A single antenna unit is 15 × 3 × 3.1 mm3 . The arrangement of the antennas in the six-antenna units is parallel, with a 3 mm separation between adjacent antennas. The antenna structure comprises of an inverted L-shaped feed branch and two inverted L-shaped short-circuit branches integrated into part of the metal frame. The proposed array can form multiple resonance paths, achieving dual-band operation at 3300–3600 MHz and 4800–5000 MHz. The measured isolation of this twelve-antenna system within the operating frequency band is over 10 dB, and the measured antenna efficiency is greater than 36%. Therefore, the system is suitable for use in smartphones with high screen-to-body ratios and metal frames.In this paper, a twelve-antenna system is designed for 5G smartphones with metal frames. The system is compact and operates on dual bands within the sub-6 GHz frequency range using multiple-input multiple-output (MIMO) technology. Two sets of six-antenna units are included in the system, arranged in a diagonal mirror-image configuration, and positioned at the center of the circuit board’s longer edges. The profile height of each of the six-antenna units is only 3 mm, and the overall array dimensions are 105 × 3 × 3.1 mm Rapid advances in communication technology have resulted in wireless communications becoming an indispensable aspect of daily life. In fifth generation 5G) mobile communications, multiple-input multiple-output (MIMO) technology is used to achieve high-speed transmission with multiple antennas. The most commonly used mobile communications devices are slim and have metallic cases, large screens, and narrow bezels. Therefore, the available space for antennas is shrinking. Correspondingly, antennas used in mobile communication devices are becoming increasingly compact with lower profiles. Designing multiple-antenna configurations within limited space to avoid excessive interference while achieving high efficiency and channel independence has become an increasingly urgent and challenging problem. Although several smartphone antenna designs using MIMO antenna arrays have been proposed in the literature ,4,5,6,7,G mobile Smartphones with metal frames are considered to have pleasing textures and aesthetics. Moreover, they are durable and can effectively dissipate heat. Some studies ,16,17,18To design decoupling mechanisms or achieve impedance matching, integrated metal-frame MIMO antennas for smartphones have been connected with components such as capacitors or inductors ,16,17,18The development of a 12 × 12 MIMO antenna for smartphones was able to improve the transmission rate, capacity, anti-interference ability, coverage, and positioning accuracy of wireless communication systems, thereby improving the performance and user experience of wireless communication ,22,23,24An antenna configuration must be compact, should be effective in a metal frame, and should achieve high throughput by using multiple antennas. We therefore propose a compact configuration for a 5G dual-band 12 × 12 MIMO antenna system that is integrated with the metal frame on a smartphone. The first feature of the proposed compact antenna design is a distance between two elements of only 3 mm. Both sides of each element have short-circuit branches, which reduces the impact of the ground plane current on adjacent antennas. Therefore, the proposed antenna design can achieve good isolation without decoupling elements and has narrow spacing between elements of only 3 mm. The second feature is the structural design of an inverted L-shaped feeding branch and two inverted L-shaped short-circuiting branches in the clearance area. Because the length of the inverted L-shaped feeding branch and the configuration of the two inverted L-shaped short-circuiting branches were adjusted, the operating frequency bands were impedance matched at 3300–3600 MHz and 4800–5000 MHz. The third feature is that the profile height of the antenna is only 3 mm, enabling it to fit in a narrow frame. The resonance path covers part of the metal frame, and the opening position of the metal frame is used to excite the low and high-frequency resonance paths. The proposed antenna system has an envelope correlation coefficient (ECC) of less than 0.38 and an isolation greater than 10 dB without any isolation components, and its efficiency is greater than 36%.This paper is structured in the following manner. We first present the design details of the MIMO antenna system in the following section. The design mechanism and parametric analyses are discussed in 3. The system circuit board is positioned at the center of the metal frame. The board comprises an FR4 glass fiber substrate with the dimensions of 84.2 × 164.2 × 0.8 mm3. The metal frame consists of a 0.4 mm thick copper-coated FR4 glass fiber substrate with a 7 mm width. The FR4 substrate has a relative dielectric constant of 4.4 and a loss tangent of 0.02. The dual-band MIMO twelve-antenna units  are arranged into two sets of six-antenna units, which are diagonally and mirror-symmetrically arranged on both sides of the system circuit board and centered on the long side edge at a distance of 30 mm from the short edges of the phone. The profile height of each antenna element is only 3 mm, and the dimensions of the antenna elements are 105 × 3 × 3.1 mm3. All six-antenna units have the same structure and size and are arranged in parallel at a distance of 3 mm from their neighbors.This design not only integrates part of the metal frame as part of the antenna resonance path but also uses a specifically designed short-circuit branch on both sides of each antenna structure, which is coupled with the opening position of the metal frame, to excite the low and high-frequency resonance paths on both sides. By arranging the six-antenna elements of each unit in a parallel and codirectional manner with 3 mm spacing, we isolate the low and high-frequency resonance paths between adjacent antennas. Additionally, regardless of whether the low and high-frequency modes are excited, the short-circuit branches can attract a ground plane current, which effectively reduces the flow of the current to adjacent antennas. This design achieves good isolation performance with a spacing of only 3 mm between the antennas without requiring isolation components.3, and the antennas are configured on the system circuit. Each antenna has a clearance zone without a ground plane with a size of 15 × 3 mm2. The clearance zone features a reversed L-shaped feed branch and two reversed L-shaped short-circuit branches. It is integrated with the upper metal frame to form multiple resonant paths for dual-frequency band sub-6-GHz operation . The metal frame has a 1 mm opening above the clearance zone at 4 mm and 10 mm from the left and right ground planes, respectively. This antenna structure has both low and high-frequency resonance modes covering the dual-frequency band operation of 3300–3600 MHz and 4800–5000 MHz. The low-frequency resonance is enhanced by the dual-coupled loop path formed by the feeding strip  and high-frequency band (4900 MHz). To further understand the contribution of each mode, we analyze the proposed structure and two other designs denoted Case 1 and Case 2. Case 1 is the proposed antenna structure without shorting strip 1  increases. This result demonstrates that the left loop path contributes to the high-frequency mode. Finally, parameter analysis for the end length d of the inverted L-shaped feeding branch is conducted. d values. Increasing d from 4.4 to 6.4 mm leads to a substantial downshift in both the low and high-frequency resonant modes. Therefore, the feeding strip path contributes to both resonant modes.For MIMO operations, certain performance parameters such as the ECC, mean effective gain (MEG), diversity gain (DG), and total active reflection coefficient (TARC) may also be of interest and can be examined. The ECC is a critical metric for evaluating MIMO antenna systems. Generally, an ECC of less than 0.5 is satisfactory for practical applications. Next, TARC is the square root of the incident power obtained from all excitations minus the radiant power, divided by the incident power. To maintain clarity and avoid a cluttered appearance, E is the expectation concerning different channel realizations, I is the identity matrix, det is the determinant, s is the signal-to-noise ratio (SNR), tn is the number of transmit antennas, H is the wireless channel matrix, and † is the Hermitian transpose of the matrix.The ergodic channel capacity refers to the average capacity observed in a multipath Rayleigh fading environment. In cases where a transmitter lacks channel state information (CSI) and its power is evenly distributed among each transmit antenna unit, the ergodic channel capacity can be calculated using the following formula :(1)C=E{lTo further investigate the isolation performance of the MIMO twelve-antenna unit, the surface current distribution between the two sets of six-antenna units and their ground planes is analyzed. The two sets of six-antenna units are configured in a diagonal mirror-image configuration. For clarity, only the surface current distribution of the first set of six-antenna when excited is presented. To emphasize the benefits of our suggested MIMO antennas, we have incorporated a comparative analysis of MIMO antennas from the existing literature. The proposed compactly configured a dual-band MIMO twelve-antenna system with a metal frame comprising two sets of six-antenna units arranged in a diagonal mirror-image configuration at the edges of the two longer sides of a phone. The profile height of each of six-antenna module is only 3 mm. The design has no isolation components but is able to achieve favorable isolation and ECC performance with only 3 mm spacing between adjacent antennas. In the designing of the sub-6GHz 5G antenna element, a metal-frame design was integrated with an inverted L-shaped feed branch and two inverted L-shaped short branch structures to form multiple resonant paths, which enabled dual-band operation in the 3300–3600 and 4800–5000 MHz 5G frequency bands. The antenna structure is simple and can be closely integrated with the metal environment. The isolation performance values for this MIMO twelve-antenna system are all above 10 dB, and the measured far-field radiation pattern ECC values are all less than 0.38. The low-frequency efficiency is 36–62%, and the high-frequency efficiency is 46–63%. This design is suitable for large-screen smartphones with a high screen-to-body ratio and metal frame.


