Modeling and Optimization of an Environmentally Safe UWB

Volume-9, Issue-4, December 2019

Modeling and Optimization of an Environmentally Safe UWB Octagonal Planar

Monopole Antenna

1M. Y. Elhefnawy, 2Aladdin Assisi, 3Ibrahim F. Tarad, 4HosnyAlmotaafy

1Department of Electronics Communication Engineering, Faculty of Engineering ,

Al-Azhar University, Cairo, Egypt. E-mail:[email protected] 2

Department of Electronic Warfare Engineering, Military Technical College, Cairo,

Egypt.E-mail: [email protected]. 3Department of Electronics Communication Engineering, Faculty of Engineering,

Al-Azhar University, Cairo, Egypt. 4Electrical and communication Engineering, Higher Technological Institute, Cairo,

Egypt. E-mail: [email protected]

Abstract Modeling and optimization of environmentally safe electromagnetic wave radiators are essential trends in modern green engineering, especially in green communication. UWB and SWB antennas introduce promising innovations for medical applications, such as UWB radars used in human tissues diagnosis and early discovery of cancer. In this paper, we discuss different techniques that can be applied to maximize the frequency coverage of a planar octagonal monopole antenna and extend it from UWB to SWB. A SWB antenna is well matched along a frequency range starting from fmin up to 20fmin. Different values of each antenna design parameter are compared to show how that parameter affects the antenna frequency coverage. Many simulation runs have been done to get insight into the effects of different design parameters. Some additional parameters are subject to optimization with the maximum frequency as an optimization goal. A design optimization problem has been formulated and solved to get a SWB planar octagonal monopole antenna with the widest possible bandwidth. The optimized

Journal of Green Engineering, Vol. 9_4, 540–558. Alpha Publishers

This is an Open Access publication. © 2019 the Author(s). All rights reserved

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541 M. Y. Elhefnawy et al

antenna performance has been calculated by simulation. Finally, a sample of the SWB antenna has been implemented and its frequency response has been measured.

Keywords: Frequency band, Printed octagonal monopole antenna, RES,

SWB antenna, Return loss, UWB antenna

1 Introduction

With the increase of Renewable Energy Resources of different sizes and types, the need for continuous remote monitoring and control of those resources increases [1]. One of the best techniques to monitor and control such renewable energy sources (RES) is wireless data transmission. It is more flexible, versatile and economic compared to wired techniques. Different resources can connect to a wireless network through time domain multiple access TDMA, code domain multiple access CDMA or frequency domain multiple access FDMA. The second technique is limited by the limited number of possible orthogonal codes. The first imposes a limitation on the communication time duty ratio; since a given resource will not be permitted to transmit its data before all the other resources have already done. Otherwise, complex priority algorithms are applied to give different resources different transmission rights according to their relative priorities.

The third technique is entirely hardware dependent. Its success is subject to the possibility to get different distant frequencies to transmit different data. Every RES can transmit its data continuously without interruption. No waiting or complex priority algorithms are required. This is possible with wideband wireless networks. The wider the network BW the more resources can easily be monitored and controlled.

The figure 1 shows a proposed N: 1 wireless monitoring network applicable to RES systems, where N different Renewable Energy Resources can be monitored by a single receiver. Since each RES uses a different frequency, the central monitor has to use an ultra wideband UWB antenna.

UWB technology is becoming more and more important to many potential applications due to larger channel capacity and higher time precision etc. [2]. Moreover; increasing data rates needs more bandwidth. It is safe to state that the demand for wideband antennas increases in response to wireless communication applications requiring more and more bandwidth. The problem of using multiple antennas for a number of applications operating in handheld devices can be solved by employing SWB monopole structures in which a single antenna can cover the entire operating bandwidth; as a result, the size of the device will become miniaturized. Both long-range and short-range communications including the ultra-wideband (UWB) range are covered by SWB antennas. A single SWB antenna can be used to cover simultaneously many communication bands such as


Monopole Antenna 542

GSM/UMTS (800/850/900/950/1800/1900/2100 MHz), GPS (1227.60/1575.42 MHz), ISM (2.4/24.25 GHz), WLAN / Wi-Fi (3.6/4.9/5/5.9 GHz), radio determination applications (4.5–7 GHz, 13.4-14 GHz), UWB communication (3.1–10.6 GHz), and radio astronomy (22.5 GHz, 24.05–27 GHz)[3-4]. Another important advantage of using a wide antenna bandwidth is a high resilience to fading [5].

