Copyright @ 2011 IEEEA miniature transparent UWB antenna with tunable notch that can be incorporated with a solar panel for harnessing solar energy has been proposed and presented. The antenna demonstrates a good omni-directional
radiation pattern throughout the FCC bandwidth of 3.1 – 10.6 GHz and a comparable gain making it a good candidate for future green wireless applications

AbuTarboush, HF

Cheung, SW

Nilavalan, R

Peter, T

Sun, YY

Yuk, TI

English

Brunel University Research Archive

Miniature Transparent UWB Antenna with Tunable Notch for Green Wireless Applications   T. Peter*(1), Y.Y. Sun(2), H.F. AbuTarboush(1), R. Nilavalan(1) and S.W. Cheung(2)  (1) Dept of Electronics and Computer Engineering, Brunel University, Kingston Lane, Uxbridge, UB8 3PH, UK Email:thomas.peter@brunel.ac.uk  (2)Dept of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Email: yysun@eee.hku.hk    ABSTRACT:   A miniature transparent UWB antenna with tunable notch that can be incorporated with a solar panel for harnessing solar energy has been proposed and presented. The antenna demonstrates a good omni-directional radiation pattern throughout the FCC bandwidth of 3.1 – 10.6 GHz and a comparable gain making it a good candidate for future green wireless applications.   INTRODUCTION  In recent years, work on transparent antennas have been actively pursued[1-2]. However, other than the few papers that have been occasionally published, not many papers have surfaced. This is because of the lossy nature of the transparent material and the low efficiency and the difficulty in fabricating the designs. One earlier work on a transparent monopole antenna using AgHT-4 showed improved efficiency with a trade-off in transparency [1]. A much more recent work on  a coplanar waveguide (CPW) ultra wideband (UWB) antenna showed a 20% improvement  to efficiency using a novel soldering technique and using the same material while maintaining full transparency “in press” [2]. One of the factors affecting the efficiency is the surface resistance of the AgHT-8 material which actually increases and reduces the conductivity as the size of the antenna is miniaturized causing further radiation losses besides the usual losses at the connectors due to soldering and impedance mismatch. In this paper, a miniature UWB AgHT-8 antenna design as shown in Fig. 1 is proposed and presented. It demonstrates almost a close but lesser efficiency than in [2] whilst giving a very good nearly omni-directional pattern throughout the entire FCC UWB band of 3.1 GHz to 10.6 GHz. The antenna also demonstrated a very wide bandwidth and comparable peak gain.   The antenna too, can be incorporated with a tunable notch as in [3] to filter out the 5 GHz frequency band so as not to cause interference to the existing 5GHz WLAN application.   The miniature, slim and transparent feature of this antenna allows it to be integrated to a mini solar panel or cell for harnessing solar energy to provide backup power for efficient management and use of the battery in UWB compact and slim devices. This has been demonstrated using a mini solar panel attached to a digital display later on in the paper. Such solar powered transparent antennas make them a good candidate for the green wireless technology of the future.                                                                                      Fig. 1 Miniature transparent UWB Antenna without slot for notch tuning. ANTENNA DESIGN  The miniature transparent UWB antenna is designed and fabricated using AgHT-8 for both the monopole and the 50 Ω CPW feed and ground planes. The AgHT-8 film is 0.175mm thick and has a surface resistance of 8 Ω-Sq which is equivalent to a conductivity (σ ) of 1.25 x 105 S/m [1]. The AgHT-8 film is made up of a coat of transparent silver layer sandwiched between two layers of tin oxide on a thin polyethylene terephthalate (PET) substrate with a relative permittivity of 3.24. The antenna is designed and optimized as an upright rectangle with bevels at the bottom end and fed by a 50 Ω CPW line as illustrated in Fig. 2. The bevel angles are optimized to give the best impedance matching [4]. The bevel edge and the top ground edge basically act as capacitors and varying the capacitance helps improve the impedance matching and thus the return loss.  The chamfers further help to improve the bandwidth by bringing the return loss curve below the -10dB line even more. Introducing a 0.3mm slot at a distance of 1mm along each vertical edge of the radiator like in [3]  can produce a tuning notch to filter out any unwanted frequency band within the obtained bandwidth. Maximizing the length of the slot will produce a notch at the lower frequency while minimizing the length of the slot will produce a notch at the upper frequency. The slots are demonstrated in Fig. 3.                   