Passive-active composite broadband antenna device based on frequency selective surface

Abstract

This invention relates to a frequency-selective surface-based active-passive composite broadband antenna device for use in radio systems such as radar and communications. It is characterized by comprising a cavity-backed 94GHz millimeter-wave antenna loaded with an FSS and a broadband conformal Vivaldi antenna array. The broadband conformal Vivaldi antenna array adopts a cylindrical conformal heel-to-heel Vivaldi antenna form, using a metal cylindrical surface as the mounting carrier for the Vivaldi antenna array, which provides physical support and electromagnetic shielding. The cavity-backed 94GHz millimeter-wave active antenna loaded with an FSS consists of a parabolic rotating surface, a feed horn, a rectangular enclosed metal cavity, and a high-pass FSS mechanism. The rectangular enclosed metal cavity provides electromagnetic isolation between the active antenna and the broadband passive antenna array, confining the near-field electromagnetic field of the parabolic rotating surface within the metal cavity, while the effective radiated field is radiated out through the top FSS. The high-pass FSS mechanism uses a square aperture FSS for high-pass spatial filtering.

Description

Technical fields:

[0001] This invention relates to the field of active-passive composite antenna and broadband antenna manufacturing technology, specifically to an active-passive composite broadband antenna device based on a frequency selective surface that can be used in radio systems such as radar and communications. Background technology:

[0002] With the development of electronic countermeasures technology, precision-guided weapons need to accurately intercept, identify, and track targets under complex backgrounds and strong interference. This places higher demands on radar guidance systems, and composite guidance technology is a means to improve radar guidance capabilities. In active-passive composite guidance systems based on aircraft platforms, high-frequency active detection radar and ultra-wideband passive detection radar are typically used. The radar system has the functions of resisting decoys, resisting frequency agility, and resisting radiation source shutdown. Due to the limited space on the aircraft platform, the design of miniaturized active-passive composite antennas has become one of the key technologies. For active antennas, in order to obtain a longer detection range, the active antenna needs to have high gain; therefore, the frequency of the active antenna needs to be selected at a higher frequency. For passive antennas, it is required to have good impedance matching and radiation characteristics in an ultra-wideband while occupying as little space as possible in the aircraft body. In the limited space of the aircraft platform, the active and passive antennas are close together. Due to the need for direction finding, the passive antenna system often adopts a multi-element form. Therefore, the electromagnetic coupling between the two is relatively serious, and the electromagnetic compatibility of the entire active-passive composite antenna system is critical. Based on the above considerations, this invention studies a common-aperture active-passive composite antenna scheme; a 94GHz high-frequency active antenna is arranged in the central region of the platform at the front of the aircraft, and a cylindrical conformal broadband antenna array is arranged in the surrounding area of ​​the platform. The electromagnetic isolation between the active and passive antennas is improved by using absorbing boundaries, and the cooperative operation between the two is achieved by using frequency selective surface loading technology.

[0003] Airborne ultra-wideband conformal antennas mainly include log-periodic antennas, planar helical antennas, and Vivaldi antennas. These antennas require extremely low profile and wide bandwidth to achieve broadband reconnaissance and guidance functions. To ensure the effectiveness of detection and guidance, the antenna sensor must have the expected beam pointing. In radar guidance and jamming modes, the antenna typically requires sufficient gain along the aircraft axis, approximating end-fire performance. The biggest design challenge for passive miniaturized ultra-wideband conformal antennas in active-passive composite guidance modes lies in the antenna element and array design within limited space, as well as the impact of the conformal installation on the antenna's electrical performance and radiation pattern correction. Therefore, key technologies for miniaturized ultra-wideband conformal antennas include curved surface conformal technology, miniaturized ultra-wideband technology, and radiation pattern correction technology. To allow ample space for related equipment in other modes, the passive antenna must be miniaturized and conformally designed to fit the fuselage. Conformal antennas have minimal impact on the aerodynamic performance of the carrier itself, simplifying antenna installation. The current missile and other carrier platforms have relatively small structural dimensions, which greatly limits the space for antenna installation. The system has high requirements for the lower frequency limit of antenna operation. This creates a significant conflict between antenna miniaturization design and low-frequency, wide-bandwidth operation. Measures are needed to achieve antenna miniaturization and broadband impedance matching to ensure reasonable gain output after miniaturization. Furthermore, after conformal antenna installation, the end-fire performance of the conformal antenna is severely interfered with by the metal materials in the guidance equipment, resulting in large-angle deviations in the radiation pattern and even cracking, which is detrimental to the normal operation of the passive mode seeker. Summary of the Invention:

