Wide-stop-band cavity inverting filtering power divider

Abstract

The invention relates to a wide-stop-band cavity inverting filtering power divider, which comprises a metal cavity, a three-stage resonator arranged in the metal cavity, an input terminal and two output terminals, the three-stage resonator is formed by cascading three double-ridge waveguide resonators, and the two output terminals are arranged in the metal cavity. Adjacent double-ridge waveguide resonators are coupled through an evanescent mode rectangular waveguide, the coupling strength between the resonators can be adjusted through the width of the evanescent mode rectangular waveguide, the width of the evanescent mode rectangular waveguide is smaller than the width of the metal cavity, and the second-stage double-ridge waveguide resonator forms cross coupling with a source and a load. And cross coupling is formed between the first-stage double-ridge waveguide resonator and the third-stage double-ridge waveguide resonator. The inverted filtering power divider is designed by adopting the double-ridge waveguide and the evanescent mode rectangular waveguides with unequal section widths, the size of the device is reduced, a zero point is introduced into an upper stop band, and the depth of out-of-band rejection is improved. In addition, a metal plate is inserted in the middle of the cavity of the filtering power divider, the upper stop band width is expanded, and good out-of-band performance is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless communications, and in particular relates to a cavity inversion filter power divider with a wide stopband. Background Art

[0002] Waveguides have the advantages of low loss and high power handling capability, and are widely used in antenna feed networks, etc. Compared with rectangular waveguides, double-ridge waveguides have lower cutoff frequencies and wider single-mode operating bandwidths. These characteristics indicate that devices based on double-ridge waveguides will have more compact sizes and better spurious-free performance at the fundamental mode frequency. In order to adapt to the development trend of high integration, small size, and low loss in modern communication systems, fusion design has received widespread attention. As important microwave devices in the RF front end, the cascade design of filters and power dividers is of great significance to improving system integration. Filter power dividers can distribute power within a specific passband to avoid cascade losses.

[0003] However, there are cavity filter power dividers using rectangular waveguides, which have the characteristics of low loss and significant power handling capacity, but are large in size and cannot meet the requirements of miniaturization of communication systems. In order to reduce the size of the device, researchers have proposed cavity filter power dividers using dielectric waveguides and dielectric resonator loaded waveguides, but dielectric resonators and dielectric waveguides have crowded resonant modes, so they have poor harmonic characteristics. In order to improve the out-of-band performance and reduce the size at the same time, the present invention uses a double-ridge waveguide to propose a wide stopband cavity reverse filter power divider. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies in the above-mentioned prior art and to provide a wide stopband cavity inverting filter power divider, which can reduce the size and improve the out-of-band performance.

[0005] In order to achieve the purpose of the present invention, the present invention provides a wide stopband cavity inverting filter power divider, which includes a metal cavity, a three-stage resonator placed in the metal cavity, an input terminal and two output terminals respectively arranged at the input end and the output end of the metal cavity, characterized in that: the three-stage resonator is composed of three double-ridged waveguide resonators in cascade, each double-ridged waveguide resonator includes two ridge blocks respectively arranged at the top and the bottom of the metal cavity, the input terminal is connected to a ridge block of the first-stage double-ridged waveguide resonator, and the two output terminals are connected to the two ridge blocks of the third-stage double-ridged waveguide resonator in a one-to-one correspondence; the adjacent double-ridged waveguide resonators are coupled by an evanescent mode rectangular waveguide, the width of the evanescent mode rectangular waveguide is smaller than the width of the metal cavity, the second-stage double-ridged waveguide resonator forms a cross coupling with the source and the load respectively, and the first-stage double-ridged waveguide resonator forms a cross coupling with the third-stage double-ridged waveguide resonator.

