Frequency-selective surface 4x4 array shielded on multiband crinkle fractal antenna to improve gain

Abstract

An antenna device (100), comprising: a substrate (106) with two metallic sections separated by a dielectric layer, wherein the first metallic section (102) is arranged on the upper layer of the dielectric and has a curled fractal geometry; and a second metallic section is arranged on the lower layer of the dielectric and has a partial ground plane configuration.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of antennas. More specifically, the present invention relates to a system for vertically integrating a 4x4 FSS array over the crinkle fractal antenna to increase peak gain through the required spatial processing. BACKGROUND OF THE INVENTION

[0002] Existing crinkle fractal antennas are of paramount importance for multi-band radiation, which is created by the fusion of magnetic and electric fields. This fractal configuration determines the operating frequencies and optimal dimensions of the antenna. Crinkle fractal antennas are widely used in wireless communication systems, radio frequency identification (RFID) tags, and other applications where compact size, wide bandwidth, and good performance are important factors. Their fractal nature enables miniaturization while maintaining efficiency, making them suitable for various modern communications devices.

[0003] In general, the peak gain of a fractal antenna is low. To improve the peak gain of this antenna, a frequency-selective surface (FSS) is predominantly used as a reflector. The spatial filtering functions of the FSS split this radiation beam into a transmitted wave at a specific frequency and a reflected wave at other frequencies.

[0004] A synthesis of crinkle fractal antenna and FSS is used to increase peak gain. This was achieved through a substantial filtering process to select frequency and polarization insensitivity.

[0005] The combination of fractal geometry and crinkle structures in these antennas offers several advantages: Compact size: The fractal geometry allows the antenna to be reduced in size while maintaining performance, making it suitable for integration into small devices such as smartphones, tablets, or wearables. Broadband operation: Crinkle fractal antennas typically exhibit broadband characteristics, meaning they can operate over a wide frequency range without tuning or adjustment.

[0006] Multi-band capability: Due to their broadband nature, crinkle fractal antennas can be designed to cover multiple frequency bands simultaneously, providing flexibility in wireless communication systems.

[0007] Robustness: The irregular and self-similar structure of crinkle fractal antennas often makes them more robust against fluctuations in environmental conditions and manufacturing defects compared to conventional antennas.

[0008] Ease of manufacturing: Crinkle fractal antennas can often be manufactured using standard printed circuit board (PCB) manufacturing processes, making their production relatively simple and inexpensive.

[0009] These antennas find application in various wireless communication systems, including Wi-Fi, Bluetooth, cellular networks, RFID (Radio Frequency Identification), and IoT (Internet of Things) devices, where compact size, broadband operation, and multi-band capability are desirable features. The present invention will effectively overcome the above-mentioned problems, limitations, and disadvantages. OBJECT OF THE INVENTION

[0010] The main objective of the present invention is to provide a microwave spatial filter with stopband performance due to the pronounced influence of the frequency selective surface (FSS) using a concentration of adjacent cells.

[0011] Another object of the present invention is to provide a technique that must significantly enhance the peak enhancement of the crinkle fractal structure by isolating the FSS 4×4 array periodic structure.

[0012] Another object of the present invention is to use a crinkle fractal antenna in conjunction with a frequency selective surface (FSS) to improve antenna gain and performance across specific frequency bands. SUMMARY OF THE INVENTION

[0013] The present invention provides a crinkle fractal antenna for multi-band radiating at 1.17 GHz, 1.83 GHz, 2.34 GHz, 2.90 GHz, 3.65 GHz, 4.96 GHz, and 5.66 GHz, respectively, constructed on a 20×20×1.6 mm3 FR-4 dielectric substrate.

[0014] An electromagnetic property of the designed FSS is a narrowband spatial notch filter at a specific frequency of 4.96 GHz. At this specific frequency, it offers better transmission and minimal reflection losses in its stopband. Therefore, the seven resonant frequencies at 1.17 GHz, 1.83 GHz, 2.34 GHz, 2.90 GHz, 3.65 GHz, 4.96 GHz, and 5.66 GHz impinge on the FSS, with the resonance at 4.96 GHz being transmitted and the reflection at 1.17 GHz, 1.83 GHz, 2.34 GHz, 2.90 GHz, 3.65 GHz, and 5.66 GHz.

