Design of Y-shaped tri-band rectangular slot DGS patch antenna at sub-6 GHz frequency range for 5G communication

Abstract

This paper presents the design and development of a rectangular slot DGS patch antenna fed by a microstrip line, designed to operate across three distinct frequency bands at 4.0 GHz, 4.9 GHz, and 5.5 GHz for 5G wireless communication applications. The antenna design outlined in this study is implemented on a Fr-4 substrate with dimensions measuring 50.5 × 41.12 × 1.5 mm³. The antenna gains at three frequency bands are 2.69 dBi, 7.27 dBi, and 11.37 dBi having impedance bandwidths of 9%, 8.9%, and 5.1%, respectively. The attained bandwidths are 356 MHz, 443 MHz, and 287 MHz for the respective frequency bands. The radiation efficiencies of the proposed antenna are 90%, 82%, and 79% of the three respective frequencies. Antenna 1 in this study exhibits single-band behavior, effectively covering the single frequency band which is 5.5 GHz (5.3578–5.9519 GHz) 5G unlicensed band 5-GHz WLAN IEEE 802.11a frequency. On the other hand, Antenna 2 demonstrates dual-band characteristics spanning the S-band 3.7 GHz (3.5619–3.8544 GHz) and C-band range 5.1 GHz (4.8496–5.2008 GHz) suitable for mid-band 5G applications. Antenna 3 proposed antenna exhibits a tri-band functionality within the C-band spectrum. The results highlight multiple-band operation, consistent high gain, high directivity, and favorable directional radiation patterns.

Introduction

In recent times, there has been notable expansion and advancement in mobile application and design, largely attributed to the anticipated emergence of the upcoming 5G mobile network. Despite the ongoing rollout of 4G cellular mobile systems in numerous countries, telecommunication industries and researchers have already initiated work on the 5G system. Motivated by the constant demand for faster network speeds and increased system capacity, many nations, including the United States, China, the European Union, Japan, and South Korea, have undertaken extensive research and development efforts to introduce 5G wireless broadband technology before 2020. Future 5G developments must prioritize user needs, ensuring reliability and high service quality in maintaining network performance, including latency, security, availability, reliability, energy efficiency, and device affordability. While microstrip antennas offer numerous advantages, they also come with certain limitations. These include losses due to leakage at the open boundary, limited radiated power and bandwidth, low-power handling capabilities, and restricted gain. The most widely used method for creating a multiband antenna involves cutting slots of various shapes, such as triangular, rectangular, T, E, and U shapes, within the patch [1,2,3,4,5,6,7,8]. The rise of wearable sensors and body-centric communication systems has underscored the importance of integrating multiple wireless communication standards into a single personal wireless device. To meet the demands of these communication protocols, there is a need for wearable multiband antennas capable of functioning across different frequency ranges. Specifically, these antennas must cover 5.15–5.825 GHz for WLAN and 5.3578–5.9519 GHz for 5G unlicensed band 5-GHz WLAN IEEE 802.11a [9,10,11].

Over the past few decades, 5G mobile communication systems have seen substantial advancements and are now in high demand due to their notable benefits, such as low latency, high data rates, and high data capacity. The adoption of high data rates, wide bandwidth, and stable gain, already implemented in many areas, will be significantly influenced by 5G. The 5G New Radio includes frequency bands like n77 (3.3–4.2 GHz), n78 (3.3–3.8 GHz), and n79 (4.4–5.0 GHz) for sub-6 GHz 5G applications [9, 12, 13].

