Adjustable notch filter based on a ridge waveguide sspp structure

Abstract

This invention provides an adjustable notch filter based on a ridge waveguide SSPP structure, relating to the field of wireless communication technology. By introducing independent planar adjustable notch units into the ridge waveguide SSPP structure, the notch frequency can be continuously adjusted without compromising the surface wave propagation characteristics and frequency-selective transmission response of the SSPP. The SSPP structure is formed by periodically etching multiple grooves along the propagation direction on a metal ridge, with continuous portions of the metal ridge maintained between adjacent grooves. These periodic grooves modulate the dispersion characteristics of the electromagnetic field within the ridge waveguide, enabling the ridge waveguide to support equivalent surface plasmon wave propagation, thereby forming a stable frequency-selective transmission response within a predetermined frequency range. The planar adjustable notch unit constructs a main transmission path and a secondary transmission path, utilizing the destructive interference of the two paths at a specific frequency to create a notch effect. Simultaneously, by changing the equivalent capacitance value of the varactor diode, the notch frequency can be continuously adjusted within the predetermined frequency range.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, specifically to an adjustable notch filter based on a ridge waveguide SSPP structure. Background Technology

[0002] In recent years, spoof surface plasmon polaritons (SSPPs) have been widely used to construct various broadband bandpass filters and frequency-selective transmission structures due to their inherent low-pass transmission characteristics and cutoff frequencies that can be flexibly adjusted through geometric parameters. Existing research typically involves introducing periodic grooves or loaded units on the metal surface to control the dispersion characteristics of SSPPs, thereby obtaining the desired bandpass response.

[0003] Building upon this foundation, some studies have attempted to introduce active devices such as varactor diodes into SSPP structures to achieve tunable bandstop or notch filtering functionality. However, these tunable structures are mostly concentrated in planar SSPP transmission lines or microstrip / stripline SSPP structures. For SSPP transmission structures based on rectangular waveguides, due to their different field distribution and high impedance characteristics compared to planar structures, traditional planar tunable circuits are difficult to directly introduce. Therefore, achieving frequency-tunable notch response and active control within cavity technology still faces significant challenges.

[0004] Therefore, how to effectively integrate cavity technology with planar technology and achieve active control without introducing complex transitions remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] Therefore, this invention provides an adjustable notch filter based on a ridge waveguide SSPP structure to solve the above problems. The adjustable notch filter based on a ridge waveguide SSPP structure provided by this invention overcomes the difficulty of integrating planar adjustable notch units and the limited active control capability of existing cavity structures. It proposes a transmission structure that achieves adjustable notch frequency while maintaining the surface wave propagation characteristics formed by the ridge waveguide SSPP structure, so as to meet the requirements of microwave systems for high-performance and adjustable frequency selective filtering functions.

[0006] The present invention provides an adjustable notch filter based on a ridge waveguide SSPP structure, the structure comprising: a rectangular cavity, wherein a metal ridge is disposed within the rectangular cavity; a groove structure is disposed on the metal ridge; the groove structure comprises five sets of T-shaped grooves disposed in the middle region of the metal ridge along the Z-axis direction, and rectangular grooves are disposed on the outer sides of the T-shaped grooves on both sides.

[0007] Furthermore, intermittent grooves are formed in the metal ridge areas on both sides of the central T-shaped groove, and strip lines are arranged in the intermittent grooves. The strip lines include a substrate, and a top layer strip line conductor and a bottom layer strip line conductor are respectively provided on the upper and lower surfaces of the substrate, and through holes are reserved to fix the substrate.

[0008] Furthermore, a slot is formed on the top strip conductor to embed a varactor diode bias circuit. The varactor diode bias circuit includes a DC blocking capacitor, a varactor diode, a high-resistance resistor, and a wire. The wire extends from one end of the high-resistance resistor to the edge of the rectangular cavity to connect to an external bias voltage source.

[0009] Furthermore, a via is provided at the end of the varactor diode to connect to the underlying stripline conductor; the underlying stripline conductor extends to the edge of the substrate to connect to the metal ridge.

[0010] Furthermore, the rectangular cavity has transition shafts forming ports at both ends that connect to the metal ridge. The bottom of the metal ridge is fitted to the bottom of the rectangular cavity.

[0011] By introducing independent planar tunable notch elements into the ridge waveguide SSPP structure, the notch frequency can be continuously adjusted without destroying the surface wave propagation characteristics and frequency-selective transmission response of the SSPP.

