A novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna

Abstract

This invention belongs to the field of antenna technology in wireless communication, specifically relating to a novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna, comprising two dielectric substrates and three metal layers, which, from top to bottom, are a first metal layer, an upper dielectric substrate, a second metal layer, a lower dielectric substrate, and a third metal layer; the upper dielectric substrate has metallized vias; the first metal layer, the upper dielectric substrate, and the second metal layer together constitute a first structure; the third metal layer and the lower dielectric substrate form a second structure for enabling the antenna to generate unidirectional radiation; the first structure includes a radiating element, which comprises two rectangular loop pairs, each of which achieves a 90° phase delay; this invention uses sequential rotation technology as its design concept, employing a rectangular loop structure with broadband characteristics to improve the antenna's operating bandwidth and gain; the use of SIW feeding not only reduces the antenna's profile height but also facilitates integration into millimeter-wave circuits.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology for wireless communication, and specifically relates to a novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna. Background Technology

[0002] The surge in applications has led to increasing scarcity of microwave spectrum resources. The millimeter-wave band, with its richer spectrum, has attracted strong interest from both academia and industry, with many popular applications such as communications, radar, and electromagnetic imaging shifting towards it. Currently, the fifth-generation (5G) wireless communication technology offers higher data transmission rates, greater system capacity, and a better user experience, making the development of the millimeter-wave band a crucial direction for future communication technology development.

[0003] Antennas are fundamental components of wireless communication systems, essential devices for radiating and receiving radio waves. In other words, they provide the conversion from guided waves on transmission lines to "free space" waves (and vice versa during reception). Therefore, antennas directly impact the performance of radio communication systems. Compared to previous communication systems, modern systems are often more complex in design and achieve superior performance, placing higher demands on antenna engineers. Previously, antennas primarily used linear polarization, but linearly polarized electromagnetic waves are prone to attenuation and distortion during propagation. Maximum signal strength is achieved only when the transmitter and receiver have the same polarization direction; otherwise, polarization mismatch occurs, affecting communication performance. Compared to linearly polarized antennas, circularly polarized antennas, where the electric field intensity vector changes along a circular trajectory over time, offer several advantages: First, circularly polarized antennas can receive electromagnetic waves of any polarization, are insensitive to polarization, thus reducing signal loss due to polarization mismatch and exhibiting strong resistance to attenuation. Second, circularly polarized antennas possess orthogonality of rotation, suppressing multipath interference. When electromagnetic waves propagate through trees, buildings, or in rainy weather, they are scattered by obstacles. The scattered waves and the direct wave are both received by the antenna, causing signal distortion and potentially multipath interference. However, the signal emitted by a circularly polarized antenna reverses its direction of rotation when it encounters an obstacle. This results in the direct and scattered waves having orthogonal directions of rotation, providing high isolation. Consequently, only the direct wave is received by the receiving antenna. Thirdly, circularly polarized antennas avoid the Faraday rotation effect. The polarization direction of linearly polarized waves rotates when passing through the ionosphere, causing signal loss. Circularly polarized waves, however, remain circularly polarized after rotation through the ionosphere, avoiding these losses. Therefore, circularly polarized antennas are widely used in satellite positioning, radar reconnaissance, and mobile communications.

[0004] The demand for wireless communication in modern society is constantly growing, and the channel capacity provided by existing wireless communication systems is becoming increasingly inadequate. High frequency and broadband have become the development direction of modern wireless communication systems. The bandwidth directly determines the communication capacity of a wireless system. Past wireless communication systems typically had low frequencies and limited bandwidth, making it difficult to meet the ever-increasing communication demands. Existing radio systems have already occupied specific frequency bands on the radio spectrum, making spectrum resources extremely congested and limiting bandwidth increases. Higher frequency bands offer abundant spectrum resources, making the design of high-frequency communication systems a hot topic. The design of circularly polarized antennas is also developing towards high frequency and broadband. In practical applications, antennas are placed in aircraft, high-speed trains, fast-moving cars, or handheld devices. In these applications, circularly polarized antennas require miniaturization, low profile, ease of integration, and high gain.

