Single-layer broadband multi-zero microstrip patch filtering antenna

Abstract

The invention discloses a single-layer broadband multi-zero microstrip patch filter antenna, which comprises a dielectric substrate, a coaxial feed probe and a grounding plate, an air cavity is formed between the dielectric substrate and the grounding plate through the coaxial feed probe, a microstrip patch is placed on the upper surface of the dielectric substrate, a metal strip is arranged on the lower surface of the dielectric substrate, and the metal strip is arranged on the upper surface of the dielectric substrate. The metal band is connected with an inner conductor of the coaxial feed probe, the coaxial feed probe sequentially penetrates through the grounding plate, the metal band and the dielectric substrate to excite the microstrip patch, two pairs of symmetrical first slots are formed in the microstrip patch and are respectively formed in two sides of the coaxial feed probe, and the coaxial feed probe is connected with the dielectric substrate. The microstrip patch between the two pairs of first slots is provided with two pairs of second slots which are perpendicular to each other. The first slot can generate two radiation zero points at a low frequency. The metal band plays a role in band-stop filtering and generates a radiation zero point at a high-frequency position. The second slot generates another radiation zero point at the high frequency, and the out-of-band rejection is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless communications, and in particular relates to a single-layer broadband multi-zero-point microstrip patch filter antenna. Background Art

[0002] As wireless communication devices have more and more functions and more and more complex structures, the area left for RF front-end circuits is getting smaller and smaller. In order to meet the diverse needs of wireless communication, modern wireless communication systems are developing in the direction of miniaturization, multi-functions, and low costs. In order to reduce the size of the RF front end while suppressing interference and reducing losses, filter antennas that integrate filters and antennas have come into being.

[0003] Filter antennas have many advantages. The first is that they do not require matching circuits, which reduces the size of the circuit while also reducing losses, and can meet the needs of a large number of miniaturized base stations in the millimeter wave communication era; the second is that they do not need to be matched when in use, which reduces the difficulty of use; the third is that there will be no incomplete matching between the filter and the antenna port, which improves the stability of the entire circuit; the fourth is the frequency decoupling effect. Due to the high out-of-band selectivity of the filter antenna, for two antennas with close operating frequencies, the energy of the stopband can be significantly suppressed, thereby significantly reducing the coupling between the two. Microstrip patch antennas have the advantages of small size, light weight, easy commonality, and simple manufacturing, and are widely used in wireless communication systems.

[0004] In traditional filter antenna design, there are generally two design methods. One is to directly cascade the antenna and the filter, and the other is to integrate the filter with the antenna so that the antenna serves as the last-order resonator of the filter. However, these design methods inevitably bring additional insertion loss to the system and increase the complexity and size of the system. In recent years, people have proposed a fusion design method that does not require additional filtering circuit structures. This method cross-uses patch slots, loads short-circuit vias, loads / stacks parasitic patch structures, adds open / short-circuit branches, and uses electromagnetic coupling to integrate the filter and antenna, so that the filter antenna has the characteristics of both in-band radiation and out-of-band filtering. Summary of the invention

[0005] The invention provides a single-layer broadband multi-zero-point microstrip patch filter antenna based on microstrip. Based on a fusion design method of the filter antenna, a single-layer broadband filter antenna with simple structure and compactness is proposed.

[0006] In order to achieve the above purpose, the specific scheme of this application is:

[0007] The single-layer broadband multi-zero-point microstrip patch filter antenna comprises a dielectric substrate, a coaxial feeding probe and a ground plate. A microstrip patch is placed on the upper surface of the dielectric substrate, a metal strip is provided on the lower surface of the dielectric substrate, the metal strip is connected to the coaxial feeding probe, the coaxial feeding probe passes through the ground plate, the metal strip and the dielectric substrate in sequence to excite the microstrip patch, two symmetrical pairs of first slots are provided on the microstrip patch, the two pairs of first slots are respectively arranged on both sides of the coaxial feeding probe, and two pairs of second slots perpendicular to each other are provided on the microstrip patch between the two pairs of first slots.

[0008] In some specific embodiments, the two pairs of first grooves include a first pair of grooves and a second pair of grooves that are symmetrical about a first symmetry axis, the first pair of grooves include a first L-shaped groove and a second L-shaped groove that are symmetrical about a second symmetry axis, the second pair of grooves include a third L-shaped groove and a fourth L-shaped groove that are symmetrical about the second symmetry axis, and the first symmetry axis and the second symmetry axis are perpendicular.