Figure 1. Proposed RES data monitoring network diagram A PCB antenna has a low profile, low manufacturing costs and can easily

be integrated with other parts of Monolithic Microwave Integrate Circuits (MMIC). This allows a compact module design [6]. The main drawback is its limited bandwidth. Planar monopole antenna has the same merits of planar structure, compact size and consistent radiation characteristics. At the same time, its bandwidth can be significantly increased. Therefore, it has become one of the most attractive candidates for wide band antennas [7], [8]. The state of the art SWB antenna focuses mainly on planar monopole microstrip antennas that can be directly printed onto printed circuit boards (PCBs) and have wide bandwidths that can be further extended as we are going to show in this letter.

AntCpld_2

AntCpld_5

Iso=30.0dB AntCpld_1

RES(1)

RES(2)

RES(i)

RES (n)




2 Previous Work Survey

Ideally, an UWB antenna ought to have a sufficiently wide bandwidth so as to cover the entire UWB spectral bandwidth. As demonstrated in [4], this is not an easy task to achieve. A lot of articles have been presented by several researchers across the globe related to SWB antennas. The major concern in SWB wireless handheld terminals is the design of the antenna; compact size with good radiation capability [9].To satisfy such requirements, various types of planar antennas have been developed and several bandwidth enhancement techniques have been released such as making slots in ground plane and patch, patch tapering, reducing ground plane and defecting it [10].A variation of the novel technique called defected microstrip structure (DMS) was employed by Peyrot-Solis et-al to enlarge the bandwidth of a planarized ultra-wide band (UWB) monopole. It was demonstrated that introducing a defect in the feeding microstrip line, the lower bandwidth limit is lowered without affecting the antenna gain and radiation pattern. The bevel technique in the ground plane near to the feeding point was used to increase the highest bandwidth limit [11].Monopole antennas with defected ground plane are also very popular for achieving (UWB) and super wideband (SWB) [9].

3 Proposed Antenna Design

In this paper we demonstrate our design approach and the main transmission line principles to design and implement a SWB antenna. We present the design techniques to spread the BW from UWB to SWB thereby enhancing the main antenna parameters for indoor applications.

The proposed antenna covers the bandwidth allocated for SWB wireless communications (2.18 GHz-44.5 GHz) which makes it appropriate for many wireless communication systems, medical applications, electronic warfare systems and SWB radar systems.

We have designed and implemented the proposed antenna on a Taconic TLY-5 laminate. The Taconic laminate has a low dielectric constant (DK=2.17), low loss tangent (DF=0.0009) and the substrate thickness is (t =1.52mm). The proposed antenna was successfully implemented on this material and the simulated results show reasonable correlation with the measured results. A 2.18 to 45 GHz frequency range was intended in this design with S11 <-10 dB and VSWR< 2 in the simulation results. Finally, the measured S11 performance of the antenna is presented.



4 Design Approach

The idea of our design approach depends on three key Transmission Line principles, namely:-

4.1 Increasing the Bandwidth of the Antenna by Decreasing the

Quality Factor (Q)

An effective way to increase the antenna’s impedance bandwidth is by decreasing the quality factor of the microstrip antenna [12]. Quality factor hinges on the reflection coefficient because a lower Quality factor means lower reflection back into the UWB monopole's "neck" towards the source. When the radiating element is made to be very wide, the Q factor at the lowest operating frequency becomes low [13].