Then, a four-element antenna is designed to meet the requirements for another application; here, each element is placed orthogonally to each other, and the isolation is improved through loading a cross-shaped branch in the middle of these elements. The size is 0.57λ × 0.57λ × 0.013λ. Both antenna samples are tested to verify the design. Measurement results show that the working bandwidth is 2.45–14.88 GHz and 2.14–14.95 GHz, the isolation is greater than 17 and 20 dB, and the peak gain is 5.7 and 5.9 dBi for the two- and four-element MIMO antenna, respectively. Compared to the references, the designed antennas have a wider bandwidth and a higher gain and radiation efficiency. They are well-suited for diverse wireless applications.Ultra-wideband (UWB) technology is widely used in many communication scenarios. However, narrowband systems can easily interfere with the UWB system, which generates multipath fading. In order to solve these interferences and meet the design requirements of high isolation of multiple-input multiple-output (MIMO) antennas, two MIMO antennas with double-notch structures are designed. Firstly, two U-shaped slots are etched on the radiating patch and feeder to achieve notch characteristics in WiMAX and ITU bands. Using this antenna element, a two-element antenna is put symmetrically in parallel, and two rectangular branches are loaded to improve the isolation. The size is 0.57 Since the application of ultra-wideband (UWB) frequency was proposed, it has become the focus of many engineers of wireless communication technology. Due to the high transmission rate and low power consumption, UWB technology has been widely used in the fields of ground-penetrating radar ,2, wirelThe disadvantages of the UWB system are that it is difficult to achieve long-distance transmission in the case of limited power, and that it is easy to produce inter-code crosstalk, which reduces the signal transmission efficiency and quality of the UWB system. In order to solve these problems, multiple-input multiple-output (MIMO) technology was introduced, which can increase the channel capacity and improve the transmission quality by means of using multiple antenna elements in the transmitter and receiver . The com2. The design is not suitable for handheld devices. In [In , a UWB dices. In , a UWB MIn this approach, we use a UWB antenna, but the interferences of the WiMAX and ITU bands must be filtered. Therefore, a UWB antenna with two-notched characteristics is investigated. A U-shaped slot was etched on the radiation patch to get the WiMAX band notch, and an inverted U-shaped slot was etched on the feeder line to get the ITU band notch. Adjusting its size, we obtained a bandwidth from 2.1 to 14.55 GHz of the antenna with stopbands of 3.28–3.75 GHz and 7.98–8.58 GHz. This design meets the requirements for the IEEE 802.16 standard. To adapt the system for higher-quality transmission, a combination of UWB technology and MIMO antenna technology is also studied. So, to use the designed antenna element, we consider the MIMO application. The two-element UWB antenna mentioned above is put in parallel style. Two rectangular branches (RBs) are added between them, which can achieve 17 dB of isolation. The notched bands were not affected. This style is only used in the one-input one-output case. In order to adapt it to real MIMO application scenarios, a four-element UWB antenna is also designed and is put into orthogonal style. Then, a cross-shaped rectangular patch is used as an isolation component. The isolation can reach 20 dB between each antenna element. The notched bands, WiMAX and ITU, were not changed. The simulation and measurement results show that the two proposed MIMO antennas have good performance while being compact in size. They can be widely used in various wireless communication systems such as automotive applications, wireless diversity applications, and portable mobile devices.The rest of the content is organized as follows. A two-element and a more compact four-element orthogonal MIMO antenna are proposed with two-notched characteristics at the WiMAX and ITU bands. The total antenna structure design with its geometric specifications is introduced in A single UWB antenna element design is based on a circular monopole antenna and the structuring of the antenna is conducted in three steps. The monopole antenna has the advantages of simple structure, easy installation and operation, small size, light weight and low cost. mW to meet the impedance matching of 50 Ω. In this paper, U-shaped slots are etched on the radiation patch of the antenna element to realize the notch of WiMAX band, and inverted U-shaped slots are etched on the feeder of the antenna element to obtain the notch of ITU band. To obtain the notch property, the most important thing to calculate is the total length of the etched slot. The total length of the slot can be estimated using Formulas (1) and (2):nf is the center frequency of notch; c is the speed of light; L is the length of the slot; eε is the equivalent permittivity; rε is the dielectric constant of the dielectric substrate. According to Formulas (1) and (2), the length of the U-shaped slot is about 26 mm when the center frequency is 3.5 GHz, and the length of the inverted U-shaped slot is about 11 mm when the center frequency is 8.3 GHz. After simulating and optimizing with the electromagnetic simulation software High Frequency Structure Simulator (HFSS), it is found that when the length of the U-shaped slot is 25.8 mm and the length of the inverted U-shaped slot is 11.8 mm, the stopband characteristics are the best, which can completely cover the WiMAX and ITU bands, respectively.One MIMO antenna consists of two elements and the other of four elements, as shown in The antenna elements of the two-element MIMO antenna are placed symmetrically, and two RBs are loaded between the antenna elements. The two RBs can generate two new current paths, reduce the coupling current between the ports, and improve the isolation between the antenna elements. The four antenna elements of the four-element MIMO antenna are placed orthogonal to each other, and the antenna elements have different polarization modes, resulting in a mismatch of polarization between adjacent antenna elements, thus improving the isolation degree between antenna elements. In order to further improve the isolation degree of the four-element MIMO antenna, a cross-shaped branch is added in the center of the dielectric substrate. The geometric dimensions of the two MIMO antennas are shown in S|-parameter simulation curve corresponding to the UWB MIMO antenna when no notch structures and different numbers of notch structures are introduced, respectively.In order to avoid the interference problem of the narrowband communication system, U-shaped slots in the radiation patch of the UWB antenna and inverted U-shaped slots in the feeder are used to generate notch properties. In order to verify the mutual independence of the two notch structures, The non-notch curve in the figure represents the reflection coefficient of the UWB MIMO antenna without a notch structure. It can be seen that the working bandwidth of the antenna is 2.12–14.73 GHz, which can cover the UWB band. When only the U-shaped slot is loaded, the working bandwidth of the antenna changes to 2.05–14.54 GHz, and the notch appears in the band of 3.28–3.75 GHz, which just covers the WiMAX band. When only the inverted U-shaped slot is loaded, the working bandwidth changes to 2.25–14.78 GHz, and the notch appears in the band of 8.01–8.61 GHz, which just covers the ITU band. When the two slots are etched on the antenna, the working bandwidth changes to 2.02–14.74 GHz, and the notch are generated in the 3.28–3.75 GHz and 7.99–8.58 GHz bands, respectively. The change in the parameters of each slot only has an effect on the corresponding notch band, and has little effect on the other parameters of the antenna and the notch band, so the two notch structures can play a relatively independent role.L3 increases from 6.8 mm to 7.2 mm and other parameters remain unchanged, the center frequency of the notch band 3.28–3.75 GHz changes significantly, decreasing from 3.6 GHz to 3.5 GHz. When L3 = 7.0 mm, the stopband bandwidth of the antenna just covers the WiMAX band. H1 increases from 20.4 mm to 20.8 mm, the center frequency of the 3.28–3.75 GHz notch band does not change significantly, but the stopband bandwidth gradually increases. It can be seen from the above analysis that the notch band can be controlled flexibly through adjusting the length and position of the slot.In order to study the influence of U-shaped slot and inverted U-shaped slot on the notch characteristics, the key dimensions of the two kinds of notch structures were parameterized and simulated. As shown in L4 of the inverted U-shaped slot. As shown in L4 increases from 4.7 mm to 5.1 mm, the notch band 3.28–3.75 GHz does not change significantly, and the center frequency gradually decreases. Through optimizing the key parameters of the two notch structures, it can be seen that the U-shaped slot mainly affects the notch band at 3.28–3.75 GHz, and the inverted U-shaped slot mainly affects the notch band at 7.99–8.58 GHz, with little mutual interference.In order to understand the principle of antenna notches, the antenna was further analyzed. Taking the element antenna as an example, the surface current distribution was simulated and analyzed. In order to study the influence of RBs on MIMO antennas and the decoupling effect, two-element MIMO antennas without and with RBs are simulated and analyzed, and the parameters of RBs are scanned and analyzed.S|-parameters before and after antenna loading RBs: (a) represents |S11|, (b) represents |S21|. As can be seen from S11| of the antenna changed little and remained below −10 dB in the UWB band, and the antenna did not exhibit an impedance mismatch phenomenon.In order to further study the influence of isolation structure on antenna performance, the key dimensions of isolation structure are simulated and optimized. Port 1 is set as the excitation port.S|-parameters corresponding to different L6 values, where (a) represents |S11| and (b) represents |S21|. As can be seen from Figure (b), with the increase of L6, the degree of isolation between the two antenna elements also increases, resulting in a better decoupling effect. As can be seen from figure (a), the change of L6 has little effect on the overall antenna impedance matching, but it has some effect on the range of the notch band. When L6 = 20 mm, the notch band just covers the WiMAX band. In summary, when L6 = 20 mm, the antenna can not only have high isolation, but also accurately cover the WiMAX band, and its isolation is higher than 15 dB, which meets the basic