CN104009271A - A Planar Bandpass Filter Based on Cascaded Four Resonators - Google Patents

Abstract

The invention discloses a plane band-pass filter based on four cascaded resonators, which comprises an input feeder line, an output feeder line, a quarter-wavelength first resonator, a quarter-wavelength fourth resonator, a three-quarter-wavelength second resonator and a three-quarter-wavelength third resonator, wherein the input feeder line is connected with the input feeder line; the first resonator, the second resonator, the third resonator and the fourth resonator are sequentially cascaded to form a ring structure; the first resonator and the fourth resonator are respectively in parallel with the input feeder line and the output feeder line correspondingly to form a first coupling structure and a fifth coupling structure respectively; the first resonator and the second resonator are connected with the first grounding through hole to form a second coupling structure; one end of the third resonator and one end of the fourth resonator are connected with the second grounding through hole to form a fourth coupling structure; a coupling gap exists between the second resonator and the third resonator to form a third coupling structure; and a coupling gap exists between the first resonator and the fourth resonator port to form a sixth coupling structure. Has the advantages of high frequency selectivity and small in-band insertion loss.

Description

A Planar Bandpass Filter Based on Cascaded Four Resonators

technical field

The invention relates to a band-pass filter, in particular to a planar band-pass filter based on cascaded four resonators.

Background technique

Radio frequency/microwave filters are an indispensable part of modern microwave relay communication, satellite communication, wireless communication and electronic countermeasure systems, and are also the most important and most technical microwave passive components. As one of the important components in the circuit system, the bandpass filter's performance determines the working quality of the system to a large extent. The bandpass filter mainly works in the RF front end of the communication system, and is used to pass useful signals in a certain frequency range with low loss, while attenuating frequency components in other frequency ranges to an extremely low level.

However, with the rapid development of modern communication requirements, the available spectrum resources are increasingly tight, so the requirements for filter frequency selection characteristics are getting higher and higher. In order to improve the communication capacity and avoid interference between adjacent channels, the filter must have a steep out-of-band suppression; in order to improve the signal-to-noise ratio, it is required to have a low insertion loss in the passband; and in order to reduce the distortion of the signal, it is required There are flat amplitude-frequency characteristics and group delay characteristics in the passband; in order to meet the miniaturization trend of modern communication terminals, the filter is required to have smaller volume and weight. The traditional Butterworth and Chebyshev filters have been difficult to meet these requirements, and the introduction of a cross-coupled filter with limited transmission zeros is currently the most commonly used and the best choice. Compared with traditional filters, this filter can not only meet the high selectivity outside the passband, but also reduce the number of resonant cavities, reduce the design cost and filter volume. So far, many scholars have proposed microwave bandpass filters with cross-coupling structures, and some of them have indeed shown good performance: low in-band insertion loss, high selectivity, etc. However, some structures use too high order to make the filter volume too large, which is not conducive to integration.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and provide a planar bandpass filter based on cascaded four resonators with higher frequency selectivity, smaller in-band loss and small volume. The invention introduces controllable cross-coupling between the resonators, so that a plurality of transmission zero points are generated outside the passband, thereby achieving the purpose of rapid roll-off and improving selectivity.

The purpose of the present invention is achieved through the following technical solutions: a planar bandpass filter based on cascaded four resonators, including an input feeder and an output feeder; the filter also includes a quarter of the same structure and symmetrical position The first resonator and the fourth resonator of the wavelength and the second and third resonators of the three-quarter wavelength with the same structure and symmetrical positions; the first resonator, the second resonator, the third resonator and the third resonator The four resonators are cascaded in turn to form a ring structure;

The first resonator and the fourth resonator are respectively parallel to the input feeder and the output feeder in one-to-one correspondence; and there is a gap between the first resonator and the input feeder, forming a first coupling structure;

One end of the first resonator and one end of the second resonator are connected to a first ground via, and the first ground via introduces magnetic coupling between the first resonator and the second resonator to form a second coupling structure;

There is a coupling gap between the second resonator and the third resonator, forming a third coupling structure;

One end of the third resonator and one end of the fourth resonator are connected to the second ground via; the second ground via introduces magnetic coupling between the third resonator and the fourth resonator, forming a fourth coupling structure ;

There is a gap between the fourth resonator and the output feeder, forming a fifth coupling structure;

There is a coupling gap between the ports of the first resonator and the fourth resonator, forming a sixth coupling structure.