[0005] Professor Hong Wei of Southeast University and Professor Wu Ke of the University of Montreal, Canada, proposed a substrate integrated waveguide structure. Substrate integrated waveguides are mainly used in microwave and millimeter-wave bands, inheriting the advantages of easy integration and low radiation loss of traditional microstrip waveguides. In substrate integrated waveguide circuits, metal pillars are embedded in printed circuit boards, with conductive sheets covering both sides of the printed circuit board, replacing the vertical metal walls of traditional waveguides. Substrate integrated waveguides possess the advantages of traditional waveguide circuits, such as low radiation loss, high quality factor, and high power capacity, while being easily manufactured using existing technologies such as printed circuit boards and low-temperature co-fired ceramics. Furthermore, substrate integrated waveguide circuits are easy to integrate with other circuits. Based on the above analysis, it is evident that substrate integrated waveguide technology offers antennas in the microwave and millimeter-wave bands with low radiation loss, high gain, high quality factor, ease of fabrication, and ease of integration, thus making it a valuable research area.

[0006] Loop antennas are a traditional type of antenna, possessing advantages such as wide bandwidth, simple structure, low cost, light weight, and ease of fabrication. They are commonly seen in various applications, including early televisions and various smart terminals. In academia, since the radiation pattern of a magnetic dipole is complementary to that of an electric dipole, loop antennas have been extensively studied and widely used as an equivalent magnetic dipole since the 1930s, often combined with electric dipoles to form magnetoelectric dipole antennas. Furthermore, thanks to their theoretical simplicity, ease of fabrication, and low processing cost, loop antennas are frequently used in wideband, high-gain communication applications, with rhomboid and circular loop antennas being the most common.

[0007] Currently, improving the bandwidth of loop antennas mainly focuses on changing the number of loops to increase their impedance bandwidth or improve their gain. However, it is worth mentioning that as the number of loops increases to a certain point, the bandwidth of the loop antenna will decrease sharply. In the paper "A new wideband modified biquad antenna at VHF for communication systems" by Abdolahi M et al., the bandwidth and gain of the antenna are improved by introducing active devices and reflectors; however, the reflector of this antenna is huge and has a high profile, occupying a large installation space. In the paper "An integrated wide-band circularly polarized antenna for millimeter-wave applications" by Mohammad Fakharzadeh et al., the antenna integration is improved by using a 6-layer IC package, but the antenna gain is low. In the paper "Arhombic antenna array solution in WLB package for millimeter-wave applications" by Hamidipour A et al., the authors propose a method for designing an array with 4 elements: by feeding one element and connecting all the other elements through a half-wavelength transmission line. Although this scheme allows all array elements to have in-phase excitation and radiation when fed differentially, the antenna faces problems such as low efficiency and can only be used in the narrow available bandwidth of 77 GHz. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna, characterized by comprising two dielectric substrates and three metal layers, which, from top to bottom, are a first metal layer, an upper dielectric substrate, a second metal layer, a lower dielectric substrate, and a third metal layer; the upper dielectric substrate is provided with metallized vias; the first metal layer, the upper dielectric substrate, and the second metal layer together constitute a first structure; the third metal layer and the lower dielectric substrate form a second structure, used to enable the antenna to generate unidirectional radiation;

[0009] The first structure is divided into five parts: a grounded coplanar waveguide, a substrate integrated waveguide-grounded coplanar waveguide transition section, a substrate integrated waveguide, a tapered microstrip line, and a radiating unit. The radiating unit includes two pairs of rectangular rings, each pair achieving a 90° phase delay. Further, the tapered microstrip line is divided into a first tapered microstrip line and a second tapered microstrip line. The radiating unit includes a first pair of rectangular rings and a second pair of rectangular rings. In the first pair of rectangular rings, the outward-opening end of the first rectangular ring is connected to the first tapered microstrip line, and the outward-opening end of the second rectangular ring is connected to the first rectangular ring via a first phase-delayed microstrip line. In the second pair of rectangular rings, the outward-opening end of the third rectangular ring is connected to the second tapered microstrip line, and the outward-opening end of the fourth rectangular ring is connected to the third rectangular ring via a second phase-delayed microstrip line.

[0010] Furthermore, the first and second rectangular rings exhibit a mirror distribution, as do the third and fourth rectangular rings.

[0011] Furthermore, a first rectangular ring pair and a first tapered microstrip line are disposed on the upper surface of the upper dielectric substrate, and a second rectangular ring pair and a second tapered microstrip line are disposed on the lower surface of the upper dielectric substrate, with the positions of the first tapered microstrip line and the second tapered microstrip line overlapping each other.

[0012] Furthermore, all four rectangular rings have broadband characteristics, and the lengths of the first and second phase-delay microstrip lines are both quarter wavelengths. By feeding the four rectangular rings with the first and second phase-delay microstrip lines, the first, second, third, and fourth rectangular rings obtain sequential phase-rotation currents of 0°, 90°, 180°, and 270°, respectively, thereby enabling the antenna to operate in a circularly polarized manner.