[0004] This invention addresses the gaps in existing technologies by proposing a frequency-selective surface-based active-passive composite broadband antenna device designed for the working environment of aircraft carrier platforms, aiming to solve the problems of electromagnetic isolation and cooperative operation of active and passive detection antennas.

[0005] This invention achieves its purpose through the following measures:

[0006] A frequency-selective surface-based active-passive composite broadband antenna device is characterized by comprising a cavity-type 94GHz millimeter-wave antenna loaded with FSS and a broadband conformal Vivaldi antenna array. The broadband conformal Vivaldi antenna array adopts a cylindrical conformal heel-to-heel Vivaldi antenna form, and uses a metal cylindrical surface as the mounting carrier for the Vivaldi antenna array. The mounting carrier provides physical support and electromagnetic shielding.

[0007] The FSS-loaded cavity-type 94GHz millimeter-wave active antenna consists of a parabolic rotating surface, a feed horn, a rectangular enclosed metal cavity, and a high-pass FSS mechanism. The rectangular enclosed metal cavity provides electromagnetic isolation between the active antenna and the broadband passive antenna array. It confines the near-field electromagnetic field of the parabolic rotating surface within the cavity, allowing the effective radiated field to be emitted through the top FSS. The high-pass FSS mechanism uses a square aperture FSS to achieve high-pass spatial filtering. The normalized inductive reactance of the high-pass FSS mechanism can be expressed as:

[0008]

[0009]

[0010]

[0011]

[0012]

[0013] Where Z0 is the characteristic impedance of free space, p is the unit period, d is the width of the infinitely long metal strip, λ is the wavelength of free space, and θ is the incident angle.

[0014] The Qualcomm FSS mechanism places square-hole FSS units on both sides of the dielectric substrate to form a double-layer FSS structure. The square-hole FSS units are periodically extended to form an FSS array with rectangular edges. The dielectric substrate is placed above the 94GHz active antenna cavity to form a closed structure. The FSS circuit board is almost electromagnetically transparent to the 94GHz active antenna, and the active antenna maintains its original gain characteristics.

[0015] This invention is laid out in a common aperture manner, with a 94GHz active antenna arranged in the central area to achieve high-gain active detection; the passive antenna is a heel-to-heel Vivaldi antenna array conforming to the cylindrical surface; the entire antenna is placed on a metal surface to achieve good isolation between the antenna and other sub-units; absorbing material is locally loaded between the broadband Vivaldi antenna and the metal base plate to adjust the beam pointing of the broadband passive antenna at low frequencies.

[0016] In this invention, the passive antenna is a heel-mounted Vivaldi antenna, which is printed on a flexible microwave circuit board and mounted in a cylindrical conformal manner using a bending and winding method. To increase the number of passive antenna elements, the Vivaldi antenna employs a tight coupling and miniaturization design. The conformal cylindrical carrier is a metal structure, and the conformal antenna faces the boundary conditions of the conductor surface, which can cause beam warping at low frequencies. To solve this problem and ensure the low profile effect of the broadband antenna, a microwave absorbing material with a certain absorption capacity is loaded in the low-frequency radiation region of the Vivaldi antenna. This changes the original electric wall boundary conditions to a mixed layered boundary condition of the absorbing layer and the electric wall, thereby adjusting the beam pointing of the broadband passive antenna to achieve the expected beam coverage requirements.

