Abstract
Ultra-wideband (UWB) technology has emerged as a promising solution for applications in indoor positioning systems, medical instrumentation, and Internet of Things (IoT) environments, owing to its extremely low power consumption, good temporal resolution, and intrinsic resilience to multipath propagation and signal attenuation. In this work, a compact two-port, multiple-input multiple-output (MIMO) antenna system with an extensive band response and low mutual coupling characteristic for ultra-wideband (UWB) application is proposed. The design simplicity, unique decoupling structure, high performance, and low mutual coupling throughout the operating band make the proposed design novel. The design has a size of 35 × 46 mm2 with 0.17 × 0.23 λ2 electrical length, making it highly compact for the desired wireless applications. The design consists of a partial ground, two radiating elements, and a decoupling structure. Multiple slots in the radiating elements and partial ground with rounded corners have helped to generate a very wide band response with good impedance matching, which covers UWB and additional bands for numerous wireless applications. The simulated and fabricated prototype has achieved 172% (1.5–20 GHz) fractional bandwidth. The decoupling structure has highly improved port isolation throughout the operating band, with a minimum of 25 dB isolation. The proposed MIMO design has demonstrated good performance in terms of simulated and measured gain throughout the operating band, with a peak gain of 4.69 dBi at 13 GHz. The proposed design demonstrates stable MIMO performance, as evidenced by low envelope correlation coefficient (ECC), high diversity gain (DG), and acceptable channel capacity loss (CCL). Given its ultra-wide operational bandwidth and robust MIMO characteristics, the antenna system is well-suited for a broad range of medical and advanced wireless communication applications.
1 Introduction
The growing requirements of wireless communication users necessitate the implementation of suitable antennas in contemporary networks to effectively manage increased data rates while minimizing losses [1]. The Federal Communications Commission (FCC) has approved ultra-wideband (UWB) technology, using an unlicensed spectrum ranging from 3.1 GHz to 10.6 GHz [2]. UWB technology has several advantages, such as wide spectrum availability and low power consumption [3]. However, multipath fading influences the performance and efficiency of the UWB system. This issue is addressed by integrating UWB with multiple-input multiple-output (MIMO) technology. Such an approach increases the capacity of the channel by employing multiple antennas on both the transmitter and receiver sides to facilitate simultaneous data transmission. MIMO antenna systems improve the received signal strength through the integration of data streams that arrive through multiple pathways and at varying times. This leads to improved data speeds and wireless connectivity while maintaining the same level of transmitter power [4]. The integration of UWB with MIMO facilitates the mitigation of co-channel interference and enhances the availability of frequency bandwidth. The combination of UWB and MIMO improves system capacity by leveraging spatial multiplexing and diversity advantages, while avoiding the need for an increase in the current frequency spectrum. MIMO technology allows the use of antennas characterized by minimal mutual coupling, especially in compact and space-limited systems [5].
UWB MIMO antennas are essential in the Internet of Things (IoT) landscape [6], significantly improving connectivity, data transmission rates, and the overall capacity of systems. They enhance dependability across various IoT settings, provide energy-efficient performance, and facilitate high data rates while reducing bandwidth needs. UWB MIMO antennas provide significant improvements in IoT connectivity, data rates, and overall system performance, thereby facilitating the broader implementation of IoT ecosystems across multiple industries. Figure 1 is an illustration of a UWB-based system for IoT applications, depicting a potential configuration of a home entertainment network connected through a high-speed wireless network. The application of high-precision location tracking and wireless charging capabilities for smart home entertainment devices represents two additional avenues through which UWB technology could enhance user experience in the IoT framework.
FIGURE 1
However, current UWB MIMO antennas in IoT applications have difficulties in attaining wide bandwidth [7, 8], ensuring isolation among antenna elements, and controlling the physical dimensions of the system, especially in densely populated IoT settings. These constraints affect the efficiency, dependability, and general usefulness of UWB MIMO across a range of IoT applications. By resolving these constraints, UWB MIMO antennas can be used more efficiently in numerous applications, such as IoT applications, industrial automation, wearable electronics, and smart home systems.
To diversify the UWB MIMO antennas in an IoT framework, antenna miniaturization while ensuring mutual coupling reduction has been achieved using various techniques, including a defected ground structure [9], parasitic elements [10, 11], metamaterials [12], neutralization lines [13, 14], and antenna orientation methods [15, 16]. A flexible two-port MIMO antenna of size 22 × 31 mm2 on Kapton as a substrate material is proposed in [17]. The reported design utilized a T-shaped stub to achieve an isolation of 15 dB over a band from 2.9 GHz to 12 GHz. The proposed design is ideally suited for the IoT systems or wireless sensor networks (WSNs) due to its small footprint, yet its complex geometry complicates the fabrication and testing process. Minor modifications in dimensions or orientation may substantially impact performance metrics. A flexible 4-element UWB MIMO antenna, with a crescent shape with dimensions of 54 × 54 × 0.13 mm3, gives a peak gain of 5 dBi [18]. However, the substantial footprint impedes its utilization in the IoT nodes. Likewise, a design with a C- and L-shaped electromagnetic band gap (EBG) based radiator, realized on a 1.6 mm thick FR4 substrate, has been proposed with a size of 34 × 34 mm2 and isolation of 30 dB within the band from 2.5 GHz to 12 GHz [19]. However, integrating the EBG-based antenna with the existing IoT node that has other sensor components is challenging due to the shorting pins of the EBG structure. This integration may also give rise to signal integrity issues and cause interference with the other electronic components. Similarly, in [20], bandwidth is increased, and isolation is improved by using a defected ground plane and meandered radiator, along with a longer stub that resulted in a larger dimension of 42 × 42 mm2. For wearable and IoT applications, a 4-port flexible UWB MIMO antenna is designed on a liquid crystal polymer (LCP) substrate working between 2.9 GHz and 10.86 GHz and is implemented using an LCP substrate in [21]. The design provides good isolation over a band from 2.0 GHz to 10.86 GHz when antenna elements are placed orthogonally. A UWB MIMO designed on a non-conventional substrate implies integration challenges between the antenna and the current hardware components of the IoT nodes. It has been proposed to use cross-shaped isolators between the UWB MIMO antenna elements to reduce mutual coupling, but such an approach significantly increases the overall size, making it difficult to seamlessly fit into IoT WSN. A crescent-shaped, 4-element MIMO antenna of sizes 56 × 56 × 1.6 mm3 has been proposed in [22] for UWB-, Ku-, and X-band applications. The complex structure and large dimensions of the proposed design significantly limit its integration into advanced IoT systems due to spatial constraints. Recently, a star fractal-type MIMO antenna measuring 38 × 66 mm2 has been proposed in [23]. It uses a parasitic decoupler to enhance IoT communication performance. However, the large dimensions do not fulfill the target of achieving compactness and seamless integration into IoT devices.
