Heart-shaped broadband circularly polarized patch antenna

Abstract

The application discloses a heart-shaped broadband circularly polarized patch antenna, which comprises a dielectric substrate, a heart-shaped radiation patch, a microstrip feed line and a ground plate. A characteristic mode analysis method suitable for irregular geometric shapes is proposed, that is, a plurality of non-orthogonal characteristic modes are used to realize a broadband circularly polarized antenna. The application has the advantages of simple structure, beauty, compactness, simple feed mode, wide impedance and axial ratio bandwidth, and stable radiation pattern. The new method has clear physical mechanism, simple steps and wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of antenna technology, and in particular to a cardioid broadband circularly polarized patch antenna. Background Technology

[0002] Circularly polarized antennas are widely used in modern wireless communication, satellite communication, radar systems, and navigation systems due to their advantages such as resistance to multipath fading and improved system sensitivity and capacity. In the field of wireless communication technology, circularly polarized antennas with broadband or ultra-wideband capabilities, good polarization performance, and lightweight design have become a research hotspot. Microstrip circularly polarized antennas, with their advantages of miniaturization, low profile, conformal design, and easy integration, have always attracted attention. Microstrip circularly polarized antennas are typically fed using single-feed and dual-feed schemes. Single-feed schemes typically employ chamfering, surface slotting, and tuning stubs to geometrically perturb the metal patch structure. Their advantage is that they do not require external power dividers and phase shift networks, but their significant disadvantages are narrow bandwidth and poor polarization characteristics. Multi-feed schemes require external feeding networks, which offer advantages such as improved VSWR bandwidth and axial ratio bandwidth, but their disadvantages include complex feeding networks and larger dimensions.

[0003] Characteristic mode theory can be used to solve many radiation and scattering problems involving all-conductive structures. Characteristic mode analysis can efficiently find the optimal excitation location for a single mode. Characteristic mode theory is also applied to the design of circularly polarized antennas. The steps involve finding two orthogonal modes with equal importance, orthogonal characteristic currents, a 90-degree phase difference in characteristic angles, and consistent radiation directions, and then optimizing the feed location. The advantage of this method is its clear physical mechanism and simple steps. Its disadvantage is that it is generally suitable for antennas with regular structures, simple characteristic current distributions, and easily identifiable current directions. For designs with irregular structures, complex characteristic currents, and difficult-to-determine current directions, this method cannot guide the design of circularly polarized antennas. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a cardioid broadband circularly polarized patch antenna with simple antenna structure and feeding method, wide operating bandwidth and good circular polarization performance.

[0005] To address the aforementioned technical problems, this invention provides a cardioid broadband circularly polarized patch antenna, comprising: a dielectric substrate, a cardioid radiating patch, a microstrip feed line, and a ground plane. The cardioid radiating patch and the microstrip feed line are located on the top layer of the antenna, and the ground plane is located on the bottom layer of the dielectric substrate. The three edges of the ground plane and the dielectric substrate are aligned, and the width of the ground plane is obtained through performance optimization.

[0006] Preferably, by changing the parameters of the cardioid and the feed position to control the operating frequency and bandwidth, the cardioid equation of the cardioid patch is determined by formula (1):

[0007] (1)

[0008] The coefficients a and b determine the size of the heart-shaped patch and the depth of the cusp. .

[0009] Preferably, the circularly polarized antenna has a wide impedance bandwidth and axial ratio bandwidth, a stable radiation pattern, and provides two different rotation directions in two opposite directions: left-hand circular polarization is obtained in the direction perpendicular to the plane where the patch is located, while right-hand circular polarization is obtained in the direction perpendicular to the ground plane.

