High-isolation compact filter bank

Abstract

The invention discloses a high-isolation compact filter bank, which belongs to the field of microwave devices and comprises a bottom grounding plate, a second filter pattern layer, a middle grounding layer, a fourth filter pattern layer, a fifth grounding plate and a top grounding plate. A first filter and a third filter are manufactured on the fourth filter pattern layer, and a second filter and a fourth filter are manufactured on the second filter pattern layer; on a horizontal projection plane, the first filter, the second filter, the third filter and the fourth filter are arranged clockwise along four sides of the square; the first filter and the second filter, the second filter and the third filter, the third filter and the fourth filter, and the fourth filter and the first filter are vertically adjacent in the horizontal position. By means of the innovative three-dimensional mixed isolation design, under the condition that an external metal cavity is not needed, the inter-channel isolation degree exceeding 60 dB is achieved, and meanwhile the advantages of being small in size, light in weight and easy to produce in batches are achieved.

Description

Technical Field

[0001] This invention relates to the field of microwave device technology, and in particular to a high-isolation compact filter bank. Background Technology

[0002] In modern wireless communication and radar systems, it is often necessary to process signals from multiple frequency bands. Filter banks are key passive devices for achieving frequency domain channel partitioning. As systems develop towards miniaturization and high integration, how to efficiently integrate multiple filters within a limited space while ensuring extremely high inter-channel isolation has become a core technological challenge.

[0003] Currently, there are two main methods for implementing multi-band filtering. One is to connect multiple independent filters in parallel along the RF path and then seal the filters in separate cavities, exposing only the input and output pins. This method is bulky and difficult to integrate into a small form factor. The other is to design a microstrip multiplexer on a single PCB board, but the performance of each passband is mutually constrained, the design is complex, and the more channels there are, the more limited the isolation becomes (generally <30dB). To further improve isolation, a metal shielding cavity is usually added to the entire filter bank, which further increases size, weight, and cost. Summary of the Invention

[0004] The purpose of this invention is to provide a high-isolation, compact filter bank to solve the problems in the prior art.

[0005] To solve the above technical problems, the present invention provides a high isolation compact filter bank, comprising: a bottom ground plane, a second filter pattern layer, an intermediate ground layer, a fourth filter pattern layer, a fifth ground plane, and a top ground plane; The fourth filter pattern layer has a first filter and a third filter fabricated on it, and the second filter pattern layer has a second filter and a fourth filter fabricated on it. On the horizontal projection plane, the first filter, the second filter, the third filter, and the fourth filter are arranged clockwise along the four sides of the square; the first filter and the second filter, the second filter and the third filter, the third filter and the fourth filter, and the fourth filter and the first filter are all vertically adjacent in the horizontal position.

[0006] In one embodiment, the first filter, the second filter, the third filter, and the fourth filter are all microstrip interdigitated structures, and the microstrip lines of the second filter and the fourth filter are perpendicular to the microstrip lines of the first filter and the third filter.

[0007] In one embodiment, a first window is formed in the intermediate ground layer, the fourth filter pattern layer, the fifth ground plane, and the top ground plane, and the position of the first window corresponds to the second filter and the fourth filter.

[0008] In one embodiment, a second window is formed in the fifth ground plane and the top ground plane, and the position of the second window corresponds to the first filter and the third filter.

[0009] In one embodiment, above the first filter and the third filter, there are multiple gold wires with both ends bonded to the grounding pads in the top ground plane. The gold wires are arranged in parallel and arched to form a fence-like shielding structure.

[0010] In one embodiment, the intermediate ground layer is a metal plane that completely isolates the filters of the second filter pattern layer from the filters of the fourth filter pattern layer in the vertical direction.

[0011] In one embodiment, the high isolation compact filter bank further includes a metal cover located above the top ground plane; the center of the inner surface of the metal cover is provided with a square metal block protruding towards the PCB. When the metal cover is installed in place, the square metal block contacts the center ground area of ​​the PCB surface, dividing the entire large cavity enclosed by the metal cover and the PCB into four independent sub-cavities.

[0012] In one embodiment, the input and output ports of the first filter, the second filter, the third filter, and the fourth filter are all led to pads on the bottom ground plane through metallized vias to form a QFN-like package interface.