[0013] Furthermore, the grounded coplanar waveguide includes a microstrip line of equal width, with a row of metallized vias on both the upper and lower sides of the microstrip line.

[0014] Furthermore, the substrate-integrated waveguide-ground coplanar waveguide transition section includes a tapered microstrip line, with a row of metallized vias on both the upper and lower sides of the tapered microstrip line. Furthermore, both dielectric substrates are Rogers 5880 dielectric substrates with a dielectric constant of 2.2 and a loss tangent of 0.0009; the upper dielectric substrate has a thickness of 0.254 mm, and the lower dielectric substrate has a thickness of 1.508 mm.

[0015] The beneficial effects of this invention are:

[0016] This invention provides a novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna. The antenna has a profile height of 1.829 mm (0.16λg), where λg is the waveguide wavelength with a center frequency of 28 GHz and a dielectric constant of 2.2. The antenna has an S11 (< -10 dB) bandwidth of 35.7%, an AR (< 3 dB) bandwidth of 38.9%, and a coincidence bandwidth of 35.7%.

[0017] The antenna proposed in this invention is mainly designed based on sequential rotation, and uses a rectangular ring with broadband characteristics as the radiation structure, which improves the antenna's operating bandwidth and gain. The use of SIW feeding not only achieves low profile characteristics, but also makes the antenna easy to integrate into millimeter-wave circuits.

[0018] This invention represents a significant improvement over the profile height of 0.5m (0.5λg) in reference 1 by Abdolahi M et al., the gain of only 6dBi in reference 2 by Mohammad Fakharzadeh et al., and the bandwidth of 1.1% in reference 2 by Hamidipour A. Attached Figure Description

[0019] Figure 1 This is a side view of the antenna according to an embodiment of the present invention;

[0020] Figure 2 Example 1: Top view of an antenna according to an embodiment of the present invention;

[0021] Figure 3 Example 2 is a top view of an antenna according to an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of the improvement process of the rectangular loop antenna according to an embodiment of the present invention;

[0023] Figure 5 This is a graph showing the variation of S11 with frequency in an embodiment of the present invention.

[0024] Figure 6 This is a graph showing the AR (Average Reduction) frequency variation according to an embodiment of the present invention.

[0025] Figure 7 This is a graph showing the change in Gain with frequency according to an embodiment of the present invention.

[0026] Wherein, 1-first metal layer, 2-upper dielectric substrate, 3-second metal layer, 4-lower dielectric substrate, 5-third metal layer, 6-radiating unit, 7-grounded coplanar waveguide, 8-transition section, 9-substrate integrated waveguide, 10-tapered microstrip line, 20-equal width microstrip line, 30-gradient microstrip line. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention proposes a novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna, which incorporates two new mechanisms: "substrate integrated waveguide (SIW)" and "sequential rotation technology." These two mechanisms are respectively designed to address the following three problems:

[0029] (1) By using the feeding structure of the substrate integrated waveguide, the problems of high antenna profile, difficult integration and difficult conformal design are solved, making the antenna easy to integrate into millimeter wave circuits;

[0030] (2) The antenna’s operating bandwidth and gain performance are further improved by using a rectangular ring structure that operates under sequential rotation technology.

[0031] (3) The problem of low antenna gain can be solved by increasing the number of rectangular rings.

[0032] In one embodiment, such as Figure 1 As shown in the antenna side view, a novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna includes two dielectric substrates and three metal layers; the two dielectric substrates are composed of an upper dielectric substrate 2 and a lower dielectric substrate 4; the three metal layers include a first metal layer 1, a second metal layer 3, and a third metal layer 5; from Figure 1 As can be seen, the overall structure consists of a first metal layer 1, an upper dielectric substrate 2, a second metal layer 3, a lower dielectric substrate 4, and a third metal layer 5 from top to bottom; the upper dielectric substrate 2 is provided with metallized vias; the first metal layer 1, the upper dielectric substrate 2, and the second metal layer 3 constitute the first structure, and the third metal layer 5 and the lower dielectric substrate 4 form the second structure, which is used to enable the antenna to generate unidirectional radiation.

[0033] like Figure 2 As shown, the first structure can be divided into a grounded coplanar waveguide (GCPW) 7, a substrate integrated waveguide-grounded coplanar waveguide transition section 8, a substrate integrated waveguide (SIW) 9, a tapered microstrip line 10, and a radiating unit 6; the radiating unit includes two rectangular ring pairs, each of which achieves a 90° phase delay.