design requirements of a MIMO antenna and has a good decoupling effect.Through simulation and optimization, it is found that other dimensions of isolation branches have little influence on antenna impedance matching, and have no significant effect on the improvement of isolation degree, so it will not be analyzed and described.In order to more directly reflect the function of RBs, S11| of each antenna element is equal, while the isolation degree between antenna elements meet |ijS| = |jiS| . In order to more conveniently study the variation of the |S|-parameters of this MIMO antenna, only the |S|-parameters of port 1 can be studied. S|-parameters of the four-element MIMO antenna. It can be seen from the figure that the working bandwidth of the antenna is 2.17–14.71 GHz, in which the notch band of the U-shaped slot is 3.26–3.79 GHz, and the notch band of the inverted U-shaped slot is 7.93–8.51 GHz. When port 1 is excited, the isolation degree between port 1 and port 2 and between port 1 and port 4 is higher than 23 dB, and the isolation degree between port 1 and port 3 is higher than 15 dB in the working bandwidth. It can be proved that the orthogonal placement of antenna elements can reduce the coupling between antenna elements and obtain a good polarization diversity effect. Since the isolation between port 1 and port 3 just meets the basic design requirements, considering that the addition of antenna elements will increase the instability of antenna operation, it is necessary to further improve the isolation between port 1 and port 3.Increasing the number of MIMO antenna elements will increase the difficulty of decoupling. Therefore, each element of the four-element MIMO antenna is placed orthogonally first. The orthogonal placement of antenna elements will lead to the polarization mismatch of adjacent antennas, thus improving the isolation degree between antenna elements. Due to the four-element MIMO antenna having a symmetrical structure, the |S|-parameters of the four-element MIMO antenna after loading the cross-shaped branch. As can be seen from In order to further improve the isolation degree between the antenna elements of the four-element MIMO antenna, the center of the dielectric substrate is loaded with a cross-shaped branch for decoupling. In order to study the influence of cross-shaped branch on antenna performance, the key parameters of the cross-shaped branch are scanned and optimized. θ of the cross-shaped branch has a great influence on the notch band of the four-element MIMO antenna, and the length of the cross branch has a significant effect on improving the isolation between port 1 and port 3. The θ was set as 10–30 deg, and the step size was set as 2 deg. S11| with different θ values. It can be seen from the figure that when θ increases from 10 to 30 deg, the center frequency of the notch band corresponding to the U-shaped slot gradually increases, while that corresponding to the notch band corresponding to the inverted U-shaped slot gradually decreases. When θ = 20 deg, the two notch bands exactly cover the WiMAX and ITU band. The L7 is set from 10 to 16 mm, and the step is set to 1 mm. |S31| corresponding to different values of L7 is shown in L7 increases, the isolation between port 1 and port 3 gradually increases. However, with the change in the value of L7, the accuracy of the notch band will be slightly affected. When L7 = 13 mm, the antenna has a high isolation degree and the notch band can achieve accurate coverage.Through simulation analysis, it is found that the rotation angle In order to more directly reflect the effect of orthogonal placement of antenna elements and the isolation effect after loading the cross-shaped branch, S|-parameter and far-field radiation pattern, as shown in In order to verify the performance of the two MIMO antennas designed, the antennas are manufactured according to the data in S|-parameters, due to the symmetry of the antenna unit, only consider the |S|-parameters of port 1. As can be seen from the figure, the measured working bandwidth of the antenna is 2.45–14.88 GHz, which can cover the UWB band. The notch band corresponding to the U-shaped slot is 3.26–3.75 GHz, and the notch band corresponding to the inverted U-shaped slot is 7.96–8.65 GHz, which can cover the WiMAX and ITU band, respectively. The measured isolation between two antenna ports is higher than 18 dB. Through comparing the simulation results and the measured results in S|-parameters are roughly consistent with the simulated |S|-parameters. However, due to the errors caused by antenna machining, the welding process, and network analysis instruments, the measured and simulated values have a small difference.S|-parameters of the four-element UWB MIMO antenna; due to the symmetry of the antenna element, only consider the |S|-parameters of port 1. As can be seen from the figure, the measured working bandwidth of the antenna is 2.14–14.95 GHz, which can cover the UWB band. The notch band corresponding to the U-shaped slot is 3.02–3.99 GHz, and the notch band corresponding to the inverted U-shaped slot is 7.56–8.58 GHz. The bandwidth of the two notch bands becomes wider. However, WiMAX and ITU bands can still be covered separately. The measured isolation degree between each antenna port is higher than 20 dB, which proves that the isolation degree between antenna elements is high and they can maintain independent normal operation. Through comparing the simulation results and the measured results in S|-parameters are roughly consistent with the simulated |S|-parameters, which proves that the antenna has good performance.The E-plane co-polarizations of the four sample frequencies have two main beams, and the cross-polarizations are small. Furthermore, the differences between the co-polarizations and the cross-polarizations are larger than 15 dB, which shows good radiation patterns in the E-plane. It can be also observed in The E-plane cross-polarizations are small. Furthermore, the differences between the co-polarizations and the cross-polarizations are larger than 16 dB, which shows good radiation patterns in the E-plane. It can be also observed from The envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), mean effective gain (MEG), and channel capacity loss (CCL) are important parameters for validating the capability and performance of MIMO antennas.The ECC is used to measure the correlation between the channels of MIMO antenna elements. It refers to the correlation between different signal amplitudes received by the antenna. For MIMO antennas, a smaller ECC means weaker channel correlation and better system performance. In general engineering applications, if the ECC is less than 0.5 , it can Diversity gain (DG) is another important parameter for measuring the performance of MIMO antenna . The ideThe measured and simulated DG of the two proposed MIMO antennas are shown in b represents the reflected signal, a represents the incident signal, N depicts the number of elements in the MIMO system, and S denotes the scattering parameter. Through deriving the formula, the TARC of the MIMO system can be calculated using the S-parameter [The TARC provides the reflected-incident power ratio, which is related to the coupling between the ports . For an arameter . The TARIn order for the MlMO antenna to work well, the TARC value must be below −10 dB . Figure iMEG is calculated using Formula (8). Similarly, ijMEG is calculated using Formula (9), and the data details are shown in In a multipath fading environment, the MEG can be used to measure the total efficiency of the MIMO system, the total gain, and the effect produced by the propagation environment . It is giMEG of the two proposed MIMO antennas is lower than 6 dB in the whole operating band, and the ijMEG is lower than 3 dB. It can be proved that the two proposed MIMO antennas perform well over the whole operating band.It can be seen that the The correlation between the elements in MIMO channel systems produces a capacity loss . For higThe CCL values of the two proposed MIMO antennas are shown in inP is the power entering the antenna, rP is the radiated power of the antenna, and dP is the lost power of the antenna.As an energy conversion device, an antenna converts high-frequency current energy into electromagnetic wave energy or electromagnetic wave energy into high-frequency current energy. However, due to various losses in the transmission process, such as antenna dielectric loss, copper loss, and component loss, the input antenna power can only be partially converted into electromagnetic wave energy. The efficiency of the antenna is used to characterize the degree of such conversion. The calculation method is shown in Formula (13):The measured radiation efficiency of the two proposed MIMO antennas is shown in As the proposed antenna is wideband, so its time-domain characterization becomes important . In ordeThe group delay of the antenna in the above two directions is shown in The transmission coefficients of the antenna in both directions were simulated, as shown in In order to further verify the effectiveness of this design, the experimental results of the designed antenna are compared with those of the references. The comparative experimental results include antenna size, antenna impedance bandwidth, relative impedance bandwidth, number of MIMO antenna units, notch band, isolation, peak gain, and ECC. The details for each comparison item are shown in ijMEG below 3 dB, and CCL below 0.4 bit/s/Hz, which can be widely used in UWB communication systems.Two compact UWB–MIMO antennas with high isolation have been checked. One is a two-element MIMO antenna located parallel with an impedance bandwidth from 2.45–14.88 GHz, which is loaded with two RBs to achieve an isolation higher than 17 dB in the passband range. The other is a four-element MIMO antenna located at quadrature with an impedance bandwidth from 2.14–14.95 GHz. Through placing the antenna elements orthogonally and loading the cross branches, the antenna has an isolation degree of more than 20 dB in the passband range. Both can suppress the interference of WiMAX and ITU bands to UWB communication and are simple in structure and easy to process. At the same time, they have stable gain, much lower ECC (<0.02), DG close to 10 dB, TRAC below 10 dB,