4.2 Smooth Impedance Transition (No Step Impedance) Impedance transitions should be smoothed wherever they occur (i.e. they

should change steadily with distance along the wave propagation path). The point where the patch starts and the angle between the lower edges and the ground plane are critical, as the wave should not experience step impedance transitions here. A steady change from the microstrip transmission line impedance to the input impedance of the patch is expected [13-14].

4.3 A Large Part of the Current Wave Flows along the Edges of the Patch

When the current wave in the feed line approaches the entrance of the patch; it splits. A large part of the current wave will flow along the edges (with certain angle θ) instead of the middle. We observed this during the simulation where we manually changed the meshing at the edges, close to the underlying ground plane to help the simulator. This current wave will experience increasing characteristic impedance when traveling sideways, as the distance between the patch edge and ground plane increases. Characteristic impedance of the patch edges increases as the distance between the patch edges and the underlying ground plane increases [13-14].


5 Different Techniques to Spread the Frequency Coverage

5.1 Changing the Dielectric Constant ( r )

Since the substrate dielectric constant has a large effect on the input impedance of any printed antenna [15, 16] the UWB antenna bandwidth should change with different dielectric constant values. Figure 2 shows the simulated frequency responses of an octagonal monopole antenna on

different substrates with r = 2.2, 6.2 and 10.2.

Figure 2. Effect of Dielectric Constant on S11 of Octagonal Antenna

It is evident that the smaller the dielectric constant; the lower S11. We

shall use r = 2.2 for all next designs of octagonal monopole antenna. In this paper, we use copper clad laminates with the smallest available dielectric constant. All the printed monopole antenna models that have been simulated, implemented and measured in this paper have been designed for the Taconic

TLY-5 with relative permittivity r = 2.2.

5.2 Increasing the Substrate Thickness (t) Increasing the substrate thickness (t) increases the antenna bandwidth.

Figure 3 shows the simulated frequency responses of an octagonal monopole antenna on a 0.78 mm TLY-5 substrate and of the same antenna on a 1.52mm substrate of the same material.



Figure 3. Effect of Substrate Thickness (t)

It is clear that increasing the substrate thickness (t) enhances the return loss and consequently increases the upper limit of the antenna frequency range. The 1.52 mm TLY-5 substrate is used in all next stages of this design.

5.3 Changing the Octagon Width (a)

Changing the octagon width (a) changes the input complex impedance of the octagon and consequently changes the frequency response of the monopole antenna. Figure 4a shows the octagonal monopole antenna with 25, 35 and 40 mm widths, while Figure 4b shows the simulated frequency responses of the octagonal monopole antenna with those widths. We cannot say that the return loss increases monotonically with octagon width. But surely there must be some optimal value of octagon width for which S11 < -10 dB and for frequency range as wide as possible. We should search for that optimal value.


Figure 4a. Octagonal Monopole Antenna with Different Width

Figure 4b. Effect of changing the octagon width

5.4 Changing the Octagon Height (b)

Changing the octagon height (b) changes the center frequency of the octagonal antenna and changes the maximum frequency at which S11 <-10 dB.Figure5 shows the simulated frequency responses of an octagonal monopole antenna with 22, 30 and 35 mm heights.



Figure 5a. Different Octagon Heights

Figure 5b. Effect of changing octagon height

We cannot yet deduce an empirical relation between the BW and octagon height. As mentioned previously, surely there must be some optimal value of octagon height for which S11 < -10 dB and for frequency range as wide as

possible.

5.5 Optimizing the Feed TL Width (w) For a certain substrate thickness and material, there is an optimal value of

microstrip TL width (w) for 50 [ ] matching. Since the octagon input impedance is not purely resistive and since its real and imaginary parts


change with frequency; there should be an optimal value of the TL width that retains the antenna matching for the highest possible frequency.

Different empirical formulas can be found for optimal microstrip TL

width for 50 [ ] matches and are offered through several references, such as [17] and [18]. We shall not repeat those equations here. However, we are going to discuss varying the TL width on the matched BW of our antenna.

Figure 6 shows the S11ofmicrostrip transmission lines with different widths on the 1.52mm TLY-5 substrate.

