CN218602717U

CN218602717U - Filter with open stub

Info

Publication number: CN218602717U
Application number: CN202221803677.5U
Authority: CN
Inventors: 李梓萌; 塔拉年科·弗拉基米尔
Original assignee: Guangzhou Sinan Technology Co ltd
Current assignee: Guangzhou Sinan Technology Co ltd
Priority date: 2022-07-13
Filing date: 2022-07-13
Publication date: 2023-03-10
Anticipated expiration: 2032-07-13

Abstract

The utility model provides a wave filter with open stub, include: at least one branched strip conductor disposed adjacent the conductive housing, forming a series portion of the transmission line, and an open stub in parallel with the series portion of the transmission line, and forming an attenuation pole within the stop band of the filter; wherein at least one of the open stubs has an electrical length of 3/4 wavelength of a frequency within the filter stop band to create an attenuation pole. The utility model discloses a simplify the passband filter to provide narrow-band, low level passive intermodulation, low insertion loss and low in production cost between passband and the stop band.

Description

Filter with open stub

Technical Field

The utility model relates to a wireless communication field specifically is the wave filter that has open stub among the frequency selective device.

Background

Many different filter designs have been developed to improve their frequency characteristics and reduce their size. Filters incorporating striplines made using conventional printed circuit board technology are inexpensive to produce, but the insertion loss of the device is excessive when the passband and stopband are separated by a narrow band. Therefore, it is desirable to dispose a metal strip conductor within a conductive housing to reduce insertion loss. The pass-band filter including the main transmission line and the open stub connected in parallel with the main transmission line is most suitably manufactured because it can be manufactured by punching.

Patents US 5015976, US 5192297 and US5291161 describe several improvements of such filters, but when the pass-band and stop-band are separated by a narrow band, the known designs cannot be used because the impedance of some of the strip lines forming the open-ended stub lines is too high and very narrow metal strip lines cannot be made by stamping. Filters providing pass and stop bands separated by narrow frequency bands therefore comprise cavity resonators as described in many patent applications, such as US 3448412, US 6735766, EP 2928011 A1, EP 3104452 A1, EP 3179552 A1. The production cost of such a filter is much higher than the production cost of a filter comprising striplines, since the manufacture of cavity resonators is more complicated than the manufacture of striplines.

Because of the large number of frequency selective devices used by the modern wireless communications industry, there is a need to create a filter that is simple in design, provides low insertion loss and low production cost when the passband and stopband are separated by a narrow frequency band.

SUMMERY OF THE UTILITY MODEL

The utility model discloses a simplify the passband filter to provide narrow-band, low level passive intermodulation, low insertion loss and low in production cost between passband and the stop band.

It is an object of the invention to overcome the disadvantage of known passband filters that provide a 1-7% band between the passband and the stopband. For example, the production cost and insertion loss of filters operating in the 600-6000MHz band used in modern mobile communications are reduced.

The utility model provides a reach the utility model discloses a wave filter contains branch strip conductor, and this strip conductor sets up between two foam dielectric substrate, foam dielectric substrate is located the electrically conductive shell inside of rectangular pipe shape, the opening has in the narrow wall of electrically conductive shell. The branched strip conductors form a series-connected transmission line and an open stub connected in parallel with the series-connected transmission line. The open stub forms an attenuation pole at frequencies above or below the passband. The branch strip conductors are made of a monolithic piece of metal isolated from the conductive housing and are connected only by their ends to the inner conductors of coaxial cables connected to the input and output ports of the filter. The branch strip conductors are fixed to the foam dielectric substrate by dielectric pins.

At least one open stub of the pass band filter has an electrical length of about 3/4 wavelength at a stop band that generates an attenuation pole.

The long open stub of the pass band filter having an electrical length of 3/4 wavelength generates an attenuation pole at a narrower frequency band, compared to the conventional open stub having an electrical length of 1/4 wavelength of the stop band. Therefore, a very narrow open stub having a high impedance and an electrical length of 1/4 wavelength may be replaced by a wide open stub having a significantly lower impedance and an electrical length of 3/4 wavelength. As a result, the branched strip conductors can be made by stamping, thus providing a filter suitable for mass production.

The filter provided does not contain metal parts in contact with each other, since the branch strip conductors are isolated from the conductive housing and are made of a monolithic piece of metal. Due to this simple design, the filter provides a lower level of passive intermodulation and lower production costs compared to known filters comprising a conductive housing with covers pressed together by screws and short-circuited stubs press-fitted or welded to the conductive housing.

