A design method for frequency reconfigurable filter antenna

Abstract

The present invention relates to a method for designing a frequency reconfigurable filter antenna, including: establishing a microstrip filter antenna model, performing mode analysis on the microstrip filter antenna, and obtaining the mode curve characteristics of the microstrip filter antenna; setting a parasitic patch on the microstrip filter antenna; performing characteristic mode analysis on the microstrip filter antenna with the parasitic patch, analyzing all modes, and modifying the structure of the antenna according to its mode current for modes that do not conform to the microstrip filter antenna; analyzing the distribution characteristics of all mode currents, adding an excitation structure, and finally simulating and optimizing the antenna structure. The present invention uses characteristic mode theory to realize the display of the potential radiation capability of the radiator within any frequency domain, so as to facilitate finding and utilizing the required mode, and changing the influence of the unnecessary mode according to its mode current; the present invention uses characteristic mode theory to guide the selection of antenna feed, and reduces the workload in the antenna design process.

Description

Technical Field

[0001] The invention relates to the technical field of antenna design, and in particular to a method for designing a frequency reconfigurable filtering antenna. Background Art

[0002] With the rapid development of wireless communications, spectrum resources are becoming increasingly scarce, and frequency bands are becoming more and more crowded. However, people realize that the current way of using spectrum does not fully utilize the existing spectrum resources. Cognitive radio is now a more recognized way to make full use of spectrum resources. It is through autonomous learning and perception of the corresponding frequency bands, and can allocate the communication bands to be carried out to unoccupied frequency bands. At the same time, due to the increasing integration of modern antennas, the mutual interference between frequency bands has become more and more serious. The filter antenna has attracted the attention and research of many scholars due to its good out-of-band suppression ability. In addition, a frequency-variable filter antenna has better application scenarios than ordinary filtering, and is more suitable for future cognitive radio systems.

[0003] Currently, frequency reconfigurable filtering antennas are mostly a combination of frequency-variable bandpass filters and broadband antennas. This structure has two disadvantages: the first disadvantage is that frequency-variable bandpass filters are often composed of PIN diodes and varactor diodes, and these devices require external bias circuits, which goes against the trend of antenna simplification and miniaturization; the second disadvantage is that the antenna gain is reduced, because filters are lossy, and gain is an important parameter of the filtering antenna. Summary of the invention

[0004] The object of the present invention is to provide a method for designing a frequency reconfigurable filtering antenna with simple structure, good filtering characteristics and high in-band gain.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for designing a frequency reconfigurable filtering antenna, the method comprising the following steps in order:

[0006] (1) establishing a microstrip filter antenna model, performing pattern analysis on the microstrip filter antenna, and obtaining the pattern curve characteristics of the microstrip filter antenna; the microstrip filter antenna model is composed of a rectangular radiation patch, a first dielectric plate, and a metal floor, the rectangular radiation patch is printed on the upper surface of the first dielectric plate, and the metal floor is printed on the lower surface of the first dielectric plate;

[0007] (2) Arranging a parasitic patch on the microstrip filter antenna;

[0008] (3) Perform characteristic mode analysis on the microstrip filter antenna with parasitic patch, analyze all modes, and modify the antenna structure according to the mode current for the modes that do not conform to the microstrip filter antenna;

[0009] (4) Analyze the distribution characteristics of all mode currents, add excitation structures, and finally simulate and optimize the antenna structure.

[0010] The step (1) specifically comprises the following steps:

[0011] (1a) First, build a microstrip filter antenna model in CST Microwave Studio and perform pattern analysis;

[0012] (1b) Start the meshing function of CST to mesh the microstrip filter antenna, and then start the solver. CST solves the following formula based on the meshing results:

[0013]

[0014] Where [X] and [R] are the imaginary and real parts of the impedance matrix, respectively, and λ n Represented as the nth eigenvector The eigenvalue of n When it is equal to zero, it means that the structure has the maximum radiation energy, that is, it is in resonance;

[0015] The calculation formula of modal significance MS is as follows:

[0016]

[0017] Where j is an imaginary unit, the value range of MS is 0 to 1, and when the MS value is 1, it means that the radiation capability is the strongest at this time; when the MS value is equal to 0.707, the radiation power is half of the previous one, and the radiation bandwidth BW is defined as the frequency range when the MS value is greater than 0.707;

[0018] (1c) Extract the MS value of the microstrip filter antenna and draw a curve graph of MS with respect to frequency, that is, the mode distribution curve of the microstrip filter antenna; observe the MS curve and obtain the mode analysis results.