[0013] The present invention provides a high-isolation compact filter bank, which has the following advantages: (1) Opening the window places the filter in the air medium, which reduces the equivalent dielectric constant, weakens the coupling, and reduces the dielectric loss, thus improving the filter performance for the first time (reducing insertion loss); constructing a gold wire bonded isolation barrier above the filter improves the filter performance for the second time (improving out-of-band rejection); the height of the air cavity of the metal block cover is determined by simulation optimization. After the height is determined, the filter performance is improved for the third time (out-of-band rejection is improved compared to the case of free air without a cover); (2) Through the above-mentioned innovative three-dimensional hybrid isolation design, the filter layout extends along the edge of the square, which is already the smallest size layout under the quarter wavelength condition; (3) Without the need for an external metal cavity, the channel isolation of more than 60dB is achieved through polarization isolation, layered isolation, gold wire isolation barrier isolation and metal block isolation. It also has the advantages of small size, light weight and easy mass production. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the three-dimensional exploded structure of the filter bank of the present invention.

[0015] Figure 2 This is a cross-sectional view of the present invention.

[0016] Figure 3 This is a block diagram illustrating the inventive principle of this invention.

[0017] Figure 4 It is a flowchart of the invention. Detailed Implementation

[0018] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the high-isolation compact filter bank proposed in this invention. The advantages and features of the invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0019] This invention provides a high-isolation compact filter bank, such as... Figure 1 and Figure 2 As shown, its structure, from bottom to top, includes: a bottom ground plane L1, a second filter pattern layer L2, an intermediate ground layer L3, a fourth filter pattern layer L4, a fifth ground plane L5, a top ground plane L6, and a metal cover 1 with a central metal lump. Since the PCB is double-sided, layer L1 is below L2, and similarly, layer L2 is below L3, and layer L4 is below L5. Due to view obstruction, these layers are not labeled in the diagram.

[0020] A high-isolation compact filter bank includes filters F1, F2, F3, and F4. For example... Figure 1 As shown, filters F1 and F3 are fabricated on the fourth filter pattern layer L4, while filters F2 and F4 are fabricated on the second filter pattern layer L2. All four filters (F1, F2, F3, and F4) are microstrip interdigitated structures, operating in four frequency bands: 7.5-8 GHz (filter F1), 8.5-9 GHz (filter F3), 9.5-10 GHz (filter F2), and 10.5-11 GHz (filter F4), respectively. Their block diagram is shown below. Figure 3 As shown.

[0021] The high-isolation compact filter bank adopts a quasi-square layout, such as Figure 1 As shown, on the horizontal projection plane, filters F1, F2, F3, and F4 are arranged clockwise along the four sides of a square. Among them, filters F1 and F2, F2 and F3, F3 and F4, and F4 and F1 are all vertically adjacent to each other in the horizontal position.

[0022] High-isolation compact filter banks employ polarization isolation design, such as Figure 1 As shown, the microstrip lines of filters F2 and F4 located in the second filter pattern layer L2 are perpendicular to the microstrip lines of filters F1 and F3 located in the fourth filter pattern layer L4.

[0023] High-isolation compact filter banks employ selective windowing: such as Figure 1 As shown, on the second filter pattern layer L2, in the area directly above the filter patterns F2 and F4, the intermediate ground layer L3, the fourth filter pattern layer L4, the fifth ground plane L5, and the top ground plane L6 are removed to form a first window. Similarly, on the fourth filter pattern layer L4, in the area directly above the filter patterns F1 and F3, the fifth ground plane L5 and the top ground plane L6 are removed to form a second window, which allows the filter body to be suspended in the air cavity.

[0024] High-isolation compact filter banks employ layered grounding shielding, such as Figure 1 As shown, the intermediate ground layer L3 is a complete metal plane (except for the window), which completely isolates the filters of the second filter pattern layer L2 and the filters of the fourth filter pattern layer L4 in the vertical direction by the intermediate ground layer.