[0015] The properties of the FSS unit cell are investigated using the electromagnetic software HFSS. Primary and secondary boundary conditions are assigned along the X and Y axes, respectively, and Floquet ports are assigned along the Z axis to investigate the band attributes of the FSS unit cell.

[0016] The proposed technique for improving the peak gain of the crinkle fractal antenna at 4.96 GHz, which is a combination of an antenna and a periodic 4x4 FSS array, is used. This 4x4 FSS-based spatial filter was isolated as a superstate on an antenna, and the distance between the antenna and the FSS cover was maintained at 10 mm to achieve the same S_11(dB) performance.

[0017] The design of the periodic shape of a square 4×4 FSS array is integrated as a superstrate with the crinkle fractal antenna to improve the peak gain of the antenna, which is modeled on a 44.5x44.5x0.8 mm3 FR-4 substrate.

[0018] Comparing the peak gain of the antenna without FSS shielding and with FSS shielding shows that the antenna without FSS shielding produces a peak gain of -0.6 dB at 4.96 GHz. However, the antenna with FSS shielding increases the peak gain by 2.3 dB.

[0019] A frequency-selective surface (FSS) is a structure or material that allows electromagnetic waves of certain frequencies to pass through while blocking or attenuating waves of other frequencies. It acts like a filter that selectively allows certain frequencies to pass through while reflecting or absorbing others.

[0020] When designing a frequency-selective surface, the geometric parameters of the elements, such as size, shape, spacing, and arrangement, are manipulated to achieve the desired frequency response characteristics. By carefully engineering these parameters, engineers can create surfaces that selectively transmit, reflect, or absorb electromagnetic waves of specific frequencies or within specific frequency bands. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1A shows a top view of a crinkle fractal antenna according to an embodiment of the present invention. Fig. Figure 1B shows the geometric representation of a crinkle fractal antenna from below according to an embodiment of the present invention. Fig. Figure 1C shows the side view of the crinkle fractal antenna according to an embodiment of the present invention. Fig. Figure 2A shows the geometric representation of a frequency-selective surface from above according to an embodiment of the present invention. Fig. Figure 2B shows the geometric representation of a frequency-selective surface from below according to an embodiment of the present invention. Fig. Figure 3 shows the proposed technique for gain enhancement of the crinkle fractal antenna. Fig. 4 shows the S_11(dB) vs. frequency diagram of the antennas as in Fig. 1 and Fig. 3 illustrated according to an embodiment of the present invention. Fig. 5 shows the gain versus frequency diagram of the antennas as in Fig. 1 and Fig. 3, according to an embodiment of the present invention.

[0021] In addition, the corresponding properties of the present invention have been illustrated in a pictorial representation. DETAILED DESCRIPTION OF THE INVENTION

[0022] In the following detailed description, fractal geometry with kinked structures is used to create compact and efficient antennas for wireless communications. These antennas are characterized by their irregular, kinked shapes and self-similar patterns, which are inspired by fractal geometry. Fractal antennas exploit the self-similar property of fractal geometry, in which a structure appears similar at different scales. This property enables the miniaturization of fractal antennas while maintaining good performance over a wide frequency range. Kinked structures add additional irregularity to the antenna shape, further improving its performance and bandwidth.

[0023] The fractal kink antenna, in particular, exhibits creases or irregularities in its fractal pattern, which can improve its bandwidth and impedance matching characteristics. These irregularities result in additional current flow paths, allowing the antenna to operate over a wider frequency range compared to conventional antenna designs. FSSs typically consist of an array of metal elements (often arranged in periodic patterns) on a dielectric substrate. The size, shape, and spacing of these metal elements determine the frequencies for which the surface is selective. By altering these parameters, engineers can design FSSs to exhibit specific frequency response characteristics. These surfaces find applications in various fields, including antenna design, radar systems, microwave engineering, and wireless communications.They can be used, among other things, to design compact and efficient antennas, radar-absorbing materials, electromagnetic shielding, and frequency-selective radomes. Frequency-selective surfaces (FSS) are structures engineered to exhibit unique electromagnetic properties, particularly related to the frequency of electromagnetic waves. They consist of periodic arrays of metal elements or apertures etched into a dielectric substrate. These elements are designed to interact with incoming electromagnetic waves in such a way that certain frequencies are passed while others are blocked or attenuated.