[0010] Accordingly, a design method for a cardioid broadband circularly polarized patch antenna includes the following steps:

[0011] Step 1: Perform characteristic mode analysis on the antenna structure to obtain characteristic parameters;

[0012] Step 2: Analyze the characteristic parameters and select two modes with equal importance. When the currents of the two modes are orthogonal, the maximum radiation direction of the characteristic radiation field is consistent, and the characteristic angles differ by 90 degrees, feed at the equiphase point of the characteristic currents of the two modes to obtain circular polarization characteristics. For irregular structures, non-orthogonal radiation fields, characteristic angles that do not differ by 90 degrees, and current directions that are difficult to determine, select the mode with the consistent maximum radiation direction of all characteristic radiation fields as the effective mode.

[0013] Step 3: Determine the equivalent direction of the mode current from the characteristic radiation field, and then decompose the mode current of each mode into two orthogonal current components in the Cartesian coordinate system, namely the x-axis and y-axis. The radiation field Ex of the current component in the x-axis direction and the radiation field Ey of the current component in the y-axis direction are also orthogonal.

[0014] Step 4: Sum the two components of all valid modes to obtain the total field E. Tx and E Ty When the ratio of the two total field amplitudes R e satisfy And the phase difference of the total field Meet the conditions At that time, a circularly polarized wave with an axial ratio of less than 3dB was obtained;

[0015] Step 5: By changing the structural dimensions, ensure that the amplitude and phase of the orthogonal radiation field satisfy the circular polarization condition over a wide frequency band, and calculate the antenna's reflection coefficient, axial ratio, and radiation pattern parameters to verify the antenna performance.

[0016] Preferably, in step 1, the characteristic parameters include the importance of the characteristic mode, the characteristic angle, the characteristic radiation field, and the characteristic current distribution.

[0017] The beneficial effects of this invention are: the antenna has advantages such as simple structure and feeding method, wide operating bandwidth, and good circular polarization performance; the method is applicable to realizing a broadband circularly polarized antenna with a single feed point on irregular structures where it is difficult to directly determine the current direction. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cardioid broadband circularly polarized antenna structure of the present invention.

[0019] Figure 2 This is a schematic diagram showing the calculation results of the characteristic parameters of the cardioid broadband circularly polarized antenna of the present invention.

[0020] Figure 3 This is a schematic diagram of the mode radiation field of the cardioid broadband circularly polarized antenna of the present invention.

[0021] Figure 4 This is a schematic diagram of the current distribution in the effective mode of the cardioid broadband circularly polarized antenna of the present invention.

[0022] Figure 5 This is a schematic diagram showing the amplitude ratio and phase difference of the orthogonal electric fields of the cardioid broadband circularly polarized antenna of the present invention.

[0023] Figure 6 This is a schematic diagram of the reflection coefficient of the cardioid broadband circularly polarized antenna of the present invention.

[0024] Figure 7 This is a schematic diagram showing the axial ratio of the cardioid broadband circularly polarized antenna of the present invention.

[0025] Figure 8 This is the radiation pattern of the cardioid broadband circularly polarized antenna of the present invention. Detailed Implementation

[0026] like Figure 1 As shown, a cardioid broadband circularly polarized patch antenna includes: a dielectric substrate, a cardioid radiating patch, a microstrip feed line, and a ground plane. The cardioid radiating patch and the microstrip feed line are located on the top layer of the antenna, and the ground plane is located on the bottom layer of the dielectric substrate. The ground plane and the three edges of the dielectric substrate are aligned, and the width of the ground plane is obtained through performance optimization.

[0027] The relative permittivity and thickness of the dielectric substrate, as well as the specific dimensions of other radiating patches and ground planes, are determined based on the operating frequency. In this embodiment, the structural dimensions are: L = 40mm, P... x = 22mm, P y = 13mm, t = 0.5mm, W f = 1.5mm, P f = 9.5mm,W g = 8mm; The equation of the heart-shaped line of the heart-shaped patch is determined by formula (1):

[0028] (1)

[0029] The coefficients a and b determine the size of the heart-shaped patch and the depth of the cusp. In this example, we choose a=8mm and b=1.65.