Figure 6. S11 of MSTL with different widths on the 1.52mm TLY-5 substrate

It can be noted that although all those widths between 3 and 6 mm give acceptable 50 [ ] match; the MSTL resonates at a certain frequency that increases with increasing its width (5.354 GHz for 4.7 width and 33 GHz for 6mm width).

Let us see how the input impedance of the octagonal antenna behaves when fed by different TL widths. Figure 7 shows the S11 of the monopole antenna fed by TL of different widths: 3, 4.7 and 6 mm. It is evident that the 3 mm wide TL gives the best performance and the widest bandwidth.



Figure 7. S11 with different TL widths

5.6 Optimizing the Angle of Departure (ѳ)

To get a smooth gradual transition from the feeding TL to the octagonal

antenna, the octagon departure angle (ѳ) should be optimized. Figure 8 shows the frequency response of an octagonal monopole antenna with optimized departure angle.

Figure 8. Octagonal monopole antenna with optimized departure angle

Ѳ


5.7 Changing the Ground Plane Shape

It has been found that a slope or curvature in the ground plane edge enhances the frequency coverage of the monopole printed antenna. Figure 9a shows an optimized octagonal monopole antenna with sloped ground boundary, while Figure 9b shows the simulated frequency response of the optimized antenna.

5.8 Changing the Distance between the Octagon and the Ground

Plane(S)

The distance (s) between the octagon and the ground plane edge is one of the design parameters to be optimized for best performance.

5.9 Using Slots

One of the most commonly used design techniques to increase the upper frequency limit of UWB antennas is to insert slots [19].The SWB antenna bandwidth can achieved by introducing slots in the ground plane and the radiating patch of the antenna [20].This is not required in this case because we have already fulfilled our goal without it.

6. Formulation of the Design Optimization Problem

The following is the canonical formulation of our optimization problem according to operation research rules.

Maximize fmax (a, b, w, ѳ, s), subject to

r = 2.17 t = 1.58 mm, where fmax= maximum frequency where S11 < -10 dB a = octagon width [mm] b = octagon height [mm] w = TL width [mm]

ѳ = departure angle [ ]

7 Design Simulation Results

Electromagnetic simulation with Zeland IE3D software was used to optimize the design. The main reason for choosing Zeland IE3D is that it is based on the method of moments (MOM) which suits planner structures very



well. In indoor applications the antenna is omnidirectional with multipath propagation.

Figure 9a. Optimized Octagonal Monopole Antenna with sloped ground boundary

Figure 9b. S11 of Optimized Octagonal Monopole Antenna with sloped ground

boundary

From these results, it can be observed that the bandwidth from 2.18:45GHz (the entire band below -10dB and continuing after 45GHz) has been achieved with the Octagonal SWB proposed antenna on the TLY-5 laminate. A good agreement is evident between experimental results and simulated ones as presented below.


8 Experimental Measurement Results

A sample of the optimized octagonal antenna has been implemented and measured. The dimensions of the proposed antenna substrate are 38mm × 38mm × 1.5mm (Figure 10) and the bandwidth is more than 42.82 GHz starting from 2.18 GHz to 45 GHz with return loss more than 10 dB (S11 < -10 dB) as shown in Figure 11.

Figure 11 shows the reading of the ROHDE & SCHWARZ ZAV-67 Vector Network Analyzer at the Electronics Research Institute in Cairo, Egypt as measured on September 19

th 2019. S11 is in dB and frequency in

GHz.

Figure 10. Photographs (radiating element and ground) of the TLY-5 Octagonal

SWB Monopole Antenna



Figure11. S11 of the Optimized Octagonal Monopole Antenna,

measured by the network analyser

9 Comparison of Results

A comparison between the proposed SWB antenna and other recently designed SWB antennas (references [4], [9] and [19]) is done in terms of shape, geometry, dimensions, bandwidth, ratio BW and percentage bandwidth. The comparison results are presented in Table1. It can be observed that the proposed antenna has the widest B.W. and heights B.W. %. The overall dimensions are comparable to or smaller than the other antennas. Moreover, it is simpler to design and easier to implement.