The spiral shape of the elongated conductor allows an open stub having a high impedance to be formed by a strip conductor having a significantly wider width than a straight shape. Thus, a filter according to the present invention provides a narrow frequency band between the pass band and the stop band. Furthermore, the matching of the provided filter is less dependent on production tolerances than the matching of known filters with very narrow open stubs. The curved shape of the other strip conductors allows the size of the filter to be reduced. The branch strip conductor, which is made from one piece of metal by stamping, has very small production tolerances, so that the filter provided can be produced without a tuning procedure and without the inclusion of tuning screws. The production cost of the filter is therefore lower than that of the known filters.

Drawings

Some embodiments of the present invention are described by the following drawings, wherein:

fig. 1a and 1b show top views of striplines of a first type of passband filter, which striplines contain a main line and open stubs described by US5291161 (prior art), and whose frequency characteristics of insertion loss sharply increase over a higher frequency band than the passband.

Fig. 2a and 2b show top views of a strip line of a second type of pass-band filter, which comprises a main line and an open stub line described by US5291161 (prior art), and whose frequency characteristics of insertion loss sharply increase at a frequency band lower than the pass-band.

Fig. 3 is a schematic diagram of a filter according to the present invention.

Fig. 4 is filter frequency characteristics S11 and S21 having the schematic diagram shown in fig. 3, having a length Ln and a transmission impedance Zn in table 1.

Fig. 5 is frequency characteristics S11 and S21 of straight open stubs having different impedances and lengths.

Fig. 6 shows the frequency characteristics S11 and S21 of a filter having the schematic diagram shown in fig. 3, the length Ln and the transmission impedance Zn of which are from table 2.

Fig. 7 shows the frequency characteristics S11 and S21 of a filter having the schematic diagram shown in fig. 3, the length Ln and the transmission impedance Zn of which are from table 3.

Fig. 8 shows the frequency characteristics S11 and S21 of a filter having the schematic diagram shown in fig. 3, the length Ln and the transmission impedance Zn of which are from table 4.

Fig. 9a-9d show top views of open stubs having different lengths and shapes.

Fig. 10a and 10b are top views of branched strip conductors of a filter and the simulated frequency characteristics of the corresponding filter.

Fig. 11a and 11b are top views of branched strip conductors comprising different shapes of open stubs and analog frequency characteristics of the corresponding filters.

Fig. 12 shows a metal housing of a filter according to the invention.

Fig. 13 is a perspective view of an assembly including the branch ribbon conductor shown in fig. 11a disposed between two foam dielectric substrates.

Fig. 14 is a side view of a filter including the elements shown in fig. 11-13.

Fig. 15 is a perspective view showing a filter according to the present invention, the coaxial cables of which are connected to the input and output ports of the filter.

It should be understood that the invention is not intended to be limited to the particular forms disclosed in the above-described drawings. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also considered as the protection scope of the present invention.

Detailed Description

The object of the invention is to reduce the production costs and insertion losses of pass-band filters, providing a separation of 1-7% between pass-band and stop-band for modern mobile communications.

The stripline of the known filter shown in fig. 1a and 2a is composed of a strip-shaped main conductor connected to input and output ports of the filter and an open-end stub electrically connected in parallel to the strip-shaped main conductor. The filter of such a structure forms a frequency characteristic of sharply increased insertion loss in a frequency band higher than the pass band, as shown in fig. 1; a frequency characteristic of insertion loss sharply increasing in a frequency band lower than the pass band is formed as shown in fig. 2.

A first embodiment of the present invention is a filter that provides low insertion loss at the passband 1710-2170MHz and approximately 30dB attenuation at the stopband 2300-2690 MHz. Different schematic diagrams are calculated and optimized, and a simple structure of the filter is found. As a result, the schematic shown in fig. 3 is selected to provide a desired match in the pass band and a desired attenuation in the stop band.

The filter comprises three open stubs connected in parallel with the series part of the stripline. Fig. 4 is a diagram for calculating the frequency characteristics S11 and S21 of the filter having the schematic diagram shown in fig. 3. The filter provides S11= -26dB at pass band 1710-2170MHz and S21= -30dB at stop band 2300-2690 MHz. The pass band and the stop band are separated by a frequency band of 130MHz, which is about 5.8% of the intermediate frequency between the pass band and the stop band.