Preferably, both the first resonator and the fourth resonator are a microstrip line, and one port of the microstrip line as the first resonator and the microstrip line as the fourth resonator are connected to the first ground respectively. The hole is connected to the second ground via hole, and there is a gap between the other ports of the two microstrip lines, forming the sixth coupling structure; wherein the two microstrip lines are arranged symmetrically and on the same straight line.

Preferably, both the second resonator and the third resonator are composed of the first microstrip line, the second microstrip line, the third microstrip line, the fourth microstrip line, the fifth microstrip line and the first microstrip line connected in sequence. Composed of six microstrip lines, wherein the angle between the above-mentioned interconnected microstrip lines is 90 degrees;

The second resonator and the third resonator are respectively connected to the first ground via hole and the second ground via hole through the first microstrip line, and there is a coupling gap between the second resonator and the third resonator That is, there is a coupling gap between the second resonator and the fifth microstrip line of the third resonator, forming the third coupling structure.

Furthermore, the included angle between the first resonator and the first microstrip line of the second resonator is 90 degrees, and there is an angle between the second microstrip line of the second resonator and the first resonator a coupling gap, forming the second coupling structure together with the first ground via;

The included angle between the fourth resonator and the first microstrip line of the third resonator is 90 degrees, and there is a coupling gap between the second microstrip line of the third resonator and the fourth resonator, and The second ground vias together form the fourth coupling structure;

The widths of the coupling gap between the second resonator and the first resonator and the coupling gap between the third resonator and the fourth resonator are the first microstrip lines of the second resonator and the third resonator length.

Preferably, the starting position of the coupling gap between the second resonator and the third resonator is: calculated from the short-circuit end of the second resonator and the third resonator in the total length of the second resonator and the third resonator two thirds.

Preferably, the input feeder and the output feeder are connected by the seventh microstrip line, the eighth microstrip line and the ninth microstrip line connected in sequence; the electromagnetic wave is fed from the seventh microstrip line of the input feeder line, from The seventh microstrip line of the output feeder is fed out; the seventh microstrip line, the eighth microstrip line and the ninth microstrip line are connected into a "7" type structure, and the seventh microstrip line and the eighth microstrip line An obtuse angle is formed between them, and an acute angle is formed between the eighth microstrip line and the ninth microstrip line;

Wherein the input feeder and the output feeder are arranged symmetrically, the ninth microstrip line of the input feeder is parallel to the first resonator, and the ninth microstrip line of the output feeder is parallel to the fourth resonator;

Preferably, there is a coupling gap between the port of the ninth microstrip line of the input feeder and the port of the ninth microstrip line of the output feeder, forming the seventh coupling structure.

Preferably, both the input port of the input feeder and the output port of the output feeder have a matching impedance of 50 ohms.

Preferably, the planar bandpass filter is fabricated on a double-sided copper-clad microstrip substrate in the form of a printed circuit board, wherein the other side of the microstrip substrate is a copper-clad ground plane.

Compared with the prior art, the present invention has the following advantages and effects:

(1) The planar filter of the present invention is composed of two quarter-wavelength resonators and two three-quarter-wavelength resonators cascaded, and has the advantage of small size and easy integration. In addition, the input feeder, the output feeder and the first resonator and the fourth resonator form a coupling structure respectively, and the resonators also form a coupling structure respectively. By adjusting the resonators and the resonator and the input feeder and output feeder The magnetic coupling and electrical coupling strength make the bandwidth of the filter adjusted within a certain range, so that the bandwidth of the filter can be conveniently controlled. In the present invention, controllable cross-coupling is introduced between the first resonator and the fourth resonator, so that multiple transmission zeros are generated on both sides of the passband of the filter of the present invention, which greatly improves the out-of-band of the filter. The suppressing effect greatly improves the frequency selection characteristic of the filter of the present invention, and meanwhile has the advantage of small insertion loss in the band.

(2) The planar filter of the present invention also introduces cross-coupling between the input feeder and the output feeder, thereby making more transmission zeros on both sides of the passband of the filter, further mentioning the frequency selection characteristics of the filter of the present invention .

(3) The planar filter of the present invention adopts a microstrip form, so it has the advantages of flexible design, low cost, small volume and easy integration.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the planar bandpass filter of the present invention.

Fig. 2 shows the insertion loss and return loss of the planar bandpass filter of the present invention in the frequency range from 1.2GHz to 4.8GHz.

