CN103779640B - Micro-band double-passband filter - Google Patents

Abstract

The invention discloses a microstrip double-passband filter used for an ultra-wideband system and a narrowband system, and belongs to the technical field of wireless communication. The microstrip double-passband filter of the present invention includes a first filter and a second filter sharing a common feeder line and input and output ports; the first filter includes a first resonator and a second resonator formed by an interdigitated line structure. The second filter includes the first resonator, the third resonator, and the U-shaped resonator loaded with the third short-circuit stub in the middle position to generate the second passband; The first to third resonators are all located in the U-shaped resonator, and the short-circuit end of the third short-circuit branch coincides with the short-circuit end of the second resonator; the first resonator and the third resonator are high-impedance feeders of the second filter. The parameters of the two passbands of the invention are independently adjusted, the passbands have high frequency selectivity and high isolation, the circuit structure is compact, the insertion loss is relatively small, and the communication quality is improved.

Description

Microstrip Dual Pass Band Filter

technical field

The invention relates to a double-passband filter, specifically a microstrip double-passband filter applied to an ultra-wideband system and a narrowband system, and belongs to the technical field of wireless communication.

Background technique

With the rapid development of modern communication technology, especially the wide application of wireless local area network, the multi-passband communication system that can be compatible with various communication resources has become a research hotspot. At present, the most common is the dual-passband communication system, and the dual-passband filter, as an essential device in the front-end of the dual-passband communication system, has become the key to the research of the dual-passband communication system.

There are many design methods for dual-passband filters, and there are two main ones: the first one is to use a single resonator with adjustable resonance frequency. The main disadvantage of the filter obtained by this method is that the bandwidth of the two passbands cannot be adjusted independently; The second is to use two different resonators to share the same input and output, so that the two bandwidths of the filter obtained can be adjusted mutually. Filters designed using the second method in the current prior art usually have a very complicated circuit structure, and in particular, there are relatively few multi-passband filters applied to broadband or ultra-wideband systems.

On June 20, 2012, Chinese invention patent application CN102509822A disclosed a dual-passband microstrip filter, as shown in Figure 1, including two sets of first sub-microstrip filters and second sub-microstrip filters with different structures filter, and a first signal transmission line and a second signal transmission line, the first signal transmission line is respectively connected to the first sub-microstrip filter and the second sub-microstrip filter and connected to the signal input end, and the second signal transmission line is respectively It is connected with the first sub-microstrip filter and the second sub-microstrip filter and connected with the signal output end, so that the first sub-microstrip filter and the second sub-microstrip filter are connected in parallel. The dual-passband microstrip filter can independently adjust the center frequency, bandwidth and in-band characteristics of the two passbands, but its internal circuit structure is complex, the insertion loss is large, the frequency selectivity is poor, and the isolation between the passbands is relatively poor. .

Contents of the invention

The technical problem to be solved by the present invention is to overcome the above defects and provide a microstrip dual-passband filter with simple structure, good frequency selectivity and high isolation between passbands, which is applied to ultra-wideband systems and narrowband systems.

In order to solve the above-mentioned technical problems, the microstrip double-pass band filter provided by the present invention includes a first filter and a second filter that share a common feeder line and input and output ports; The first resonator, the second resonator and the third resonator are formed to produce the first passband; the second filter includes the first resonator, the third resonator and the U-shaped structure loaded with the third short-circuit stub in the middle position The resonator produces a second passband; the first to third resonators are all located in the U-shaped resonator, and the short-circuit end of the third short-circuit branch coincides with the short-circuit end of the second resonator; the first resonator and the second resonator The tri-resonator is the high-impedance feed for the second filter.

In the present invention, the common feeder includes a first feeder and a second feeder; one end of the first feeder and the second feeder are vertically connected to the short-circuit ends of the first resonator and the third resonator respectively, and the other ends are respectively used as the second An input/output port common to the first filter and the second filter.

In the present invention, it also includes a first short-circuit stub and a second short-circuit stub, the first short-circuit stub is loaded on the first feeder, and a transmission zero point is generated at the lower edge of the first passband; the second short-circuit stub is loaded on the first feeder On the second feeder, a transmission zero is created at the upper edge of the second passband.

In the present invention, it also includes a fourth resonator located outside the first short-circuit branch, which is an inverted L-shaped structure, and a fifth resonator located outside the second short-circuit branch, which is a forward L-shaped structure; the fourth resonator The short-circuit end of the resonator is opposite to the short-circuit end of the first short-circuit stub, and a transmission zero point is generated at the upper edge of the first passband; the short-circuit end of the fifth resonator is opposite to the short-circuit end of the second short-circuit stub, and at the A transmission zero is created at the lower edge of the two-passband.

