Dual-frequency microstrip planar array antenna working at Ka band

Abstract

The invention discloses a design method of a novel Ka-band microstrip planar array antenna. The antenna has a dual-band working mode. By adopting the one-to-eight power division feed network, efficient feed of the array unit is realized, and good impedance matching is ensured. In addition, the designed decoupling structure DS effectively reduces mutual coupling between the antenna units, the mutual coupling effect is inhibited, and the antenna performance is further optimized. The dual-frequency working frequency band of the antenna is 34-35 GHz and 35-36 GHz, the inter-unit isolation degree is smaller than 35 dB, the average gain exceeds 13 dBi, and the H-surface half-power lobe width is smaller than 20 degrees. The antenna has the advantages of stable bandwidth, low isolation, high gain, high directionality and the like, and is suitable for multiple fields of millimeter wave communication, radar systems, satellite remote sensing and the like.

Description

Technical Field

[0001] The invention relates to an antenna, and in particular to a microstrip patch array antenna with a dual-frequency working mode. Background Art

[0002] In the field of wireless communication technology, antenna design and Ka-band communication are two important research directions. An antenna is a converter that converts guided waves propagating on a transmission line into electromagnetic waves propagating in an unbounded medium (usually free space), or vice versa. The Ka-band is one of the important frequency bands in millimeter wave communication technology, and its frequency range is approximately between 26.5 GHz and 40 GHz. In 5G mobile communication technology, the Ka-band is considered to provide high-capacity and high-speed wireless access, and has a wide range of applications in communication satellites, radar systems, military applications and other fields.

[0003] Dual-frequency antennas are also often used in the design of millimeter-wave antennas. The design methods are mainly divided into two categories: multi-mode and combined. Among them, the multi-mode dual-frequency antenna uses the characteristics of different resonant modes of the antenna to work at different frequencies to achieve dual-frequency operation. The combined dual-frequency antenna combines two antennas working at different frequencies to achieve dual-frequency operation. Each antenna can work independently in its own frequency band, with the advantages of wide frequency coverage, stable communication operation, and strong signal transmission capability.

[0004] In the existing technology, circularly polarized array antennas are usually used to achieve Ka-band dual-band wireless communication. However, these antenna design solutions often have some shortcomings, such as: the antenna size is too large, the gain is not high enough, and the directivity is not concentrated.

[0005] Therefore, it is particularly important to design an antenna that works in the Ka band and has high gain and high directivity while being small in size. Summary of the invention

[0006] The problem to be solved by the present invention is that a microstrip planar array antenna operating in the Ka band satisfies the problems of miniaturization, high gain and high directivity.

[0007] To achieve the above object, an embodiment of the present invention provides a design method for a dual-frequency microstrip planar array antenna operating in the Ka band, comprising:

[0008] The antenna is composed of a bottom dielectric substrate, a metal ground plane, a top dielectric substrate, and a metal patch from bottom to top. The two dielectric substrates and the metal ground plane are circular structures with equal diameters, but their thickness and materials are different.

[0009] Among them, the bottom substrate material provides reinforcement for the antenna as a whole. Metal grounding improves antenna impedance matching, forms an electromagnetic field edge, and enhances radiation. The top dielectric substrate controls the electromagnetic characteristics of the antenna and determines the resonant frequency. The top dielectric substrate radiates and receives electromagnetic waves, forms a resonant structure, controls the antenna directivity, feeds with equal amplitude and phase, and reduces coupling. The left and right sides of the front are covered with two groups of four transmitting antenna arrays and receiving antenna arrays working in two different frequency bands.

[0010] Each receive / transmit antenna array has 4×2 uniform microstrip array antenna units with equal amplitude and phase. There are two 90° chamfers at the edge of the patch unit. On both sides of the patch unit, there are rectangular grooves of the same size and spacing. The rectangular grooves and chamfers increase the antenna bandwidth and improve the frequency band characteristics.