[0024] According to this invention, the metal portion of the crinkle fractal structure is located on top of the dielectric substrate.

[0025] According to this invention, the fractal structure can process multiple frequencies while maintaining a compact size and efficient radiation characteristics.

[0026] According to this invention, the partial ground plane improves impedance matching.

[0027] According to this invention, the crinkle fractal geometry tailors the antenna's properties to achieve multi-band radiation characteristics. According to this invention, the frequency-selective surface consists of periodic patterns of conductive elements on a dielectric substrate. According to this invention, the FSS interacts with incoming electromagnetic waves to selectively filter or reflect certain frequencies while transmitting others.

[0028] According to this invention, by placing an FSS in front of a crinkle fractal antenna, the radiation pattern, frequency response, and impedance matching characteristics of the antenna can be controlled.

[0029] According to this invention, the crinkle fractal antenna has a size of 20 × 20 × 1.6 mm3.

[0030] Fig. shows the top view 100A of the crinkle fractal antenna 100 according to this invention. It includes the number of folds (102) with ideal spacing (104) on the top surface of the first layer of the substrate (106). The first metal section is formed as a crinkle fractal geometry, while the second metal section (116) is formed on the underside of the substrate (106). The feed line (108) is controlled by the 50Ω microstrip line to the first metal section.

[0031] Fig. 1B shows the bottom view 100B of the crinkle fractal antenna as in Fig. 1A. It has a partial ground plane configuration (116) to guide the EM waves through the crinkle structure and thus achieve better impedance matching.

[0032] Fig. 1C shows the side view 100C of the developed crinkle fractal structure, since different configurations are possible, as shown in the Fig. 1A-2B shown.

[0033] Fig. Figure 2A shows the top view 200A of the FSS according to this invention. It has a 4x4 array of metallic elements (203) and non-metallic elements (204) on a dielectric substrate (202). Fig. Figure 2B shows the bottom view 200B of the FSS according to this invention. It can help improve antenna gain by controlling the radiation pattern and enhancing the antenna's performance in a specific frequency band.

[0034] Fig. Figure 3 shows the proposed invention (300). The upper dielectric substrate is formed by the FSS configuration, and the lower dielectric substrate is formed by the crinkle fractal structure. The distance between the upper and lower substrates (302) is maintained according to this invention.

[0035] Fig. 4 shows the return loss vs. frequency diagram (400) of a conventional crinkle fractal antenna vs. a shielded crinkle fractal antenna from FSS, as in Fig. 1 and Fig. 3. Both counterparts agree with each other.

[0036] Fig. 5 shows the gain vs. frequency diagram (500) of a conventional crinkle fractal antenna compared to an FSS-shielded crinkle fractal antenna, as in Fig. explained. Without FSS shielding, the crinkle fractal antenna produces a negative gain. However, a crinkle fractal antenna with FSS shielding produces a positive gain at the same frequency.

[0037] The dimensions of the developed invention Fig. 1, Fig. 2 and Fig. 3 are listed in Table 1 below. L W W1 L1 W2 L2 L3 W3 d 20 mm 20 mm 9 mm 10.5 mm 2 mm 6 mm 44.5 mm 44.5 mm 10 mm

[0038] The invention has two configurations, referred to as a crinkle fractal antenna without FSS and a crinkle fractal antenna with FSS. The crinkle fractal antenna without FSS generates the multiband at 1.17 GHz, 1.83 GHz, 2.34 GHz, 2.90 GHz, 3.65 GHz, 4.96 GHz, and 5.66 GHz. To achieve better impedance matching, the partial ground plane is introduced into the crinkle fractal structure. It provides the multiband from 1 GHz to 6 GHz with a maximum S_11(dB) of -28 dB. However, the gain at 4.96 GHz is negative. To achieve a positive gain at 4.96 GHz, the crinkle fractal antenna with FSS is introduced by shielding the radiating element. Now the gain at 4.96 GHz increases from -0.6 dB to a maximum gain of 2.3 dB due to the microwave spatial filter characteristics.A microwave spatial filter is a device used in microwave technology to manipulate electromagnetic waves based on their spatial properties such as direction or position.

