High Isolation Microstrip Annular Slot Dual-Band Filter

Abstract

The present invention discloses a high-isolation microstrip annular slot dual-band filter, comprising a ring resonator. Four orthogonal slots and four bent rectangular slots are arranged on the same plane along the center of the ring resonator patch. The four bent rectangular slots are symmetrically arranged with respect to the orthogonal slots. Two microstrip lines are arranged along the outer edges of a pair of diametrically symmetrical orthogonal slots. The two microstrip lines on each side are parallel and connected to the outer edge of the ring resonator, and all microstrip lines have consistent structural dimensions. A rectangular microstrip is arranged outside the midsection of each microstrip line, and all rectangular microstrips have consistent structural dimensions. A feed line is arranged in the gap between the two microstrip lines on each side, with the outer end of the feed line connected to the feed line port. The device structure of the present invention enables the dual-band filter to operate reliably at center frequencies of 6.9 GHz and 12.9 GHz, respectively.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave microstrip filters, is a planar dual-frequency filter made of microstrip lines and working at multiple frequencies, and relates to a high-isolation microstrip annular gap dual-frequency filter. Background Art

[0002] With the rapid development of commercial wireless communications, radio frequency (RF) and microwave circuits have received increasing attention and development. Wireless communication systems are moving towards multi-standard, multi-mode, and multi-frequency systems. For example, mobile communications use frequencies such as GSM's 0.9 GHz and 1.8 GHz, while third-generation mobile communications operate at 2 GHz. Wireless local area networks (WLANs) include IEEE 802.11b / g, which operates at 2.4 GHz, and IEEE 802.11a, which operates at 5.2 GHz. Similarly, navigation systems operate at different frequencies, including the US GPS, Europe's Galileo, and China's BeiDou. To fully utilize existing spectrum and infrastructure resources, communication systems must simultaneously operate in multiple frequency bands. One effective approach is to research and develop high-performance dual- and multi-band microwave filters. Filters are essential components in modern communications equipment. The rapid development of modern communications requires the efficient use of an increasing number of frequency channels. To reduce the size and weight of communication circuitry, research on dual-band devices is gaining increasing attention. Therefore, the study of dual-band filters is of great significance and practical value.

[0003] Research on dual-band filters is a relatively recent emerging topic. The successful development of dual-band antennas and dual-band low-noise amplifiers (LNAs) in recent years has enabled microwave dual-band filter devices to gradually enter the market. Numerous new dual-band filter structures have been proposed. Because microstrip filters are small, easy to process, and integrate, and can be used across a wide frequency range using a variety of substrate materials, many international research reports on dual-band filters are based on planar microstrip structures. In 2005, Professor Zhu Lei of Singapore proposed a model and simulation results for a second-order dual-band filter designed using a SIR. By adjusting the electrical length and impedance ratios of the SIR, the desired two passband frequencies could be achieved. In 2007, Professor Wu Ke of Canada proposed a design method for multi-band filters based on substrate-integrated waveguides (SIWs). He demonstrated how to implement a J-converter using SIWs. Starting from a low-pass prototype, he designed a dual-band Chebyshev filter, a triple-band Chebyshev filter, and a dual-band quasi-elliptic filter. In 2008, Indian scholar Mondal P loaded stubs at arbitrary locations on a split-ring resonator. This loading method achieved a wider frequency range, resulting in both physical and simulated test results for the filter, demonstrating good out-of-band performance. In 2012, Fu Sen proposed a method for constructing a dual-band filter using a dual-mode resonator with large-scale perturbations. He designed a new capacitor-loaded square resonant ring. The addition of stubs not only facilitated the miniaturization of the resonant cavity but also effectively altered the average current distribution.

[0004] However, all of the above-mentioned dual-band filters have common shortcomings, namely, insufficient isolation between passbands and attenuation outside the passband, and large circuit size. Therefore, there is still much room for research in the design of high-isolation and miniaturized dual-band filters. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-isolation microstrip annular slot dual-band filter, which solves the problem that the existing dual-band filter has insufficient isolation between passbands and small attenuation outside the passband, making it difficult to meet the application requirements of miniaturized multi-band filters.

