TE-tm polarized response consistent broadband super large incidence angle frequency selective electromagnetic structure

Abstract

The application provides a TE-TM polarization consistent wideband super large incidence angle frequency selective electromagnetic structure, and belongs to the technical field of radomes. The application adopts a polarization decoupling design strategy, and respectively constructs a TE polarization frequency selective structure and a TM polarization frequency selective structure. The TE polarization structure adopts a horizontal dipole parallel to an electric field, and the TM polarization structure adopts an open resonant ring vertical to a magnetic field. Both of them adopt a vertical substrate configuration and a "frequency-angle" multi-domain equivalent circuit model design, so that wideband wide-angle domain frequency selection response is realized, and cross polarization is extremely low. After orthogonal combination and optimization of the two structures, an electromagnetic structure with a periodic square hole grid arrangement is finally formed. The structure realizes a 1dB passband of 7-13GHz (60%) in a 45-75° incidence angle range, a TE-TM polarization transmission phase difference of less than 25° in the passband, and excellent out-of-band suppression characteristics. The application can be widely applied to occasions requiring wide-angle domain dual-polarization stable filtering, such as aircraft radar radomes, communication radomes and the like.

Description

Technical Field

[0001] This application relates to the field of radome and electromagnetic structure technology, and in particular to a broadband ultra-large incident angle frequency selective electromagnetic structure with consistent TE-TM polarization response. Background Technology

[0002] As a core external component of radar and communication systems, the radome primarily protects the internal antenna from harsh environments while ensuring efficient and stable transmission and reception of electromagnetic waves. It is a key device for achieving integrated electromagnetic performance and structural protection within the system. Currently, Frequency Selective Surface (FSS) technology is widely used in radome design. Compared to traditional purely dielectric radomes, FSSs are composed of periodically arranged subwavelength elements, allowing for selective control of electromagnetic waves at specific frequencies, angles, and polarizations, including reflection, transmission, or absorption.

[0003] Currently, a large amount of research is dedicated to promoting the development of FSS (Flat Radome for Sensors) towards broadband, high selectivity, multi-band, and three-dimensional capabilities. However, most of the related results are only applicable to scenarios with small incident angles. As aircraft platforms increasingly demand more integrated, lightweight, and multifunctional antenna systems, radomes must achieve both aerodynamic stealth and wide-band, high-efficiency wave transmission and wide-angle polarization stability. In typical airborne scenarios such as nose and wing radomes, the incident angle of electromagnetic waves can easily reach [a very high angle]. θ i The FSS has an ultra-wide incident angle range of >60°. Since the wave impedance of TE and TM polarized waves changes in opposite directions with the incident angle, and the difference between the two increases significantly at large incident angles, it causes serious impedance mismatch and inconsistent dual-polarization response, thus limiting the application of FSS in high-performance airborne radomes.

[0004] Existing methods for improving the angular stability of the FSS mainly include unit miniaturization, cascaded non-resonant units, loading matching layers, and design based on effective dielectric theory. However, most of these methods can only maintain good performance within 60°, the bandwidth is usually limited to less than 20%, and there is a lack of research and optimization on the phase consistency of TE and TM polarization transmission. Therefore, there is an urgent need for a method that can maintain good performance within ultra-large incident angles (…). θ i A frequency-selective electromagnetic structure that maintains broadband, high selectivity, and excellent dual-polarization amplitude and phase consistency even at >60°. Summary of the Invention

[0005] The main objective of this invention is to propose a broadband ultra-large incident angle frequency selective electromagnetic structure with consistent TE-TM polarization response, so as to overcome the technical defects of existing frequency selective surfaces such as dual polarization impedance mismatch, narrow bandwidth, and inconsistent polarization at large incident angles.

[0006] To achieve the above objectives, one aspect of this invention proposes a broadband ultra-large incident angle frequency-selective electromagnetic structure with consistent TE-TM polarization response, comprising: A TE polarization frequency selective structure is used to achieve a wide bandwidth angular domain frequency selective response for TE polarized waves at ultra-large incident angles, and exhibits full transmission characteristics for TM polarized waves. A TM polarization frequency selective structure is used to achieve a wide bandwidth angular domain frequency selective response for TM polarized waves at ultra-large incident angles, and exhibits full transmission characteristics for TE polarized waves. The TE polarization frequency selection structure and the TM polarization frequency selection structure are orthogonally combined in space, and their frequency responses remain consistent under ultra-large incident angles, thereby achieving consistent frequency selection electromagnetic control of dual polarizations.

[0007] In some embodiments, the TE polarization frequency selection structure adopts a vertical substrate configuration, with its incident surface perpendicular to the substrate plane, a metal pattern printed on the sidewall of the substrate, and its resonant element being a horizontal dipole parallel to the direction of the TE polarization wave electric field.

[0008] In some embodiments, the metal pattern of the TE polarization frequency selection structure includes: Horizontal metal lines printed on the center of the back side of the substrate; Two or more pairs of horizontal dipoles printed on the front side of the substrate and symmetrically distributed about the horizontal metal lines; The horizontal metal wire is used for low-frequency suppression and adjustment of coupling between dipoles, and multiple pairs of dipoles are cascaded to broaden the operating bandwidth at large incident angles.