[0017] This invention addresses the technical requirements of broadband active-passive composite detection radar systems and, specifically for the operating environment of aircraft platforms, proposes an antenna device employing a composite structure of a conformal broadband antenna array and a millimeter-wave active antenna to solve the electromagnetic isolation and cooperative operation problems of the active and passive detection antennas. A millimeter-wave cavity-backed parabolic rotating surface antenna with a frequency selective surface (FSS) is designed. A square-aperture high-pass FSS is used as the isolation device between the active and passive antennas. This FSS structure is transparent to the millimeter-wave cavity-backed parabolic rotating surface antenna. The FSS design considers in-band insertion attenuation, out-of-band suppression, and grating lobe suppression. The cavity structure further enhances the electromagnetic isolation between the active and passive antennas, achieving better electromagnetic compatibility. The broadband passive antenna adopts a cylindrical conformal heel-to-heel Vivaldi antenna form, using a metal cylindrical surface as the mounting carrier for the Vivaldi antenna array. This mounting carrier provides physical support and electromagnetic shielding. The entire active-passive composite antenna is placed on a metal platform. To control the beam pointing of the broadband antenna, this invention locally loads microwave absorbing material between the broadband Vivaldi antenna and the metal mounting carrier, changing the boundary condition of the ideal electric wall to a layered boundary condition of absorbing boundary and electric wall boundary. This adjusts the beam pointing at low frequencies, obtaining the required beam coverage range for the radar. The broadband active-passive composite detection radar antenna and its beam control and electromagnetic coordination scheme designed in this invention are characterized by simple structure, low cost, stable performance, and stable mechanical characteristics, making them suitable for engineering applications. The broadband active-passive composite detection radar antenna device in this invention is suitable for application in passive guidance radar, electronic reconnaissance systems, electronic jamming systems, and electronic countermeasures systems, possessing significant theoretical value and application potential, and also exhibiting platform adaptability. Attached image description:

[0018] Appendix Figure 1 This is a schematic diagram of the antenna system in this invention, wherein... Figure 1 (a) is a model of a combined active and passive antenna system. Figure 1(b) Front view of the active-passive composite antenna system Figure 1 (c) Rear view of the active-passive composite antenna system Figure 1 (d) Side view of the active-passive composite antenna system.

[0019] Appendix Figure 2 This is a schematic diagram of the cavity-backed 94GHz millimeter-wave antenna structure based on FSS loading in this invention, wherein... Figure 2 (a) is a millimeter-wave active antenna model. Figure 2 (b) Millimeter-wave active antenna model with hidden premises Figure 2 (c) is a top view of the active-passive composite antenna system. Figure 2 (d) Side view of the active-passive composite antenna system.

[0020] Appendix Figure 3 This is a schematic diagram of the Vivaldi antenna structure model. Figure 3 (a) is a schematic diagram of the Vialdi structure model. Figure 3 (b) is the radiation mechanism of the Vivaldi antenna.

[0021] Appendix Figure 4 Qualcomm FSS structure and equivalent circuit, in which Figure 4 (a) is a square aperture. Figure 4 (b) is the equivalent circuit.

[0022] Appendix Figure 5 The simulation results for the return loss and port isolation at the antenna port are shown, where, Figure 5 (a) represents the return loss at port 1. Figure 5 (b) represents the return loss at port 2. Figure 5 (c) represents the isolation between antenna port 1 and port 2. Figure 5 (d) Isolation between antenna port 3 and port 2, Figure 5 (e) represents the isolation between antenna port 4 and port 2. Figure 5 (f) Isolation between antenna port 5 and port 2, Figure 5 (g) represents the isolation between antenna port 6 and port 2. Figure 5 (h) Isolation between antenna port 7 and port 2, Figure 5 (i) represents the isolation between antenna port 8 and port 2. Figure 5 (j) Isolation between antenna port 9 and port 2.