In this manuscript, we have numerically investigated and experimentally verified the six-element split ring resonator and circular patch-shaped multiple input, multiple output antenna operating in the 1–25 GHz band. MIMO antennas are analyzed in terms of several physical parameters, such as reflectance, gain, directivity, VSWR, and electric field distribution. The parameters of the MIMO antenna, for instance, the envelope correlation coefficient (ECC), channel capacity loss (CCL), the total active reflection coefficient (TARC), directivity gain (DG), and mean effective gain (MEG), are also investigated for identification of a suitable range of these parameters for multichannel transmission capacity. Ultrawideband operation at 10.83 GHz is possible for the theoretically designed and practically executed antenna with the return loss and gain values of −19 dB and −28 dBi, respectively. Overall, the antenna offers minimum return loss values of −32.74 dB for the operating band of 1.92 to 9.81 GHz with a bandwidth of 6.89 GHz. The antennas are also investigated in terms of a continuous ground patch and a scattered rectangular patch. The proposed results are highly applicable for the ultrawideband operating MIMO antenna application in satellite communication with C/X/Ku/K bands.  MIMO  antennas have emerged as an effective solution to enhance the wireless communication system’s capacity and reliability . They arIn this manuscript, we have numerically investigated and experimentally verified the design of a six-element split-ring resonator and circular patch-shaped multi-input, multi-output antenna in the 1–25 GHz frequency range. MIMO antennas are analyzed in terms of several physical parameters, such as reflectance, gain, directivity, VSWR, and electric field distribution. In order to determine whether or not this antenna is suitable for multichannel transmission, we have also provided additional MIMO antenna characteristics, including envelope correlation coefficient, total active reflection coefficient, channel capacity loss, mean effective gain and diversity gain. This manuscript is majorly divided into three subdivisions. The first segments include the design and specification of all five stages of the proposed antenna. The second segment consists of measurement and simulation results and discussions of the proposed antenna. Finally, the last segment demonstrates the influence of the various antenna characteristics in a situation where numerous ports are excited simultaneously.2. We have performed numerical analysis on five distinct antenna designs that contain the radiation patch elements either on a split ring resonator or in a circular patch shape of the structure. In all the antenna designs, the ground is either continuous for all patches in the shape of a rectangle, or individual rectangular copper patches are placed over the individual MIMO elements, which can be seen in The schematic of the six-element, split-ring resonator-shaped MIMO antenna is depicted in ij, where i and j refer to 1, 2, 3, 4, 5, and 6, are <−10 dB and other S parameters S12, S13, … are also <−10 dB. These conditions are satisfied for the identification of the overall resonating band where the co-port and cross-port reflectance values are <10% for the effective radiation. We have calculated the reflectance response of all five types of antennas by applying the excitation at all antenna ports. The reflectance response achieved through the numerical study is depicted in ij < −10 dB are satisfied. In Design 1 of the antenna, we observed the three operating bands with bandwidth values of 7.88 GHz, 5.17 GHz, and 5.46 GHz. This antenna covers an overall area of 74% of the 1–25 GHz band in the frequency spectrum for radiation conversion. The reflection coefficient’s minimum value is observed at −34.51 dB. The maximum peak gain observed is 12.64 GHz with a return loss of −16.11 dB and a band of 5.46 GHz. We can observe similar types of antenna operating bandwidth, peak gain, and bandwidth for all the antennas in The bands derived from this calculation are shown in We have fabricated the proposed structures, and the measurement results for the proposed structure are shown in The split ring resonator shape provides advantages over a normalized patch structure in terms of compact size, metamaterial effect, broadband response, and flexibility of operation. The results shown in Additionally, the gain over the frequency range of 1–25 GHz is presented as the second antenna parameter for identifying the antenna’s efficient operation. Gain values for each suggested antenna design have been computed and shown in Different electric field distributions for two-port and three-port excitation are shown in ECC is calculated using the electric field’s magnitude in Equation (1). The ECC solid angle components are indicated by ith and jth. It is time-consuming and labor-intensive to evaluate ECC using far-field radiation characteristics. Equation (2) demonstrates an alternate way of calculating ECC with the help of S-parameters, as described in .(1)ρij=The results of the ECC calculations for antenna Design 5 are shown in For a given channel, the diversity gain  may be cTwo isotropic antennas combined average power in the absence of noise is less than or equal to the noise-averaged power delivered to a diversity antenna, as measured by the mean error gain (MEG) parameter (or interference). It demonstrates how environmental factors influence the enhanced performance of a MIMO antenna. The MEG may be validated by using Equation (4), which is based on the equation proposed in . In thisIn cases where more than one port is being utilized, the total active reflection coefficient (TARC) provides the most precise measurement of radiation performance and frequency response. This is because TARC is the most trustworthy metric. The mathematical expression for determining this value is as follows:   . Using a metric called the total active reflection coefficient (TARC), researchers may determine how effective a MIMO system is at re-directing light. This methodology was developed in the 1990s. This tactic takes into consideration both the reciprocal coupling that exists on the network as well as the random pairings of signals that exist on the network. In this example, we see how the properties of both incident and reflected waves may be described using Equation (5). It suggests that one way to find out the answer to this question is by solving Equation (6) using S-parameters . In While assessing the GHz antenna’s MIMO performance, it’s also important to take into account the channel capacity loss (CCL). The greatest data transfer rate that may be achieved across a given channel without incurring a discernible quality loss is determined by the channel’s capacity loss. Rates below 0.5 bits/s/Hz are required to show that information may be sent without corruption using a well-planned MIMO system. The CCL parameter may be determined with the help of Equations (7)–(9), which can be found in . As can Our analysis involved a comparative table of the radiation element of the antenna between our computed results and those previously published, such as S parameter isolation, peak gain, bandwidth, and antenna area. The comparative analysis with other antennas is shown in We have identified a few advantages and disadvantages from our previously published results ,10,35 anSimplicity: A 1 × 2 MIMO structure involves one transmit antenna and two receive antennas. It is a relatively simple configuration compared to higher-order MIMO structures, such as 2 × 3, in terms of hardware complexity, implementation, and cost.Lower System Complexity: With fewer antennas involved, a 1 × 2 MIMO system typically has lower system complexity in terms of signal processing, antenna design, and RF (radio frequency) front-end requirements. This can result in easier system design and reduced complexity in terms of implementation and deployment.Lower Power Consumption: Due to its lower system complexity, a 1 × 2 MIMO structure may require less power consumption compared to higher-order MIMO configurations, which can be beneficial in scenarios where power efficiency is a concern, such as in battery-powered devices or energy-constrained environments.Advantages of 1 × 2 MIMO:Higher Spatial Diversity: A 2 × 3 MIMO structure provides higher spatial diversity compared to a 1 × 2 MIMO structure. With two transmit antennas and three receive antennas, it can leverage multiple spatial paths for communication, leading to improved performance in terms of signal quality, reliability, and robustness against fading and interference.Increased Capacity: A 2 × 3 MIMO system can potentially offer higher capacity compared to a 1 × 2 MIMO system, as it can support the transmission of more data streams simultaneously. This can result in higher data rates and increased throughput, which can be advantageous in high-data-rate communication scenarios.Enhanced Performance: With more antennas involved, a 2 × 3 MIMO system can offer improved performance in terms of link quality, coverage area, and interference mitigation. It can provide better signal strength, extended coverage, and increased resilience against channel impairments, leading to more reliable and robust communication.Flexibility in Spatial Multiplexing: A 2 × 3 MIMO system can support higher-order spatial multiplexing, which refers to the simultaneous transmission of multiple data streams on the same frequency band. This allows for more flexibility in terms of data transmission and can enable higher capacity and improved spectral efficiency.Advantages of 2 × 3 MIMO:We can identify from the key points above that the advantages of a 1 × 2 MIMO versus a 2 × 3 MIMO structure depend on the specific requirements of the communication system and the trade-offs between system complexity, performance, and capacity. While a 1 × 2 MIMO structure offers simplicity and lower system complexity, a 2 × 3 MIMO structure provides higher spatial diversity, increased capacity, and enhanced performance. The choice between the two would depend on the specific application, deployment scenario, and performance requirements of the wireless communication system.This manuscript explores the use of a six-element split ring resonator with a circular patch-shaped multi-input multi-output (MIMO) antenna in the 1 to 25 GHz band and provides experimental verification of the computational results. Reflectance, gain, directivity, VSWR, and electric field distribution are only a few of the physical factors that are taken into account while analyzing MIMO antennas. The proposed antenna offers the multichannel MIMO antenna values of TARC (<−5 dB), ECC (0 to 0.15), CCL (0–1 bits/s/Hz), MEG (−1 to 1 dB), and DG (10 dB) for effective communication. The suggested antenna has a return loss of −19 dB and a gain of −28 dBi, making it suitable for ultra-wideband (10.83 GHz) applications. The antenna’s lowest return loss is −32.74 dB over its 6.89 GHz bandwidth operational range of 1.92 to 9.81 GHz. Both the continuous ground patch and the dispersed rectangular patch properties of the antennas are explored. The proposed antenna can be used for the multichannel satellite communication application with the C, X, Ku, and K bands.


