International Journal of Antennas and Propagation
Volume 2018 (2018), Article ID 5172960, 5 pages
https://doi.org/10.1155/2018/5172960

Research Article

Miniaturized Printed Inverted-F Antenna for Internet of Things: A Design on PCB with a Meandering Line and Shorting Strip

Cheuk Yin Cheung,¹ Joseph S. M. Yuen,² and Steve W. Y. Mung²

¹The Hong Kong University of Science and Technology, Hong Kong
²Innovation Technology Company Limited, Hong Kong

Correspondence should be addressed to Steve W. Y. Mung; mungwaiyin@hotmail.com

Received 29 July 2017; Revised 21 December 2017; Accepted 24 January 2018; Published 26 March 2018

Academic Editor: Xing Lan

Copyright © 2018 Cheuk Yin Cheung et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

This paper focuses on a printed inverted-F antenna (PIFA) with meandering line and meandering shorting strip under 2.4 GHz industrial, scientific, and medical (ISM) band for Internet of things (IoT) applications. Bluetooth Low Energy (BLE) technology is one of potential platforms and technologies for IoT applications under ISM band. Printed circuit board (PCB) antenna commonly used in commercial and medical applications because of its small size, low profile, and low cost compared to low temperature cofired ceramic (LTCC) technology. The proposed structure of PIFA is implemented on PCB to gain all these advantages. Replacing conventional PCB line in PIFA by the meandering line and meandering shorting strip improves the efficiency of the PIFA as well as the bandwidth. As a case study, design and measurement results of the proposed PIFA are presented.

1. Introduction

Internet of things (IoT) is a concept that applies current network technology to improve different industries and environment for a higher quality of life in society. IoT is a worldwide network that provides a platform allowing big data transfer and connection between people and things. In a smart city, the wireless connections between sensors and users provide real-time monitoring [1, 2]. Big data is received by sensors, which can be used for solving parking problem [3] and traffic congestion [3] and controlling the quality of air and water [4]. For example, in medical application, data is shared with patients and medical professionals through IoT; therefore, consulting efficiency is enhanced as well as lowering the medical cost [5]. These several applications provide a successful improvement in our society. There are three main layers in the IoT architecture, sensing, network, and application [6]. In the network layer, wireless parts including an antenna and RF front-end circuits are the main challenges for IoT development [7, 8]. There are different wireless solutions, in which Bluetooth Low Energy (BLE) [9] and Zigbee [10] are highly potential suitable platforms for IoT applications. These wireless technologies are operated under 2.4 GHz industrial, scientific, and medical (ISM) band. Nowadays, minimizing the size of the wireless part especially the antenna is still the main challenging research area.

There are many existing size-reduced solutions, and one of the common types is low temperature cofired ceramic (LTCC) antenna [11, 12]. They have different sizes and lengths among these LTCC antennas such as length with 7 mm, 5 mm, and 3 mm. In Figure 1(a), it shows an incident E-field propagates to a vertical dipole of length , where λ₁ is the wavelength used. If the current distribution of the dipole is uniform, the actual current distribution is nearly sinusoidal. If the same dipole is used at a longer wavelength, λ₂, so the length is only long. The current tapers almost linearly from the central feed point to zero at the ends in a triangular distribution in Figure 1(b). Assuming dipole with uniform current distribution, the radiation resistance in a free space is given by [13]

(a)

(b)

Figure 1: (a) Antenna (length = 0.5λ₁) with sinusoidal current distribution. (b) Antenna (length = 0.1λ₂) with triangular current distribution.

For triangular current distribution in Figure 1(b), the radiation resistance is smaller than those in Figure 1(a). Small values of radiation resistance indicate that the performance of the antenna is not very efficient. An antenna with a shorter length but not resonant in the correct frequency leads to poor overall performance since its resonant frequency is higher than the operating frequency, and so a matching network is added to tune to the correct resonant frequency. This matching network is used for maximum power transfer from the radio transceiver to the antenna; however, the antenna still gives poor efficiency as well as resulting extra cost and circuit area.

Several designs [14–16] were proposed to reduce the antenna size by loading with capacitance since this lowers the resonant frequency, making it appear electrically longer. However, the performance of the antenna depends on the quality factor Q of the capacitors used. In general, the components with higher Q have a higher cost. In this paper, a new implementation of the antenna which has the advantages of low profile, small size, and foldable configuration is presented. No matching network is required, and it can be implemented on standard printed circuit board (PCB).