Table 1 contains the length Ln and the impedance Zn of the transmission line forming a filter providing the frequency characteristics as shown in fig. 4. The last row of table 1 contains the width of the strip conductors that form the elements of the schematic shown in fig. 3. The width Wn was calculated for a strip conductor having a thickness of 0.5mm, which was arranged between foamed dielectric substrates having a dielectric permeability of 1.06, located within a conductive housing having a distance of 10mm between the wide walls thereof.

Table 1

	N1	N2	N3	N4	N5	N6	N7
								L,mm	6.8	27.1	85.1	30.2	23.3	32.4	47.1
Z,Ohm	150.0	153.2	150.0	193.1	56.2	224.5	34.8
								W,mm	1.17	1.08	1.17	0.273	10.49	0.05	19.94

The calculated filter cannot be manufactured because the narrowest strip line N6 of W =0.05mm cannot be manufactured by stamping and is therefore not suitable for mass production. The distance between the broad walls of the conductive housing needs to be increased to make the strip line N6 wider, but all other strip lines will also be wider and the size of the filter will be larger than specified. Therefore, other methods are sought to increase the width of the narrow strip-shaped conductor.

The frequency characteristics of the open stub were investigated, and a new method for increasing the width of the strip conductor forming the open stub was found. The open stub having an electrical length of 3/4 wavelength at a frequency where the attenuation pole is generated generates attenuation over a narrower frequency band than a general open stub having an electrical length of 1/4 wavelength. The simulated frequency characteristics S11 and S21 of three open stubs with an attenuation pole at the frequency 1880MHz are shown in fig. 5, where 1 and 2 are S11 and S21 of the open stub of L =39.1mm, Z =224Ohm and W =0.05mm, 3 and 4 are S11 and S21 of the open stub of L =117.6mm, Z =224ohm and W =0.05mm, and 5 and 6 are S11 and S21 of the open stub of L =119.2mm, Z =72.3Ohm, W =7.08 mm.

The calculation results show that an open stub with Z =224ohm, w =0.05mm provides 10dB attenuation in the 183MHz band at an electrical length of about 1/4 wavelength and 10dB attenuation in the 64MHz band at an electrical length of about 3/4 wavelength. Comparison of 2 and 6 in fig. 5 shows that the open stub having Z =72.4Ohm, W =7.08mm and an electrical length of about 3/4 wavelength provides 10dB of attenuation at the frequency band 183MHz, which is the same as the open stub having Z =224Ohm, W =0.05mm and an electrical length of about 1/4 wavelength. A method of replacing a narrow open stub having an electrical length of 1/4 wavelength with a wide open stub having an electrical length of 3/4 wavelength and about 3 times low impedance is used to design a filter suitable for mass production.

The second filter is calculated using an open stub N6 having an electrical length of about 3/4 of the stop band wavelength. Table 2 contains the length Ln and the impedance Zn of the transmission line constituting one filter, providing the frequency characteristics as shown in fig. 6. The filter provides S11= -27dB at the passband 1710-2170MHz and S21= -30dB at the stopband 2300-2690 MHz. The width Wn was calculated for a strip conductor having a thickness of 0.5mm, which was disposed between foamed dielectric substrates having a dielectric permeability of 1.06, the foamed conductive substrates being located inside a conductive housing having a distance of 10mm between the wide walls of the conductive housing.

Table 2

	N1	N2	N3	N4	N5	N6	N7
								L,mm	6.9	27.0	85.1	30.2	21.9	97.2	45.0
Z,Ohm	150.0	153.2	150.0	183.0	56.2	67.9	34.1
								W,mm	1.17	1.08	1.17	0.42	10.49	7.85	20.45

As shown in table 2, all the portions of the branched strip conductors except N4 where W =0.42mm were wider than 1mm. The open stub N4 may be formed in a flat spiral shape to increase the width of the strip conductor, and the filter may be manufactured by stamping. Thus, the filter provided is suitable for mass production.

Open stubs, having an electrical length of about 3/4 wavelength, can also be used to design filters with a narrower band between the pass band and the stop band.