[0006] Furthermore, the coupling strength between adjacent double-ridged waveguide resonators is reduced by reducing the width of the evanescent mode rectangular waveguide; the coupling strength between adjacent double-ridged waveguide resonators is increased by reducing the spacing between adjacent double-ridged waveguide resonators, and at the same time, cross-coupling is formed between the second-stage double-ridged waveguide resonator and the source and the load respectively, and cross-coupling is formed between the first-stage double-ridged waveguide resonator and the third-stage double-ridged waveguide resonator.

[0007] The filter power divider proposed by the present invention is formed by cascading a double-ridge waveguide and an evanescent mode rectangular waveguide with unequal cross-sectional widths. The double-ridge waveguide serves as a resonator, and the evanescent mode rectangular waveguide between adjacent double-ridge waveguides serves as a coupling to connect the resonators. When the double-ridge waveguide works in the fundamental mode state, it has the inherent property of equal amplitude and inversion, so that the output of the filter power divider is inverted. The coupling strength between the resonators is determined by the width of the evanescent mode rectangular waveguide used as a coupling between the two resonators and the distance between the resonators. Reducing the width of the evanescent mode rectangular waveguide can reduce the coupling strength. Therefore, it is necessary to shorten the distance between the resonators to achieve the required coupling strength. Therefore, using an evanescent mode rectangular waveguide with unequal cross-sectional widths as a coupling between the resonators can reduce the size of the device. In addition, due to the reduction in the distance between the resonators, cross-coupling is introduced. Specifically, the second-stage double-ridge waveguide resonator forms cross-coupling with the source and the load respectively, and the first-stage double-ridge waveguide resonator forms cross-coupling with the third-stage double-ridge waveguide resonator. The introduced cross-coupling generates additional zeros in the upper stopband, and the additional zeros can increase the depth of out-of-band suppression. In order to expand the bandwidth of the upper stopband and achieve good out-of-band performance, a metal plate is inserted in the middle of the filter power divider cavity, extending from the middle ridge waveguide resonator to the output end. Because the middle plane of the filter power divider is an open surface of the common mode, the metal plate plays a key role in blocking the propagation of common mode high-order modes. The fundamental mode of the double-ridge waveguide exhibits mirror symmetry along the xz plane, so the inserted metal plate will not affect the fundamental mode, but can effectively suppress harmonics and achieve good out-of-band performance. The power distribution ratio designed by the present invention is 1:1, and weak coupling can be used to extract the external quality factors of the excitation source and the load respectively. When the external quality factor of the load is twice the quality factor of the external excitation source, the position of the probe connection on the ridge can be determined.

[0008] Experiments show that the present invention has better power handling capability, smaller size, and lower insertion loss, with the simulated insertion loss being less than 0.06 dB; the stopband suppression bandwidth on the differential mode is wide, reaching 30 dB in the frequency range of 4.35 GHz to 11.26 GHz, achieving spurious-free suppression of 3 times the center frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be further described below in conjunction with the accompanying drawings; Figure 1It is a schematic diagram of the 3D structure of a wide stopband cavity inversion filter power divider according to an embodiment of the present invention.

[0010] 2 is a schematic diagram of a wide stopband cavity inverting filter power divider according to an embodiment of the present invention, (a) a front view structural diagram, (b) a top view structural diagram, and (c) a side view structural diagram.

[0011] Figure 3 It is a topological diagram of the wide stopband cavity inversion filter power divider of this embodiment.

[0012] Figure 4 The invention is a wide stopband cavity inversion filter power divider (a) external excitation source quality factor Q eS (b) Load external quality factor Q eL Extract result graph.

[0013] Figure 5 The coupling coefficient of the cavity inversion filter power divider with a wide stopband of the present invention is K 12 Extract result graph.

[0014] Figure 6 This is a diagram of S-parameter simulation results of a wide-stopband cavity inverting filter power divider of the present invention.

[0015] Figure 7 This is a simulation result diagram of phase and amplitude imbalance of a wide stopband cavity inversion filter power divider of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0017] The cavity inverse phase filter power divider with wide stopband in the embodiment of the present invention has a three-dimensional structure as shown in FIG. Figure 1 As shown, for the purpose of specific description, FIG2 shows a schematic diagram of the structure of the present invention in front view, top view and side view.