[0034] Specifically, both dielectric substrates are Rogers 5880 dielectric substrates with a dielectric constant of 2.2 and a loss tangent of 0.0009; wherein the upper dielectric substrate 2 has a thickness of 0.254 mm and the lower dielectric substrate 4 has a thickness of 1.508 mm.

[0035] Specifically, such as Figure 1 As shown, the three metal layers are the same size as the two dielectric substrates; among them, the lower dielectric substrate 4 and the third metal layer 5 are for realizing unidirectional radiation of the antenna and further improving the antenna gain.

[0036] In one embodiment, such as Figure 3 As shown, the grounded coplanar waveguide 7 also includes a microstrip line 20 of equal width. The microstrip line 20 of equal width has a row of metallized vias on both the upper and lower sides to facilitate impedance matching with the port. A rectangular gap is provided between each row of metallized vias and the microstrip line 20 of equal width. The microstrip line 20 of equal width in the grounded coplanar waveguide 7 is replaced with a tapered microstrip line 30. At the same time, the rectangular gap between each row of metallized vias and the tapered microstrip line 30 is replaced with a tapered gap to form a substrate integrated waveguide-grounded coplanar waveguide transition section 8. The substrate integrated waveguide-grounded coplanar waveguide transition section 8 is adjacent to the grounded coplanar waveguide 7.

[0037] Substrate integrated waveguides (SIWs) are dielectric-filled metallic waveguides with a planar structure. Compared to traditional metallic waveguides, they offer advantages such as low profile, low loss, and ease of integration with planar circuits. Compared to planar transmission lines like microstrip lines, they offer advantages such as low loss and less susceptibility to external influences. SIW structures have been widely used in millimeter-wave band circuit and antenna design. Furthermore, SIWs feature parallel feeding characteristics, which are beneficial for improving antenna performance. To achieve broadband circular polarization, sequential rotation technique (SRT) is employed, where the antenna's radiating elements are fed with uniform amplitude and a 90° progressive phase shift.

[0038] Specifically, such as Figure 2 As shown, a row of periodic metallized vias is provided on each side of the middle part of the upper dielectric substrate 2. These two rows of periodic metallized vias connect the first metal layer 1 and the second metal layer 3 to form SIW, i.e., substrate integrated waveguide 9.

[0039] In one embodiment, such as Figure 2 As shown, the loop antenna proposed in this invention has a very simple structure. Overall, it consists of a radiating element and a feed line, wherein the feed line includes a grounded coplanar waveguide 7, a substrate integrated waveguide-grounded coplanar waveguide transition 8, a substrate integrated waveguide 9, and a tapered microstrip line 10, with the remainder being the radiating part.

[0040] Specifically, the grounded coplanar waveguide 7 and the substrate integrated waveguide-grounded coplanar waveguide transition 8 enable the antenna to achieve maximum transmission power from the feed port to the SIW, thus achieving impedance matching. Furthermore, the SIW excites the radiating portion via a tapered microstrip line 10 for antenna radiation. The two large through-holes etched at the top and bottom corners of the leftmost part of the antenna structure (the portion containing the grounded coplanar waveguide 7) are for antenna fixation and facilitate antenna measurements.

[0041] A rectangular ring is set on the upper surface and the lower surface of the upper dielectric substrate, forming a shape like... Figure 4 The structure shown in (a) allows for circular polarization of a single rectangular ring antenna, but its operating bandwidth is relatively narrow. Therefore, coupling between the rectangular rings allows them to resonate at their corresponding frequencies, thus widening the antenna's bandwidth. Figure 4 As shown in (b), an additional rectangular ring is added to both the upper and lower surfaces of the upper dielectric substrate. To further broaden the antenna bandwidth, a pair of rectangular rings on the same surface are connected by a phase-delay microstrip line with a length of one-quarter wavelength, achieving a 90° phase delay, as shown below. Figure 4 As shown in (c), the overall antenna forms a "ring-microstrip line-ring" structure, which further broadens the antenna's operating bandwidth.

[0042] To further improve impedance matching, the SIW is connected to the rectangular ring patch of the radiating unit via a tapered microstrip line.

[0043] Specifically, as shown in Figure 1, a first rectangular ring pair and a first tapered microstrip line are disposed on the upper surface of the upper dielectric substrate, and a second rectangular ring pair and a second tapered microstrip line are disposed on the lower surface of the upper dielectric substrate, as shown in Figure 1. Figure 2 As shown, the positions of the first tapered microstrip line and the second tapered microstrip line overlap.