[0009] In some specific embodiments, the two pairs of first grooves include a first pair of grooves and a second pair of grooves that are symmetrical about a first symmetry axis, the first pair of grooves include a first J-shaped groove and a second J-shaped groove that are symmetrical about a second symmetry axis, the second pair of grooves include a third J-shaped groove and a fourth J-shaped groove that are symmetrical about the second symmetry axis, and the first symmetry axis and the second symmetry axis are perpendicular.

[0010] In some specific embodiments, the two pairs of second grooves include a pair of vertical grooves and a pair of horizontal grooves, the vertical grooves include two first rectangular grooves parallel to each other, the horizontal grooves include two second rectangular grooves parallel to each other, the two second rectangular grooves are respectively arranged at both ends of the first rectangular groove and the first rectangular groove and the second rectangular groove are perpendicular to each other.

[0011] In some embodiments, the width of the first rectangular slot is greater than the width of the second rectangular slot.

[0012] In some specific embodiments, two first rectangular slots are respectively disposed on two sides of the coaxial feeding probe, and two second rectangular slots are respectively disposed on two sides of the coaxial feeding probe.

[0013] In some specific embodiments, the metal tape is an F-type metal tape, and the F-type metal tape is connected to the inner conductor of the coaxial feeding probe.

[0014] In some specific embodiments, the metal strip includes a first metal strip, a second metal strip, and a third metal strip, which are respectively perpendicular to the side metal strip and parallel to each other. The first metal strip, the second metal strip, the third metal strip, and the side metal strip are integrally formed into an F shape, and the side metal strip is parallel to the second rectangular groove.

[0015] In some specific embodiments, the length of the first metal strip is 1 m1, the length of the second metal strip is 1 m2, and the length of the third metal strip is 1 m3, wherein 1 m1>1 m2>1 m3.

[0016] In some specific embodiments, an air cavity is formed between the dielectric substrate and the ground plane by the coaxial feeding probe to improve impedance matching.

[0017] The present invention has the beneficial effects:

[0018] The present invention designs a single-layer broadband multi-zero point microstrip patch filter antenna based on the concept of fusion design of filter antenna, including a microstrip patch, a dielectric substrate, a metal strip and a ground plane. Two pairs of symmetrical first slots are added to the microstrip patch on the dielectric substrate to generate two radiation zero points at low frequencies. An F-shaped metal strip is added to the lower surface of the substrate and connected to a feeding probe. The probe passes through the substrate and the metal strip to excite the microstrip patch to generate a radiation pattern TM 10 Mode and TM 02 Mode. The F-type metal strip mainly plays the role of band-stop filtering, producing a radiation zero point at high frequencies. Adding two pairs of slots near the feeding point on the microstrip patch produces another radiation zero point at high frequencies and further improves the out-of-band suppression.

[0019] The antenna provided in the present application generates two radiation zero points on both sides of the passband, generating filtering characteristics at the upper and lower sidebands respectively. There is an air cavity gap between the dielectric substrate and the ground plane, which can improve impedance matching. The antenna structure of the present application is simple and does not require an additional filtering circuit structure. The impedance bandwidth of the antenna is 16.76% (4.32GHz~5.11GHz), the gain is 7.5dBi, and it has high frequency selectivity and out-of-band suppression of more than 11dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A top view of a single-layer broadband multi-zero-point microstrip patch filter antenna structure provided by an embodiment of the present invention;

[0021] Figure 2 A schematic diagram of structural parameters of a single-layer broadband multi-zero-point microstrip patch filter antenna provided by an embodiment of the present invention;

[0022] Figure 3 A bottom view of a single-layer broadband multi-zero-point microstrip patch filter antenna structure provided by an embodiment of the present invention;

[0023] Figure 4 A layered structure diagram of a single-layer broadband multi-zero-point microstrip patch filter antenna provided by an embodiment of the present invention;

[0024] Figure 5A schematic diagram of the evolution of the antenna structure during the design process provided by an embodiment of the present invention; wherein, Figure 5 (a) is a schematic diagram of the structure of antenna I. Figure 5 (b) is a schematic diagram of the structure of antenna II. Figure 5 (c) is a schematic diagram of the structure of antenna III. Figure 5 (d) is the schematic diagram of the structure of antenna IV. Figure 5 (e) is a schematic diagram of the structure of antenna V;

[0025] Figure 6 Based on Figure 5 Antenna simulation reflection coefficient of antenna structure;

[0026] Figure 7 Based on Figure 5 Antenna simulation gain of antenna structure;

