A sub-terahertz band wideband microstrip line filter

Abstract

The application discloses a sub-terahertz band wide-band microstrip line filter, in the case of the same circuit area, the first resonator, the second resonator, the third resonator and the fourth resonator are in the case of the same length microstrip line, the length of the long side, the width side, the upper side arm and the lower side arm of the microstrip line after folding is adjusted by increasing the line width W1 of the microstrip line, the internal gap width W2 of each resonator after folding reaches the requirement of self-coupling, and the distributed coupling capacitance and mutual inductance are formed between the long side and the upper side arm and the lower side arm of each resonator and between adjacent resonators. The application adopts an asymmetric open loop resonator structure, and the mutual coupling between the four edges of a single resonator is generated by widening the resonator line width and simultaneously compressing the resonator ring width, so that the frequency distribution and field distribution of each high-order resonant mode of the resonator are flexibly regulated and controlled.

Description

Technical Field

[0001] This invention relates to a wide stopband microstrip line filter in the Asia-Pacific Hertz band, belonging to the field of filter technology. Background Technology

[0002] Terahertz waves (0.1–10 THz) lie between microwaves and infrared light waves, possessing both the penetrability of microwaves and the wide bandwidth of light waves. They show great promise for applications in 6G mobile communication, high-resolution radar imaging, security monitoring, radio astronomy, biomedical diagnostics, and material spectral analysis. Among these, the Asia-Pacific Hertz band, as a key window for the transition from millimeter waves to terahertz, has become a hot topic in terahertz solid-state circuit and system research both domestically and internationally. With the rapid development of terahertz transceiver front-ends, monolithic integrated circuits, and on-chip antenna technology, systems are placing increasingly higher demands on the integration, miniaturization, and out-of-band rejection performance of various functional devices in the RF front-end.

[0003] As a key passive component in terahertz transceiver links, filters play a crucial role in frequency selection, spurious and harmonic suppression, and out-of-band interference isolation. Especially in Asia-Pacific Hertz (APH) systems, the quality of harmonic suppression directly affects the overall spectral purity and anti-interference performance. Systems commonly rely on nonlinear devices such as frequency multipliers, mixers, and harmonic oscillators, which inevitably generate abundant harmonics and intermodulation components during operation. If the filter cannot achieve deep suppression over a wide frequency range, leaked harmonics will pollute the output spectrum, crowd out adjacent channel spectrum resources, reduce transmission efficiency, and even fail to meet spectrum management requirements. On the other hand, out-of-band interference and harmonic signals falling into the parasitic passband will easily pass through the front-end link, leading to amplifier saturation, increased mixer spurious response, and a significant deterioration in receiver sensitivity and dynamic range. Therefore, wide stopband and strong harmonic suppression capabilities have become one of the core performance indicators of APH filters.

[0004] However, filter design faces many unique challenges in the Asia-Pacific Hertz band:

[0005] Firstly, the electromagnetic wavelength in this frequency band is extremely short, and the physical size of the resonant structure has entered the micrometer scale, making it extremely sensitive to processing precision and process tolerance, and complex structures are difficult to realize.

[0006] Secondly, planar filters based on half-wavelength or quarter-wavelength resonators exhibit parasitic passbands, or higher-order resonant modes, periodically appearing in their transmission response near integer multiples of the fundamental frequency. These parasitic passbands severely limit the filter's stopband width, enabling it to suppress out-of-band signals only near the fundamental frequency and failing to cover the wide frequency range of harmonics.

[0007] To address the issues of stopband widening and high-order harmonic suppression, existing technologies typically employ the following methods: loading notch stubs onto the transmission line to suppress parasitic passbands one by one using the band-stop characteristics of the stubs; introducing slotted resonant structures into the circuit to form additional transmission zeros; or etching defective ground structures (DGS) on the ground plane to achieve a stopband response at a specific frequency by perturbing the return current. While these methods can extend the stopband to some extent, they all require adding independent band-stop structures outside the original filter body, which has significant drawbacks: notch stubs occupy additional layout area and introduce new discontinuities; slotted lines and defective ground structures disrupt the integrity of the ground plane, easily causing ground current disturbances, cavity mode excitation, and packaging interconnection problems; furthermore, the design of the additional structure is intertwined with the main passband design, resulting in low design freedom, cumbersome debugging processes, and difficulty in compressing the overall circuit size, which contradicts the compactness and ease of layout requirements of terahertz systems.

