Design of Printed Dipole Antenna with Reflector and ...

International Journal on Communications Antenna and Propagation (IRECAP), Vol. xx, n. x June 2010

Design of Printed Dipole Antenna with Reflector and Multi-Directors Jean-Marie Floc'h1, Ahmad El Sayed Ahmad1, Jean-Michel Denoual1, Hatem Rmili2

Abstract – A printed dipole Yagi antenna operating at 3 GHz is designed for wireless applications. The antenna was obtained from a simple printed dipole structure by adding a reflector and a number of directors. Intermediate structures were simulated optimized, realized and characterized experimentally by measuring their return losses and gain over the frequency bands 2-4 GHz and 2.5-3.3 GHz, respectively, and radiation patterns at 3 GHz. It is shown, that the gain of the antenna increases continually with the number of directors, with a good impedance matching at the resonant frequency and bandwidth. Keywords: Printed dipole antenna, gain enhancement, director, reflector, Yagi antenna.

I.

Introduction

Printed dipole antennas are very well stated in wireless communications due to their advantages such as low profile, small size, light weight, low cost, as well as their ease of fabrication and integration in solid-state devices, which make them very suitable for some broadband and multiband applications [1-5]. Among various types of printed dipole antenna, planar Yagi structures are attractive for wireless applications due to their high gain and directive property in addition to the common qualities of printed antennas [6-8]. By printing the driver and the directors on the top of the substrate, and the ground reflector on the bottom, we can obtain a printed dipole Yagi with better bandwidth characteristics. But the feeding technique is complicated and creates an unbalanced condition for the antenna operation [9]. To overcome this problem, we can print the microstrip line and one driver arm on the top of the substrate and a ground reflector with another driver arm at the bottom side of the substrate. The obtained bi-planar printed Yagi antenna may achieve a gain greater than 7 dBi and 10 % bandwidth at 2.45 GHz [10]. In this paper, we present a design procedure of a printed Yagi antenna operating at 3 GHz. First, we have studied an elementary dipole antenna which is composed of one dipole arm and a microstrip line printed on the top side of the substrate whereas the second arm and a small rectangular ground plane were printed on the other side. Next, a printed rectangular reflector was added and connected to the ground plane, for the increase the antenna gain and the improvement of the front-to-back ratio. Finally, multiple directors were added in order to obtain the printed Yagi dipole configuration. We have studied especially three structures composed of 1, 5 and 12 directors, respectively. It is shown that the antenna gain and directivity may be enhanced by increasing the number of directors. For the design and optimization of

Manuscript received and revised xx 2010, accepted xx 2010

antennas, we use HFSS CAD software from ANSOFT. All the designed antennas were simulated, realized and characterized by measuring their return loss, radiation patterns and gain at operating frequencies.

II.

Elementary Dipole

The geometry of the elementary dipole, as a part of the printed Yagi antenna dipole, is given in Fig. 1. The two arms of the dipole of length L and width W are printed on each side of a CuClad substrate of thickness 0.8 mm and permittivity 2.17. The first arm and a microstrip feedline of width W were printed on the top side of the substrate, and both the second arm and the ground plane were printed on the bottom side. The dimensions of the rectangular ground plane are L1×W1, and the distance separating the dipole from the ground plane is H. The Length L of these arms and the distance H+W1 between them and the connector are close to a quarterwavelength (λ0/4). λ0 is the wavelength in free space corresponding to resonant frequency 3 GHz. The design parameters are: W = 2.5 mm, W1 = 10 mm, H = 12 mm, L = 22 mm and L1 = 15 mm. The printed dipole has been simulated with AnsoftHFSS software, realized (Fig. 2) and characterized by measuring the return loss over the frequency band 2-4 GHz and the radiation patterns, in both E (xoz) and H (yoz) planes, at the resonant frequency 3 GHz. Fig. 3 presents both simulated and measured results of the antenna return loss. The antenna resonates at around 3 GHz (measurement) with a fractional impedance bandwidth of 15% (for S11 < - 10 dB). Fig. 4 and Fig. 5 illustrate simulated and measured radiation patterns. We can notice a good agreement between simulations and measurements. Moreover, the measured gain in the directions corresponding to θ = 0° and θ = 180° are 2.58 dBi and 0 dBi, respectively.

Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

Jean-Marie Floc'h, Ahmad El Sayed Ahmad, Jean-Michel Denoual, Hatem Rmili

Fig. 1. Geometry of the printed dipole antenna

Fig. 5. Measured radiation results

III. Elementary Dipole with Reflector In order to improve the gain of the printed dipole antenna in the front direction (θ = 0°), we add a rectangular reflector of length 2L2+W and width W2, by connecting it to the ground plane of the structure as it is shown in Fig. 6. The width of the ground plane was reduced by W2 = 6 mm. All previous design parameters, except W1, were unchanged (Fig. 6). These parameters are: W = 2.5 mm, W1 = 4 mm, W2 = 6 mm, H = 12 mm, L = 22 mm, L1 = 15 mm and L2 = 24 mm. The added reflector should be slightly longer than the total length 2L-W of the dipole in order to reflect the radiated power in the front direction (θ = 0°). In the case of a shorter reflector, the radiation is concentrated in the back direction (θ = 180°), and the added element acts as a simple director. A photo of the realized antenna is given in Fig. 7. The measured and simulated return loss characteristics of the antenna are shown in Fig. 8. One resonant band is observed at frequency 2.9 GHz (measurement) with bandwidth (VSWR ≤ 2) of 10%. The simulated and measured radiation patterns at the resonant frequency are presented in Fig. 9 and Fig. 10, respectively. By comparing the obtained results to those of the previous antenna without reflector (Fig. 3, Fig. 4 and Fig. 5), we can deduce that the addition of the reflector has reduced the antenna bandwidth, and deteriorated the impedance matching. In the other hand, the antenna directivity and gain were increased in both simulation and measurements. In measurement, for example, the antenna gain is equal to 5.4 dBi and -9 dBi in the front (θ = 0°) and back direction (θ = 180°), respectively. However, these values are 2.58 dBi and 0 dBi, in the front and back direction, respectively, for the elementary dipole without reflector. We note also a good agreement between simulated and experimental results for both return loss and radiation patterns.

Fig. 2. Photo of the printed dipole antenna 0

-5

Return loss, dB

-10

-15

-20

-25

Measurement Simulation

-30 2

2,5

3

3,5

4

Frequency, GHz

Fig. 3. Simulated and measured return loss

Fig. 4. Simulated radiation results Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved

Int. Journal on Communications Antenna and Propagation, Vol. x, N. x


Fig. 6. Geometry of the printed dipole antenna with reflector

Fig. 10. Measured radiation results

IV.

In order to increase more the antenna gain in the front direction (θ = 0°), we have added multi-elements on the bottom side of the substrate where one dipole arm; the reflector and the ground plane were printed. Each director element should be shorter than the length of the two dipole-arms for better concentration of the radiated power. In our simulations performed with CST Software, we have studied multi-elements Yagi antennas with respectively 1, 2, 3, 5, 8, 12, 20 and 32 directors. For the experimental study, we have realized 6 antenna prototypes with 0, 1, 3, 5, 8 and 12 directors, but in this paper, we present detailed results of only 3 structures corresponding to one-director, five-directors and twelvedirectors printed Yagi-antennas. We have used free software to calculate the different lengths of directors [11] and distances between them. For the presented three structures, simulated and measured results dealing with the impedance matching, radiation patterns and gain are given. A Photo of the realized antennas is given in Fig. 11.

Fig. 7. Photo of the printed dipole antenna with reflector 0

Return loss, dB

-5

-10

-15 Measurement Simulation

-20 2

2,5

3

3,5

Elementary Dipole with Reflector and Multi-Directors

4

Frequency, GHz Fig. 8. Simulated and measured return loss

Fig. 11. Multi-elements Yagi antennas with 0, 1, 3, 5, 8 and 12 directors

Fig. 9. Simulated radiation results Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved



IV.1. Structure with One Director

of the one-director Yagi antenna is shown in Fig. 13. One resonant band is observed around the frequency 2.9 GHz with a clear deterioration of the impedance matching due to the presence of the director. This intermediate result may be ameliorated easily by reducing the length L3 of the director, or by adding other directors. Fig. 14 presents simulated radiation patterns at 3 GHz in both E- and H-planes. The antenna gain of the dipole is now 6.5 dBi in the direction θ = 0° and -10.5 dBi in the direction θ = 180°, which means that the gain has been increased in the desired direction (θ = 0°) compared to the structure without director (5.4 dBi). The simulated HPBW are 70° and 120° in E- and H- planes, respectively.

