CN103915666A - Micro-strip double-pass-band filter - Google Patents

Abstract

The invention discloses a microstrip double-passband filter, which is respectively applied to a broadband system and a narrowband system. The dual passband filter is formed on a dielectric substrate, including a first resonator, a second resonator, a third resonator, a fourth resonator, a first feeder, a second feeder, a first short-circuit branch and a second short-circuit stub, wherein the first feeder, the second feeder, the first resonator, the second resonator, and the third resonator form a third-order interdigital filter, producing a wideband passband; the first feeder, the second feeder, the first resonator The resonator, the third resonator, and the fourth resonator form a dual-mode filter, producing a narrow passband. The parameters of the two passbands of the double passband filter of the invention can be adjusted independently, and the passbands have high frequency selectivity and isolation, simple circuit structure and good performance.

Description

A Microstrip Dual-Passband Filter

technical field

The invention relates to the technical field of wireless communication, in particular to a microstrip double-passband filter.

Background technique

With the rapid development of modern wireless communication technology, the communication system working in two or more frequency bands at the same time has become a key direction of current research, and the dual-passband system is more widely used. As filter components are crucial components in communication systems, the research on dual-passband filters has also attracted much attention. The microstrip structure has great advantages in miniaturization and low cost, so microstrip dual-passband filters have an important role in the industry. Extensive research.

Among the many design methods of dual-passband filters, two are widely used. One is to use a single resonator with tunable frequency, such as stepped impedance resonator (SIR), etc., so that the obtained filter can be very It is convenient to control the center frequency of each passband, but its bandwidth is difficult to adjust independently; the second method is the resonator combination method, which is to combine different resonators in a certain way, so that each group of resonators produces a passband , by adjusting different resonator parameters to control the center frequency and passband of its corresponding bandwidth, the filter obtained in this way is often complex in structure and large in size.

In the existing technology, the dual-passband filter generally has problems such as that the passband parameters cannot be adjusted independently, the bandwidth is narrow, and the insertion loss is large.

Contents of the invention

The technical problem to be solved by the present invention is to provide a microstrip double-passband filter with simple structure, good frequency selectivity, high isolation between passbands and wide passband for the defects of the background technology.

The present invention adopts the following technical solutions for solving the problems of the technologies described above:

A microstrip double-pass band filter, comprising a first resonator, a second resonator, a third resonator, a fourth resonator, a first feeder, a second feeder, a first short-circuit stub, and a second short-circuit stub;

The first resonator, the second resonator and the third resonator adopt a parallel coupled line structure;

The first feeder, the second feeder, the first resonator, the second resonator and the third resonator form a third-order interdigital filter to generate a wide passband, wherein the second resonator is located between the first resonator and the third resonator In the middle of the three resonators, and the terminals are short-circuited;

One end of the first feeder is connected to the first resonator, and one end of the second feeder is connected to the third resonator;

The first short-circuit stub and the second short-circuit stub are loaded on the fourth resonator to form a dual-mode resonator;

The first feeder, second feeder, first resonator, third resonator and fourth resonator form a dual-mode filter producing a narrow passband.

As a further optimization scheme of a microstrip double-pass band filter of the present invention, it also includes a third short-circuit branch, a fourth short-circuit branch, a fifth resonator, and a sixth resonator, and the third short-circuit branch is loaded on the first feeder and coupled with the fifth resonator, the fourth short-circuit stub is loaded on the second feeder and coupled with the sixth resonator.

As a further optimization scheme of a microstrip dual-passband filter of the present invention, the first to third resonators are equal in size, and the length is a quarter of the wavelength corresponding to the center frequency of the wideband passband, and the first resonator cross-coupled with the third resonator.

As a further optimization scheme of a microstrip dual-passband filter of the present invention, one end of the first feeder is vertically connected to the first resonator, one end of the second feeder is vertically connected to the third resonator, and the fifth resonator The resonator adopts an inverted L-shaped structure, and the sixth resonator adopts a forward L-shaped structure.

