TWI848700B - Four-bandpass filter with substrate-synthesized coaxial cavity structure - Google Patents

Abstract

A four-band pass filter with a substrate-synthesized coaxial cavity structure includes two input/output ports, a substrate, and a plurality of grounding through holes. The substrate includes two outer layers, two circuit layers, and a spacer layer spaced apart in a stacking direction, and includes a plurality of connecting through holes. The outer layers are provided with the input/output ports, respectively, and are paved with an external grounding region. Each of the circuit layers is provided with a connecting port electrically connected to the input/output ports and resonance regions surrounding the connecting port. Each of the resonance regions is electrically connected to the external grounding region through at least one of the connecting through holes. Each of the spacer layers is paved with a spacer grounding region, and is hollowed out to form four hollowed-out regions corresponding to the resonance regions. Therefore, it has the advantages of good electromagnetic interference resistance, low cost, and low technical threshold, and is suitable for low-cost circuit use in the industry.

Description

Four-bandpass filter with substrate-synthesized coaxial cavity structure

The present invention relates to a four-band pass filter, and in particular to a four-band pass filter with a substrate-synthesized coaxial cavity structure.

Reference 1 "Liu JC, Wang JW, Zeng BH, Chang DC. CPW-fed dual-mode double-square-ring resonators for quad-band filter. IEEE Microw. Wirel. Compon. Lett. 2010; 20(3): pp. 142-144" describes a "CPW (coplanar waveguide) fed dual-mode double-square-ring resonator as a quad-band pass filter". This reference is a microstrip planar structure and is an open structure, so its anti-electromagnetic interference capability is relatively weak. The resonator structure used in the document is two sets of square microstrip loops, and its resonant frequency depends on the size of the microstrip loop and the electric field perturbation structure attached to the microstrip loop. Therefore, the freedom to adjust the passband frequency is relatively limited. The two microstrip resonant loops (square microstrip loops) in the document are arranged in an overlapping manner, which will produce a strong coupling effect, resulting in a decrease in the circuit quality factor (Q value).

Reference 2 "Wu HW, Yang RY. A new quad-band bandpass filter using asymmetric stepped impedance resonators. IEEE Microw. Wirel. Compon. Lett. 2011; 21(4): pp. 203-205" describes a "quad-bandpass filter using asymmetric stepped impedance resonators". The structure uses four sets of stepped impedance microstrip resonators. Too many resonators are too close to each other, which makes the coupling effect between the resonators too strong, making it difficult to independently design the resonant frequency of each passband of the filter circuit. In particular, the area of the stepped impedance microstrip resonator is not small, which makes the overall circuit area larger.

Therefore, the purpose of the present invention is to provide a four-bandpass filter with a substrate-synthesized coaxial cavity structure that can solve the above-mentioned problems.

Therefore, the four-band pass filter of the substrate-synthesized coaxial cavity structure of the present invention includes two input and output ports, a substrate and a plurality of ground through holes.

These ports are used for input and output respectively.

The substrate includes two outer layers, two circuit layers and a spacer layer spaced apart along a stacking direction, and includes a plurality of connecting through holes. The arrangement order along the stacking direction is one of the outer layers, one of the circuit layers, the spacer layer, another of the circuit layers, and another of the outer layers. The outer layers are provided with the input and output ports, respectively, and each of the outer layers is provided with an external grounding area not connected to the input and output ports, and each of the circuit layers is provided with an electrical connection hole. The connection ports adjacent to the input/output ports and the resonance regions surrounding but not connected to the connection ports, each of the resonance regions is electrically connected to the adjacent external grounding region through at least one of the connection through holes, the area of each of the resonance regions and the number of the connected connection through holes are all different, each of the spacer layers is paved with a spacer grounding region, and the spacer grounding region is hollowed out to form four hollowed-out regions corresponding to the resonance regions respectively.

The grounding through holes are arranged on the substrate around the resonance regions.

The effect of the present invention is that: through the above-mentioned structure, the structure of the printed circuit board can be used to simulate and synthesize the resonant cavity structure of the coaxial characteristics, and there is a strict metal coating structure around the circuit, so that it has excellent anti-electromagnetic interference ability. Therefore, it can have the excellent characteristics of the coaxial cavity and the printed circuit board circuit at the same time, and has the advantages of high anti-electromagnetic interference ability and low cost. In addition, since the printed circuit board is a standard circuit board process, the technical threshold is low, and it is suitable for low-cost circuit use in the industry.

