Single-layer broadband multi-zero microstrip patch filter antenna

Abstract

The present invention discloses a single-layer broadband multi-zero microstrip patch filter antenna, comprising a dielectric substrate, a coaxial feed probe, and a ground plane. The coaxial feed probe forms an air cavity between the dielectric substrate and the ground plane. A microstrip patch is placed on the upper surface of the dielectric substrate, and a metal strip is provided on the lower surface of the dielectric substrate. The metal strip is connected to the inner conductor of the coaxial feed probe. The coaxial feed probe sequentially passes through the ground plane, the metal strip, and the dielectric substrate to excite the microstrip patch. Two symmetrical pairs of first slots are provided on the microstrip patch, the two pairs of first slots being arranged on either side of the coaxial feed probe. Two pairs of second slots, perpendicular to each other, are provided on the microstrip patch between the two pairs of first slots. The first slot can generate two radiation nulls at low frequencies. The metal strip acts as a band-stop filter, generating a radiation null at high frequencies. The second slot generates another radiation null at high frequencies, further improving out-of-band suppression.

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 become increasingly complex and feature-rich, the area available for RF front-end circuitry is shrinking. To meet the diverse demands of wireless communication, modern wireless communication systems are evolving towards miniaturization, multi-functionality, and low cost. To reduce the size of the RF front-end while suppressing interference and minimizing losses, filter antennas—integrated filters and antennas—have emerged.

[0003] Filter antennas offer numerous advantages. First, they eliminate the need for matching circuits, reducing circuit size and losses, thus meeting the demand for a large number of miniaturized base stations in the millimeter-wave communication era. Second, they eliminate the need for matching between the two, simplifying their use. Third, they eliminate the possibility of incomplete matching between the filter and antenna ports, improving overall circuit stability. Fourth, they provide inter-frequency decoupling. Due to the high out-of-band selectivity of filter antennas, the energy in the stopband of two antennas operating at close frequencies can be significantly suppressed, significantly reducing the coupling between them. Microstrip patch antennas, with their compact size, light weight, ease of integration, and simple manufacturing, are widely used in wireless communication systems.

[0004] Traditional filter antenna design generally employs two approaches. One involves directly cascading the antenna and filter, while the other integrates the filter with the antenna, making the antenna the filter's final resonator. However, these approaches inevitably introduce additional insertion loss, increasing system complexity and size. In recent years, a fusion design approach has been proposed that eliminates the need for additional filtering circuitry. This approach utilizes techniques such as patch slotting, loading short-circuit vias, loading / stacking parasitic patch structures, adding open / short-circuit stubs, and leveraging electromagnetic coupling to achieve a fused, integrated filter and antenna design. This results in a filter antenna that combines both in-band radiation and out-of-band filtering. Summary of the Invention

[0005] The present 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 a simple and compact structure is proposed.

[0006] In order to achieve the above objectives, the specific solutions of this application are as follows:

[0007] A single-layer broadband multi-zero point microstrip patch filter antenna includes a dielectric substrate, a coaxial feeding probe, and a ground plane. A microstrip patch is placed on the upper surface of the dielectric substrate, and 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 plane, 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, and the two pairs of first slots are respectively arranged on both sides of the coaxial feeding probe. 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 the first axis of symmetry, the first pair of grooves include a first L-shaped groove and a second L-shaped groove that are symmetrical about the second axis of symmetry, and the second pair of grooves include a third L-shaped groove and a fourth L-shaped groove that are symmetrical about the second axis of symmetry, and the first axis of symmetry and the second axis of symmetry 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 axis of symmetry, the first pair of grooves include a first J-shaped groove and a second J-shaped groove that are symmetrical about a second axis of symmetry, the second pair of grooves include a third J-shaped groove and a fourth J-shaped groove that are symmetrical about the second axis of symmetry, and the first axis of symmetry and the second axis of symmetry 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, the two first rectangular slots are respectively disposed on both sides of the coaxial feeding probe, and the two second rectangular slots are respectively disposed on both sides of the coaxial feeding probe.

[0013] In some specific embodiments, the metal tape is an F-shaped metal tape, and the F-shaped 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 strips and parallel to each other. The first metal strip, the second metal strip, the third metal strip, and the side metal strips are integrally formed into an F shape, and the side metal strips are parallel to the second rectangular slot.