[0006] The technical solution adopted by the present invention is a high-isolation microstrip annular slot dual-band filter, comprising a ring resonator, four orthogonal slots and four bent rectangular slots arranged on the same surface along the center of the ring resonator patch, the four bent rectangular slots being symmetrically arranged with respect to the orthogonal slots;

[0007] Two microstrip lines are arranged along the outer edges of a pair of diameter-symmetrical orthogonal slots. The two microstrip lines on each side are parallel and connected to the outer edge of the ring resonator, and the structural dimensions of all microstrip lines are consistent. A rectangular microstrip is arranged on the outer side of the middle section of each microstrip line, and the structural dimensions of all rectangular microstrips are consistent. A feeder is arranged in the gap between the two microstrip lines on each side, and the outer end of the feeder is led from the feeder port.

[0008] The high isolation microstrip annular slot dual-band filter of the present invention is further characterized in that:

[0009] The outer radius of the ring resonator is 2±0.2 mm, and the inner radius is 0.3±0.1 mm.

[0010] The length of the orthogonal slit is 4±0.2 mm and the width is 0.1±0.05 mm.

[0011] The long side length of the bent rectangular gap is 1.2±0.2mm, the short side length is 0.8±0.2mm, the width is 0.2±0.1mm, the vertical distance from the long side to the ring diameter is 0.4±0.1mm, and the vertical distance from the short side to the ring diameter is 0.35±0.1mm.

[0012] The length of the microstrip line is 3.6±0.2mm and the width is 0.2±0.05mm.

[0013] The length of the rectangular microstrip is 2.4±0.2 mm and the width is 0.3±0.1 mm.

[0014] The length of each feed line is 3.6±0.2mm and the width is 0.39±0.1mm; the width of the groove between the inner end of the feed line and the ring resonator is 0.2±0.05mm, and the width of the groove between the microstrip line and the feed line is 0.1±0.05mm.

[0015] The beneficial effect of the present invention is that the innovation lies in introducing four bent rectangular slot structures symmetrical along orthogonal diameters into the resonator to excite two degenerate modes, thereby achieving dual-mode dual-band filter characteristics and increasing the isolation within the passband. A rectangular microstrip is added to the middle section of the four outer microstrip lines, and the size is adjusted to increase the appropriate coupling degree, thereby reducing the influence of insertion loss. Finally, the filter structure is more compact, the adjustment is convenient and flexible, and it can effectively filter out various useless signals and noise signals, reduce signal interference between communication channels, and realize reliable operation of the dual-frequency filter with center frequencies at 6.9 GHz and 12.9 GHz respectively, playing an important role in the applied communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the planar structure of the device of the present invention;

[0017] Figure 2 This is a schematic diagram of an embodiment of the device application installation structure of the present invention;

[0018] Figure 3 It is the frequency response characteristic curve of the device of the present invention.

[0019] In the figure, 1. Dual-band antenna, 2. Amplifier 1, 3. Amplifier 2, 4. Dual-band tunable filter 1, 5. Down-conversion circuit, 6. Dual-band tunable filter 2, 7. Amplifier 3, 8. Reference crystal oscillator, 9. Frequency synthesizer, 10. AGC module, 11. A / D conversion, 12. Microprocessor, 13. Related channels, 14. Memory, 15. Ring resonator, 16. Orthogonal slots, 17. Bent rectangular slots, 18. Microstrip line, 19. Rectangular microstrip, 20. Feed line. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0021] Reference Figure 1 The main structure of the high-isolation microstrip annular slot dual-band filter (hereinafter referred to as the dual-band filter) of the present invention includes a ring resonator 15. Four orthogonal slots 16 and four bent rectangular slots 17 are arranged on the same surface along the center of the ring resonator 15 patch. That is, a bent rectangular slot 17 is provided in the area separated by each two adjacent orthogonal slots 16. The four bent rectangular slots 17 are arranged symmetrically with respect to the orthogonal slots 16. Such a structure can excite degenerate dual modes and improve isolation between passbands.

