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Triple band-notched UWB CPW and microstrip line fed monopole antenna using broken ∩-shaped slot
Int. J. Electron. Commun. (AEÜ) 65 (2011) 734–741
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International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.de/aeue
Triple band-notched UWB CPW and microstrip line fed monopole antenna using broken ∩-shaped slot Parisa Lotfi a , Saber Soltani a,∗ , Mohammadnaghi Azarmanesh b a b
Young Researchers Club, Islamic Azad University, Urmia, Iran Microelectronics Research Laboratory, Urmia University, Urmia, Iran
a r t i c l e
i n f o
Article history: Received 21 January 2010 Accepted 6 November 2010 Keywords: Multiple band notches Monopole antenna UWB antenna
a b s t r a c t This paper describes a compact ultra-wideband CPW and microstrip line printed monopole antenna with multi band-rejection characteristics. The small antenna fed by CPW and microstrip line has small volume of 44 mm × 12 mm × 0.8 mm. By adding broken ∩-shaped slot on the tapered radiating patch, the antenna provides band-rejection characteristics. The center frequency of three notched bands centered on 2.4, 3.8, and 5.5 GHz can be adjusted by modifying the length and width of the inserted slot. Good agreement is achieved between the simulated and measured results. The measured impedance bandwidth of the proposed antenna ranges from 2.2 to 11.3 GHz for VSWR ≤ 2, excluding the rejection bands. The omnidirectional radiation patterns of the fabricated antenna are presented, which show that the designed antennas are good candidate for various UWB applications. The measured gain variation is less than 3 dB over the operating frequency band. © 2010 Elsevier GmbH. All rights reserved.
1. Introduction Monopole antennas have advantages of small size, ease of fabrication, low cost, and compatibility to the rest of the RF front ends. Therefore a lot of researchers have been attracted to the development of the monopole antennas. The Federal Communication Commission (FCC) has allocated 3.1–10.6 GHz for commercial ultra-wideband (UWB) communication systems [1]. Several planar UWB monopole antennas, which have the potential to meet such requirements, were reported in [2–5]. Due to the overlap of the currently allocated UWB frequency band with the communication systems such as: WLAN1 (2400–2484 MHz), WLAN2 (5.2 GHz (5150–5350 MHz) and 5.8 GHz (5725–5825 MHz)), WiMAX (3400–3690 MHz) and C-band (3.7–4.2 GHz). Therefore, it is necessary for UWB antennas performing band-notched function in those frequency bands to avoid interferences. Generally, there are few ways for monopole planar antennas to achieve band-notched characteristics. One way is cutting a proper slot (such as a U-shaped slot [6,7], an arc-shaped slot [8], a V-shaped slot [9], square-slot [10], defected ground structure (DGS) [11], a bent slot or C-shaped slot [12]). Putting parasitic elements near or rear the printed monopole [13,14], C-shaped attachment element in patch [15], are acting as filter to reject a sub-band. By using
∗ Corresponding author. Tel.: +98 441 3452807; fax: +98 441 3452807. E-mail addresses: ps.lotfi@gmail.com (P. Lotfi), st [email protected] (S. Soltani), [email protected] (M. Azarmanesh). 1434-8411/$ – see front matter © 2010 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2010.11.001
simple open-end slits, which are usually quarter-wave-length long, frequency notches can also be obtained [16]. An advanced antenna design with steep fall-off rate and sufficient bandwidth at the rejection band has been demonstrated in [17]. However, these methods have some weakness that the notch frequency cannot be easily adjusted after fabrication. Recently, the use of rectangular resonant slot and inserting quarter-wavelength stubs with varactor diodes has been proposed in [18,19], respectively. However, all of these monopole antennas mentioned above have concerned no more than one notched band. A triple frequencynotched antenna is obtained in [20], but the performance of the notches deteriorates at the same time. In [21], instead of integrating the band notched element with the radiating element, half mode substrate integrated waveguide cavity is used to create multiple stop-bands. By combining two methods, inserting split ring slots and two arc slots or special feed line coupled by SRRs and split ring slot or cascading several pairs of SRRs to the monopole antenna, triple notched frequency bands are achieved in [22,23]. Then, researchers changed the conventional SRR structure to reverse split rings into the two sets of the co-directional square split rings [24]. Although the antenna in [25–27] can perform two or three notched bands using three kinds of slots in the interior of the radiating element, it only covers a frequency band from 2 to 6.5 GHz. Moreover, it has been designed on a non-planar configuration with large size that could not meet the demand of integrating with planar printed circuits nowadays. In [27–34], multiple bandnotch characteristic is obtained by hybrid method. UWB monopole antenna with single or dual band-notches for lower WLAN band and upper WLAN band is presented in [35]. Recently, in [36] triple
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generate a stronger resonance than any other shape due to the current distribution concentration at the edge of the patch. Furthermore, in our antenna due to patch shape restriction, we cannot change position of slots. The etched slots would resonate in certain frequencies upon which the antenna performs band-notched characteristics. Details of design to generate triple notched bands with central frequency of 2.4 and 3.8, and 5.5 GHz will be studied in this section.