Referring to FIG. 1 to FIG. 4 , an embodiment of a substrate integrated coaxial cavity four-band pass filter of the present invention comprises two input/output ports 2, a substrate 3, and a plurality of grounding through holes 9. For the sake of clarity, the structure of the substrate 3 in FIG. 1 is drawn with imaginary lines, and the circuit structure inside the substrate 3 is shown in a perspective manner, and the grounding through holes 9 are omitted. The unit of the distance shown in FIG. 2 to FIG. 4 is millimeter (mm).

Referring to FIG. 1 and FIG. 2 , the input/output ports 2 are used for input and output respectively, and are suitable for connecting to an SMA socket (not shown) disposed on the outer layer 4 so as to be connected to an SMA plug (not shown) for input and output. In this embodiment, for example, the input/output port 2 at the top of FIG. 1 is used as an input port, and the input/output port 2 at the bottom is used as an output port.

The substrate 3 includes two outer layers 4, two circuit layers 5 and a spacer layer 6 arranged at intervals along a stacking direction L, and includes a plurality of connecting through holes 7 (VIA, the material is, for example, copper). The substrate 3 is implemented using a four-layer printed circuit board (PCB) structure, or using two double-layer printed circuit boards arranged closely. The substrate 3 has four insulating layers 8 stacked along the stacking direction L. The length of the insulating layer 8 between each outer layer 4 and the adjacent circuit layer 5 along the stacking direction L is, for example, 1.58 mm, and the length of the insulating layer 8 between each circuit layer 5 and the spacer layer 6 along the stacking direction L is, for example, 0.254 mm. The arrangement order along the stacking direction L is one of the outer layers 4, one of the circuit layers 5, the spacer layer 6, another of the circuit layers 5, and another of the outer layers 4.

The outer layers 4 are provided for the input/output ports 2, respectively, and each outer layer 4 is provided with an external grounding region 41 which is not connected to the input/output port 2 and provides a ground potential. In this embodiment, the surface of the outer layer 4 is covered with a copper layer as the external grounding region 41 except for the input/output port 2 and the required gap, so that it can have a better anti-electromagnetic interference capability.

1 and 3 , each circuit layer 5 is provided with a connection port 51 and a resonance region 52 surrounding but not connected to the connection port 51. The connection port 51 is electrically connected to the adjacent input/output port 2 through the connection via 7, and is electrically connected to the spacer layer 6 through another connection via 7. Each resonance region 52 is electrically connected to the adjacent external ground region 41 through at least one connection via 7.

The resonance regions 52 correspond to different frequency bands respectively. For the sake of clarity, the resonance regions 52 are defined as a first resonance region 521, a second resonance region 522, a third resonance region 523, and a fourth resonance region 524 in order from low frequency to high frequency.

The combination of the area of each resonance region 52 and the number of the connecting through holes 7 connected thereto is different, thereby adjusting each resonance region 52 to correspond to different frequency bands. When the areas of the resonance regions 52 are not equal, the frequency of the frequency band corresponding to the resonance regions 52 is negatively correlated with the area of the resonance regions 52. When the areas of the resonance regions 52 are equal, the number of the connecting through holes 7 connected to the resonance regions 52 of equal area is positively correlated with the frequency of the frequency band corresponding to the resonance regions 52. In this embodiment, the first resonance region 521 and the second resonance region 522 are designed to have equal areas, the third resonance region 523 is the second largest area, and the fourth resonance region 524 is the third largest area. In addition, except for the first resonance region 521 connected to one connection hole 7, the second resonance region 522, the third resonance region 523, and the fourth resonance region 524 are all connected to two connection holes 7. The number of connection holes 7 connected to each resonance region 52 is at least one, so as to provide a ground potential through the external ground region 41. The number of connection holes 7 connected to each resonance region 52 is preferably not more than three, and more preferably within two, because providing more connection holes 7 can increase the corresponding frequency, but will lead to increased loss.