[0019] The step (2) refers to: a parasitic patch having a substantially same aspect ratio as the rectangular radiation patch is arranged above the rectangular radiation patch, the parasitic patch is printed on the surface of the second dielectric plate, the parasitic patch is consistent in size with the second dielectric plate, the surface of the second dielectric plate is parallel to the surface of the first dielectric plate, and a connector is arranged between the second dielectric plate and the first dielectric plate.

[0020] The step (3) specifically comprises the following steps:

[0021] (3a) Performing mode analysis on the microstrip filter antenna with parasitic patch, obtaining the curve of the MS curve with respect to frequency, recording the frequency values ​​of each mode when the MS value is equal to 1, and setting these values ​​as the monitoring points of the CST calculation current diagram, and starting the CST calculation current distribution;

[0022] (3b) extract and draw the current diagram of each mode of the microstrip filter antenna with parasitic patches, and observe the current flow direction of the obtained current diagram; when the overall current flow direction of the rectangular radiation patch of a certain mode is the same as the current flow direction of the parasitic patch, it is judged that the mode meets the characteristics of the microstrip filter antenna; conversely, when the overall current flow direction of the rectangular radiation patch of a certain mode is opposite to the current flow direction of the parasitic patch, it is judged that the mode does not meet the characteristics of the microstrip filter antenna;

[0023] (3c) Analyze all modes of the microstrip filter antenna with a parasitic patch, and modify the antenna structure for the modes that do not meet the characteristics of the microstrip filter antenna. Specifically, for the mode in which the current flow of the parasitic patch is parallel to the X-axis, etch a slot parallel to the Y-axis on the parasitic patch, and the slot length is less than the length of the parasitic patch; for the mode in which the current flow of the parasitic patch is parallel to the Y-axis, etch a slot parallel to the X-axis on the parasitic patch.

[0024] The step (4) specifically comprises the following steps:

[0025] (4a) Performing mode analysis on the microstrip filter antenna with a slot and plotting the current distribution of each mode, observing the current flow direction of the rectangular radiation patch, using a first microstrip line parallel to the X-axis with a 1 / 4 wavelength impedance match for excitation for the mode in which the current flows parallel to the X-axis; using a second microstrip line parallel to the Y-axis with a 1 / 4 wavelength impedance match for excitation for the mode in which the current flows parallel to the Y-axis;

[0026] (4b) The microstrip filter antenna containing the excitation structure is modeled in the high-frequency structure simulation software HFSS, and all structural variables are parameterized for modeling; HFSS is started for simulation optimization, and the antenna size that meets the expected results is optimized.

[0027] It can be seen from the above technical scheme that the beneficial effects of the present invention are: first, the present invention uses the characteristic mode theory to realize the display of the potential radiation capability of the radiator within any frequency domain, which is convenient for finding the required mode and utilizing it, and for the unnecessary mode, its influence can be changed according to its mode current; second, the present invention uses the characteristic mode theory to guide the selection of antenna feeding, reducing the workload in the antenna design process; third, the present invention has a simple structure, a high in-band gain, and an obvious out-of-band suppression capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1(a) is a structural diagram of a microstrip antenna;

[0029] Figure 1(b) is a schematic diagram of the microstrip antenna pattern distribution;

[0030] Figure 2(a) is a schematic diagram of the current in mode 1;

[0031] Figure 2(b) is a schematic diagram of the current in mode 2;

[0032] Figure 2(c) shows the far-field pattern of mode 1;

[0033] Figure 2(d) shows the far-field pattern of mode 2;

[0034] FIG3( a ) is a side view of an antenna with a parasitic patch added;

[0035] FIG3( b ) is a front view of the antenna with a parasitic patch added;