[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 a coaxial feeding probe to improve impedance matching.

[0017] The present invention has the beneficial effects:

[0018] Based on the concept of integrated filter antenna design, this paper designs a single-layer broadband multi-null microstrip patch filter antenna, which includes 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 nulls at low frequencies. An F-shaped metal strip is added to the lower surface of the substrate and connected to a feed probe. The probe passes through the substrate and the metal strip to excite the microstrip patch, generating a radiation pattern TM. 10 Patterns and TMs 02 mode. The F-type metal strip primarily acts as a band-stop filter, creating a radiation null at high frequencies. Adding two pairs of slots near the feed point on the microstrip patch creates another radiation null at high frequencies and further improves out-of-band rejection.

[0019] The antenna provided in this application generates two radiation nulls on either side of the passband, producing filtering characteristics at the upper and lower sidebands, respectively. An air cavity is provided between the dielectric substrate and the ground plane to improve impedance matching. The antenna structure of this application is simple and does not require additional filtering circuit structures. The antenna has an impedance bandwidth of 16.76% (4.32 GHz to 5.11 GHz) and a gain of 7.5 dBi, with high frequency selectivity and out-of-band suppression exceeding 11 dB. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0024] Figure 5Schematic diagram of antenna structure evolution 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 1, 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 a schematic diagram of the structure of antenna IV. Figure 5 (e) is a schematic diagram of the antenna V structure;

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

[0029] Figure 10 Schematic diagram of the structural parameters of one pair of L-shaped slots in Antenna II;

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

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

[0032] Figure 13 Schematic diagram of the structure of reference antenna III-I;

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

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

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

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

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

[0038] Figure 19 Schematic diagram of the input impedance of antenna V;

[0039] Figure 20 Schematic diagram of the reflection coefficient and gain simulation and test results obtained based on the antenna physical model;

[0040] Figure 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 from simulation and testing based on the measurement of the antenna physical model, 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 numbers in the accompanying drawings correspond to the following names: 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 following will be described with reference to the accompanying drawings and specific embodiments, but the embodiments of the present invention are not limited thereto.

[0045] Example 1:

[0046] like Figure 1-Figure 4 As shown, this embodiment provides a single-layer broadband multi-zero point microstrip patch filter antenna 1, 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 a 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, and an F-shaped metal strip 4 is provided on the lower surface of the dielectric substrate 2. The F-shaped 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 frequencies, 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 that are symmetrical about a first symmetry axis 7. The first pair of slots includes a first L-shaped slot and a second L-shaped slot that are symmetrical about a second symmetry axis 8. The second pair of slots includes a third L-shaped slot and a fourth L-shaped slot that are symmetrical about the second symmetry axis 8. The first symmetry axis 7 and the second symmetry axis 8 are perpendicular. The first L-shaped slot and the third L-shaped slot are symmetrical about the first symmetry axis 7, and the second L-shaped slot and the fourth L-shaped slot are symmetrical about the first symmetry axis 7. The L-shaped inflection points of the four L-shaped slots are close to each other, as shown in FIG. Figure 5 (b) The structure shown in antenna II.

[0048] Although the L-shaped slot can generate two radiation nulls at low frequencies and the F-shaped metal strip 4 can generate a radiation null in the upper frequency band, the out-of-band suppression effect at high frequencies is not good. Therefore, to further improve out-of-band suppression and adjust impedance matching, in this embodiment, the L-shaped slot is replaced with four mutually symmetrical J-shaped slots. Specifically, 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 includes 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 includes a third J-shaped slot 63 and a fourth J-shaped slot 64 symmetrical about the second symmetry axis 8. The first symmetry axis 7 and the second symmetry axis 8 are perpendicular.