The relative bandwidth is 2.98%, which satisfies the standard of wide-band patch antennas.This paper proposed a right-handed circularly polarized (RHCP) micro-strip antenna for multi-navigation system applications. The size of the antenna is 70 mm × 70 mm × 2 mm, which is fabricated on an FR4 substrate. A meandering technique on a patch layer and asymmetrical defected ground structures (DGS) are employed to achieve the purpose of miniaturization and increase the bandwidth of the axial ratio. The prototype of this antenna is fabricated according to simulations where the bandwidth of return loss, bandwidth of axial ratio, and radio pattern are further testified. The bandwidth of return loss (S With the development of the civil aviation industry, aircraft are favored for efficiency in medium- and long-distance travel. Air safety is always the critical issue in transportation. With the increasingly dense air routes, which contain both passenger and cargo traffic, high-accuracy tracking and location of aircraft has become the focus of research ,2,3. TheAn antenna is a critical component of airborne equipment. Within the corresponding operating frequency band of targeted navigation systems, an antenna serves as the transceiver of navigation information that would be applied for real-time positioning ,9. SinceUp to now, three polarization modes of antennas have been proposed, namely linear polarization, elliptical polarization, and circular polarization. Recent research has shown that circularly polarized waves will benefit from their strong ability to resist multi-path interference and polarization mismatches affected by various environmental factors. They can also be converted into linear polarized waves as needed ,12,13. IIn the design of navigation antennas at present, in addition to the requirements of wide operating frequency band and gain, it is also necessary to take the installation environment into account. For example, antennas work with other complex avionics, and it is significant to reduce the size to improve the portability ,16. Amon11) and axial ratio (AR) is the limit of the micro-strip antenna [At present, the narrow bandwidth of both return loss . All the design indicators are satisfied after parameter optimizing. In section four, the antenna is tested by a vector network analyzer and microwave anechoic chamber. Comparisons of simulation and experimental results are given, which prove that the antenna meets the design requirements.In this paper, the designed wideband RHCP micro-strip antenna is proposed, which would be available for aircraft tracking in B1I and B1C for BDS-3, L1 of GPS, L1 of SBAS as well as E1 of Galileo. In section two, the principles of the meandering technique and DGS are introduced, which provide the theoretical support for broadening the band width of Sf denotes the resonant frequency, c is the speed of light, L refers to the length of the antenna patch, and rε is the relative dielectric constant of the dielectric substrate.The resonant frequency of the antenna can be retrieved as given by Equation (1),f will be affected by both dielectric constant and patch length. However, this will inevitably increase the risk of occurrence of both wave loss and the shortening of frequency bands. Therefore, our work will focus on structure optimization by applying meandering technology and defect ground structure to broaden the bandwidth of both the return loss and the axial ratio of antennas.From Equation (1), it can be observed that The meandering technique shown in gL and capacitors gC and pC in ω1 and ω2 refer to central frequency and cutoff frequency, and rB and pB are the electromagnetic induction intensity generated by gR and pR, respectively.Recently, more attention has been paid to DGS for performance enhancement of CP antennas. When the electrons move in the periodic potential field formed by the high-impedance surface, an electronic band structure will be generated due to the Bragg scattering , and theStep 1: Determine the basic parameters of the proposed micro-strip antenna patches. The step will be carried out according to the Equations (4)–(8) given in Step 2: According to the meandering technique, T-shaped and F-shaped gaps are added to adjust the current direction to generate the current that can flow counterclockwise and produce right-handed circularly polarized electromagnetic waves. At the same time, a square gap in the center of the patch is employed to increase the forward gain of the antenna. By means of the gap structure, the enhancement of the surface current path will then reduce the patch size of the antenna.Step 3: Design a defective structure by introducing two L-shaped slots on the diagonal of the same side of the coaxial feed, aiming at forming a high-impedance surface and expanding the axial bandwidth.Step 4: Scan the main parameters that would potentially affect the performance of antenna to determine the size of all antenna parameters.The main design steps of the antenna proposed in this article are as follows:In the S-band and below, the FR4 material has the ability to act as an antenna dielectric substrate. To be precise, FR4 material is a glass fiber mixed with epoxy resin. The heat resistance of this material can reach 300 degrees, the operating frequency is about a few GHz, and the nominal value of the permittivity is about 4.4. FR4 material has nearly zero water absorption and can maintain its working performance in both dry and wet conditions, making it suitable for installation on aircraft. At the same time, its price is much lower than the dielectric substrate material of high-frequency boards, which meets the requirements of industry to reduce production costs.Step 1: Complete the preliminary design of the patch antenna using the nominal value of FR4 material;11 and AR distributions, respectively;Step 2: Perform simulations to the designed antenna and extract corresponding S11 and AR of the designed antenna using vector network analyzer;Step 3: Measure the SStep 4: Compare the simulation results of the antenna with the measured results to obtain the deviation distribution. Afterward, the values of FR4 in the simulation are adjusted within a certain range to obtain a series of simulated distributions under different values;rε of FR4 is calculated and set as 4.52;Step 5: Perform least squares analysis on simulated and measured distributions. At this point, the dielectric constant with the smallest least squares estimation value is closest to the true value. In the design of process, permittivity Step 6: Perform antenna design and optimization with the permittivity of FR4 extracted from Step 5.At present, the nominal permittivity value of FR4 material is generally employed for antenna simulations as 4.4. However, due to the deviation of the dielectric substrate material selected by the manufacturer and the inevitable processing errors varying from 4.2 to 4.6, there will be significant differences between the simulated and measurement results of the antenna. This will lead to serious effects on the reliability of the antenna design. To reduce the impact of FR4 parameters on antenna design accuracy, we propose a feedforward optimization method that corrects the estimated value of FR4 through the deviation between sampled simulation and measured results. The critical correction steps are as follows:R denotes the radius of patch, f is the center frequency of working band, h refers to the thickness of antenna, and rε is the permittivity of substrate.In the recent implementations of micro-strip antenna, the features of patch could be generally summarized as circle and square one, respectively. Circular patch antennas possess more characteristics for structure design and more easily generate circularly polarized waves. In addition, circular patch antennas will generate higher radiation and lower losses. The radius of circle patch can be formulated given by Equation (3),f, rε, and h equal 5.8 GHz, 4.4, and 2 mm, respectively. In the same condition, the length of square micro-strip antenna only measures 3.14 mm. This proves that square micro-strip antennas perform better in terms of miniaturization. Compared with circle patch antenna, the square micro-strip antennas now are proven as the reasonable choice in combination with other electronic components, especially in some complex environments such as airborne systems. Moreover, the square patches are easier to produce than the circle ones, saving production costs and resources. Therefore, a square structure will be employed in the design of our antenna, and corresponding simulations as well as analysis will be carried out to improve the effectiveness of our design.Based on this structure, Si et al.  have proWT is printed on the substrate  of the antenna. According to [WT can be calculated according to the equations that follow.According to the analysis above, the circular polarized antenna serving the BDS-3 system is developed and designed with corresponding geometrical configurations as given in rding to , the lenL can be preliminarily defined as Equation (4),c refers to the velocity of light, f is the resonant frequency of antenna, and rε is the permittivity of FR4. Height of the antenna h is set as 2 mm. Then, the effective permittivity of antenna could be defined as Equation (5),refε denotes the effective permittivity. Here, we introduce the length extension of patch given by Equation (6),L refers to length extension. From Equation (4), we can obtain effective length as shown in Equation (7),efL refers to the effective length. The actual length WT could be calculated as Equation (8),The initial length of patch WT is calculated as 45.5 mm according to Equation (8).In this work, p × q is embedded along the x axis. In this patch, a single probe feed is implemented at  and works for exciting right-handed CP radiation. By using the theory of the meandering technique, one T-shaped structure is added to each edge of the square patch, as given by On the patch of the antenna, a narrow slot with dimensions of As shown in As shown in In order to improve antenna performance, especially AR, DGS is designed on the ground of the antenna. 11 and AR can be adjusted by changing parameter values.The geometry of the antenna is further optimized based on the analysis of simulated bandwidth retrieved from software HFSS. As given by 11 and AR shift to a high-frequency band with the increase in parameter dw. 11 and AR move down with the increase in db. In 11 moves up with increase in p, while in pg. In X1g increases, the axis ratio moves downwards to the high frequency, and the effect on S11 is not significant within the operating frequency band.11 and AR as a whole by changing parameters dw and db. Parameter p can be used for changing S11 separately, while pg and X1g are for AR.It is practical to adjust S11 and AR are given in 11 and AR are from 1.540 GHz to 1.612 GHz and 1.554 GHz to 1.601 GHz, which indicate the working band of the design is the second one.The antenna after validation is modeled and processed based on PCB printing. (1)Since the dielectric substrate material is FR4, its dielectric constant is 4.2 to 4.6, the dielectric constant of FR4 material used by the manufacturer cannot be guaranteed to be identical with the set value of 4.52 in thesofware HFSS (version 19.2). And the dielectric constant of the substrate material has a large effect on the resonant frequency of the antenna, which causes the difference between the simulation and the actual measurement.(2)In the manufacture of the antenna, high manufacturing accuracy is required due to the use of a loaded seam and defective ground structure. Manufacturing errors within the process allowable errors can also cause errors in the test results of the antenna’s performance.