As a further optimization scheme of the microstrip double-pass band filter of the present invention, the impedance of the first feeder and the second feeder is 50 ohms, and a source-load coupling structure is formed near the first feeder and the second feeder.

Compared with the prior art, the present invention adopts the above technical scheme and has the following technical effects:

1. The parameters of the two passbands can be controlled independently;

2. Broadband passband meets the needs of modern communication systems to develop towards broadband; narrowband passband can be used in wireless local area network (WLAN) and other systems through reasonable selection;

3. The frequency selectivity of the passband and the isolation between the passbands are high, the performance is good, and the structure is simple and easy to process.

Description of drawings

Fig. 1 is the printed circuit board section schematic diagram of microstrip double-pass band filter of the present invention;

Fig. 2 is the structure schematic diagram that the present invention microstrip double pass band filter is positioned at the dielectric substrate upper layer;

Fig. 3 is the structural representation of the third-order interdigitated filter in the microstrip dual-passband filter of the present invention;

Fig. 4 is the structural representation of dual-mode filter in the microstrip dual-passband filter of the present invention;

Fig. 5 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. 6 is the scattering parameter simulation and test result of the microstrip double-passband filter of the present invention;

Fig. 7 is the group delay simulation and test results of the microstrip dual-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; 7. The first short-circuit branch; 8. The second short-circuit stub; 9. The third short-circuit stub; 10. The fifth resonator; 11. The fourth short-circuit stub; 12. The sixth resonator; 13. The first ground via; 14. The second ground via ; 15, the third ground via hole; 16, the fourth ground via hole; 17, the fifth ground via hole; 18, the sixth ground via hole; 19, the seventh ground via hole; S1, the dielectric substrate; S2, the upper metal ; S3, underlying metal; P1, input port; P2, output port; S ₁₁ , reflection coefficient of port 1 when port 2 is matched; S ₂₁ , forward transmission coefficient from port 1 to port 2 when port 2 is matched.

Detailed ways

Below in conjunction with accompanying drawing, technical scheme of the present invention is described in further detail:

The invention discloses a microstrip double-pass band filter, which includes a first resonator, a second resonator, a third resonator, a fourth resonator, a first feeder, a second feeder, a first short-circuit branch and a second short circuit stub;

The first resonator, the second resonator and the third resonator adopt a parallel coupled line structure;

The first feeder, the second feeder, the first resonator, the second resonator and the third resonator form a third-order interdigital filter to generate a wide passband, wherein the second resonator is located between the first resonator and the third resonator In the middle of the three resonators, and the terminals are short-circuited;

One end of the first feeder is connected to the first resonator, and one end of the second feeder is connected to the third resonator;

The first short-circuit stub and the second short-circuit stub are loaded on the fourth resonator to form a dual-mode resonator;

The first feeder, second feeder, first resonator, third resonator and fourth resonator form a dual-mode filter producing a narrow passband.

The microstrip double-passband filter disclosed in the present invention may also include a third short-circuit branch, a fourth short-circuit branch, a fifth resonator, and a sixth resonator, the third short-circuit branch is loaded on the first feeder, and is connected to the second short-circuit branch. The fifth resonator is coupled, and the fourth short-circuit stub is loaded on the second feeder and coupled with the sixth resonator.

The first to third resonators are equal in size, and the length is a quarter of the wavelength corresponding to the central frequency of the wideband passband, and the first resonator and the third resonator are cross-coupled.

One end of the first feeder is vertically connected to the first resonator, one end of the second feeder is vertically connected to the third resonator, the fifth resonator adopts an inverted L-shaped structure, and the sixth resonator adopts a positive To the L-shaped structure.

The impedance of the first feeder and the second feeder is 50 ohms, and a source-load coupling structure is formed near the first feeder and the second feeder.

Take the wideband passband with a center frequency of 3.2GHz and a relative bandwidth of 78% as an example, and the narrowband passband with a center frequency of 5.8GHz and a relative bandwidth of 6% as an example.