Fig. 1. Schematic diagram of CPW-fed monopole antenna.
notched bands are obtained by using a -shaped slot in the radiating patch, a semi-octagon-shaped resonator on the backed side, and a defected grounded structure. However, it is difficult to create multiple frequency notches in all of the antennas shown above. In this paper, we present a simple novel planar UWB monopole antenna with multiple notched bands using CPW and microstrip line. Three band interferences are considered to be notched, frequency bands centered on 2.4, 3.8, and 5.5 GHz. The proposed antenna has three broken ∩-shaped slots etched on the patch to generate multiple notched bands. Note that using these inverted U-shaped slots instead of three split ring resonator presented in [22] decreases the area to be occupied by slots on the patch. Unlike [27–34], in our antenna, multiple band-notch characteristic is obtained by one simple method. The antenna with triple notched bands is fabricated and experimentally verified. Good agreement is achieved between the measured data and simulated results which are obtained using HFSS v10 (method of finite-element by Ansoft). The configuration of the CPW-fed antenna is firstly introduced in Section 2. The proposed antenna were fabricated and measured, and the corresponding measured results are shown in Section 3. Radiation patterns and gain are also presented in that section. The guideline and results of the microstrip line fed antenna are presented in Section 4. The conclusion is made in Section 5.
2.1.1. The effect of variation of the ground plane length Lg Fig. 2(a) gives the simulated VSWR of the antenna as a function of frequency for different values of length Lg of the two symmetric ground planes. From Fig. 2, one can find that a greater Lg has more significant effects on the bandwidth of the proposed antenna. This is due to the capacitive and inductive effects caused from the electromagnetic coupling effects between the patch and ground planes. Therefore, that region plays an important role in impedance matching. From the simulation results in Fig. 2(a), it is observed that the impedance bandwidth at the upper operating frequency increases as Lg increases. In turn, additional resonances occur at 8 GHz, while the lower operating frequency remains almost unchanged. The size of the ground plane is an important parameter of the E-plane radiation pattern. Fig. 2(b) shows that the changes of Lg have significant effect on the co-pol/cross-pol ratio at normalized E-plane radiation patterns at 4 GHz. At the other frequencies over the bandwidth, increase in Lg has positive effect on the reduction of cross-pol level at normalized E-plane radiation patterns, but co-polar is almost fixed. In the H-plane, co-pol/cross-pol ratio is insensitive to changes in Lg . When the size of the ground plane is increased to a certain value (20.3 mm × 2 mm), optimum radiation patterns can be obtained. However, if the size of the ground
2. Antenna design The proposed UWB monopole antenna geometry with a 50 CPW-fed, having a fixed signal strip thickness Wf = 2.8 mm and gap of distance g = 0.3 mm between the signal strip and the finite coplanar rectangular ground plane is depicted in Fig. 1. The feed of antenna that fabricated on a FR4 epoxy substrate with thickness of 0.8 mm and relative permittivity εr of 4.4 and loss tangent of (around 0.02) is designed using standard design equations [37]. The use of low-cost FR4 as substrate introduces some additional complexity on the antenna design. This additional complexity is due to the inaccuracy of the FR4 relative permittivity and its high loss tangent. Variations in the FR4 electrical permittivity can shift the operating frequency. The antenna consists of a tapered-shape patch. Nevertheless, the slot’s width and first slot’s (L1 ) distance from patch edge and distance between slots are set to 0.5 mm due to the manufacturing tolerance. It is known that the equivalent L–C components of slots give rise to form a band rejection characteristic. 2.1. Parametric analyze A parametric study of the proposed monopole antenna was carried out in order to achieve UWB and band rejection operation. To decrease the complexity of the design, some of antenna parameters are fixed as shown in Fig. 1. To achieve band-notched characteristics, broken ∩-shaped slots have been etched on UWB antenna patch. Through full-wave EM simulation, we have found that, in particular, a slot with the similar shape of the antenna patch can
Fig. 2. Variations of Lg with fixed other optimized dimensions of the UWB CPW-fed antenna (L1 = L2 = L3 = 0 mm): (a) VSWR; (b) normalized E-plane radiation patterns at 4 GHz.
