CN114122653B

CN114122653B - Implementation method of ultra-wideband band-pass filter applied to 5G frequency band

Info

Publication number: CN114122653B
Application number: CN202111418706.6A
Authority: CN
Inventors: 王韧
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2021-11-26
Filing date: 2021-11-26
Publication date: 2022-12-23
Anticipated expiration: 2041-11-26
Also published as: CN114122653A

Abstract

The invention discloses a realization method of an ultra-wideband band-pass filter applied to a 5G frequency band, which is applied to the technical field of communication and aims at solving the problem that the performance of the existing filter is difficult to meet the requirement of high-frequency bandwidth; the invention directly etches the defect ground on the micro-strip line on the top layer of the filter substrate to form the inductance capacitor, thereby realizing the broadband characteristic, further realizing the high-frequency band out-of-band inhibition by a method of connecting the short-circuit branch lines in parallel, and improving the integral filtering performance of the filter.

Description

Implementation method of ultra-wideband band-pass filter applied to 5G frequency band

Technical Field

The invention belongs to the technical field of communication, and particularly relates to an ultra wide band technology of a 5G frequency band.

Background

With the rapid development of wireless communication technology, available bandwidth resources are gradually saturated, and therefore, the development of bandwidth resources with higher frequencies is urgently needed. In this case, research and development of Ultra Wideband (UWB) technology has been proposed. UWB has the advantages of high bandwidth, high speed, low power consumption and low delay, and has wide application prospect and great market value. The ultra-wideband band-pass filter designed on the basis has high application value and practical significance.

At present, the method for realizing the ultra-wideband filter mainly comprises the following five steps:

1. the high-low pass filter cascade method realizes the ultra-bandwidth characteristic by connecting a low-pass filter and a high-pass filter in series to form a band-pass filter.

2. Multimode resonators are resonators having more than one resonant mode within the passband. The theoretical basis of multimode resonators is to use SIR impedance ratios and electrical lengths to control the center frequency and the location of the resonance points so that the resonator resonance points are evenly distributed throughout the ultra-wideband. And then a flat ultra-wideband band-pass response is realized by a parallel coupling line feeding mode.

3. The short circuit/open circuit stub method improves the stop band characteristic of the filter by short circuit stub wires and realizes transmission zero near the stop band of the filter, thereby realizing a miniaturized high-performance ultra-wideband microwave filter with compact structure by using less stages.

4. By adopting a defect structure method, the inductance and the capacitance of the microstrip line are changed by etching a defect pattern on the ground, so that the microstrip line has resonance and stop band characteristics.

5. The generalized Chebyshev method can place resonance points at any position in the stop band, the method can more flexibly adjust the out-of-band rejection degree of the filter, and the rectangular coefficient of the filter can be made very low. In addition, the generalized Chebyshev filter can realize the transmission zero point of a complex frequency domain through specific cross coupling, optimize the group delay in a band and reduce the signal distortion.

With the rapid development of modern radar systems, the need for highly integrated and miniaturized transceiver systems is also increasing. The filter is one of important devices in a radio frequency system, miniaturization and integration of the filter are always challenges for researchers, at present, the researchers turn the target to miniaturization of a microwave system to high-integration design, however, most of the existing filters are planar filters, the space utilization rate is not high, and therefore the design is difficult to meet the requirements of miniaturization and high performance. Because the pulse signal time required for ultra-wideband systems is very short, an ultra-wideband filter that complies with the FCC regulations must have a small and flat group delay characteristic over a bandwidth of 110%. It is also contemplated to filter out frequencies in use within the passband, such as GPS,3g,4g and X-band satellite signals. Secondly, the filter should be small and compact for integration purposes, otherwise the miniaturization of integrated microwave circuits is not achieved. The above specification requirements are the main challenges for wideband filter design. However, the 5 methods commonly adopted at present have certain defects, for example, a band-pass filter is formed by connecting a low-pass filter and a high-pass filter in series, the defects are that the filter is large in size, ripple coefficients in a pass band often exceed indexes, and the bandwidth of the cascaded filter is difficult to widen due to the limitation of harmonics of the high-pass filter and the low-pass filter; the parallel coupling line feeding mode can realize flat ultra-wideband band-pass response. However, in order to obtain stronger coupling, the distance between the parallel coupling lines is only 0.05mm, and a higher-level processing technology is required for realizing the gap, so that the cost is increased; the filter designed by the short circuit/open circuit stub method has good frequency response and has the defect of large volume and is only suitable for the cascaded stub parallel microstrip filter; however, the processing technology of the LTCC structure is far more complex than that of a plane filter, so that the cost is greatly increased.

