A planar resonator and filter

Abstract

This invention discloses a planar resonator and filter, belonging to the field of electronic communication technology. The planar resonator is fabricated on a circuit board and consists of two metal strips with lengths ranging from 1 / 4λ to 1 / 12λ: a first metal strip and a second metal strip arranged in parallel and interleaved configurations. One end of the first metal strip is connected to an upper metal ground strip, while the other end is left unconnected; one end of the second metal strip is connected to a lower metal ground strip, while the other end is left unconnected. Using this resonator to construct a planar bandpass filter reduces the inherent size of planar filters, achieving miniaturization. Furthermore, by introducing transmission zeros through cross-coupling between the resonators, frequency selectivity is improved, and a higher level of stopband suppression is achieved, meeting the needs of a wider range of applications. The proposed planar resonator and filter design can be implemented in microstrip circuits, stripline circuits, and suspended microstrip circuits, and is applicable to both broadband and narrowband filter designs, showing broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of electronic communication technology, specifically relating to resonators and filters. Background Technology

[0002] In modern communication systems, resonators and filters play a crucial role in signal transmission and processing. A resonator is an electronic component or device that generates resonance at a specific frequency and can serve as a key component such as a filter or oscillator. Filters constructed from resonators can select signals within a specific frequency range, suppressing unwanted frequency signals or interference signals, thereby improving the performance and reliability of the communication system. In existing technologies, resonators and filters can be implemented using various different structures. Among them, planar resonators and filters are widely used due to their small size, low cost, and ease of integration.

[0003] With the continuous development of communication technology, the performance requirements for traditional planar resonators and filters are also increasing. For example, smaller size to meet miniaturization needs, lower loss to meet energy saving or long-distance transmission needs, and wider stopband suppression to meet high-quality communication needs, so as to adapt to more applications.

[0004] The present invention aims to provide a planar resonator and filter design technology with small size, high performance and easy integration to meet the development needs of modern communication systems. Summary of the Invention

[0005] This invention discloses a new type of planar resonator, such as... Figure 1 As shown, by employing this resonator to construct a planar bandpass filter, the inherent size of planar filters is reduced, achieving miniaturization. Furthermore, by introducing transmission zeros through cross-coupling between resonators, frequency selectivity is improved and a higher level of stopband rejection is achieved, meeting the needs of a wider range of applications. The proposed planar resonator and filter design can be implemented in microstrip circuits, stripline circuits, and suspended microstrip circuits, and is applicable to both broadband and narrowband filter designs, showing broad application prospects.

[0006] The technical solution of the present invention is a planar resonator, which includes: a first metal strip (1), a second metal strip (2), an upper metal ground strip (3), and a lower metal ground strip (4); the upper metal ground strip and the lower metal ground strip (4) are arranged in parallel, the first metal strip (1) and the second metal strip (2) are arranged in parallel and located between the upper metal ground strip and the lower metal ground strip (4), one end of the first metal strip (1) is connected to the upper metal ground strip (3), and the other end is left empty; one end of the second metal strip (2) is connected to the lower metal ground strip (4), and the other end is left empty; the overall length of the coupling structure formed by the first metal strip (1) and the second metal strip (2) is 1 / 4λ to 1 / 12λ, where λ is the waveguide wavelength of the resonant frequency of the resonator; because the first metal strip (1) and the second metal strip (2) overlap in most positions, and the capacitive loading effect formed by the gap (5) between the two can shorten the length of the conventional planar resonator.

[0007] Furthermore, the upper metal grounding strip (3) and the lower metal grounding strip (4) are grounded through metallized vias (6).

[0008] A planar bandpass filter employing the aforementioned planar resonator, such as Figures 2-5 The filter includes: multiple planar resonators, an input feed line (7), and an output feed line (8). Each resonator shares the same upper metal ground strip (3) and the same lower metal ground strip (4). The upper metal ground strip (3) and the lower metal ground strip (4) are parallel. The input feed line (7) is connected to the first-stage planar resonator by taps or coupling, and the output feed line (8) is connected to the last-stage planar resonator by taps or coupling.

[0009] Furthermore, the input feed line (7) is connected to the metal strip outside the first-stage planar resonator by means of taps or coupling, and the output feed line (8) is connected to the metal strip outside the last-stage planar resonator by means of taps or coupling.

[0010] Furthermore, the first metal strip (1) of each planar resonator in the planar bandpass filter can be on the left or right side of the second metal strip (2).

[0011] Furthermore, in the planar bandpass filter, the first metal strip (1) of all planar resonators is on the same side of the second metal strip (2).

[0012] Furthermore, in two adjacent planar resonators in a planar bandpass filter, if the first metal strip (1) of one planar resonator is to the left of the second metal strip (2), then the first metal strip (1) of the other planar resonator is to the right of the second metal strip (2).

