A Small Dual-Band Bandpass Filter Based on CSRR

Abstract

The invention discloses a small dual-frequency bandpass filter based on CSRR, which comprises a dielectric substrate, a first metal coating layer arranged on the upper surface of the dielectric substrate, a second metal coating layer arranged on the lower surface of the dielectric substrate and used as a grounding layer, and metal vias respectively arranged at four corners of the substrate; the first metal coating layer is etched with two large complementary open ring resonators CSRR and two small complementary open ring resonators CSRR; the large complementary open ring resonators CSRR and the small complementary open ring resonators CSRR are arranged alternately; the two large complementary open ring resonators CSRR and the two small complementary open ring resonators CSRR are respectively arranged diagonally on the metal coating layer; the two large complementary open ring resonators CSRR are of the same size, and the two small complementary open ring resonators CSRR are of the same size; the invention solves the problems of the existing microwave filter, such as over-large size, single frequency band, excessive insertion loss, complex structure, etc.

Description

Technical Field

[0001] The present invention relates to a dual-band pass filter, and in particular to a small dual-frequency band pass filter based on CSRR that can be used for 5G communication. Background Art

[0002] At present, 5G communication technology has attracted much attention due to its high transmission rate, and the research and development of related communication devices in various frequency bands has also attracted the attention of many researchers. Multi-band filters are an important component to meet the capacity and coverage requirements of future 5G mobile communications, and their structure and performance have a direct impact on the characteristics of the entire communication system. In addition, the loss degree, size, and processing difficulty of the filter components are also related to the integration of the entire system. In order to meet the trend of miniaturization of modern communication terminals, the designed devices are required to have smaller size and volume, while traditional filters have poor transmission performance and larger size. Therefore, it is particularly important to design a dual-band, low-loss, small-size, and simple-structured bandpass filter suitable for 5G communication. On the premise of ensuring good transmission performance of the filter, miniaturized multi-band filters have broad application prospects in the future. Summary of the invention

[0003] The main purpose of the present invention is to provide a small dual-frequency bandpass filter based on CSRR, aiming to solve the problems of existing microwave filters such as too large size, single frequency band, too large insertion loss, and complex structure.

[0004] The technical scheme adopted by the present invention is: a small dual-frequency bandpass filter based on CSRR, which comprises a dielectric substrate, a first metal coating layer arranged on the upper surface of the dielectric substrate, a second metal coating layer arranged on the lower surface of the dielectric substrate and used as a grounding layer, and metal vias respectively arranged at the four corners of the substrate; the first metal coating layer is etched with two large complementary open ring resonators CSRR and two small complementary open ring resonators CSRR; the large complementary open ring resonators CSRR and the small complementary open ring resonators CSRR are arranged alternately; the two large complementary open ring resonators CSRR and the two small complementary open ring resonators CSRR are respectively arranged diagonally on the metal coating layer; the two large complementary open ring resonators CSRR are of the same size, and the two small complementary open ring resonators CSRR are of the same size; and lumped ports are arranged on both sides of the dielectric substrate for feeding.

[0005] Furthermore, the two large complementary split ring resonators CSRR are used for resonance at a first passband center frequency of 3.45 GHz, and the two small complementary split ring resonators CSRR are used for resonance at a second passband center frequency of 4.82 GHz.

[0006] Furthermore, the first metal coating layer and the second metal coating layer are both copper foils, and the dielectric substrate is made of Rogers 5880 material with a relative dielectric constant of 2.2 and a thickness of 0.8 mm.

[0007] Furthermore, four metal vias with a radius of 0.2 mm are respectively arranged at the four corners of the small dual-frequency bandpass filter based on CSRR to improve the frequency band transmission characteristics.

[0008] Furthermore, the small dual-band pass filter based on CSRR includes two signal passbands, namely 3.28 GHz to 3.62 GHz and 4.53 GHz to 5.11 GHz, covering the current 5G communication operating frequency band.

[0009] Advantages of the present invention:

[0010] The present invention solves the problems of the existing microwave filter, such as oversized size, single frequency band, large insertion loss, and complex structure. It can realize the characteristics of dual frequency band, small size, simple structure, low insertion loss, and has very good transmission performance.