[0036] Figure 3(c) shows the distribution of the mode with the added parasitic patch;

[0037] FIG4(a) is a schematic diagram of the current of the parasitic patch and the rectangular radiation patch in mode 1;

[0038] FIG4( b ) is a schematic diagram of the current of the parasitic patch and the rectangular radiation patch in mode 2;

[0039] FIG4( c ) is a schematic diagram of the current of the parasitic patch and the rectangular radiation patch in mode three;

[0040] FIG4( d ) is a schematic diagram of the current of the parasitic patch and the rectangular radiation patch in mode 4;

[0041] Figure 5(a) shows the model of the parasitic patch after groove engraving;

[0042] Figure 5(b) is a schematic diagram of the mode distribution curve after the parasitic patch is grooved;

[0043] FIG6(a) is a schematic diagram of the current of the parasitic patch and the rectangular radiation patch after the parasitic patch is grooved;

[0044] FIG6( b ) is a schematic diagram of the current of the parasitic patch and the rectangular radiation patch in mode 2 after the parasitic patch is grooved;

[0045] FIG6( c ) is a schematic diagram of the current of the parasitic patch and the rectangular radiation patch in the third mode after the parasitic patch is grooved;

[0046] FIG6( d ) is a schematic diagram of the current of the parasitic patch and the rectangular radiation patch in the fourth mode after the parasitic patch is grooved;

[0047] Figure 7(a) is the far-field pattern of mode 1 after the parasitic patch is grooved;

[0048] Figure 7(b) is the far-field pattern of mode 2 after the parasitic patch is grooved;

[0049] Figure 7(c) shows the far-field pattern of mode 3;

[0050] Figure 7(d) is the far-field pattern of mode 4;

[0051] FIG8( a ) is a schematic diagram of the antenna geometry structure;

[0052] FIG8( b ) is a schematic diagram of the antenna mode distribution curve;

[0053] Fig. 9(a) is a schematic diagram of MWC when the first port is excited;

[0054] Figure 9(b) is a schematic diagram of the MWC when the second port is excited;

[0055] FIG10( a ) is a schematic diagram of S-parameter simulation of the first port;

[0056] FIG10( b ) is a schematic diagram of S-parameter simulation of the second port;

[0057] Figure 11(a) is the xoz directional diagram when the first port is used as excitation;

[0058] Figure 11(b) shows the yoz pattern when the first port is used as the excitation;

[0059] Figure 12(a) is the xoz pattern when the second port is used as excitation;

[0060] Figure 12(b) shows the yoz pattern when the second port is used as the excitation. DETAILED DESCRIPTION

[0061] A method for designing a frequency reconfigurable filtering antenna comprises the following steps in order:

[0062] (1) Establishing a microstrip filter antenna model, performing pattern analysis on the microstrip filter antenna, and obtaining the pattern curve characteristics of the microstrip filter antenna; the microstrip filter antenna model consists of a rectangular radiation patch 1, a first dielectric plate 2, and a metal floor 3, the model of the first dielectric plate 2 is FR-4, the rectangular radiation patch 1 is printed on the upper surface of the first dielectric plate 2, and the metal floor 3 is printed on the lower surface of the first dielectric plate 2;

[0063] (2) Arranging a parasitic patch 4 on the microstrip filter antenna;

[0064] (3) Performing characteristic mode analysis on the microstrip filter antenna with parasitic patch 4, analyzing all modes, and modifying the antenna structure according to the mode current for the modes that do not conform to the microstrip filter antenna;

[0065] (4) Analyze the distribution characteristics of all mode currents, add excitation structures, and finally simulate and optimize the antenna structure.

[0066] The step (1) specifically comprises the following steps:

[0067] (1a) First, a microstrip filter antenna model is established in CST Microwave Studio, as shown in FIG. 1( a ), and a mode analysis is performed; the CST is a three-dimensional electromagnetic field simulation software.