2. Operation of Proposed Printed Inverted-F Antenna (PIFA)

The printed inverted-F antenna (PIFA) is commonly used in the commercial and medical devices compared to other inverted-F antennas (IFAs) [17–20] since it is small, low profile, and low cost. These IFAs [17–20] are in a 3D shape and nonfoldable which occupy a large volume in portable devices. PIFA, therefore, is widely used in small portable devices [21–23]. PIFA is like a monopole printed on the PCB, but it has a shorting feed point along the main resonant structure shown in Figure 2. It has the advantage that the folded part introduces capacitance to the input impedance of the PIFA which is cancelled by the shorting feed point. This shorting feed point configuration, therefore, reduces the antenna’s size. The matching network may be required for maximum power transfer and, hence, efficient radiation.

Figure 2: Printed inverted-F antenna (PIFA).

Figure 3 shows the proposed antenna which contains two parts, meandering line and meandering shorting strip. Since the ground is classified as part of the antenna during the design, the size W × (L₁ + L₂) = 15 mm × (6 + 30) mm is chosen (this is the common size of a wireless part). The antenna is simulated and designed on an FR4 PCB with dielectric constant = 4.6, and the PCB thickness used is 0.3 mm. These parameters are used to model the first 2 layers in the multiple-layered PCB structure, and the simulation is obtained by Advanced Design System (ADS).

(a)

(b)

Figure 3: (a) Proposed antenna. (b) Antenna with meandering line and meandering shorting strip.

The resonant frequency of PIFA decreases when the length of the conventional PCB line increases, because of the longer wavelength [13]. This PCB line in the conventional PIFA is replaced by the meandering line in Figure 4. The combination of horizontal and vertical lines forms turns in Figure 4, and the number of turns increases efficiency. The resonant frequency in Figure 4 is much lower than that of the PCB line in the PIFA with equal length [24, 25].

Figure 4: Meandering line used in PIFA.

However, one of the disadvantages of the meandering line used is the narrow bandwidth [26, 27] compared to the traditional PIFA in Figure 2. Another disadvantage is a matching network required to be placed at the antenna’s input to achieve a good impedance matching for maximum efficiency [28]. The shorting strip of the PIFA becoming a meandering shape increases the bandwidth [29, 30]. Therefore, the meandering shorting strip is then added to increase its bandwidth shown in Figure 3(b). Designing the meandering segment to be a log periodic pattern can improve the antenna’s impedance matching [26] shown in Figure 3. Table 1 shows the final dimension used in simulation so that the resonance frequency is close to the operating frequency, 2.45 GHz.

Table 1: Parameter used in the simulation.

Parameters
Dimension

The width of the strip, w
0.6 mm

The space of each turn, s
0.4 mm

The length of each turn, l
3.5 mm

Distance between shorting feed point and feed point
2.3 mm

Distance to the ground plan
0.8 mm

Area of the antenna (W × L₁)
15 × 6 mm²

Ground plane (W × L₂)
15 × 30 mm²

3. Experimental Results

A prototype was designed and fabricated on the FR4 PCB based on the dimension in Table 1, and the photo of the prototype is shown in Figure 5. The return loss is measured by a network analyzer, and the radiation patterns are carried out by an antenna measurement system. In Figure 6, the measured return loss is shown as the red line together with the simulated result as the blue line. The return loss is better than 10 dB within the ISM band. Figure 7 shows the measured radiation patterns in total fields of the proposed PIFA at 2.45 GHz as well as the gain of the antenna in Table 2.

Figure 5: Photo of proposed PIFA.

Figure 6: Simulated and measured S-parameter, S₁₁.

(a)

(b)

(c)

Figure 7: Measured radiation patterns in total fields (horizontal plane (H-Plane) and vertical plane (V-Plane)): (a) Y-Z plane, (b) X-Z plane, and (c) X-Y plane.

Table 2: The gain of the proposed PIFA.

Plane
Peak (dBi)
Average (dBi)

Horizontal
Vertical
Horizontal
Vertical

Y-Z
2.31
2.75
−4.12
−3.35

X-Z
1.92
−2.00
−3.25
−7.94

X-Y
4.00
−1.12
−2.51
−7.28

Figure 8 shows the photo of the proposed PIFA compared to the Walsin (monopole) antenna [12] and the Murata antenna [14], which are LTCC antennas. Both need the extra components for good impedance matching. An extra capacitive is added in the Murata antenna [14] to achieve the size reduction, and the large ground plane is required to achieve better efficiency as well. Table 3 shows the comparison table of these 3 antennas. It shows that the Walsin and Murata antennas have a little size smaller than the proposed PIFA. However, the proposed PIFA has only the PCB metal trace’s thickness (around 35 μm), which is approximately zero in thickness since it was printed on the PCB; therefore, this can be easily fabricated on the flexible printed circuit (FPC) as well, which is highly foldable for the mechanical housing in portable devices compared to those nonfoldable IFA designs [17–20]. And there is no extra cost required (printed on the PCB) on this proposed PIFA compared to the other two antennas as well as no extra matching network and capacitive load. In Table 4, it shows that the overall gain performance is better than that of the other two antennas.