In the present invention, a source-load coupling is formed near the first feeder line and the second feeder line, and a transmission zero point is generated at the lower edge of the first passband.

In the present invention, the coupling between the first resonator and the third resonator generates a transmission zero at the upper edge of the second passband.

In the present invention, the lengths of the first to third resonators are the same, and the length is one-fourth of the wavelength corresponding to the central frequency of the first passband.

In the present invention, the length of the U-shaped resonator is half of the wavelength corresponding to the center frequency of the second passband.

In the present invention, the lengths of the fourth resonator and the fifth resonator are respectively a quarter of the wavelength corresponding to the two transmission zero frequencies at the upper edge of the first passband and at the lower edge of the second passband.

The beneficial effects of the present invention are: (1), the parameters of the two passbands of the present invention are independently adjusted, and the passbands have high frequency selectivity and high isolation; (2), the double passband filter of the present invention By sharing resonators, feeders and input and output ports, the circuit has a compact structure, relatively small insertion loss, and improves communication quality.

Description of drawings

Fig. 1 is a kind of double-pass band microstrip filter in the prior art;

Fig. 2 is the schematic diagram of the printed circuit board section of the microstrip double-pass band filter of the present invention;

Fig. 3 is the structure schematic diagram that the present invention microstrip double pass band filter is positioned at the dielectric substrate upper layer;

Fig. 4 is the structural representation of the first filter in the microstrip double pass band filter of the present invention;

Fig. 5 is the structural representation of the second filter in the microstrip double passband filter of the present invention;

Fig. 6 is a schematic diagram of the grounding via hole of the microstrip double-passband filter of the present invention located in the lower layer of the dielectric substrate;

Fig. 7 is the scattering parameter curve of the independent response of the first filter in the microstrip double-passband filter of the present invention;

Fig. 8 is the scattering parameter curve of the independent response of the second filter in the microstrip double-pass band filter of the present invention;

Fig. 9 is the scattering parameter simulation and test result of the microstrip double-pass band filter of the present invention;

Fig. 10 is the group delay simulation and test result of the microstrip double-passband filter of the present invention;

In the figure: 1. The first feeder; 2. The second feeder; 3. The first resonator; 4. The second resonator; 5. The third resonator; 6. The fourth resonator; 6-1. The first grounding Via hole; 7. Fifth resonator; 7-1. Second ground via; 8. U-shaped resonator; 9. First short-circuit stub; 9-1. Third ground via; 10. Second short-circuit stub ; 10-1, the fourth ground via; 11, the third short-circuit stub; 12, the fifth ground via; 13, source-load coupling region; S1, dielectric substrate; S2, upper metal; S3, lower metal; P1 , input port/output port; P2, output port/input port.

detailed description

The microstrip dual-passband filter applied to the ultra-wideband system and the narrowband system of the present invention will be further described in detail below in conjunction with the accompanying drawings. Among them, the ultra-wideband passband is described by taking an ultra-wideband system with a center frequency of 3.1 GHz as an example; the narrow-band passband is described by taking a wireless local area network system with a center frequency of 5.2 GHz as an example.

As shown in FIG. 2 , in the printed circuit board of the microstrip double-pass band filter of the present invention, its relative permittivity is 2.2 and its thickness is 0.508 mm. Of course, dielectric substrates of other specifications can also be used. The upper and lower surfaces of the dielectric substrate S1 of the dielectric substrate are coated with an upper metal layer S2 and a lower metal layer S3 respectively. The filter in the present invention is formed on the upper metal layer, and the lower metal layer forms a ground plane.