[0018] The wide stopband cavity inversion filter power divider of this embodiment comprises a metal cavity 4, a three-stage resonator placed in the metal cavity 4, an input terminal Port1 and two output terminals Port2 and Port3 respectively arranged at the input and output ends of the metal cavity 4, wherein the input terminal Port1 is the source S; the two output terminals Port2 and Port3 are the loads L. + , L -. The three-stage resonator is composed of three double-ridged waveguide resonators (first-stage double-ridged waveguide resonator R1, second-stage double-ridged waveguide resonator R2, and third-stage double-ridged waveguide resonator R3) in cascade. Each double-ridged waveguide resonator includes two metal ridge blocks located at the top and bottom of the metal cavity 4. The input terminal Port1 is connected to the metal ridge block on the upper side of the first-stage double-ridged waveguide resonator R1, and the two output terminals Port2 and Port3 are respectively connected to the two metal ridge blocks of the third-stage double-ridged waveguide resonator R3 in a one-to-one correspondence. In this example, the output terminals Port2 and Port3 are placed at symmetrical positions of the upper and lower ridges at the output end to achieve a one-to-two power distribution. When the double-ridged waveguide works in the fundamental mode, it has the inherent property of equal-amplitude inversion, which makes the output of the filter power divider inverted. As shown Figure 1 As shown in FIG2 , the ridge block length of the first-stage double-ridged waveguide resonator R1 is equal to the ridge block length of the third-stage double-ridged waveguide resonator R3 and is greater than the ridge block length of the second-stage double-ridged waveguide resonator R2, the ridge block width of the first-stage double-ridged waveguide resonator R1 is equal to the ridge block width of the second-stage double-ridged waveguide resonator R2 and the ridge block width of the third-stage double-ridged waveguide resonator R3, and the spacing between adjacent resonators is equal. The ridge block height of the second-stage double-ridged waveguide resonator R2 is equal to the ridge block height of the third-stage resonator R3 and is less than the ridge block height of the first-stage double-ridged waveguide resonator R1.

[0019] Shortening the width of the evanescent mode rectangular waveguide between adjacent resonators can reduce the coupling strength. In order to achieve the required coupling strength, the distance between the resonators must be shortened. Therefore, using evanescent mode rectangular waveguides with unequal widths can reduce the size of the device. Figure 1 As shown in Figure 2 (b), in this embodiment, adjacent double-ridged waveguide resonators are coupled through an evanescent mode rectangular waveguide, and the width of the evanescent mode rectangular waveguide is less than the width of the metal cavity 4. That is, the metal cavity between adjacent double-ridged waveguide resonators is narrower, that is, the metal cavity uses an evanescent mode rectangular waveguide with unequal cross-sectional widths. The coupling strength between the resonators is determined by the width of the evanescent mode rectangular waveguide used as the coupling between the two resonators and the distance between the resonators. Reducing the width of the evanescent mode rectangular waveguide can reduce the coupling strength. Therefore, it is necessary to shorten the distance between the resonators to achieve the required coupling strength. Therefore, using an evanescent mode rectangular waveguide with unequal cross-sectional width as the coupling between the resonators can reduce the size of the device. In addition, due to the reduction in the distance between the resonators (adjusting the spacing between adjacent double-ridged waveguide resonators to a certain distance), cross-coupling will be introduced. Specifically, the second-stage double-ridged waveguide resonator R2 is respectively connected to the load L + , L - (Two output terminals Port2, Port3) form cross coupling, and the first-stage double-ridge waveguide resonator R1 and the third-stage double-ridge waveguide resonator R3 form cross coupling. The topological structure of this filter power divider is shown in Figure 3The cross coupling creates additional zeros in the upper stopband. The additional zeros can increase the depth of out-of-band suppression.