[0023] Appendix Figure 6 These are simulation results of the radiation characteristics of the Vivaldi antenna at a frequency of 1 GHz. Figure 6 (a) is the gain pattern on the xoz plane. Figure 6 (b) is the axial ratio pattern in the xoz plane. Figure 6(c) Gain pattern in the yoz plane. Figure 6 (d) is the axial ratio pattern in the yoz plane. Figure 6 (e) is the three-dimensional gain pattern. Figure 6 (f) is the three-dimensional axial ratio pattern.

[0024] Appendix Figure 7 These are simulation results of the radiation characteristics of the Vivaldi antenna at a frequency of 2 GHz. Figure 7 (a) is the gain pattern on the xoz plane. Figure 7 (b) is the axial ratio pattern in the xoz plane. Figure 7 (c) is the gain pattern in the yoz plane. Figure 7 (d) is the axial ratio pattern in the yoz plane. Figure 7 (e) is the three-dimensional gain pattern. Figure 7 (f) is the three-dimensional axis ratio pattern.

[0025] Appendix Figure 8 These are simulation results of the radiation characteristics of the Vivaldi antenna at a frequency of 3 GHz. Figure 8 (a) is the gain pattern on the xoz plane. Figure 8 (b) is the axial ratio pattern in the xoz plane. Figure 8 (c) is the gain pattern in the yoz plane. Figure 8 (d) is the axial ratio pattern in the yoz plane. Figure 8 (e) Three-dimensional gain pattern Figure 8 (f) is the three-dimensional axis ratio pattern.

[0026] Appendix Figure 9 These are simulation results of the radiation characteristics of a millimeter-wave antenna at a frequency of 92 GHz. Figure 9 (a) Gain pattern in the xoz plane. Figure 9 (b) Axial ratio pattern in the xoz plane. Figure 9 (c) is the gain pattern in the yoz plane. Figure 9 (d) is the axial ratio pattern in the yoz plane. Figure 9 (e) is the three-dimensional gain pattern. Figure 9 (f) is the three-dimensional axial ratio pattern.

[0027] Appendix Figure 10 These are simulation results of the radiation characteristics of a millimeter-wave antenna at a frequency of 93 GHz. Figure 10 (a) is the gain pattern on the xoz plane. Figure 10 (b) is the axial ratio pattern in the xoz plane. Figure 10 (c) is the gain pattern in the yoz plane. Figure 10 (d) is the axial ratio pattern in the yoz plane. Figure 10 (e) is the three-dimensional gain pattern. Figure 10 (f) is the three-dimensional axial ratio pattern.

[0028] Figure 11 These are simulation results of the radiation characteristics of a millimeter-wave antenna at a frequency of 94 GHz. Figure 11 (a) is the gain pattern on the xoz plane. Figure 11 (b) is the axial ratio pattern in the xoz plane. Figure 11 (c) is the gain pattern in the yoz plane. Figure 11 (d) is the axial ratio pattern in the yoz plane. Figure 11 (e) Three-dimensional gain pattern Figure 11 (f) Three-dimensional axis ratio pattern.

[0029] Reference numerals in the figures: 1 is the boundary of the metal cavity of the broadband antenna, 2 is the millimeter-wave active antenna, 3 is the absorber, 4 is the broadband Vivaldi antenna, 5 is the FSS structure, 6 is the rectangular metal cavity of the millimeter-wave antenna radiator, 7 is the FSS unit structure, 8 is the millimeter-wave active feed horn, 9 is the parabolic rotating surface, and 10 is the dielectric substrate of the FSS. Detailed implementation method:

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Based on the technical requirements of a combined active-passive radar guidance system, and considering the spatial dimensions of an aircraft platform, this invention proposes a composite antenna system consisting of a cavity-type 94GHz millimeter-wave antenna with FSS loading and a broadband conformal Vivaldi antenna array. The active and passive composite antennas are arranged in a common-aperture configuration, with a 94GHz active antenna positioned in the central region for high-gain active detection. The passive antenna is a heel-to-heel Vivaldi antenna array conformally arranged on a cylindrical surface. The entire antenna is placed on a metal surface to achieve good isolation between the antenna and other components. Absorbing material is locally loaded between the broadband Vivaldi antenna and the metal base plate to adjust the beam pointing of the broadband passive antenna at low frequencies. A 94GHz FSS-loaded cavity-type rotating parabolic antenna is designed, using a metal cavity to improve the electromagnetic isolation performance of the active and passive antennas, and FSS loading to achieve coordinated operation between the active and passive antennas. The model of the designed combined active-passive radar guidance antenna is shown below. Figure 1 As shown. Figure 2 This is a schematic diagram of a cavity-type 94GHz millimeter-wave antenna structure based on FSS loading. Figure 3 This is a schematic diagram of the Vivaldi antenna structure. Figure 1 In the diagram, 1 represents the boundary of the broadband antenna's metal cavity, 2 represents the millimeter-wave active antenna, 3 represents the absorber, and 4 represents the broadband Vivaldi antenna. Figure 2In the diagram, 5 represents the FSS structure, 6 represents the rectangular metal cavity of the millimeter-wave antenna radiator, 7 represents the FSS unit structure, 8 represents the millimeter-wave active feed horn, 9 represents the parabolic rotating surface, and 10 represents the dielectric substrate of the FSS.

[0032] In this invention, the passive antenna is a heel-type Vivaldi antenna, printed on a flexible microwave circuit board and mounted in a cylindrical conformal manner using a bending and winding method. To increase the number of passive antenna elements, the Vivaldi antenna employs a tight coupling and miniaturization design. The conformal cylindrical carrier is a metal structure. The conformal antenna faces boundary conditions on the conductor surface, which can cause beam warping at low frequencies. To address this issue and ensure the low profile effect of the broadband antenna, a microwave absorbing material with a certain absorption capacity is loaded in the low-frequency radiation region of the Vivaldi antenna. This changes the original electric wall boundary conditions to a mixed layered boundary condition of the absorbing layer and the electric wall, thereby adjusting the beam pointing of the broadband passive antenna to achieve the desired beam coverage. The Vivaldi antenna is a special case of a tapered slot antenna, featuring exponential slot lines and a relatively simple structure that can be directly printed on a dielectric substrate. Compared to a regular Vivaldi antenna, the heel-type Vivaldi antenna is more compact, has a wider bandwidth, is easier to achieve impedance matching, and exhibits superior cross-polarization. A heel-to-heel Vivaldi antenna is a printed structure on a dielectric substrate, where radiating metal patches are printed on both sides of the substrate. This structure makes impedance matching easier. A heel-to-heel Vivaldi antenna consists of three parts: a radiating region, a transmission region, and a feeding region. At low frequencies, it can be considered a resonant antenna; at high frequencies, it can be considered a non-resonant traveling-wave antenna. Conventional Vivaldi antenna structures are not easily conformal and have large dimensions, which directly affect the electrical performance of the passive antenna after conformal installation with the projectile. To solve the problems of passive conformal antennas, this invention comprehensively considers the antenna form and installation environment, and meets the system's requirement for a miniaturized ultra-wideband conformal antenna through the spatial layout of the active and passive antennas. This invention uses a miniaturized heel-to-heel Vivaldi radiator, minimizing the area of ​​the metal part while meeting radiation performance requirements. During antenna manufacturing, an integrated antenna array design and integral fabrication are adopted, achieving one-time molding, ensuring performance consistency between antenna elements, reducing manufacturing errors, and improving the performance and feasibility of the passive direction-finding algorithm.

[0033] This invention proposes an FSS-loaded cavity-type 94GHz millimeter-wave active antenna, such as... Figure 2As shown, the antenna consists of a parabolic rotating surface, a feed horn, a rectangular enclosed metal cavity, and a high-pass FSS structure. The rectangular enclosed metal cavity provides electromagnetic isolation between the active antenna and the broadband passive antenna array, confining the near-field electromagnetic field of the parabolic rotating surface inside the metal cavity, while the effective radiated field is radiated out through the top FSS. Figure 4 In this context, square aperture FSSs can be used to design high-pass spatial filters, and their normalized inductive reactance values ​​can all be expressed as:

[0034]

[0035]

[0036]

[0037]

[0038]

[0039] Where Z0 is the characteristic impedance of free space, p is the unit period, d is the width of the infinitely long metal strip, λ is the wavelength of free space, and θ is the incident angle.