It has been well established that the U-slot patch antenna can offer impedance bandwidths exceeding 30% for air substrate thicknesses around 0.08 λ₀ and over 20% for microwave substrates of similar thickness. The U-slot was primarily introduced to enhance bandwidth rather than to introduce band notches. In [14], the authors demonstrate that the U-slot technique can also be utilized for designing patch antennas with dual- and multiband characteristics. In [10], the author presented a novel planar compact slot antenna featuring C-shaped and inverted L-shaped slots designed for multiband WiMAX communication. The utilization of triple-band antennas employing slot configurations such as T-shaped, Y-shaped, and triangular slots has been documented in references [10, 14]. This article demonstrates that the Y-shaped technique can extend to designing patch antennas with tri-band characteristics. This Y-shaped configuration can provide a higher impedance BW of the desired tri-band that belongs to the 5G communication lower sub-6 GHz frequencies band (see Table 1).

Table 1 Comparative analysis of with existing antenna designs in terms of antenna performance matrices like sizes, operating bands, design techniques, and antenna parameters like gain, BW, and efficiency

A range of antennas has been developed to address this need, including wideband, narrowband, dual-band, ultra-wideband (UWB), and multiband antennas. Among these, multiband antennas hold an advantage over ultra-wideband antennas due to their ability to mitigate electromagnetic interference and pulse distortion. These antennas offer a more favorable solution, allowing the incorporation of multiple communication standards into a compact, cost-effective system with high data rate capabilities. The literature contains various examples of multiband and UWB antennas featuring diverse structures [11, 17, 18].

DGS, known as defected ground structures, are geometrically compact slots incorporated into the ground plane of microwave components such as antennas and filters. These structures consist of either a solitary unit cell (single defect) or multiple periodic arrangements. By incorporating defected ground structure (DGS) onto the ground plane of an antenna, the flow of current is disturbed, resulting in changes to the effective capacitance and inductance of the system. This phenomenon ultimately facilitates antenna miniaturization. Numerous research efforts have documented the application of DGS to reduce the size of patch antennas [4, 15, 16, 19, 20]. Defected ground structure (DGS) is an emerging method aimed at enhancing narrow bandwidth, high selectivity, and low gain in microwave circuits [21]. DGS finds applications in antennas [22,23,24] and various other microwave components. Previous studies [10, 25] have employed circular and rectangular DGS shapes to perturb the electric field on the ground layer [16].

EMI, or electromagnetic interference, arises from the interaction of electrical and magnetic fields. It occurs when the electromagnetic field of one electronic or electrical device disrupts another device’s operation. EMI occurs when both electrical and magnetic fields are active. When multiple signals run concurrently, they generate electric and magnetic fields, emitting electromagnetic waves. These waves from one signal can interfere with those of other signals and vice versa [26].

The microstrip patch antenna exhibits limitations such as low gain, narrow bandwidth, and radiation power losses. To address these issues, a solution involving the integration of slot pairs at opposing edges of the rectangular patch was introduced in reference. The patch and ground plane configuration adjustments improved the antenna’s bandwidth [27,28,29].

This research paper introduces a semicircular rectangular slot DGS structure microstrip patch antenna featuring strips slotted DGS geometry used for achieving high gain. This DGS geometry helps to operate the tri-band functionality and enhance the antenna’s gain. This antenna design effectively operates across three distinct frequencies, exhibiting high gain across all three frequency bands. Additionally, the antenna maintains a compact size, measuring 50.5 × 41.21 mm².

Proposed antenna design methodology

Figure 1 depicts a tri-band patch antenna featuring a rectangular slot defected ground structure (DGS) arrangement. The 26.5 mm × 10 mm rectangular slot is positioned on the top of the patch along the y-axis. Notably, one end of the rectangular slot is open, while the other end is enclosed within the antenna’s patch. This configuration utilizes Fr-4 as the dielectric substrate, having a permittivity of 4.4 and a thickness of 1.5 mm. FR-4 is used in 5G antenna design mainly due to its cost-effectiveness, mechanical strength, thermal stability, and sufficient electrical performance for numerous 5G applications, particularly within the sub-6 GHz frequency range. The antenna is designed for triple-band operation within the C-frequency range and employs a 50 Ω microstrip feed setup along with a rectangular slot. The FR4 dielectric substrate’s dimensions measure 50.5 mm in width and 41.21 mm in length, while the height (h) is set at 1.5 mm.