[0011] Each receiving / transmitting antenna array is fed by a separate power splitter feeding network. The smallest unit patch unit consists of a left-right symmetrical one-to-two T-type power splitter. Two one-to-two T-type power splitters are symmetrically transformed and cascaded into a one-to-four T-type power splitter. Two one-to-four T-type power splitters are symmetrically transformed and cascaded into a one-to-eight T-type power splitter. In this structure, each port at the end of the power splitter maintains the same phase difference, equal horizontal spacing and vertical spacing.

[0012] The starting section of the power divider is connected to the coaxial line interface, and the coaxial feed line is connected to the impedance matching network of the antenna through the coaxial line interface. The coaxial line passes through the circular holes on the bottom dielectric substrate and the metal ground, and is connected to the power divider feed network on the front of the top dielectric substrate and the metal ground on the back. There are four circular convex grooves around the coaxial interface probe. The convex grooves fix the connection between the coaxial line and the antenna on the one hand, and prevent the displacement of the antenna structure caused by vibration or temperature changes on the other hand.

[0013] In addition, the axis of the top dielectric substrate also has a symmetrically distributed new decoupling structure. Each new decoupling structure unit is composed of three groups of ring resonators, including one large and two small ones, and the large sub-ring resonator is placed opposite to the small sub-ring resonator. Each sub-ring resonator is composed of three metal patches, one long and two short.

[0014] The embodiments of the present invention have the following advantages:

[0015] The present invention proposes a novel Ka-band microstrip planar array antenna, which has a dual-band working mode. By adopting a one-to-eight power-dividing feeding network, efficient feeding of the array unit is achieved, ensuring good impedance matching. In addition, the designed decoupling structure DS effectively reduces the mutual coupling between antenna units, suppresses the mutual coupling effect, and further optimizes the antenna performance. The antenna has the advantages of stable bandwidth, low isolation, high gain, high directivity, etc., and is suitable for millimeter wave communications, radar systems, satellite remote sensing and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the contents of the embodiments of the present invention and these drawings without paying any creative work.

[0017] Figure 1 These are the front and back views of the physical model of the antenna provided in Example 1 of the present invention.

[0018] Figure 2 This is a schematic diagram of the structure of the patch unit and array provided in Example 1 of the present invention.

[0019] Figure 3 A one-to-eight power division feeding network diagram provided in Example 1 of the present invention.

[0020] Figure 4 The front view and side view of the coaxial line interface provided in Example 1 of the present invention.

[0021] Figure 5 This is an overall diagram of the decoupling structure provided in Example 1 of the present invention.

[0022] Figure 6 A diagram of the components of the decoupling structure unit provided in Example 1 of the present invention.

[0023] Figure 7 It is the reflection coefficient of the two working modes of the antenna provided in Example 1 of the present invention.

[0024] Figure 8 The isolation between the antenna units provided in Embodiment 1 of the present invention.

[0025] Fig. 9 Embodiment 1 of the present invention provides an antenna with a gain within an operating frequency.

[0026] Fig.10 The antenna radiation pattern provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0028] Example 1

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0030] like Figure 1 As shown in the figure, the antenna is composed of a bottom dielectric substrate, a metal ground plane, a top dielectric substrate, and a metal patch from bottom to top. Both the two dielectric substrates and the metal ground plane are circular structures with a diameter of 78 mm, but their thickness and material are different. Among them, the bottom substrate is made of FR4 with a relative dielectric constant of 4.3, a loss tangent of 0.025, and a thickness of 1.6 mm, which provides reinforcement for the antenna as a whole. The metal grounding material is a metal copper with a thickness of 0.035 mm, which is used to improve the impedance matching of the antenna. The top dielectric substrate is made of RogersRT5880 with a relative dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of 0.254 mm. The left and right sides of the top layer are covered with two groups of four transmitting antenna arrays and receiving antenna arrays working in two different frequency bands, respectively represented by Tx1, Rx1, Tx2, and Rx2. The top patch material is the same as the metal grounding, which is copper with a thickness of 0.035 mm and a conductivity of 5.8×107S / m.

