CN104051832A - Miniaturized broadband band-pass filter based on spiral resonator - Google Patents

Abstract

The invention discloses a miniaturized broadband bandpass filter based on a spiral resonator, which is implemented in the form of a microstrip, including a microstrip substrate, a bottom layer and a top layer microstrip circuit, wherein the microstrip substrate is formed between the bottom layer Above, the top-level microstrip circuit is formed on the microstrip substrate; wherein, the top-level microstrip circuit includes input taps, output taps and resonator columns, and the resonator columns are connected between the input taps and the output taps. The invention adopts the nested coupling to greatly increase the coupling strength between the resonators, cooperates with the tap type feeding mode, and is easy to realize the broadband band-pass filter. The invention proposes that the resonator has a simple and compact structure, is easy to process and manufacture, and is suitable for microwave integrated circuits.

Description

A Miniaturized Broadband Bandpass Filter Based on Helical Resonators

technical field

The invention relates to the technical field of microstrip filters, in particular to a miniaturized wideband bandpass filter based on a spiral resonator.

Background technique

Filters are important passive components that are indispensable for suppressing interfering signals in wireless communication systems. With the rapid development of wireless communication, the requirements for communication channel capacity are increasing day by day, and it is necessary to use broadband filters for broadband signal processing to improve the channel capacity of the entire system.

In microwave/RF equipment for communications, bandwidth is usually expressed in Hertz (Hz). From the perspective of bandwidth, a relative bandwidth greater than 20% or an absolute bandwidth greater than 1GHz is a broadband filter. Wherein, the relative bandwidth BW=(f ₂ -f ₁ )/f ₀ . f ₂ and f ₁ are the upper and lower cut-off frequencies of the passband respectively, and f ₀ is the center frequency.

Most of the wideband filters implemented by microstrip are implemented with interdigitated or comb-shaped line structures, but these filters need to be grounded, and they face inevitable interference from other circuits during system integration.

Contents of the invention

(1) Technical problems to be solved

In view of this, the main purpose of the present invention is to provide a miniaturized broadband bandpass filter based on spiral resonators, to solve the problem that traditional broadband filters are difficult to avoid grounding, increase the coupling strength between resonators, and reduce the size of the filter .

(2) Technical solution

In order to achieve the above object, the present invention provides a miniaturized broadband bandpass filter based on a spiral resonator, which is realized in the form of a microstrip, including a microstrip substrate, a bottom layer and a top layer microstrip circuit, wherein the microstrip substrate is formed on the bottom ground, and the top-level microstrip circuit is formed on the microstrip substrate; wherein, the top-level microstrip circuit includes an input tap 5, an output tap 6 and a resonator column, and the resonator The columns are connected between the input tap 5 and the output tap 6 .

In the above solution, the input tap 5 or the output tap 6 is a transmission line with a characteristic impedance of 50 ohms.

In the above solution, a tapered transmission line is used between the input tap 5 or the output tap 6 and the resonator column.

In the above solution, the resonator column includes a plurality of resonator units with a parallel coupling structure, and each resonator unit includes two spiral resonators nested and coupled to each other. The spiral resonator adopts a uniform impedance transmission line or a stepped impedance transmission line, and its electrical length is 1/2 wavelength at the center frequency. The resonator units of the plurality of parallel coupling structures are spatially staggered at a certain position, so that the first spiral resonator in all the resonator units is at the same horizontal position.

In the above scheme, the relative dielectric constant of the microstrip substrate is 1-100, and the thickness is 0.05-5 mm.

In the above solution, the miniaturized broadband bandpass filter adopts a direct-connected feeding method or a coupled feeding method.

(3) Beneficial effects

As can be seen from the foregoing technical solutions, the present invention has the following beneficial effects:

1. The miniaturized broadband bandpass filter based on the helical resonator provided by the present invention is greatly reduced in size compared with the traditional 1/2 wavelength hairpin resonator due to the helical structure.

2. The spiral resonator-based miniaturized broadband bandpass filter provided by the present invention can realize nested coupling in a spiral structure, greatly enhances the coupling strength between resonators, and is easy to realize broadband characteristics.