[0030] A design method for a cardioid broadband circularly polarized patch antenna includes the following steps:

[0031] Step 1: Perform characteristic mode analysis on the antenna structure to obtain characteristic parameters;

[0032] Step 2: Analyze the characteristic parameters. Figure 2 This demonstrates the importance and characteristic angles of three main modes in the 3-7 GHz frequency range, from Figure 2 The mode importance curves on the left show that the first mode M1 and the third mode M3 intersect at 4.6 GHz, and the first mode M1 and the second mode M2 ​​intersect at 5.9 GHz, indicating equal mode importance, which meets the condition of equal circular polarization amplitude; however, from Figure 2 As can be seen from the characteristic angle curve on the right, the difference in characteristic angles at the first intersection point is only 42 degrees, and the difference at the second intersection point is only 40 degrees. In traditional characteristic mode analysis methods, the above conditions cannot be used to achieve circular polarization.

[0033] Figure 3 This is a top view of the characteristic field radiation patterns of the three modes, where darker colors indicate stronger field strengths. As can be seen from the figure, the maximum radiation direction of the second mode, M2, is not along the z-axis, so it cannot be considered a valid mode. The first and third modes are valid modes, but their radiation patterns are not orthogonal. Similarly, the traditional characteristic mode method is not applicable to this situation.

[0034] Figure 4 These are current distribution diagrams for two effective modes. It can be seen that, due to the non-regular square or circular structure of the radiating patch, the current distribution is rather chaotic, making it difficult to determine whether the current directions are orthogonal.

[0035] Step 3: Determine the equivalent direction of the mode current from the characteristic radiation field, such as... Figure 2 As shown, the equivalent direction of the mode current is perpendicular to the plane containing the maximum radiation field (represented by the dashed line in the figure), where the angle between the equivalent direction of mode current J1 and the x-axis is α1, and the angle between the equivalent direction of mode current J3 and the x-axis is α3. The radiation field of the current of the nth mode... It can also be decomposed into x-axis and y-axis directions. In this example, the electric fields of mode 1 and mode 3 can be decomposed as follows:

[0036] (2)

[0037] MS1 and MS3 represent the mode importance of the first mode M1 and the third mode M3, respectively. and These are the characteristic angles of the first mode M1 and the third mode M3. and These represent unit vectors in the x and y directions, respectively.

[0038] Step 4: Add the x-direction and y-direction values ​​of all valid modes separately to obtain the total electric field of radiation in the x-direction. The amplitude and the total electric field of radiation in the y direction The range;

[0039] (3)

[0040] in This means that for the first valid pattern to the nth pattern, the corresponding values ​​within the parentheses are incremented. For the pattern importance of the i-th pattern, Let α represent the characteristic angle of the i-th pattern. i This represents the angle between the equivalent current direction of the i-th mode and the x-axis.

[0041] electric field phase , phase They are respectively:

[0042] (4)

[0043] Calculate the amplitude ratio and phase difference When 0.5 ≤ R e When ≤2, the phase difference required to obtain a circularly polarized wave with an axial ratio less than 3dB needs to satisfy the following condition:

[0044] (5)

[0045] Figure 5 These are the amplitude ratio and phase difference curves of two orthogonal electric fields obtained through calculation in this embodiment. As can be seen from the figure, in the frequency range of 3-6 GHz, 0.5 ≤ R e ≤2, satisfying the amplitude condition of circular polarization axial ratio <3dB; the phase difference satisfies the phase condition in the range of 3.4-5.6GHz. Figure 5 The threshold line in the right subgraph is determined by formula (5).

[0046] Step 5: By changing the structural dimensions, ensure that the amplitude and phase of the orthogonal radiation field satisfy the circular polarization condition over a wide frequency band, and calculate the antenna's reflection coefficient, axial ratio, and radiation pattern parameters to verify the antenna performance.

[0047] Figure 6 The reflection coefficient S of the antenna in this embodiment 11 As can be seen from the figure, the antenna has a very wide impedance bandwidth, spanning the frequency range of 2.9-7 GHz, |S 11 | <-10dB.

