Wi-Fi 6 (802.11ax) and Wi-Fi 6E (802.11az) are recent wireless network technologies that offer both faster speed and wider coverage. In addition, this technology uses more channels, leading to a better overall experience for internet users. A larger number of channels reduces the signal-to-noise ratio, thereby improving throughput and response time to offer high-quality network connections to users [1, 2]. However, the demand for miniaturization of mobile devices is increasing rapidly, necessitating a further decrease in the antenna area. Notably, a decrease in antenna input impedance variation by the area of the antenna [1] leads to a relative decline in antenna performance and bandwidth. To address this issue, previous studies [3–6] have either resorted to a larger antenna size or attained a bandwidth that does not sufficiently cover the entire frequency of Wi-Fi 6/6E bands. Therefore, developing miniaturized antennas that offer high efficiency, wide bandwidth, and good performance remains a common challenge for antenna designers.

In this letter, we propose a novel compact multi-resonance antenna structure that uses the ground radiation technique to achieve wideband coverage in the target frequency of 2.4–2.5 GHz and (5.125–7.125 GHz) Wi-Fi 6/6E dual band. According to the measurement results, the proposed antenna achieved a −6 dB bandwidth of 450 MHz (ranging from 2.20 GHz to 2.65 GHz) in the lower band, along with an average total efficiency of 60.7%, and a −6 dB bandwidth of 2,640 MHz (ranging from 4.81 GHz to 7.45 GHz) in the higher band, with an average total efficiency of 53.4%. Overall, the proposed miniaturized antenna exhibits strong prospects for implementation in the advancement of mobile communication applications.

The proposed antenna is composed of a 40 mm × 80 mm × 1 mm board set on an FR-4 (Frame Retardant Type 4) substrate (ɛ_r = 4.4, tanδ = 0.02), as shown in Fig. 1(a). It was designed with a 6 mm × 8 mm clearance from the ground plane. As shown in Fig. 1(b), a 2.5 mm × 4 mm feeding structure was employed, along with a series chip capacitor C_f (0.38 pF), parallel chip capacitor C_s (0.1 pF), shunt chip capacitor C_a (0.31 pF), and shunt chip inductor L_f (1.1 nH) to control the impedance matching of the proposed antenna. In particular, the central loop resonance frequency of the lower band (2.4 GHz) was controlled by chip capacitor C_r (0.62 pF), while the central L_f–C_h loop resonance frequency of the higher band (5.0–7.125 GHz) was controlled by chip capacitor C_h (0.055 pF). Furthermore, an increase in antenna clearance led to an increase in inductance, accompanied by a decline in loop resonance frequency. To explain the operating principle of the proposed antenna when using the ground radiation technique in the lower and higher bands, Fig. 2 shows the simulated reflection coefficient of the proposed antenna with regard to variations in chip capacitors C_r and C_h. As shown in Fig. 2(a) and 2(b), the reflection coefficient of both the lower band and higher band changed significantly with an increase in the values of chip capacitors C_r and C_h.

Drawing on the reaction theorem, the ground radiation technique was used for the proposed antenna by considering the entire ground plane as a radiator that forms a dipole-type radiator that can excite the ground plane [7, 8]. Notably, ground-radiation antenna technology can be applied to different situations featuring various kinds of evaluation boards and frequency antenna designs. Moreover, it offers high efficiency, target frequency coverage, and good antenna performance [3, 6–8]. The relationship between the ground plane and the proposed antenna can be expressed using the modal excitation coefficient, formulated as follows [7]:

where H̄^ground is the magnetic field emanating from the ground plane and M̄^antenna is the magnetic current produced by the antenna. The antenna was coupled with the ground plane, while the loop type current (M̄^antenna) reacted with the ground plane magnetic field (H̄^ground) [7, 8]. To further investigate the principle of the proposed antenna, the simulated surface current distributions of the operating current modes in the lower and higher bands were evaluated, as shown in Fig. 3. It is observed that the current in Loops 1 and 2 in the feeding structure controls the lower band input impedance matching using the small ground radiator loop, thus achieving a wider impedance bandwidth in the lower band. Simultaneously, the current in Loops 3 and 4 controls the higher band input impedance matching by means of the L_f–C_h radiator loop, attaining a wider impedance bandwidth in the higher band.

The proposed antenna was fabricated and measured using Agilent 8753ES network analyzers and a 3D CITA OTA chamber (sized 6 m × 3 m × 3 m), as shown in Fig. 4. The antenna structure was relatively compact and easy to operate. Furthermore, the use of 0603-type capacitors and inductors for impedance matching in the measurement facilitated operations and did not pose much difficulty in terms of antenna engraving and printing. The simulation and measurement results obtained using the proposed antenna reflection coefficient are shown in Fig. 5. The simulation results show that the −6 dB bandwidth achieved for the lower band was 220 MHz (ranging from 2.33 GHz to 2.55 GHz), while that for the higher band was 2,470 MHz (ranging from 4.98 GHz to 7.45 GHz). Notably, a −6 dB bandwidth corresponding to the 3:1 voltage standing wave ratio (VSWR) is generally accounted for in most studies, although the 2:1 VSWR (–10 dB bandwidth) has also been used in some cases [1, 3, 6, 8, 9]. Furthermore, as per the measured results, −6 dB bandwidths of 450 MHz (ranging from 2.20 GHz to 2.65 GHz) and 2,640 MHz (ranging from 4.81 GHz to 7.45 GHz) were achieved for the lower band and the higher band, respectively. Fig. 5 indicates that the lower band attained an average total efficiency of 60.7% from 2.4 GHz to 2.5 GHz, while the higher band achieved 53.4% from 5.0 GHz to 7.125 GHz. In addition, Fig. 6 shows the measured far-field radiation patterns of the proposed antenna at 2.47 GHz and 5.60 GHz. Both the E-theta and E-phi components are present in the xz- and yz-planes, indicating good radiation performance. Table 1 presents the results obtained from comparing the proposed antenna with those used in previous studies with regard to their overall size, bandwidth, efficiency, operating frequency, and antenna type. It is evident that the proposed antenna attained a wider bandwidth and approximately the same efficiency as the other antennas operating in the same frequency band proposed by previous studies [3–6, 9, 10]. Moreover, the proposed antenna allows easier manipulation of impedance matching compared to previous studies.

In this letter, we propose a novel compact multi-resonance antenna structure constructed using the ground-radiation technique. The proposed antenna achieved the intended target frequency bands of 2.4–2.5 GHz and (5.125–7.125 GHz) the Wi-Fi 6/6E dual band. Furthermore, the measurement results, calculated considering a 3:1 voltage standing wave ratio, show that the proposed antenna achieved a bandwidth of 450 MHz (ranging from 2.20 GHz to 2.65 GHz) in the lower band, with an average total efficiency of 60.7% from 2.4 GHz to 2.5 GHz. It also achieved a bandwidth of 2,640 MHz (ranging from 4.81 to 7.45 GHz) in the higher band, with an average total efficiency of 53.4% from 5.0 GHz to 7.125 GHz. Overall, it is established that the proposed antenna has significant potential for use in mobile communication applications.