MEASUREMENT AND SIMULATION RESULTS  The transparent polymer UWB antenna was designed and simulated on CST Microwave Studio. The performance of the proposed antenna was verified by fabricating and testing the transparent UWB antenna and measuring the return loss. Results of the simulated and measured return loss are shown in Fig. 4 and 5.  The measured return loss show better performance than that of the simulated. This improvement can be attributed to the shape of the chamfer during fabrication. The measured return loss shows a -10dB level response from 3 GHz onwards.                               Fig. 2  Layout of the UWB Transparent Antenna                                  Fig. 3 Transparent UWB Antenna with Slots for notch       tuning   Fig. 4 Simulated and measured return loss of the miniature transparent UWB antenna                  Efficiency, gain and radiation pattern measurements of the fabricated prototype tested on Satimo’s radiation pattern measurement equipment, StarLab further affirmed the findings based on the return loss. The measured peak gain and efficiency are shown in Fig. 6 and Fig. 7. The measured 3-D radiation patterns of the antenna as shown in Fig. 8 show a very good omni-directional pattern at the 3, 5, 7 and 9 GHz frequencies which makes this antenna suitable for receiving signal from all direction throughout the FCC stipulated bandwidth of 3.1 - 10.6 GHz.                                                                        Fig. 5. Simulated return loss of the miniature uwb with a notch at 5 GHz         a)                                         b)                                           c)                                         d)   Fig. 8   Measured 3-D radiation patterns of the antenna: a) 3 GHz  b) 5 GHz  c) 7 GHz  d)  9GHz               Fig. 6. Measured peak gain                                                        Fig. 7 Measured Efficiency  INTEGRATION OF SOLAR PANEL   Integrating a miniature solar panel to the back of the transparent UWB antenna enables solar rays to be harnessed through the transparent surface of the antenna to produce solar energy to provide back-up power for efficient management of the batteries in devices in which this type of antenna can be employed.  Fig. 9 further illustrates this. A digital display is powered on to display a zero when the light from the room’s lighting falls onto the mini solar panel from TRONY Solar (Model: 1025I). The display slowly powers off when the solar panel is obstructed or blocked from the lighting. This solar panel also works in dim lighting and hence makes the integrated antenna suitable for indoor wireless applications.                CONCLUSIONS  A miniature transparent ultra wideband antenna that can be integrated with solar panels for solar energy harvesting or providing back up power for wireless application batteries has been proposed and demonstrated. Although the efficiency is quite low probably as mentioned earlier due to higher resistance being encountered on the AgHT-8 with miniaturization in experiment, the 3-D patterns indicate a very nearly omni-directional pattern that is suitable for ultra wideband requirements. Increasing the size of this antenna design may increase the efficiency and could be used with larger solar panels for harvesting greater amounts of energy for various use in wireless applications or even buildings. Work on these are still ongoing and results are expected to be published in later publications.   ACKNOWLEDGEMENTS  The authors wish to acknowledge CPFilms, Portsmouth, UK for their support in providing the AgHT-8 film used in this research.   REFERENCES   [1] Hyok Jae Song; Tsung Yuan Hsu; Sievenpiper, D.F.; Hui Pin Hsu; Schaffner, J.; Yasan, E., "A Method for Improving the Efficiency of Transparent Film Antennas," Antennas and Wireless Propagation Letters, IEEE , vol.7, pp.753-756, 2008. [2] T.Peter, R. Nilavalan, H.F. Abu Tarboush, S.W. Cheung, “A Novel Technique and Soldering Method To Improve Performance Transparent Polymer Antennas” (Accepted for publication in Antennas and Wireless Propagation Letters – August 2010). [3] Su Won Bae, Hyung Kuk Yoon, Woo Suk Kang, Young Joong Yoon, Cheon-Hee Lee, “A Flexible Monopole Antenna with Band-notch Function for UWB Systems”, Proceedings of the Asia-Pacific Microwave Conference 2007. [4] M. J. Ammann, “Control of the impedance bandwidth of wideband planar monopole antennas using a beveling technique,”Microwave Optical Technology Letters, vol.30(4), pp. 229–232, 2001.                                     a)                                                                              b) Fig.9   a) Display being powered on when solar panel is not blocked   b) Display being powered off when the solar panel is blocked  

