2013 Loughborough Antennas & Propagation Conference 11-12 November 2013, Loughborough, UK

978-1-4799-0091-6/13/$31.00 ©2013 IEEE

A GPS/Wi-Fi Dual-Band Arc-Shaped Slot Patch Antenna for UAV Application

Jianling Chen and Junhong Wang Department of Electronics and Information Engineer

Beijing Jiaotong University Beijing, China

j.chen@ee.ucl.ac.uk

Kin-Fai Tong and Allann Al-Armaghany Department of Electronic and Electric Engineer

University College London London, UK

Abstract—In this paper, a dual-band capacitive-fed circular patch antenna with an arc-shaped slot is proposed for 1.575 GHz GPS and Wi-Fi 2.4 GHz applications. The antenna will be embedded on an unmanned aerial vehicle (UAV) for Wi-Fi 2.4 GHz communication with a base station and GPS reception. A circular feeding disk is sandwiched between two substrate layers. Foam is used for the bottom layer and the top layer is Rogers Duroid 5880 microwave laminate. The capacitive feeding disk is used for improving the impedance bandwidth of the antenna, so the antenna can cover 2390 to 2515 MHz for full support of the 2.4 GHz band Wi-Fi communication between UAV and GBS. The foam-Duroid stacked geometry can further enhance the bandwidths for both GPS 1.575 GHz and Wi-Fi 2.4 GHz when compared to purely Duroid form. The antenna has been simulated and fabricated. The simulation and measurement results are presented in this paper.

Keywords— patch antenna; capacitive feeding; UAV; Wi-Fi; GPS;

I. INTRODUCTION Modern Unmanned Aerial Vehicles (UAVs) usually carry a large number of surveillance and communication equipment for information gathering and surveillance purposes [1]. It requires extensive communications and data transferring between the sensors, such as GPS receiver and accelerometer, and the Ground Base Station (GBS) [2]. Therefore, antenna systems integrated on the UAV device are critical to establish reliable radio communication links. For this application, patch antenna becomes a good candidate due to its simple geometry, low profile and inexpensive cost. A S-band EBG antenna has been reported in [3], which achieved 80MHz bandwidth at 2.35GHz. It is embedded on the wing of a mini UAV. Arc-shaped slot for obtaining dual-frequency operation on a microstrip-line-fed circular patch antenna is described in [4]. The antenna performs at 1.6 GHz and 2.05-2.29 GHz. Modifying the subtending angle of the arc-shaped slot allows tuning of the frequency bands and the band spacing ratio. In [5], a compact dual-band circularly polarized GPS antenna, which works at 1227 MHz and 1575 MHz is reported. In [6], a triangular patch antenna with a parasitic element over a

modified small ground plane is presented. The antenna operates at two frequencies at 2.45 and 5 GHz network bands. In [7], a rectangular microstrip patch antenna has been investigated. An additional rectangular conductive plate of comparable dimensions was placed above the patch in order to enhance th e bandwidth. However, the enhancement the bandwidth for both GPS 1.575 GHz and Wi-Fi 2.4 GHz is still under investigation. In this paper, a patch antenna with capacitive feeding disk and stacked substrates is presented. Using the capacitive feeding disc and stacked substrate geometry, the impedance bandwidths at both bands are considerably improved. It can fully support the GPS and Wi-Fi 2.4 GHz band communications.

II. UAV AND ANTENNA DESIGN

The proposed patch antenna will be mounted on the UAV illustrated in Fig. 1. There are three separate communication systems on the UAV – GPS, Wi-Fi 2.4 GHz and a remote control unit also operating at 2.4GHz. Therefore, a dual-band antenna is required for 1.575 GHz and 2.4 GHz bands. Several antenna types have been attempted, including spiral antenna, monopole antenna and patch antenna. Amongst these antenna types, patch antenna is least susceptible to the rest of UAV device because of its full ground plane, which shields most RF

Fig. 1. Quadrocopter with three antenna communication systems used in the project

x

y

z

490

(a)

(b)

Fig. 2. Geometry and the fabricated prototype of the proposed antenna

interferences and demonstrates stable and efficient communication links. The dual-band slot patch antenna is designed to realize the communication for GPS, Wi-Fi and remote control and the result won’t be affected much by the structure of the UAV and the presence of other hardware. Fig. 2 shows the configuration of the patch antenna. It is composed of a circular patch, a circular feeding disk stacked between two substrate layers and a square ground plane. The bottom substrate is a 7mm-thick polystyrene foam. The copper feeding disc with diameter D1 = 10 mm is placed on the top of the foam. The top substrate layer stacked on the foam is a single sided Rogers Duroid 5880 laminate with the thickness of 1.575 mm. The relative permittivity ( rε ) of the laminate is 2.2. The circular feeding disk between these two substrate layers is connected to the center conductor of a coaxial cable which is located at the distance of d1 = 2.4mm with respect to

Fig. 3. Measured S11 in free space against simulated S11 in free space and on UAV the center of the circular patch, whose diameter is D2 = 74.4 mm. A 3mm-wide arc-shaped slot on the patch is also centered with respect to the x-axis shown in Fig. 2 (a) and subtended by an angle θ = 127.5°. The slot is embedded to the edge of circular patch with distance d2 = 13.3 mm. The lengths and widths of both substrates are 50×50 mm square, as well as the ground plane attached on the bottom of the polystyrene foam. Fig. 2 (b) shows a photo of the fabricated antenna prototype. A capacitive feeding disk is used to improve the impedance bandwidth of the antenna, so the antenna can cover 2390 to 2515 MHz for fully support of the Wi-Fi communication between UAV and GBS. The foam-Duroid stacked geometry can further enhance the bandwidths for both GPS 1.575 GHz and Wi-Fi 2.4 GHz when compared to purely Duroid form.