[0012] The groove structure is an SSPP structure, which is formed by periodically etching multiple grooves along the propagation direction on a metal ridge, with continuous portions of the metal ridge maintained between adjacent grooves. The periodic grooves are used to modulate the dispersion characteristics of the electromagnetic field within the ridge waveguide, enabling the ridge waveguide to support the propagation of equivalent surface plasmon waves, thereby forming a stable frequency-selective transmission response within a predetermined frequency range.

[0013] At the continuous metal ridge between adjacent grooves, an axially discontinuous region is set along the propagation direction as a discontinuous groove, and a stripline transmission line is embedded in this discontinuous region as an intermediate connecting segment, so that the two ends of the stripline are connected to the metal ridges on both sides of the discontinuous region. By setting the stripline in the continuous metal ridge between the grooves, rather than directly embedding it inside the SSPP groove, significant disturbances to the electromagnetic field distribution and dispersion characteristics in the SSPP structure can be avoided, thereby maintaining the original SSPP transmission characteristics.

[0014] The stripline transmission line further embeds a varactor diode bias circuit, and a via is provided at the end of the varactor diode to connect to the underlying stripline conductor to realize two transmission paths, main and secondary. When the signal is transmitted through the main path and the secondary path respectively, it satisfies the requirements of similar amplitude and phase difference at a specific frequency. When the conditions are met, the two signals cancel each other out at the point of convergence, thus introducing a significant notch characteristic within the SSPP transmission passband. By adjusting the equivalent capacitance of the varactor diode, the phase characteristics and equivalent impedance of the secondary transmission path can be changed, thereby altering the frequency position at which the primary and secondary paths meet the cancellation condition, thus achieving adjustable notch frequency.

[0015] The present invention has the following advantages over the prior art:

[0016] 1. This invention maintains good transmission performance over a wide operating frequency band. Within a frequency bandwidth of 1.5-2.4 GHz, the insertion loss is less than 0.3 dB and the return loss is better than 15 dB, exhibiting low-loss and wide-bandwidth transmission characteristics. Simultaneously, this invention constructs a main transmission path and a secondary transmission path, and utilizes the destructive interference effect of the two paths at a specific frequency to form a significant notch response at 2.14 GHz, thereby effectively suppressing signals near this specific frequency point. Furthermore, by adjusting the equivalent capacitance value of the varactor diode, the notch frequency can be continuously adjusted within the range of 2.07-2.23 GHz, indicating that the filter has good electrical tuning capability.

[0017] 2. This invention spatially and functionally separates the SSPP modulation structure and the planar adjustable notch structure. The SSPP structure is mainly used to realize surface wave guidance and broadband transmission, while the adjustable notch function is mainly realized by the embedded stripline resonant unit. This achieves flexible control of the notch frequency while maintaining the overall low loss and high power capacity characteristics.

[0018] 3. This invention integrates a planar tuned structure with a ridge waveguide SSPP structure by embedding a stripline transmission structure at the axial discontinuity of the metal ridge, making it an intermediate connecting segment in the SSPP transmission path, and introducing an adjustable notch filter unit while minimizing the impact on the main transmission characteristics. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 These are schematic diagrams of the present invention: (a) is a schematic diagram of the overall structure, (b) is a schematic diagram of the top strip conductor structure, and (c) is a schematic diagram of the bottom strip conductor structure.

[0021] Figure 2This is a top view of the present invention, (a) is a structural schematic diagram, and (b) is a parameter annotation diagram;

[0022] Figure 3 These are side views of the present invention, (a) being a structural schematic diagram and (b) being a parameter annotation diagram;

[0023] Figure 4 This is a graph showing the simulation results of the S-parameters of this invention.

[0024] Explanation of reference numerals in the attached figures:

[0025] 1. Rectangular cavity; 2. Metal ridge; 3. Grating; 4. T-slot; 5. Rectangular slot; 6. Spacing slot; 7. Substrate; 8. Non-metallized via; 9. Top strip conductor; 10. DC blocking capacitor; 11. Varactor diode; 12. High resistance resistor; 13. Wire; 14. Bottom strip conductor; 15. Metallized via. Detailed Implementation