The gain of the antenna in the front direction (θ = 0°), can be improved by adding, to the previous structure (Fig. 6), a rectangular microstrip line, of length L3 and width W, parallel to the main radiating dipole (Fig. 12), which acts as a director and contribute to the focalization of the radiated electromagnetic power in the desired direction. The director, which should be shorter than the elementary dipole (L3 < 2L-W), is located on the same side of the substrate where the ground plane and the reflector were printed. The design parameters of the antenna with one director (Fig. 12) are the same for the previous structure (Fig. 6), with two new parameters H1 = 15.5 mm, and L3 = 36 mm. L3 W H1 L W

H Z

L2 X

W2 W1

Fig. 14. Simulated radiation results

L1

IV.2. Structure with Five Directors

Fig. 12. Geometry of the printed dipole antenna with reflector and director

We have continued the design procedure in order to increase further the gain of the antenna in the direction (θ = 0°) by adding five directors to the structure shown in Fig. 6. The geometry of the obtained antenna is given in Fig. 15. The new design parameters are H2 = 15 mm, H3 = 14.5 mm, L4 = 35 mm and L5 = 34 mm. By placing the 5 directors, the antenna impedance matching was clearly improved as it is shown in Fig. 16 (measurement), where we can observe a resonant band around 3 GHz with 11% impedance bandwidth (for S11 < - 10 dB). We can also remark a good agreement between simulated and measured results. The simulated and measured 3D-radiation patterns are plotted in Fig. 17 and Fig. 18, respectively. From Fig. 17, we can notice an increase of the simulated gain, in the front direction (θ = 0°), of the 5-directors antenna (11.5 dBi) compared to the 1-director antenna (6.5 dBi).

0

Return loss, dB

-2

-4

-6

-8

-10

Measurement Simulation

-12 2

2,5

3

3,5

4

Frequency, GHz Fig. 13. Simulated and measured return loss

The simulated and measured return loss characteristics Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved



Z X H3

H3

H2

H2

H1

H L5

L5

L4

L4

L3

L1 L

L2

W1

W

W2

Fig. 15. Geometry of the dipole antenna with reflector and five directors

0

Return loss, dB

-5

-10

-15 Simulation measurements

-20 2,5

Fig. 18. Measured 3D radiation pattern of the antenna 3 3,5 Frequency, GHz


Fig. 17. Simulated 3D radiation pattern of the antenna


4

IV.3. Structure with Twelve Directors The measured return loss of the 12-directors antenna (Fig. 19) over the frequency band shows a resonant frequency around 3 GHz with a fractional bandwidth of 13%. We can notice some discrepancies between simulated and measured results in Fig. 20, which may be attributed to the relatively large size of the structure compared to the others with 1 or 5 directors. The obtained results of the 12-directors antenna gain are similar to those of 5-directors structure with a further increase in the front direction (θ = 0°), where the simulated gain attempt the value of 13.6 dBi (Fig. 21, 22). The new design parameters are H4 = 14 mm, H5 = 13.75 mm, H6 = 13.5 mm, H7 = 13 mm, L6 = 33.5 mm, L7 = 33 mm, L8 = 32.5 mm and L9 = 32 mm.



Z X H5

H6

H6

H7

L7

L8

L8

L9

H5

L6

L5

H4

H3

L5

L6

H3

L4

H4

H2

H2

H1

H L7

L4

L3

L1 L

L2

W1

W

W2

Fig. 19. Geometry of the dipole antenna with reflector and twelve directors 0

Return loss, dB

-5

-10

-15 Simulation measurements

Fig. 22. Measured 3D radiation pattern of the antenna

V.

-20 2

2,5

3

3,5

Frequency, GHz


Gain

4

We have measured the gain of the 4 antennas, obtained by increasing the number of directors in the Yagi-structure. The antennas correspond respectively to 1, 5, 8 and 12 directors. The gain was measured over the frequency band 2.5 – 3.3 GHz where all resonant bands are situated. The obtained results are given in Fig. 23. We can observe from this Figure that the gain increases clearly with the number of added directors.

Fig. 21. Simulated 3D radiation pattern of the antenna




Proceedings of the Microwave Conference, 2008. APMC 2008. Asia-Pacific. [7] Avila-Navarro E., Carrasco J.A., and Reig C.: "Desing of yagilike printed antennas for wlan applications", Microw. Opt. Technol. Lett., vol.49, no.9, pp. 2174-2178, 2007. [8] Noriaki Kaneda, W.R. Deal, Yongwi Qian, Rod Waterhouse, and Tatsuo Itho: "A Broad-Band Planar Quasi-Yagi Antenna", IEEE Transactions on Antennas and Propagation, vol.50, no.8, pp. 1158-1160, 2002. [9] Phillip R. Grajek, Bernhard Schoenlinner, and Gabriel M. Rebeiz: "A 24-GHz High-Gain Yagi–Uda Antenna Array", IEEE Transactions on Antennas and Propagation, vol.52, no.5, pp. 1257-1261, 2004. [10] Floc'h J.M., Queudet F., and Fourn E.: "Design of printed dipole with reflector", in Proceedings of the EuCAP 2007 Birmingham, United Kingdom. [11] Yagi Calculator by John Drew VK5DJ ([email protected]).

14 12

Gain, dBi

10 8 6 1 Director 5 Directors 8 Directors 12 Directors

4 2 0 2,4

2,6

2,8

3

3,2

3,4

Frequency, GHz

Fig. 23. Measured gain versus frequency of the antenna with 1, 5, 8 and 12 directors

VI.