Fig. 1

Illustrating the designed antenna in parts. a Top radiating sight. b Defective ground sight. c 3D representation

The antenna’s configuration involves arranging semi-circular rectangular radiating elements horizontally in a scoop-like pattern on the upper surface of the Fr-4 substrate material. The lower surface features a rectangular DGS ground plane.

For impedance matching, a 50 Ω strip lines measuring 6 mm × 11 mm is integrated into the design. To achieve tri-frequency bands, a DGS geometry is introduced. This DGS geometry encompasses a central rectangle situated at the ground plane’s center, complemented by two half rectangles positioned at the edges along the X-axis. The antenna’s patch has dimensions of 41.5 mm × 26.71 mm, and it is excited through a microstrip feed line measuring 6 mm × 10 mm.

Figure 2a, b, and c illustrates the progressive development of the antenna design to get tri-band functionality for 5G communication applications. The diagram showcases the evolutionary steps taken in the antenna’s design process to enable it to operate across three distinct frequency bands. As the design progresses, it undergoes modifications and enhancements to cater to the specific requirements of 5G and WLAN and WiMAX communication standards. The ultimate goal is to create an antenna that can efficiently and effectively transmit and receive signals in all three frequency bands, thereby offering seamless connectivity for both WLAN, WiMAX, and 5G communication applications.

Fig. 2

Antenna evolution progress with reflection coefficient. a Iteration slot patch antenna (Antenna 1). b Two-rectangular strip slot patch antenna (Antenna 2). c Rectangular slot patch (Antenna 3) studies of the proposed antenna

The design procedure and prototype of the proposed antenna are visually explained in Fig. 2a, b, and c. In Fig. 2a, the initial design involves a single-band antenna with dimensions of 50.5 mm × 41.21 mm × 1.5 mm, as presented in this configuration “Antenna 1”. This antenna is referred to as the “iteration slot patch antenna”. In this geometry, an iteration strip slot is introduced on the patch of the antenna, resulting in the antenna being resonant at a single frequency band of 5.5 GHz. By introducing these iteration slots, the total current path length is increased, leading to a disturbance in the surface current distribution of “Antenna 1”. As a consequence of these changes, the proposed antenna resonates at 5.5 GHz.

Antenna 2 in Fig. 2b demonstrates that it has achieved resonances at two different frequencies 3.7 GHz and 5.1 GHz. These resonances are made possible by modifying the radiating patch of the antenna. The modification involves the two strip slots inserted on the open side of the radiating patch. The dimensions of the strip slots are 2 mm × 10 mm. These slots play a crucial role in enabling the antenna to resonate at the specified frequencies, allowing it to operate effectively in both the 3.7 GHz and 5.1 GHz bands. This design enhancement enables the antenna to support multiple frequency bands, making it suitable for 5G smartphones, and WLAN/WiMAX applications that require operation across different frequency ranges.

In Antenna 3, a rectangular slot is introduced, leading to significant improvements in its performance. As a result of this change, the antenna becomes capable of operating over three distinct frequencies, which are 4.0 GHz, 4.9 GHz, and 5.5 GHz. In this geometric configuration, a rectangular slot measuring 26.5 mm × 10 mm is introduced on the open side of the patch, aligned with the Y-axis.

The dimensions of the substrate and the ground plane geometry are as proposed antenna. The DGS geometry starts with the rectangular slot etched on the ground plane having a dimension of width slot ground (Wsg) which is 14 mm and length slot ground (Lsg) is 8 mm. And the thickness of the strip used to form rectangular slot WgSlot11 is 2 mm. After being etched above the rectangular slot, the two half-rectangular slots are etched centered to the outer arm and connected with the single strip slot to the centered rectangular slot. The half-rectangular slot in DGS plane, Wsg2 width slot ground 2 is 6 mm and Lsg1 is 11 mm and the thickness of the strip is Wgslot1 is 2 mm and Wgslot 2 is 1 mm (Table 2).