Fig. 3 shows the insertion loss and return loss of the planar bandpass filter of the present invention in the frequency range from 1 GHz to 10 GHz.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

As shown in Figure 1, this embodiment discloses a planar bandpass filter based on cascaded four resonators, wherein the planar bandpass filter of this embodiment is fabricated on a double-sided copper-clad microchip in the form of a printed circuit board. On the strip substrate 1 , the other side of the microstrip substrate 1 is a copper-clad ground plane. The relative dielectric constant of the microstrip substrate is 2.55, and the dielectric height is 0.80 mm.

The planar bandpass filter of this embodiment includes the input feeder 2 and the output feeder 3 with the same structure and symmetrical position, the quarter-wavelength first resonator 4 and the fourth resonator 5 with the same structure and symmetrical position, and the same structure and position Symmetrical three-quarter wavelength second resonator 6 and third resonator 7; wherein the first resonator 4, the second resonator 6, the third resonator 7 and the fourth resonator 5 are sequentially cascaded to form a ring structure ;

In this embodiment, the input feeder 2 and the output feeder 3 are connected by the seventh microstrip line, the eighth microstrip line and the ninth microstrip line connected in sequence; Port feed-in, from the port2 port of the seventh microstrip line of the output feeder 3, the useful signal of the specific frequency range selected by the filter is fed out; the seventh microstrip line, the eighth microstrip line and the ninth microstrip line The lines are connected into a "7" structure, an obtuse angle is formed between the seventh microstrip line and the eighth microstrip line, and an acute angle is formed between the eighth microstrip line and the ninth microstrip line. The ninth microstrip lines of the input feeder and the output feeder are arranged symmetrically and on the same straight line. The width W2 of the ninth microstrip line of the input feeder 2 and the output feeder 3 is 1.1 mm. Among the three feeders of the input feeder and the output feeder, the widths of the seventh microstrip line, the eighth microstrip line and the ninth microstrip line decrease sequentially. Both the input port 2 of the input feeder and the output port 3 of the output feeder have a matching impedance of 50 ohms.

In this embodiment, the first resonator 4 is composed of microstrip lines, and the fourth resonator 5 is composed of microstrip lines, wherein the two microstrip lines are arranged symmetrically and on the same straight line. The length L ₁ of the two microstrip lines is 16.9mm.

In this embodiment, the second resonator 6 and the third resonator 7 are all composed of the first microstrip line, the second microstrip line, the third microstrip line, the fourth microstrip line, the fifth microstrip line and The sixth microstrip line, wherein the angle between the above-mentioned interconnected microstrip lines is 90 degrees; as shown in Figure 1, the second resonator 6 and the third resonator 7 composed of six microstrip lines are similar to spiral structure. The first microstrip lines of the two resonators are parallel to each other, the second microstrip lines are on the same straight line, the third microstrip lines are parallel to each other, the fourth microstrip lines are on the same straight line, and the fifth microstrip lines are parallel to each other. The sixth microstrip line is on the same straight line. The length of the second microstrip line L ₂ =4.9mm, the length of the third microstrip line L ₃ =16.0mm, the length of the fourth microstrip line L ₄ =11.0mm, the length of the fifth microstrip line L ₅ =11.0mm, the length of the sixth microstrip line The length of the microstrip line L ₆ =9.3mm. The width of each of the above microstrip lines is W ₁ =1.0 mm.

In this embodiment, the ninth microstrip line of the input feeder 2 is parallel to the microstrip line of the first resonator 4, and there is a gap 14 between the first resonator 4 and the input feeder 2, forming a first coupling structure; by adjusting the gap The size of 14 can adjust the coupling strength between the first resonant filter 4 and the input feeder 2 .

In this embodiment, the microstrip line of the first resonator 4 and the first microstrip line of the second resonator 6 are respectively connected to the first ground via 8, and the microstrip line of the first resonator 4 and the second resonator 6 The included angle between the first microstrip lines is 90 degrees, the magnetic coupling is introduced through the first ground via 8, and the second microstrip line of the second resonator 6 is parallel to the microstrip line of the first resonator 4 and A gap 10 is formed, and the second coupling structure is formed through the gap 10 and the first ground via 8. In this embodiment, the first resonator 4 and the first resonator 4 can be adjusted by adjusting the size of the gap 10 or the size of the first ground via 8. The coupling strength between the second resonators 6 .

In this embodiment, there is a gap 11 between the fifth microstrip line of the second resonator 6 and the third resonator 7, which constitutes a third coupling structure, and the second resonator 6 and the third resonator 7 are adjusted by adjusting the gap 11 The coupling strength between them. Wherein the starting position of the gap 11 is: counted from the short-circuit end of the second resonator 6 and the third resonator 7 at two-thirds of the total length of the second resonator 6 and the third resonator 7 .