[0027] Figure 8 Based on Figure 5 Schematic diagram of the electric field distribution of antenna II; Figure 8 (a) is a schematic diagram of the electric field distribution at 3.82 GHz. Figure 8 (b) is a schematic diagram of the electric field distribution at 4.94 GHz;

[0028] Fig. 9 Based on Figure 5 Schematic diagram of the surface current distribution of antenna II. Fig. 9 (a) is a schematic diagram of the current distribution at 3.6 GHz. Fig. 9 (b) is a schematic diagram of current distribution at 4.74 GHz;

[0029] Fig.10 A schematic diagram of the structural parameters of a pair of L-shaped slots in Antenna II;

[0030] Fig.11 Based on Fig.10 Equivalent structural diagram of the radiation zero point of the antenna structure;

[0031] Fig.12 Based on Fig.10 Schematic diagram of gain simulation results of the effect of antenna structural parameters on the radiation zero point; Fig.12 (a) is a schematic diagram showing the effect of the L-shaped slot width sl1 on the radiation zero point. Fig.12 (b) is a schematic diagram showing the effect of the L-shaped slot long side length sw1 on the radiation zero point. Fig.12 (b) is a schematic diagram showing the effect of the length of the short side of the L-shaped slot pl2 on the radiation zero point;

[0032] Fig.13 This is the structural diagram of reference antenna III-I;

[0033] Fig.14Schematic diagram of the equivalent circuit model of the reference antenna III-I structure;

[0034] Fig.15 Schematic diagram for verification of reference antenna III-I and equivalent circuit model;

[0035] Fig.16 Schematic diagram of the effect of length wms4 on the zero point in the reference antenna;

[0036] Fig.17 Schematic diagram of current distribution of reference antenna III-I at 5.7GHz;

[0037] Fig.18 Schematic diagram of the surface current distribution of the microstrip patch of antenna IV at the 5.33GHz radiation zero point;

[0038] Fig.19 Schematic diagram of input impedance of antenna V;

[0039] Fig. 20 A schematic diagram of the simulation and test results of the reflection coefficient and gain obtained by measuring the physical model of the antenna;

[0040] Fig.21 The normalized radiation patterns of the antenna at 4.56 GHz, 4.76 GHz, and 5.06 GHz in the E-plane (XOZ plane) and H-plane (YOZ plane) obtained by simulation and testing based on the physical model of the antenna, where (a) 4.56 GHz E-plane; (b) 4.56 GHz H-plane;

[0041] (c) 4.76 GHz E-plane; (d) 4.76 GHz E-plane;

[0042] (e) 5.06 GHz E-plane; (f) 5.06 GHz H-plane;

[0043] The corresponding names of the numbers in the accompanying drawings are: 1-microstrip patch, 2-dielectric substrate, 3-ground plate, 4-metal strip, 41-side metal strip, 42-first metal strip, 43-second metal strip, 44-third metal strip, 5-coaxial feeding probe, 6-first slot, 61-first J-slot, 62-second J-slot, 63-third J-slot, 64-fourth J-slot, 7-first symmetry axis, 8-second symmetry axis, 9-second slot, 91-first rectangular slot, 92-second rectangular slot. DETAILED DESCRIPTION

[0044] In order to reflect the creativity and novelty of the present invention, the present invention will be described below in conjunction with the accompanying drawings and specific embodiments, but the embodiments of the present invention are not limited thereto.

[0045] Embodiment 1:

[0046] like Figure 1-Figure 4 As shown, this embodiment provides a single-layer broadband multi-zero point microstrip patch 1 filtering antenna, including a dielectric substrate 2, a coaxial feeding probe 5 and a ground plate 3, as shown in FIG. Figure 3 As shown, an air cavity is formed between the dielectric substrate 2 and the ground plate 3 by the coaxial feeding probe 5. The coaxial feeding probe 5 forms a feeding point on the dielectric substrate 2 for improving impedance matching. A microstrip patch 1 is placed on the upper surface of the dielectric substrate 2. An F-type metal strip 4 is provided on the lower surface of the dielectric substrate 2. The F-type metal strip 4 is connected to the inner conductor of the coaxial feeding probe 5. The coaxial feeding probe 5 sequentially passes through the ground plate 3, the metal strip 4 and the dielectric substrate 2 to excite the microstrip patch 1. Two symmetrical pairs of first slots 6 are provided on the microstrip patch 1. The two pairs of first slots 6 are respectively arranged on both sides of the coaxial feeding probe 5. Two pairs of second slots 9 perpendicular to each other are provided on the microstrip patch 1 between the two pairs of first slots 6.