Analysis from the literature indicates that many previously published arrays are ineffective in activating the lower UWB frequency range. [24] presents excellent work for RADAR optimization of a spectrally crowded V2I communication environment. [25] highlights a novel idea related to air-ground integrated infrastructure. [26] is about beam-forming design for hybrid RIS-aided sensing and communication, while [27] discusses radio-frequency amplifiers for different temperature scenarios. [28–30] discuss wireless network performance and optimization for wireless applications. [31–33] focus on the design of antenna arrays and amplifiers for multiband wireless applications. The large physical dimensions of the UWB MIMO antennas impose limitations in terms of their seamless integration into IoT systems. Additionally, some multi-port array setups use separate ground planes, which makes MIMO operation less stable due to different voltage levels on each ground plane. Similarly, compact single-input single-output (SISO) designs fail to address the issues related to data rates and multipath loss. The MIMO designs do address these technical challenges, but their large sizes and low port isolation reduce their effectiveness for enhancing IoT communication. Based on the average IoT sizes, the proposed design is compact enough for easy integration with the IoT devices.
In this work, a semi-circular geometry with numerous radiating slot elements is proposed to address the existing technological challenges and achieve 170% fractional bandwidth over the 2.1–20 GHz operational spectrum. A curve-shaped ground plane and an innovative decoupling technique are implemented to achieve a maximum port isolation of 30 dB. Simple geometry provides ease of integration with the IoT systems to mitigate the associated challenges of the existing MIMO antennas. Thus, design simplicity, unique shape, compact size, and high performance are the novel aspects of the proposed design. The remaining part of the article is organized as follows: Section 2 describes the antenna design, Section 3 discusses its evolution steps and equations, Section 4 presents the parametric study, Section 5 presents the design’s simulated and measured results, Section 6 discusses the MIMO performance of the design, Section 7 details the link budget, Section 8 describes the application environment, and Section 9 concludes the proposed work.
2 Antenna design overview
The geometry of the proposed two-element MIMO antenna is shown in Figures 1a–d. The design includes two circular patches with multiple slots and a decoupling structure. The partial ground and radiating elements are separated by a FR4 substrate of standard 1.6 mm thickness and 4.3 dielectric constant. Ls and Ws are the length and width of the substrate, respectively. Given in Figure 2a, the identical linear MIMO array has a decoupling structure of length b with two added stubs of length c and width a. Given in Figure 2c, the outer major slot and two subsequent slots in the radiating elements have lengths d and e, respectively. The innermost slot in the radiating element has a length of radius r from the center of the radiating element. R is the radiating patch radius from the center. Figure 2b shows the bottom view of the design with a truncated ground plane of length Lg. The center of the ground plane has a V-shaped slot, while the outer edges of the ground plane are smoothed with curved etching. The truncated ground has been transformed to a curved shape with radius r1. Figures 2c,d show the exploded 3D and side views of the proposed design, respectively. The detailed dimensions are given in Table 1.
FIGURE 2
TABLE 1
| Parameter | mm | Parameter | mm |
|---|---|---|---|
| A | 2 | r, r1 | 4, 10 |
| B | 20 | Lf | 20 |
| c | 8 | wf | 2.8 |
| d | 20 | R | 11 |
| e | 16 | Ls, Ws | 46, 35 |
Dimensions of the proposed design.
3 Design equation and evolution of the proposed UWB antenna
The proposed two-port MIMO design starts with the design of a single circular patch antenna, which is based on the foundational Equation 1, used for the initial design operating with TM11 mode [24].
In Equation 1, is the resonant frequency of the single-element patch antenna, c is the speed of light in free space, a is the radius of the path, and is the relative permittivity or dielectric constant of the substrate. In cases where the substrate height is not negligible, the effective permittivity is given by Equation 2:
The effective radius aeff includes the fringing field effect [24] and is given by Equation 3:
The above equations help determine the initial dimensions of the design. In order to obtain the final design, the antenna system passes through several evolution steps, which are explained in Figures 3a–f. Figure 3a explains step 1 of the proposed design. In Figure 3b, the design is converted to a moon-type structure. In Figure 3c, the central slot is further enhanced. In Figure 3d, another slot is added while the corner of the truncated ground is etched round, and the SISO arrangement is converted to a two-port MIMO. In Figure 3e, a novel decoupling technique is added to improve port isolation and reduce mutual coupling. Figure 4 shows the corresponding reflection coefficients generated because of the design evolution steps. In Figure 3a, the design resonates at multiple undesired bands. In order to enhance the impedance matching and the operating band, a part of the circular patch is removed, as shown in Figure 3b. It modifies the current distribution, producing the localized field and improving the impedance matching to the feedline. In Figure 3c, the central slot is extended to the edges of the upper part of the circular patch. This step further improves the impedance matching at higher frequencies. In Figure 3d, an additional central slot further enhances the impedance matching over the entire operating band. This slot acts as a capacitive discontinuity, thereby extending the operating band to lower frequencies.