[0048] Figure 7 These are the axial ratio parameters of the antenna in this embodiment. As can be seen from the figure, along the +z direction, the electromagnetic wave emitted by the antenna is a left-hand circularly polarized wave, and the bandwidth with an axial ratio AR < 3dB is relatively wide, covering a frequency range of 3.3-5.6GHz; along the -z direction, the electromagnetic wave emitted by the antenna is a right-hand circularly polarized wave, and the bandwidth with an axial ratio AR < 3dB covers two frequency bands, the low frequency band is 3.4-3.9GHz, and the high frequency band is 4.6-5.5GHz.

[0049] Figure 8 This is the radiation pattern of the antenna in this embodiment, showing the three frequencies of 3.5GHz, 4.5GHz and 5.5GHz. As can be seen from the figure, the radiation pattern is stable within the operating frequency band.

[0050] from Figure 6 , Figure 7 and Figure 8 As can be seen, based on the circularly polarized antenna design method based on characteristic mode analysis proposed in this invention, this embodiment realizes a single-point fed, cardioid broadband circularly polarized antenna with wide impedance bandwidth and axial ratio bandwidth, stable radiation pattern, and provides two different rotation directions in two opposite directions.

Claims

1. A cardioid broadband circularly polarized patch antenna, characterized in that, include: The antenna consists of a dielectric substrate, a cardioid radiating patch, a microstrip feed line, and a ground plane. The cardioid radiating patch and the microstrip feed line are located on the top layer of the antenna, and the ground plane is located on the bottom layer of the dielectric substrate. The ground plane and the three edges of the dielectric substrate are aligned. The design method includes the following steps: Step 1: Perform characteristic mode analysis on the antenna structure to obtain characteristic parameters; Step 2: Analyze the characteristic parameters and select two modes with equal importance. When the currents of the two modes are orthogonal, the maximum radiation direction of the characteristic radiation field is consistent, and the characteristic angles differ by 90 degrees, feed at the equiphase point of the characteristic currents of the two modes to obtain circular polarization characteristics. For irregular structures, non-orthogonal radiation fields, characteristic angles that do not differ by 90 degrees, and current directions that are difficult to determine, select the mode with the consistent maximum radiation direction of all characteristic radiation fields as the effective mode. Step 3: Determine the equivalent direction of the mode current from the characteristic radiation field, and then decompose the mode current of each mode into two orthogonal current components in the Cartesian coordinate system, namely the x-axis and y-axis. The radiation field Ex of the current component in the x-axis direction and the radiation field Ey of the current component in the y-axis direction are also orthogonal. Step 4: Sum the two components of all valid modes to obtain the total field E. Tx and E Ty When the ratio of the two total field amplitudes R e satisfy And the phase difference of the total field Meet the conditions At that time, a circularly polarized wave with an axial ratio of less than 3dB was obtained; Step 5: By changing the structural dimensions, ensure that the amplitude and phase of the orthogonal radiation field satisfy the circular polarization condition over a wide frequency band, and calculate the antenna's reflection coefficient, axial ratio, and radiation pattern parameters to verify the antenna performance.

2. The cardioid broadband circularly polarized patch antenna as described in claim 1, characterized in that, By changing the parameters of the cardioid and the feed position to control the operating frequency and bandwidth, the cardioid equation of the cardioid patch is determined by formula (1): （1） The coefficients a and b determine the size of the heart-shaped patch and the depth of the cusp. .

3. The cardioid broadband circularly polarized patch antenna as described in claim 1, characterized in that, Circularly polarized antennas provide two different directions of rotation in two opposite directions: left-hand circular polarization is obtained in the upward direction perpendicular to the plane of the patch, while right-hand circular polarization is obtained in the downward direction perpendicular to the ground.

4. The cardioid broadband circularly polarized patch antenna as described in claim 1, characterized in that, Characteristic parameters include the importance of characteristic modes, characteristic angles, characteristic radiation fields, and characteristic current distributions.

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