[0031] A 4×2 uniform microstrip array antenna with equal amplitude and phase between elements is designed, with two groups of four. Figure 2 As shown. In the designed antenna array, the sizes of the Tx1 and Rx1 patch units are 2.97mm and 2.62mm respectively, while the sizes of the Tx2 and Rx2 patch units are 2.97mm and 2.57mm. In order to optimize the bandwidth characteristics of the antenna, two 90° chamfers with a diameter of 0.2mm are added to the edge of each patch unit. The main function of these chamfers is to widen the bandwidth frequency of the antenna unit by increasing the gap size between the patch and the dielectric substrate. In addition, on both sides of the patch unit, there are rectangular grooves of the same size and the same spacing. The dimensions of the rectangular grooves are 0.2mm (length) and 0.1mm (width), and the groove spacing is 0.1mm. The role of the rectangular grooves is the same as that of the chamfers, which aims to further increase the bandwidth of the antenna and improve the frequency band characteristics.

[0032] The antenna is fed by coaxial cable. Four 50-ohm coaxial interfaces pass through the FR4 dielectric substrate to connect the metal feeder on the front of the Rogers substrate. Each feeder is connected to a one-to-eight-way T-type power divider to provide feed for each array unit. The designed feed network is as follows: Figure 3As shown, the characteristic impedance of each section is 50Ω, 70.7Ω, 100Ω, 60Ω, 70Ω, and 132Ω. The size parameters of each section of the transmission line are calculated from the characteristic impedance and substrate material according to the transmission line theory, among which the 50Ω impedance matching line is 5.5mm long and 0.755mm wide; the 70.7Ω impedance matching line is 1.596mm long and 0.415mm wide; the 100Ω impedance matching line is 2.62mm long and 0.192mm wide; the 60Ω impedance matching line is 1.58mm long and 0.192mm wide; the 70Ω impedance matching line is 4.451mm long and 0.42mm wide; the 132Ω impedance matching line is 1.67mm long and 0.0785mm wide.

[0033] In this feeding structure, the transmission line is connected to the impedance matching network of the antenna through a coaxial line interface. The structure of the coaxial line access part is as follows: Figure 4 As shown in the figure, four 50Ω coaxial lines pass through the circular holes on the FR4 dielectric substrate and are connected to the metal feed line on the front of the Rogers substrate and the metal ground on the back. The diameters of the coaxial connectors are 0.4mm, 1.38mm, 1.58mm, and 5.50mm from the inside to the outside; the probe lengths are 0.29mm, 1.60mm, and 3.40mm. In order to further enhance the mechanical stability of the antenna, four circular convex grooves with a diameter of 0.7mm are carefully designed around the coaxial line. These convex grooves not only fix the coaxial line and the antenna, but also avoid displacement of the antenna structure caused by vibration or temperature changes, thereby ensuring the reliable performance of the antenna in complex environments.

[0034] Finally, a special decoupling structure is introduced between the antenna arrays. This structure is loaded between the antennas to further reduce the coupling effect. The specific design is as follows: Figure 5 A unit of DS is mainly composed of three components of ring resonator (SRR), including a large one and two small ones, such as Figure 6 As shown in the figure, the width of SSR is 0.50mm, and the lengths are 0.78mm, 1.8mm, and 4.80mm from small to large. To ensure the electromagnetic compatibility and consistency of the overall design, the material of DS is the same as that of the patch, which is also metal copper. In terms of the propagation direction of electromagnetic waves, the electromagnetic waves emitted by the antenna array are mainly incident longitudinally, and the electric field is in the horizontal direction. Through the design of this decoupling structure, the coupling between antenna arrays can be effectively reduced, thereby improving the overall performance of the array antenna.

[0035] The reflection coefficient S11 is the ratio of the reflected wave to the incident wave amplitude. Because it is directly related to the performance of the antenna system, it is usually used to describe the reflection characteristics of the antenna and measure the effective working frequency band. For this design example, the working frequency band of the first group of antennas is 33.5-35.9GHz, and the working frequency band of the second group of antennas is 33.75-36.5GHz. Both bands are in the Ka band range. Figure 7 shown.