(3)When welding the coaxial feed probe, the corner of the L-shaped slot of the defective ground structure is inevitably blocked by the SM joint, resulting in a deviation in the measured results.(4)The unavoidable presence of non-insulating materials in the measurement environment would impact the measurement reliability.11 and AR retrieved from experiments, the operating band is 0.047 GHz. The relative band width (RBW) is defined by Equation (9),Hf and Lf are the are the highest and lowest values of the operating band.According to the bandwidths of SRBW of this design is calculated as 2.98%, which is greater than 1% and satisfies the definition of a wideband patch antenna. The following table shows a comparison between the proposed antenna and other designs.Although there exist some deviations between the measurement results and the theoretical values, our proposed concept for micro-strip antenna design still has significant advantages compared to the existing methods in refs ,33,34,3511 and radiation patterns. The performance of the antenna and quality of our work are validated according to the comparisons between simulated and measured results. The relative bandwidth of the antenna is determined as 2.98%. The suggested antenna also possesses high application potential compatible with L1 of GPS, L1 of SBAS, and E1 of Galileo.In this work, a circularly polarized antenna is proposed for BDS-3 applications. By means of the meandering technique, the geometry of the antenna is obtained as 7 mm × 7 mm × 2 mm. Afterward, rectangular-shaped and L-shaped DGS are introduced to broaden the bandwidth of the axial ratio of the antenna. After a series of optimizations, the bandwidth of return loss and axial ratio of antenna can be retrieved as 1.540 GHz to 1.612 GHz and 1.554 GHz to 1.601 GHz. The suggested antenna is fabricated and experiments are carried out on analysis of S


A wideband low-profile radiating G-shaped strip on a flexible substrate is proposed to operate as biomedical antenna for off-body communication. The antenna is designed to produce circular polarization over the frequency range 5–6 GHz to communicate with WiMAX/WLAN antennas. Furthermore, it is designed to produce linear polarization over the frequency range 6–19 GHz for communication with the on-body biosensor antennas. It is shown that an inverted G-shaped strip produces circular polarization (CP) of the opposite sense to that produced by G-shaped strip over the frequency range 5–6 GHz. The antenna design is explained and its performance is investigated through simulation, as well as experimental measurements. This antenna can be viewed as composed of a semicircular strip terminated with a horizontal extension at its lower end and terminated with a small circular patch through a corner-shaped strip extension at its upper end to form the shape of “G” or inverted “G”. The purpose of the corner-shaped extension and the circular patch termination is to match the antenna impedance to 50  Recently, a lot of research work has been focused on the wideband flexible antennas for biomedical applications ,4,5,6,7.The proposed antenna is designed to communicate not only with the biosensors on the body but also with the surrounding medical apparatus attached to the body in a health care system and, also, to communicate with the WLAN access points. To allow better mobility of the patient and the attached medical equipment, this antenna is designed to operate near body and not stuck to the body, as shown in Polarization is a critical and significant feature of antennas in modern wireless communication technology . The oriLately, different antenna types have been employed to attain circular polarization, including patch antennas, slot antennas, and spiral antennas ,17,18,19The flexibility of a circularly polarized (CP) antenna’s substrate can significantly impact its performance . When thThe proposed G-shaped and inverted G-shaped printed strip CP antennas are designed on a low-loss flexible Roger RO3003The WiMAX/WLAN antennas may have arbitrary polarization depending on their orientation as shown in The G-shaped and inverted G-shaped strip antennas are designed to operate over the frequency band (5–19 GHz). The main issue of the proposed antenna design is to fulfill the requirements of the dual function to produce dual polarization (circular/linear) over a wide frequency band with good impedance matching and high radiation efficiency. The G-shaped radiating strip is a turn-like antenna, i.e., it is similar to a helix or spiral of one turn. Therefore, it can produce both circular and linear polarization by adjusting its dimensions relative to the wavelength. The frequency band 5–6 GHz is actually the unique frequency band that is commonly dedicated for WiMAX and WLAN applications together. Therefore, the frequency band 5–6 GHz is selected for circular polarization. The CST® Studio Suite 3D EM simulator (CST-MWS) is used to design the antenna and evaluate its performance. The geometry of the inverted G-shaped antenna is presented in L followed by vertical strip extension of length L to form a right-angle corner-shaped extension that is terminated by a small circular patch of radius R. At its lower end, the semicircular strip is terminated with a horizontal strip extension of length L and width W, as shown in D and D, respectively. The antenna is excited through a CPW feeding line. The CPW has a length of L, the width of its central strip is W, and the width of each side slot is S. The characteristic impedance of the CPW is obtained based on W and S that are calculated using the CPW design equations [L. The antenna and the CPW feeder are printed on a flexible Rogers RO3003. The best dimensions of the proposed antenna are shown in Both the G-shaped and inverted G-shaped antennas can be viewed as composed of semicircular strip connected, at its upper end, to horizontal strip extension of length quations ,45. The The proposed antenna design has evolved in three main steps as presented in The first step is a trial to produce circular polarization by using a semicircular strip radiator with small horizontal extensions at the end points of the circular arc, as shown in the geometry of Antenna#1. From the curves of In the next step of the antenna design, the end points of the radiating strip are further extended to obtain the geometry of Antenna#2. This step of the design results in a great improvement of the impedance matching bandwidth as shown in The G-shaped antenna being proposed consists of five parts, (i) the semicircular strip, (ii) the vertical extension of the central strip of the CPW region, (iii) the horizontal extension at the lower end of the semicircular strip, (iv) the corner extension at the upper end of the semicircular strip, and (v) the small circular patch that terminates the corner extension of the semicircular patch. It is required to obtain the widest impedance matching and 3dB-AR bandwidth and to enhance the radiation efficiency. For this purpose, A thorough investigation of various parameters has been conducted to determine the optimal dimensions of the antenna. The effects of various dimensional parameters on D and D, respectively, are depicted in the present section. The effects of changing the outer diameters D on D leads to a decrease in the lower and higher frequency bands and the entire impedance matching band is shifted towards the left. However, D = 16.6 mm.The effects of changing the outer and inner diameters, D, of the semicircular strip on the impedance matching and 3dB-AR bandwidths are presented in D decreases the lower frequency at which the impedance bandwidth matches whereas the higher frequency seems to insensitive to such changes of D. The proposed antenna performs optimally in terms of the 3dB-AR bandwidth when D = 11.2 mm, as illustrated in On the other hand, the effects of changing the inner diameter, L and L, respectively, of the corner-shaped extension of the curved strip on the reflection coefficient magnitude and the AR are investigated in the present section. The effects of changing vertical length, L, on the frequency response of the reflection coefficient magnitude, L. On the other hand, the AR seems to be strongly dependent on L, as shown in L = 6 mm gives the best 3dB-AR bandwidth.The effects of changing the vertical and horizontal dimensions, L, on the frequency response of the reflection coefficient magnitude, L. On the other hand, the AR seems to be strongly dependent on L as shown in L = 6.4 mm gives the best 3dB-AR bandwidth.The effects of changing horizontal length, R, of the small circular patch termination of the G-shaped strip antenna on the frequency dependence of the magnitude of the reflection coefficient, R. On the other hand, the AR seems to be strongly dependent on R as shown in R = 1.9 mm gives the best 3dB-AR bandwidth.The impact of altering the radius, L of the CPW central strip extension on the magnitude of the reflection coefficient, L. However, the widest bandwidth is obtained by setting L = 7.2 mm. This value of L results in a 3dB-AR frequency range covering 5 GHz to 6 GHz as shown in The impact of altering the length The parametric sweeps presented in Owing to its flexible structure, the proposed antenna shall preserve its high performance even while being subjected to bend strains (to some extents) in the different directions.For studying the effects of the bend stresses on the characteristics of the proposed antenna, it is subjected to different bend angles The frequency dependence of the reflection coefficient, The frequency dependence of the axial ratio for different values of the longitudinal bend angle, The frequency dependence of the reflection coefficient, The frequency dependence of the axial ratio for different values of the transverse bend angle, The dependence of the percent impedance matching bandwidth on both the longitudinal and transverse bend angles, The dependence of the percent bandwidth of 3dB-AR on both the longitudinal and transverse bend angles, Thus, it can be concluded that the proposed antenna preserves the impedance matching bandwidth and the 3dB-AR bandwidth for longitudinal and transverse bend angles less than The way that the proposed inverted G-shaped strip antenna produces circular polarization can be demonstrated by showing the surface current distribution on the semi-circle strip radiator, as depicted in It is shown that the surface current on the inverted-G-shaped antenna is circulating in the counter clockwise direction, thereby producing RHCP in the +ve z-direction. As the dielectric substrate is very thin relative to the wavelength  can be expressed as followsLet The power accepted by the AUT excitation port can be expressed as follows:Let The far field radiation pattern can be expressed as followsEmploying , the farThe normalized radiation pattern can be evaluated as follows:The power density at the reference-gain antenna when the AUT is directed at follows.PR=ρSubstituting from  into 1010, the pMaking use of , 3), an, an3), aThus, the AUT antenna gain, Substituting from  into 1313, the fNote that  side of  are know side of  can be uThe realized antenna gain of the AUT can be expressed as follows:The power received by the reference-gain horn antenna can be obtained by calculating the following double integralThe total power radiated by the AUT can be calculated using the following double integral.Dividing both sides of  by P0, tSubstituting from  into 1818, the fThe radiation efficiency of the AUT can be expressed as follows.The expression  can be rMaking