[0008] Therefore, how to efficiently broaden the stopband of a filter and achieve harmonic suppression without compromising its passband characteristics has become a pressing technical problem in the design of Asia-Pacific Hertz band filters. Summary of the Invention

[0009] Objective: In order to overcome the shortcomings of the existing technology, the present invention provides a wide stopband microstrip line filter in the Asia-Pacific Hertz band.

[0010] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0011] A wide stopband microstrip line filter for the Asia-Pacific Hertz band includes: a first resonator, a second resonator, a third resonator, and a fourth resonator. The first resonator has a first notch, the second resonator has a second notch, the third resonator has a third notch, and the fourth resonator has a fourth notch. The first resonator has a first tap, and the fourth resonator has a second tap.

[0012] Among them, under the same circuit area, the first resonator, the second resonator, the third resonator, and the fourth resonator, under the same microstrip line length, by increasing the linewidth W1 of the microstrip line and adjusting the length of the long side, the wide side, the upper arm, and the lower arm after the microstrip line is folded, so that the internal gap width W2 of each resonator after folding meets the self-coupling requirements, and a distributed coupling capacitance and mutual inductance are formed between the long side of each resonator and the upper and lower arms, as well as between adjacent resonators.

[0013] Optionally, the first notch and the second notch are positioned opposite each other, and the third notch and the fourth notch are positioned opposite each other. The first resonator, the second resonator, the third resonator, and the fourth resonator have the same length in terms of their long side, wide side, upper arm, and lower arm. The first resonator, the second resonator, the third resonator, and the fourth resonator are aligned in the same plane, and the positions of the first notch, the second notch, and the fourth notch are on the same horizontal straight line.

[0014] Optionally, the first, second, third, and fourth resonators are all formed by folding microstrip lines to create an open-loop structure, where the microstrip line width W1 = 43 μm. In the folded open-loop structure, the long side length L1 = 330 μm, the wide side length L2 = 100 μm, the upper arm length L3 = 159 μm, the lower arm length L4 = 159 μm, and the gap width W2 = 14 μm.

[0015] Optionally, the first notch and the second notch are positioned opposite each other, and the third notch and the fourth notch are positioned opposite each other. The long side and the wide side of the first resonator, the second resonator, the third resonator, and the fourth resonator are of the same length. The upper arm and the lower arm of the first resonator, the second resonator, the third resonator, and the fourth resonator are of different lengths. The first resonator, the second resonator, the third resonator, and the fourth resonator are arranged alternately in the same plane, and the positions of the first notch, the second notch, the third notch, and the fourth notch are on the same horizontal straight line.

[0016] Optionally, the first, second, third, and fourth resonators are all formed by folding microstrip lines to create an open-loop structure. Each stage of the resonator is formed by folding microstrip lines to create an open-loop structure, where the microstrip linewidth W1 = 43 μm. After folding, the long side length L1 = 330 μm and the wide side length L2 = 100 μm in the open-loop structure of the first, second, third, and fourth resonators. The upper arm length L3 = 159 μm and the lower arm length L4 = 159 μm for the first resonator. The upper arm length L3 = 147 μm and the lower arm length L4 = 171 μm for the second resonator. The upper arm length L3 = 183 μm and the lower arm length L4 = 135 μm for the third resonator; the upper arm length L3 = 171 μm and the lower arm length L4 = 147 μm for the fourth resonator, with a gap width W2 = 14 μm.

[0017] Optionally, the first notch and the second notch are positioned opposite each other, and the third notch and the fourth notch are positioned opposite each other. The long side and the wide side of the first resonator, the second resonator, the third resonator, and the fourth resonator are of the same length. The upper arm and the lower arm of the first resonator, the second resonator, the third resonator, and the fourth resonator are of different lengths. The first resonator and the second resonator are aligned in the same plane. The third resonator and the fourth resonator are aligned in the same plane. The first resonator and the second resonator are translated by a distance L0 relative to the third resonator and the fourth resonator along the Y-axis in the plane. The positions of the first notch, the second notch, the third notch, and the fourth notch are not on a horizontal straight line.