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Fig. 3. Relations between the VSWR and variations of L1 with fixed other optimized dimensions of the UWB CPW-fed antenna (L2 = L3 = 0 mm). Fig. 4. Relations between the VSWR and variations of L2 with fixed other optimized dimensions of the UWB CPW-fed antenna (L1 = 39.7 mm, L3 = 0 mm).
plane is further increased, the radiation patterns start deteriorating. Moreover, the ground plane affects the operating bandwidth of the proposed antenna. A larger ground plane deteriorates operating bandwidth. 2.1.2. The effect of first slot length (L1 ) to generate band notched in WLAN1 of 2.4 GHz Fig. 3 shows simulated VSWR characteristics with the optimum values of other dimensions and L2 = L3 = (0 mm) for different values of L1 . As the length L1 increases from 25.3 to 39.7 mm, the center frequency of notched band is varied from 3.6 to 2.5 GHz. It can be seen that the bandwidth of notch remains almost fixed and the notch intensity varies between 3.5 GHz and 5.5 GHz. From this result, one can conclude that the intensity and frequency of notched band is controllable by changing length L1 . It is also seen that by increasing L1 , the total electrical length of the antenna is increased and hence the lowest frequency of the antenna is markedly decreased from 3 to 2.2 GHz. The relation between central notched frequencies and Lnotch1 can be expressed approximately based on the results of Fig. 3 as follows: Lnotch1 (mm) = (0.09(L1 − 24)2 − 0.61(L1 − 24) − 4.7) + 24 c = d = √ 2 2fnotch εr
(1)
where d is the dielectric wave length, fnotch is the center of the undesired band base as shown in Fig. 3, c is the speed of light in free space, and εr is the dielectric constant.
where d is the dielectric wave length, fnotch is the center of the undesired band base as shown in Fig. 4, c is the speed of light in free space, and εr is the dielectric constant. 2.1.4. The effect of third slot length (L3 ) to generate band notched in WLAN2 of 5.5 GHz The simulated VSWR curve with different values of L3 is plotted in Fig. 5. As the L3 increases from 12 to 15.2 mm with other fixed dimensions and L1 = (39.7 mm), L2 = (28.9 mm), the center frequency of notched band varies from 5.2 GHz to 5.8 GHz. Of course this variation is very regular. It can be seen that bandwidth of notch remains almost fixed. On the other hand, the filtering frequency of notch at 3.8 GHz and bandwidth of notch at 2.4 GHz is insensitive to the changes of L3 . The relation between central notched frequencies and Lnotch3 can be expressed approximately based on results of Fig. 5 as follows: Lnotch3 (mm) = (−0.1(L3 − 14)2 + 0.36(L3 − 14) − 0.55) + 14 =
d c = √ 2 2fnotch εr
(3)
where d is the dielectric wave length, fnotch is the center of the undesired band base as shown in Fig. 5, c is the speed of light in free space, and εr is the dielectric constant. Table 1 shows comparison data between central notched frequencies in Figs. 3–5 and Eq. (1–3). Good agreement is achieved between these data. The optimized dimensions of antenna using parametric analysis and designer’s experience for antenna can be summarized as follows: Lg = 20.3 mm, L1 = 39.7 mm, L2 = 28.9 mm, L3 = 13 mm.