FIGURE 3
FIGURE 4
The design is converted to a MIMO arrangement in step 5, as shown in Figure 3e. This step is helpful in improving the data rates; however, as shown in Figure 4, the design has very high mutual coupling. In order to suppress the current flow between the ports and reduce the mutual coupling, a decoupling technique is introduced in step 6, as shown in Figure 3f. Figure 5 shows that adding a decoupling technique symmetrically between the two MIMO elements highly reduces mutual coupling and enhances the port isolation.
FIGURE 5
4 Parametric analysis of the proposed design
The two-port MIMO design is finalized by performing a thorough parametric analysis. These parameters help define the design behavior and responses to get results. They include the width of the outer slot, the length of the ground plane, the central slot length, the length of the decoupling line, and the length of stubs on the decoupling line.
4.1 Impact of outer slot width on the reflection coefficient
Figure 6a shows the impact of outer slot width on the reflection coefficient. The simulated results of the reflection coefficient indicate that increasing the outer slot width enhances the impedance matching. A maximum operating band with relatively better impedance matching is achieved at a slot width of 8 mm. Further increasing the slot width reduces the impedance matching and bandwidth.
FIGURE 6
4.2 Impact of ground plane length
Figure 6b shows the impact of the ground plane length on the impedance matching and bandwidth. The simulated results of the parametric study show that gradually increasing the ground length improves the impedance matching. This response to changing the ground length happens because the ground plane acts as a return path for the current flow. A shorter ground plane has a stronger fringing field, which leads to impedance mismatch. For the proposed design, the final ground plane has a length of 8 mm, which offers better impedance matching.
4.3 Impact of the stub width on the mutual coupling
The decoupling technique plays a key role in enhancing the port isolation by reducing the mutual coupling. The decoupling structure consists of a microstrip patch line with top and bottom stubs. The impact of stub width is given in Figure 6c. Gradually increasing the stub width improves the port isolation at lower frequencies, while a minor improvement is witnessed at higher frequencies. The maximum improvement is witnessed at a stub width of 2 mm. Any further increase in the stub width decreases the port isolation.
4.4 Impact of decoupling line length on the mutual coupling
The decoupling line length also affects the mutual coupling. The impact of decoupling line length is shown in Figure 6d. The figure shows that gradually increasing the line length decreases the mutual coupling. The maximum response is achieved at a line length of 14 mm. Increasing the line length beyond 14 mm reduces the port isolation.
5 Simulated and measured results
The final simulated and measured findings are described in this section, including every major aspect of the suggested design performance. These include the simulated and measured results of the reflection coefficients, radiation patterns at resonance frequencies, gain, efficiencies, and current distribution at the desired resonance frequencies, time-domain analysis, and simulated efficiency of the suggested antenna system. The isolation coefficient between the radiating elements is also examined to assess the degree of contact between them.
5.1 Experimental setup
CST Microwave Studio software 2024 is used to model, simulate, and assess the suggested MIMO array. The performance of the antenna system could be accurately represented and evaluated using this electromagnetic (EM) simulation tool. The proposed layout is constructed, and experimental measurements are made to validate the simulated results. Antenna performance is properly tested in an anechoic chamber, which provides a space free from external influences such as interference and reflection. Accurate measurements of the reflection coefficients, gain, and other important parameters are made possible through the use of a vector network analyzer (VNA). To guarantee accurate impedance matching and measurement of the reflection coefficients throughout the measurement procedure, the suggested design terminates one port with a 50 Ω impedance. Accurate and precise measurements are made possible by eliminating the negative effects arising from open or short-circuited ports.
5.2 Scattering parameters
Figure 7 displays the simulated and measured outcomes of the S-parameters of the proposed design. Overall, the simulated and experimental results are quite similar, indicating that the design is sufficiently accurate. Nonetheless, a small discrepancy in impedance matching remains, particularly at the resonant frequency. These shortcomings and inconsistencies may result from inaccurate manufacturing of the prototype and experimental settings. The actual and simulated findings validate the design’s performance despite these discrepancies. The simulated values of the reflection coefficient (2.1–20 GHz) and measured values of the reflection (2–20 GHz) have shown similar impedance matching. Similarly, the simulated isolation coefficient for the entire operating range is better than 20 dB. The measured isolation coefficient has shown an even better response, with a value below 25 dB. This response is due to the multiple reflections within the measuring facility, which have enhanced the measured port isolation. The fabricated prototype top and bottom views are shown in Figures 8a,b. Figure 8a shows that the upper side of the fabricated prototype has two radiating elements with antenna 1 and antenna 2, separated by a decoupling technique, while Figure 8b shows the bottom view of the fabricated prototype. The fabricated prototype S-parameters measurement setup is shown in Figures 8c,d. Figure 8c shows the measurement setup for the reflection coefficients, while Figure 8d shows the measurement setup for the mutual coupling.
FIGURE 7
FIGURE 8
5.3 Simulated and measured gain and efficiency
When examining the antenna performance, gain and efficiency are crucial factors. These performance parameters provide useful information about the power transmitted to the receiver. The suggested design’s measured and simulated gain and efficiency across the operating band are shown in Figures 9a,b, respectively. The simulated and measured results closely match across the whole band.
