the present invention.

[0035] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A microstrip dual-band tunable bandpass filter based on a folded split ring, the filter covers the frequency band range of 2.4 GHz and 3.5 GHz, characterized in that: The filter is composed of a dielectric substrate, a radiation patch located on the front of the dielectric substrate, a varactor diode short-circuit grounding point, a branch short-circuit grounding point, a grounding surface on the back of the dielectric substrate, and a first varactor diode and a second varactor diode loaded on the radiation patch; the grounding surface on the back of the dielectric substrate completely covers the back of the dielectric substrate; The radiation patch located on the front of the dielectric substrate comprises three parts, and the overall structure is axisymmetric, wherein the first part is two C-shaped open ring resonators placed in mirror symmetry about the symmetry axis, and the open ends thereof are arranged opposite to each other, and the upper and lower sides of each open end are connected by a No. 1 variable capacitance diode to form two closed frames; a rectangular notch is provided at the lower top corner of the two closed frames on the side close to the symmetry axis, and the upper edge of the rectangular notch is higher than the upper edge of the lower side of the closed frame, and its width is smaller than the width of the vertical side where it is located; a right-angle step is provided along the diagonal of the rectangular notch toward the inside of the closed frame, and the two right-angle sides of the right-angle step are parallel to the right-angle sides of the top angle of the rectangular notch, the bottom of the right-angle step is connected to the terminal end face of the upper edge of the lower side of the closed frame, and the side edge is connected to the inner side face of the lower edge of the vertical side of the closed frame close to the symmetry axis, and the position of the No. 1 variable capacitance diode is higher than the upper end face of the right-angle step; except for the part between the right-angle step and the rectangular notch, the width of the radiation patch constituting the C-shaped open ring resonator is the same; The second part is a stepped impedance resonator with an approximately U-shaped structure in which two C-shaped open ring resonators are mounted; a boss-shaped branch extends upward from the middle of the bottom of the stepped impedance resonator, and the top surface of the boss-shaped branch is connected to the branch short-circuit grounding point; the boss-shaped branch and the branch short-circuit grounding point are located between two rectangular notches, and the top of the branch short-circuit grounding point is lower than the upper edge of the rectangular notch; the top surface of the boss-shaped branch is higher than the lower edge of the rectangular notch, and its bottom surface is lower than the lower edge of the lower part of the C-shaped open ring resonator; the left and right sides of the stepped impedance resonator are all at right angles to the bottom The tops of the left and right sides are connected with "n"-shaped branches; one vertical side of the two "n"-shaped branches is the top extension of the left and right sides respectively, and the other vertical sides are located outside the left and right sides and the middle of the outer side of the vertical side is connected to a second varactor diode, and the other end of the second varactor diode is connected to the short-circuit grounding point of the varactor diode; the short-circuit grounding point of the varactor diode is connected to the grounding surface on the back of the dielectric substrate; the radiating patch constituting the step impedance resonator has the same width except for the vertical side of the outer side of the "n"-shaped branches; The third part is two symmetrical feeding ports arranged on both sides of the stepped impedance resonator. The feeding ports are composed of two three-section feeding microstrip lines connected at right angles. The first section is horizontally arranged below the stepped impedance resonator; the second section is located outside the left and right sides of the stepped impedance resonator and arranged parallel to each other; the third section is horizontally connected to the top of the second section and extends to the edges of both sides of the dielectric substrate.

2. A microstrip dual-band tunable bandpass filter based on a folded open ring according to claim 1, characterized in that: The material of the dielectric substrate is Rogers 5880, which has a dielectric constant of 2.2, a width of 27 mm, a length of 22 mm, and a thickness of 0.787 mm; The distance d1 between the inner vertical sides of the two C-shaped open ring resonators in the radiation patch is 0.4mm, and the width W1 of the main body is 1.0mm; the outer length L1 of the upper horizontal side of the C-shaped open ring resonator is 5.0mm, the outer length L3 of the lower horizontal side is 4.2mm, the outer length L2 of the outer vertical side is 5.5mm, the length L4 of the rectangular notch is 1.1mm, and the width W2 is 0.8mm; the distance L6 between the upper end of the open end of the C-shaped open ring resonator and the upper horizontal side is 1.1mm, and the distance L5 between the upper end of the lower side of the open end and the upper end of the rectangular notch is 1.3mm; the width of the right-angle step is 0.8mm, and the length is 1.0mm; The distance between the upper edge of the bottom of the step impedance resonator and the lower edge of the lower horizontal side of the C-shaped open ring resonator is 0.4mm, and the width W3 of the main body is 0.6mm; the length L11 of the boss-type branch extending upward from the middle of the bottom of the step impedance resonator is 1.2mm, and the width W4 is 0.6mm; the length L7 of half the outer length of the bottom of the step impedance resonator is 6.1mm, and the length L8 of the left and right sides connected at right angles to the bottom is 6.5mm; the distance L9 between the left and right sides of the "n"-shaped branch is 2.5mm, the distance between the upper and lower sides is 2.0mm, the length L10 of the outer vertical side is 1.5mm, and the distance W5 between the upper and lower edges of the internal notch of the "n"-shaped branch is 1.4mm; The horizontal distance d2 between the two feeding ports is 0.4mm, and the distance between the upper edge of the first section of the feeding microstrip line and the lower edge of the bottom of the stepped impedance resonator is 0.4mm; the outer length L12 of the first section of the feeding microstrip line is 6.7mm, and its width W6 is 0.5mm; the distance L13 from the upper end of the second section to the bottom of the first section is 2.5mm, and the width of the second section is equal to the width of the first section; the width W7 of the third section is 3mm, and the distance L14 from the outer side of the third section to the outer side of the second section is 6.6mm.

3. The microstrip dual-band tunable bandpass filter based on a folded open ring according to claim 1, characterized in that: The initial capacitance of the first and second varactor diodes is 0.4 pf.

4. The microstrip dual-band tunable bandpass filter based on a folded open ring according to claim 1, characterized in that: The short-circuit grounding point of the varactor diode and the short-circuit grounding point of the branch are both circles with a radius of 0.25 mm.

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