[0025] The high-isolation compact filter bank uses a gold wire shielding grid 3: such as Figure 1 As shown, in the top ground plane L6, above filters F1 and F3, there are multiple gold wires with both ends bonded to the grounding pads in the top ground plane L6. These gold wires are arranged in parallel and arched to form a fence-like shielding structure.

[0026] like Figure 1 As shown, the inner surface of the metal cover 1 has a square metal block protruding towards the PCB, i.e., the central metal lump. When the metal cover 1 is installed in place, the central metal lump contacts the central grounding area 2 on the PCB surface, thereby dividing the entire large cavity formed by the metal cover 1 and the PCB into four independent sub-cavities (the sub-cavities are also perpendicular to each other and are isolated by secondary polarization).

[0027] All filter input and output ports are led to pads on the bottom ground plane through metallized vias, forming a QFN-like package interface.

[0028] like Figure 4 The diagram shows the design flow of this invention. This invention employs polarization isolation. Since adjacent filters (such as F1 and F2) are perpendicular, their electric field directions are orthogonal, resulting in naturally weak coupling. The complete intermediate grounding layer acts as an "electromagnetic firewall," blocking vertical coupling. The gold wire array forms a waveguide structure below the cutoff frequency for microwave signals, effectively suppressing surface wave coupling between parallel filters (F1 and F3) on the same layer. The central metal block divides the large cavity, pushing up its resonant frequency and preventing energy coupling through the cavity resonant mode. Selective windowing places the filter in an air medium, reducing the equivalent dielectric constant, which not only weakens coupling but also reduces dielectric loss and improves filter performance.

[0029] Through the above-mentioned innovative three-dimensional hybrid isolation design, this invention achieves an inter-channel isolation of over 60dB without the need for an external metal cavity, while also having the advantages of small size, light weight, and ease of mass production.

[0030] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A high-isolation compact filter bank, characterized in that, include: Bottom ground plane, second filter pattern layer, middle ground layer, fourth filter pattern layer, fifth ground plane, top ground plane; The fourth filter pattern layer has a first filter and a third filter fabricated on it, and the second filter pattern layer has a second filter and a fourth filter fabricated on it. On the horizontal projection plane, the first filter, the second filter, the third filter, and the fourth filter are arranged clockwise along the four sides of the square; the first filter and the second filter, the second filter and the third filter, the third filter and the fourth filter, and the fourth filter and the first filter are all vertically adjacent in the horizontal position.

2. The high-isolation compact filter bank as described in claim 1, characterized in that, The first filter, the second filter, the third filter, and the fourth filter are all microstrip interdigitated structures. The microstrip lines of the second filter and the fourth filter are perpendicular to the microstrip lines of the first filter and the third filter.

3. The high-isolation compact filter bank as described in claim 1, characterized in that, A first window is formed in the intermediate ground layer, the fourth filter pattern layer, the fifth ground plane, and the top ground plane, and the position of the first window corresponds to the second filter and the fourth filter.

4. The high-isolation compact filter bank as described in claim 1, characterized in that, A second window is formed in the fifth ground plane and the top ground plane, and the position of the second window corresponds to the first filter and the third filter.

5. The high-isolation compact filter bank as described in claim 4, characterized in that, In the top ground plane, above the first filter and the third filter, there are multiple gold wires with both ends bonded to the grounding pads in the top ground plane. The gold wires are arranged in parallel and arched to form a fence-like shielding structure.

6. The high-isolation compact filter bank as described in claim 1, characterized in that, The intermediate grounding layer is a metal plane that completely isolates the filters of the second filter pattern layer from the filters of the fourth filter pattern layer in the vertical direction.

7. The high-isolation compact filter bank as described in claim 1, characterized in that, The high isolation compact filter bank also includes a metal cover located above the top ground plane; the center of the inner surface of the metal cover has a square metal block protruding towards the PCB. When the metal cover is installed in place, the square metal block contacts the center ground area of ​​the PCB surface, dividing the entire large cavity formed by the metal cover and the PCB into four independent sub-cavities.

8. The high-isolation compact filter bank as described in claim 1, characterized in that, The input and output ports of the first filter, the second filter, the third filter, and the fourth filter are all led to the pads on the bottom ground plane through metallized vias to form a QFN-like package interface.

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