[0011] The overall size of the present invention is relatively small, with a volume of 17.2mm*16.2mm*0.8mm, which meets the needs of miniaturization of modern 5G communication equipment.

[0012] The present invention selects Rogers 5880 material, which has low loss, low moisture absorption rate, stable performance, and is convenient for use in specific environments.

[0013] The present invention includes two signal passbands, namely 3.28GHz to 3.62GHz and 4.53GHz to 5.11GHz, covering the current working frequency bands of 5G communications.

[0014] The four square CSRRs etched on the upper surface of the dielectric substrate of the present invention are symmetrically distributed about the center of the substrate, and CSRRs of different sizes provide different resonant frequencies. The first passband center frequency of 3.45 GHz mainly resonates near the large CSRR, while the second passband center frequency of 4.82 GHz mainly resonates near the small CSRR.

[0015] Four metal vias with a radius of 0.2 mm are respectively arranged at the four corners of the substrate of the present invention to improve the frequency band transmission characteristics.

[0016] The passband insertion loss of the present invention is less than 0.95 dB, the return loss is better than 14.7 dB, and the overall transmission performance is good.

[0017] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0019] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention;

[0020] Figure 2 is a top schematic diagram of the present invention;

[0021] Figure 3 It is a side schematic diagram of the present invention;

[0022] Figure 4 is a comparison diagram of four transmission characteristics of the present invention;

[0023] Figure 5 is a transmission characteristic simulation curve diagram of the present invention;

[0024] Figure 6 It is a measured curve diagram and a physical diagram of the transmission characteristics of the present invention.

[0025] Reference numerals:

[0026] 1 is a dielectric substrate, 2 is a first metal coating layer, 3 is a second metal coating layer, 4 is a metal via, 5 is a lumped port, 6 is a large complementary split ring resonator CSRR, and 7 is a small complementary split ring resonator CSRR. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] refer to Figures 1 to 3 ,like Figures 1 to 3As shown, a small dual-frequency bandpass filter based on CSRR (Complementary Split Ring Resonators) includes a dielectric substrate 1, a first metal coating layer 2 arranged on the upper surface of the dielectric substrate, a second metal coating layer 3 arranged on the lower surface of the dielectric substrate and used as a grounding layer, and metal vias 4 respectively arranged at the four corners of the substrate; the first metal coating layer 2 is etched with two large complementary split ring resonators (CSRR) 6 and two small complementary split ring resonators (CSRR) 7; the large complementary split ring resonators (CSRR) 6 and the small complementary split ring resonators (CSRR) 7 are arranged alternately; the two large complementary split ring resonators (CSRR) 6 and the two small complementary split ring resonators (CSRR) 7 are respectively arranged diagonally on the metal coating layer 2; the two large complementary split ring resonators (CSRR) 6 are of the same size, and the two small complementary split ring resonators (CSRR) 7 are of the same size; lumped ports 5 are arranged on both sides of the dielectric substrate 1 for feeding.

[0029] The present invention solves the problems of the existing microwave filter, such as oversized size, single frequency band, large insertion loss, and complex structure. It can realize the characteristics of dual frequency band, small size, simple structure, low insertion loss, and has very good transmission performance.

[0030] In this embodiment, two large complementary split ring resonators (CSRR) 6 are used for resonance at the first passband center frequency of 3.45 GHz, and two small complementary split ring resonators (CSRR) 7 are used for resonance at the second passband center frequency of 4.82 GHz.

[0031] In this embodiment, the first metal coating layer 2 and the second metal coating layer 3 are both copper foils, and the dielectric substrate 1 is made of Rogers 5880 material with a relative dielectric constant of 2.2 and a thickness of 0.8 mm.

[0032] In this embodiment, four metal vias with a radius of 0.2 mm are respectively arranged at the four corners of the small dual-band pass filter based on CSRR to improve the frequency band transmission characteristics.

[0033] In this embodiment, the small dual-band pass filter based on CSRR includes two signal passbands, namely 3.28 GHz to 3.62 GHz and 4.53 GHz to 5.11 GHz, covering the current 5G communication operating frequency band.