FIGURE 9
As shown in Figure 9a, a maximum gain of 4.5 dBi at a 5.5 GHz frequency and more than 3 dBi across the operational band is attained. In the simulated and measured results, there are a few variations approximately 5 GHz and 12 GHz. These minor variations can be caused by a variety of factors, including human error, cable losses, and poor manufacturing. This slight discrepancy between the measured and simulated gains clearly confirms the efficacy of the suggested approach. Figure 9b shows the simulated and measured efficiency of the proposed design. The simulated total efficiency is obtained from CST software, while the measured total efficiency is determined using the Wheeler–Cap method. Due to multiple reflections within the measuring facility, the measured total efficiency is higher, but overall, there is a close resemblance between the simulated and measured total efficiency. At lower frequencies, the design has maintained a high efficiency of 0.8 due to minimum losses, while at higher frequencies, due to conductor and substrate losses, there is a decline in the overall efficiency, with a 0.4 minimum value. Based on the S11 response, the design has the potential to transfer information with maximum power. However, a decline in efficiency at higher frequencies may impact communication.
5.4 Current distribution
The antenna system’s specific behavior and mode of operation are provided by the current flow within the suggested design at the intended resonance frequencies of 5.3 GHz, 7.6 GHz, and 13 GHz. While analyzing the current distribution for the three resonance frequencies, only one port is excited while the second port is terminated with a 50 Ω load. For the current distribution on the individual radiating element, the design steps elaborate that at the dominant operating mode (TM11), the design resonates at 8 GHz and some additional bands beyond 14 GHz. Multiple slots and ground truncation have changed the current distribution on the radiating element and ground, ultimately generating a wideband response (2.1–20 GHz). Figures 10a,b show the current distribution of the proposed design at ports 1 and 2 at 5.3 GHz, respectively. The current across both ports is uniformly distributed across the feedlines, showing maximum power flow toward the radiating elements. Moreover, the outer edges and lower part of the radiating elements are the major contributors to the 5.3 GHz resonance frequency. The current activity on the decoupling line shows that the decoupling technique has highly suppressed the current flow between the ports. This current suppression has caused high port isolation between the ports of the design. Figures 10c,d represent the current distribution of the proposed design at 7.6 GHz. The outer part of the radiating element contributes to this resonance frequency. Moreover, minimum current flow is observed between the ports, showing low mutual coupling. At 13 GHz, as shown in Figures 10e,f, the current distribution on the patch is focused on the central lower part with minimum current flow between the ports.
FIGURE 10
5.5 Simulated and measured far-field patterns
The far-field patterns of the proposed design in terms of E-field (XY plane) and H-field (YZ plane) are given in Figures 11a–f. Figures 11a–c show E-field co- and cross-polarization of the proposed design at 5.3 GHz, 7.6 GHz, and 13 GHz, respectively. Figures 13d–f show the H-field co- and cross-polarization of the proposed design at 5.3 GHz, 7.6 GHz, and 13 GHz, respectively. For all the simulated and measured values of the E-field patterns of the proposed design, the design has a main beam directed toward 0°, except for the E-field at 13 GHz, which is directed toward 150°. The design has maintained a difference of 10 dB between co- and cross-polarization, which is acceptable for compact MIMO IoT antennas. Simulated and measured E- and H-fields are stable and in close match. The minor deviation is due to the fabrication tolerances and measurement inaccuracies. Figures 12a–d shows the measurement setup for measuring E and H far-field patterns.
FIGURE 11
FIGURE 12
5.6 Time-domain analysis
Time-domain analysis is an important consideration for the suggested design performance validation. The transmitting and receiving signals in UWB technology are narrow pulses that are distorted and dispersed by multipath and channel losses. Twin antennas are set up, side by side and face to face, at a spacing of 240 mm (24 cm, two times λ) to produce far-field conditions [34]. The simulated group delay is displayed for both side-by-side and face-to-face configurations in Figure 13. Group delay appears to be approximately 1 ns for face-to-face orientations and 1.3 ns for side-by-side orientations. Therefore, the group delay of the suggested antenna design is highly stable throughout the operating band. These features confirm the suggested design’s potential and appropriateness for real-time use.
FIGURE 13
6 MIMO performance analysis
To assess the MIMO and diversity features of the suggested antenna, in this section, the key MIMO parameters are computed, including the envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss (CCL).
6.1 Envelope correlation coefficient (ECC)
To determine a wireless link’s reliability and quality, diversity analysis is crucial. The antenna array’s ECC must be ascertained to calculate the diversity gain. High isolation in array elements and minimal fluctuation in radiation patterns result in low ECC values, which in turn produce high diversity gain (DG). ECC is calculated by applying Equation 4 [35].
The cross-discrimination (XPR) ratio between vertical and horizontal powers, denoted by Pθ and Pφ, respectively, is obtained using and , which are the electric field components in the elevation and azimuth directions, respectively. For a promising MIMO performance, the minimum ECC value is 0.5, and any value below this reference digit will further enhance the MIMO performance [36]. Figure 14 shows the simulated ECC of the proposed design. From the figure, it is clear that for most of the operating band, the design has maintained ECC close to zero. This value confirms the high performance of the proposed design.
FIGURE 14
6.2 Diversity gain (DG) of the proposed design
DG is also an important MIMO antenna system characteristic, which is calculated using (11). The improvement of signal quality achieved through the diversity approach is the main goal of DG computation. Equation 5 is used to determine the DG of the proposed design [37].