Table 2 Measurement specifications of the DGS ground plane of the proposed antenna

Table 3 provides an overview of the resonant frequencies achieved with this modified antenna design. Additionally, Fig. 5 illustrates the 10-dB bandwidths for the three operating bands, which are measured at 356 MHz, 443 MHz, and 287 MHz for the 1st, 2nd, and 3rd frequency bands, respectively.

Table 3 Resonant frequency bands for three different versions of antenna geometry

Incorporating the rectangular slot is a critical improvement that enables the antenna to cover a broader range of frequencies, making it more versatile and suitable for various applications, particularly in 5G smartphones, WLAN, and WiMAX scenarios where multiple frequency bands are utilized.

The visual representation in Fig. 3 illustrates the progressive development of a 5G tri-band proposed antenna that incorporates DGS, specifically of the rectangular slot etched on the semi-half circular rectangular patch. The proposed Antenna configuration, namely a rectangular slot (SW × SL), a radiating patch (Pw × PL), a microstrip feedline (FW × FL), a substrate plane (SW × SL), and a grounding surface (W × L) (Table 4).

Fig. 3

Proposed antenna structure design. a Antenna patch surface. b Surface of the grounding plane

Table 4 Measurement specifications of the proposed antenna

At first, an iteration slot patch antenna was formulated using a defective ground structure geometry to function within a sole frequency band at 5.5 GHz. To facilitate two frequency band operations encompassing 3.7 GHz and 5.1 GHz, a two 2 mm × 10 mm rectangular strip slot patch was integrated onto the antenna’s configuration 2. This Antenna 2 configuration is called a two-rectangular strip slot patch antenna. And the final and proposed configuration was used to cut the rectangular slot positioned at the upper part of the patch. This proposed antenna is named a rectangular slot patch antenna. This modification resulted in an additional operating band; we get the three operating frequencies band 4.0 GHz, 4.9 GHz, and 5.5 GHz.

A tri-band antenna with dimensions 50.5 × 41.21 × 1.6 mm³ has been developed, as demonstrated in the “Antenna 3” configuration or rectangular slot patch antenna in Fig. 3. This antenna achieves its tri-band functionality by implementing rectangular slots on the top of the radiating patch element. Incorporating this slot extends the overall path that the current follows, causing alterations in the surface current distribution. Consequently, the “Antenna 3” configuration or rectangular slots patch exhibits resonance at 4.0-, 4.9-, and 5.5-GHz frequencies. These resonant frequencies are visually represented in Fig. 2c.

The proposed antenna is achieved by incorporating defected ground structure (DGS) geometry, as depicted in Fig. 3b. The integration of the DGS structure introduces modifications in the effective inductance and capacitance, resulting in changes to the surface current distribution and input impedance. This adjustment enables a reduction in the size of the antenna while maintaining the desired resonant frequencies. This antenna geometry introduces defected ground structure geometry for achieving high gain and highly directive antenna. DGC geometry consists of a rectangle placed in the center of the ground plane and two half rectangles placed on the Y-axis edges of the ground plane. The antenna design consists of semi-circular rectangular radiating elements resembling scoop shape, arranged adjacently on the upper surface of the substrate. On the underside of the substrate, there is a rectangular defected ground plane. The excitation of the radiating element is achieved through a microstrip feed line, which measures 6 mm in width and 11 mm in length. The optimized value of the parameters is illustrated in Table 3. The dimension of the DGS tri-band antenna are determined via the following equations provided below (Fig. 4).