[0009] In some embodiments, the TM polarization frequency selection structure adopts a vertical substrate configuration, with its incident surface parallel to the substrate plane, a metal pattern printed on the sidewall of the substrate, and its resonant element being an open resonant ring perpendicular to the direction of the TM polarization wave magnetic field.

[0010] In some embodiments, the metal pattern of the TM polarization frequency selection structure includes: Horizontal metal lines printed on the center of the back side of the substrate; An open-ended resonant ring is printed on the center of the front side of the substrate. The openings of the open-ended resonant ring are symmetrically distributed vertically, and an interdigitated structure is used to enhance the coupling capacitance. A pair or more pairs of dipoles symmetrically distributed along the open resonant ring; The horizontal metal wire is used for low-frequency suppression and adjustment of resonant ring coupling, and the dipole is used to improve frequency selectivity in the high-frequency band.

[0011] In some embodiments, the TE polarization frequency selection structure and the TM polarization frequency selection structure are designed using a frequency-angle multi-domain equivalent circuit model, so that their center frequency, passband bandwidth and stopband frequency remain generally consistent under ultra-large incident angles.

[0012] In some embodiments, the TE polarization frequency selection structure and the TM polarization frequency selection structure have the same unit horizontal period size, cross-sectional height and substrate selection, so as to facilitate orthogonal combination.

[0013] In some embodiments, the substrates of the TE polarization frequency selection structure and the TM polarization frequency selection structure are respectively provided with gaps, and the metal patterns of the two are relatively displaced in the vertical direction to avoid electrical connection between the orthogonally arranged metal lines, and the final structure is a periodic square hole grid structure.

[0014] In some embodiments, the frequency-selective electromagnetic structure has a dual-polarized 1dB passband of 7GHz to 13GHz in the incident angle range of 45° to 75°, and the transmission phase difference between TE polarization and TM polarization within the passband is less than 25°.

[0015] In some embodiments, the operating incident angle range can be adjusted by modifying the dimensional parameters of the structure without changing the circuit topology.

[0016] To achieve the above objectives, another aspect of this invention proposes a wide-bandwidth TE polarization frequency selection structure with low cross-polarization interference. This structure employs a vertical substrate configuration, with the incident surface perpendicular to the substrate. A metal pattern is printed on the sidewall of the substrate. The metal pattern includes a horizontal metal line printed at the center of the back side of the substrate, and two or more pairs of horizontal dipoles printed on the front side of the substrate and symmetrically distributed about the metal line. The horizontal dipoles are parallel to the electric field direction of the TE polarization wave to achieve angularly stable frequency selection characteristics under TE polarization and full transmission characteristics for TM polarization waves.

[0017] To achieve the above objectives, another aspect of this invention proposes a wide-bandwidth TM polarization frequency selection structure with low cross-polarization interference. This structure employs a vertical substrate with the incident surface parallel to the substrate, and a metal pattern is printed on the substrate sidewall. The metal pattern includes a horizontal metal line printed at the center of the back side of the substrate, and an open-ended resonant ring printed at the center of the front side of the substrate, along with one or more pairs of dipoles symmetrically distributed along the resonant ring. The openings of the open-ended resonant ring are symmetrically distributed vertically and employ an interdigital structure, perpendicular to the magnetic field direction of the TM polarized wave, to achieve angularly stable frequency selection characteristics under TM polarization and full transmission characteristics for TE polarized waves.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: 1) Polarization decoupling design: The independent TE and TM frequency selection structures achieve matching of their respective polarizations, effectively overcoming the impedance mismatch problem caused by the impedance difference of dual-polarized waves under ultra-large incident angles.

[0019] 2) Wide bandwidth angle domain performance: The proposed single-polarization frequency selection structure is based on an angle-stable horizontal dipole and an open resonant ring, respectively. Combined with the "frequency-angle" multi-domain equivalent circuit model, it achieves a relatively stable frequency selection response in an ultra-wide incident angle range of 0–80°.

[0020] 3) Low cross-polarization interference: The two single-polarization structures transmit almost all cross-polarized waves without interfering with each other, which facilitates independent control of the polarization performance of TE and TM, and ensures the dual polarization performance after orthogonal combination.

[0021] 4) Excellent polarization consistency: The dual-polarization frequency-selective electromagnetic structure obtained by orthogonal combination achieves a 1dB dual-polarization passband of 7–13 GHz (60% relative bandwidth) in the ultra-large incident angle range of 45–75°. Moreover, the phase difference between TE and TM polarization transmission within the passband is less than 25°, and the transmission amplitude and phase have excellent polarization consistency, providing key support for applications with high phase consistency requirements such as circular polarization.

[0022] 5) Structural adjustability and engineering applicability: The working angle range can be changed by simply adjusting the size parameters, and it can be integrated into a honeycomb sandwich radome, which has good prospects for engineering transformation. Attached Figure Description

[0023] Figure 1 This is a unit structure diagram of the wide bandwidth TE polarization frequency selection structure with low cross-polarization interference provided in Embodiment 1 of the present invention.

[0024] Figure 2 This is the multi-domain equivalent circuit model of the wide-bandwidth angular domain TE polarization frequency selection structure with low cross-polarization interference provided in Embodiment 1 of the present invention.