use of  and 19)19), the In this section, the antenna fabrication is described, and the experimental assessment of the antenna performance are presented and compared to the simulation results.For experimental investigations, both the G-shaped and inverted G-shaped antennas are fabricated. The antenna prototypes are presented in To measure the reflection coefficient magnitude, The antenna is designed to produce circular polarization over the frequency range 5–6 GHz (for the 5GHz band of the WLAN/WiMAX applications) with left-hand sense in the directions of one half-space and right-hand polarization in the opposite directions of the other half-space. On the other hand, it is designed to produce linear polarization over the frequency range 6–19 GHz. This makes the proposed antenna more able to operate in the applications requiring wideband with varying polarization characteristics.The frequency bands allocated for the WiMAX and WLAN applications are listed in the in The dependence of the maximum gain generated by the inverted G-shaped antenna on the frequency is shown in The results of the simulation and experimental testing of the radiation efficiency of the inverted G-shaped antenna, which were conducted over the frequency range of (4–20 GHz), are presented in The measured far field radiation patterns of the circularly polarized components E-left and E-right generated by the inverted G-shaped antenna have been added and compared to those obtained by simulation in the plane It is shown that the radiated field of the inverted G-shaped antenna is dominated by RHCP component in upper half-space (+ve z-direction) and LHCP component in the lower half of the space (-ve z-direction).The measured far field radiation patterns of the total electric field (Linearly Polarized) produced by the inverted G-shaped in the plane To demonstrate the contribution of the present work in the context of the published work with similar interest, some performance measures of the proposed G-shaped antenna are provided in By comparison with the other antennas listed in On the other hand, the proposed antenna can use the remaining part of the operational band (6–19 GHz) for high data rate and wideband communication with the on-body (and in-body) biosensor antennas attached to (or implantable in) the patient body through linear polarization. During this mode of operation, the alignment between the proposed antenna and the biosensor antennas can be easily maintained. Regarding the above requirements  can be uniquely satisfied by the antenna proposed in the present work when compared to the other antennas listed in A wideband low-profile G-shaped strip antenna on a flexible substrate has been proposed for biomedical for the application of WBAN to work as off-body communication. The antenna produces circular polarization over the frequency band 5–6 GHz to communicate with WiMAX/WLAN antennas and to produce linear polarization over the frequency band 6–19 GHz for communication with the biosensor antennas. It has been shown that an inverted G-shaped strip produces CP of the opposite sense to that produced by G-shaped strip over the frequency range 5–6 GHz. The antenna structure is composed of a semicircular strip terminated with a horizontal extension at its lower end and terminated with a small circular patch through a corner-shaped strip extension at its upper end to form the shape of “G” or inverted “G”. The corner-shaped extension and the circular patch termination has been added to the antenna geometry for impedance matching over the entire frequency band (5–19 GHz) and to improve the circular polarization over the frequency band (5–6 GHz). The antenna has been fed through a CPW to allow the fabrication on only one face of the flexible dielectric substrate. The dimensions of the antenna as well as the CPW have been optimized to obtain the best performance regarding the impedance matching bandwidth, 3dB-AR bandwidth, radiation efficiency, and maximum gain. The results have shown that the achieved 3dB-AR bandwidth is


The demand for vehicular antennas increases in tandem with the need for multiple features in automobiles. The development of optically transparent antenna (OTA) has made it possible to deploy antennas on delicate surfaces such as glass. Earlier studies on OTA demonstrated its viability using materials such as transparent conducting oxides (TCO) and conductive polymers. A tri-band OTA is proposed in this paper for vehicular applications. The antenna operates at 1.8 GHz, 2.4 GHz and 3.39–12 GHz bands, covering automotive/wireless applications such as GSM, Bluetooth, Wi-Fi, vehicular communication and electronic toll collection. The proposed OTA is developed on soda lime glass, and the material TCO is used for the radiator and the ground plane. The antenna prototype is tested on windshield and in an anechoic chamber, the gain and efficiency are found to be greater than 1 dBi and 80%, respectively. Furthermore, a machine learning technique for vehicle classification is proposed, which could help in electronic toll collection, automatic vehicle identifier, and parking management applications. The presented algorithm achieves 80% classification accuracy with a minimum window size. Therefore, significance has to be given to maintain balance among size, weight, and need for the applications. The multiband approach in a single antenna not only reduces the number of antennas required, it also lessens the system complexity, cost, and overall device size.For futuristic electronic communication, multiband, multiservice antennas are necessary elements. In addition to the integration of multiple bands, the applications also demand for lightweight, low-profile, inexpensive and compact sized antennas. The size of the antenna increases as multiple bands are incorporated in the design2. The antenna developed on the transparent substrates including glass can be used on windshield. It does not affect the aesthetic appearance and technical functionality of the vehicle. A challenging part of optically transparent antenna (OTA) design is to achieve improved gain and efficiency. The OTA is developed using transparent substrates such as soda lime glass, plexiglass, Perspex, quartz, and borosilicate glass. Transparent conducting oxide (TCO) like fluorine doped tin oxide (FTO), indium doped tin oxide (ITO), silver tin oxide (AgHT), and other films like MMMC are used as conducting layer in the OTA. Decreasing the thickness of the film reduces the efficiency3, whereas increasing the thickness affects the transparency. The thin-film transparent conductors also include surface losses, ground losses, and skin-depth losses, which induces low efficiency and reduces the conductivity of the OTA4. In5, a polyamide substrate transparent antenna with 86% optical transmittance is proposed. The antenna resonates for a bandwidth of 5.18–5.32 GHz, and offers a peak gain of 1.9 dBi and maximum efficiency of 65.87%. Many transparent substrates are used to develop OTA, and, in6, cellulose acetate is used to develop the substrate with a transparent film of ITO. It provides a peak gain of 5.4 dBi and the overall size of the antenna is 50 mm × 51 mm. The graphene is used to develop the conducting film on a substrate in7. Graphene has low sheet resistance, which increases gain, and a good flexibility and environmental stability. The reported antenna is designed on a glass substrate with an overall size of 60 µm × 100 µm and provides an efficiency of 67%.Also, area required for placing the prototype in the systems such as automobiles, satellites, mobile phones, and wearable electronics is to be considered. The antenna for automobiles can be mounted on the roof, mirror, trunk, and windshield of the vehicle8, a multilayer conducting film with layers of IZTO/Ag/IZTO and polyimide substrate is used. The peak gain and efficiency of the antenna are 1.84 dBi and 54% respectively. In9, a high transparent antenna with optical transparency of 88% is developed with borosilicate glass substrate and ITO film. The antenna radiates for UWB with a peak gain of 3 dBi. But, the efficiency of the antenna is low ~ 27%. The fabrication of the OTA can be done using many methods like dc sputtering and chemical vapor deposition, and in10 the antenna is fabricated using inkjet printing. The prototype is bendable with PDMS substrate and ITO film. The antenna resonates at 2.4 GHz with 5.75 dBi. In11, a 300 mm × 300 mm corning glass of good transparency is used to design the antenna with AgCl film. The proposed antenna offers 60% efficiency and peak gain of 5.5 dBi. The OTA with borosilicate substrate is developed in12 with fluorine doped tin oxide film. The proposed antenna offers transparency greater than 50% and resonate over 5 GHz. Antenna with acryl substrate with three types of films  is developed and compared in13. The study showed that the antenna developed with multilayer film (IZTO/Ag/IZTO) showed low efficiency of 7.76% and negative gain of − 4.23 dB, but transparency greater than 80%. Wired metal mesh (WMM) and micro metal mesh (µMM) are used as transparent conductive film in14 to fabricate radiating patch of the antenna with acrylic substrate. An optical transparency of 80% is achieved with 49% efficiency, and the overall size of the antenna is 50 mm × 50 mm. (1) In15, a two-port MIMO antenna is designed, where the antenna elements are placed vertically to achieve vertical polarization. In16, a two-port OTA is designed on soda lime glass, and the antenna elements are placed in vertical orientation with single polarization vector. In17, a four-port MIMO antenna is designed using AgHT-8 and plexiglass materials. The antenna operates in the frequency range of 0.69–2.82 GHz, and the antenna elements are placed horizontally to provide horizontal polarization vector. The MIMO antennas reported in the literature provides only single polarization vector and operates at single frequency.The transparent antenna can be developed with multilayer film to increase efficiency. InIn this work, a four-port optically transparent antenna is designed for automotive applications. The antenna is dual-polarized with tri-band resonances. The ITO coated soda lime glass substrate is chosen due to its affordability and availability, and wet chemical etching method is opted for easy fabrication. The overall size of the proposed MIMO antenna is 55 mm × 55 mm.The OTA is developed with TCO like tin oxide, indium oxide, zinc oxide, and cadmium oxide. These oxides are further doped with dopants like fluorine, indium, gallium, aluminum, silver, and so on. These oxides conduct when doped with the appropriate dopants. For better conductivity, the optical absorptions should be less than 104/cm and optical energy gap should be more than 3 eV.19. The surface resistance is calculated by Eq. . For additional resonance of 2.4 GHz, the surface current of the radiator is observed, and an inverted L-slot is introduced (Antenna 3). The 1.8 GHz is achieved by incorporating a bent stub in the radiator (Antenna 4). The added stubs create impedance mismatch over the UWB, which is further compensated by loading a slot (Antenna 5) in the radiator and a defect in the ground (Antenna 6). The inverted L-shaped slot has a resonant length of 0.11λ0. The isolation is greater than 15 dB over the operating frequency range. Good isolation is achieved with minimum element spacing. A connected ground structure is used to ensure a common reference voltage. Polarization diversity with dual polarization is achieved when the antennas are placed perpendicular to each other. The measured reflection coefficients and mutual coupling of the MIMO are shown in Fig. Vehicular