Table1. Comparison of the proposed antenna with other SWB antennas

Item

Proposed Antenna [4] [9] [19]

Geometry Shaped Octagonal Bevelled Circular Octagonal

Fmin : Fmax [GHz] 2.18 : 44.5 0.3 : 20 3 : 30 13.05 : 23.52

Bandwidth [GHz] 42.32 19.7 27 10.47

Ratio B.W. 20.4 : 1 66.6 : 1 10 : 1 1.8 : 1

Band width % 220% 194% 163% 58%

Dimensions [mm] 38*38 80*80 36*27 40*40


10 Conclusion

Different design parameters for a SWB planar octagonal antenna have been studied. A SWB planar monopole octagonal antenna has been designed and optimized for maximum frequency coverage. The return loss of a SWB antenna is > 10 dB between fmin and 20fmin. Our antenna covers the frequency range 2.1 GHz < f < 45 GHz and more where S11 < -10 dB. A sample of the optimized antenna has been implemented and measured.

References

[1] Mohamed A. Ahmed, Yong Cheol Kang, and Young-Chon Kim, “Communication Network Architectures for Smart-House with Renewable Energy Resources”, Energies, 8, pp. 8716-8735, 2015.

[2] D. Tran, P. Aubrey, A. Szilagyi and I.E. Lager “On the design of a super wideband antenna”, In Tech Publication, pp.399-426, 2011.

[3] Xiaobo Zhang, Saeed Ur Rahman. “A Novel SWB Antenna with Triple Band-Notches Based on Elliptical Slot and Rectangular Split Ring Resonators”, Research gate - electronics, vol.8, no.202, pp.1-17, 2019.

[4] Umair RAFIQUE, Sami UD DIN, “Beveled-shaped super-wideband planar antenna”,Turkish Journal of Electrical Engineering & Computer Sciences, vol.26, pp.2417-2425, (2018).

[5] Ben Allen, Mischa Dohler and Ernest E. Okon, “Ultra-Wide-Band Antennas and Propagation for Communications”, Radar and Imaging, John Wiley & Sons Ltd, pp.508, 2006.

[6] M Karlsson, S Gong, “Wideband patch antenna array for multi-band UWB”, Proc. IEEE 11th Symp. on Communications and Vehicular Tech., Ghent, Belgium, 2004.

[7] Z. N. Low, J. H. Cheong, and C. L. Law “Low cost PCB antenna for UWB application” Antennas Wireless Propagation .vol. 4, pp. 237-239, 2005.

[8] D. C. Chang, M. Y. Liu and C. H. Lin, “A CPW-fed U type monopole antenna for UWB Application,” IEEE AP-S Int. Symp. Dig., vol. 2A, pp. 512-515,2005.

[9] Devvrat Tyagi, Sachin Kumar, “A Low Profile Super Wideband Antenna with Circularly Polarized Band’’, International Conference on Computational Intelligence and Communication Technology, 2018.

[10]H. M. Bernety, B.Zakeri and R. Gholami, “Design of A Novel Directional Microstrip-fed Super-wideband Antenna’’, Modares Journal of Electrical Engineering, vol.11, no.3,pp.13-18, 2011.

[11] M. A. Peyrot-Solis, J. A. Tirado-Mendez, “Design of Multiband UWB



Planarized Monopole Using DMS Technique’’, IEEE Antennas And Wireless Propagation Letters, vol. 6, pp.77-79, 2007.

[12] Kin-Lu Wong, “Compact and Broadband Microstrip Antennas’’, Wiley, pp. 13, 2002.

[13] M.Y. Alhefnawy, Aladdin Assisi, “Design and Implementation of a Novel Planer UWB Monopole Antenna for Multipath Environments”, 13th International Conference on Aerospace Sciences &Aviation Technology, 2009,

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Monopol antenna For Multipath Environments’’, Journal of Al Azhar University Engineering Sector, 2009.