[0025] Figure 3 The theoretical calculation and full-wave simulation transmission performance of the wide-bandwidth angular domain TE polarization frequency selection structure with low cross-polarization interference provided in Embodiment 1 of the present invention are presented.

[0026] Figure 4 This is a unit structure diagram of the wide bandwidth angular domain TM polarization frequency selection structure with low cross-polarization interference provided in Embodiment 2 of the present invention.

[0027] Figure 5 This is the multi-domain equivalent circuit model of the wide-bandwidth angular domain TM polarization frequency selection structure with low cross-polarization interference provided in Embodiment 2 of the present invention.

[0028] Figure 6 The theoretical calculation and full-wave simulation transmission performance of the wide-bandwidth angular domain TM polarization frequency selection structure with low cross-polarization interference provided in Embodiment 2 of the present invention are presented.

[0029] Figure 7 This is a three-dimensional schematic diagram of the broadband ultra-large incident angle frequency selective electromagnetic structure with consistent TE-TM polarization response provided in Embodiment 3 of the present invention.

[0030] Figure 8 The unit structure diagram of the broadband ultra-large incident angle frequency selective electromagnetic structure with consistent TE-TM polarization response provided in Embodiment 3 of the present invention is shown.

[0031] Figure 9 The dual-polarized full-wave simulation transmission performance of the broadband ultra-large incident angle frequency-selective electromagnetic structure with consistent TE-TM polarization response provided in Embodiment 3 of the present invention is shown.

[0032] Figure 10 This is a three-dimensional schematic diagram of the improved TE-TM polarization response consistent broadband ultra-large incident angle frequency selective electromagnetic structure provided in Embodiment 4 of the present invention.

[0033] Figure 11 This is a unit structure diagram of the improved TE-TM polarization response consistent broadband ultra-large incident angle frequency selective electromagnetic structure provided in Embodiment 4 of the present invention.

[0034] Figure 12 The dual-polarized full-wave simulation transmission performance of the improved TE-TM polarization response consistent broadband ultra-large incident angle frequency-selective electromagnetic structure provided in Embodiment 4 of the present invention is shown.

[0035] Figure 13 This is the implementation scheme of the improved TE-TM polarization response consistent broadband ultra-large incident angle frequency selective electromagnetic structure honeycomb sandwich radome provided in Embodiment 4 of the present invention. Detailed Implementation

[0036] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The step numbers in the following embodiments are set only for ease of explanation, and there is no limitation on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0037] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0038] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0039] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0040] Currently, the most common method to improve the angular stability of the FSS is miniaturization, i.e., reducing the horizontal period size of the unit cell. This is mainly achieved through methods such as introducing lumped elements, bent structures, strongly coupled units, or 2.5D composite structures. While this method can effectively suppress grating lobes and stabilize resonant frequencies, it is usually limited to first-order responses, and the quality factor is angle-dependent. Another miniaturization approach is to cascade non-resonant units and increase the number of cascaded layers to obtain higher-order frequency responses, but its angular stability is still mostly limited to within 60°.

[0041] Alternatively, matching layers can be loaded on both sides of the FSS to improve angular stability. However, the thickness of such matching layers is typically a quarter wavelength, and the dielectric constant must satisfy 1+cosθ. θ m ( θ m (for the maximum angle of incidence). These requirements not only make material implementation difficult, but also significantly increase the overall profile height.

[0042] In recent years, the effective medium theory has been introduced into FSS design to achieve angular stability. By adjusting the equivalent electromagnetic parameters, ideal matching conditions can theoretically be met over a wide angle domain. Based on this idea, some ultra-wide-angle stable single-polarization FSSs have been proposed, but their bandwidth is limited to less than 20%. For more complex dual-polarization FSSs, existing work also struggles to guarantee a wide operating bandwidth and good selectivity over incident angles exceeding 60°. Furthermore, in applications such as circular polarization, the consistency of the transmission phase between TE and TM polarization is crucial, but current FSS research lacks sufficient studies on phase consistency at large incident angles.

[0043] In summary, existing FSS systems are inadequate when dealing with large incident angles ( θ i Within a wide angle range (>60°), it is difficult to guarantee excellent working performance. To overcome the shortcomings and deficiencies of existing technologies, the purpose of this invention is to propose a method suitable for large incident angles (>60°). θ i This invention provides a high-performance frequency selection structure for scenarios with angles greater than 60°, effectively improving the operating bandwidth, out-of-band suppression, and dual-polarization consistency of the frequency selection structure in a wide-angle domain, thereby enhancing its usability in high-performance airborne radar radomes. Firstly, to overcome the significant wave impedance difference between TE and TM polarization under ultra-large incident angles, unlike conventional symmetrical designs, this invention introduces a TE / TM polarization decoupling design strategy. This involves achieving frequency selection responses for TE and TM polarization respectively through orthogonal TE and TM polarization frequency selection structures with low cross-polarization interference, thus simultaneously achieving good dual-polarization matching. To this end, a horizontal dipole with angular stability under TE polarization and an open-circuit resonator with angular stability under TM polarization are used, combined with a "frequency-angle" multi-domain equivalent circuit model, to realize wide-bandwidth TE and TM polarization frequency selection structures with low cross-polarization interference in a vertical substrate configuration. By combining these two orthogonally inserted plates and further fine-tuning the dimensional parameters, a broadband ultra-large incident angle frequency selection electromagnetic structure with consistent TE-TM polarization response is obtained. Furthermore, the operating incident angle range of the frequency selection structure can be flexibly adjusted by fine-tuning the size parameters without changing the circuit topology.