[0020] In order to expand the upper stopband bandwidth and achieve good out-of-band performance, in this embodiment, a metal plate 5 with a thickness of 0.4 mm parallel to the bottom surface of the metal cavity 4 is provided at the waistline inside the metal cavity 4, and the metal plate 5 and the metal cavity 4 are grounded. The metal plate 5 extends inward from the output end of the metal cavity 4 to between the two ridge blocks of the second-stage double-ridged waveguide resonator R2, and there is a gap between the metal plate 5 and the two ridge blocks of the second-stage double-ridged waveguide resonator R2 and the two ridge blocks of the third-stage double-ridged waveguide resonator R3. Because the middle plane A-A1 of the filter power divider is an open surface of the common mode, the metal plate 5 can block the transmission of the common mode high-order mode. The fundamental mode of the double-ridged waveguide shows mirror symmetry along A-A1, so the inserted metal plate 5 will not affect the fundamental mode of the double-ridged waveguide, but can effectively suppress harmonics and expand the upper stopband bandwidth. However, the insertion of the metal plate will affect the phase and amplitude imbalance of the filter power divider, so the metal plate is designed to be in the shape of a step width to achieve good matching. Specifically, the portion of the metal plate 5 located between the two ridge blocks of the second-level double-ridged waveguide resonator coincides with the projection of the ridge block of the second-level double-ridged waveguide resonator, the portion of the metal plate 5 located between the second-level double-ridged waveguide resonator and the third-level double-ridged waveguide resonator coincides with the projection of the lost mode rectangular waveguide there, and the portion of the metal plate 5 located between the two ridge blocks of the third-level double-ridged waveguide resonator coincides with the projection of the metal cavity 4 there, as shown in FIG2(b).

[0021] The parameters involved in the filter power divider of this embodiment are as follows: a = 25.2 mm, b = 12.8 mm, a 1 = 10 mm, b 1 = 11.8 mm, b 2 = 12 mm, l 1 = 8mm, l 2 = 4.3 mm, d 1 = 2.4 mm, d 2 = 6.2 mm, d 3 = 2.2 mm, h 1 = 11.3 mm, h 2 = 5.6mm, w = 4.6 mm.

[0022] The present invention sets a third-order filter passband with a ripple factor of 0.05dB, a center frequency of 3.5GHz, and a relative bandwidth of 20%. The circuit can be fitted by a Chebyshev low-pass prototype filter, and the theoretically required coupling coefficient and quality factor can be calculated by a formula. Then, the quality factor and the coupling coefficient between adjacent resonant cavities can be extracted by electromagnetic simulation software, such as Figure 4 , Figure 5 Give separately Q eS , Q eL The relationship between the probe length and height, as well as the relationship between the coupling coefficient and the reduced width and distance of the evanescent mode rectangular waveguide between the two double-ridge waveguide resonators, are used to obtain specific physical parameters by making the two equal. After fine-tuning, a cavity inverting filter power divider with good performance and wide stopband is finally designed. The final S parameter simulation results are shown in the figure below. Figure 6 , with a center frequency of 3.5 GHz, a 3 dB fractional bandwidth (FBW) of approximately 20%, and a frequency range of 3.18 to 3.89 GHz. The measured return loss (|S 11 |) and the insertion loss at both output ends (|S 21 |) are less than 16 dB and 0.06 dB respectively. The additional zero introduced by cross coupling improves the depth of upper stopband suppression, and the upper stopband bandwidth is wide, greater than 30 dB in the range of 4.35 ~ 11.26 GHz, achieving spurious-free suppression of three times the center frequency. The inserted metal plate has a slight effect on the amplitude and phase imbalance, such as Figure 7 , the amplitude and phase imbalances at the two output ends are 0.21 dB and 2° respectively.