[0036] Isolation is an important indicator for measuring the performance of a multi-transmitter and multi-receiver antenna. It refers to the ratio of the signal transmitted by one antenna to the signal received by another antenna and the signal of the transmitting antenna. The antenna isolation depends on the radiation direction of the antenna, the spatial distance between the antennas, etc. The isolation between the transmitting and receiving antennas in this embodiment is as follows: Figure 8 As shown, the isolation between Tx1 and Tx2 is less than -50dB, the isolation between Tx1 and Rx2 is less than -45dB, and the isolation between Tx1 and Rx1 is less than -35dB; the isolation between Tx2 and Tx1 is less than -40dB, the isolation between Tx2 and Rx2 is less than -35dB, and the isolation between Tx2 and Rx1 is less than -45dB. Obviously, the isolation between each antenna is lower than -35dB in the whole frequency band, which verifies that the addition of DS structure satisfies the expected decoupling function well.

[0037] exist Fig. 9 The gain of antennas 1 and 2 in the full operating frequency can be observed in Figure 1. The gain of antenna 1 is greater than 13.26dB in the operating frequency band 34-35GHz, and the gain of antenna 2 is greater than 13.63dB in the operating frequency band 35-36GHz, which meets the expected indicator of full-band gain greater than 13dB and shows a high antenna gain.

[0038] like Fig.10 As shown, at the three operating frequencies of 34 GHz, 34.5 GHz and 35 GHz, the E-plane half-power lobe width of antenna 1 is less than 45°, and the H-plane half-power lobe width is less than 20°; at the three operating frequencies of 35 GHz, 35.5 GHz and 36 GHz, the E-plane half-power lobe width of antenna 2 is less than 40°, and the H-plane half-power lobe width is also less than 20°, showing a stable high-directional radiation characteristic.

[0039] In summary, the present invention proposes a design method for a dual-frequency microstrip planar array antenna operating in the Ka band, which can make the antenna have the advantages of stable bandwidth, low isolation, high gain, high directivity, etc. It is suitable for millimeter wave communication, radar system, satellite remote sensing and other fields.

[0040] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A dual-frequency microstrip planar array antenna operating in the Ka band, characterized in that: include: Metal patch; an upper dielectric substrate; Metal ground plane; a bottom dielectric substrate; SMA coaxial cable interface.

2. The metal patch according to claim 1, characterized in that: include: Patch unit array, power division feeding network, and new decoupling structure.

3. The metal patch unit array according to claim 2, characterized in that: include: There are two groups of four 4×2-element uniform microstrip array antennas with equal amplitude and phase between units; the edge of each patch unit contains two 90° chamfers; There are rectangular grooves of the same size and spacing on both sides of the patch unit.

4. The power division feeding network of the metal patch according to claim 2, characterized in that: Each part is a one-to-two T-type power divider that is symmetrical on the left and right. Two one-to-two T-type power dividers are symmetrically transformed and cascaded into a one-to-four T-type power divider. Two one-to-four T-type power dividers are symmetrically transformed and cascaded into a one-to-eight T-type power divider. The ports at the end of the power divider maintain the same phase difference, equal horizontal spacing and equal vertical spacing.

5. The novel decoupling structure of the metal patch according to claim 2 is characterized in that: A unit of the new decoupling structure is mainly composed of three split-ring resonators, one large and two small, which are printed on the axial position of the top dielectric substrate. The large split-ring resonator is placed opposite to the small split-ring resonator, and each split-ring resonator is composed of three metal patches, one long and two short.

6. The SMA coaxial line interface according to claim 1, characterized in that: The transmission line is connected to the impedance matching network of the antenna through the SMA coaxial cable interface; the four coaxial interfaces pass through the circular holes on the two layers of dielectric substrates and the metal ground, and are connected to the power division feeding network on the front side of the top dielectric substrate and the metal ground on the back side; there are four circular convex grooves around the coaxial interface probe.

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