2.1.3. The effect of second slot length (L2 ) to generate band notched in WiMAX of 3.5 GHz and C band Fig. 4 indicates the simulated VSWR results for proposed antenna in terms of length L2 . For L2 = 21, 24.4 and 28.9 mm with other fixed dimensions and L1 = (39.7 mm), L3 = (0 mm), the notch frequencies decrease from 4.2 to 3.5 GHz. It can be seen that tuning the length L2 has significant effects on shifting notch frequency. Of course this variation is very regular. It can be seen that intensity of filtering frequency and bandwidth of notch remains almost fixed. On the other hand, the filtering frequency and bandwidth of notch at 2.4 GHz is insensitive to the change of L2 . The relation between central notched frequencies and Lnotch2 can be expressed approximately based on results of Fig. 4 as follows: Lnotch2 (mm) = (−0.02(L2 − 20)2 + 0.64(L2 − 20) − 3.62) + 20 =
d c = √ 2 2fnotch εr
(2)
Fig. 5. Relations between the VSWR and variations of L3 with fixed other optimized dimensions of the UWB CPW-fed antenna (L1 = 39.7 mm, L2 = 28.9 mm).
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Table 1 Center frequency of rejection band. L1
L2
L3
fnotch (Fig. 3)
fnotch (Eq. (1))
Lnotch (Fig. 3)
Lnotch (Eq. (1))
39.7 32.5 25.3
0 0 0
0 0 0
2.41 3.0 3.6
2.4137 3.0046 3.6055
29.626 23.8 19.8333
29.6166 23.7970 19.8333
L1
L2
L3
fnotch (Fig. 4)
fnotch (Eq. (2))
Lnotch (Fig. 4)
Lnotch (Eq. (2))
39.7 39.7 39.7
21.0 24.4 28.9
0 0 0
4.2 3.8 3.5
4.2065 3.8058 3.5054
17.0 18.7895 20.4
17.1 18.7898 20.4013
L1
L2
L3
fnotch (Fig. 5)
fnotch (Eq. (3))
Lnotch (Fig. 5)
Lnotch (Eq. (3))
39.7 39.7 39.7
28.9 28.9 28.9
12 13 15.2
5.8 5.5 5.2
5.8089 5.5084 5.2080
12.3103 12.9818 13.7308
12.3102 12.9818 13.7307
3. Results and discussion 3.1. Impedance bandwidth The dimensions of CPW-fed monopole antenna geometry parameters used in measurement are based on optimized dimensions using parametric analysis in Section 2. Fig. 6 shows the measurement, simulation frequency response of the voltage standing wave ratio (VSWR) and return loss for the proposed CPW-fed monopole antenna. The VSWR and return loss was measured by an Agilent 8722ES network analyzer. The measured impedance bandwidth (VSWR < 2) is about 9.4 GHz starting from 1.9 GHz to 11.3 GHz including the notched bands of the IEEE 802.11a in the US and the HIPERLAN/2 in Europe and WiMAX and C-band and WLAN1 . It can be seen that measured notched frequencies and bandwidths for each of the notches are very suitable to suppress the disturbances from WLAN and WiMAX systems. Very low VSWR is observed in the measurement between notches. Comparison between simulated results and the measured results show reasonable agreement at lower frequencies. This may be due to little differences of the FR4 substrate between the practical and simulated models. In addition, the dielectric constant and dissipation factor are not stable when the frequency increases.
