As global data demands surge, driven by advances in AI, immersive virtual applications, and the Internet of Things (IoT), existing GHz-based wireless communication systems are reaching their limits. The transition to the next-generation 6G network is poised to address these challenges by exploring the THz spectrum, specifically from 0.1 to 10 THz, where abundant, underutilized bandwidth holds the key to unprecedented data capacity and ultra-low latency1. Unlike the GHz frequencies, which are increasingly saturated and unable to meet future performance demands, the THz band can provide the high-speed, high-capacity connectivity essential for emerging technologies. Researchers are now actively exploring THz communication to overcome GHz limitations, as THz waves not only enable faster data transfers but also offer shorter wavelengths, which allow for smaller, more efficient antennas and novel system architectures2.
A significant focus of this research lies in integrating THz communication with Multiple Input Multiple Output (MIMO) technology. This method maximizes data throughput by using multiple antennas to send and receive concurrent signals3. This MIMO-THz combination is especially promising for 6G applications due to its ability to support robust, high-throughput links over short distances, making it highly effective for high-speed, short-range wireless communication scenarios4. This characteristic is particularly crucial for IoT devices deployed in dense environments, real-time analytics, and the massive interconnectivity anticipated in future smart environments5.
Figure 1 illustrates the diverse and evolving landscape of IoT applications that stand to benefit from the integration of THz-MIMO technologies in 6G networks4. The image highlights key sectors such as smart agriculture, industrial automation, rural and urban area coverage, and IoT-based smart cities, each relying on real-time data exchange, dense connectivity, and low-latency communication. Satellite communication and drone-based wireless infrastructure are also depicted as crucial components enabling widespread and flexible deployment, especially in remote and infrastructure-limited regions. These use cases align well with the performance characteristics of the proposed antenna, particularly its 0.3 THz resonance, which supports high-speed, short-range transmission with improved penetration for complex indoor or urban environments typical of IoT deployments6. This visual representation underscores the role of THz-MIMO in enabling seamless interaction across heterogeneous IoT ecosystems, supporting critical applications like precision agriculture, smart industry, healthcare, and urban management with robust connectivity.
Illustration of 6G-enabled IoT use cases supported by dual-band THz MIMO communication.
In high-speed short-range wireless networks, the ability to deliver ultra-fast data transmission within confined spaces—such as smart homes, industrial automation floors, or medical monitoring systems—is becoming essential. THz-MIMO architectures are uniquely suited to meet these demands due to their compact form factors and exceptional data-handling capacity7. IoT applications benefit uniquely from this THz-MIMO integration, as it allows devices to operate seamlessly within dense, interconnected networks while minimizing latency. Furthermore, THz-MIMO is projected to revolutionize high-speed, data-intensive sectors beyond IoT, including secure satellite communications, autonomous transportation systems, and next-generation data centers, all of which demand the kind of high-capacity, low-latency performance only achievable at THz frequencies8.
In the context of 6G, THz-MIMO systems thus serve as a backbone for critical applications in healthcare, defense, and smart infrastructure, where high-speed data exchange is essential for real-time monitoring, diagnostics, and decision-making. For instance, in healthcare, wearable IoT devices and remote diagnostic systems enabled by THz communication could provide instant data transfer, improving patient care in remote areas. Likewise, smart city infrastructure will rely on the seamless, ultra-fast connectivity offered by MIMO-enabled THz systems to support everything from autonomous vehicles to intelligent traffic management, creating safer, more efficient urban environments9. By unlocking the potential of the THz band, researchers aim to overcome GHz constraints and establish 6G networks as a foundational platform for the interconnected, data-driven world of tomorrow.
Table 1 presents a comparative analysis of multiple ongoing initiatives, delving into their conceptual foundations. It scrutinizes a range of operational parameters, including operating frequency, board dimensions, bandwidth, gain, isolation, and efficiency. Among these endeavors listed in the table, the suggested antenna stands out as the most compact, boasting the broadest bandwidth, and achieving commendable levels of isolation and gain. Referenced gains from previous works, such as 8.2 dB, 11.67 dB, 11.80 dB, 4.4 dB, 4.6 dB, 4.4 dB, 7.9, 5.17, 6.24, 11.89 and 7.5 are provided10,11,12,13,14,15,16,17,18,19, and20. In contrast, simulations in CST-2018 reveal an observed gain of 12.213dB. CST-2018 asserts a bandwidth of 1.6 THz for the proposed architecture, notably higher than the BW cited in the sources: 0.0404 THz, 0.05 THz, 0.614 THz, 0.78 THz, 1.59 THz, 0.114 THz, 0.4 THz, 0.44 THz, 0.036 THz, 0.025 THz, 0.0061 THz, and 0.723 THz. Isolation levels in the proposed layout surpass − 36.1 dB, contrasting with measured levels of −22.26 dB, ≥ 25 dB, −25 dB, −20 dB, −25 dB, −17 dB, −25 dB, −20 dB, −20 dB, −20 dB, −25 dB, −27.34 dB, and − 20 dB for the reference works10,11,12,13,14,15,16,17,18,19,21,22, and20. The recommended Multiple-Input Multiple-Output (MIMO) antenna exhibits outstanding performance metrics compared to alternatives, with an ECC of less than 0.0005 dB, and a DG exceeding 9.999 dB. Its radiation efficiency of 92.42% outshines values of 76.45%, 92%, 74.5%, 94%, 82%, 15%, 85.64%, 92.48%, 90%, 88.9%, and 97% cited in studies11,13,14,15,16,17,18,19,21,22, and20.
