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Compact Planar Ultrawideband Antennas with 3.5/5.2/5.8 GHz Triple Band-Notched Characteristics for Internet of Things Applications

ABSTRACT

Ultrawideband (UWB) antennas, as core devices in high-speed wireless communication, are widely applied to mobile handsets, wireless sensor networks, and Internet of Things (IoT). A compact printed monopole antenna for UWB applications with triple band-notched characteristics is proposed in this paper. The antenna has a very compact size of 10 × 16 mm2 and is composed of a square slotted radiation patch and a narrow rectangular ground plane on the back of the substrate. First, by etching a pair of inverted T-shaped slots at the bottom of the radiation patch, one notched band at 5–6 GHz for rejecting the Wireless Local Area Network (WLAN) is generated.

Then, by cutting a comb-shaped slot on the top of the radiation patch, a second notched band for rejecting 3.5 GHz Worldwide Interoperability for Microwave Access (WiMAX) is obtained. Further, by cutting a pair of rectangular slots and a C-shaped slot as well as adding a pair of small square parasitic patches at the center of the radiating patch, two separate notched bands for rejecting 5.2 GHz lower WLAN and 5.8 GHz upper WLAN are realized, respectively. Additionally, by integrating the slotted radiation patch with the narrow rectangular ground plane, an enhanced impedance bandwidth can be achieved, especially at the higher band. The antenna consists of linear symmetrical sections only and is easy for fabrication and fine-tuning.

The measured results show that the designed antenna provides a wide impedance bandwidth of 150% from 2.12 to 14.80 GHz for VSWR < 2, except for three notched bands of 3.36–4.16, 4.92–5.36, and 5.68–6.0 GHz. Additionally, the antenna exhibits nearly omnidirectional radiation characteristics, low gain at the stopbands, and flat group delay over the whole UWB except at the stopbands. Simulated and experimental results show that the proposed antenna can provide good frequency-domain and time-domain performances at desired UWB frequencies and be an attractive candidate for portable IoT applications.

ANTENNA DESIGN

Figure 1. Geometry of the proposed antenna: (a) side view; (b) top view; (c) bottom view

Figure 1. Geometry of the proposed antenna: (a) side view; (b) top view; (c) bottom view

Figure 1 presents the schematic geometry of the proposed antenna. This antenna is printed on 1.5-mm-thick FR4 substrates with a relative permittivity of 4.4 and a loss tangent of 0.02, while the overall areas are only 10 × 16 mm2. The basic antenna structure is composed of a square radiation patch, a microstrip feedline, and a ground plane. The width of the microstrip feedline is set to be 2 mm to achieve 50 Ω characteristic impedance. A narrow rectangular ground plane with dimensions of 10 × 1.5 mm2 is placed on the back of the substrate.

Figure 4. Input impedance Z of the antenna versus frequency

Figure 4. Input impedance Z of the antenna versus frequency

The input impedance Zin of the antenna versus frequency is given in Figure 4. When the antenna is operating at the passbands, the input resistance is around 50 Ω and the input reactance is around 0 Ω, indicating that the proposed antenna is suitable for UWB applications. At the stopbands, their values largely deviate from the nominal values, indicating obvious impedance mismatch at these frequencies.

EXPERIMENTAL RESULTS AND DISCUSSIONS

Figure 10. Photos of the fabricated triple band-notched UWB antenna: (a) front view; (b) back view

Figure 10. Photos of the fabricated triple band-notched UWB antenna: (a) front view; (b) back view

Figure 11. Simulated and measured VSWR of the proposed triple band-notched UWB antenna

Figure 11. Simulated and measured VSWR of the proposed triple band-notched UWB antenna

The prototype antenna with the optimal dimensions listed in Table 1 was fabricated and tested, as shown in Figure 10. Figure 11 presents the simulated and measured VSWR of the proposed antenna. The measured results are obtained by using an Anritsu 37347D vector network analyzer (40 MHz–20 GHz, Anritsu Corporation, Atsugi, Kanagawa, Japan). It can be seen that the simulated impedance bandwidth for VSWR

CONCLUSIONS

In this paper, a compact planar printed monopole antenna with 3.5/5.2/5.8 GHz triple band-notched characteristics and broad bandwidth characteristic for UWB applications is proposed. The antenna can operate from 2.12 GHz to 14.80 GHz with triple-notched bands of 3.36–4.16, 4.92–5.36, and 5.68–6.0 GHz for rejecting the 3.5 GHz WiMAX and 5.2/5.8 GHz WLAN interferences. By etching several slots with various shapes and dimensions on the radiation patch, triple band-notched properties are generated, and by integrating the slotted radiating patch with a rectangular ground plane on the back of the substrate, improved impedance bandwidth can be achieved, especially at the higher band.

The designed antenna has a simple symmetrical linear structure and a very compact size of 10 × 16 mm2, such that it is easily embedded within portable IoT sensors. The proposed antenna provides good frequency-domain and time-domain performances, such as nearly omnidirectional radiation characteristics, a sharply decreased gain at the stopbands, a flat group delay, and low pulse distortion, which make it suitable for short-range pulse-based UWB communications.

Source: Central South University
Authors: Jian Dong | Qianqian Li | Lianwen Deng

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