Fig. 1 is a dielectric substrate used in the present invention, its relative permittivity is 2.2, its thickness is 0.508 mm, and its loss tangent is 0.0009. Of course, other specifications of the dielectric board can also be selected. The upper and lower surfaces of the dielectric substrate S1 are coated with an upper metal layer S2 and a lower metal layer S3 respectively, wherein the dual passband filter of the present invention is formed on the upper metal layer S2, and the lower metal layer S3 serves as a ground plane.

As shown in Figure 2, the microstrip double-pass band filter of the present invention includes a first feeder 1, a second feeder 2, a first port P1, a second port P2, a first resonator 3, a second resonator 4, The third resonator 5, the fourth resonator 6, the first short-circuit branch 7, the second short-circuit branch 8, the third short-circuit branch 9, the fifth resonator 10, the fourth short-circuit branch 11, the sixth resonator 12 and for The first to seventh ground vias 13-19 forming the short circuit structure. As shown in Figure 3, the first feeder 1, the second feeder 2, the first resonator 3, the second resonator 4 and the third resonator 5 form a third-order interdigital filter to produce a broadband passband; The three resonators (3-5) are equal in size and are short-circuited quarter-wavelength resonators (QWR) whose length is a quarter of the wavelength corresponding to the center frequency of the first passband; the terminal of the second resonator is connected to the The first ground vias 13 are connected to form a short circuit; the short-circuited ends of the first resonator 3 and the third resonator 5 are vertically connected to the ends of the first feeder 1 and the second feeder 2 respectively, and the first feeder 1 and the second feeder 2 are vertically connected. The other ends of the two feeders 2 are respectively used as input/output ports (P1 and P2) of the filter; the center frequency and bandwidth of the first passband can be adjusted by the length and spacing of the first to third resonators (3-5). As shown in Figure 5, the first feeder 1, the second feeder 2, the first resonator 3, the third resonator 5, the fourth resonator 6, the first short-circuit stub 7 and the second short-circuit stub 8 form a dual-mode filter The first resonator 3 and the third resonator 5 provide strong coupling as a high-impedance feeder; the first short-circuit stub 7 and the second short-circuit stub 8 are loaded on the fourth resonator 6 to form a symmetrical structure The dual-mode resonator can generate a transmission zero point Tz4 between the two passbands according to the cancellation effect of its odd and even modes in the main path; the first short-circuit stub 7 and the second short-circuit stub 8 are equal in size and pass through the second ground via hole respectively 14 and the third ground via 15 to realize short circuit; the bandwidth of the second passband can be controlled by the length of the fourth resonator 6 and the first short-circuit stub 7, and its bandwidth can be controlled by the length of the first short-circuit stub 7 and the second short-circuit stub 8 The spacing is adjusted. As shown in Figure 2, the first filter and the second filter have common input/output ports (P1/P2) and feeders, that is, the first feeder 1 and the second feeder 2; the first feeder 1 and the second feeder 2 A source-load coupling structure is formed close to each other, a transmission zero Tz1 is generated at the lower edge of the first passband and a transmission zero Tz7 is generated at the upper edge of the second passband; the first resonator 3 and the third resonator 5 There is cross-coupling between them, which produces a transmission zero Tz6 at the upper edge of the second passband. The third short-circuit stub 9 is loaded on the first feeder 1, which can generate a transmission zero point Tz8 at the upper edge of the second passband, which deepens the stopband; the fifth resonator 10 adopts an inverted L-shaped structure, located in the third short-circuit Next to the stub, there is a coupling with the third short-circuit stub, resulting in transmission zero Tz3. The fourth short-circuit stub 11 is loaded on the second feeder 2, which can generate a transmission zero point Tz2 at the lower edge of the first passband to improve the frequency selectivity of the passband; the sixth resonator 12 adopts a positive L-shaped structure, Located next to the fourth short-circuit stub 11, there is coupling between the fourth short-circuit stub 11, which can generate a transmission zero point Tz5 between the two passbands, improving the frequency selectivity of the passband and the isolation between the passbands; Both the fifth resonator 10 and the sixth resonator 12 are quarter-wavelength resonators with short-circuit terminals, and their lengths are one-fourth of the corresponding wavelengths of the transmission zeros Tz3 and Tz5 respectively. The mutual loading effect of the first filter and the second filter can enhance the source-load coupling and improve the isolation between the two passbands.