[0018] Optionally, the first, second, third, and fourth resonators are all formed by folding microstrip lines to create an open-loop structure, where the microstrip line width W1 = 43 μm. After folding, the long side length L1 = 330 μm and the wide side length L2 = 100 μm in the open-loop structure of the first, second, third, and fourth resonators are: L3 = 157 μm and L4 = 157 μm; L3 = 141 μm and L4 = 173 μm; L3 = 189 μm and L4 = 125 μm; and L3 = 173 μm and L4 = 141 μm, with a gap width W2 = 14 μm. The resonators are arranged laterally, with the first and second resonators horizontally aligned, and the third and fourth resonators also horizontally aligned. The first and second resonators are translated along a direction parallel to the long side, with a translation amount L0 = 6um.

[0019] Optionally, the first, second, third, and fourth resonators are made of copper microstrip lines.

[0020] Beneficial Effects: This invention provides a wide-stopband microstrip line filter for the Asia-Pacific Hertz band, employing an asymmetric open-loop resonator structure. By widening the resonator linewidth while compressing the resonator ring width, mutual coupling is generated between the four sides of a single resonator, thereby allowing flexible control of the frequency and field distributions of the resonator's higher-order resonant modes. The significance of this invention lies in:

[0021] First, a relatively wide upper stopband is achieved in the Asia-Pacific Hertz band. This invention optimizes the upper stopband of the bandpass filter through resonator self-coupling and asymmetric open-loop methods, exhibiting good stopband performance in a relatively long range of approximately 200 GHz to 800 GHz. This can suppress multiple harmonics and help improve the overall system performance.

[0022] Second, it eliminates all additional band-stop structures. Without using any additional band-stop structures such as notch stubs, slot lines, or defective grounds, this invention achieves wide stopband characteristics simply by adjusting the higher-order resonant modes of each resonator, shifting parasitic passbands out of the target stopband range or causing them to cancel each other out. This fundamentally avoids the problems of area overhead, discontinuity losses, and ground plane integrity disruption caused by additional structures.

[0023] Third, it has a compact structure and is easy to lay out. Since it does not contain any additional band-stop structures, the filter consists only of resonator units and taps, which significantly reduces the layout area. Its regular shape makes it easy to integrate with other active and passive circuits in terahertz monolithic integrated circuits, meeting the miniaturization and high integration requirements of terahertz systems.

[0024] Fourth, the design method is simple and highly flexible. The four-sided coupling formed by the asymmetric opening position and the widened linewidth provides designers with a direct and effective means of mode control. The integrated design of the fundamental passband and stopband can be carried out relatively independently, reducing the sensitivity of the band-stop structure to manufacturing process errors. This is beneficial for ensuring yield and performance consistency under Asia-Pacific Hertz microscale manufacturing conditions. Attached Figure Description

[0025] Figure 1 This is a structural diagram of a first embodiment of a wide stopband microstrip line filter in the Asia-Pacific Hertz band according to the present invention.

[0026] Figure 2 The electromagnetic simulation results are for the first embodiment of the present invention.

[0027] Figure 3 This is a structural diagram of a second embodiment of a wide stopband microstrip line filter in the Asia-Pacific Hertz band according to the present invention.

[0028] Figure 4 The electromagnetic simulation results are for the second embodiment of the present invention.

[0029] Figure 5 This is a structural diagram of a third embodiment of the Asia-Pacific Hertz band wide stopband microstrip line filter of the present invention.

[0030] Figure 6 The electromagnetic simulation results are for the third embodiment of the present invention.

[0031] Figure 7 This is a structural diagram of the control group filter of the present invention.

[0032] Figure 8 The electromagnetic simulation results are for the control group filter of this invention. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] Example 1:

[0036] This embodiment describes a first embodiment of a wide stopband microstrip line filter in the Asia-Pacific Hertz band, such as... Figure 1 As shown, it includes: a first resonator 2, a second resonator 3, a third resonator 4, and a fourth resonator 5. The first resonator 2 is provided with a first notch 201, the second resonator 3 is provided with a second notch 301, the third resonator 4 is provided with a third notch 401, and the fourth resonator 5 is provided with a fourth notch 501. The first resonator 2 is provided with a first tap 1, and the fourth resonator 5 is provided with a second tap 6.