[15] Atser A. Roy, Joseph M. Môm and Douglas T. Kureve, “Effect of Dielectric Constant on the Design of Rectangular Microstrip Antenna’’, IEEE International Conference on Emerging & Sustainable Technologies for Power & ICT in a Developing Society (NIGERCON) , 2013.

[16] Md. MarufAhamed, Kishore Bhowmik and Md. Shahidulla, “Rectangular Microstrip Patch Antenna at 2 GHZ on Different Dielectric Constant forPervasive Wireless Communication’’, International Journal of Electrical and Computer Engineering (IJECE), Vol.2, No.3, pp. 417-424, June 2012.

[17] D. M. Pozar, “Microwave Engineering’’, J. Wiley & Sons, 1998. [18] Y. Rahayu, R. Ngah and T. A. Rahman, “Various Slotted UWB Antenna

Design’’, Sixth International Conference on Wireless and Mobile Communications, 2010.

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Biographies

Eng. Mohamed Yassin Elhefnawy was born in Cairo, Egypt in 1973. He received his B.Sc. degree in Electronics and computer science from Higher Technological Institute Ramadan Tenth City in 1997.He received his M.Sc. degrees in Electronics and Communication Eng. from the Faculty of Engineering, Al-Azhar University, Cairo, Egypt in 2009.he is currently pursuing his Ph.D. in Electronics and Communication Engineering from the Faculty of Engineering, Al-Azhar University, Cairo, Egypt . His main research interests are in the area of the planar UWB and SWB antennas and the Ph.D. research title is “Contribution to the improvement of the performance of UWB microwave antenna with application in modern communication” From his graduation He worked in the field of research and development electronics and communication projects, also and he has published papers in international journals and conference.

Dr Aladdin H. Assisi was born in 1947 in Egypt; He received his B. Sc. in Electrical Engineering, Radar Guidance systems from the Military Technical College, Cairo in 1970. He received his M. Sc. in Electronic Engineering, from the Military Technical College, M. T. C., Cairo in 1986.He received his PhD. in Electronices Engineering, from the Military. Technical College, Cairo in 1993. He is got Associate Professor in the Military Technical College since 1999.He worked as Technical Consultant of the Electronic Warfare Department in the Egyptian Armed Forces till 1998.He got the Head of Electronic Warfare Engineering Department in the Military Technical College in 2011 to 2013, Also, the Head of the Electrical Engineering Branch of the Egyptian Engineering Syndicate in 2012 to 2014.He published 22 papers in microwave and RF systems and electronic engineering.



Dr. Ibrahim Fathy Tarrad was born in 1959 in Egypt. He received his B.Sc. degree and M.Sc. degrees in Electronics and Communication Eng. from the Faculty of Engineering, Al-Azhar University, Cairo, Egypt in 1984 and 1989.He received his PhD from the Technical University of Budapest in 1996.In 1996 he has appointed as Lecturer at Department of Electronics Communication Engineering, Al-Azhar University.In 2015 He is got Associate Professor in communication Eng. at Faculty of Engineering, Al-Azhar University. His research activities are within Wireless Communication and digital communication.

Dr. Hosny Ahmed Ahmed Al-Motaafy was born in 1951 in Egypt. He received his B. Sc. in Electrical Engineering; Radar systems from the Military Technical College of Cairo (M. T. C.) in 1974.He received his M. Sc. in Electronic Engineering, from the Military Technical College, M. T. C., Cairo, Egypt in 1979.He received his Ph. D. in Electronic Engineering, from L'École Nationale Supérieure de l'Aéronautique et de l'Espace ("SUPAERO" or "ENSAE"), Université de soutenance: Université Paul Sabatier de Toulouse, France, 1982.He has got the degree of Associate Professor in Military Technical College in 11/1988.He is a professor in Electrical and communication Engineering in the Higher Technological Institute, Tenth of Ramadan City since 2001.His research activities are within the fields microwave devices, circuits, and systems.

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Modeling and Optimization of an Environmentally Safe UWB