[0040] Square-hole FSS units are placed on both sides of a dielectric substrate to form a double-layer FSS structure. The square-hole FSS units are then periodically extended to form an FSS array with rectangular edges. This dielectric substrate is placed above the cavity of a 94GHz active antenna to form a closed structure. This FSS circuit substrate is almost electromagnetically transparent to the 94GHz active antenna, allowing the active antenna to maintain its original gain characteristics. At the same time, the FSS provides shielding for the low-frequency ultra-wideband antenna array, achieving good isolation between the two. During the operation of both active and passive radar, the radiation pattern of the passive wideband antenna remains stable, ensuring the effectiveness and stability of the passive direction-finding algorithm.

[0041] The broadband active-passive composite detection radar antenna device of the present invention is suitable for use in passive guidance radar, electronic reconnaissance system, electronic jamming system and electronic countermeasures system.

[0042] Example:

[0043] This example presents a dual-layer rectangular ring FSS-loaded active-passive hybrid antenna system. Performance simulations of the antenna were performed using full-wave electromagnetic simulation software. The simulation results verify the performance of the proposed dual-layer rectangular ring FSS-loaded active-passive hybrid antenna system. The simulation results for the return loss and port isolation of the dual-layer rectangular ring FSS-loaded active-passive hybrid antenna system are as follows: Figure 5As shown in the figure, port 1 corresponds to a millimeter-wave active antenna, and port 2 corresponds to a Vivaldi antenna element. As can be seen from the figure, in the operating frequency range of 92GHz to 94GHz, the average return loss of port 1 of this antenna is about -18dB, and the average return loss of port 2 is about -8dB. The isolation between ports 1 and 2 is about 125dB, which achieves good electromagnetic isolation. The isolation between ports 3 and 2, 4 and 2, 5 and 2, 6 and 2, 7 and 2, 8 and 2, and 9 and 2 are the isolation between low-frequency antenna array elements. Since the elements are designed to be very close together, the coupling between adjacent elements is large. However, the isolation of slightly farther elements is improved more quickly.

[0044] Figures 6 to 11 Simulation results of the radiation characteristics of the Vivaldi passive antenna and the millimeter-wave active antenna are presented separately. At low frequencies, the passive antenna is small in size and close to the metal wall, resulting in a slight upward beam tilt. Using an absorber adjusts the beam, and at frequencies above 3 GHz, the beam becomes normal end-firing. Due to the absorber and the metal wall, the polarization of the Vivaldi antenna changes significantly, exhibiting typical elliptic polarization within the spatial range. The gain and polarization characteristics of the millimeter-wave active antenna are less affected by the FSS and can operate normally. Due to the FSS, the isolation between the active and passive antenna arrays is good, and the influence between their radiation characteristics is minimal, allowing them to work together.