Fig. 4

DGS design optimization process

The patch dimensions are acquired using the equations presented below:

$$PW=\frac{c}{2fr\sqrt{(\varepsilon r+1)/2}}$$

(1)

$$PL=\frac{c}{2fr\sqrt{\varepsilon ff}}-2\Delta L$$

(2)

$$\varepsilon ff=\frac{\varepsilon r+1}{2}+\frac{\varepsilon r-1}{2}{\{1+12h/PW\}}^{0.5}$$

(3)

$$\Delta L=0.412[(\varepsilon ff+0.3)(\frac{PW}{h}+0.264)/(\varepsilon ff-0.258)(\frac{PW}{h}+0.8)]$$

(4)

Here, “c” symbolizes the velocity of light, “fr” represents the operational frequency, “∆L” signifies the extension length, and “εff” corresponds to the effective dielectric constant.

The dimensions of the ground plane are derived using the equations presented below.

$$GL=6h+PL$$

(5)

$$GW=6h+PW$$

(6)

Here, “h” represents the substrate thickness, “PW” corresponds to the patch width, and “PL” indicates the patch length.

Results and discussion

The S11 characteristics of the tri-band microstrip patch antenna (MPA) demonstrate resonance frequencies at 4.0 GHz, 4.9 GHz, and 5.5 GHz, as illustrated in Fig. 5. The S11 characteristics of the designed antenna cover the frequency ranges of 3.82–4.18 GHz (impedance bandwidth of 356 MHz or 9%), 4.69–5.13 GHz (impedance bandwidth of 443 MHz or 8.9%), and 5.33–5.61 GHz (impedance bandwidth of 287 MHz or 5.1%), centered at frequencies of 4 GHz, 4.9 GHz, and 5.5 GHz, respectively.

Fig. 5

Simulated reflection coefficient of the proposed antenna

$$\%\, Impedance \,Bw= \frac{{F}_{H}-{F}_{L}}{\frac{{F}_{H}+{F}_{L}}{2}}\times 100$$

The simulated VSWR plotted against frequency for the proposed antenna consistently showed values lower than 1.5 at the designated operating frequencies, as depicted in Fig. 6. This observation signifies that the designed antenna is well-suited for utilization across the three intended frequency bands. VSWR serves as a metric for assessing the degree of impedance mismatch between the antenna and the feeding system. Higher VSWR values correspond to increased mismatch. A VSWR of 1 indicates a perfect match, while VSWR values greater than 2 indicate a level of mismatch. The VSWR is quantified as the ratio between the maximum and minimum voltages along the transmission line. Figure 5 illustrates the VSWR values for the designed antenna, indicating VSWR values of 1.25 at the 4.0-GHz frequency band, 1.22 at the 4.9-GHz frequency band, and 1.28 at the 5.5-GHz frequency band.

Fig. 6

Depicts the VSWR plot for the tri-band antenna

From Fig. 7, the simulated gain for the tri-band antenna is documented as 2.69 dB, 7.26 dB, and 11.36 dB at the respective frequency bands of 4.0 GHz, 4.9 GHz, and 5.5 GHz. Directivity measures the extent of power concentration in a specific direction relative to the power distribution across all directions. Figure 8 illustrates the directivity graph of the antenna design at three distinct operational frequencies: 4.0 GHz, 4.9 GHz, and 5.5 GHz. The depicted values for directivity are 3.17 dBi, 8.13 dBi, and 12.39 dBi for the respective frequencies.

Fig. 7

Gain (dB) of the tri-band antenna

Fig. 8

Directivity (dBi) of the proposed antenna

The radiation efficiency is a crucial factor in assessing the performance of the microstrip patch antenna as it is inversely related to radiation losses. A higher radiation efficiency is preferred for improved suitability to users, with values ranging from 0 to 100%. The CST software is used to compute the total efficiency of the proposed design concerning Antenna 1, Antenna 2, and Antenna 3. Figure 9 presents the simulated radiation efficiency values of the designed antenna. The simulation results reveal that the antenna’s radiation efficiency consistently exceeds 78% across the entire operational bandwidth. The highest radiation efficiency was achieved 90% at 4.0 GHz, 82% at 4.9 GHz, and 79% at 5.5-GHz operating frequencies, which is more than that of those presented monopole antenna designs [9, 11, 30, 31].