[0013] Furthermore, when the input feed line (7) and output feed line (8) are connected to the plane resonator in a coupled connection manner, the input feed line (7) and output feed line (8) are in the shape of a "T". The upper horizontal line of the "T" shape is parallel to the metal strip of the corresponding plane resonator, and the lower "I" shape faces outward, serving as an input or output port.

[0014] Furthermore, the impedance of the input feed (7) and the output feed (8) is 50 ohms.

[0015] The design of the novel planar filter proposed in this invention is applicable to microstrip circuits, stripline circuits, and suspended microstrip circuits, such as... Figure 6 As shown. This invention reduces the inherent size of planar filters, achieving miniaturized design, and further improves frequency selectivity and achieves a higher level of stopband rejection by introducing transmission zeros through cross-coupling between resonators, thus meeting the needs of more applications. Attached Figure Description

[0016] Figure 1 This is a circuit diagram of a single planar resonator of the present invention.

[0017] Figure 2 This is a circuit diagram of the tapped interdigitated planar bandpass filter of the present invention.

[0018] Figure 3 This is a circuit diagram of the coupled interdigital planar bandpass filter of the present invention.

[0019] Figure 4 This is a circuit diagram of the tapped comb-type planar bandpass filter of the present invention.

[0020] Figure 5 This is a circuit diagram of the coupled comb-type planar bandpass filter of the present invention.

[0021] Figure 6 These are three planar circuit cross-sectional structure diagrams suitable for the present invention.

[0022] Figure 7 This is a physical diagram of a fourth-order tapped interdigital microstrip bandpass filter, a specific embodiment of the present invention.

[0023] Figure 8 The graph shows the test data of the tapped interdigital microstrip bandpass filter, a specific implementation of the present invention. The horizontal axis represents frequency in GHz, and the vertical axis represents S-parameters in dB. The dashed line represents the reflection S11 curve, and the solid line represents the transmission S21 curve.

[0024] In the figure, 1-first metal strip, 2-second metal strip, 3-upper metal grounding strip, 4-lower metal grounding strip, 5-internal coupling gap of a single resonator, 6-metallized via, 7-input feed line, 8-output feed line. Detailed Implementation

[0025] The technical solution of this invention employs a novel planar resonator structure to construct a planar microwave bandpass filter. For example... Figure 1 As shown, the proposed resonator consists of two metal strips, one end open and the other shorted to ground. Each metal strip is of equal length, with an initial length of 1 / 4λ. The two metal strips are placed offset from each other, and coupling occurs through the gap between them. The resonator overlaps in most areas, and the capacitive loading effect created by the gap coupling can shorten the overall length of the resonator; therefore, its overall length should be less than 1 / 4λ. If the coupling gap is smaller, the width of the metal strips is narrower, and the overlap is greater, the coupling effect is stronger, thus resulting in a shorter resonator length. Theoretically, the maximum length of the resonator can approach 1 / 12λ. Figures 2-5 As shown, the proposed planar bandpass filter circuit consists of multiple planar resonators, input / output feed lines, and upper and lower metal grounding strips. Depending on the feeding method of the input / output feed lines and the arrangement of the planar resonators, four different circuit structures can be constructed:

[0026] 1. Tapped interdigitated type: Its circuit is as follows Figure 2 As shown, the input / output feed lines are tapped to the resonators at the beginning and end, and the positions of each stage of the resonators are arranged symmetrically with respect to the geometric center of the filter.

[0027] 2. Coupled interdigital type, its circuit is as follows: Figure 3 As shown, the input / output feed lines are coupled to the resonators at both ends, and the positions of each stage of the resonators are arranged symmetrically with respect to the geometric center of the filter.

[0028] 3. Tapped comb type, its circuit is as follows: Figure 4 As shown, the input / output feed lines are tapped to the resonators at the beginning and end, and the positions of each stage of the resonators are arranged in a mirror-symmetric manner with respect to the geometric center of the filter.

[0029] 4. Coupled comb type, its circuit is as follows: Figure 5 As shown, the input / output feed lines are coupled to the resonators at both ends, and the positions of each stage of the resonators are arranged in a mirror-symmetric manner with respect to the geometric center of the filter.

[0030] Tapped circuits produce stronger coupling effects than coupled circuits, making them suitable for broadband filter design. Interdigitated circuits also produce stronger coupling effects than comb circuits, making them suitable for broadband filter design as well. Conversely, for narrowband filter design, using coupled and comb circuits allows for a more compact filter size.

[0031] The proposed planar bandpass filter has the following advantages compared to conventional planar bandpass filters:

[0032] 1. Conventional planar filters typically use resonators with open circuits at both ends, and their length is 1 / 2λ. However, the resonator length of the planar filter is between 1 / 4λ and 1 / 12λ, thus enabling miniaturized filter design.