[0044] First, see Figure 1This invention provides a wide-bandwidth angular-domain TE polarization frequency selectivity structure with low cross-polarization interference. The structure employs a vertical substrate configuration, with the incident surface perpendicular to the substrate. Metal patterns are printed on the sidewalls of the substrate to achieve wide-bandwidth angular-domain frequency selectivity for TE polarized waves. The metal patterns include a horizontal metal line printed at the center of the back side of the substrate, and two or more pairs of horizontal dipoles printed on the front side of the substrate and symmetrically distributed about the metal line. The horizontal dipoles are parallel to the electric field direction of the TE polarized wave and serve as the main resonant elements to improve angular stability under TE polarization. Cascading multiple pairs of dipoles effectively broadens the TE polarization operating bandwidth at large incident angles, while the horizontal metal line is used to achieve low-frequency suppression and adjust the coupling between dipoles. Because this structure is naturally perpendicular to the electric field of the TM polarized wave, and the metal patterns are all horizontal structures, it achieves near-full transmission of the TM polarized wave and exhibits extremely low cross-polarization interference.

[0045] Secondly, see Figure 4 This invention provides a wide-bandwidth angular-domain TM polarization frequency selectivity structure with low cross-polarization interference. The structure employs a vertical substrate configuration with the incident surface parallel to the substrate, and a metal pattern printed on the substrate sidewalls. The metal pattern includes a horizontal metal line printed at the center of the back side of the substrate, and an open-ended resonant ring printed at the center of the front side of the substrate, along with one or more pairs of dipoles symmetrically distributed along the resonant ring. The openings of the open-ended resonant ring are symmetrically distributed vertically and employ an interdigital structure to enhance coupling capacitance. The open-ended resonant ring is perpendicular to the magnetic field direction of the TM polarized wave and serves as the primary resonant element to improve angular stability under TM polarization. The horizontal metal line is used to achieve low-frequency suppression and adjust the resonant ring coupling, while the electric dipoles are used to improve frequency selectivity in the high-frequency band. Because this structure is naturally perpendicular to the electric field of the TE polarized wave, it achieves near-full transmission of the TE polarized wave and exhibits extremely low cross-polarization interference.

[0046] Finally, see Figure 7This invention provides a broadband frequency selection electromagnetic structure with consistent TE-TM polarization response at ultra-large incident angles. Based on a polarization decoupling design strategy, this structure employs both the aforementioned TE and TM polarization frequency selection structures to independently achieve broadband frequency selection characteristics of TE and TM polarization at ultra-large incident angles, and then orthogonally combines the two structures. The two frequency selection structures are designed using a "frequency-angle" multi-domain equivalent circuit model to ensure that their frequency responses (including center frequency, passband bandwidth, and stopband frequency) remain generally consistent at ultra-large incident angles. The horizontal periodic dimensions, cross-sectional height, and substrate selection of both structures are identical to facilitate orthogonal combination. The substrates of both structures are slotted, and the metal patterns are appropriately adjusted vertically to accommodate orthogonal splicing, ultimately forming a periodic square grid structure. The dimensions of the combined structure can be fine-tuned to further improve the consistency of dual-polarization transmission amplitude and phase consistency within the passband; without changing the circuit topology, the operating incident angle range can also be flexibly adjusted simply by changing the dimensional parameters.

[0047] In addition, see Figure 10 This invention proposes an improved broadband ultra-large incident angle frequency selective electromagnetic structure with consistent TE-TM polarization response. While retaining the original electromagnetic characteristics, this structure replaces the outer dipole pairs in the TE and TM polarization frequency selective structures with those printed on a horizontal substrate, effectively reducing the overall profile height. Furthermore, this configuration better suits the design concept of a honeycomb sandwich radome, offering greater engineering adaptability and facilitating practical engineering applications.

[0048] The following is a detailed description and explanation of the embodiments of the present invention, in conjunction with the accompanying drawings and specific application examples.

[0049] Example 1 This embodiment provides a wide-bandwidth angular-domain TE polarization frequency selection structure with low cross-polarization interference, and its unit structure diagram is shown below. Figure 1 As shown in (a), this structure adopts a vertical substrate configuration, and the substrate is a Rogers RO4350 dielectric substrate with a thickness of 0.168 mm (relative permittivity). ε r =3.66, loss tangent tan δ =0.0037), the incident surface is perpendicular to the substrate plane, and the metal pattern is printed on the sidewall of the substrate, including the connecting metal lines printed on the back of the substrate (e.g., Figure 1 As shown in (c), and two pairs of dipoles symmetrically distributed along the metal lines on the front side of the substrate (as shown in (c)). Figure 1As shown in (b)). Using horizontal dipoles that are always parallel to the TE polarized wave electric field as the main resonant element effectively improves the angular stability of the structure under TE polarization; cascading multiple dipoles can increase the passband order and extend the TE polarization passband bandwidth at large incident angles; while connecting metal lines can achieve low-frequency out-of-band suppression and control the coupling strength between dipoles. Furthermore, since this structure is a vertical substrate configuration, it is naturally perpendicular to the horizontal tangential component of the TM polarized wave electric field, and the metal patterns are all horizontal structures, making it difficult to couple with the vertical normal component of the TM polarized wave electric field. Therefore, it achieves almost full transmission of TM polarized waves and has extremely low cross-polarization interference. The unit period is 6 mm × 6 mm (0.2 λ 0×0.2 λ 0), a smaller unit period improves angular stability and avoids higher-order mode interference at large angles. Specific dimensional parameters are indicated in [reference needed]. Figure 1 For detailed numerical values, please refer to Table 1.