[0047] In order to form two radiation zero points at low frequency, the two pairs of first slots 6 are four mutually symmetrical L-shaped slots, specifically including a first pair of slots and a second pair of slots symmetrical about the first symmetry axis 7, the first pair of slots including a first L-shaped slot and a second L-shaped slot symmetrical about the second symmetry axis 8, the second pair of slots including a third L-shaped slot and a fourth L-shaped slot symmetrical about the second symmetry axis 8, the first symmetry axis 7 and the second symmetry axis 8 being perpendicular. The first L-shaped slot and the third L-shaped slot are symmetrical about the first symmetry axis 7, the second L-shaped slot and the fourth L-shaped slot are symmetrical about the first symmetry axis 7, and the L-shaped inflection points of the four L-shaped slots are arranged close to each other, such as Figure 5 (b) The structure shown in antenna II.

[0048] Although the L-shaped slot can generate two radiation zero points at low frequency and the F-shaped metal strip 4 can generate a radiation zero point in the upper frequency band, the out-of-band suppression effect at high frequency is not good. Therefore, in order to further improve the out-of-band suppression and adjust the impedance matching, the L-shaped slot is changed into four mutually symmetrical J-shaped slots in this embodiment. Specifically, the two pairs of first slots 6 include a first pair of slots and a second pair of slots symmetrical about the first symmetry axis 7, the first pair of slots include a first J-shaped slot 61 and a second J-shaped slot 62 symmetrical about the second symmetry axis 8, and the second pair of slots include a third J-shaped slot 63 and a fourth J-shaped slot 64 symmetrical about the second symmetry axis 8, and the first symmetry axis 7 and the second symmetry axis 8 are perpendicular.

[0049] In order to further improve the out-of-band suppression and adjust the impedance matching, the width of the metal strip 4 is adjusted and the size parameters are optimized, such as Fig.13As shown, the metal belt 4 includes a first metal belt 42, a second metal belt 43 and a third metal belt 44 which are respectively perpendicular to the side metal belt 41 and parallel to each other. The first metal belt 4, the second metal belt 43, the third metal belt 44 and the side metal belt 41 are integrally formed into an F shape, and the side metal belt 41 is parallel to the second rectangular slot 92. When adjusting the size of the metal belt 4, the length of the first metal belt 42 is 1m1, the length of the second metal belt 43 is 1m2, the length of the third metal belt 44 is 1m3, the length of the side metal belt 41 is 1m2, and the width of the entire F-shaped metal belt 4 is wm2, wherein 1m1>1m2>1m3.

[0050] In order to further improve the out-of-band suppression at high frequencies and enhance the selectivity of the upper frequency band, two pairs of second slots 9 are added near the feeding point. The specific structure is as follows: Figure 1 As shown, the two pairs of second slots 9 include a pair of vertical slots and a pair of horizontal slots, the vertical slots include two first rectangular slots 91 parallel to each other, the horizontal slots include two second rectangular slots 92 parallel to each other, the two second rectangular slots 92 are respectively arranged at both ends of the first rectangular slot 91, and the first rectangular slot 91 and the second rectangular slot 92 are perpendicular to each other. The two first rectangular slots 91 are respectively arranged on both sides of the coaxial feeding probe 5, and the two second rectangular slots 92 are respectively arranged on both sides of the coaxial feeding probe 5. That is, the feeding point is within the rectangular area enclosed by the two first rectangular slots and the two second rectangular slots.

[0051] Specifically, the width of the first rectangular slot 91 is greater than the width of the second rectangular slot 92. The length of the second rectangular slot 92 is greater than the spacing between the two first rectangular slots 91 but less than the spacing between the two pairs of first slots 6, and the spacing between the two second rectangular slots 92 is the same as the length of the first rectangular slot 91. The two pairs of second slots 9 are arranged in the lower half of the second symmetry axis 8, that is, the lower half of the feeding point.

[0052] According to Figure 2 The structural parameters shown in the figure are as follows. This embodiment provides a specific antenna structural parameter value. The dielectric substrate 2 uses Rogers 5880 with a thickness of h1=0.508mm. A microstrip patch 1 is placed on the dielectric substrate 2. The microstrip patch 1 is placed at the center of the dielectric substrate 2 and is wg away from the edge of the substrate. There is a ground plane 3 below the dielectric substrate 2. The interval between the dielectric substrate 2 and the ground plane 3 is 4mm, forming an air cavity. Four symmetrical J-shaped grooves are etched on the patch, and a pair of grooves are also etched in the horizontal and vertical directions near the feeding point. An F-shaped metal strip 4 is introduced on the lower surface of the dielectric substrate 2 and connected to the coaxial probe for feeding, which generates a radiation zero point at high frequency and improves the filtering characteristics. The specific structural parameter values ​​of the antenna are shown in Table 1.