[0045] This invention addresses the technical requirements of broadband active-passive composite detection radar systems and, specifically for the operating environment of aircraft platforms, proposes an antenna device employing a composite structure of a conformal broadband antenna array and a millimeter-wave active antenna to solve the electromagnetic isolation and cooperative operation problems of the active and passive detection antennas. A millimeter-wave cavity-backed parabolic rotating surface antenna with a frequency selective surface (FSS) is designed. A square-aperture high-pass FSS is used as the isolation device between the active and passive antennas. This FSS structure is transparent to the millimeter-wave cavity-backed parabolic rotating surface antenna. The FSS design considers in-band insertion attenuation, out-of-band suppression, and grating lobe suppression. The cavity structure further enhances the electromagnetic isolation between the active and passive antennas, achieving better electromagnetic compatibility. The broadband passive antenna adopts a cylindrical conformal heel-to-heel Vivaldi antenna form, using a metal cylindrical surface as the mounting carrier for the Vivaldi antenna array. This mounting carrier provides physical support and electromagnetic shielding. The entire active-passive composite antenna is placed on a metal platform. To control the beam pointing of the broadband antenna, this invention locally loads microwave absorbing material between the broadband Vivaldi antenna and the metal mounting carrier. This changes the boundary condition of the ideal electric wall to a layered boundary condition of absorbing and electric wall boundaries, adjusting the beam pointing at low frequencies to obtain the required beam coverage range for the radar. The broadband active-passive composite detection radar antenna designed in this invention, along with its beam control and electromagnetic coordination scheme, features a simple structure, low cost, stable performance, and stable mechanical characteristics, making it suitable for engineering applications.

Claims

1. A combined active-passive broadband antenna device based on a frequency-selective surface, characterized in that, This includes a cavity-backed 94GHz millimeter-wave antenna based on FSS loading and a broadband conformal Vivaldi antenna array. The broadband conformal Vivaldi antenna array adopts a cylindrical conformal heel-to-heel Vivaldi antenna form, using a metal cylindrical surface as the mounting carrier for the Vivaldi antenna array. The mounting carrier provides physical support and electromagnetic shielding. The FSS-loaded cavity-type 94GHz millimeter-wave active antenna consists of a parabolic rotating surface, a feed horn, a rectangular enclosed metal cavity, and a high-pass FSS mechanism. The rectangular enclosed metal cavity provides electromagnetic isolation between the active antenna and the broadband passive antenna array. It confines the near-field electromagnetic field of the parabolic rotating surface within the cavity, allowing the effective radiated field to be emitted through the top FSS. The high-pass FSS mechanism uses a square aperture FSS to achieve high-pass spatial filtering. The normalized inductive reactance of the high-pass FSS mechanism can be expressed as: Where Z0 is the characteristic impedance of free space, p is the unit period, d is the width of the infinitely long metal strip, λ is the wavelength of free space, and θ is the incident angle. The Qualcomm FSS mechanism places square-hole FSS units on both sides of the dielectric substrate to form a double-layer FSS structure. The square-hole FSS units are periodically extended to form an FSS array with rectangular edges. The dielectric substrate is placed above the 94GHz active antenna cavity to form a closed structure. The FSS circuit board is almost electromagnetically transparent to the 94GHz active antenna, and the active antenna maintains its original gain characteristics.

2. The active-passive composite broadband antenna device based on a frequency selective surface according to claim 1, characterized in that, The antenna is arranged in a common aperture configuration, with a 94GHz active antenna in the central area to achieve high-gain active detection. The passive antenna is a heel-to-heel Vivaldi antenna array conforming to the cylindrical surface. The entire antenna is placed on a metal surface to achieve good isolation between the antenna and other sub-units. Absorbing material is locally loaded between the broadband Vivaldi antenna and the metal base plate to adjust the beam pointing of the broadband passive antenna at low frequencies.

3. The active-passive composite broadband antenna device based on a frequency selective surface according to claim 1, characterized in that, The passive antenna employs a heel-mounted Vivaldi antenna, which is printed on a flexible microwave circuit board and mounted in a cylindrical conformal manner using a bending and winding method. To increase the number of passive antenna elements, the Vivaldi antenna adopts a tight coupling and miniaturization design. The conformal cylindrical carrier is a metal structure, and the conformal antenna faces the boundary conditions of the conductor surface, which can cause beam warping at low frequencies. To solve this problem and ensure the low profile effect of the broadband antenna, a microwave absorbing material with a certain absorption capacity is loaded in the low-frequency radiation region of the Vivaldi antenna. This changes the original electric wall boundary conditions to a mixed layered boundary condition of the absorbing layer and the electric wall, thereby adjusting the beam pointing of the broadband passive antenna to achieve the expected beam coverage requirements.

Images