Conclusion

In this paper, we have presented a design procedure for a printed Yagi dipole antenna operating at 3 GHz. First, we have realized the elementary dipole antenna with two arms printed on each side of the substrate. Then, we have added a reflector, which is connected to a small rectangular ground plane in order to focus the radiation in the front side (θ = 0°). Next, we have printed several directors (parallel to the dipole) in order to increase more and more the gain of the structure. It is shown, that the gain of the antenna increases by adding the reflector, and by increasing the number of directors. The impedance bandwidth of the studied prototypes is around 11%. This proposed structure, with easy method of fabrication, compact size, high gain and bandwidth can be a good candidate for wireless applications with array antennas.

References [1]

[2]

[3]

[4]

[5]

[6]

Chang K., Kim H., and Yoon Y.J.: "A triple-band printed dipole antenna using parasitic elements", Microw. Opt. Technol. Lett., vol.47, no.3, pp. 221–223, 2005. Chi Y.W., Wong K.L., and Su S.W.: "Broadband printed dipole antenna with a step-shaped feed gap for DTV signal reception", IEEE Transactions on Antennas and Propagation, vol.55, no.11, pp. 3353–3356, 2007. Floc'h J.M., and Rmili H.: "Design of multi-band printed dipole antennas using parasitic elements", Microw. Opt. Technol. Lett., vol.48, no.8, pp. 1639–1645, 2006. Khaleghi A.: "Dual Band Meander Line Antenna for Wireless LAN Communication", IEEE Transactions on Antennas and Propagation, vol.55, no.3, pp. 1004–1009, 2007. Samiha Mekerta: "Printed Dipole Antenna for Wireless Communications", International Journal on Communications Antenna and Propagation, vol.2, no.2, pp. 160–165, 2012. Dong-Zo Kim, Seo-Young Park, and Won-Seok Jeong: "A small and slim printed Yagi antenna for mobile applications", in




Authors’ information 1

IETR CNRS UMR 6164, 20 avenue des Buttes de Coesmes 35708 Rennes, France. 2 King Abdulaziz University Electrical and Computer Engineering Department P.O. Box 80204, Jeddah 21589, Saudi Arabia.

Jean Marie Floc'h was born in 1952 in Dinan in Brittany France. He made much of his studies at the University of Rennes 1. He received his Ph.D. in 1992. He currently holds a position as research engineer in IETR (Institut of Electronics and Telecommunication of Rennes). It is supported in the Institute the Industrial Relations and he is deputy director of the CCMO (Centre Commun de Microelectronique de l’Ouest). His research focuses on antennas, multiband, broadband, miniature, reconfigurable and associate microwave circuits.

Ahmad El Sayed Ahmad was born in Tripoli, Lebanon, in 1984. He received the M.S. degree in high frequency telecommunications from University of Limoges, France, in 2007. He received his Ph.D. degree in Telecommunications from the XLIM research laboratory, University of Limoges, France, in 2010. Since 2011, he has been a R&D engineer at the systems and communication networks department of the IETR research Laboratory, INSA of Rennes, France. His research interests include mutual couplings effects, broadband and multiband antennas, circular polarized antennas, printed dipole antennas and yagi antennas.

Jean Michel Denoual received his MS degree in Electronic in 2005 from the University of Brest in France. He works as PHD student in Spatial Power combining techniques at Telecom Bretagne in collaboration with TAS and the French space agency (CNES). From 2008 to 2010, he was a post doctoral researcher in UWB radar and planar antennas in Institut Supérieur d'électronique de Rennes. Since 2010, he works at TRW Automotive in Brest.

Hatem Rmili was born in Sakiet Sidi Youssef, Tunisia. He received the B.S. degree in general physics from the Science Faculty of Monastir, Tunisia in 1995, and the DEA diploma from the Science Faculty of Tunis, Tunisia, in quantum mechanic, in 1999. He received the Ph.D. degree in physics (electronics) from both the University of Tunis, Tunisia, and the University of Bordeaux 1, France, in 2004. From December 2004 to March, 2005, he was a research assistant in the PIOM laboratory at the University of Bordeaux 1. During March 2005 to March 2007, he was a Postdoctoral Fellow at the Rennes Institute of Electronics and Telecommunications, France. From March to September 2007, he was a Postdoctoral Fellow at the ESEO engineering school, Angers, France. From September 2007 to August 2012, he was an associate professor with the Mahdia Institute of Applied Science and Technology, department of Electronics and Telecommunications, Tunisia. Actually, he is with the Electrical and Computer Engineering Department, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia. His main research activities concern design of antennas for wireless applications.