As shown in Figure 3, the microstrip double-pass band filter of the present invention includes a first feeder 1, a second feeder 2, a first resonator 3, a second resonator 4, a third resonator 5, a fourth resonator 6, The fifth resonator 7 , the U-shaped resonator 8 , the first short-circuit branch 9 , the second short-circuit branch 10 , and the third short-circuit branch 11 . As shown in FIG. 4 , the first feeder 1 , the second feeder 2 , the first resonator 3 , the second resonator 4 , and the third resonator 5 form a first filter to generate a first passband. The first resonator 3, the second resonator 4, and the third resonator 5 are arranged in an interdigitated linear structure, and their lengths are all 1/4 of the wavelength corresponding to the center frequency of the first passband, and the length of the first passband The center frequency and bandwidth are adjusted by the lengths of the first resonator 3 , the second resonator 4 and the third resonator 5 and the distance between them. The first resonator 3, the second resonator 4, and the third resonator 5 all have an open-circuit terminal and a short-circuit terminal, wherein the short-circuit terminals of the first resonator 3 and the third resonator 5 are respectively connected to the first feeder 1 and the second feeder 1. One end of the feeder 2 is vertically connected, and the other ends of the first feeder 1 and the second feeder 2 are respectively used as input and output ports (the input and output ports can be interchanged) P1 and P2, and the characteristic impedance of the first feeder 1 and the second feeder 2 is the same as The input and output ports P1 and P2 have the same impedance, and the rest of the microstrip line circuit has the same impedance, that is, the same width; the short-circuit terminal of the second resonator 4 is short-circuited by connecting the fifth ground via hole 12 . As shown in Figure 5, the first feeder 1, the second feeder 2, the first resonator 3, the third resonator 5, and the U-shaped resonator 8 with the third short-circuit stub 11 loaded in the center form a second filter, generating a second Passband; the length of the U-shaped resonator 8 is 1/2 of the wavelength corresponding to the center frequency of the second passband, and the center frequency and bandwidth of the second passband can pass the length of the U-shaped resonator 8 and the third short-circuit branch 11 respectively Make adjustments. As shown in Figure 3, the first filter and the second filter have the same feeder and input and output ports, the first resonator 3, the second resonator 4, and the third resonator 5 are all located in the U-shaped resonator 8, The first resonator 3 and the third resonator 5 provide strong coupling as the high-impedance feeder of the second filter, the third short-circuit branch 11 is loaded on the middle position in the U-shaped resonator 8, and the short-circuit end of the third short-circuit branch 11 is connected to the second The short-circuit terminals of the resonators 4 coincide, which is achieved by connecting the fifth ground vias 12 . As shown in Figures 3, 4, and 5, the first feeder 1 and the second feeder 2 form a source-load coupling 13 close to each other, which can form a transmission zero at the lower edge of the first passband; the first resonator 3 and The coupling between the third resonators 5 can create a transmission zero at the upper edge of the second passband. As shown in Figure 3, the first short-circuit stub 9 is loaded on the first feeder 1, one end is open-circuited and the other end is short-circuited through the third ground via 9-1, which can generate a transmission zero at the lower edge of the first passband ; The second short-circuit stub 10 is loaded on the second feeder 2, one end is an open circuit terminal, and the other end short-circuit terminal is short-circuited through the fourth grounding via 10-1, which can generate a transmission zero on the upper edge of the second passband; the fourth resonance Both the resonator 6 and the fifth resonator 7 are bent resonators, wherein the fourth resonator 6 adopts an inverted L-shaped structure, is located outside the first short-circuit branch 9 and is coupled with it, and the short-circuit terminal of one end is connected through the first ground connection. Hole 6-1 is short-circuited, and the other end is an open-circuit terminal, and its short-circuit end is opposite to that of the first short-circuit stub 9, and a transmission zero point can be generated at the upper edge of the first passband. The length of the fourth resonator 6 It is a quarter of the wavelength corresponding to the transmission zero frequency. The fifth resonator 7 adopts a positive L-shaped structure and is located outside the second short-circuit branch 10 to couple with it. The short-circuit terminal at one end is short-circuited through the second grounding via 7-1, and the other end is an open-circuit terminal. The position of the short-circuit end of the second short-circuit stub 10 is opposite, and a transmission zero point can be generated at the lower edge of the second passband. The length of the fifth resonator 7 is a quarter of the wavelength corresponding to the frequency of the transmission zero point. The transmission zero mentioned above can improve the frequency selectivity of the passband and the isolation between the two passbands.

As shown in Figure 6, the lower layer of the dielectric substrate of the double-pass band filter of the present invention, wherein the first ground via 6-1 is the short-circuit end of the fourth resonator 6, and the second ground via 7-1 is the fifth resonator 7, the third ground via 9-1 is the short-circuit end of the first short-circuit branch 9, the fourth ground via 10-1 is the short-circuit end of the second short-circuit branch 10, and the fifth ground via 12 is the short-circuit end of the second short-circuit branch 9. The short-circuit end shared by the resonator 4 and the third short-circuit branch 11 .

As shown in Figure 7, the first passband produced under the independent response of the first filter of the microstrip double passband filter of the present invention, its passband center frequency is 3.1GHz, and its 3dB relative bandwidth is 70%. There is a transmission zero at the lower edge and upper edge respectively, which improves the frequency selectivity.