Fig. 9

Radiation efficiency of the proposed antenna

Figure 10 displays the radiation pattern of the tri-band antenna at frequencies of 4.0 GHz, 4.9 GHz, and 5.5 GHz. It portrays patterns in both the E-field (azimuthal plane) and the H-field (elevation plane). At these frequencies, the most pronounced radiation pattern occurs when theta is at 0° in both planes. This pattern is symmetrically replicated in the H-plane. The radiation pattern graph underscores the nearly omnidirectional radiation traits of the tri-band antenna in both the E and H fields (Tables 5 and 6).

Fig. 10

Illustrating the radiation pattern in both the E-Field and H-field at a 4.0-GHz, b 4.9-GHz, and c 5.5-GHz frequency bands

Table 5 A concise overview of simulated outcomes of Antenna 1, Antenna 2, and Antenna 3

Table 6 Comparison of proposed work with previous related works

Measured results

The reflection coefficient of the fabricated antenna was simulated using Computer Simulation Tools (CST) Microwave Studio (MWS) and measured with a vector network analyzer (VNA). Figure 11a, b, and c illustrate the measurement setup for the proposed Antenna 3. Figure 12 presents the reflection coefficient plot for measured results. For Antenna 3, the |S11| value at the desired frequency ranges was below −10 dB, resonating at 4.0 GHz with a bandwidth of 356 MHz (from 3.8295 to 4.1856 GHz) (n77) and also resonating at 4.9 GHz with a bandwidth of 443 MHz (from 4.6917 to 5.1349 GHz) (n79). Additionally, it achieved a bandwidth of 287 MHz (from 5.3304 to 5.6180 GHz) while resonating at 5.5 GHz. In contrast, the measured results for the n77 (3.3–4.2 GHz) and n79 (4.4 GHz–5.0 GHz) bands showed that the antenna operated at 4 GHz with a bandwidth of 326 MHz (from 3.681 to 4.007 GHz) and at 4.87 GHz, covering a range from 4.539 to 4.982 GHz (443 MHz) for the n79 band.

Fig. 11

a Fabricated measured top radiating sight. b Fabricated measured defective ground sight. c Measured S11 graph

Fig. 12

Measured Reflection coefficient result

Conclusions

A tri-band 5G rectangular slot strip DGS patch antenna, incorporating rectangular slot and strip slotted DGS geometry, has been developed, simulated, and evaluated for operation across three distinct frequency bands: 4.0 GHz, 4.9 GHz, and 5.5 GHz. This multiband patch antenna (MPA) is simulated using an FR-4 substrate material with dimensions of 50.5 mm × 41.21 mm × 1.5 mm. The antenna design demonstrates favorable performance attributes, including a notable gain of 2.69 dB, 7.27 dB, and 11.37 dB and a directivity of 3.17, 8.14, and 12.39 dBi at the designated operating frequency of 4.0 GHz, 4.9 GHz, and 5.5 GHz. The reported antenna’s radiation efficiencies achieve 90%, 82%, and 79% at the respective central frequency, indicating efficient utilization of input power for radiation.

In summary, the introduced microstrip patch antenna incorporating two-strip slotted DGS showcases considerable potential, rendering it well-suited for applications in the realm of 5G and IoT. Notably, it proves advantageous within the LTE band 46 frequencies. With its effective radiation, substantial gain, and omnidirectional radiation pattern, the antenna holds promise as a viable option for diverse 5G communication systems across various scenarios. This proposed antenna is useful for 5G handheld devices. Integrating novel circuitry with antennas is essential to address the demand for active beamforming antenna arrays in 5G telecommunications, particularly within the sub-6 GHz (FR1) frequency range. Future research is necessary to enhance antenna performance by transitioning from a single-element antenna to an array antenna. Antenna arrays with heightened directivity are deployed for fixed-beam communication in the lower sub-6 GHz frequency bands.