[0023] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A wide stopband cavity inverting filter power divider, comprising a metal cavity (4), a three-stage resonator disposed in the metal cavity (4), an input terminal (Port1) and two output terminals (Port2, Port3) disposed at the input and output ends of the metal cavity (4), characterized in that: The three-stage resonator is composed of three double-ridged waveguide resonators (R1, R2, R3) connected in cascade, each double-ridged waveguide resonator comprising two ridge blocks respectively arranged at the top and bottom of a metal cavity (4), the input terminal (Port1) is connected to a ridge block of the first-stage double-ridged waveguide resonator (R1), and the two output terminals (Port2, Port3) are connected to two ridge blocks of the third-stage double-ridged waveguide resonator (R3) in a one-to-one correspondence; the adjacent double-ridged waveguide resonators are coupled via an evanescent mode rectangular waveguide, the width of the evanescent mode rectangular waveguide being smaller than the width of the metal cavity (4), and the second-stage double-ridged waveguide resonator is respectively connected to a source (S) and a load (L + , L - ) forms a cross coupling, and a cross coupling is formed between the first-stage double-ridged waveguide resonator (R1) and the third-stage double-ridged waveguide resonator (R3).

2. The wide stopband cavity inversion filter power divider according to claim 1, characterized in that: The cross coupling creates an additional zero in the upper stop band.

3. The wide stopband cavity inversion filter power divider according to claim 1, characterized in that: The coupling strength between adjacent double-ridge waveguide resonators is reduced by reducing the width of the evanescent mode rectangular waveguide; The coupling strength between adjacent double-ridged waveguide resonators is improved by reducing the spacing between adjacent double-ridged waveguide resonators, and the second-stage double-ridged waveguide resonator is connected to the source (S) and the load (L + , L - ), and cross coupling is formed between the first-stage double-ridged waveguide resonator (R1) and the third-stage double-ridged waveguide resonator (R3).

4. The wide stopband cavity inversion filter power divider according to claim 1, characterized in that: A metal plate (5) parallel to the bottom surface of the metal cavity (4) is arranged at the waistline inside the metal cavity (4), and the metal plate (5) and the metal cavity (4) are grounded; the metal plate (5) extends inward from the output end of the metal cavity (4) to between two ridge blocks of the second-stage double-ridge waveguide resonator, and there is a gap between the metal plate and the two ridge blocks of the second-stage double-ridge waveguide resonator and the two ridge blocks of the third-stage double-ridge waveguide resonator; the metal plate (5) is used to block the transmission of common-mode high-order modes, effectively suppress harmonics, and expand the upper stopband bandwidth.

5. The wide stopband cavity inversion filter power divider according to claim 3, characterized in that: The metal plate (5) has a trapezoidal structure; a portion of the metal plate (5) located between two ridge blocks of the second-level double-ridged waveguide resonator coincides with a projection of the ridge block of the second-level double-ridged waveguide resonator; a portion of the metal plate (5) located between the second-level double-ridged waveguide resonator and the third-level double-ridged waveguide resonator coincides with a projection of the lost mode rectangular waveguide there; and a portion of the metal plate (5) located between two ridge blocks of the third-level double-ridged waveguide resonator coincides with a projection of the metal cavity (4) there.

6. The wide stopband cavity inverse filter power divider according to claim 1, characterized in that: The spine block is a metal block.

7. The wide stopband cavity inversion filter power divider according to claim 1, characterized in that: The ridge block length of the first-level double-ridged waveguide resonator is equal to the ridge block length of the third-level double-ridged waveguide resonator and is greater than the ridge block length of the second-level double-ridged waveguide resonator, and the ridge block width of the first-level double-ridged waveguide resonator is equal to the ridge block width of the second-level double-ridged waveguide resonator and the ridge block width of the third-level double-ridged waveguide resonator.

8. The wide stopband cavity inversion filter power divider according to claim 1, characterized in that: The spacings between adjacent resonators are equal.

9. The wide stopband cavity inversion filter power divider according to claim 1, characterized in that: The ridge block height of the second-stage double-ridged waveguide resonator is equal to the ridge block height of the third-stage resonator and is smaller than the ridge block height of the first-stage double-ridged waveguide resonator.

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