[0053] Table 1 Antenna structural parameters (unit: mm)

[0054]

[0055] In order to understand the working mechanism of the single-layer broadband multi-zero-point microstrip patch filter antenna proposed in this embodiment, the design process will be explained in detail below, and the principle analysis of each antenna structure in the design process will be performed.

[0056] 1. Principle analysis

[0057] First, the design process of the antenna structure is as follows Figure 5 As shown in (a)-(e). Figure 5 The antenna I shown in (a) is similar to a conventional microstrip patch antenna. Figure 5 Antenna II shown in (b) is based on antenna I, with four symmetrical L-shaped slots added to the patch; Figure 5 Antenna III shown in (c) is an F-shaped metal strip added to the lower surface of the dielectric substrate of antenna II; Figure 5 Antenna IV shown in (d) is based on antenna III with two pairs of slots added near the feeding point; Figure 5 Antenna V shown in (e) is based on antenna IV, but the L-shaped slot is changed to a J-shaped slot. The simulation results of |S11| of these five antennas are shown in Figure 6 As shown, the gain simulation is as follows Figure 7 As shown, the evolution from antenna Ⅰ to antenna Ⅴ is described as follows.

[0058] (1) Design of Antenna I to Antenna II

[0059] Antenna I is similar to a conventional rectangular microstrip patch antenna, except that the lower surface of the substrate is not directly covered with metal as a ground plane, but there is an air gap of height h2 between the substrate and the ground. By adjusting the size of the air gap h2, the input impedance of the antenna can be tuned.

[0060] Based on antenna I, four symmetrical L-shaped slots are added to the patch to obtain the following Figure 5 (b) Antenna II is shown. Figure 6 It can be seen that antenna II produces two resonant modes with resonant frequencies of 3.82 GHz and 4.94 GHz respectively. Their electric field distributions are shown in Figure 8 At the same time, it can be found that antenna II produces a radiation zero point at 3.6GHz and 4.74GHz respectively, and its surface current distribution is shown in Fig. 9 shown.

[0061] Depend on Figure 8 (a) It can be seen that the area with larger electric field intensity at 3.82 GHz is distributed around the slot, mainly through the introduction of L-shaped slot radiation, generating TM 02 Mode. Figure 8 (b) It can be seen that the maximum field strength at 4.94 GHz is distributed around the patch, producing TM 10 Mode. Fig. 9 (a) It can be seen that the larger surface current at 3.6GHz is mainly concentrated in the area between the L slots, and the surface currents are symmetrically distributed on the left and right sides, canceling each other out in the horizontal direction. The energy at the frequency cannot be radiated, thus generating a radiation zero point. Fig. 9 (b) It can be seen that the areas with large surface currents generated at 4.74GHz are mainly on both sides of the slot, and the current flows mainly in the longitudinal direction, and the current flows in opposite directions along the two sides of the slot. The current flowing upward and the current flowing downward on both sides of the slot cancel each other out, thus generating another radiation zero point.

[0062] In order to more clearly explore the formation principle of the radiation zero point of antenna II, its position is now analyzed by formulating a formula, and one pair of the first L-shaped slots is analyzed. The size parameters of this pair of L-shaped slots are as follows: Fig.10 As shown, the equivalent structure diagram explaining the radiation zero point is as follows Fig.11 As shown, Fig.11 As shown, Z in1 and Z in2 They represent the input impedances indicated in the figure respectively, then the input impedance can be Z in1 Expressed as:

[0063]

[0064] When the slot width sl1 is very small, it can be considered that Z1 = Z2. in2 It can be expressed as

[0065]

[0066] Substituting (2) into (1) we get:

[0067]

[0068] According to the filter theory, the transmission zero point can be mainly determined by the equivalent electrical length θ of the parallel open-circuit branches. When , the minimum frequency of the transmission zero point is obtained. At this moment, the input impedance Z at the cross section of the open port is in It can be expressed as:

[0069] Z in =-jZ0 / tan(βl)=-jZ0 / tanθ=0 (4)

[0070] Under the condition of satisfying formula (4), formula (3) can be obtained:

[0071] Z3-Z1tan(θ1)tan(θ3)=0 (5)

[0072] Since the width of the microstrip line is inversely proportional to the characteristic impedance Z, the characteristic impedance Z1 of the corresponding transmission line can be represented by 1 / pw2, where pw2 is the distance between the two L-shaped slots of each pair of first slots, and pl2 is the electrical length θ1 of the corresponding transmission line. Similarly, (1 / (pw2+2sl1), pl3-pl2) and (1 / pl3, sw1-sl l ) are used to represent (Z2, θ2) and (Z3, θ3) respectively. Therefore, the frequency of the first radiation zero point can be obtained by simplifying equation (5):

[0073]

[0074] Among them, ε eff is the effective relative dielectric constant, which is obtained by equivalently combining a substrate with a thickness of h1 and an air medium with a thickness of h2:

[0075]

[0076] In the formula, ε e ′ is the effective dielectric constant. It can be seen from equation (6) that the first radiation zero point is mainly affected by pl2, pw2 and sw1.

[0077] For the second radiation zero point f n2 = 4.74 GHz, which is due to the vertical currents canceling each other out. Fig.11 It can be seen that at this frequency point, Z in3 =0, then:

[0078]

[0079] From formula (8), we can see that the second radiation zero point is mainly related to sw1 and sl1. When sw1 increases, the position of the radiation zero point moves to low frequency. The position of the radiation zero point can be changed by adjusting sw1 and sl1.

[0080] In order to verify equations (6) and (8), we will now discuss the radiation zero point f n1 and f n2 The position of the L-shaped slot has important parameters sw1, sl1 and pl2 that have a relatively large impact. When other parameters remain unchanged, the L-shaped slot width sw1, the L-shaped slot long side length sl1 and the L-shaped slot short side length pl2 are changed respectively, and the gain simulation results are obtained as follows: Fig.12 As shown. Fig.12 (a) It can be seen that when sl1 changes, the first radiation zero point f n1 The position of the second radiation zero point f n2As sl1 increases, it moves to high frequency. Fig.12 (b) It can be seen that the radiation zero point f n1 and the radiation zero point f n2 The positions of both move toward lower frequencies as sw1 increases, except that the radiation zero point f n1 Specific radiation zero point f n2 The influence of sw1 is more obvious. Fig.12 (c) It can be seen that when pl2 changes, the first radiation zero point f n1 As pl2 increases, it moves to low frequency, and the second radiation zero point f n2 The position will not change.

[0081] (2) Design of Antenna II to Antenna III

[0082] From the above analysis, we can see that by adding two pairs of symmetrical L-shaped slots, Antenna II can generate two radiation zero points at low frequencies, but it does not have filtering characteristics at high frequencies. Then, an F-shaped metal strip is added to the lower surface of the substrate of Antenna II, and the F-shaped metal strip is connected to the inner conductor of the 50-ohm coaxial probe, as shown below. Figure 5 (c) Antenna III is shown. Figure 7 It can be seen that the F-type metal strip produces a radiation zero point at high frequencies.

[0083] In order to further explain the principle of the generation of this zero point, the effect of the patch slot is not considered, and only the effect of introducing the F-type metal strip is considered. Fig.13 The model of antenna III-I shown in the figure is that the slots on the radiation patch of antenna III are removed, and the radiation patch and other parts are kept intact. The antenna III-I is simulated and analyzed equivalently, and its equivalent circuit structure is shown in the figure below. Fig.14 As shown. The F-type metal strip is equivalent to an inductor L s and capacitor C s , L a and C a is derived from the equivalent of an air cavity, L p and C p are the equivalent inductance and equivalent capacitance of the radiation patch, R p Represents the equivalent radiation resistance of the patch. s and C s When resonance occurs, a zero point is generated, and the zero point position is:

[0084]

[0085] The gain of antenna III-I and its equivalent circuit S 21 The simulation verification results are as follows Fig.15 As shown. Fig.15It can be seen that the trend of the antenna gain curve is similar to the filter transmission coefficient S 21 Curve. This shows that the introduced F-type metal strip mainly plays the role of band-stop filtering, thus generating a zero point.

[0086] according to Fig.14 It can be seen that changing the size of the metal strip is equivalent to changing Fig.14 Medium s and C s The value of can directly affect the position of the newly added radiation zero point. Fig.16 As shown, when the length of lm1 is increased, the zero point moves toward lower frequencies.