[0050] Table 1 Dimensional parameters of the TE polarization frequency selection structure

[0051] The equivalent circuit parameters of the TE polarization frequency selection structure, namely the frequency-angle, are as follows: Figure 2 As shown. Specifically, the two pairs of dipoles can be equivalently represented as parallel branches. L 1 C 1 and L 2 C 2. In a series resonant circuit, the connecting metal wire is equivalent to a parallel ground inductance. L g1 The gaps between dipoles and between dipoles and metal wires can be approximated as air transmission lines, and their characteristic impedance is consistent with the impedance of a TE-polarized wave obliquely incident in free space. Z 0 TE = η 0 / cos θ i The electrical lengths Θ1 and Θ2 are determined by the gap size. h 1 and h 2. Decision. Since a horizontal dipole is coupled only to an electric field parallel to itself, and the electric field direction of a TE-polarized wave is always parallel to the dipole, therefore... L 1. C 1. L 2 and C 2. Under TE polarization, it exhibits angle insensitivity, meaning that circuit parameter values ​​across the entire incident angle range can be quickly extracted using empirical formulas for normal incidence. Furthermore, this characteristic ensures the angular stability of the transmission zeros generated by the dipole, thereby achieving angle-stable out-of-band rejection and frequency selectivity. Similarly, the grounding inductor… Lg1 It also exhibits angle insensitivity, and its value can be determined using an empirical formula for normal incidence. Specific equivalent circuit parameter values ​​are shown in Table 2.

[0052] Table 2 Equivalent circuit parameters of TE polarization frequency selection structure

[0053] Figure 3 Figure (a) presents the scattering parameters of this TE polarization frequency-selective structure under 70° oblique incidence, obtained through theoretical calculation and full-wave simulation. It can be seen that the cascaded multi-stage dipoles enable the structure to achieve a fourth-order bandpass filter response, with a 1dB passband covering 7–13 GHz. Simultaneously, the series resonance of the dipoles introduces two transmission zeros outside the high-frequency band, significantly improving high-frequency out-of-band suppression and frequency selectivity; while the back-connected metal wire ensures good low-frequency out-of-band suppression. Figure 3 Figure (b) further presents the transmission characteristics of the structure over a wide incident angle range of 0–80°, demonstrating excellent angular stability. Thanks to the angle-insensitive transmission null point, the structure achieves high out-of-band rejection of over 20 dB in the 14–20 GHz band, and exhibits a steep roll-off characteristic in the upper sideband. In terms of passband performance, a 3 dB passband covering 7.2–13.3 GHz over 0–80° is achieved.

[0054] Example 2 This embodiment provides a wide-bandwidth angular-domain TM polarization frequency selection structure with low cross-polarization interference, and its unit structure diagram is shown below. Figure 4 As shown in (a). This structure also adopts a vertical substrate configuration, but the incident surface is parallel to the substrate plane, and the metal pattern is printed on the sidewall of the substrate, including the connecting metal lines printed on the back of the substrate (such as...). Figure 4 As shown in (c), and the open resonant ring printed on the front side of the substrate, and a pair of dipoles symmetrically distributed along the resonant ring (as shown in (c)). Figure 4 As shown in (b), the openings of the resonant rings are symmetrically distributed vertically, and an interdigital structure is used to enhance the coupling capacitance. Using an open resonant ring (which can be considered a magnetic resonator) that is always perpendicular to the magnetic field of the TM polarized wave as the main resonant element effectively improves the angular stability of the structure under TM polarization. External dipole pairs improve high-frequency out-of-band suppression and selectivity. Connecting metal lines mainly achieve low-frequency out-of-band suppression and regulate the coupling of the resonant rings. In this case, because the structure has a vertical substrate configuration, it is naturally perpendicular to the electric field of the TE polarized wave, thus achieving almost full transmission of the TE polarized wave and exhibiting extremely low cross-polarization interference. It should be noted that the unit horizontal period dimensions, cross-sectional height, substrate selection, etc., of this TM polarization frequency selection structure are completely identical to the TE polarization frequency selection structure in Example 1, to facilitate subsequent orthogonal splicing. Specific dimensional parameters are marked on [the relevant section]. Figure 4For detailed numerical values, please refer to Table 3.