[0037] Among them, under the same circuit area, the first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5, under the same microstrip line length, by increasing the linewidth W1 of the microstrip line and adjusting the length of the long side 7, the wide side 8, the upper arm 9, and the lower arm 10 after the microstrip line is folded, so that the internal gap width W2 of each resonator after folding meets the self-coupling requirements, and a distributed coupling capacitance and mutual inductance are formed between the long side of each resonator and the upper and lower arms, as well as between adjacent resonators.

[0038] Furthermore, the first notch 201 and the second notch 301 are positioned opposite each other, and the third notch 401 and the fourth notch 501 are positioned opposite each other. The long side 7, wide side 8, upper arm 9, and lower arm 10 of the first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5 are of the same length. The first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5 are aligned in the same plane, and the positions of the first notch 201, the second notch 301, the third notch 401, and the fourth notch 501 are on the same horizontal straight line. This invention creates a strong electric field at the notch, with corresponding antinodes on both sides of the adjacent notch, which can effectively improve the coupling coefficient, reduce losses, and optimize passband performance.

[0039] Furthermore, in one embodiment, the first, second, third, and fourth resonators are all formed by folding microstrip lines to create an open-loop structure, wherein the microstrip line width W1 = 43 μm. In the folded open-loop structure, the long side length L1 = 330 μm, the wide side length L2 = 100 μm, the upper arm length L3 = 159 μm, the lower arm length L4 = 159 μm, and the gap width W2 = 14 μm.

[0040] Figure 2 Electromagnetic simulation results of the filter in the first embodiment are presented. This filter has a center frequency of approximately 170 GHz, a passband insertion loss of 2.54 dB, a 1 dB bandwidth of 18.2%, and a 3 dB bandwidth of 20.6%, exhibiting good selectivity. In the lower stopband... It reaches a maximum of -46.4dB at 108GHz, demonstrating the filter's good out-of-band rejection performance. (Upper stopband...) It reaches a maximum of -7.8dB at approximately 372GHz, and its stopband performance is better than -15dB in the 198GHz-359GHz range, with a stopband width of 2.11. It exhibits a relatively wide stopband width.

[0041] In the first embodiment, resonator self-coupling is achieved internally by widening the linewidth and compressing the resonator width. Traditional open-loop resonators have large spacing between their edges, resulting in negligible coupling and the entire loop approximating an isolated transmission line, thus maintaining quasi-integer multiples of higher-order mode frequencies. This design significantly widens the linewidth, lengthens the long sides, and shortens the short sides, bringing the four edges of a single resonator closer together on the layout. This generates significant self-coupling within the loop, forming distributed coupling capacitance and mutual inductance between opposing and adjacent edges. The entire loop is no longer an isolated line segment but a ring network with multiple internal coupling points. This internal coupling exhibits a clear selectivity in the effect on each order mode. In the fundamental mode, there is only one current-suppressing region and one electric-field-suppressing region on the ring. The field distribution is gentle, and the coupling of each side only produces a slight overall correction to the total electric length, so the fundamental frequency remains almost unchanged. However, higher-order modes have multiple field-suppressing regions on the ring. The distribution of electric field and current on the four sides varies greatly with the mode order. The additional load applied by the coupling of each side to different modes varies, and each higher-order mode is pushed to different frequencies. The quasi-integer multiple relationship of each resonant frequency inside a single resonator disappears.

[0042] Example 2:

[0043] This embodiment describes a second embodiment of an Asia-Pacific Hertz band wide stopband microstrip line filter, such as... Figure 3As shown, it includes: a first resonator 2, a second resonator 3, a third resonator 4, and a fourth resonator 5. The first resonator 2 is provided with a first notch 201, the second resonator 3 is provided with a second notch 301, the third resonator 4 is provided with a third notch 401, and the fourth resonator 5 is provided with a fourth notch 501. The first resonator 2 is provided with a first tap 1, and the fourth resonator 5 is provided with a second tap 6.

[0044] Among them, under the same circuit area, the first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5, under the same microstrip line length, by increasing the linewidth W1 of the microstrip line and adjusting the length of the long side 7, the wide side 8, the upper arm 9, and the lower arm 10 after the microstrip line is folded, so that the internal gap width W2 of each resonator after folding meets the self-coupling requirements, and a distributed coupling capacitance and mutual inductance are formed between the long side of each resonator and the upper and lower arms, as well as between adjacent resonators.