applications demand an antenna array as there is a need to receive signals from all directions. The single element shown in Fig. The soda lime glass of thickness of 1.1 mm coated with ITO on both sides of the glass is used. The thickness of the ITO film is 200 nm. Wet chemical etching is followed to pattern the required antenna design on the substrate. The etching process requires first cleaning the ITO-coated glass with deionized water. Then the required pattern is prepared as a mask using the etch-resistant tape (Kapton tape). The masking is placed on the ITO-coated glass, and the masked ITO is immersed in the HCL: H2O (1:1) solution. The setup is undisturbed for a few minutes. The etching rate varies with the change in HCL concentration. The HCL molecules remove the ITO from the unmasked area, and the required pattern is obtained in the ITO glass. After this process, the patterned glass is exposed to sunlight for about 1 min and cleaned with deionized water. Since hot soldering can melt the layer of ITO material in the substrate, conductive silver epoxy adhesive is used to solder the connector to the antenna. The wet chemical etching of the patterned ITO glass is shown in Fig. Figure 22. The ECC is calculated using far-field and S-parameter, as given in Eqs. , diversity gain (DG), total active reflection coefficient (TARC), and channel capacity loss (CCL) are calculated. ECC is a crucial performance parameter that assesses the effectiveness of diversity in the MIMO system in Eqs.  and 6),,22. The 24. Equation Equation  shows th25. TARC is calculated using Eq. , electronic toll collection (ETC), parking management, fleet management, and advanced driving assisting system (ADAS). For the classification of vehicles, two input parameters are used: frequency and reflection coefficients. The reflection coefficients of different vehicles (auto (three wheeler), car, and truck) are obtained by placing the antenna in the corresponding vehicle. The machine learning method reduces the dimensionality of the features using linear discriminant analysis (LDA). The trained multilayer perceptron (MLP) has given the projected feature obtained from the LDA. The system performance is tested for the vehicle classification using the MLP classifier. The required training set is obtained by placing the antenna in the windshield of vehicle, and it is tested on the set of values obtained by placing the antenna in the sidemirror of the vehicles. For classification, maximum sample size of 30,000 and minimum of 3000 is chosen (see Table 47. The columns of a confusion matrix are normally the same categories as those established by a ground survey, and the cell values are the number of observations attributed to each grouping of categories. One dimension of a confusion matrix is indexed by the actual class of an object, and the other is indexed by the predicted class of the classifier. The confusion matrix for the vehicle classification is shown in Table A concept from machine learning called a confusion matrix contains data on both actual and anticipated classifications made by a classification systemTo determine a classification model's performance metrics, the confusion matrix is analyzed with some metrics. Precision describes the percentage of all favorable predictions that come true. Precision is the proportion of recovered instances that are relevant, also known as positive predictive value.Sensitivity, probability of detection, and true positive rate are other names for recall. It relates to the percentage of real positives that are appropriately identified.Specificity, often known as the real negative rate, is the percentage of actual negatives that are correctly identified as such. Recall's opposite is specificity.The accuracy of a test is assessed using the F1 score (see Table The negative predictive value in machine learning is the proportion of anticipated negatives that actually happen.The proposed OTA antenna operates for tri-band frequencies covering 1.8 GHz, 2.4 GHz, and 3.39–12 GHz for GSM, Bluetooth, Wi-Fi, and vehicle to vehicle communication applications. The transparent antenna is developed using the wet chemical etching process. The MIMO antenna with four elements placed orthogonally provides dual polarization. The antenna prototype is tested in the anechoic chamber and the gain and efficiency are found to be greater than 1 dBi and 80%, respectively. The diversity parameter values are within the acceptable limit. The antenna prototype is mounted in the windshield of a vehicle and study shows that there is no effect on the antenna performance. Machine learning for the classification of vehicles in different scenarios is proposed, and required parameters are studied, which provide classification accuracy of 80% for minimum window size. Hence, the proposed antenna is suitable for vehicular applications.


In this article, we propose a light weight, low profile Multiple Input Multiple Output (MIMO) antenna system for compact 5th Generation (5G) mmwave devices. Using a RO5880 substrate that is incredibly thin, the suggested antenna is made up of circular rings stacked vertically and horizontally on top of one another. The single element antenna board has dimensions of 12 × 12 × 0.254 mm In the modern world, wireless communication is impacting countless areas , unmanned transportation systems, smart grid concepts in power transmission and distribution, digital banking systems, smart home HDTV through effective satellite communication systems), and these technologies are providing great significance in improving human lives ,2,3. AntMIMO antennas are extremely beneficial in densely populated areas where Line of Sight (LOS) communication is impossible. The signal may be in-phase or out-of-phase when it arrives at the receiver via multi-path in these circumstances, causing multi-path fading. The MIMO antenna, which is coupled with a combiner to increase the mean signal-to-noise (SNR) ratio and produce diversity gain, reduces the multi-path problem. There are four types of diversity combiners: switching, equal gain combining (EGC), maximum ratio combining, and selection combining (MRC). The branch with the highest SNR is chosen at any point in time in selection combining. The signal from the branch that meets the minimal threshold value is chosen by the switched combiner. The co-phased branch signals are added by EGC. Each branch in MRC has its phase weights applied so that the result is the sum of all of the SNR ratios. MIMO antennas when initially employed, boost spatial variety in order to combat channel fading. The information is being considered in a Rayleigh fading environment, where it is sent by antennas that take various routes to independently reach receiving antenna. The highest diversity increase in this scenario is referred to as Spatial Diversity. When separate information is delivered over antennas, the data rate is increased, which is known as Spatial Multiplexing. MIMO antennas have given wireless communication a new direction and are now particularly desirable for 5G applications. Higher data rate, low latency and with better system stability are the characteristics which make 5G a potential candidate for future wireless communication systems. Designing a MIMO antenna system is a complex task since modern communication devices are desired to be compact and slim. A wide scale placement of a 5G network requires the preparation of antenna infrastructure and the execution of new technical clarifications . The miltenna in  providestenna in ,11,12,13tenna in . Additio dBi. In  was desi dBi. In ,16.In , for upcFour different random array types were contrasted in . SpecifiIn order to enhance the isolation among the radiating elements, several approaches are considered. These techniques include isolating structures insertion such as neutralization lines (NL), Defected Ground Structures (DGS), Electromagnetic Bandgap Structures (EBG) and Artificial Magnetic Conductors (AMC) ,20,21. AAn innovative EBG design and a hair-pin-shaped DGS are used in combination in  to achieThis research presents a simple planar monopole MIMO antenna system arranged in linear manner. The proposed MIMO antenna exhibits dual wide-band characteristics covering two mmwave 5G alloted resonances of 28 and 38 GHz, respectively. The four element linear MIMO system satisfies the MIMO performance parameters and also gives high gain of 11 dBi. The paper is organized as follows. The impedance matching of the proposed olympeak antenna in evolution stage is shown in The surface current patterns at two resonances of 28 and 38 GHz are shown in The effect of the ground plane notch etched at the top mid-section of the copper ground plane is given in The radiation and total efficiency of the antenna is >82% in the operating band. The peak gain is noted to be 4.9 dBi while on 28 GHz its 4.2 dBi with radiation and total efficiency of 94 and 95%, respectively.The performance parameters of the antenna mentioned above are shown in The proposed olympeak antenna is transformed into a four element MIMO antenna system. The MIMO elements are transformed into a linear element, having 12 mm distance among each element centre to centre. The distance among the MIMO elements is kept at 1.2 The MIMO simulated s-parameters are shown in The proposed olympeak MIMO antenna system is fabricated, and using in-house facilities, the measurements have been taken from the developed prototype. The fabricated prototype is shown in The measured and simulated s-parameters are superimposed on the plots in The antenna is so thin and flexible that it requires a delicate mechanical balance to keep steady during the measurement. It is seen from the plots in The array is symmetric from the center. The radiation patterns of the left two elements are identical to the right two elements in the array. Therefore, analyzing only half of the array would be adequate to obtain an idea for the overall array. We will present the results of Antenna 1 and Antenna 2 when the antennas are sequentially numbered from left to right. The simulated and measured radiation patterns of Antenna 1 and Antenna 2 at two principle planes of Phi = 90 and Theta = 90, at two resonating bands are shown in The MIMO performance of the proposed antenna systems were evaluated. These parameters included Enveloper Correlation Coefficient (ECC), Diversity Gain (DG) and Mean Effective Gain (MEG).The Envelope Correlation Coefficient reveals the degree of radiation pattern independence between two antennas. Therefore, the two radiating structures would have a correlation of 0 if one was totally horizontally polarized and the other was completely vertically polarised. The ECC of these antennas would also be zero if one antenna exclusively radiated energy towards the sky and the other just radiated energy towards the earth. Therefore, Envelope Correlation Coefficient considers the polarization, shape, and even the relative phase of the fields between the two antennas of the antennas. The ECC is evaluated using far field characteristics of proposed antenna using Equation  27,28,2,228,29. i-th antenna and j-th antenna. r is the cross-polar ratio which can be expressed as Equation  fading conditions with high channel capacity, channel aggregation and a higher number of users. On the other hand, new portable gadgets are becoming lighter and thinner, while requiring powerful processing capabilities. This work presented a four-port MIMO antenna system with high performance characteristics. The proposed antenna was shaped in a hybrid Olympic sign, hence it was named as Olympeak antenna. The total unit size of the proposed antenna was 12 × 14 × 0.254 mm