3. The miniaturized broadband bandpass filter based on the spiral resonator provided by the present invention, because every two resonators are nested and coupled, when the order of the filter is increased by two steps, only one resonator area is increased, and the stop band suppression is improved. while increasing the smaller size.

Description of drawings

FIG. 1 is a schematic diagram of a miniaturized broadband bandpass filter based on a spiral resonator according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a resonator unit in the miniaturized broadband bandpass filter shown in FIG. 1 .

FIG. 3 is a schematic diagram of a spiral resonator in the resonator unit shown in FIG. 2 .

FIG. 4 is a schematic diagram of parallel coupling of two resonator units in the miniaturized broadband bandpass filter shown in FIG. 1 .

FIG. 5 is a diagram showing the results of a simulation test for the miniaturized wideband bandpass filter shown in FIG. 1 .

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

As shown in Figure 1, the present invention provides a miniaturized broadband bandpass filter based on a spiral resonator, which is implemented in the form of a microstrip, including a microstrip substrate, a bottom layer and a top layer microstrip circuit, wherein the microstrip substrate The chip is formed on the bottom ground, and the top-level microstrip circuit is formed on the microstrip substrate; wherein, the top-level microstrip circuit includes an input tap 5, an output tap 6 and a resonator row, and the resonator row is connected to the input tap 5 and the between output taps 6. The relative dielectric constant of the microstrip substrate is 1-100, and the thickness is 0.05-5mm. The miniaturized broadband bandpass filter adopts a direct-connected feeding method or a coupled feeding method.

Wherein, the resonator column includes a plurality of resonator units with a parallel coupling structure, and each resonator unit includes two spiral resonators nested and coupled to each other, as shown in FIG. 2 . The spiral resonator adopts a uniform impedance transmission line or a stepped impedance transmission line, and its electrical length is 1/2 wavelength at the center frequency. The resonator units of the plurality of parallel coupling structures are spatially staggered at a certain position, so that the first spiral resonator in all the resonator units is at the same horizontal position.

For this resonator column, the spiral resonators are from left to right, the (2N+1)th resonator and the (2N+2)th resonator are nested (N=0, 1, 2...) , the area of the resonator is increased by about one resonator every time the order of the filter is increased by two, which greatly reduces the size of the filter. The (2N+1)th (N=0, 1, 2...) resonator is nested with the (2N+2)th resonator, on the one hand to achieve stronger coupling, on the other hand to greatly reduce the filter area. The use of nested coupling greatly increases the coupling strength between resonators, and it is easy to realize a broadband bandpass filter with the tapped feeding method. The number of spiral resonators depends on the selected filter order. The number of folded turns of the spiral resonator is determined by the process precision, frequency band, etc.

The input tap 5 or the output tap 6 is a transmission line with a characteristic impedance of 50 ohms. A tapered transmission line is used between the input tap 5 or the output tap 6 and the column of resonators. The location of the input and output taps is determined by the selected bandwidth, order, and return loss.

In this embodiment, the substrate has a relative dielectric constant of 3.55 and a thickness of 0.508 mm.

As shown in Figure 1, Figure 1 is a schematic diagram of a miniaturized broadband bandpass filter based on a spiral resonator according to an embodiment of the present invention. This embodiment is a 6-order bandpass filter realized by a spiral resonator, with a center frequency of 6.6 GHz, relative bandwidth 25%, initial design callback loss -20dB. The coupling coefficients K12=K56=0.215, K23=K45=0.154, and K34=0.146 are calculated according to the look-up table. where the numbers represent the resonator order from left to right. For example, K12 represents the coupling coefficient between the first resonator and the second resonator, and so on. The loaded quality factor Qex=3.85, which determines the tap position T.

In Fig. 1, the 6th-order bandpass filter consists of an input tap 5, an output tap 6, a first resonator 7, a second resonator 8, a third resonator 9, a fourth resonator 10, a fifth resonator 11 and a first resonator Six resonators 12 constitute. The coupling spacing between the first resonator 7 and the second resonator 8 is 0.375mm, the coupling spacing between the second resonator 8 and the third resonator 9 is 0.15mm, and the coupling spacing between the third resonator 9 and the fourth resonator 10 is 0.225mm , the coupling distance between the fourth resonator 10 and the fifth resonator 11 is 0.15 mm, and the coupling distance between the fifth resonator 11 and the sixth resonator 12 is 0.375 mm.