[0087] In antenna III, the addition of the metal strip can produce a radiation zero point at a high frequency of 5.7 GHz. The current distribution of the patch and the metal strip at this frequency is shown in Fig.17 As shown. Fig.17 It can be seen that there is a strong current on the metal strip, while the patch on the upper surface of the substrate has very little strong current, and most of it is weak current. It can be seen that the metal strip acts as a band-stop filter, which greatly reduces the energy reaching the patch from the coaxial feed.

[0088] (3) Design of Antenna III to Antenna IV

[0089] Although antenna III can generate a radiation zero point in the upper frequency band, the out-of-band suppression effect at high frequencies is not good. In order to further improve the out-of-band suppression at high frequencies and increase the selectivity of the upper frequency band, two pairs of slots are added near the feeding point to obtain antenna IV. Figure 7 Gain simulation curve, antenna IV generates a new zero point f at 5.33GHz n3 The surface current distribution of the patch at the radiation zero point is as follows: Fig.18 shown.

[0090] Depend on Fig.18 It can be seen that at 5.33GHz, the left and right sides of the patch have weaker current distribution, and the middle part of the patch, especially around the newly added slot, has stronger current distribution. Strong currents flow in opposite directions on both sides of the slot and cancel each other out, causing this frequency point to become a new radiation zero point.

[0091] (4) Design of Antenna IV to Antenna V

[0092] To further improve out-of-band suppression and adjust impedance matching, four symmetrical slots are added to antenna IV to change the L-shaped slot into a J-shaped slot. At the same time, the width of the metal is adjusted and the size parameters are optimized to obtain antenna V. Figure 6 It can be seen that antenna V has four resonance points and the impedance matching is optimized. The input impedance of the antenna is as follows: Fig.19 shown.

[0093] Based on transmission line theory, the reflection coefficient S at the antenna feed end is 11 It can be expressed as follows:

[0094]

[0095] Among them, Z in is the input impedance, Z0 is the input impedance. in When it is close to 50Ω, S 11 →-∞, a resonance point will be generated; when the input impedance Z in When it is close to 0Ω or ∞, the reflection coefficient S 11 →0, a zero point will be generated. Fig.19 It can be seen that within the passband range, the four frequency points where the input impedance real part curve intersects with the 50Ω reference line are 4.32GHz, 4.42GHz, 4.7GHz and 5.06GHz, corresponding to the four resonance points of the antenna. The pole where the real part of the input impedance is close to 0Ω corresponds to the radiation zero point of the antenna, and most of the energy will be reflected back. Fig.19 The corresponding frequencies are 3.42 GHz, 4.4 GHz and 5.3 GHz. In addition, the metal strip introduces a radiation zero point at 6.2 GHz in the upper frequency band, which makes a total of four radiation zero points, greatly improving the filtering characteristics.

[0096] 2. Antenna test results and analysis

[0097] In order to verify the design concept of the filtering antenna proposed in this chapter, a physical model of the antenna was made according to the above structure and measured. The Rohde & Schwarz ZNA vector network analyzer and the Satimo spherical near-field test system were used to measure the reflection coefficient and radiation parameters of the physical antenna. The antenna was placed in a microwave darkroom for testing, and the simulation and test results of the reflection coefficient and gain of the filtering antenna were obtained as shown in the figure. Fig. 20 As shown. Fig. 20 It can be seen that the impedance bandwidth of the antenna test is 16.76% (4.32GHz-5.11GHz), which is consistent with the simulation results. Fig. 20 It can also be seen that the tested gain curve is basically consistent with the simulated gain curve, and the maximum gain tested in the working frequency band is about 7.5dBi. The two radiation zero points at the upper edge of the passband appear at 5.36GHz and 6.26GHz, and the two radiation zero points at the lower edge of the passband appear at 3.4GHz and 4.38GHz. The out-of-band suppression level of the lower sideband is greater than 11dB, and the out-of-band suppression of the upper sideband is greater than 17dB.

[0098] Fig.21The simulated and tested normalized radiation patterns of the proposed antenna in the E-plane (XOZ-plane) and H-plane (YOZ-plane) at 4.56 GHz, 4.76 GHz, and 5.06 GHz are shown. It can be observed from the figure that the antenna has a stable radiation pattern in the E-plane and H-plane, and the maximum radiation direction is in the direction of θ = 0°. The tested cross-polarization levels of the radiation patterns of the E-plane and H-plane are both lower than -20 dB, which is slightly higher than the simulated cross-polarization level. This may be affected by the welded SMA connector and the test environment, but the tested radiation pattern is consistent with the simulated radiation pattern as a whole.