[0049] In order to further improve out-of-band suppression and adjust impedance matching, the width of the metal strip 4 is adjusted and the size parameters are optimized, such as Figure 13As shown, the metal strip 4 includes a first metal strip 42, a second metal strip 43, and a third metal strip 44, each perpendicular to and parallel to the side metal strip 41. 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. When adjusting the size of the metal strip 4, the length of the first metal strip 42 is 1m1, the length of the second metal strip 43 is 1m2, the length of the third metal strip 44 is 1m3, and the length of the side metal strip 41 is 1m2. The width of the entire F-shaped metal strip 4 is wm2, where 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 mutually parallel first rectangular slots 91, and the horizontal slots include two mutually parallel second rectangular slots 92. 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 respectively arranged at right angles to each other. The two first rectangular slots 91 are respectively arranged on either side of the coaxial feed probe 5, and the two second rectangular slots 92 are respectively arranged on either side of the coaxial feed probe 5. In other words, 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 distance between the two first rectangular slots 91 but less than the distance between the two pairs of first slots 6. The distance 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 specific antenna structural parameter values ​​for this embodiment. The dielectric substrate 2 uses Rogers 5880 with a thickness of h1 = 0.508 mm. A microstrip patch 1 is placed on top of the dielectric substrate 2, centered above the dielectric substrate 2 and spaced wg from the substrate edge. A ground plane 3 is located below the dielectric substrate 2, separated by a distance of 4 mm, forming an air cavity. Four symmetrical J-shaped slots are etched into the patch, and a pair of slots are also etched horizontally and vertically near the feed point. An F-shaped metal strip 4 is introduced on the bottom surface of the dielectric substrate 2 and connected to the coaxial probe for feeding. This creates a radiation null at high frequencies, improving 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] 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 of each antenna structure in the design process will be analyzed.

[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) has 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 feed 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| for these five antennas are shown in the figure below. 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 traditional rectangular microstrip patch antenna, except that the lower surface of the substrate is not directly covered with metal as a ground plane. Instead, an air gap of height h2 exists between the substrate and the ground plane. Adjusting the size of air gap h2 can tune the antenna's input impedance.

[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 as follows: 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 as follows Figure 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, which produces 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. Figure 9 (a) shows that the large 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 in the horizontal direction. The energy at the frequency cannot be radiated, thus generating a radiation zero point. Figure 9 As shown in Figure (b), the areas with the largest surface currents at 4.74 GHz are primarily on either side of the slot. The currents flow primarily in the longitudinal direction, with opposite directions along the slot. The upward and downward currents on either side of the slot cancel each other out, creating another radiation null.

[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: Figure 10 As shown, the equivalent structure diagram explaining the radiation zero point is as follows Figure 11 As shown, Figure 11 As shown, Z in1 and Z in2 Respectively represent the input impedance indicated in the figure, 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 can 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 branch. It is generally set to When , the minimum frequency of the transmission zero point is obtained. At this moment, the input impedance Z at the open port cross section 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 expressed as 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] Where, 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 =4.74GHz, which is due to the vertical currents canceling each other. Figure 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 a relatively large influence on the important parameters sw1, sl1 and pl2. 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 as follows: Figure 12 As shown. Figure 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 toward high frequency. Figure 12 (b) It can be seen that the radiation zero point f n1 and 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. Figure 12 (c) It can be seen that when pl2 changes, the first radiation zero point f n1 As pl2 increases, it moves to the 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 nulls 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 the introduction of the F-type metal strip is considered. Figure 13 The model of antenna III-I is shown in the figure. Antenna III-I is the same as antenna III, in which the slots on the radiating patch are removed, leaving the radiating patch and other parts intact. Antenna III-I is simulated and analyzed equivalently, and its equivalent circuit structure is shown below. Figure 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 equivalent to the 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 Figure 15 As shown. Figure 15It can be seen that the trend of the antenna gain curve is similar to the filter transmission coefficient S 21 The curve shows that the introduced F-type metal strip mainly plays the role of band-stop filtering, thus generating a zero point.

[0086] according to Figure 14 It can be seen that changing the size of the metal strip is equivalent to changing Figure 14 Medium L s and C s The value of can directly affect the position of the newly added radiation zero point. Figure 16 As shown in FIG, 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 as follows: Figure 17 As shown. Figure 17 It can be seen that there is a strong current on the metal strip, while the patch on the substrate surface has very little strong current, and most of the current is weak. This shows that the metal strip acts as a band-stop filter, greatly reducing 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 null 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 feed point to obtain Antenna IV. Figure 7 The gain simulation curve of antenna IV shows a new zero point f at 5.33 GHz. n3 The surface current distribution of the patch at the radiation zero point is as follows: Figure 18 shown.