III. SIMULATION AND MEASUREMENT RESULTS

A. Simulated and meaured results of S11

Fig. 3 shows the simulated and measured S11 of the proposed patch antenna. As presented, the antenna operates at 1.575 GHz with 47 MHz bandwidth and 2.45 GHz with 125 MHz bandwidth, which is sufficient for both GPS and full Wi-Fi at the 2.4GHz band. The simulation and measurement results show good agreement. In addition, the effect on the antenna performance from UAV shown in Fig. 1 is also considered in the investigation. Fig. 3 shows the S11 comparison for the antenna in free space and mounted on the UAV. It can be seen that the S11 is slightly affected when the antenna is fixed on UAV, as the ground plane of the patch antenna is large enough to shield it from any interference from other parts of the device. So it effectively solves the problem when using monopole antenna for Wi-Fi communication. The technology of capacitive feeding and stacked substrates improve the bandwidth with at both frequencies.

1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4-35

-30

-25

-20

-15

-10

-5

0

Frequency (GHz)

S11

(d

B)

Simulated S11

Measured S11

Simulated S11 of the patch antenna on UAV

Centre of feeding disk

Ground plane

D2 D1 t1

t2

y

x

θ

W1

d2

Patch centre

Circular feeding disc

d1

. z

491

(a)

(b)

Fig. 4. Simulated surface current distribution of frequency (a) f1=1.575 GHz and (b) f2=2.4 GHz

B. Surface current distribution at 1.575 and 2.4 GHz

Fig. 4 shows current distributions of the patch at 1.575 GHz and 2.4 GHz. For the case of surface current shown in Fig. 5 (a), the resonant mode is perturbed TM11 mode, it can be observed that the excited current distribution is very similar to that of the TM11 mode of the case without the slot. With the presence of the slot, the fundametal mode TM11 of the circular mode has been slightly pertured because the slot is located close to the patch boundary, where the excied patch surface current for the TM11 mode had a minumum value. The second resonant mode excited in the present design is the purturbed TM01 mode.

C. Simualted and measured results of radiation pattern Radiation patterns simulated and measured in two principle

planes (E plane and H plane) are plotted in Fig. 5 and Fig. 6 at 1.575 GHz and 2.45 GHz. The measured antenna gain is 7.07 dBi and 7.47 dBi at each band. Simulated radiation pattern of the antenna on UAV is presented in Fig. 7.

E-plane H-plane

(a)

E-plane H-plane

(b) Co-pol Cross-pol

Fig. 5. Simulated radiation pattern for the antenna (a) f1=1.575 GHz, (b) f2=2.45 GHz

E-plane H-plane

(a)

E-plane H-plane

(b) Co-pol Cross-pol

Fig. 6 Measured radiation pattern for the antenna (a) f1=1.575 GHz, (b)f2=2.45 GHz

492

E-plane H-plane

(a)

E-plane H-plane

(b) Co-pol Cross-pol

Fig. 7. Simulated radiation pattern of the antenna on UAV (a) f1=1.575 GHz, (b) f2=2.45 GHz

IV. CONCULSION

The performance of a circular patch antenna with a capacitive feeding disk and an arch-shaped slot is reported. Adding the slot and modifying its dimensions provide s a dual-frequency band antenna operating at GPS 1.575 GHz and Wi-Fi 2.4 GHz. The antenna is applied on an UAV device to support three communication systems. In order to minimize interferences from the rest of the UAV device, patch antenna becomes a good candidate to offer an independent working environment due to its full-sized ground plane. The bandwidth

of the proposed antenna, benefiting from the capacitive feeding and the stacked substrates, has achieved 47 MHz at GPS band and 125 MHz at Wi-Fi band, giving the antenna gain of 7.07 dBi at 1.575 GHz and 7.47 dBi at 2.45 GHz, respectively.

V. ACKNOWLEDGEMENT

This work is supported in part by the National Program on Key Basic Research Project under Grant No.2013CB328903, and in part by the National Natural Science Foundation of China under Grant No.61271048.

REFERENCE

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[2] Chen-Mou Cheng; Hsiao, Pai-Hsiang; Kung, H. T.; Vlah, D., "Performance Measurement of 802.11a Wireless Links from UAV to Ground Nodes with Various Antenna Orientations," Computer Communications and Networks, 2006. ICCCN 2006. Proceedings.15th International Conference on , vol., no., pp.303,308, 9-11 Oct. 2006

[3] Salonen, P.; Rintala, K., "An S-band EBG antenna for mini-UAV," Antennas and Propagation Society International Symposium 2006, IEEE , vol., no., pp.2373,2376, 9-14 July 2006

[4] Hsieh, G.-B.; Wong, K. -L, "Inset-microstrip-line-fed dual-frequency circular microstrip antenna and its application to a two-element dual-frequency microstrip array," Microwaves, Antennas and Propagation, IEE Proceedings , vol.146, no.5, pp.359,361, Oct

[5] Ming Chen; Chi-Chih Chen, "A Compact Dual-Band GPS Antenna Design," Antennas and Wireless Propagation Letters, IEEE , vol.12, no., pp.245,248, 2013

[6] Liu, L.; Zhu, S.; Langley, R., "Dual-band triangular patch antenna with modified ground plane," Electronics Letters , vol.43, no.3, pp.140,141, Feb. 1 2007

[7] Trivedi, R.D.; Dwivedi, V., "Stacked Microstrip Patch Antenna: Gain and Bandwidth Improvement, Effect of Patch Rotation," Communication Systems and Network Technologies (CSNT), 2012 International Conference on , vol., no., pp.45,48, 11-13 May 2012

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