As shown in Figure 5, the lower layer of the dielectric substrate of the microstrip double-pass band filter of the present invention, the first grounding via 13 is the short-circuit terminal of the second resonator 4; the second grounding via 14 is the short-circuit terminal of the first short-circuiting stub 7 ; The third ground via 15 is the short-circuit terminal of the second short-circuit branch 8; the fourth ground via 16 is the short-circuit terminal of the third short-circuit branch 9; the fifth ground via 17 is the short-circuit terminal of the fifth resonator 10; The six ground vias 18 are the short-circuit terminal of the fourth short-circuit branch 11 ; the seventh ground via 19 is the short-circuit terminal of the sixth resonator 12 .

As shown in FIG. 6 , the simulation and actual measurement results of the scattering parameters of the microstrip dual-passband filter of the present invention can be seen from the figure in good agreement with the simulation results and the actual measurement results, and has good working performance. The wideband passband has a center frequency of 3.2GHz and a relative bandwidth of 78%; the narrowband passband has a center frequency of 5.8GHz and a relative bandwidth of 6%; the resulting multiple transmission zeros make both passbands highly frequency selective And the isolation between high passbands, the isolation is greater than 30dB.

As shown in FIG. 7 , the group delay simulation and test results of the microstrip dual-passband filter of the present invention, for wideband and ultra-wideband filters, group delay is a parameter that characterizes the delay characteristic caused by it to the signal. It can be seen from the figure that in the first passband, its group delay has very flat performance.

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 (5)

1. A kind of microstrip double-pass band filter, is characterized in that, comprises the first resonator, the second resonator, the 3rd resonator, the 4th resonator, the first feeder, the second feeder, the first short-circuit stub and Second short-circuit stub; The first resonator, the second resonator and the third resonator adopt a parallel coupled line structure; The first feeder, the second feeder, the first resonator, the second resonator and the third resonator form a third-order interdigital filter to generate a wide passband, wherein the second resonator is located between the first resonator and the third resonator In the middle of the three resonators, and the terminals are short-circuited; One end of the first feeder is connected to the first resonator, and one end of the second feeder is connected to the third resonator; The first short-circuit stub and the second short-circuit stub are loaded on the fourth resonator to form a dual-mode resonator; The first feeder, second feeder, first resonator, third resonator and fourth resonator form a dual-mode filter producing a narrow passband. 2. The microstrip double-pass band filter according to claim 1, is characterized in that, also comprises the 3rd short-circuit stub, the 4th short-circuit stub, the 5th resonator and the 6th resonator, described 3rd short-circuit stub load On the first feeder and coupled with the fifth resonator, the fourth short-circuit stub is loaded on the second feeder and coupled with the sixth resonator. 3. The microstrip dual-passband filter according to claim 1, wherein the first to the third resonator are equal in size, and the length is 1/4 of the corresponding wavelength of the broadband passband center frequency, and the said The first resonator and the third resonator are cross-coupled. 4. The microstrip dual-pass band filter according to claim 2, wherein one end of the first feeder is vertically connected to the first resonator, and one end of the second feeder is vertically connected to the third resonator, so The fifth resonator adopts an inverted L-shaped structure, and the sixth resonator adopts a forward L-shaped structure. 5. The microstrip double-pass band filter according to claim 1, wherein the impedance of the first feeder and the second feeder is 50 ohms, and the first feeder and the second feeder form a source-load close to the place coupling structure.