Disclosure of Invention

In order to solve the technical problem, the invention provides a method for realizing an ultra-wideband band-pass filter applied to a 5G frequency band, which can realize the working bandwidth in the range of 4-8 GHz.

The technical scheme adopted by the invention is as follows: a method for realizing an ultra-wideband band-pass filter applied to a 5G frequency band comprises the steps of etching a plurality of defected grounds with different sizes on a metal copper-clad layer on the back of a dielectric substrate close to the input end of the filter, and then connecting a plurality of short-circuit branch lines with different sizes on the metal copper-clad layer on the back of the dielectric substrate close to the output end of the filter in parallel.

The defected ground is of an I-shaped defected microstrip structure.

The microstrip line comprises five serial I-shaped defect microstrip structures.

The five I-shaped defect microstrip structures connected in series are sequentially marked as follows: the first I-shaped defect micro-strip structure, the second I-shaped defect micro-strip structure, the third I-shaped defect micro-strip structure, the fourth I-shaped defect micro-strip structure and the fifth I-shaped defect micro-strip structure are sequentially arranged; the five I-shaped defects are divided into three groups, the first I-shaped defect micro-strip structure and the fifth I-shaped defect micro-strip structure are the first group, the second I-shaped defect micro-strip structure and the fourth I-shaped defect micro-strip structure are used as the second group, and the third I-shaped defect micro-strip structure is used as the third group; the sizes of the three groups of I-shaped defect micro-strips are mutually independent, and the sizes of the I-shaped defect micro-strips in each group are the same.

The three-phase short circuit comprises six short circuit branch lines, wherein the six short circuit branch lines are symmetrically divided into three groups, and 2 short circuit branch lines in each group are the same in size.

The invention has the beneficial effects that: the method of the invention has the following advantages:

1. the five-defect microstrip structure is divided into three groups, the sizes of the three groups of structures are mutually independent, each group can independently provide one resonance frequency point, and the three groups of structures can provide three different resonance frequency points in total;

2. each group of I-shaped defect microstrip structures independently optimizes the size and realizes broadband filtering characteristics;

3. the sizes of the six short-circuit branch lines with different sizes are independently optimized, so that the high-pass filtering characteristic is realized;

4. three groups of I-shaped defect microstrip structures are connected in series with six short-circuit branch lines with different sizes, so that the series connection work of band-pass filtering and high-pass filtering is realized, and a band-pass filter with excellent ultra-wideband and out-of-band inhibition capability is realized;

5. the I-shaped defect microstrip structure and the short-circuit branch line can be independently optimized, and different pass band widths and working frequencies can be realized.

Drawings

FIG. 1 is a schematic diagram of an I-shaped microstrip structure;

FIG. 2 is an equivalent circuit diagram of an I-shaped microstrip structure;

FIG. 3 is a parallel short circuit branch line;

FIG. 4 is an overall circuit diagram of a filter

Wherein, (a) is an integral top view, (b) is an I-shaped defect microstrip structure, (c) is a short circuit branch structure, and (d) is an integral side view;

FIG. 5 is an overall passband transmission characteristic;

reference numerals are as follows: 1 is an input port of an I-shaped defect microstrip structure; 2 is an output port of an I-shaped defected ground structure; 3. 4 are input and output ports of the integral filter circuit respectively; 5. 6 are input and output ports of the I-shaped circuit respectively; 10. 11 are input and output ports of the branch type filter circuit respectively; 7. 8 and 9 are structures with three I-shaped defects; 12-14 are three pairs of short-circuit branch lines; 15 is a dielectric substrate; 16. 17 is a metal-clad copper layer.