A Method for Improving the Efficiency of Transparent Film Antennas,&quot; Antennas and Wireless Propagation Letters,

A Novel Technique and Soldering Method To Improve Performance Transparent Polymer Antennas” (Accepted for publication

Control of the impedance bandwidth of wideband planar monopole antennas using a beveling technique,”Microwave

Hyung Kuk Yoon, Woo Suk Kang, Young Joong Yoon, Cheon-Hee Lee, “A Flexible Monopole Antenna with Band-notch Function for UWB Systems”,

Miniature transparent UWB antenna with tunable notch for green wireless applications

In this paper, the design of a UWB antenna using a transparent AgHT-8 material is proposed for green wireless applications. Computer simulation is used for studies. For verification of the design, the proposed antenna is fabricated on an AgHT-8 film and measured. Results show that the antenna has better radiation efficiency relative to its size than the previous designs, good omni-directional radiation patterns throughout the FCC bandwidth of 3.1 - 10.6 GHz and a comparable gain. To filter out the unwanted signals in the WLAN band, two vertical slots are introduced to produce a tuning notch in the 5 GHz frequency band. For demonstration of green wireless applications, the transparent antenna is incorporated with a solar panel for harnessing solar energy. Results show that the transparency of the antenna makes it a good candidate for future green wireless applications. © 2011 IEEE.link_to_subscribed_fulltextThe 2011 International Workshop on Antenna Technology (iWAT), Hong Kong, China, 7-9 March 2011. In Proceedings of iWAT, 2011, p. 259-26