[0026] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] This embodiment provides an tunable notch filter based on a ridge waveguide SSPP structure, the structure of which is as follows: Figures 1 to 3As shown, the structure comprises two parts: a ridge waveguide (SSPP) and a stripline. A metal ridge 2 extends axially along the signal propagation direction and forms a ridge waveguide transmission structure with the rectangular cavity 1. Periodic grooves are etched on the metal ridge 2 to form the SSPP structure, including T-grooves 4 and rectangular grooves 5. By rationally designing the period, depth, and width of the grooves, the dispersion characteristics of the electromagnetic field within the ridge waveguide can be modulated, enabling the structure to support equivalent surface plasmon wave propagation within the target frequency band, thereby effectively controlling the upper cutoff frequency of the filter. However, the slotting alters the impedance of the original continuous metal ridge. Therefore, slots are formed on the side of the rectangular cavity 1 to create a grating structure 3 to balance the impedance between the slotted region and the continuous metal ridge region. Based on this, an axially discontinuous groove 6 is introduced along the propagation direction on the continuous metal ridge 2 of adjacent grooves, and a stripline transmission line is arranged in this discontinuous region. This stripline is composed of a substrate 7, a top stripline conductor 9, and a bottom stripline conductor 14. The substrate 7 and the top stripline conductor 9 connect the stripline as an intermediate connecting segment to the metal ridges 2 on both sides of the discontinuity. A varactor diode bias circuit is further introduced into the stripline transmission line. The end of the varactor diode is connected to the bottom stripline 14 and then to the metal ridge 2 through a metallized via 15, creating two transmission paths, a main path and a secondary path. The two signals cancel each other out at the junction, thus introducing a significant notch characteristic in the SSPP transmission passband. By adjusting the equivalent capacitance value of the varactor diode 11, the phase characteristics and equivalent impedance of the secondary transmission path can be changed, thereby changing the frequency position where the main path and the secondary path satisfy the cancellation condition, and realizing the adjustable notch frequency. The rectangular cavity 1 and the metal ridge 2 of the ridge waveguide are both made of aluminum. The stripline is made of RO4350B dielectric substrate and copper is deposited on its surface.

[0029] Parameters involved: a = 45, b = 20, l = 154.8, l s Unit: mm)

[0030] Figure 4 The S-parameter simulation results for this embodiment are presented. Figure 4It can be seen that by adjusting the equivalent capacitance value of the varactor diode 11, the notch frequency point within the passband of the filter can be significantly shifted, indicating that the structure can achieve effective electrical tuning of the notch frequency position. With the change in the capacitance value of the varactor diode 11, the notch response changes continuously within the range of 2.07-2.23 GHz, while the notch depth remains at a high level (< -13 dB). Simultaneously, within the passband range of 1.5-2.4 GHz, the insertion loss is less than 0.3 dB, and the return loss is better than 15 dB. This demonstrates that the adjustable notch unit achieves frequency tuning while having a relatively limited impact on the original transmission characteristics of the ridge waveguide SSPP structure.

[0031] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An tunable notch filter based on a ridge waveguide SSPP structure, characterized in that, include: A rectangular cavity (1) is provided with a metal ridge (2); a grating structure (3) is provided on the rectangular cavity (1); and a groove structure is provided on the metal ridge (2).

2. The tunable notch filter based on a ridge waveguide SSPP structure according to claim 1, characterized in that, The groove structure includes five sets of T-shaped grooves (4) set in the middle area of ​​the metal ridge (2) along the Z-axis direction, and rectangular grooves (5) are set on the outer side of the T-shaped grooves (4) on both sides.

3. The tunable notch filter based on a ridge waveguide SSPP structure according to claim 2, characterized in that, The metal ridge (2) has an intermittent groove (6), and a strip wire structure is provided in the intermittent groove (6).

4. The tunable notch filter based on a ridge waveguide SSPP structure according to claim 3, characterized in that, The stripline includes a substrate (7), on the upper and lower surfaces of the substrate (7) respectively, a top stripline conductor (9) and a bottom stripline conductor (14) are provided, and non-metallized through holes (8) are reserved in both to fix the substrate.

5. The tunable notch filter based on a ridge waveguide SSPP structure according to claim 4, characterized in that, A slot is formed on the top strip conductor (9) to embed a varactor diode bias circuit; the varactor diode bias circuit includes a DC blocking capacitor (10), a varactor diode (11), a high-resistance resistor (12), and a wire (13); the wire extends from the end (12) of the high-resistance resistor to the edge of the rectangular cavity (1) to connect to an external bias voltage source.

6. The tunable notch filter based on a ridge waveguide SSPP structure according to claim 5, characterized in that, A via (15) is provided at the end of the varactor diode bias circuit embedded in the top strip conductor (9) to connect to the bottom strip conductor (14); the bottom strip conductor (14) extends to the edge of the substrate (7) to connect to the metal ridge (2).

7. The tunable notch filter based on a ridge waveguide SSPP structure according to claim 6, characterized in that, The rectangular cavity (1) has transition shafts at both ends that connect to the metal ridge (2) to form ports.

8. The tunable notch filter based on a ridge waveguide SSPP structure according to claim 7, characterized in that, The bottom of the metal ridge (2) is attached to the bottom of the rectangular cavity (1).

Images