[0045] Furthermore, the first notch 201 and the second notch 301 are positioned opposite each other, and the third notch 401 and the fourth notch 501 are positioned opposite each other. The long side 7 and the wide side 8 of the first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5 are of the same length. The upper arm 9 and the lower arm 10 of the first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5 are of different lengths. The first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5 are arranged alternately in the same plane, and the positions of the first notch 201, the second notch 301, the third notch 401, and the fourth notch 501 are on the same horizontal straight line. This invention creates a strong electric field at the notch, with antinodes corresponding to both sides of the adjacent notch. Combined with the inherent wavelength of the higher harmonics, this restricts the field distribution on the ring. The asymmetrical upper and lower arms, on the one hand, combine with the self-coupling of the resonators to change the inherent resonant frequency of the higher harmonics, and on the other hand, disperse the antinode nodes on the coupling edge to suppress harmonic transmission.

[0046] Furthermore, in one embodiment, the first, second, third, and fourth resonators are all formed by folding microstrip lines to create an open-loop structure. Each stage of the resonator is formed by folding microstrip lines to create an open-loop structure, where the microstrip line width W1 = 43 μm. After folding, the long side length L1 = 330 μm and the wide side length L2 = 100 μm in the open-loop structure of the first, second, third, and fourth resonators. The upper arm length L3 = 159 μm and the lower arm length L4 = 159 μm for the first resonator. The upper arm length L3 = 147 μm and the lower arm length L4 = 171 μm for the second resonator. The upper arm length L3 = 183 μm and the lower arm length L4 = 135 μm for the third resonator; the upper arm length L3 = 171 μm and the lower arm length L4 = 147 μm for the fourth resonator, with a gap width W2 = 14 μm. The resonators are arranged laterally, with the first, second, third, and fourth gaps horizontally aligned.

[0047] Figure 4 Electromagnetic simulation results of the filter in the second embodiment are presented. This filter has a center frequency of approximately 170 GHz, a passband insertion loss of 2.60 dB, a 1 dB bandwidth of 17.1%, and a 3 dB bandwidth of 20.0%, exhibiting good selectivity. In the lower stopband... It reaches a maximum of -46.8dB at 104GHz, demonstrating the filter's good out-of-band rejection performance. (Upper stopband...) It reaches a maximum of -15.4dB at approximately 456GHz, and its stopband performance is better than -15dB in the 197GHz-795GHz range, with a stopband width of 4.68. This demonstrates a wider stopband width, which is wider than that of Example 1, further illustrating the role of the asymmetric open-loop design of the resonator in suppressing harmonics and widening the stopband.

[0048] Example 2, building upon Example 1, further introduces an asymmetric open-loop design for the resonators. In this design, the notch offsets of the four resonators are different, and the resonant frequencies of the first and fourth resonators are determined by the first and second taps, respectively. This is equivalent to assigning distinct higher-order mode spectra to each resonator while maintaining a completely consistent fundamental frequency. The four sets of higher-order resonant frequencies are staggered and non-overlapping within the stopband, preventing parasitic signals from establishing synchronously along the four-stage coupling link, thus achieving an inter-stage blocking mechanism. Simultaneously, the electric field is strongest and the current weakest at the open-loop notch. The notch position determines the ratio of electric and magnetic field coupling between adjacent resonators and the corresponding relationship of the field distribution of each mode. After the notches are arranged in the above manner, inter-stage coupling of the fundamental mode can still be effectively established, and the center frequency, bandwidth, and in-band characteristics of the passband remain essentially unchanged.

[0049] Example 3:

[0050] This embodiment describes a third embodiment of an Asia-Pacific Hertz band wide stopband microstrip line filter, as shown in Figure 5, including: a first resonator 2, a second resonator 3, a third resonator 4, and a fourth resonator 5. The first resonator 2 is provided with a first notch 201, the second resonator 3 is provided with a second notch 301, the third resonator 4 is provided with a third notch 401, and the fourth resonator 5 is provided with a fourth notch 501. The first resonator 2 is provided with a first tap 1, and the fourth resonator 5 is provided with a second tap 6.