The integration of both RLC components and machine learning algorithms in the proposed design sets it apart from most of the works cited in the comparison. Among the studies, only a few incorporate either machine learning or RLC circuit modeling. Specifically, RLC modeling is present in16,17, and19, while machine learning techniques are applied in16,19, and20. However, the simultaneous use of both RLC and machine learning within a single framework, as demonstrated in the proposed antenna, remains unique among these works. This combined approach not only enhances circuit-level insight but also enables performance prediction and optimization, representing a meaningful advancement in antenna design methodology. The comprehensive comparison in Table 1 highlights the novelty and significance of the proposed design in the context of current research trends.
Research gap and contribution
The rapid growth of THz technology shows great promise for future 6G wireless and Internet of Things (IoT) applications, which require very fast data transfer, high efficiency, and compact device sizes. However, many current THz MIMO antenna designs face challenges in achieving a good balance between high gain, efficiency, and small size. Most of these designs rely heavily on full-wave electromagnetic simulations, which are time-consuming and do not provide a clear theoretical understanding of the antenna’s behavior.
In addition, very few studies provide a circuit-level model, such as an RLC equivalent circuit, to explain how the antenna works. This makes it harder to optimize or modify the design. Moreover, the use of machine learning for improving antenna performance is still limited in this field, especially for predicting and optimizing key performance parameters. These gaps make it difficult to design antennas that can meet the high demands of 6G and IoT systems quickly and effectively.
This study addresses these issues and offers the following key contributions:
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RLC Equivalent Circuit Model: A detailed RLC equivalent circuit model is proposed to explain the antenna’s operation more clearly. This model supports the full-wave simulation results and helps in understanding the antenna’s behavior from a circuit point of view.
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Machine Learning for Fast Optimization: Machine learning methods, especially regression models, are used to predict and optimize antenna performance. This reduces the need for long simulation times and allows faster design updates.
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High Gain, Efficiency, and Compact Size: The proposed antenna achieves high gain, high efficiency, and a compact structure, making it suitable for integration into next-generation 6G and IoT devices.
Design methodology
The transformation illustrated in Fig. 2 captures the evolution of the antenna from a compact single-element configuration to an advanced MIMO architecture. This progression is not merely a structural enhancement but a response to the ever-increasing demands for higher data throughput, enhanced signal fidelity, and broader bandwidth, particularly in the context of the upcoming 6G era23.
Given the miniaturized dimensions required for THz band operation, the material selection becomes pivotal. Copper is chosen for both the radiating and ground elements due to its excellent electrical conductivity and fabrication compatibility. The entire configuration is embedded on a 10 μm-thick polyimide substrate, which offers a dielectric constant (εr) of 3.5 and a low loss tangent of 0.0030. This substrate provides a reliable balance of flexibility, thermal stability, and low-loss performance, key attributes for sustaining high-frequency signal integrity in 6G systems24.
The evolution from a single-element to a dual-port MIMO antenna represents a strategic integration of design innovation and material engineering. This advancement not only meets the stringent performance requirements of next-generation wireless systems but also sets a strong foundation for scalable, high-efficiency THz communication technologies.
Structural evolution of the antenna from a single-element to MIMO configuration.
Single element antenna
To develop our single-element antenna as the initial step in its evolution, we follow a structured methodology aimed at optimizing its performance and capabilities. Figure 3(a) shows the single-element antenna. The initial phase of the design focuses on selecting suitable materials and defining accurate dimensions for optimal results. The antenna has a compact size of 75 × 77 μm², specially designed for high-frequency applications as depicted in Table 2. Copper stands as the prime radiating material chosen for its superconductivity and flexibility, which contributes to enhanced radiation and the general performance of the signal25. The antenna is built on a polyimide substrate with a thickness of 10 μm, ensuring low dielectric loss and stable electromagnetic performance. A completely solid copper ground plane is placed on the opposite side to provide effective shielding and improve impedance matching.