[0034] In this embodiment, the passband insertion loss of the small dual-band pass filter based on CSRR is less than 0.95 dB, and the return loss is better than 14.7 dB.

[0035] The four square CSRRs etched on the surface of the dielectric substrate of the small dual-band pass filter based on CSRR that can be used for 5G communication are symmetrical and equal about the diagonals. CSRRs of different sizes provide different resonant frequencies to achieve dual bands. The center frequency of the first passband at 3.45GHz mainly resonates near the large CSRR, while the center frequency of the second passband at 4.82GHz mainly resonates near the small CSRR. Specifically, the resonant frequency of the CSRR is f CSRR =1 / [2π(L r C r ) 1 / 2 ], where Lr and Cr are the equivalent inductance and equivalent capacitance between the metal disk and the floor, respectively. The study found that when the side length of the CSRR is reduced, the equivalent inductance value Lr decreases, which causes the resonant frequency of the CSRR to increase, that is, resonance occurs at a higher frequency. By exploring four structures: ① four equal CSRRs; ② reducing the two CSRRs above or below; ③ reducing the two CSRRs on the left or right; ④ reducing the two CSRRs in the diagonal position, four different transmission characteristics were obtained. Among them, ④ has the best passband characteristics. After optimized design, a dual-bandpass filter covering the 5G operating frequency band was realized.

[0036] Among them, the center frequencies of the two passbands of Scheme 4 are 3.45 GHz and 4.82 GHz respectively. The insertion loss of the passband is less than 0.95 dB, and the return loss is greater than 14.7 dB, which meets the filtering requirements of the 5G communication system.

[0037] The upper surface metal coating layer and the lower surface grounding metal coating layer of the small dual-band pass filter based on CSRR that can be used for 5G communication are both copper foil, and the dielectric substrate uses Rogers 5880 material with a relative dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of 0.8mm.

[0038] The small dual-band pass filter based on CSRR that can be used for 5G communication has four metal vias with a radius of 0.2mm at the four corners. The metal vias run through the upper and lower surfaces of the dielectric substrate, optimizing the insertion loss and return loss in the low-frequency band, enhancing the passband selectivity, and thus improving the frequency band transmission characteristics.

[0039] The small dual-band bandpass filter based on CSRR that can be used for 5G communication uses narrow microstrip lines to achieve matching, further reducing the physical size of the filter.

[0040] The size of the small dual-band bandpass filter based on CSRR that can be used for 5G communication is 17.2mm*16.2mm*0.8mm. The outer ring side length of the large CSRR is 6.4mm, the inner ring side length is 4.4mm, the outer ring side length of the small CSRR is 5mm, and the inner ring side length is 3mm. The width of the ring is 0.3mm, the opening length is 1mm, the spacing between the inner and outer rings is 0.7mm, and the gap between the large CSRR and the small CSRR is 0.4mm. In addition, the port width is 2.5mm, the substrate thickness is 0.8mm, the metal via radius is 0.2mm, and the distance between the via and the edge of the substrate is 0.5mm.

[0041] The present invention includes two signal passbands, namely 3.28GHz to 3.62GHz and 4.53GHz to 5.11GHz, covering the current working frequency bands of 5G communications.

[0042] The dual-band is achieved through four CSRR structures. Existing research has used two CSRR structures to achieve a single-band. The resonant frequency is related to the size of the ring. By increasing the number of rings, one frequency band is added, and by reducing the size of the ring, two different frequency bands are achieved (the resonance point moves to high frequency as the ring size decreases). The two frequency bands are obtained by scanning and optimizing the structural parameters according to the frequency bands below 5G sub 6, 3.3-3.6GHz and 4.8-5.0GHz.

[0043] The four square CSRRs etched on the upper surface of the dielectric substrate of the present invention are symmetrically distributed about the center of the substrate, and CSRRs of different sizes provide different resonant frequencies. The first passband center frequency of 3.45 GHz mainly resonates near the large CSRR, while the second passband center frequency of 4.82 GHz mainly resonates near the small CSRR.