FIG. 2 is a schematic diagram of a resonator unit in the miniaturized broadband bandpass filter shown in FIG. 1 . As shown in Figure 2, two spiral resonators in the resonator unit adopt a nested coupling structure. Resonator 1 and resonator 2 are oddly symmetrical about the center, and changing the spacing S1 can adjust the coupling coefficient. In the following description, the coupling pitch of the nested coupling structure refers to S1.

FIG. 3 is a schematic diagram of a spiral resonator in the resonator unit shown in FIG. 2 . The electrical length of the spiral resonator is 1/2 wavelength at the center frequency, and the transmission line width W is 0.3mm. In practical applications, the initial design length of the spiral resonator is 1/2 wavelength at the center frequency. Due to the influence of adjacent resonators, the resonator length in the final realization is slightly longer than the initial design length. For the folding criterion of the helical resonator, H1, H2, W1 and W2 are greater than twice the minimum machining accuracy of W, which is not less than 0.8mm in this example. In this embodiment, the spiral resonator resonates at 6.6 GHz.

FIG. 4 is a schematic diagram of parallel coupling of two resonator units in the miniaturized broadband bandpass filter shown in FIG. 1 . The resonator 3 and the resonator 4 are oddly symmetrical about the center, and the coupling coefficient can be adjusted by changing the distance S2. In the following description, the coupling pitch of the parallel coupling structure is referred to as S2.

As shown in FIG. 5 , FIG. 5 is a result diagram of a simulation test for the miniaturized wideband bandpass filter shown in FIG. 1 . The frequency characteristics of the simulation and test results of the implementation example of the present invention include: S11 and S21, the abscissa represents the frequency variable, the unit is GHz; the ordinate represents the amplitude variable, the unit is dB. The dotted line represents the simulation result, and the realization represents the test result. It can be seen from FIG. 5 that the center frequency of the bandpass filter of the present invention is 6.6 GHz, and the absolute bandwidth is greater than 1.5 GHz.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (8)

1. the minimized wide-band band pass filter based on helical resonator, it is characterized in that, this minimized wide-band band pass filter adopts micro-band forms to realize, comprise microstrip substrate, bottom and top layer microstrip circuit, wherein, microstrip substrate is formed on bottom ground, and top layer microstrip circuit is formed on microstrip substrate; Wherein, top layer microstrip circuit comprises input tap (5), output tap (6) resonator row, and these resonator row are connected between input tap (5) and output tap (6).

2. the minimized wide-band band pass filter based on helical resonator according to claim 1, is characterized in that, the transmission line that described input tap (5) or output tap (6) are 50 ohm of characteristic impedances.

3. the minimized wide-band band pass filter based on helical resonator according to claim 1, is characterized in that, adopts the transmission line of gradual change between described input tap (5) or output tap (6) and this resonator row.

4. the minimized wide-band band pass filter based on helical resonator according to claim 1, it is characterized in that, described resonator row comprise the resonator element of a plurality of parallel coupling structures, and each resonator element comprises the helical resonator of two mutually nested couplings.

5. the minimized wide-band band pass filter based on helical resonator according to claim 4, is characterized in that, described helical resonator adopts uniform impedance transmission line or stepped impedance transmission line, and its electrical length is 1/2 wavelength at centre frequency place.

6. the minimized wide-band band pass filter based on helical resonator according to claim 4, it is characterized in that, the resonator element of the described a plurality of parallel coupling structures certain position that spatially staggers up and down, makes first helical resonator in all resonator elements in same level position.

7. minimized wide-band band pass filter according to claim 1, is characterized in that, the relative dielectric constant 1-100 of described microstrip substrate, and thickness is 0.05-5mm.

8. the minimized wide-band band pass filter based on helical resonator according to claim 1, is characterized in that, this minimized wide-band band pass filter adopts direct-connected feeding classification or coupling feed way.