Among the resonance regions 52, the first resonance region 521 and the second resonance region 522 corresponding to the two frequency bands of lower frequencies are respectively located at two opposite sides of the connection port 51, and the third resonance region 523 and the fourth resonance region 524 corresponding to the two frequency bands of higher frequencies are respectively located at two opposite sides of the connection port 51, and are sandwiched between the first resonance region 521 and the second resonance region 522 corresponding to the two frequency bands of lower frequencies.

Each of the resonance regions 52 is substantially in the shape of a sector with the connection port 51 as the center, so that the resonance regions 52 are substantially in the shape of a circle. The sector tip of each of the resonance regions 52 is truncated in the shape of a concave arc. In this way, the resonance regions 52 are spaced from the connection port 51 by a certain distance and are not connected to the connection port 51.

In this embodiment, the distribution of the resonance regions 52 is to define a cross line C with the connection port 51 as the center, and the symmetry axes of the sectors of the resonance regions 52 are respectively located on the four line segments of the cross line C. However, the sector-shaped resonance regions 52 can also be arranged to have equal spacing distances along the circumferential direction.

The radius of each of the resonance regions 52 may be the same or different, and the angle of each of the resonance regions 52 may also be the same or different. The area of the resonance region 52 may be adjusted by changing the respective radius and angle.

Referring to FIG. 1 and FIG. 4 , each of the spacer layers 6 is provided with a spacer grounding region 61, and four hollow regions 62 are formed in the spacer grounding region 61, which correspond to the resonant regions 52. The spacer grounding region 61 is made of copper, which is basically filled with the spacer layer 6, and is at ground potential through the grounding through holes 9. The hollow regions 62 are hollow regions without metal layers formed by etching the spacer grounding region 61.

The hollow regions 62 correspond to the resonance regions 52 of different frequency bands, respectively, and the frequencies of the frequency bands corresponding to the hollow regions 62 are negatively correlated with the areas of the hollow regions 62. For the sake of clarity, the hollow regions 62 are defined as a first hollow region 621, a second hollow region 622, a third hollow region 623, and a fourth hollow region 624 in the order from low frequency to high frequency of the frequency bands of the corresponding resonance regions 52.

The symmetry axis of each of the resonance regions 52 coincides with the symmetry axis of the corresponding hollow region 62 in the stacking direction L. That is, the symmetry axes of the first resonance region 521, the second resonance region 522, the third resonance region 523, and the fourth resonance region 524 coincide with the symmetry axes of the first hollow region 621, the second hollow region 622, the third hollow region 623, and the fourth hollow region 624 in the stacking direction L, respectively.

1 and 3 , each of the connecting through holes 7 is disposed on the symmetry axis of the corresponding resonance region 52 , thereby obtaining a better resonance performance.

1 to 4 , the grounding vias 9 are disposed on the substrate 3 around the resonance regions 52 and extend upward from the outer layer 4 below to the outer layer 4 above to form a frame-shaped grid structure located on the outer periphery of the side of the substrate 3 .

By means of the above arrangement, the two layers of circuit boards on the upper side and the two layers of circuit boards on the lower side of FIG. 1 can be respectively regarded as two substrate-integrated coaxial cavities, each of which has four resonators, and each resonator can be regarded as a parallel LC resonant circuit between one of the sector-shaped patches (the resonance region 52) and the ground end (the external ground region 41). By changing the radius and angle of the sector (the resonance region 52), the capacitance of the resonator can be adjusted, and by changing the number of the connecting through holes 7 connected to the sector, the inductance of the resonator can be adjusted. In this way, the frequency band corresponding to each of the resonance regions 52 can be easily adjusted. In addition, please refer to FIG. 1 and FIG. 5 to FIG. 8, which are electric field distributions of the circuit layer 5 of the present embodiment at the first passband resonant frequency, the second passband resonant frequency, the third passband resonant frequency and the fourth passband resonant frequency respectively corresponding to the first resonant region 521, the second resonant region 522, the third resonant region 523 and the fourth resonant region 524. It can be clearly seen from the figure that each passband resonant frequency is only controlled by the corresponding one of the resonant regions 52. In other words, the frequency band corresponding to each of the resonant regions 52 of the present embodiment can be adjusted independently without affecting the frequency bands corresponding to the other resonant regions 52. Therefore, the present embodiment has a high degree of freedom in adjusting the passband resonance frequency and is easy to adjust and design.