[0039] In general, a spatial filter is a device or technique used to change the spatial properties of a wave, including its direction, phase, polarization, or amplitude. In the context of microwave engineering, spatial filters are commonly used in antennas, radar systems, and other microwave devices to control the propagation and reception of electromagnetic waves.

[0040] Different types of microwave room filters, including: Reflective spatial filters: These filters use reflective surfaces or structures to control the direction of microwave waves. They can be designed to reflect waves in certain directions while allowing waves in other directions to pass through.

[0041] Dielectric spatial filters: Dielectric materials with specific properties can be used to manipulate the propagation of microwave waves. By controlling the geometry and composition of the dielectric material, engineers can design filters that selectively pass or block specific frequencies or propagation directions.

[0042] Waveguide spatial filters: Waveguides are structures that confine and guide electromagnetic waves along a specific path. Waveguide-based spatial filters can be designed to manipulate the spatial properties of microwave waves by controlling the dimensions and shapes of the waveguide structure. Spatial antenna filters: Antennas can be designed with spatial filtering functions to selectively receive or transmit waves from specific directions. Phased array antennas, for example, use multiple antenna elements with adjustable phase shifts to control the direction of the transmitted or received waves.

[0043] Spatial metamaterial filters: Metamaterials are artificial materials engineered to exhibit unique electromagnetic properties not found in naturally occurring materials. By engineering the structure and composition of metamaterials at the subwavelength scale, engineers can create spatial filters with unprecedented control over the propagation of microwave waves. ADVANTAGES OF THE INVENTION

[0044] The present invention provides a technique for gain enhancement using a miniaturized crinkle fractal antenna.

[0045] Improved Gain: The combined structure of crinkle fractal antenna and FSS can improve the gain of the antenna by controlling the direction and efficiency of the radiation.

[0046] Frequency Selectivity: FSS allows for the selective transmission or reflection of certain frequencies, which can help filter out unwanted interference or harmonics, resulting in cleaner signal reception or transmission.

[0047] Compactness and integration: Both crinkle fractal antennas and FSS can be designed to be compact and conformal, making them suitable for integration into various devices and systems, including wireless communication devices, radar systems, and sensors.

[0048] Overall, the integration of crinkle fractal antennas with frequency-selective surfaces offers a versatile solution to improve antenna performance, especially in terms of gain enhancement and frequency selectivity across desired bands. APPLICATIONS OF THE INVENTION

[0049] The present invention is useful for detecting microwave devices and wireless applications, including: Antennas: FSSs can be used as reflectors, lenses, or radomes in antenna systems to improve performance, for example, for beamforming or beam steering.

[0050] Radar systems: FSS can be integrated into radar systems for frequency filtering, polarization control, or radar cross-section reduction.

[0051] Wireless communications: FSS can be used in wireless communications systems for frequency-selective filtering, interference suppression, or signal-to-noise ratio improvement. Microwave technology: FSS is used in microwave devices and components such as filters, couplers, and isolators.

[0052] Electromagnetic shielding: FSS can be used to design electromagnetic shielding materials that selectively block or attenuate electromagnetic interference at specific frequencies while allowing desired signals to pass through.

[0053] Sensors: FSSs can be used in sensing applications, where they can be designed to interact at specific frequencies that indicate specific environmental conditions or materials. Photonic devices: In the field of photonics, FSSs can be used to control light propagation, enabling applications in optical filters, sensors, and modulators.

[0054] Overall, frequency-selective surfaces offer versatile solutions for controlling electromagnetic waves over a wide frequency range, making them indispensable in modern telecommunications and radar systems, as well as in various other technologies.

Claims

[1] An antenna device (100) comprising: a substrate (106) having two metallic sections separated by a dielectric layer, the first metallic section (102) being disposed on the upper layer of the dielectric and having a rippled fractal geometry; and a second metallic portion is disposed on the lower layer of the dielectric and has a partial ground plane configuration. [2] The antenna of claim 1, wherein the microstrip feed line (108) is correlated with the first metallic portion on the upper layer of the dielectric substrate. [3] The antenna of claim 1, wherein the multi-band radiation is guided by inductive and capacitive components. [4] The antenna according to claim 1, wherein the antenna has a size of 20×20×1.6 mm3.

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