The simulated and measured DG is shown in Figure 15. For the entire operating band, the design has maintained a DG of more than 9.98 dB, showing stable MIMO performance of the proposed design.
FIGURE 15
6.3 Channel capacity loss (CCL)
CCL is another important parameter to evaluate the MIMO performance of the proposed design. The quality of the transmission throughput is determined through the MIMO antenna array channel capacity loss (CCL). The optimal rate of data transfer is demonstrated by smaller CCL values. A CCL of 0.4 bits/sec/Hz is regarded as good with regard to data transmission; however, values exceeding 0.4 bits/sec/Hz indicate increasing transmission inefficiency [25]. The simulated CCL of the proposed design is given in Figure 16, which shows that for most of the operating band, the design has maintained a CCL less than 0.4 bits/sec/Hz. This shows the stable MIMO performance of the MIMO design.
FIGURE 16
7 Link budget analysis
To guarantee the effective communication range of the designed antenna, a link budget analysis was executed at 5.6 GHz, 7.6 GHz, and 13 GHz. The link margin was calculated taking into account all of the gains and losses the signal encounters while passing over the medium. The widely recognized formulas from [35] were used to calculate the link margin. Table 2 lists the values of the various parameters used. Equation 6 was used to assess the noise margin or receiver sensitivity [38].
TABLE 2
| Parameter | Value |
|---|---|
| Pt (transmit power) | 21 dBm, 27 dBm, and 30 dBm |
| Gt (tx antenna gain) | 3.49 dBi @ 5.6 GHz, 4.65 dBi@ 7.6 GHz, and 3.13 dBi@ 13 GHz |
| Gr (rx antenna gain) | 3.49 dBi @ 5.6 GHz, 4.65 dBi@ 7.6 GHz, and 3.13 dBi@ 13 GHz |
| f (Operating frequency) | 5.6 GHz, 7.6 GHz, and 13 GHz |
Parameter details of the link budget analysis.
where T is the temperature, which is 290 kelvin, MDS is the minimum detectable signal, and Boltzmann’s constant is k = −228 dBW/(kHz). The calculated MDS for the given antenna is −71 dBm with a bandwidth of 1000 MHz and a noise figure of 13.87 dB. The link budget is explained by Equation 7:
where GMIMO represents MIMO antenna system gain, and FSPL represents free space path loss, with Lother representing additional losses not specifically taken into consideration. The link margin determined for the numerous transmitted powers (21 dBm, 27 dBm, and 30 dBm) is given in Figure 17. The link margin assessed at 5.6 GHz with 3.49 dBi gain is given in Figure 17a. The figure shows that the proposed design has the potential to maintain a communication link up to 60 m, 120 m, and 169 m for Pt = 21 dBm, 27 dBm, and 30 dB m, respectively. Similarly, for the transmission power of 21 dBm, 27 dBm, and 30 dB m at 7.6 GHz with 4.65 dBi, the gain is given in Figure 17b. The proposed design has the potential to establish a communication link of 58 m, 115 m, and 163 m, respectively. As given in Figure 17c, at 13 GHz with 3.13 dBi gain, the proposed design can maintain a communication link of 24 m, 48 m, and 67 m, respectively.
FIGURE 17
A detailed comparison of the proposed research with the recently published works is provided in Table 3. Research work in [39] has achieved a high gain, but it does not cover the UWB band, and the design has larger dimensions, which reduces its usefulness. In [40], the research work proposes a UWB antenna with good performance, but the larger dimension has reduced its usefulness. The research work in [41] has a very wideband but bulky size, and low MIMO performance reduces its usefulness. In [42], the design does not cover the UWB band; moreover, the design has a bulky size and low MIMO performance. In [43], the design has good performance; however, the design does not cover the UW band. The research work in [44] is compact but has low port isolation with no coverage of UWB applications. Research works in [45, 46] are also bulky, which minimizes their usefulness. The proposed work has outperformed all the recently published works in terms of physical sizes and electrical lengths, operating band, and port isolation, while covering numerous wireless applications.
TABLE 3
| Ref. | Size (mm2)/λ2g | Freq BW (GHz) | Avg gain(dB) | ECC | Isolation (dB) | DG | Application |
|---|---|---|---|---|---|---|---|
| [39] | 150 × 100/(0.76 × 0.68) | 2–5 | 6.1 | >0.32 | −17 | 9.7 | Mobile communication |
| [40] | 65 × 65/(0.65 × 0.65) | 3–10.86 | -- | 0.01 | −22 | 9 | UWB wireless applications |
| [41] | 116 × 84/(0.72 × 0.84) | 2.5–20 | 5.4 | 0.044 | −17.5 | 8.4 | WLAN/satellite communication/UWB communication |
| [42] | 90 × 90/(0.87 × 0.76) | 5–9 | 4.95 | 0.09 | −17 | 9.3 | Vehicular communication |
| [43] | 30 × 40/(0.6 × 0.48) | 3.34–9.2 | 3.5 | 0.05 | −20 | 9.98 | Sub-6 GHz/WLAN/vehicular communication |
| [44] | 45 × 45/(0.3 × 0.3) | 2.2–6.28 | 3 | 0.25 | −14 | 9 | Sub 6 GHz wireless communication |
| [45] | 55 × 55/(0.612 × 0.612) | 3.34–9.2 | 4.3 | 0.017 | −20 | 8.9 | 5G and X band |
| [46] | 58 × 58/(0.5 × 0.5) | 2.7–12.1 | >5.96 | >0.003 | −20 | 9.95 | UWB and Sub-6 GHz wireless applications |
| This work | 35 × 46/(0.17 × 0.23) | 1.5–20 | 4.65 | 0.002 | −25 | 9.99 | UWB/Sub-6 GHz/K-band wireless application |
Proposed design compared with recently published work.