[0068] (1b) Start the meshing function of CST to mesh the microstrip filter antenna, and then start the solver. CST solves the following formula based on the meshing results:

[0069]

[0070] Where [X] and [R] are the imaginary and real parts of the impedance matrix, respectively, and λ n Represented as the nth eigenvector The eigenvalue of n When it is equal to zero, it means that the structure has the maximum radiation energy, that is, it is in resonance;

[0071] The calculation formula of modal significance MS is as follows:

[0072]

[0073] Where j is an imaginary unit, the value range of MS is 0 to 1, and when the MS value is 1, it means that the radiation capability is the strongest at this time; when the MS value is equal to 0.707, the radiation power is half of the previous one, and the radiation bandwidth BW is defined as the frequency range when the MS value is greater than 0.707;

[0074] (1c) The MS value of the microstrip filter antenna is extracted, and a curve diagram of MS with respect to frequency is plotted, namely, the mode distribution curve of the microstrip filter antenna, as shown in FIG1(b). By observing the MS curve, it is found that the curve of the microstrip filter antenna within its radiation bandwidth BW is very sharp. In addition, as shown in FIG2(a) and FIG2(b), the current flows of mode 1 and mode 2 are parallel to the long side and short side of the rectangular radiation patch 1, respectively. In addition, as shown in FIG2(c) and FIG2(d), the maximum gains of mode 1 and mode 2 are both around 6.5dBi.

[0075] The step (2) refers to: a parasitic patch 4 having a substantially same aspect ratio as the rectangular radiation patch 1 is arranged above the rectangular radiation patch 1, the parasitic patch 4 is printed on the surface of the second dielectric plate 5, the model of the second dielectric plate 4 is Rogers 4003, the parasitic patch 4 is consistent in size with the second dielectric plate 5, the surface of the second dielectric plate 5 is parallel to the surface of the first dielectric plate 2, a connector is arranged between the second dielectric plate 5 and the first dielectric plate 2, as shown in FIG. 3(a) and FIG. 3(b), the connector is made of foam 6, double-sided tape is pasted on both end surfaces of the foam 6, one surface is pasted on the first dielectric plate 2, and the other surface is pasted on the second dielectric plate 5.

[0076] The step (3) specifically comprises the following steps:

[0077] (3a) Performing mode analysis on the microstrip filter antenna with parasitic patch 4, obtaining the curve of the change of MS curve with respect to frequency, as shown in FIG3(c), due to the addition of parasitic patch 4 and second dielectric plate 5, the mode of the entire antenna is increased from two modes of the microstrip filter antenna to the current four modes, recording the frequency value of each mode when the MS value is equal to 1, and setting these values ​​as the monitoring points of the CST calculation current diagram, and starting the CST calculation current distribution;

[0078] (3b) The current diagrams of each mode of the microstrip filter antenna with the parasitic patch 4 are extracted and plotted, and the current flow direction of the obtained current diagrams is observed; when the overall current flow direction of the rectangular radiation patch 1 of a certain mode is the same as the current flow direction of the parasitic patch 4, the mode is judged to meet the characteristics of the microstrip filter antenna; conversely, when the overall current flow direction of the rectangular radiation patch 1 of a certain mode is opposite to the current flow direction of the parasitic patch 4, the mode is judged not to meet the characteristics of the microstrip filter antenna; as shown in Figures 4(a) and 4(b), the current flow directions of the upper and lower patches of Mode 1 and Mode 2 are the same, that is, the current flow directions of the parasitic patch 4 and the rectangular radiation patch 1 are the same, which meets the characteristics of the filter antenna, while from Figures 4(c) and 4(d), the current flow directions of the upper and lower patches of Mode 3 and Mode 4 are opposite, that is, the current flow directions of the parasitic patch 4 and the rectangular radiation patch 1 are opposite, which does not meet the characteristics of the filter antenna.

[0079] (3c) Analyze all modes of the microstrip filter antenna with the parasitic patch 4, and modify the antenna structure of the modes that do not meet the characteristics of the microstrip filter antenna, specifically: for mode three, for the mode in which the current flow direction of the parasitic patch 4 is parallel to the X-axis, a slot parallel to the Y-axis is etched on the parasitic patch 4, and the slot length is less than the length of the parasitic patch 4; for mode four, for the mode in which the current flow direction of the parasitic patch 4 is parallel to the Y-axis, a slot parallel to the X-axis is etched on the parasitic patch 4, as shown in FIG5(a), the slot parallel to the X-axis is to suppress the influence of the reverse current of mode three, and the slot parallel to the Y-axis is to suppress the influence of the reverse current of mode four; the slot parallel to the Y-axis and the slot parallel to the X-axis together form a cross slot 7.