[0055] Table 3 Dimensional parameters of TM polarization frequency selection structure

[0056] The frequency-angle equivalent circuit parameters of this TM polarization frequency selection structure are as follows: Figure 5 As shown, it can be roughly divided into three parts: the interior of the resonant ring, the dipole, and the electrical coupling between the two. Regarding the most important part, the interior of the resonant ring, L s It is a resonant toroidal inductor. C s The interdigital capacitance corresponding to the gap. C d The capacitance between adjacent resonant rings is represented by the metal wire, which is equivalent to the grounding inductance. L g2 The free space inside the resonant ring can be equivalent to a transmission line. Z s TM , Θ s Since the resonant ring can be considered a magnetic resonator and is always perpendicular to the magnetic field of the TM-polarized wave, all the circuit parameters inside the resonant ring are angle-insensitive. This means that the circuit parameter values ​​over the entire incident angle range can be quickly extracted using empirical formulas for normal incidence. This characteristic also ensures the angular stability of the transmission zero point generated by the magnetic resonance of the resonant ring, thereby achieving angle-stable out-of-band suppression and frequency selectivity. The dipole can be considered as a series circuit in a parallel branch. C p L p Resonance can introduce transmission zeros at high frequencies, improving out-of-band suppression and selectivity. The gap between the dipole and the resonant ring can be regarded as an air-medium transmission line, and its characteristic impedance is consistent with the impedance of a TM-polarized wave obliquely incident in free space. Z 0 TM = η 0cos θ i The electrical length is determined by the gap size. Since the dipole and resonant ring are relatively close, the electrical coupling between them needs to be considered to better match the actual response. This electrical coupling can be achieved using an inverting converter. J = C m The specific equivalent circuit parameter values ​​are shown in Table 4. It should be noted that because the dipole exhibits angular dispersion under TM polarization, these parameters need to be determined through fitting; therefore, Table 4 only provides values ​​for 70°. L p and Cp The value of .

[0057] Table 4 Equivalent circuit parameters of TM polarization frequency selection structure

[0058] Figure 6 Figure (a) presents the scattering parameters of the TM polarization frequency selective structure under 70° oblique incidence, calculated theoretically and simulated in full-wave simulation. Due to the interaction between the resonant ring and the metal wire, a stable transmission zero is generated at low frequencies, achieving out-of-band suppression and selectivity at low frequencies. Meanwhile, the dipole pairs and their electrical coupling with the resonant ring generate multiple transmission zeros at high frequencies, effectively improving high-frequency selectivity and out-of-band suppression. Figure 6 Figure (b) further demonstrates the angular stability of this structure, showing a steep roll-off near 6 GHz within an incident angle range of 0–80°, with lower stopband suppression stable at over 10 dB. (The last sentence appears to be incomplete and possibly refers to a different image or diagram.) θ i The upper stopband edge frequency increases with increasing dipole angle, primarily due to the angular dispersion effect of the dipole. However, despite this dispersion, the structure maintains a 3dB passband of 7–12.3 GHz over the 0–80° angle range and retains good frequency selectivity.

[0059] Example 3 This embodiment provides a broadband, ultra-large incident angle frequency-selective electromagnetic structure with consistent TE-TM polarization response, and its three-dimensional schematic diagram is shown below. Figure 7 As shown, this structure is based on the TE-TM polarization decoupling design concept. It employs the TE polarization frequency selection structure from Example 1 and the TM polarization frequency selection structure from Example 2 to achieve frequency selection responses for their respective polarizations. These are then combined via orthogonal insertion to obtain a dual-polarization frequency selection electromagnetic structure. First, since both the selected TE and TM polarization frequency selection structures have extremely low cross-polarization interference, they can independently achieve their respective frequency selection functions without interference. Second, because the unit horizontal periodicity, cross-sectional height, and substrate selection of the two frequency selection structures are completely identical, their orthogonal splicing will not disrupt the original periodicity conditions. Therefore, referring to the relevant designs of Examples 1 and 2, and based on angle-stable resonant elements, a "frequency-angle" multi-domain resonant circuit model can be used to design a system where the center frequency, passband bandwidth, and stopband range of the two polarization structures remain essentially consistent under ultra-large incident angles, ultimately achieving a consistent dual-polarization frequency selection response under ultra-large incident angles.

[0060] Figure 8The unit structure diagram of this dual-polarization frequency selective electromagnetic structure is shown. To meet the orthogonal splicing requirements, the substrate was periodically slotted, and these slots were processed using laser cutting. Simultaneously, the pattern of the TM polarization frequency selective structure was shifted downwards by a certain distance, and periodic cuts were added to its connecting metal lines to prevent electrical connections between orthogonally arranged metal lines. The above structural adjustments have a minimal impact on overall performance; relevant parameters are detailed in Table 5, and all other parameters remain consistent with those in Examples 1 and 2.

[0061] Table 5. New dimensional parameters of the dual-polarization frequency selection structure