[0051] Among them, under the same circuit area, the first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5, under the same microstrip line length, by increasing the linewidth W1 of the microstrip line and adjusting the length of the long side 7, the wide side 8, the upper arm 9, and the lower arm 10 after the microstrip line is folded, so that the internal gap width W2 of each resonator after folding meets the self-coupling requirements, and a distributed coupling capacitance and mutual inductance are formed between the long side of each resonator and the upper and lower arms, as well as between adjacent resonators.

[0052] Furthermore, the first notch 201 and the second notch 301 are positioned opposite each other, and the third notch 401 and the fourth notch 501 are positioned opposite each other. The long side 7 and the wide side 8 of the first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5 are of the same length. The upper arm 9 and the lower arm 10 of the first resonator 2, the second resonator 3, the third resonator 4, and the fourth resonator 5 are of different lengths. The first resonator 2 and the second resonator 3 are aligned in the same plane, and the third resonator 4 and the fourth resonator 5 are aligned in the same plane. The first resonator 2 and the second resonator 3 are translated by a distance L0 along the Y-axis direction in the plane relative to the third resonator 4 and the fourth resonator 5. The positions of the first notch 201, the second notch 301, the third notch 401, and the fourth notch 501 are not on a horizontal straight line. For the 170GHz fundamental frequency, the notches are not horizontally aligned, and the superposition at the antinodes is weak, which has a certain impact on the passband insertion loss. As the harmonic order increases, the wavelength shortens while the offset remains constant. At the fundamental frequency, the ratio of offset to wavelength is approximately 1 / 100, while at the fourth harmonic it is approximately 1 / 25. This enhances the suppression of higher harmonic transmission and produces the performance characteristic of harmonic suppression.

[0053] Furthermore, in one embodiment, the first, second, third, and fourth resonators are all formed by folding microstrip lines to create an open-loop structure, wherein the microstrip line width W1 = 43 μm. After folding, the long side length L1 = 330 μm and the wide side length L2 = 100 μm in the open-loop structure of the first, second, third, and fourth resonators. The upper arm length L3 = 157 μm and the lower arm length L4 = 157 μm of the first resonator; the upper arm length L3 = 141 μm and the lower arm length L4 = 173 μm of the second resonator; the upper arm length L3 = 189 μm and the lower arm length L4 = 125 μm of the third resonator; and the upper arm length L3 = 173 μm and the lower arm length L4 = 141 μm of the fourth resonator, with a gap width W2 = 14 μm. The resonators are arranged laterally, with the first resonator 14 and the second resonator 15 kept horizontally aligned, and the third resonator 16 and the fourth resonator 17 kept horizontally aligned. The first resonator 14 and the second resonator 15 are considered as a whole, and the third resonator 16 and the fourth resonator 17 are considered as another whole. In order to better meet the 50 ohm impedance matching principle at the port, the first resonator 14 and the second resonator 15 are translated along the direction parallel to the long side, and the translation amount L0 = 6 μm.

[0054] Figure 6 Electromagnetic simulation results for the filter in the third embodiment are presented. This filter has a center frequency of approximately 170 GHz, a passband insertion loss of 2.74 dB, a 1 dB bandwidth of 17.6%, and a 3 dB bandwidth of 20.6%, exhibiting good selectivity. In the lower stopband... It reaches a maximum of -46.6dB at 110GHz, demonstrating the filter's good out-of-band rejection performance. (Upper stopband...) It reaches a maximum of -17.3dB at approximately 470GHz, and its stopband performance is better than -15dB in the 197GHz-803GHz range, with a stopband width of 4.72. It exhibits a relatively wide stopband width.

[0055] Figure 5 Example 3 in Figure 3 and Example 2 in Figure 3 use similar resonators, both being asymmetric open-loop resonators with self-coupling. The main difference lies in the resonator layout. In both arrangements, the higher-order mode spectra of each stage of the resonator are staggered, blocking parasitic signals during inter-stage transmission. Therefore, both structures can achieve wide stopband characteristics while maintaining essentially unchanged passband characteristics. This comparison shows that this design method does not rely on a specific notch arrangement; as long as the higher-order resonant frequencies of adjacent resonators are staggered, stopband widening can be achieved. The position, offset, and width of the notch can be flexibly selected according to the actual layout and performance requirements.

[0056] Example 4:

[0057] To further illustrate the advantages of resonator self-coupling and asymmetric open-loop resonator in suppressing harmonics and widening the stopband, this embodiment further uses a traditional fourth-order filter as a control group to conduct a comparative experiment.