[0080] The step (4) specifically comprises the following steps:

[0081] (4a) The mode analysis of the microstrip filter antenna with a slot is shown in Figure 5(b). It can be seen that each mode meets the mode curve characteristics of the filter antenna, and the current distribution of each mode is plotted; as shown in Figures 6(a) and 6(c), the current flow directions of the rectangular radiation patch 1 of Mode 1 and Mode 3 are the same and parallel to the X-axis. At the same time, as shown in Figures 6(b) and 6(d), the current flow directions of the rectangular radiation patch 1 of Mode 2 and Mode 4 are the same and parallel to the Y-axis. For gain, as shown in Figures 7(a) and 7(c), the maximum gain of Mode 1 and Mode 3 is roughly equal. At the same time, Figures 7(b) and 7(d) show that the maximum gain of Mode 1 and Mode 3 is roughly equal. It can be obtained that the maximum gains of mode two and mode four are also approximately the same; for the mode in which the current flows in parallel to the X-axis, a first microstrip line 10 parallel to the X-axis with a 1 / 4 wavelength impedance match is used for excitation; for the mode in which the current flows in parallel to the Y-axis, a second microstrip line 11 parallel to the Y-axis with a 1 / 4 wavelength impedance match is used for excitation; the rectangular radiation patch 1 extends the first microstrip line 10 and the second microstrip line 11, and a first port 8 and a second port 9 are set on the metal floor 3, and the first port 8 and the second port 9 both use coaxial cables, the first port 8 is connected to the first microstrip line 10, and the second port 9 is connected to the second microstrip line 11.

[0082] As shown in FIG8(a), the microstrip line parallel to the X-axis can excite mode 1 and mode 3, and the microstrip line parallel to the Y-axis can excite mode 2 and mode 4; the mode bandwidth at this time is shown in FIG8(b). After adding the excitation structure, the radiation bandwidth BW of mode 3 and mode 4 is increased; as shown in FIG9(a), when the first port 8 is used as an excitation, mode 1 and mode 3 can be excited, and when the second port 9 is used as an excitation, as shown in FIG9(b), mode 2 and mode 4 can be excited.

[0083] (4b) The microstrip filter antenna with the excitation structure is modeled in the high-frequency structure simulation software HFSS, and all the structural variables are parameterized and modeled; HFSS is started to perform simulation optimization, and the antenna performance that meets the expected results is obtained by optimization; as shown in FIG. 10(a) and FIG. 10(b), when the first port 8 is working, the working frequency of the antenna is 2.4-2.6 GHz, and when the second port 9 is working, the frequency band covered by the antenna is 2.4-2.6 GHz; and as shown in FIG. Figure 11(a) and 11(b) As shown, when the first port 8 is working, the antenna has an omnidirectional radiation pattern; when the second port 9 is working, Figure 12(a) and 12(b) It can be seen that the antenna also has the ability of omnidirectional radiation at this time.

[0084] The present invention uses characteristic mode theory to demonstrate the potential radiation capability of a radiator within any frequency domain, making it easy to find and utilize the required modes. The influence of unnecessary modes can be changed according to their mode currents. The present invention uses characteristic mode theory to guide the selection of antenna feed, reducing the workload in the antenna design process.