Abutarboush, HF

HKU Scholars Hub

Title Miniature transparent UWB antenna with tunable notch for greenwireless applicationsAuthor(s) Peter, T; Sun, YY; Yuk, TI; Abutarboush, HF; Nilavalan, R;Cheung, SWCitationThe 2011 International Workshop on Antenna Technology(iWAT), Hong Kong, China, 7-9 March 2011. In Proceedings ofiWAT, 2011, p. 259-262Issued Date 2011URL http://hdl.handle.net/10722/140289Rights International Workshop on Antenna Technology Small Antennasand Novel Metamaterials (iWAT) Proceedings. Copyright © IEEE.Miniature Transparent UWB Antenna with Tunable Notch for Green Wireless Applications T. Peter*(1), Y.Y. Sun(2), T.I. Yuk(2), H.F. AbuTarboush(1), R. Nilavalan(1) and S.W. Cheung(2)(1) Dept of Electronics and Computer Engineering, Brunel University, Kingston Lane, Uxbridge, UB8 3PH, UKEmail: [thomas.peter, hattan.abutarboush, rajagopal.nilavalan]@brunel.ac.uk (2)Dept of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Email: [yysun, swcheung, tiyuk]@eee.hku.hkABSTRACT: In this paper, the design of a UWB antenna using a transparent AgHT-8 material is proposed for green wireless applications. Computer simulation is used for studies. For verification of the design, the proposed antenna is fabricated on an AgHT-8 film and measured. Results show that the antenna has better radiation efficiency relative to its size than the previous designs, good omni-directional radiation patterns throughout the FCC bandwidth of 3.1 – 10.6 GHz and a comparable gain. To filter out the unwanted signals in the WLAN band, two vertical slots are introduced to produce a tuning notch in the 5 GHz frequency band. For demonstration of green wireless applications, the transparent antenna is incorporated with a solar panel for harnessing solar energy.  Results show that the transparency of the antenna makes it a good candidate for future green wireless applications. INTRODUCTION In recent years, works on transparent antennas have been attracting attention [1-2]. However, other than the few papers that have been published, there are not many papers surfaced. The main problems of using transparent materials for antennas are 1) lossy nature of the transparent materials, 2) low efficiency and 3) difficulty in fabricating the designs.One earlier work on a transparent monopole antenna using the AgHT-4 material showed efficiency improvement with a trade-off in transparency for the material [1]. However, with the use of the same material AgHT-8 but with a higher surface resistance, yet maintaining full transparency, a much more recent work on a coplanar waveguide (CPW) ultra wideband (UWB) antenna showed that a further 20% improvement in efficiency could be obtained by using a novel soldering technique [2]. One of the factors affecting the efficiencies of AgHT-8 material is the surface resistivity which is inversely proportional to conductivity. The surface resistivity is noticed to increase and hence reduce the conductivity as the size of the antenna is miniaturized causing radiation losses. These losses are additional to the usual losses in the connectors due to soldering and impedance mismatching. In this paper, the design of a miniature transparent UWB antenna using the AgHT-8 material is proposed and presented. Results show that it has a slightly less efficiency than theone proposed in [2]. However, it has very good nearly omni-directional radiation pattern throughout the entire FCC UWB band of 3.1 GHz to 10.6 GHz. The antenna also demonstrates a very wide bandwidth and comparable peak gain.  To produce a tuning notch to filter out the unwanted signal in the WLAN band, two vertical slots are introduced as proposed in [3] to filter out the 5 GHz frequency band, avoiding interfering with the existing 5 GHz WLAN applications.The miniature, slim and transparent features of the proposed transparent antenna allow it to be integrated with a mini solar panel or cell for harnessing solar energy. This can be used to provide backup and complimentary power for efficient use of the batteries in the UWB compact and slim devices. In this paper, this idea is demonstrated using a mini solar panel attached to a digital display. Such solar powered transparent antennas make them a good candidate for the green wireless technology of the future.  ANTENNA DESIGN The miniature UWB antenna is designed using a transparent material, AgHT-8 as shown in Fig. 1. The rectangular radiator, the 50-Ω CPW feed and the ground plane of the antenna are all designed on a AgHT-8 film which has athickness of 0.175mm and a surface resistance of 8 Ω-Sq equivalent to a conductivity (  ) of 1.25 x 105 S/m [1]. The 259978-1-4244-9134-6/11/$26.00 ©2011 IEEEAgHT-8 film is made of a transparent silver layer sandwiched by two layers of tin oxide on a thin polyethylene terephthalate (PET) substrate with a relative permittivity of 3.24. The dimensions of the antenna are designed and optimized using the EM simulation tool, CST Studio.  The main rectangular part of the antenna serves as an upright radiator which has bevels at the bottom end and is fed by a 50-Ω CPW line as shown in Fig. 2. The bevel angle is very critical for impedance matching and so is optimized to give the best impedance matching [4]. The bevel edges and the top ground-plane edges together basically act as capacitors. Varying the capacitance helps improve the impedance matching and thus reducing the reflection coefficient of the antenna. The chamfers can also be used to further improve the bandwidth by increasing the reflection coefficient to more than 10 dB. All these result in a miniature transparent antenna with an ultra wide frequency band. In [3], a slot along the vertical edge of the radiator was introduced to produce a tuneable notch to filter out the possibly unwanted signal within the operation frequency band.  Increasing the length of the slot would produce a notch at the lower frequency range, while decreasing the length of the slot would produce a notch at the higher frequency range.  