8 Application environment
The numerous designs proposed in the literature provide integrated solutions for a wide range of wireless applications. Numerous wireless schemes, services, and real-time implementation topologies have been highlighted in [47–49]. Resource allocation and service management for satellite communication are addressed in [50–52]. Higher performance metamaterials and antenna arrays have been detailed in [53, 54]. [55] is about the control of multilayer networks and their applications. These studies highlight techniques that are helpful in the deployment of radio-frequency (RF) devices for wireless networks. The integration of the proposed design with IoT devices shows that the proposed design is highly useful for its real-time IoT applications. Other than UWB, the proposed design covers important additional bands, useful for V2X IoT applications, which are illustrated in Figure 18a [56]. Figure 18b shows the simulation environment of the proposed design on an unmanned aerial vehicle (UAV) for vehicle-to-things (V2X) communication. The plastic body of the quadcopter helps with the seamless simulation of the proposed design [57]. Figure 18c shows the simulation results of the proposed design UAV, highlighting the effectiveness of the proposed design for real-time IoT applications.
FIGURE 18
9 Conclusion
In this study, a high-performance two-port MIMO antenna system for ultra-wideband (UWB) applications was successfully designed, simulated, and validated through fabrication. The proposed antenna’s compact design, partial ground, several radiating element slots, and efficient decoupling mechanism allow for an operational bandwidth of 172% (1.5–20 GHz). The design achieves strong impedance matching and excellent isolation between ports, with a minimum isolation of 25 dB across the entire band. Thus, overall design simplicity, novel decoupling structure, and enhanced performance are the novel aspects of the design. The antenna provides consistent MIMO performance, as demonstrated by low ECC, high DG, acceptable CCL, and steady gain characteristics, with a peak gain of 4.2 dBi, according to measured and simulated results. These attributes underscore the antenna’s capability to support high data rate, low-interference, and highly reliable communication, making it an ideal candidate for modern UWB applications, including indoor positioning, IoT systems, and medical instrumentation.
Statements
Data availability statement
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.
Author contributions
AU: Data curation, Investigation, Methodology, Writing – original draft. OK: Conceptualization, Data curation, Investigation, Methodology, Software, Writing – original draft. AI: Formal Analysis, Methodology, Project administration, Software, Writing – review and editing. SK: Conceptualization, Data curation, Investigation, Writing – review and editing. MD: Conceptualization, Data curation, Project administration, Resources, Software, Supervision, Writing – review and editing.
Funding
The author(s) declared that financial support was not received for this work and/or its publication.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was used in the creation of this manuscript. Figure 18(a) was generated using Google Gemini.
Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.
Publisher’s note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
References
1.
AlsabahMNaserMAMahmmodBMAbdulhussainSHEissaMRAl-BaidhaniAet al6G wireless communications networks: a comprehensive survey. IEEE Access (2021) 9:148191–243. 10.1109/access.2021.3124812
2.
DayoZACaoQWangYSootharPMuneerBChowdhryBS. A compact broadband high gain antenna using slotted inverted omega shape ground plane and tuning stub loaded radiator. Wireless Personal Commun (2020) 113(1):499–518. 10.1007/s11277-020-07227-z
3.
FontanaRJ. Recent system applications of short-pulse ultra-wideband (UWB) technology. IEEE Trans Microwave Theory Techniques (2004) 52(9):2087–104. 10.1109/tmtt.2004.834186
4.
AbdulkawiWMMalikWARehmanSUAzizAShetaAFAAlkanhalMA. Design of a compact dual-band MIMO antenna system with high-diversity gain performance in both frequency bands. Micromachines (2021) 12(4):383. 10.3390/mi12040383
5.
SundaravadivelPRajaMRAnnaduraiCRajesh KumarD. A novel moon-shaped flexible four-element co-planar antenna for 5G applications. Opt Quan Electronics (2024) 56(10):1612. 10.1007/s11082-024-07326-2
6.
ElsanhouryMMäkeläPKoljonenJVälisuoPShamsuzzohaAMantereTet alPrecision positioning for smart logistics using ultra-wideband technology-based indoor navigation: a review. IEEE Access (2022) 10:44413–45. 10.1109/access.2022.3169267
7.
KaurHSinghHSUpadhyayR. Design and analysis of compact quad-element MIMO antenna with asymmetrical ground structures for ultra-wideband communication. Wireless Personal Commun (2022) 124(4):3105–27. 10.1007/s11277-022-09504-5
8.
SheriffNKamal Abdul RahimSTariq ChatthaHKim GeokT. Multiport single element MIMO antenna systems: a review. Sensors (2023) 23(2):747. 10.3390/s23020747
9.
WeiKLiJ-YWangLXingZ-JXuR. Mutual coupling reduction by novel fractal defected ground structure bandgap filter. IEEE Transactions Antennas Propagation (2016) 64(10):4328–35. 10.1109/tap.2016.2591058
10.
TranHHNguyen-TrongN. Performance enhancement of MIMO patch antenna using parasitic elements. IEEE Access (2021) 9:30011–6. 10.1109/access.2021.3058340
11.
LiMCheungS. A novel calculation-based parasitic decoupling technique for increasing isolation in multiple-element MIMO antenna arrays. IEEE Trans Vehicular Technology (2020) 70(1):446–58. 10.1109/tvt.2020.3045231
12.
IqbalAA SaraerehOBouaziziABasirA. Metamaterial-based highly isolated MIMO antenna for portable wireless applications. Electronics (2018) 7(10):267. 10.3390/electronics7100267
13.