Detailed Description

In order to facilitate the understanding of the technical contents of the present invention by those skilled in the art, the present invention will be further explained with reference to the accompanying drawings.

The i-shaped defected microstrip structure provided by the invention is shown in fig. 1, wherein 1 and 2 are input and output port structures of the i-shaped defected microstrip structure respectively. Similar to the DGS microstrip line, the change of the effective inductance and capacitance is controlled by changing the defect structure, resulting in the change of the propagation characteristic of the filter. This configuration can thus be equivalent to a parallel circuit of an inductor and a capacitor as shown in fig. 2, with the parameter extraction of the inductor L and the capacitor C expressed as:

wherein epsilon ₀ For a resonant angular frequency, epsilon _C To cut off the angular frequency, f _c Is the resonant frequency, Z, of the filter ₀ Is the characteristic impedance of the microstrip line, g ₁ Is a butterworth first order low pass element. The parameters can be known from the formula (2), and the central frequency of the resonator can be adjusted by adjusting the size of the structure, so that the resonance frequency point can be adjusted.

Fig. 4 (b) includes five i-shaped defective microstrip structures, which include three groups of structures with different sizes, that is, a first group of i-shaped defective microstrip structures 7, a second group of i-shaped defective microstrip structures 8, and a third group of i-shaped defective microstrip structures 9, where the first group of i-shaped defective microstrip structures 7 and the third group of i-shaped defective microstrip structures 9 each include two i-shaped defective microstrip structures, and the second group of i-shaped defective microstrip structures 8 includes one i-shaped defective microstrip structure; different resonance frequency points are obtained by optimizing the structure size, the integral band-pass characteristic of the filter is realized, and the relation among the resonance frequency points meets the condition given by the formula (2). As shown in fig. 4 (c), three pairs of short-circuit stubs with different sizes are located on the same side of the main transmission microstrip line (transmission line where the

ports

10 and 11 are located), and are of a symmetrical structure. The sizes of the three pairs of short-circuit branch lines can be independently adjusted to obtain different high-frequency transmission zero points, so that the high-pass characteristic is realized. Then, by connecting fig. 4 (b) and fig. 4 (c) in series, two filter combinations of band pass and high pass can be realized. The broadband filter with the I-shaped defect microstrip structure is etched on the metal copper-clad layer 16 on the back of the filter, then the method of connecting short-circuit branch lines in parallel, etching the defect ground and cascading a high-pass filter is used for optimization, the rectangular coefficient is greatly reduced, the in-band fluctuation is effectively reduced, as shown in figure 5, the rectangular coefficient in a pass band reaches 0.95, the average value of the out-of-band suppression degrees of the upper and lower sidebands reaches below-30 dB, and good out-of-band suppression capability is realized.

The final design structure is shown in fig. 4. Fig. 4 is mainly composed of three groups of i-shaped

defective microstrip structures

7, 8 and 9 on the left side and six pairs of short-circuit branch lines 12-14 with different sizes on the same side of the main transmission microstrip line. As shown in fig. 4 (d), 15 is a dielectric substrate, 16 and 17 are metal copper-clad layers, and three i-shaped defective microstrip structures with different sizes can provide 3 resonance points with lower frequency, thereby realizing the band-pass characteristic. And three pairs of short-circuit branch lines with different sizes, which are positioned on the same side of the main transmission microstrip line, provide high-frequency transmission zero points, so that the high-pass characteristic is realized. The structure is thus generally a cascade combination of band-pass filtering and high-pass filtering. The sizes of the three I-shaped defect microstrip structures can be adjusted, so that the bandpass characteristic is realized; the three pairs of short circuit branch lines with different sizes are positioned on the same side of the main transmission microstrip line and are of symmetrical structures, and the sizes of the three pairs of short circuit branch lines can be independently adjusted.

Therefore, each group of I-shaped defective microstrip structures can provide 1 dynamic resonant frequency point. The frequency band superposition and bandwidth expansion of the LC resonance circuit can be realized through the series connection of three groups of I-shaped defective microstrip structures. In addition, as shown in fig. 3, the parallel short-circuited stub structure can generate a resonance point at 0GHz by connecting one stub in parallel, thereby generating out-of-band rejection of the upper band. Wherein Zin is the input impedance of the resonator, Z is the characteristic impedance of the branch line, and θ is the electrical length of the branch line.