The third filter with the schematic shown in fig. 3 is calculated for a pass band of 1710-1880MHz and a stop band of 1920-2170MHz, the pass band and stop band being separated by a frequency band of 40MHz, 40MHz being about 2.1% of the intermediate frequency between the pass band and the stop band. Table 3 contains the length Ln and the impedance Zn of the transmission line constituting one filter, providing the frequency characteristics as shown in fig. 7. The filter provides S11= -26dB at the passband 1710-1880MHz and S21= -28dB at the stopband 1920-2170 MHz. The width Wn was calculated for a strip conductor having a thickness of 0.5mm, which was disposed between foamed dielectric substrates having a dielectric permeability of 1.06, the foamed conductive substrates being located inside a conductive housing having a distance of 10mm between the wide walls of the conductive housing.

Table 3

The calculated filter cannot be produced because the impedance of the open stubs N2 and N4 is greater than 300Ohm. Therefore, the open stubs N2 and N4 are replaced with open stubs having an electrical length of 3/4 wavelength, and a fourth filter having the same schematic diagram and frequency band is calculated. Table 4 contains the length Ln and the impedance Zn of the transmission line constituting the filter, providing the frequency characteristics as shown in fig. 8. The filter provides S11= -26dB at the passband 1710-1880MHz and S21= -27dB at the stopband 1920-2170 MHz.

The width Wn was calculated for a strip conductor having a thickness of 0.5mm, which was disposed between foamed dielectric substrates having a dielectric permeability of 1.06, the foamed conductive substrates being located inside a conductive housing having a distance of 10mm between the wide walls of the conductive housing.

TABLE 4

	N1	N2	N3	N4	N5	N6	N7
								L,mm	56.5	114.1	6.4	116.8	9.5	35.4	8.9
Z,Ohm	42.5	110.6	140.0	127.1	140.0	182.1	135.0
								W,mm	15.43	3.01	1.51	2.07	1.51	0.44	1.71

The calculation results shown in table 4 show that all parts of the branched strip conductor are wider than 1mm, except N6 where W =0.44 mm.

Fig. 9a shows one branch of a branched strip conductor comprising a straight open stub having an electrical length of 1/4 wavelength and connected in parallel with a main strip conductor. Fig. 9b shows one branch of the branched strip conductor, which comprises a straight open stub having an electrical length of 3/4 wavelength and connected in parallel with the main strip conductor. The open-ended stubs, which are curved and flat spiral-shaped as shown in fig. 9c and 9d, therefore have a significantly reduced size. Further, the impedance of the open stub having the flat spiral shape is about twice as large as that of a straight open stub having a strip conductor of the same width. Therefore, if the long open stub has a flat spiral shape, the width of the strip conductor forming the long open stub can be increased.

A filter having the length and impedance shown in table 4 was simulated and its dimensions were optimized to compensate for the effect of discontinuities at connecting conductors having different widths.

Fig. 10a is a plan view of a branched strip conductor providing the frequency characteristics shown in fig. 10 b.

The filter provides S11= -23dB and S21= -0.38dB at pass band 1710-1880MHz, and S21= -28dB at stop band 1920-2170 MHz.

The straight open stub N6 of the filter is too thin to be made by stamping and is therefore replaced by a flat spiral of width 1.4 mm.

Fig. 11a is a plan view of the branched strip conductor 1 including the open stub N6 in the shape of a flat spiral. The long open stubs N2 and N4 and part of the branched strip conductor 1 are bent to fit inside the metal case 7. The branch strip conductor 1 has a cylindrical hole 4 for inserting a dielectric pin 6 for fixing the branch strip conductor 1 to a foamed dielectric substrate. After further optimization, the filter provides a frequency characteristic as shown in fig. 11 b. The filter provides S11= -22.5dB and S21= -0.34dB at pass band 1710-1880MHz, and S21= -25dB at stop band 1920-2170 MHz. All parts of the branched strip conductor shown in fig. 11a are sufficiently wide and can be made by stamping. Therefore, the filter is inexpensive to manufacture according to the present invention.

Fig. 12 shows a metal housing 7 of a filter according to the invention. The conductive housing 7 contains a cavity 8 formed by two

wide walls

9 and 10 and two

narrow walls

11 and 12. The narrow wall 11 comprises a longitudinal cavity 20 with a longitudinal slit 19. The

openings

13a and 13b penetrate the inside of the cavity 8. The openings 14a and 14d in the narrow wall 11 cut the longitudinal cavity 20 in the vicinity of the

openings

13a and 13 b. The

openings

14a and 14b separate the

portions

24a and 24b from the rest of the narrow wall 11.