Figure 8: Compared result to Walsin (left) and Murata (right) antennas.

Table 3: Comparison between proposed PIFA, Walsin [12], and Murata antennas [14].

Antenna
Type
Volume (include the matching network)
Extra components

Proposed PIFA
PCB
15 × 6.0 × 0.035 mm³
No extra cost required

Walsin
LTCC
12 × 5.0 × 1.2 mm³
1 antenna and 2 passive components

Murata
LTCC
12 × 5.0 × 1.2 mm³
1 antenna and 2 passive components

Table 4: Gain between proposed PIFA, Murata [13], and Walsin monopole antennas [12].

Antenna
Plane
Total average (dBi)

Proposed
Y-Z
−0.708

X-Z
−1.980

X-Y
−1.260

Murata
Y-Z
No data in datasheet

X-Z
−1.761

X-Y
−3.318

Walsin
Y-Z
0.891

X-Z
−1.846

X-Y
−2.556

4. Conclusion

This paper proposes a minimized PIFA design suitable for IoT and other ISM band applications. To elaborate on this, the architecture of the PIFA on PCB with meandering line and meandering shorting strip was proposed. The measurement result of return loss and gain performances has shown that it has better performances compared to the LTCC antennas and there are no extra components required for good impedance matching. This proposed PIFA is a paradigm of choice compared to others keeping the portability of devices with low cost and good performance.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

Acknowledgments

This work was supported by Innovation Technology Company Limited, Hong Kong.

References

B. Ahlgren, M. Hidell, and E. C.-H. Ngai, “Internet of things for smart cities: interoperability and open data,” IEEE Internet Computing, vol. 20, no. 6, pp. 52–56, 2016.

Y. Sun, H. Song, A. J. Jara, and R. Bie, “Internet of things and big data analytics for smart and connected communities,” IEEE Access, vol. 4, pp. 766–773, 2016.

W. He, G. Yan, and L. Da Xu, “Developing vehicular data cloud services in the IoT environment,” IEEE Transactions on Industrial Informatics, vol. 10, no. 2, pp. 1587–1595, 2014.

A. Zanella, N. Bui, A. Castellani, L. Vangelista, and M. Zorzi, “Internet of things for smart cities,” IEEE Internet of Things Journal, vol. 1, no. 1, pp. 22–32, 2014.

U. Satija, B. Ramkumar, and M. Sabarimalai Manikandan, “Real-time signal quality-aware ECG telemetry system for IoT-based health care monitoring,” IEEE Internet of Things Journal, vol. 4, no. 3, pp. 815–823, 2017.

S. Chen, H. Xu, D. Liu, B. Hu, and H. Wang, “A vision of IoT: applications, challenges, and opportunities with China perspective,” IEEE Internet of Things Journal, vol. 1, no. 4, pp. 349–359, 2014.

S. Shinjo, K. Nakatani, K. Tsutsumi, and H. Nakamizo, “Integrating the front end: a highly integrated RF front end for high-SHF wide-band massive MIMO in 5G,” IEEE Microwave Magazine, vol. 18, no. 5, pp. 31–40, 2017.

C.-S. Yoo, J.-K. Lee, D. Kim et al., “RF front-end passive circuit implementation including antenna for ZigBee applications,” IEEE Transactions on Microwave Theory and Techniques, vol. 55, no. 5, pp. 906–915, 2007.

R. Tabish, A. Ben Mnaouer, F. Touati, and A. M. Ghaleb, “A comparative analysis of BLE and 6LoWPAN for U-HealthCare applications,” in 2013 7th IEEE GCC Conference and Exhibition (GCC), pp. 286–291, Doha, Qatar, 2013.

Z. Zhang and X. Hu, “ZigBee based wireless sensor networks and their use in medical and health care domain,” in 2013 Seventh International Conference on Sensing Technology (ICST), pp. 756–761, Wellington, New Zealand, 2013.

D. Seo, S. Jeon, N. Kang, J. Ryu, and J.-H. Choi, “Design of a novel compact antenna for a Bluetooth LTCC module,” Microwave and Optical Technology Letters, vol. 50, no. 1, pp. 180–183, 2008.