SuS-WLeeC-TChangF-S. Printed MIMO-antenna system using neutralization-line technique for wireless USB-dongle applications. IEEE Transactions Antennas Propagation (2011) 60(2):456–63. 10.1109/tap.2011.2173450
14.
ZhangSPedersenGF. Mutual coupling reduction for UWB MIMO antennas with a wideband neutralization line. IEEE Antennas Wireless Propagation Letters (2015) 15:166–9. 10.1109/lawp.2015.2435992
15.
RekhaVSDPardhasaradhiPMadhavBTPDeviYU. Dual band notched orthogonal 4-element MIMO antenna with isolation for UWB applications. IEEE Access (2020) 8:145871–80. 10.1109/access.2020.3015020
16.
DevPGuptaSKBageAMurmuL. High isolated MIMO antenna for WLAN applications. J Circuits, Syst Comput (2022) 31(06):2250109. 10.1142/s0218126622501092
17.
LiWHeiYGrubbPMShiXChenRT. Compact inkjet-printed flexible MIMO antenna for UWB applications. IEEE Access (2018) 6:50290–8. 10.1109/access.2018.2868707
18.
IbrahimAAAhmedMIAhmedMF. A systematic investigation of four-port MIMO antenna depending on flexible material for UWB networks. Scientific Rep (2022) 12(1):14351. 10.1038/s41598-022-18551-8
19.
ChenZZhouWHongJ. A miniaturized MIMO antenna with triple band-notched characteristics for UWB applications. IEEE Access (2021) 9:63646–55. 10.1109/access.2021.3074511
20.
AlsathMGNKanagasabaiM. Compact UWB monopole antenna for automotive communications. IEEE Trans Antennas Propagation (2015) 63(9):4204–8. 10.1109/tap.2015.2447006
21.
ZhangJDuCWangR. Design of a four-port flexible UWB-MIMO antenna with high isolation for wearable and IoT applications. Micromachines (2022) 13(12):2141. 10.3390/mi13122141
22.
AddepalliTKamiliJBBodduSMandaRNellaAKumarBK. A 4-element crescent-shaped two-sided MIMO antenna for UWB, X and Ku band wireless applications. Wireless Networks (2023) 29(8):3333–48. 10.1007/s11276-023-03390-w
23.
SohiAK. Novel star fractal MIMO antenna integrated with a unique parasitic decoupler for enhanced 5 G/IoT/UWB communication performance. Physica Scripta (2025) 100(3):035524. 10.1088/1402-4896/adb24a
24.
YaoYShuFChengXLiuHMiaoPWuL. Automotive radar optimization design in a spectrally crowded V2I communication environment. IEEE Trans Intell Transportation Syst (2023) 24(8):8253–63. 10.1109/tits.2023.3264507
25.
ChenPLuoLGuoDTangGZhaoBLiYet alWhy and how lasagna works: a new design of air-ground integrated infrastructure. IEEE Netw (2024) 38(2):132–40. 10.1109/mnet.2024.3350025
26.
HongyunCMengyaoYXuePGeX. Joint active and passive beamforming design for hybrid RIS-aided integrated sensing and communication. China Commun (2024) 21(10):1–12. 10.23919/jcc.ja.2023-0213
27.
SunJZhouS. Cuckoo search-ExtraTrees model for Radio-frequency power amplifier under different temperatures. Frequenz (2025)(0). 10.1515/freq-2024-0298
28.
YaoYXiaoWMiaoPChenGYangHChaeC-Bet alUAV-relay-aided secure maritime networks coexisting with satellite networks: robust beamforming and trajectory optimization. IEEE Trans Wireless Commun (2025). 10.1109/TWC.2025.3596136
29.
LuoYZhuMChenTZhengZ. Remaining useful life prediction for stratospheric airships based on a channel and temporal attention network. Commun Nonlinear Sci Numer Simulation (2025) 143:108634. 10.1016/j.cnsns.2025.108634
30.
ZhangCZhangHDangSShihadaBAlouiniM-S. Gradient compression and correlation driven federated learning for wireless traffic prediction. IEEE Trans Cogn Commun Networking (2024). 10.1109/TCCN.2024.3524183
31.
LiPLiRFanZHanJDingGWangQet al3D printed high-temperature ceramic conformal array antenna: design, analysis, manufacturing, and testing. Defence Technology (2025). 10.1016/j.dt.2025.05.012
32.
WangQLiPZhangYTanGYangYRoccaP. Robust design and tolerance analysis of shaped reflector antennas based on interval analysis. IEEE Antennas Wireless Propagation Lett (2025). 10.1109/LAWP.2025.3564436
33.
ZhaoZChenXMengFYangZLiuBZhuNet alDesign and analysis of a 22.6-to-73.9 GHz low-noise amplifier for 5G NR FR2 and NR-U multiband/multistandard communications. IEEE J Solid-State Circuits (2025). 10.1109/JSSC.2025.3545463
34.
KhanSKhanOShahSAAMalikBTGoharNKozielS. A compact circularly polarized dielectric resonator antenna with MIMO characterizations for UWB applications. Sci Rep (2024) 14:22627. 10.1038/s41598-024-73282-2
35.
KhanSMarwatSNKKhanMAAhmedSGoharNAlimMEet alA self-decoupling technique to realize dense packing of antenna elements in MIMO arrays for wideband Sub-6 GHz communication systems. Sensors (2023) 23:654. 10.3390/s23020654
36.
RaheelKAhmadAWKhanSShahSAAShahIADalarssonM. Design and performance evaluation of orthogonally polarized corporate feed MIMO antenna array for next-generation communication system. IEEE Access (2024) 12:30382–97. 10.1109/access.2024.3369251
37.