[0090] Depend on Figure 18 It can be seen that at 5.33 GHz, the current distribution is weak on the left and right sides of the patch, while the current distribution is strong in the center of the patch, especially around the newly added slot. The strong currents flow in opposite directions on both sides of the slot, canceling each other out, resulting in a new radiation null at this frequency.

[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, changing 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: Figure 19 shown.

[0093] Based on the 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. Figure 19 It can be seen that within the passband, the four frequency points where the input impedance real part curve intersects the 50Ω reference line are 4.32GHz, 4.42GHz, 4.7GHz and 5.06GHz, corresponding to the four resonance points of the antenna. The extreme point where the input impedance real part is close to 0Ω corresponds to the radiation zero point of the antenna, and most of the energy will be reflected back. Figure 19 The corresponding frequencies are 3.42 GHz, 4.4 GHz, and 5.3 GHz. Together with the metal strip creating a radiation null at 6.2 GHz in the upper band, there are four radiation nulls, significantly 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 based on the above structure and measured. The reflection coefficient and radiation parameters of the physical antenna were measured using a Rohde & Schwarz ZNA vector network analyzer and a Satimo spherical near-field test system. 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 below. Figure 20 As shown. Figure 20 It can be seen from the figure that the impedance bandwidth of the antenna test is 16.76% (4.32GHz-5.11GHz), which is consistent with the simulation results. Figure 20 The measured gain curves are essentially consistent with the simulated ones, with the maximum gain measured within the operating band being approximately 7.5 dBi. The two radiation nulls at the upper edge of the passband appear at 5.36 GHz and 6.26 GHz, respectively, while the two radiation nulls at the lower edge appear at 3.4 GHz and 4.38 GHz, respectively. Out-of-band suppression at the lower sideband exceeds 11 dB, while that at the upper sideband exceeds 17 dB.

[0098] Figure 21The proposed antenna's normalized radiation patterns for the E-plane (XOZ plane) and H-plane (YOZ plane) at 4.56 GHz, 4.76 GHz, and 5.06 GHz are shown, both simulated and tested. The figure shows that the antenna exhibits stable radiation patterns in both the E-plane and H-plane, with maximum radiation at θ = 0°. The tested cross-polarization levels for both the E-plane and H-plane radiation patterns are below -20 dB, slightly higher than the simulated cross-polarization levels. This is likely due to the soldered SMA connector and the test environment. However, the tested radiation patterns are generally consistent with the simulated radiation patterns.

[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 existing antenna structure

[0101]

[0102] It is understandable that the embodiments listed above are intended to illustrate a single-layer broadband multi-zero-point microstrip patch filter antenna proposed by the present invention based on the concept of fusion design of filter antennas, which has advantages such as high frequency selectivity and high out-of-band suppression. Its bandwidth can reach 16.76% (4.32GHz to 5.11GHz), and its gain reaches 7.5dBi, with high frequency selectivity and out-of-band suppression of more than 11dB. Those skilled in the art will appreciate that the embodiments described here are intended 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 skilled in the art can make various other specific variations and combinations based on the technical inspiration disclosed by the present invention without departing from the essence of the present invention, and these variations 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), and characterized in that: It also includes a coaxial feeding probe (5), 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 provided 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); 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; 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, and 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 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 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).

2. The single-layer broadband multi-zero 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.

3. The single-layer broadband multi-zero microstrip patch filter antenna according to claim 1, characterized in that: The width of the first rectangular slot (91) is greater than the width of the second rectangular slot (92).

4. The single-layer broadband multi-zero microstrip patch filter antenna according to claim 1, 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).

5. The single-layer broadband multi-zero microstrip patch filter antenna according to claim 4, characterized in that: The metal strip (4) includes 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 (42), 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).

6. The single-layer broadband multi-zero point microstrip patch filter antenna according to claim 5, characterized in that: The length of the first metal strip (42) is 1m1, the length of the second metal strip (43) is 1m2, and the length of the third metal strip (44) is 1m3, wherein 1m1>1m2>1m3.

7. The single-layer broadband multi-zero 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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