[0022] Two microstrip lines 18 are arranged along the outer edges of a pair of diameter-symmetrical orthogonal slots 16 (a total of four microstrip lines 18). The two microstrip lines 18 on each side are parallel and connected to the outer edge of the ring resonator 15. The structural dimensions of all microstrip lines 18 are consistent. A rectangular microstrip 19 is arranged on the outer side of the middle section of each microstrip line 18 (a total of four rectangular microstrips 19). Each rectangular microstrip 19 is attached to the microstrip line 18 by merging or fusing. The structural dimensions of all rectangular microstrips 19 are consistent. A feed line 20 is arranged in the gap between the two microstrip lines 18 on each side. The outer end of the feed line 20 is led from the feed line port, which not only increases the coupling between the feed line 20 and the filter, but also reduces the insertion loss.

[0023] The parameter range of the dual-frequency filter of the present invention is:

[0024] The outer radius of the ring resonator 15 is 2±0.2 mm, and the inner radius is 0.3±0.1 mm;

[0025] Each orthogonal slit 16 has a length of 4±0.2 mm and a width of 0.1±0.05 mm;

[0026] Each bent rectangular slit 17 has a long side length of 1.2±0.2mm, a short side length of 0.8±0.2mm, a width of 0.2±0.1mm, a vertical distance from the long side to the ring diameter of 0.4±0.1mm, and a vertical distance from the short side to the ring diameter of 0.35±0.1mm;

[0027] Each microstrip line 18 has a length of 3.6±0.2 mm and a width of 0.2±0.05 mm;

[0028] Each rectangular microstrip 19 has a length of 2.4±0.2 mm and a width of 0.3±0.1 mm;

[0029] The length of each feed line 20 is 3.6±0.2 mm, and the width is 0.39±0.1 mm. The feed line 20 is preferably a 50-ohm impedance line.

[0030] The width of the groove between the inner end of the feed line 20 and the ring resonator 15 is 0.2±0.05 mm, and the width of the groove between the microstrip line 18 and the feed line 20 is 0.1±0.05 mm.

[0031] The dual-frequency filter adopts reasonable structural parameters and can work in a wide frequency range, thereby reducing the influence of machining accuracy on the performance of the dual-frequency filter.

[0032] In practical applications, the high-isolation microstrip annular slot dual-band filter of the present invention can adjust the center frequencies of the two passbands of the dual-band filter by selecting the above-mentioned size parameters of each part according to different communication occasions and application requirements to meet different application requirements.

[0033] Example

[0034] Reference Figure 2 The high-isolation microstrip annular slot dual-band filter of the present invention is applied to a communication system receiver. The installation structure of the receiver includes a dual-band antenna 1, which is sequentially connected to a related channel 13 through a (dual-band low-noise) amplifier 1 2, an amplifier 2 3, a dual-band tunable filter 1 4, a down-conversion circuit 5, a dual-band tunable filter 2 6, an amplifier 3 7, and an A / D converter 11. In addition, a reference crystal oscillator 8 is connected to the down-conversion circuit 5 (the other input end) through a frequency synthesizer 9, and the amplifier 3 7 is provided with an AGC module 10. The related channel 13 is also connected to a microprocessor 12 and a memory 14 at the same time, and the microprocessor 12 and the memory 14 are connected to each other.

[0035] In the above-described embodiment structure, the dual-band antenna 1 and amplifier 1 2 together constitute the antenna unit; amplifier 2 3, dual-band tunable filter 1 4, down-conversion circuit 5, dual-band tunable filter 2 6, amplifier 3 7, reference crystal oscillator 8, frequency synthesizer 9, and AGC module 10 together constitute the down-conversion circuit unit; and the A / D converter 11, microprocessor 12, related channels 13, and memory 14 together constitute the baseband signal processing unit.

[0036] The structures of the dual-frequency tunable filter 1 4 and the dual-frequency tunable filter 2 6 are the same.

[0037] Amplifier 1 (2) is a dual-band, low-noise model, preferably Avago's MGA683P8 or Skyworks' SKY65047-360LF. Amplifier 2 (3) and amplifier 3 (7) can be the same model.

[0038] The down-conversion circuit 5 is preferably an RFX1200 daughter board from Ettus Research.

[0039] The baseband signal processing unit is preferably a universal software radio platform USRP1 of Ettus research company.

[0040] The above-mentioned circuit modules or units are all system circuits. According to different application requirements, other relevant specific models can also be selected for combination design.