Tariq MalikBKhanSNasirJKozielS. Enhanced gain and isolation dual-band dual-port MIMO antenna with integrated lens for millimeter-wave 5G internet-of-things applications. IEEE Access (2025) 13:40859–74. 10.1109/access.2025.3547085
38.
KumariRGangwarRK. Circularly polarized slot-coupled square dielectric resonator antenna for WLAN applications. Microw Opt Technol Lett (2018) 60:2787–94. 10.1002/mop.31460
39.
JamalMLiMYeungKL. Isolation enhancement of closely packed dual circularly polarized MIMO antenna using hybrid technique. IEEE Access (2020) 8:11241–7. 10.1109/access.2020.2964902
40.
IbrahimAAAhmedMIAhmedMF. A systematic investigation of a four-port MIMO antenna depending on flexible material for UWB networks. Sci Rep (2022) 12:14351.
41.
AhmedBCarrerasD. E. G. Design and implementation of super wideband triple band-notched MIMO antennas. Wireless Pers Commun (2021).
42.
Ez-ZakiFBelahrachHGhammazAAhmadSKhabbaABelaidKAet alDouble negative (DNG) metamaterial-based koch fractal MIMO antenna design for Sub-6-GHz V2X communication. IEEE Access (2023) 11:77620–35. 10.1109/access.2023.3296599
43.
JayshriKDesaiDSimC. Wideband four-port MIMO antenna array with high isolation for future wireless systems. Int J Electron Commun (Aeü) (2021).
44.
JehangirSSSharawiMS. A miniaturized UWB biplanar yagi-like MIMO antenna system. IEEE Antennas Wirel Propag Lett (2017) 16:2320–3. 10.1109/lawp.2017.2716963
45.
KulkarniNPBhaskarraoBKulkarniS. Flexible interconnected 4-port MIMO antenna for sub-6 GHz 5G and X band applications. Aeu-int J Electron Commun (2022). 10.1016/j.aeue.2022.154243
46.
KhanOKhanSMarwatSNKGoharNBilalMDalarssonM. A novel densely packed 4 × 4 MIMO antenna design for UWB wireless applications. Sensors (2023) 23:8888. 10.3390/s23218888
47.
LiY-FZhaoWZhangCYeJHeH. A study on the prediction of service reliability of wireless telecommunication system via distribution regression. Reliability Eng and Syst Saf (2024) 250:110291. 10.1016/j.ress.2024.110291
48.
LiDLiPZhaoJLiangJLiuJLiuGet alGround-to-UAV sub-terahertz channel measurement and modeling. Opt Express (2024) 32(18):32482–94. 10.1364/OE.534369
49.
XuGWangLChenSZhuLGuizaniMShiL. MPAEE: a multi-path adaptive energy-efficient routing scheme for low Earth orbit-based industrial internet of things. IEEE Internet Things J (2025). 10.1109/JIOT.2025.3581314
50.
LyuTXuYLiuFXuHHanZ. Task offloading and resource allocation for satellite-terrestrial integrated networks. IEEE Internet Things J (2024). 10.1109/JIOT.2024.3465656
51.
WangFZhangSHongE-KQuekTQS. Constellation as a service: tailored connectivity management in direct-satellite-to-device networks. IEEE Communications Magazine (2025) 63(11):30–36. 10.1109/MCOM.001.2500138
52.
XuYLiuYLeiMGaoMFangZJiangC. Joint pseudo-range and doppler positioning method with LEO satellites ‘signals of opportunity. Satellite Navigation (2025) 6(1):10. 10.1186/s43020-025-00163-y
53.
GaoNHuangQPanG. Ultra‐broadband sound absorption characteristics in underwater ultra‐thin metamaterial with three layer bubbles. Eng Rep (2024) 6(11):e12939. 10.1002/eng2.12939
54.
ZouX-JWangY-WZongB-FXuX-GHanL-XZhuHet alMiniaturized low-profile ultrawideband antipodal vivaldi antenna array loaded with edge techniques. IEEE Trans Antennas Propagation (2025). 10.1109/TAP.2025.3606193
55.
TangQQuSZhengWTuZ. Fast finite-time quantized control of multi-layer networks and its applications in secure communication. Neural Networks (2025) 185:107225. 10.1016/j.neunet.2025.107225
56.
Google Gemini. Google gemini (2025). Available online at: https://gemini.google.com/app/cf8805346f046e31b (Accessed October 27, 2025).
57.
SufianMAHussainNAbbasALeeJParkSGKimN. Mutual coupling reduction of a circularly polarized MIMO antenna using parasitic elements and DGS for V2X communications. IEEE Access (2022) 10:56388–400. 10.1109/access.2022.3177886
Summary
Keywords
channel capacity loss, diversity gain, envelope correlation coefficient, Internet of Things, multiple input multiple output, ultra-wideband
Citation
Ullah A, Khan O, Iftikhar A, Khan S and Dalarsson M (2026) A highly compact two-port UWB MIMO antenna with enhanced performance and low mutual coupling for IoT applications. Front. Phys. 14:1704074. doi: 10.3389/fphy.2026.1704074
Received
12 September 2025
Revised
17 December 2025
Accepted
15 January 2026
Published
13 February 2026
Volume
14 - 2026
Edited by
Lei Guo, The University of Queensland, Australia
Reviewed by
Njitacke Tabekoueng Zeric, University of Buea, Cameroon
Noor Asmawati Samsuri, University of Technology Malaysia, Malaysia
Updates
Copyright
© 2026 Ullah, Khan, Iftikhar, Khan and Dalarsson.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Mariana Dalarsson, mardal@kth.se
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.