The design of the ultra-wideband filter mainly uses a short-circuit branch line positioned on a common input and output end microstrip line to be mutually coupled with an I-shaped defect microstrip structure. The size of each I-shaped defect microstrip structure is reasonably adjusted, the movement of resonance frequency can be realized, and the wide bandwidth characteristic of 4-8GHz is realized through the size series connection of three groups of I-shaped defect microstrip structures; furthermore, 6 short-circuit branch lines with different lengths are connected in parallel to the common input and output end microstrip line, and the LC (inductance-capacitance) characteristic of the circuit is regulated and controlled by regulating the lengths of the 6 branch lines, so that better out-of-band rejection capability can be realized finally, and the in-band fluctuation and the out-of-band rejection capability of the filter are improved. Three microstrips in the I-shaped structure are equal in width, the width is recorded as W1, the length of the microstrip connected in the middle is recorded as W2, the length of the two parallel microstrips is recorded as L1, and a group of specific parameter values are given as follows:

7 sizes of the I-shaped structure: w1=0.5mm; w2=3.5mm; l1=4.3mm; 8 sizes of the I-shaped structure: w1=0.5mm; w2=3.2mm; l1=4.0mm; the size of the I-shaped structure 9 is as follows: w1=0.5mm; w2=2.8mm; l1=3.6mm; the branch knot 12 is 0.6mm wide and 6.2mm long; the length and width of the branch knot 13 are 0.6mm, and the length is 5.3mm; the branch knot 14 is 0.5mm long and wide and 4.5mm long.

Based on the above parameters, the obtained out-of-band rejection effect is shown in fig. 5, and it can be seen that the method of the present invention can achieve a good out-of-band rejection effect.

It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A realization method of an ultra wide band-pass filter applied to a 5G frequency band is characterized by comprising the steps of etching a plurality of groups of defect places with different sizes on a metal copper-clad layer on the back of a dielectric substrate close to the input end of the filter, wherein the defect places in each group have the same size, the sizes of the defect places in each group are independently adjusted, each group of defect places independently provides a resonance point, then a plurality of groups of short circuit branch wires with different sizes are connected in parallel on the metal copper-clad layer on the back of the same dielectric substrate close to the output end of the filter, the short circuit branch wires in each group have the same size, the sizes of the short circuit branch wires in each group are independently adjusted, and each group of short circuit branch wires independently provides a high-frequency transmission zero point.

2. The implementation method of the ultra-wideband band-pass filter applied to the 5G frequency band according to claim 1, wherein the defected ground is an I-shaped defected microstrip structure.

3. The implementation method of the ultra-wideband band-pass filter applied to the 5G frequency band according to claim 2, wherein the filter comprises five serially connected I-shaped defected microstrip structures.

4. The implementation method of the ultra-wideband band-pass filter applied to the 5G frequency band according to claim 3, wherein the five serially connected I-shaped defective microstrip structures are sequentially recorded as: the first I-shaped defect micro-strip structure, the second I-shaped defect micro-strip structure, the third I-shaped defect micro-strip structure, the fourth I-shaped defect micro-strip structure and the fifth I-shaped defect micro-strip structure are sequentially arranged; the five I-shaped defects are divided into three groups, the first I-shaped defect micro-strip structure and the fifth I-shaped defect micro-strip structure are the first group, the second I-shaped defect micro-strip structure and the fourth I-shaped defect micro-strip structure are used as the second group, and the third I-shaped defect micro-strip structure is used as the third group; the sizes of the three groups of I-shaped defect micro-strips are mutually independent, and the sizes of the I-shaped defect micro-strips in each group are the same.

5. The implementation method of the ultra-wideband band-pass filter applied to the 5G frequency band according to claim 4, comprising six short-circuit branch lines, wherein the six short-circuit branch lines are symmetrically divided into three groups, and 2 short-circuit branch lines in each group have the same size.