[0062] In fact, the size parameters of the combined structure can be fine-tuned to further optimize the consistency of the frequency response of TE and TM polarization, especially the consistency of the transmission phase within the passband. However, the adjustment of parameters has already been covered in Implementations 1 and 2, so it is not reflected in this embodiment. Figure 9 The full-wave simulated transmission response of the final dual-polarization frequency-selective structure in the wide-angle domain is presented. Observation Figure 9 The results of transmission amplitude in (a) show that it is similar to that in Example 1. Figure 3 (b) and Example 2 Figure 6 The simulation results shown in (b) are highly similar to those of the corresponding single-polarization frequency-selective structure, which fully demonstrates the feasibility of the polarization decoupling design method. Specifically, a 3 dB passband of 7.0–13.0 GHz (60%) with dual polarization is achieved within a very large incident angle range of 45–80°, while the passband insertion loss is further kept below 1 dB under the incident angle condition of 45–75°. Furthermore, within the same angle range, this structure maintains good stopband suppression and frequency selectivity under dual polarization: out-of-band suppression is higher than 18 dB from 14.5 GHz to 20 GHz, and suppression is greater than 10 dB below 3.5 GHz. And as... Figure 9 As shown in (b), after parameter optimization, the structure also exhibits excellent polarization consistency in the transmission phase within the passband. Within the passband, the transmission phase difference between TE and TM polarizations is less than 25° at 50–80° incidence, and can be controlled within 15° at 60–80° incidence. Due to the structural angular dispersion effect, phase consistency decreases slightly at small incident angles; however, in the 7.2–10 GHz band, the structure can still maintain a transmission phase difference below 25° within an ultra-wide angle range of 0–80°. It is worth noting that since this invention primarily focuses on performance at ultra-large incident angles, the optimization is mainly aimed at… θ iThe amplitude and phase consistency is >60°, but the operating incident angle range can be flexibly adjusted by optimizing the size parameters without changing the circuit topology.

[0063] Example 4 This embodiment proposes an improved TE-TM polarization-response-consistent broadband ultra-large incident angle frequency-selective electromagnetic structure, the three-dimensional structure of which is as follows: Figure 10 As shown. The working mechanism of this structure is basically the same as that of Embodiment 3. The main improvement is that the outer dipole pairs in the TE polarization and TM polarization frequency selection structure are instead printed on a horizontal substrate, which also uses the same 0.168mm thick Rogers RO4350 board material. This can effectively reduce the profile height (from the original 13mm to 9mm) while ensuring that the transmission response remains basically unchanged. It also better conforms to the design concept of a honeycomb structure sandwich radome and is more conducive to engineering transformation.

[0064] Figure 11 A unit structure diagram of the improved structure is given. Compared with Embodiment 3, except... Figure 11 Aside from the differences in substrate gap size, overall pattern translation distance, and metal wire cut size shown in (b) and (c), the most significant structural adjustment lies in the arrangement of the outer dipoles, such as... Figure 11 As shown in (d), the outer dipole of the TE polarization frequency selection structure is printed on the outer side of the horizontal substrate and along... x The axis is shifted by half a cycle to ensure that the gap capacitance is not affected by the orthogonal dipoles. Therefore, except for the different dipole printing positions, the size parameters of the dipoles remain unchanged from those in Example 3. The outer dipole pairs of the TM polarization frequency selective structure are printed on the inner side of the horizontal substrate to avoid interference with the orthogonal dipoles. However, since the coupling effect at the gap is inevitably enhanced, it is necessary to... Figure 11 The dimensions marked in (d) w The size of dipole 6 was reduced from 1.8 mm in Example 3 to 1.1 mm, while the other dipole parameters remained the same. Specific adjusted dimensional parameters are shown in Table 6; parameters not mentioned remain the same as in Example 3.

[0065] Table 6. New dimensional parameters for dual-polarization frequency selective structures

[0066] Figure 12 The full-wave simulated transmission response of this improved structure in the wide-angle domain is presented, compared with that of Example 3. Figure 9 The results shown are basically consistent. For example... Figure 9As shown in Figure (a), a 3 dB passband of 7.0–13.0 GHz (60%) with dual polarization was achieved within an incident angle range of 45–75°, with good stopband suppression and frequency selectivity: better than 18 dB suppression in the 14.5 GHz to 20 GHz band and greater than 10 dB suppression below 3.5 GHz. And as... Figure 9 As shown in Figure (b), after parameter optimization, the structure also exhibits excellent polarization consistency in the transmission phase within the passband. Within the passband, the transmission phase difference between TE and TM polarizations is less than 25° at 40–75° incidence and less than 15° at 50–70° incidence. The phase consistency decreases slightly at small incidence angles, but the transmission phase difference remains less than 25° within the ultra-wide 0–80° angle range of the 7.2–10 GHz band.

[0067] Figure 13 This paper demonstrates the application of this improved structure in a honeycomb sandwich radome. Currently, sandwich radomes (such as the typical "ABA" structure) are widely used in engineering to replace all-dielectric radomes. These structures feature an outer skin with excellent mechanical and thermal properties, while the inner core layer must also ensure electromagnetic transmission performance. Among various core layer structures, honeycomb structures are widely used due to their advantages of being lightweight, having a low dielectric constant, and possessing high mechanical strength. Common configurations include hexagonal and quadrilateral honeycomb structures. For the improved frequency selection structure proposed in this embodiment, its metal pattern can be adapted and optimized before being loaded into a quadrilateral honeycomb sandwich radome, enabling the radome to achieve TE over a very large incident angle range. TM polarization-consistent broadband transmission and frequency selectivity characteristics.