In this embodiment, the first microstrip line of the third resonator 7 and the microstrip line of the fourth resonator 5 are connected to the second ground via 9, and the magnetic coupling is introduced through the second ground via 9. In addition, the third resonator The second microstrip line is parallel to the microstrip line of the fourth resonator and forms a gap 12. The fourth coupling structure is formed through the gap 12 and the second ground via 9. In this embodiment, the size of the gap 12 can be adjusted or The size of the second ground via hole 9 is used to adjust the coupling strength between the third resonator and the fourth resonator.

In this embodiment, the ninth microstrip line of the output feeder 3 is parallel to the microstrip line of the fourth resonator 5, and there is a gap 15 between the microstrip line of the fourth resonator 5 and the output feeder 3, forming a fifth coupling structure; The coupling strength between the fourth resonant filter 5 and the output feeder 3 can be adjusted by adjusting the size of the gap 12 .

In this embodiment, there is a gap 13 between the end of the microstrip line of the first resonator 4 that is not connected to the first ground via 8 and the end of the microstrip line of the fourth resonator 5 that is not connected to the second ground via 9, forming The sixth coupling structure, through which a controllable cross-coupling is introduced between the first resonator 4 and the fourth resonator 5, in this embodiment, the cross-coupling causes both sides of the passband of the planar bandpass filter to generate There are two transmission zeros, and the cross-coupling strength between the first resonator 4 and the fourth resonator 5 can be adjusted by adjusting the size of the gap 13 .

In this embodiment, a gap is formed between the ports of the ninth microstrip line of the input feeder 2 and the output feeder 3, constituting the seventh coupling structure, and cross-coupling is introduced between the feeders at the source and load ends through the seventh coupling structure. In this embodiment , the cross-coupling produces four transmission zeros on both sides of the passband of the planar bandpass filter, and the cross-coupling strength between the input feeder 2 and the output feeder 3 can be adjusted by adjusting the size of the gap.

Wherein the simulation results of the scattering parameters of the planar bandpass filter of this embodiment are shown in Figure 2, wherein the frequency range is 1.2GHz to 4.8GHz, the horizontal axis represents the input signal frequency of the bandpass filter of this embodiment, and the vertical axis represents logarithm Amplitude (dB), including the magnitude of the insertion loss S21 and the magnitude of the return loss S11. Wherein S21 represents the relationship between the signal input power and the signal output power passing through the bandpass filter of this embodiment, and its corresponding mathematical function is:

10*lg(Pi/Po)(dB)＝20*lg|S21|;

Among them, Pi represents the input power, and Po represents the output power.

In the signal transmission process of the band-pass filter of this embodiment, part of the power of the signal is reflected back to the signal source, and the reflected power becomes the reflected power; wherein S11 represents the difference between the input power of the signal of the band-pass filter of this embodiment and the signal The relationship between reflected power, and its corresponding mathematical function is:

10*lg(Pr/Pi)(dB)＝20*lg|S11|;

Among them, Pr represents the reflected power, and Pi represents the input power.

The center frequency of the filter in this embodiment is 3GHz. According to the curve of return loss S11 in Fig. 2, it can be concluded that there are four clear reflection zero points in the passband, wherein the absolute value of the insertion loss in the band is less than 1.5dB, and the return loss The absolute value is greater than 20dB, and six transmission zeros are generated on both sides of the passband, which effectively increases the steepness of the cutoff frequency, makes the stopband drop faster, and the band edge is steeper, which greatly improves the frequency selection characteristics of the filter.

As shown in Figure 3, when the frequency range is 1GHz to 10GHz, the simulation results of the scattering parameters of the planar bandpass filter of this embodiment can be drawn from the figure, the planar bandpass filter of this embodiment can produce Multiple transmission zeros, -20dB out-of-band rejection from 3.22GHz to 8.92GHz, the spurious passband of double frequency is suppressed, it can be seen that the out-of-band rejection characteristic is very good.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (9)

1. the plane bandpass filter based on four resonators of cascade, comprises incoming feeder and output feeder; It is characterized in that, described filter also comprises structure is identical and position is symmetrical quarter-wave the first resonator and the 4th resonator and structure is identical and position is symmetrical four/three-wavelength the second resonator and the 3rd resonator; Described the first resonator, the second resonator, the 3rd resonator and the 4th resonator successively cascade form a loop configuration;