[0044] The radiating unit includes a first rectangular ring pair and a second rectangular ring pair; in the first rectangular ring pair, the outward opening end of the first rectangular ring is connected to a first tapered microstrip line, and the outward opening end of the second rectangular ring is connected to the first rectangular ring through a first phase delay microstrip line; in the second rectangular ring pair, the outward opening end of the third rectangular ring is connected to a second tapered microstrip line, and the outward opening end of the fourth rectangular ring is connected to the third rectangular ring through a second phase delay microstrip line.

[0045] Specifically, the first and second rectangular rings are mirror images of each other, as are the third and fourth rectangular rings.

[0046] The antenna structure proposed in this invention uses a rectangular ring with broadband characteristics as the radiating structure. The currents on the two wide sides of the SIW are out of phase and are fed through a pair of phase delay lines with a length of one-quarter wavelength. Therefore, the four rectangular rings obtain sequential phase rotation currents of 0°, 90°, 180° and 270° respectively, thereby further improving the working bandwidth and gain of the antenna.

[0047] In one embodiment, such as Figure 5 The simulation results for the antenna |S11| < -10dB show that the impedance bandwidth is 35.7%, covering a bandwidth from 23.8GHz to 33.8GHz. Figure 6 The simulation results for this antenna with AR < 3dB are shown. The bandwidth at AR < 3dB is 38.9%, covering a bandwidth from 22.2 to 33.1 GHz. Figure 7 The simulation results for the antenna gain show that the peak gain is 9.9 dBic.

[0048] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "rotation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna, characterized in that, It includes two dielectric substrates and three metal layers, which are arranged from top to bottom as a first metal layer, an upper dielectric substrate, a second metal layer, a lower dielectric substrate, and a third metal layer; the upper dielectric substrate is provided with metallized vias; the first metal layer, the upper dielectric substrate, and the second metal layer together constitute a first structure; the third metal layer and the lower dielectric substrate form a second structure, which is used to enable the antenna to generate unidirectional radiation; The first structure is divided into five parts: a grounded coplanar waveguide, a substrate integrated waveguide-grounded coplanar waveguide transition section, a substrate integrated waveguide, a tapered microstrip line, and a radiating unit; the radiating unit includes two rectangular ring pairs, each of which achieves a 90° phase delay; The tapered microstrip line is divided into a first tapered microstrip line and a second tapered microstrip line; the radiating unit includes a first rectangular ring pair and a second rectangular ring pair; in the first rectangular ring pair, the outward opening end of the first rectangular ring is connected to the first tapered microstrip line, and the outward opening end of the second rectangular ring is connected to the first rectangular ring through a first phase delay microstrip line; in the second rectangular ring pair, the outward opening end of the third rectangular ring is connected to the second tapered microstrip line, and the outward opening end of the fourth rectangular ring is connected to the third rectangular ring through a second phase delay microstrip line; All four rectangular rings have broadband characteristics, and the lengths of the first and second phase delay microstrip lines are both quarter wavelengths. By feeding four rectangular rings with the first and second phase delay microstrip lines, the first, second, third, and fourth rectangular rings obtain sequential rotating phase currents of 0°, 90°, 180°, and 270°, respectively.

2. A novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna according to claim 1, characterized in that, The first and second rectangular rings are mirror images of each other, as are the third and fourth rectangular rings.

3. A novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna according to claim 1, characterized in that, A first rectangular ring pair and a first tapered microstrip line are disposed on the upper surface of the upper dielectric substrate, and a second rectangular ring pair and a second tapered microstrip line are disposed on the lower surface of the upper dielectric substrate, with the positions of the first tapered microstrip line and the second tapered microstrip line overlapping each other.

4. A novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna according to claim 1, characterized in that, The grounded coplanar waveguide includes a microstrip line of equal width, with a row of metallized vias on the upper and lower sides of the microstrip line.

5. A novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna according to claim 1, characterized in that, The substrate integrated waveguide-ground coplanar waveguide transition section includes a tapered microstrip line, and a row of metallized vias is provided on the upper and lower sides of the tapered microstrip line.

6. A novel SIW broadband millimeter-wave circularly polarized rectangular loop antenna according to claim 1, characterized in that, Both dielectric substrates are Rogers 5880 dielectric substrates with a dielectric constant of 2.2 and a loss tangent of 0.0009; the upper dielectric substrate has a thickness of 0.254 mm and the lower dielectric substrate has a thickness of 1.508 mm.

Images