The patch structure consists of a periodic grid-like arrangement of interconnected rectangular sections, strategically designed to enhance both gain and bandwidth. The periodic pattern facilitates better current distribution, reducing surface wave losses and increasing radiation efficiency. Additionally, the interconnected structure enables better impedance control, minimizing reflection losses for improved signal propagation.
The antenna and the signal source are directly connected by a thin feedline that extends from the patch’s bottom center. This feedline is essential to the antenna’s design because it ensures effective energy transmission without the need for further tuning components. It contributes to the optimization of the antenna’s performance by maintaining impedance matching and resonance. The feedline is designed to maintain impedance matching, contributing to stable operation across the target frequency range.
To evaluate its performance, the antenna is simulated using CST-2018 software, where key parameters such as the reflection coefficient, gain, radiation efficiency, and bandwidth are analyzed. As shown in Fig. 3(b), the single-element antenna resonates at 1.92 THz with a very good return loss of − 38 dB and a significantly wider bandwidth of 2.85 THz, highlighting its excellent impedance matching and wideband capability. Iterative optimizations are performed to fine-tune the grid structure, ensuring superior performance in terms of both radiation characteristics and frequency response. This grid-based copper antenna, with its compact size, high conductivity, and structured design, is highly suitable for next-generation high-frequency communication systems. Employing copper for both the radiating patch and ground plane, combined with a finely tuned periodic structure, renders the design highly suitable for practical applications such as ultra-high-speed THz communication and IoT-driven wireless networks26.
(a) Final structure of the single-element antenna. (b) Simulated reflection coefficient (S11).
Design development of the single-element antenna
To optimize its suitability for 6G communication, the single-element antenna was designed using a systematic five-phase development approach. Each step introduces modifications to the structure, leading to improvements in resonance, return loss, gain, and bandwidth. Figure 4 illustrates the evolution of the antenna, while the corresponding simulation results are presented in Fig. 5, where Fig. 5a presents the S-parameter and Fig. 5b illustrates the gain. The detailed design modifications and performance comparisons for each step are discussed below.
The first step begins with a basic structure consisting of a central feedline connected to a periodic grid-like patch. Two vertical stubs are placed at the far-left and far-right corners of the grid, forming a rudimentary radiating structure. However, this configuration exhibits poor performance, resonating at two distinct frequencies of 1.51 THz and 2.58 THz with return losses of − 20.37 dB and − 16.99 dB, respectively. The bandwidth is limited to 0.48 THz and 0.2 THz at the respective bands. The maximum gain is also quite low, reaching only 4.57 dB, indicating the need for significant structural refinement. To address these limitations, the second step introduces an additional periodic grid-like arrangement, positioned opposite to the original patch and connected via the two vertical stubs. This dual-sided configuration enhances current distribution and symmetry. The simulation results reveal an oscillatory response in the first frequency band with no distinct resonance. In the second band, a resonance frequency is observed at 2.5 THz, but the return loss remains poor, indicating inefficient radiation. The gain at this step is 4.2 dB, which is inadequate for THz applications. Structural modifications are introduced in the next step to address these limitations. In the third step, additional slot structures are incorporated inside the grid-like arrangement to improve impedance matching and radiation efficiency. These modifications lead to a shift in the resonance frequency to 2.9 THz, with a significant improvement in return loss. Furthermore, the gain increases to 5.85 dB, demonstrating better radiation performance. However, despite these enhancements, the bandwidth remains narrow, limiting the antenna’s applicability for THz communication. To overcome this issue, further structural adjustments are made in the fourth step. In this step, the antenna structure undergoes further refinement by introducing additional inner slot elements within the grid-like framework to enhance coupling and broaden the bandwidth. As a result, the resonance frequency shifts to 2.4 THz, and while the return loss slightly decreases compared to the previous step, the bandwidth significantly improves to 2.3 THz. Additionally, the gain increases to 7.1 dB, marking a notable improvement. However, the gain remains suboptimal for high-performance THz applications. To achieve superior performance, the antenna structure is further optimized in the final step. In the final step, further refinements are made by introducing a more complex slot pattern within the periodic grid-like structure, leading to enhanced impedance matching and radiation efficiency. This results in a well-defined resonance frequency with a very good return loss of −38 dB and a significantly wider bandwidth of 2.85 THz. The gain is also drastically increased to 9.97 dB, making the antenna highly suitable for 6G communication. This final step represents an optimized structure, ensuring superior performance across all key metrics.
The iterative design process successfully enhances the antenna’s performance by systematically improving resonance, return loss, gain, and bandwidth27. The final structure achieves optimal characteristics for THz applications, demonstrating its potential for high-speed and high-frequency wireless communication in future 6G networks.
The single antenna and the development of its design.
Analysis of (a) S-parameter, (b) Gain.