Fig. 13 is a perspective view of an assembly comprising a branch strip conductor 1, which branch strip conductor 1 is arranged between two foamed

dielectric substrates

5a and 5b and is fixed to them by means of dielectric pins 6.

Fig. 14 is a side view of a filter comprising the elements shown in fig. 11a, 12 and 13. The assembly shown in fig. 13 is mounted in the metal housing 7 shown in fig. 12 and moved towards the

openings

13a and 13b to place the

ends

1a and 1b in the

openings

13a and 13b and thus opposite the longitudinal cavity 20 having the longitudinal slit 19.

Fig. 15 is a perspective view showing a second embodiment of the filter according to the present invention, in which

coaxial cables

21a and 21b are connected to ports of the filter.

Coaxial cables

21a and 21b are mounted in the longitudinal cavity 20 and their inner conductors are soldered to the two

ends

1a and 1b of the branch conductors, respectively. The assembly shown in fig. 13 is arranged at the cavity 8 in the housing 7. The

end portions

1a and 1b of the branch strip conductor 1 are disposed in the

openings

13a and 13b and soldered to the

inner conductors

22a and 22b of the

coaxial cables

21a and 21 b. The

outer conductors

23a and 23b of the

coaxial cables

21a and 21b are disposed inside the longitudinal cavity 20 and soldered at

locations

24a and 24b, respectively. The solder penetrates into the longitudinal cavity 20 through the longitudinal slit 19. The

openings

14a and 14b separate the

locations

24a and 24b from the rest of the narrow wall 11, preventing heat from spreading from the

locations

24a and 24b when the

external conductors

23a and 23b are soldered to the

locations

24a and 24b. Thus, less heating is required for the welding process.

The filter of the present invention provides low level passive intermodulation because it only contains four soldered locations.

The branched strip conductor with the long open stub can also be manufactured by conventional printed circuit board technology, which provides a very narrow strip conductor width and forms an open stub with a high impedance. For example, a strip conductor of W =0.1mm formed on a substrate of thickness 0.27mm and dielectric constant 2.5, separated by 10mm of air, is placed between two metal plates, and has an impedance of about 250Ohm. Thus, the filter provided can be used in many applications where a narrow band is required to separate the passband and the stopband. It is also possible to create a notch filter that rejects very narrow bands from a wide band.

Claims

1. A filter with open stubs, comprising:

a branched strip conductor disposed in the vicinity of at least one of the conductive plates for forming a series portion of the transmission line, an

An open stub in parallel with the series portion of the transmission line forming an attenuation pole within the stop band of the filter;

at least one open stub has an electrical length of 3/4 wavelength of a frequency within the filter stop band to create an attenuation pole.

2. The filter with open stub of claim 1, wherein said branch strip conductor is a monolithic piece of metal isolated from said conductive plate, connected only to the inner conductor of a coaxial connector or cable at said filter port.

3. The filter having open stubs of claim 1, wherein at least one of the open stubs has a flat spiral shape.

4. The filter having open stubs of claim 1, wherein at least one of the open stubs has a curved shape.

5. The filter having the open stubs of claim 1, wherein at least one of the open stubs has an electrical length of 3/4 wavelength of a frequency within a stop band disposed above the pass band.

6. The filter having open stubs of claim 1, wherein the at least one open stub has an electrical length of 3/4 wavelength of a frequency disposed within a stop band below the pass band.

7. The filter with open stub of claim 1, wherein the branch strip conductor is disposed between two foamed dielectric substrates located within a conductive housing having a rectangular tube shape with openings in walls of the conductive housing.

8. The filter with an open stub of claim 7, wherein the foam dielectric substrate comprises an aperture disposed opposite a portion of the branched strip conductor, the portion of the branched strip conductor forming an open stub.

9. The filter with open stub of claim 7 or 8, wherein said branch strip conductors are fixed on said foam dielectric substrate by dielectric pins.

10. The filter with open stub of claim 7, wherein the conductive housing has an opening in a narrow wall.

11. The filter with open stub of claim 10, wherein the conductive housing comprises a circular longitudinal channel along a narrow wall containing the opening.

12. The filter with open stubs of claim 11, wherein said circular longitudinal channel comprises a longitudinal slit.