[0058] As shown in Figure 7, the microstrip linewidth of each resonator in the control group filter is W1=25um and the gap is W2=50um. Each resonator is aligned in the same plane, and each gap is on the same horizontal line and is located in the middle of each resonator.

[0059] Figure 8 Electromagnetic simulation results for the control group filter are presented. This filter has a center frequency of approximately 170 GHz, a passband insertion loss of 2.10 dB, a 1 dB bandwidth of 19.4%, and a 3 dB bandwidth of 22.3%, exhibiting good selectivity. In the lower stopband... It reaches a maximum of -44.9dB at 100GHz, demonstrating the filter's good out-of-band rejection performance. (Upper stopband...) It reaches a maximum of -4.8dB at approximately 346GHz, and its stopband performance is better than -15dB in the 186GHz-323GHz range, with a stopband width of only 1.90. The stopband width is significantly shorter than the three embodiments mentioned above, and it is significantly affected by the second harmonic.

[0060] Traditional square open-loop resonators are constructed by bending a half-wavelength microstrip line into a loop with a notch on one side. However, the notch in a traditional open-loop resonator is located at the center of the loop edge, resulting in a symmetrical structure about the centerline. The frequencies of each higher-order resonant mode approximately fall near integer multiples of the fundamental frequency and are fixed in position. When a filter is constructed by cascading several identical open-loop resonators, the higher-order resonant frequencies of each resonator overlap, and the parasitic responses are progressively amplified along the coupling link, eventually forming a periodic parasitic passband within the stopband. Furthermore, this superposition effect becomes increasingly pronounced as the filter order increases, severely limiting the stopband width of traditional square open-loop resonator filters.

[0061] For a bandpass filter composed of cascaded resonators, the parasitic signal can only be transmitted and accumulated along the coupling link, ultimately passing from the input to the output and forming a significant parasitic passband within the stopband, when all resonators simultaneously satisfy the resonance condition at the same parasitic frequency. Conversely, if the fundamental frequencies of each resonator are kept consistent while the higher-order resonant frequencies are staggered, at any given parasitic frequency, at most a few resonators can satisfy the resonance condition. The parasitic signal cannot be continuously transmitted by adjacent resonators, and the stages block each other, preventing the establishment of a parasitic passband. Furthermore, even if the higher-order mode frequencies of individual resonators are similar, as long as the current density distributions of adjacent resonators at that frequency are staggered, the parasitic coupling between them will be greatly weakened due to the field distribution mismatch, thus making the parasitic suppression effect more thorough. Therefore, it can be seen that widening the stopband does not rely on an external band-stop structure. The key is to disperse the higher resonant frequencies at two levels: the higher mode frequencies between each resonator and the quasi-integer multiples of the higher mode frequencies within each resonator, while keeping the fundamental frequency of each resonator constant.

[0062] This invention revolves around these two levels and proposes two complementary measures based on the structure of the open-loop resonator itself: using an asymmetric open-loop resonator to achieve inter-stage staggering of the higher-order mode frequencies of each resonator; and introducing resonator self-coupling to break up the inherent frequency relationship of the higher-order modes within a single resonator.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A wide stopband microstrip line filter for the Asia-Pacific Hertz band, characterized in that: include: A first resonator, a second resonator, a third resonator, and a fourth resonator; the first resonator has a first notch, the second resonator has a second notch, the third resonator has a third notch, and the fourth resonator has a fourth notch; the first resonator has a first tap, and the fourth resonator has a second tap. Among them, under the same circuit area, the first resonator, the second resonator, the third resonator, and the fourth resonator, under the same microstrip line length, by increasing the linewidth W1 of the microstrip line and adjusting the length of the long side, the wide side, the upper arm, and the lower arm after the microstrip line is folded, so that the internal gap width W2 of each resonator after folding meets the self-coupling requirements, and a distributed coupling capacitance and mutual inductance are formed between the long side of each resonator and the upper and lower arms, as well as between adjacent resonators.

2. The Asia-Pacific Hertz band wide stopband microstrip line filter according to claim 1, characterized in that: The first notch and the second notch are positioned opposite each other, and the third notch and the fourth notch are positioned opposite each other. The first resonator, the second resonator, the third resonator, and the fourth resonator have the same length in terms of their long side, wide side, upper arm, and lower arm. The first resonator, the second resonator, the third resonator, and the fourth resonator are aligned in the same plane, and the positions of the first notch, the second notch, and the fourth notch are on the same horizontal straight line.