Through the above description, the effects of this embodiment are as follows:

1. By stacking the outer layers 4, the circuit layers 5 and the spacer layer 5 in a circuit board structure, and providing four resonant regions 52 on the circuit layers 5, and then providing four corresponding hollow regions 62 on the spacer layer 6, a four-band pass filter can be implemented with a printed circuit board circuit. By paving the outer layers 4 with the external grounding regions 41 and providing the grounding through holes 9 surrounding the resonant regions 52 on the substrate, a metal mesh layer structure similar to a coaxial cable can be formed to achieve a better anti-electromagnetic interference effect.

Since the substrate synthesized coaxial cavity structure uses the structure of a printed circuit board to simulate and synthesize the resonant cavity structure of the coaxial characteristics, it is also a planar circuit of the printed circuit board type and has the characteristics and advantages of the coaxial line. That is, the substrate 3 can be used to synthesize the coaxial line and operate in the TEM mode, and because there is a strict metal coating structure around the circuit, it has excellent anti-electromagnetic interference ability. Therefore, this embodiment has the excellent characteristics of the coaxial cavity and the printed circuit board circuit, and can avoid the shortcomings of the coaxial cavity and the printed circuit board circuit, as described below:

The advantages of this embodiment are: because its structure is a planar printed circuit structure, compared with the complex three-dimensional mechanical structure of a general coaxial cavity, this embodiment has the advantages of being suitable for mass production, effectively reducing the circuit manufacturing cost, small circuit area, light weight, a large number of passbands, and easy to combine with other microwave components. At the same time, this embodiment synthesizes the structure and function of the coaxial cavity. Compared with the microstrip line resonant circuit of the general printed circuit board structure, this embodiment has higher power and excellent anti-electromagnetic interference capability.

The disadvantages avoided by this embodiment are: because its structure is a planar printed circuit structure, it does not have the complex three-dimensional mechanical structure, high weight, high cost and difficulty in combining with other planar circuits of the coaxial cavity, and also avoids the disadvantages of the microstrip line circuit of the printed circuit board structure, such as low power and susceptibility to external noise interference.

Second, by setting four resonant regions 52 on the circuit layers 5, and setting four corresponding hollow regions 62 on the spacer layer 6, and adjusting the corresponding frequencies by changing the areas of the resonant regions 5 and the number of the connected through holes 7, a four-band passband design can be achieved with a smaller area of the resonant region 52 and a smaller number of the connected through holes 7. Moreover, in this embodiment, the frequency band corresponding to each resonant region 52 can be adjusted independently without affecting the frequency bands corresponding to other resonant regions 52. Therefore, this embodiment has a high degree of freedom in adjusting the passband resonant frequency and has the advantage of being easy to adjust the design frequency band.

3. Through the above overall configuration, this embodiment provides a four-band pass filter with reduced size, high power, anti-electromagnetic interference, and high freedom to adjust the passband resonant frequency. The four band center frequencies are 1.9, 2.62, 3.63, and 4.63 GHz, respectively, and the corresponding fractional bandwidths are 3.2%, 2.8%, 1.4%, and 1.7%. The passband loss of each passband is only about 1.9, 1.7, 2.1, and 2.2 dB.

In summary, the four-bandpass filter with a substrate-synthesized coaxial cavity structure of the present invention can indeed achieve the purpose of the present invention.

However, the above is only an example of the implementation of the present invention, and it cannot be used to limit the scope of the implementation of the present invention. All simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the patent specification are still within the scope of the patent of the present invention.

2: Input/output port 3: Substrate 4: External layer 41: External ground area 5: Circuit layer 51: Connection port 52: Resonance area 521: First resonance area 522: Second resonance area 523: Third resonance area 524: Fourth resonance area 6: Spacer layer 61: Spacer ground area 62: Hollow area 621: First hollow area 622: Second hollow area 623: Third hollow area 624: Fourth hollow area 7: Connection via 8: Insulation layer 9: Ground via L: Stacking direction C: Cross line

Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: FIG. 1 is a three-dimensional schematic diagram of an embodiment of a four-band pass filter of a substrate-synthesized coaxial cavity structure of the present invention; FIG. 2 is a schematic diagram of an outer layer of the embodiment; FIG. 3 is a schematic diagram of a circuit layer of the embodiment; FIG. 4 is a schematic diagram of a spacer layer of the embodiment; and FIG. 5 to FIG. 8 are respectively the electric field distribution of the circuit layer of the embodiment at the first passband resonant frequency, the second passband resonant frequency, the third passband resonant frequency and the fourth passband resonant frequency.