Claims

1. A method for designing a frequency reconfigurable filter antenna, characterized in that: The method comprises the following steps in order: (1) establishing a microstrip filter antenna model, performing pattern analysis on the microstrip filter antenna, and obtaining the pattern curve characteristics of the microstrip filter antenna; the microstrip filter antenna model is composed of a rectangular radiation patch, a first dielectric plate, and a metal floor, the rectangular radiation patch is printed on the upper surface of the first dielectric plate, and the metal floor is printed on the lower surface of the first dielectric plate; (2) Arranging a parasitic patch on the microstrip filter antenna; (3) Perform characteristic mode analysis on the microstrip filter antenna with parasitic patch, analyze all modes, and modify the antenna structure according to the mode current for the modes that do not conform to the microstrip filter antenna; (4) Analyze the distribution characteristics of all mode currents, add excitation structures, and finally simulate and optimize the antenna structure; The step (1) specifically comprises the following steps: (1a) First, build a microstrip filter antenna model in CST Microwave Studio and perform pattern analysis; (1b) Start the meshing function of CST to mesh the microstrip filter antenna, and then start the solver. CST solves the following formula based on the meshing results: Where [X] and [R] are the imaginary and real parts of the impedance matrix, respectively, and λ n Represented as the nth eigenvector The eigenvalue of n When it is equal to zero, it means that the structure has the maximum radiation energy, that is, it is in resonance; The calculation formula of modal significance MS is as follows: Where j is an imaginary unit, the value range of MS is 0 to 1, and when the MS value is 1, it means that the radiation capability is the strongest at this time; when the MS value is equal to 0.707, the radiation power is half of the previous one, and the radiation bandwidth BW is defined as the frequency range when the MS value is greater than 0.707; (1c) Extract the MS value of the microstrip filter antenna and draw a curve graph of MS with respect to frequency, that is, the mode distribution curve of the microstrip filter antenna; observe the MS curve and obtain the mode analysis results.

2. The method for designing a frequency reconfigurable filtering antenna according to claim 1, characterized in that: The step (2) refers to: a parasitic patch having a substantially same aspect ratio as the rectangular radiation patch is arranged above the rectangular radiation patch, the parasitic patch is printed on the surface of the second dielectric plate, the parasitic patch is consistent in size with the second dielectric plate, the surface of the second dielectric plate is parallel to the surface of the first dielectric plate, and a connector is arranged between the second dielectric plate and the first dielectric plate.

3. The method for designing a frequency reconfigurable filtering antenna according to claim 1, characterized in that: The step (3) specifically comprises the following steps: (3a) Performing mode analysis on the microstrip filter antenna with parasitic patch, obtaining the curve of the MS curve with respect to frequency, recording the frequency values ​​of each mode when the MS value is equal to 1, and setting these values ​​as the monitoring points of the CST calculation current diagram, and starting the CST calculation current distribution; (3b) extract and draw the current diagram of each mode of the microstrip filter antenna with parasitic patches, and observe the current flow direction of the obtained current diagram; when the overall current flow direction of the rectangular radiation patch of a certain mode is the same as the current flow direction of the parasitic patch, it is judged that the mode meets the characteristics of the microstrip filter antenna; conversely, when the overall current flow direction of the rectangular radiation patch of a certain mode is opposite to the current flow direction of the parasitic patch, it is judged that the mode does not meet the characteristics of the microstrip filter antenna; (3c) Analyze all modes of the microstrip filter antenna with a parasitic patch, and modify the antenna structure for the modes that do not meet the characteristics of the microstrip filter antenna. Specifically, for the mode in which the current flow of the parasitic patch is parallel to the X-axis, etch a slot parallel to the Y-axis on the parasitic patch, and the slot length is less than the length of the parasitic patch; for the mode in which the current flow of the parasitic patch is parallel to the Y-axis, etch a slot parallel to the X-axis on the parasitic patch.

4. The method for designing a frequency reconfigurable filtering antenna according to claim 1, characterized in that: The step (4) specifically comprises the following steps: (4a) Performing mode analysis on the microstrip filter antenna with a slot and plotting the current distribution of each mode, observing the current flow direction of the rectangular radiation patch, using a first microstrip line parallel to the X-axis with a 1 / 4 wavelength impedance match for excitation for the mode in which the current flows parallel to the X-axis; using a second microstrip line parallel to the Y-axis with a 1 / 4 wavelength impedance match for excitation for the mode in which the current flows parallel to the Y-axis; (4b) The microstrip filter antenna containing the excitation structure is modeled in the high-frequency structure simulation software HFSS, and all structural variables are parameterized for modeling; HFSS is started for simulation optimization, and the antenna size that meets the expected results is optimized.

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