[0099] Table 2 lists the comparison between the proposed filtering antenna and the existing filtering antenna. It can be seen that the filtering antenna type proposed in this embodiment has the advantages of broadband, high gain and multiple zero points.

[0100] Table 2 Comparison of the proposed filtering antenna and the existing antenna structure

[0101]

[0102] It can be understood that the embodiments listed above are to illustrate a single-layer broadband multi-zero-point microstrip patch filter antenna proposed by the present invention based on the idea of ​​fusion design filter antenna, which has the advantages of high frequency selectivity and high out-of-band suppression, and its bandwidth can reach 16.76% (4.32GHz~5.11GHz), and the gain reaches 7.5dBi, with high frequency selectivity and out-of-band suppression of more than 11dB. Those of ordinary skill in the art will realize that the embodiments described here are to help readers understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not deviate from the essence of the present invention based on the technical inspirations disclosed by the present invention, and these deformations and combinations are still within the scope of protection of the present invention.

Claims

1. A single-layer broadband multi-zero-point microstrip patch filter antenna, comprising a dielectric substrate (2) and a ground plane (3), wherein a microstrip patch (1) is placed on the upper surface of the dielectric substrate (2), characterized in that: The invention also comprises a coaxial feeding probe (5), wherein a metal strip (4) is provided on the lower surface of the dielectric substrate (2), the metal strip (4) is connected to the coaxial feeding probe (5), the coaxial feeding probe (5) sequentially passes through the ground plate (3), the metal strip (4) and the dielectric substrate (2) to excite the microstrip patch (1), two symmetrical pairs of first slots (6) are provided on the microstrip patch (1), the two pairs of first slots (6) are respectively arranged on both sides of the coaxial feeding probe (5), and two pairs of second slots (9) perpendicular to each other are provided on the microstrip patch (1) between the two pairs of first slots (6).

2. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 1, characterized in that: The two pairs of first slots (6) include a first pair of slots and a second pair of slots symmetrical about a first symmetry axis (7), the first pair of slots include a first L-shaped slot and a second L-shaped slot symmetrical about a second symmetry axis (8), the second pair of slots include a third L-shaped slot and a fourth L-shaped slot symmetrical about the second symmetry axis (8), and the first symmetry axis (7) and the second symmetry axis (8) are perpendicular.

3. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 1, characterized in that: The two pairs of first slots (6) include a first pair of slots and a second pair of slots symmetrical about a first symmetry axis (7), the first pair of slots include a first J-shaped slot (61) and a second J-shaped slot (62) symmetrical about a second symmetry axis (8), the second pair of slots include a third J-shaped slot (63) and a fourth J-shaped slot (64) symmetrical about the second symmetry axis (8), and the first symmetry axis (7) and the second symmetry axis (8) are perpendicular.

4. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 1, characterized in that: The two pairs of second slots (9) include a pair of vertical slots and a pair of horizontal slots. The pair of vertical slots include two first rectangular slots (91) parallel to each other. The pair of horizontal slots include two second rectangular slots (92) parallel to each other. The two second rectangular slots (92) are respectively arranged at two ends of the first rectangular slot (91). The first rectangular slot (91) and the second rectangular slot (92) are perpendicular to each other.

5. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 4, characterized in that: The width of the first rectangular slot (91) is greater than the width of the second rectangular slot (92).

6. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 4, characterized in that: The two first rectangular slots (91) are respectively arranged on both sides of the coaxial feeding probe (5), and the two second rectangular slots (92) are respectively arranged on both sides of the coaxial feeding probe (5).

7. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 4, characterized in that: The metal strip (4) is an F-type metal strip (4), and the F-type metal strip (4) is connected to the inner conductor of the coaxial feeding probe (5).

8. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 7, characterized in that: The metal strip (4) comprises a first metal strip (42), a second metal strip (43) and a third metal strip (44) which are respectively perpendicular to the side metal strip (41) and parallel to each other; the first metal strip (4), the second metal strip (43), the third metal strip (44) and the side metal strip (41) are integrally formed into an F shape, and the side metal strip (41) is parallel to the second rectangular slot (92).

9. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 8, characterized in that: The length of the first metal strip (42) is lm1, the length of the second metal strip (43) is lm2, and the length of the third metal strip (44) is lm3, wherein lm1>lm2>lm3.

10. The single-layer broadband multi-zero-point microstrip patch filter antenna according to claim 1, characterized in that: An air cavity is formed between the dielectric substrate (2) and the grounding plate (3) through a coaxial feeding probe (5).

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