Here, we use two 0.3 mm vertical slots, each at a distance of 1 mm from the vertical edges of the rectangular radiator, as shown in Fig. 2, to produce a tuneable notch for the purpose of filtering out the unwanted signals. MEASUREMENT AND SIMULATION RESULTSThe transparent UWB antennas, with and without the slots for notch tuning, have been designed and optimised using the EM simulation tool, CST Microwave Studio. To verify the design, the two antennas have also been fabricated on the actual AgHT-8 films. Fig. 3 shows the prototype UWB antenna without slots for the notch tuning. The antennas have been measured using the Satimo antenna measurement equipment, Starlab. The simulated and measured reflection coefficients without the slots are shown in Fig. 4 which indicates that the measured reflection coefficient is larger than that of the simulated reflection coefficient. The measured reflection coefficient is larger than 10 dB from 3 GHz onwards. With the slots for notch tuning, the return reflection coefficient is shown in Fig. 5, indicating that a notch is created at the frequency of 5 GHz. The variation in results between the simulated and measured reflection coefficients in both Figs. 4 and  5, could be mainly attributed to fabrication accuracy.Fig. 1 Layout of transparent UWB antenna.                                             Fig. 3 Prototype-transparent UWB Antenna without slotsfor notch tuning.Fig. 2 Layout of transparent UWB antenna with slots for notch tuning.260The efficiency, peak gain and radiation patterns of the prototype antenna without slots for notch tuning have also been measured using the Starlab.  The measured peak gain and efficiency of the antenna are shown in Figs. 6 and 7, respectively. It can be seen that the maximum peak gain is about -2 dBi at around 15 GHz and ranging from -6 dBi to -4.5 dBi within the UWB band assigned by the FCC. The maximum efficiency is about 18% at around 7.5 GHz. The low values of peak gain and efficiency obtained are expected considering the high loss of the AgHT-8 material.  The measured 3-D radiation patterns of the antenna at different frequencies are shown in Fig. 8.  It has very good omni-directional patterns at the frequencies of 3, 5, 7 and 9 GHz, making the antenna suitable for receiving signals from all directions throughout the FCC stipulated UWB bandwidth of 3.1-10.6 GHz. Fig. 5 Simulated and measured reflection coefficients of the antenna with slots for notch tuning tuned at 5 GHz.Fig. 4 Simulated and measured reflection coefficientsof the antenna without slots for notch tuning. Z Y X a)                                         b)                                           c)                                         d)            Fig. 8 Measured 3-D radiation patterns of antenna: a) 3 GHz, b) 5 GHz, c) 7 GHz and d) 9 GHzFig. 6 Measured peak gain Fig. 7 Measured efficiency261INTEGRATION OF SOLAR PANEL To demonstrate the use of the antenna for green wireless applications, we integrated a miniature solar panel to the back of the transparent UWB antenna. This enabled the solar rays to be harnessed through the transparent surface of the antenna to produce solar energy. This arrangement could be used to provide back-up power to complement the batteries used in the UWB devices. Fig. 9 further illustrates this arrangement. A digital display was powered on to display a ‘zero’ when the light from the room’s lighting fell onto the mini solar panel from TRONY Solar (Model: 1025I) through the surface of the antenna. The digital display slowly powered off and the ‘zero’ display went off when the solar panel was obstructed or blocked from the room’s lighting. This solar panel also could work in dim lighting and hence make the integrated antenna suitable for indoor wireless applications. This result shows that the transparency of the antenna makes it a good candidate for green wireless applications.  Increasing the size of the antenna may increase the efficiency. Thus it is quite possible that we can use a larger solar panel for harvesting a greater amount of energy for various wireless applications and in different environments. Research on this is still ongoing and results are expected to be published in later publications. CONCLUSIONS The design of a miniature transparent UWB antenna with a tunable notch for green wireless applications using an AgHT-8 film has been presented. The antenna has been studied using computer simulation, fabricated and measured.  Results have shown that the antenna has a reasonable radiation efficiency, good omni-directional patterns and comparable gain. It has also been demonstrated that the transparency of the antenna makes it a good candidate for green wireless applications. ACKNOWLEDGEMENTS The authors wish to acknowledge CPFilms, Portsmouth, UK for their support in providing the AgHT-8 film used in this research.REFERENCES [1] H. J. Song; T. Y. Hsu; D.F. Sievenpiper; H. P. Hsu; J. Schaffner; E. Yasan, "A Method for Improving the Efficiency of Transparent Film Antennas," Antennas and Wireless Propagation Letters, IEEE , vol.7, pp.753-756, 2008.[2] T. Peter; R. Nilavalan; H.F. Abu Tarboush; S.W. Cheung, “A Novel Technique and Soldering Method To Improve Performance of Transparent Polymer Antennas,” Antennas and Wireless Propagation Letters, IEEE, vol.9, pp. 918-921, 2010. [3] S. W. Bae; H. K. Yoon; W. S. Kang; Y. J. Yoon; C.H. Lee, “A Flexible Monopole Antenna with Band-notchFunction for UWB Systems”, Proceedings of the Asia-Pacific Microwave Conference 2007.[4] M. J. Ammann, “Control of the impedance bandwidth of wideband planar monopole antennas using a bevelling technique,” Microwave Optical Technology Letters, vol.30 (4), pp. 229–232, 2001.Fig. 9 a) Digital display powered on when solar panel is not blocked to display a ‘zero’.  b) Digital display being powered off when the solar panel is blocked and ‘zero’ disappears.262

Miniature transparent UWB antenna with tunable notch for green wireless applications

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