Described the first resonator is parallel with incoming feeder, and has gap between described the first resonator and incoming feeder, forms the first coupled structure;

One end of described first resonator one end and the second resonator is connected the first grounding through hole, and described the first grounding through hole is to introduce magnetic coupling between the first resonator and the second resonator, forms the second coupled structure;

Between described the second resonator and the 3rd resonator, there is coupling gap, form the 3rd coupled structure;

One end of described the 3rd resonator one end and the 4th resonator is connected with the second grounding through hole; Described the second grounding through hole is to introduce magnetic coupling between the 3rd resonator and the 4th resonator, forms the 4th coupled structure;

Described the 4th resonator is parallel with output feeder, and has gap between described the 4th resonator and output feeder, forms the 5th coupled structure;

Between described the first resonator and the 4th resonator port, there is coupling gap, form the 6th coupled structure.

2. the plane bandpass filter based on four resonators of cascade according to claim 1, it is characterized in that, described the first resonator and the 4th resonator are a microstrip line, one of them port as the microstrip line of the first resonator and microstrip line as the 4th resonator is connected with the second grounding through hole with the first grounding through hole respectively, article two, between another port of microstrip line, there is a gap, form described the 6th coupled structure; Wherein two microstrip lines are symmetrical arranged and on same straight line.

3. the plane bandpass filter based on four resonators of cascade according to claim 1, it is characterized in that, described the second resonator forms by the first microstrip line being connected successively, the second microstrip line, the 3rd microstrip line, the 4th microstrip line, the 5th microstrip line and the 6th microstrip line with the 3rd resonator, and wherein the angle between above-mentioned interconnected microstrip line is 90 degree;

Described the second resonator is connected with the second grounding through hole is corresponding with the first grounding through hole respectively by the first microstrip line with the 3rd resonator, between described the second resonator and the 3rd resonator, exist a coupling gap to be between the second resonator and the 3rd resonator the 5th microstrip line and have coupling gap, formed described the 3rd coupled structure.

4. the plane bandpass filter based on four resonators of cascade according to claim 3, it is characterized in that, angle between described the first resonator and the first microstrip line of the second resonator is 90 degree, between the second microstrip line of described the second resonator and the first resonator, there is coupling gap, form described the second coupled structure together with the first grounding through hole;

Angle between described the 4th resonator and the first microstrip line of the 3rd resonator is 90 degree, between the second microstrip line of described the 3rd resonator and the 4th resonator, has coupling gap, forms described the 4th coupled structure together with the second grounding through hole;

The width of the coupling gap between the coupling gap between described the second resonator and the first resonator and the 3rd resonator and the 4th resonator is the length of the first microstrip line of the second resonator and the 3rd resonator.

5. the plane bandpass filter based on four resonators of cascade according to claim 1, it is characterized in that, between described the second resonator and the 3rd resonator, the original position of coupling gap is: from the second resonator and the 3rd resonator short-circuit end, start at 2/3rds of the second resonator and the 3rd resonator total length.

6. the plane bandpass filter based on four resonators of cascade according to claim 1, is characterized in that, described incoming feeder is connected by the 7th microstrip line being connected successively, the 8th microstrip line and the 9th microstrip line with output feeder; Described electromagnetic wave, from the 7th microstrip line feed-in of incoming feeder, feeds out from the 7th microstrip line of output feeder; Described the 7th microstrip line, the 8th microstrip line and the 9th microstrip line connect into " 7 " type structure, between the 7th microstrip line and the 8th microstrip line, form an obtuse angle, between the 8th microstrip line and the 9th microstrip line, form an acute angle;

Wherein incoming feeder and output feeder are symmetrical arranged, and the 9th microstrip line of incoming feeder is parallel with the first resonator, and the 9th microstrip line of output feeder is parallel with the 4th resonator.

7. the plane bandpass filter based on four resonators of cascade according to claim 6, is characterized in that, between the port of incoming feeder the 9th microstrip line and the port of output feeder the 9th microstrip line, has a coupling gap, forms the 7th coupled structure.

8. the plane bandpass filter based on four resonators of cascade according to claim 1, is characterized in that, the input port of described incoming feeder and the output port of output feeder are the matched impedance of 50 ohm.

9. the plane bandpass filter based on four resonators of cascade according to claim 1, it is characterized in that, described plane bandpass filter is produced on the micro-belt substrate of double-sided copper-clad in the mode of printed circuit board (PCB), and wherein the other one side of micro-belt substrate is to cover copper ground plate.