L. K. Yeung, J. Wang, Y. Huang, S.-C. Lee, and K.-L. Wu, “A compact LTCC Bluetooth system module with an integrated antenna,” International Journal of RF and Microwave Computer-Aided Engineering, vol. 16, no. 3, pp. 238–244, 2006.

J. D. Kraus and R. J. Marhefka, Antennas: For All Applications, McGraw-Hill, Upper Saddle River, NJ, USA, 2002.

A. Zhao, J. Xue, C. Jing, and A. Salo, “The use of Murata ceramic Bluetooth antenna for wrist device based on flexible printed circuit boards,” in 2008 European Conference on Wireless Technology, pp. 334–337, Amsterdam, Netherlands, 2008.

P. Tornatta, “A method to design an aperture-tuned antenna using a MEMS digital variable capacitor,” Microwave Journal, vol. 57, no. 1, pp. 102–114, 2014.

C. R. Rowell and R. D. Murch, “A capacitively loaded PIFA for compact mobile telephone handsets,” IEEE Transactions on Antennas and Propagation, vol. 45, no. 5, pp. 837–842, 1997.

H. D. Hristov, H. Carrasco, and R. Feick, “Bent inverted-F antenna for WLAN units,” Microwave and Optical Technology Letters, vol. 50, no. 6, pp. 1505–1510, 2008.

M. J. Ammann and L. E. Doyle, “A loaded inverted-f antenna for mobile handsets,” Microwave and Optical Technology Letters, vol. 28, no. 4, pp. 226–228, 2001.

V. K. Palukuru, A. Pekonen, V. Pynttäri, R. Mäkinen, J. Hagberg, and H. Jantunen, “An inkjet-printed inverted-F antenna for 2.4-Ghz wrist applications,” Microwave and Optical Technology Letters, vol. 51, no. 12, pp. 2936–2938, 2009.

S.-W. Su, “Linearly-polarized patch PIFA for GPS/GLONASS operation for tablet-computer applications,” Microwave and Optical Technology Letters, vol. 57, no. 1, pp. 149–153, 2015.

C. Soras, M. Karaboikis, G. Tsachtsiris, and V. Makios, “Analysis and design of an inverted-F antenna printed on a PCMCIA card for the 2.4 GHz ISM band,” IEEE Antennas and Propagation Magazine, vol. 44, no. 1, pp. 37–44, 2002.

H. Y. D. Yang, “Printed straight F antennas for WLAN and Bluetooth,” in IEEE Antennas and Propagation Society International Symposium. Digest. Held in conjunction with: USNC/CNC/URSI North American Radio Sci. Meeting (Cat. No.03CH37450), vol. 2, pp. 918–921, Columbus, OH, USA, 2003.

M. Ali and G. J. Hayes, “Small printed integrated inverted-F antenna for Bluetooth application,” Microwave and Optical Technology Letters, vol. 33, no. 5, pp. 347–349, 2002.

V. B. Ambhore and A. P. Dhande, “An overview on properties, parameter consideration and design of meandering antenna,” International Journal of Smart Sensors and Ad Hoc Networks, vol. 1, pp. 59–62, 2012.

S. R. Best and J. D. Morrow, “Limitations of inductive circuit model representations of meander line antennas,” in IEEE Antennas and Propagation Society International Symposium. Digest. Held in conjunction with: USNC/CNC/URSI North American Radio Sci. Meeting (Cat. No.03CH37450), vol. 1, pp. 852–855, Columbus, OH, USA, 2003.

A. Jahanbakhshi, G. Moradi, and R. Sarraf Shirazi, “Design and simulation of different types of meander line antennas with improved efficiency,” in Progress In Electromagnetics Research Symposium Proceeding, pp. 594–597, Moscow, Russia, 2012.

D. Misman, “The effect of conductor line to meander line antenna design,” in 2007 Asia-Pacific Conference on Applied Electromagnetics, pp. 1–5, Melaka, Malaysia, 2007.

T. J. Warnagiris and T. J. Minardo, “Performance of a meandered line as an electrically small transmitting antenna,” IEEE Antennas and Propagation Magazine, vol. 46, no. 12, pp. 1797–1801, 1998.

P. W. Chan, H. Wong, and E. K. N. Yung, “Wideband planar inverted-F antenna with meandering shorting strip,” Electronics Letters, vol. 44, no. 6, p. 395, 2008.

P. W. Chan, H. Wong, and E. K. N. Yung, “Dual-band printed inverted-F antenna for DCS, 2.4GHz WLAN applications,” in 2008 Loughborough Antennas and Propagation Conference, pp. 185–188, Loughborough, UK, 2008.