[0068] In summary, this invention first proposes a frequency-selective electromagnetic structure design scheme for TE-TM polarization decoupling, providing an effective solution to the impedance mismatch and polarization inconsistency problems caused by the impedance difference between TE and TM polarized waves at large incident angles. Then, based on angle-stable resonant elements and using a "frequency-angle" multi-domain equivalent circuit model, orthogonally arranged, low-cross-polarization, wide-bandwidth angular-domain TE and TM polarized frequency-selective structures are designed, ensuring their frequency responses are essentially identical. Finally, after orthogonally integrating the two types of structures and further optimizing polarization consistency, the resulting dual-polarization frequency-selective electromagnetic structure significantly outperforms traditional frequency-selective electromagnetic structures in terms of passband bandwidth, out-of-band suppression, and polarization consistency at ultra-large incident angles, and shows good application potential in aircraft cellular sandwich radomes.

[0069] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] Although embodiments of the invention have been shown and described, those skilled in the art will understand 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 claims and their equivalents.

[0071] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A TE-TM polarisation response consistent broadband super- wide angle of incidence frequency selective electromagnetic structure, characterised in that, include: A TE polarization frequency selective structure is used to achieve a wide bandwidth angular domain frequency selective response for TE polarized waves at ultra-large incident angles, and exhibits full transmission characteristics for TM polarized waves. A TM polarization frequency selective structure is used to achieve a wide bandwidth angular domain frequency selective response for TM polarized waves at ultra-large incident angles, and exhibits full transmission characteristics for TE polarized waves. The TE polarization frequency selection structure and the TM polarization frequency selection structure are orthogonally combined in space, and their frequency responses remain consistent under ultra-large incident angles, thereby achieving consistent frequency selection electromagnetic control of dual polarizations.

2. The frequency selective electromagnetic structure of claim 1, wherein, The TE polarization frequency selection structure adopts a vertical substrate configuration, with its incident surface perpendicular to the substrate plane, a metal pattern printed on the sidewall of the substrate, and its resonant element being a horizontal dipole parallel to the direction of the TE polarization wave electric field.

3. The frequency selective electromagnetic structure of claim 2, wherein, The metal pattern of the TE polarization frequency selection structure includes: Horizontal metal lines printed on the center of the back side of the substrate; Two or more pairs of horizontal dipoles printed on the front side of the substrate and symmetrically distributed about the horizontal metal lines; The horizontal metal wire is used for low-frequency suppression and adjustment of coupling between dipoles, and multiple pairs of dipoles are cascaded to broaden the operating bandwidth at large incident angles.

4. The frequency selective electromagnetic structure of claim 1, wherein, The TM polarization frequency selection structure adopts a vertical substrate configuration, with its incident surface parallel to the substrate plane, a metal pattern printed on the sidewall of the substrate, and its resonant element being an open resonant ring perpendicular to the direction of the TM polarization wave magnetic field.

5. The frequency selective electromagnetic structure of claim 4, wherein, The metal pattern of the TM polarization frequency selective structure includes: Horizontal metal lines printed on the center of the back side of the substrate; An open-ended resonant ring is printed on the center of the front side of the substrate. The openings of the open-ended resonant ring are symmetrically distributed vertically, and an interdigitated structure is used to enhance the coupling capacitance. A pair or more pairs of dipoles symmetrically distributed along the open resonant ring; The horizontal metal wire is used for low-frequency suppression and adjustment of resonant ring coupling, and the dipole is used to improve frequency selectivity in the high-frequency band.

6. The frequency selective electromagnetic structure of claim 1, wherein, The TE polarization frequency selection structure and the TM polarization frequency selection structure are designed using a "frequency-angle" multi-domain equivalent circuit model, so that the center frequency, passband bandwidth and stopband frequency of the two remain consistent under ultra-large incident angles.

7. The frequency selective electromagnetic structure of claim 1, wherein, The TE polarization frequency selection structure and the TM polarization frequency selection structure have the same unit horizontal period size, cross-sectional height and substrate selection, so as to facilitate orthogonal combination.

8. The frequency selective electromagnetic structure of claim 1, wherein, The substrates of the TE polarization frequency selection structure and the TM polarization frequency selection structure are respectively provided with gaps, and the metal patterns of the two are relatively displaced in the vertical direction to avoid electrical connection between the orthogonally arranged metal lines, and the final structure is a periodic square hole grid structure.

9. A low cross-polarized interference wide bandwidth angular domain TE polarization frequency selective structure, characterized in that, The substrate is vertical, with the incident surface perpendicular to the substrate, and a metal pattern is printed on the sidewall of the substrate. The metal pattern includes a horizontal metal line printed on the center of the back side of the substrate, and two or more pairs of horizontal dipoles printed on the front side of the substrate and symmetrically distributed about the metal line. The horizontal dipoles are parallel to the electric field direction of the TE polarized wave to achieve frequency selectivity with stable angle under TE polarization and full transmission characteristics for TM polarized waves.

10. A low cross-polarized interference wide bandwidth angular domain TM polarized frequency selective structure, characterized in that, The substrate is vertically oriented with the incident surface parallel to the substrate. A metal pattern is printed on the sidewall of the substrate. The metal pattern includes a horizontal metal line printed on the center of the back side of the substrate, and an open resonant ring printed on the center of the front side of the substrate, along with one or more pairs of dipoles symmetrically distributed along the resonant ring. The openings of the open resonant ring are symmetrically distributed vertically and adopt an interdigital structure, and are perpendicular to the magnetic field direction of the TM polarized wave, so as to achieve frequency selectivity with stable angle under TM polarization and full transmission characteristics for TE polarized waves.

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