3. The Asia-Pacific Hertz band wide stopband microstrip line filter according to claim 2, characterized in that: The first, second, third, and fourth resonators are all formed by folding microstrip lines to create an open-loop structure. The microstrip line width W1 = 43 μm. In the folded open-loop structure, the long side length L1 = 330 μm, the wide side length L2 = 100 μm, the upper arm length L3 = 159 μm, the lower arm length L4 = 159 μm, and the gap width W2 = 14 μm.

4. The Asia-Pacific Hertz band wide stopband microstrip line filter according to claim 1, characterized in that: The first notch and the second notch are positioned opposite each other, and the third notch and the fourth notch are positioned opposite each other. The long side and the wide side of the first resonator, the second resonator, the third resonator, and the fourth resonator are of the same length. The upper arm and the lower arm of the first resonator, the second resonator, the third resonator, and the fourth resonator are of different lengths. The first resonator, the second resonator, the third resonator, and the fourth resonator are arranged alternately in the same plane, and the positions of the first notch, the second notch, the third notch, and the fourth notch are on the same horizontal straight line.

5. The Asia-Pacific Hertz band wide stopband microstrip line filter according to claim 4, characterized in that: The first, second, third, and fourth resonators are all formed by folding microstrip lines to create an open-loop structure. Each stage of the resonator is formed by folding microstrip lines to create an open-loop structure. The microstrip line width is W1 = 43 μm. After folding, the long side length L1 = 330 μm and the wide side length L2 = 100 μm in the open-loop structure of the first, second, third, and fourth resonators are: the upper arm length L3 = 159 μm and the lower arm length L4 = 159 μm; the upper arm length L3 = 147 μm and the lower arm length L4 = 171 μm in the second resonator; the upper arm length L3 = 183 μm and the lower arm length L4 = 135 μm in the third resonator; and the upper arm length L3 = 171 μm and the lower arm length L4 = 147 μm in the fourth resonator. The gap width W2 = 14 μm.

6. The Asia-Pacific Hertz band wide stopband microstrip line filter according to claim 1, characterized in that: The first notch and the second notch are positioned opposite each other, and the third notch and the fourth notch are positioned opposite each other. The long side and the wide side of the first resonator, the second resonator, the third resonator, and the fourth resonator are of the same length. The upper arm and the lower arm of the first resonator, the second resonator, the third resonator, and the fourth resonator are of different lengths. The first resonator and the second resonator are aligned in the same plane, and the third resonator and the fourth resonator are aligned in the same plane. The first resonator and the second resonator are translated by a distance L0 relative to the third resonator and the fourth resonator along the Y-axis in the plane. The positions of the first notch, the second notch, the third notch, and the fourth notch are not on a horizontal straight line.

7. The Asia-Pacific Hertz band wide stopband microstrip line filter according to claim 6, characterized in that: The first, second, third, and fourth resonators are all formed by folding microstrip lines into open-loop structures, where the microstrip line width W1 = 43 μm. After folding, the long side length L1 = 330 μm and the wide side length L2 = 100 μm in the open-loop structures of the first, second, third, and fourth resonators are 157 μm and 157 μm respectively. The upper arm length L3 = 157 μm and the lower arm length L4 = 157 μm for the first resonator; the upper arm length L3 = 141 μm and the lower arm length L4 = 157 μm for the second resonator are 141 μm and 157 μm respectively. The arm length L4 = 173 μm; the upper arm length L3 = 189 μm and the lower arm length L4 = 125 μm of the third resonator; the upper arm length L3 = 173 μm and the lower arm length L4 = 141 μm of the fourth resonator, and the gap width W2 = 14 μm; the resonators are arranged laterally, with the first and second resonators kept horizontally aligned, and the third and fourth resonators kept horizontally aligned; the first and second resonators are translated along a direction parallel to the long side, with a translation amount L0 = 6 μm.

8. A wide-stopband microstrip line filter for the Asia-Pacific Hertz band according to any one of claims 1 to 7, characterized in that: The first, second, third, and fourth resonators are made of copper microstrip lines.

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