[0044] CSRR itself is a left-handed material, and its harmonic suppression and compact structure characteristics are widely used in filter design. By observing the electric field distribution and magnetic field distribution of CSRR, it is found that CSRR is mainly excited by the electric field perpendicular to the ring plane, thereby generating resonance. When it is near the resonant frequency, it can be equivalent to an electric dipole. CSRRs of different sizes can provide different resonant frequencies.

[0045] Four metal vias with a radius of 0.2 mm are respectively set at the four corners of the substrate of the present invention. These four holes are metal grounding holes. Before the vias are added, the low-frequency characteristics of the filter are not good. After the metal vias are loaded at the four corners, it can be found that S 21 It is pulled down, the frequency selectivity becomes better, and from the electric field distribution diagram, the electric field at the four corners is the smallest, thereby achieving the purpose of improving the frequency band transmission characteristics.

[0046] The present invention adopts Rogers 5880 material, and the loss tangent is 0.0009, which can achieve very low loss for the filter. The passband insertion loss of the present invention is less than 0.95dB, the return loss is better than 14.7dB, and the overall transmission performance is good.

[0047] refer to Figure 5 , the transmission characteristic simulation curve of this scheme, the present invention includes two signal passbands, 3.28GHz ~ 3.62GHz and 4.53GHz ~ 5.11GHz, covering the main working frequency bands of current 5G communications. The center frequencies of the present invention are 3.45GHz and 4.82GHz, and the passband widths are 340MHz and 580MHz, respectively. The return loss is better than 14.7dB near the passband, and the insertion loss is less than 0.95dB near the passband, with good passband effect.

[0048] refer to Figure 6 ,The measured transmission characteristic curve of this scheme ,due to the connection loss of the SMA connector, the measured ,results are slightly different from the simulation results, but the ,overall results are consistent.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A small dual-band bandpass filter based on CSRR, It is characterized in that The invention comprises a dielectric substrate (1), a first metal coating layer (2) arranged on the upper surface of the dielectric substrate, a second metal coating layer (3) arranged on the lower surface of the dielectric substrate and used as a grounding layer, and metal vias (4) respectively arranged at four corners of the substrate; the first metal coating layer (2) is etched with two large complementary open ring resonators CSRR (6) and two small complementary open ring resonators CSRR (7); the large complementary open ring resonators CSRR (6) and the small complementary open ring resonators CSRR (7) are arranged alternately; the two large complementary open ring resonators CSRR (6) and the two small complementary open ring resonators CSRR (7) are respectively arranged diagonally on the metal coating layer (2); the two large complementary open ring resonators CSRR (6) are of the same size, and the two small complementary open ring resonators CSRR (7) are of the same size; lumped ports (5) are provided on both sides of the dielectric substrate (1) for feeding; the two large complementary open ring resonators CSRR (6) and the two small complementary open ring resonators CSRR (7) are respectively arranged by nesting an outer open large square ring and an inner open small square ring; The opening direction of the outer open square ring of each split ring resonator CSRR is toward the edge of the substrate. The opening direction of the inner small square ring of each split ring resonator CSRR is opposite to the opening direction of the outer large square ring; The opening directions of the external open large square rings of the two small complementary open ring resonators CSRR (7) are opposite; the opening directions of the external open large square rings of the two large complementary open ring resonators CSRR (6) are opposite and are the same as the opening direction of the external open large square ring of one of the two small complementary open ring resonators CSRR (7); The two large complementary split ring resonators CSRR (6) are used for resonance at a first passband center frequency of 3.45 GHz, and the two small complementary split ring resonators CSRR (7) are used for resonance at a second passband center frequency of 4.82 GHz; The first metal coating layer (2) and the second metal coating layer (3) are both copper foils, and the dielectric substrate (1) is made of Rogers 5880 material with a relative dielectric constant of 2.2 and a thickness of 0.8 mm; The small dual-band pass filter based on CSRR is provided with four metal vias with a radius of 0.2 mm, and the four metal vias are respectively provided at the four corners of the dielectric substrate to improve the frequency band transmission characteristics; The small dual-band pass filter based on CSRR includes two signal passbands, namely 3.28 GHz to 3.62 GHz and 4.53 GHz to 5.11 GHz, covering the current 5G communication operating frequency band.

Images