2: Input and output ports

3: Substrate

4: Outer layer

41: External ground area

5: Circuit layer

51:Port

52: Resonance region

521: First resonance region

522: Second resonance region

523: The third resonance region

524: The fourth resonance region

6: Interlayer

61: Interval grounding area

62: Hollowed-out area

621: The first hollowed-out area

622: The second hollowed-out area

623: The third hollowed-out area

624: The fourth hollowed-out area

7: Connecting through hole

8: Insulating layer

L: Overlapping direction

Claims (9)

A four-band pass filter with a substrate-synthesized coaxial cavity structure comprises: Two input/output ports, used for input and output respectively; A substrate, comprising two outer layers, two circuit layers and a spacing layer spaced along a stacking direction, and comprising a plurality of connecting through holes, wherein the arrangement sequence along the stacking direction is one of the outer layers, one of the circuit layers, the spacing layer, another of the circuit layers, and another of the outer layers, wherein the outer layers are respectively provided with the input/output ports, and each of the outer layers is provided with an external grounding area not connected to the input/output ports, and each of the circuit layers is provided with an electrical connection through hole. A connection port connected to the adjacent input/output port and four resonant regions surrounding but not connected to the connection port, each of the resonant regions is electrically connected to the adjacent external grounding region through at least one of the connecting through holes, the area of each of the resonant regions and the number of the connected connecting through holes are different, each of the spacer layers is paved with a spacer grounding region, and the spacer grounding region is hollowed out to form four hollowed-out regions corresponding to the resonant regions; and a plurality of grounding through holes are arranged on the substrate around the resonant regions. A four-band pass filter with a substrate-synthesized coaxial cavity structure as described in claim 1, wherein the resonant regions correspond to different frequency bands respectively, and when the areas of the resonant regions are unequal, the frequencies of the frequency bands corresponding to the resonant regions are negatively correlated with the areas of the resonant regions, and when the areas of the resonant regions are equal, the number of connecting through holes connecting the resonant regions of equal area is positively correlated with the frequencies of the frequency bands corresponding to the resonant regions. A four-band pass filter with a substrate-synthesized coaxial cavity structure as described in claim 1, wherein the hollow regions correspond to the resonant regions of different frequency bands respectively, and the frequencies of the frequency bands corresponding to the hollow regions are negatively correlated with the areas of the hollow regions. A four-bandpass filter with a substrate-synthesized coaxial cavity structure as described in claim 1, wherein each of the resonance regions is substantially fan-shaped with the connection port as the center, and the fan-shaped tip is truncated and not connected to the connection port. A four-bandpass filter with a substrate-synthesized coaxial cavity structure as described in claim 4, wherein a cross line centered on the connection port is defined, and the symmetry axes of the sectors of the resonance regions are respectively located on four line segments of the cross line. A four-bandpass filter with a substrate-synthesized coaxial cavity structure as described in claim 4, wherein the spacing distances between the fan-shaped resonance regions along the circumferential direction are equal. A four-bandpass filter with a substrate-synthesized coaxial cavity structure as described in claim 4, wherein the resonance regions correspond to different frequency bands respectively, the resonance regions corresponding to the two lower frequency bands are located on opposite sides of the connection port, and the resonance regions corresponding to the two higher frequency bands are located on opposite sides of the connection port and sandwiched between the resonance regions corresponding to the two lower frequency bands. A four-bandpass filter with a substrate-synthesized coaxial cavity structure as described in claim 1, wherein each of the connecting through holes is arranged on the symmetry axis of the corresponding resonance region. A four-bandpass filter with a substrate-synthesized coaxial cavity structure as described in claim 1, wherein the symmetry axis of each of the resonance regions coincides with the symmetry axis of the corresponding hollow region in the overlapping direction.