As shown in Figure 8, the second passband produced under the independent response of the second filter of the microstrip dual-passband filter of the present invention, its passband center frequency is 5.2GHz, and the 3dB relative bandwidth is 4.5%. There is a transmission zero at the upper edge, and the U-shaped resonator loaded with the third short-circuit stub produces a transmission zero below the passband due to the cancellation of the odd and even modes.

As shown in Figure 9, it can be seen from the figure that the simulation results are in good agreement with the test results and the simulation results. The center frequency of the first passband is at 3.1GHz, and its 3dB relative bandwidth reaches 73.2%. In the passband, its return loss is less than 10dB; the center frequency of the second passband is at 5.2GHz, and its 3dB relative The bandwidth is 4.8%. There are two transmission zeros at the lower edge of the first passband and the upper edge of the second passband, respectively, and one transmission zero at the upper edge of the first passband and the upper edge of the second passband, greatly The frequency selectivity of the passband and the isolation between the passbands are improved, so it can be seen that the double passband filter of the present invention has very good performance.

For wideband and ultra-wideband filters, group delay is a parameter that characterizes the delay characteristics it causes to signals. As shown in Figure 10, it can be seen that the group time in the first passband (ultra-wideband passband) of the filter is 0.4ns to 0.7ns, the group delay is very small, and has very flat characteristics.

Both the output port P1 and the input port P2 of the microstrip double-pass band filter of the present invention are welded with SMA heads, so as to be connected to a test or connected to a circuit.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, some improvements can be made without departing from the principle of the present invention, and these improvements should also be regarded as the present invention. scope of protection.

Claims (7)

1. a micro-band double-passband filter, is characterized in that: the first filter and the second filter that comprise share common feeder line and input/output port; Described first filter comprises the first resonator (3), the second resonator (4) and the 3rd resonator (5) that adopt interdigital linear structure composition, produces the first passband; Described second filter comprises the U-shaped resonator (8) that the first resonator (3), the 3rd resonator (5) and centre position load the 3rd short circuit minor matters (11), produces the second passband; Described the first to three resonator (3,4,5) is all positioned at U-shaped resonator (8), and the short-circuit end of the 3rd short circuit minor matters (11) overlaps with the short-circuit end of the second resonator (4); Described first resonator (3) and the 3rd resonator (5) are the high impedance feeder line of the second filter; Comprise the first short circuit minor matters (9), the second short circuit minor matters (10), described first short circuit minor matters (9) are carried on the first feeder line (1), produce a transmission zero at the lower limb of the first passband; Described second short circuit minor matters (10) are carried on the second feeder line (2), produce a transmission zero at the top edge of the second passband; Comprise be positioned at the first short circuit minor matters (9) outside, for reversion L-type structure the 4th resonator (6) and to be positioned at outside the second short circuit minor matters (10), be the 5th resonator (7) of forward L-type structure; The short-circuit end of described 4th resonator (6) is contrary with the short-circuit end position of the first short circuit minor matters (9), produces a transmission zero in the upper edge of the first passband; The short-circuit end of described 5th resonator (7) is contrary with the short-circuit end position of the second short circuit minor matters (10), produces a transmission zero in the lower edge of the second passband.

2. micro-band double-passband filter according to claim 1, is characterized in that: described common feeder comprises the first feeder line (1) and the second feeder line (2); Described first feeder line (1) is connected with the short-circuit end of the 3rd resonator (5) is vertical respectively with the first resonator (3) with one end of the second feeder line (2), the other end is respectively as the first filter and common I/O (P1, the P2) port of the second filter.

3. micro-band double-passband filter according to claim 1 and 2, is characterized in that: described first feeder line (1) and the second feeder line (2), near place's formation source-load coupling, produce a transmission zero in the lower edge of the first passband.

4. micro-band double-passband filter according to claim 3, is characterized in that: be coupled between described first resonator (3) and the 3rd resonator (5), produce a transmission zero in the upper edge of the second passband.

5. micro-band double-passband filter according to claim 4, is characterized in that: the length of the described first to the 3rd resonator (3,4,5) is identical, and its length is 1/4th of the first passband centre frequency corresponding wavelength.

6. micro-band double-passband filter according to claim 5, is characterized in that: the length of described U-shaped resonator (8) is 1/2nd of the second passband centre frequency corresponding wavelength.

7. micro-band double-passband filter according to claim 6, is characterized in that: the length of described 4th resonator (6) and the 5th resonator (7) is respectively 1/4th of two transmission zero frequency corresponding wavelength of the first passband upper edge and the second passband lower edge.