[0033] 2. As the resonator shortens, the parasitic passband of the filter it forms will be stretched to the far end of the spectrum, thus achieving wider stopband suppression and causing spurious frequencies to move away from the fundamental resonant frequency.

[0034] 3. Since one end of the resonator is connected to the metal ground strip, non-adjacent resonators are connected through the metal ground strip, forming a second coupling path, thus generating cross-coupling. Therefore, the upper stopband edge of the filter will introduce a near-end transmission zero, thereby improving the stopband steepness and stopband depth, resulting in better filtering characteristics; or a filter of a lower order can be used to achieve the required filtering characteristics, thereby reducing the in-band insertion loss of the filter.

[0035] This invention relates to a novel planar resonator, characterized by circuitry etched onto a metal layer on the surface of a circuit board. Each resonator circuit comprises two metal strips of equal length, ranging from 1 / 4λ to 1 / 12λ, placed offset from each other and coupled through a gap to form a planar resonator. One end of each metal strip is open-circuited, while the other end is connected to a metal ground strip to achieve a short circuit to ground. The metal ground strip passes through multiple metallized vias and connects to the metal ground on the back of the circuit board.

[0036] Based on the input / output feed method and the resonator arrangement, four types of planar bandpass filter circuits can be constructed: tapped interdigital filter circuits, coupled interdigital filter circuits, tapped comb filter circuits, and coupled comb filter circuits. Among them, the tapped interdigital filter circuit is most suitable for broadband filter design, while the coupled comb filter circuit is most suitable for narrowband filter design.

[0037] A physical diagram of a fourth-order microstrip bandpass filter is shown below. Figure 7As shown. The circuit is housed within a metal cavity, and the connectors are connected to the input / output feed lines through the metal cavity. The circuit board is a Rogers 5880, 0.254mm thick, and uses a tapped interdigitated design, etched onto the surface metal layer of the circuit board. The circuit dimensions are 10mm × 6.4mm. The test curves are shown below. Figure 8 As shown, the center frequency is 14.2GHz, the operating bandwidth is 400MHz, the in-band reflection is better than 18dB, the out-of-band rejection is greater than 30dB@10GHz~13GHz&14.8GHz~25.2GHz, and a transmission null occurs at 15.2GHz.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A planar bandpass filter employing a planar resonator, the filter comprising: Multiple planar resonators, input feed line (7), and output feed line (8) are provided. Each planar resonator shares the same upper metal ground strip (3) and the same lower metal ground strip (4). The upper metal ground strip (3) and the lower metal ground strip (4) are parallel. The input feed line (7) is connected to the first-stage planar resonator by taps or coupling. The output feed line (8) is connected to the last-stage planar resonator by taps or coupling. The planar resonator includes: a first metal strip (1), a second metal strip (2), an upper metal ground strip (3), and a lower metal ground strip (4); the upper metal ground strip and the lower metal ground strip (4) are arranged in parallel, the first metal strip (1) and the second metal strip (2) are arranged in parallel and located between the upper metal ground strip and the lower metal ground strip (4), one end of the first metal strip (1) is connected to the upper metal ground strip (3), and the other end is left unattended; one end of the second metal strip (2) is connected to the lower metal ground strip (4), and the other end is left unattended; the overall length of the coupling structure formed by the first metal strip (1) and the second metal strip (2) is... , The waveguide wavelength is the resonant frequency of the resonator; the upper metal grounding strip (3) and the lower metal grounding strip (4) are grounded through metallized vias (6); The first metal strip (1) of each planar resonator can be on the left or right side of the second metal strip (2); In two adjacent planar resonators, if the first metal strip (1) of one planar resonator is to the left of the second metal strip (2), then the first metal strip (1) of the other planar resonator is to the right of the second metal strip (2).

2. The planar bandpass filter as described in claim 1, characterized in that, The input feed line (7) is connected to the metal strip outside the first-stage planar resonator by tapping or coupling, and the output feed line (8) is connected to the metal strip outside the last-stage planar resonator by tapping or coupling.

3. The planar bandpass filter as described in claim 1, characterized in that, When the input feed line (7) and output feed line (8) are connected to the plane resonator in a coupled connection manner, the input feed line (7) and output feed line (8) are in the shape of a "T". The upper horizontal line of the "T" shape is parallel to the metal strip of the corresponding plane resonator, and the lower "1" shape faces outward, serving as the input or output port.

4. The planar bandpass filter as described in claim 1, characterized in that, The impedance of the input feed (7) and the output feed (8) is 50 ohms.

5. The planar bandpass filter according to any one of claims 1-4, characterized in that... It can be applied to microstrip circuits, stripline circuits, or suspended microstrip circuits.

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