[0041] The specific parameters of the two dual-band filters in this embodiment are: the outer radius of the ring resonator 15 is 2 mm, and the inner radius is 0.3 mm; the length of each orthogonal slot 16 is 4 mm, and the width is 0.1 mm; the long side length of each bent rectangular slot 17 is 1.2 mm, the short side length is 0.8 mm, and the width is 0.2 mm. The vertical distance between the long side and the ring diameter is 0.4 mm, and the vertical distance between the short side and the ring diameter is 0.35 mm; the length of each microstrip line 18 is 3.6 mm; the length of each rectangular microstrip 19 is 2.4 mm, and the width is 0.3 mm; the length of each feed line 20 is 3.6 mm, and the width is 0.39 mm.

[0042] When the system is in operation, the dual-band antenna 1 first receives weak electrical signals from the air. The signal power is amplified to the required level by amplifier 2 and then sent to the dual-band tunable filter 4. Various useless signals and noise signals are filtered out before entering the down-conversion circuit 5 to reduce signal interference between communication channels. At the same time, the signal of the reference crystal oscillator 8 (TCXO) also enters the down-conversion circuit 5 through the frequency synthesizer 9. Then, according to different application requirements, the down-conversion circuit 5 is selected to down-convert the GPS signal or WLAN signal to an intermediate frequency. The signal is then passed through the dual-band tunable filter 6 and the self-circulating loop of amplifier 3 7 before being sent to the subsequent baseband signal processing unit. The baseband signal processing unit completes the baseband signal processing work.

[0043] Reference Figure 3 , is the frequency response characteristic curve of the above embodiment. The center frequencies of the two passbands are located at 6.9GHz and 12.9GHz respectively, the in-band differential loss are -0.28dB and -1.72dB respectively, the out-of-band differential loss of the first passband is minimized to -75dB, and the out-of-band differential loss of the second passband is minimized to -60dB, the isolation between passbands reaches -57dB, and the performance fully meets the relevant technical requirements.

Claims

1. A high-isolation microstrip annular slot dual-band filter, characterized by: It comprises a ring resonator (15), four orthogonal slots (16) and four bent rectangular slots (17) arranged on the same surface along the center of the patch of the ring resonator (15), and the four bent rectangular slots (17) are symmetrically arranged with respect to the orthogonal slots (16); Two microstrip lines (18) are respectively arranged along the outer edges of a pair of diameter-symmetrical orthogonal slots (16), the two microstrip lines (18) on each side are parallel, the two microstrip lines (18) on each side are connected to the outer edge of the ring resonator (15), and the structural dimensions of all the microstrip lines (18) are consistent; a rectangular microstrip (19) is respectively arranged on the outer side of the middle section of each microstrip line (18), and the structural dimensions of all the rectangular microstrips (19) are consistent; a feeder line (20) is arranged in the gap between the two microstrip lines (18) on each side, and the outer end of the feeder line (20) is led from the feeder port.

2. The high-isolation microstrip annular slot dual-band filter according to claim 1, characterized in that: The outer radius of the annular resonator (15) is 2±0.2 mm, and the inner radius is 0.3±0.1 mm.

3. The high-isolation microstrip annular slot dual-band filter according to claim 1, characterized in that: The length of the orthogonal gap (16) is 4±0.2 mm and the width is 0.1±0.05 mm.

4. The high-isolation microstrip annular slot dual-band filter according to claim 1, characterized in that: The long side length of the bent rectangular gap (17) is 1.2±0.2mm, the short side length is 0.8±0.2mm, the width is 0.2±0.1mm, the vertical distance between the long side and the ring diameter is 0.4±0.1mm, and the vertical distance between the short side and the ring diameter is 0.35±0.1mm.

5. The high-isolation microstrip annular slot dual-band filter according to claim 1, characterized in that: The length of the microstrip line (18) is 3.6±0.2 mm, and the width is 0.2±0.05 mm.

6. The high-isolation microstrip annular slot dual-band filter according to claim 1, characterized in that: The rectangular microstrip (19) has a length of 2.4±0.2 mm and a width of 0.3±0.1 mm.

7. The high-isolation microstrip annular slot dual-band filter according to claim 1, characterized in that: Each feed line (20) has a length of 3.6±0.2 mm and a width of 0.39±0.1 mm; The width of the groove between the inner end of the feed line (20) and the ring resonator (15) is 0.2±0.05 mm, and the width of the groove between the microstrip line (18) and the feed line (20) is 0.1±0.05 mm.

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