normalized E and H planes radiation patterns and simulated current distribution at the three resonance frequencies at 3.2, 4.5, 6.2, and 10.2 GHz and three center stop-band frequencies at 2.4, 3.8, and 5.5 GHz for two state with and without slots in Fig. 7(a)–(g). The gain and radiation patterns were measured using the ETS 3115 system. Errors in the measured bandwidth, radiation pattern, and antenna peak gain can be expected owing to the feed cable placed in the near field of the antenna. The co and cross-polarized components of the field are different in the x–z (H plane) and y–z (E plane) planes. In the H plane, the co-polarized component is EФ , the cross-polarized component is E . It is the contrary in the E plane. The radiation characteristics for the proposed antenna in the two principal planes, E plane and H plane at the pass-band frequencies are dipole-like patterns and are about the same due to the same current distribution at two states as shown in Fig. 7(b, d, f, and g). In the case of the stop-band frequency as shown in Fig. 7(a, c, and e), comparison between states with and without slots show that cross-polar level is increased and dipole like pattern is eliminated. The reason of these phenomena is that high density of surface current around the broken ∩-shaped slots of L1 , L2 , and L3 was observed at 2.4, 3.8, 5.5 GHz, which implies that the slots resonate near center frequency of WLAN1, WiMAX, C, and WLAN2 bands, respectively. 4. Microstrip-fed monopole antenna design
3.2. Radiation pattern and gain results For complete study of far field performance of proposed antenna, from return loss results in Fig. 6, we present measured
Fig. 6. Measured and simulated VSWR and return loss of the triple band-notched CPW-fed monopole antenna.
The microstrip-fed antenna module is derived from the CPW-fed antenna configuration by transferring the feeding network from CPW to microstrip line, as seen in Fig. 8. We have chosen a 50 impedance line to feed the tapered patch, whereas the rest of the dimensions are kept the same as for the CPW-fed model as presented in Section 2. The monopole antenna using a mictrostip line termination not only has similar ultra-wideband with multi band-rejection characteristics compared to the CPW-fed antenna, but also the two metallization layers used are very easy to construct in single or multi-substrate PCB boards, therefore making this antenna structure suitable for direct integration with UWB circuitry. Fig. 9 shows the measured and simulated VSWR results for the fabricated band-notched microstrip-fed monopole antenna and excellent agreement between them is observed. It can be seen that measured notched frequencies and bandwidths for each of the notches has very suitable to suppress the disturbances from WLAN and WiMAX systems. Very low VSWR is observed in the measurement between notches. Fig. 10 shows the measured gain and simulated radiation efficiencies for proposed antenna fed by CPW and microstrip line from 2 to 11 GHz. The figure indicates that the realized triple bandnotched antenna has good gain flatness except in three notched bands. As desired, three sharp gains decrease in the vicinity of
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Fig. 7. Simulated results of the surface current distributions and measured radiation patterns for the antenna at (a) 2.4 GHz; (b) 3.2 GHz; (c) 3.8 GHz; (d) 4.5 GHz; (e) 5.5 GHz; (f) 6.2 GHz; and (g) 10.2 GHz.
2.4, 3.8 and 5.5 GHz. This figure shows that the antenna gain values of the proposed antenna with only three slots (without triple band-notch) are similar to those without them (simple monopole). Therefore, these slots will not have negative effect on the radiation performance of the antenna, in UWB band. On the other hand, the simulated radiation efficiencies of the proposed triple band-
notched antenna, at 2.4, 3.8 and 5.5 GHz, are only about 48, 35 and 57%, respectively. We see again that the radiation efficiency plots of the antenna with and without triple stop-bands structures are similar to each other, except at the notch frequencies. From the measured VSWR and simulated surface current distribution, measured gain and radiation pattern and simulated radiation effi-
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Fig. 7. (Continued. )
Fig. 8. Schematic diagram of microstrip-fed monopole antenna.
Fig. 9. Measured and simulated VSWR of the triple band-notched microstrip-fed monopole antenna.
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Fig. 10. Simulated radiation efficiency and measured gains values of the proposed triple band-notched UWB CPW and microstrip-fed monopole antenna monopole antenna.
Fig. 11. Photograph of the fabricated antennas. Top view: Right, CPW-fed monopole antenna; Left, microstrip-fed monopole antenna.
ciencies for proposed antenna, we conclude that the slots structure can help resonate at three given frequencies which play a role as band-notched filters. The photograph of the proposed antenna fed by CPW and microstrip line printed on FR4 substrate is shown in Fig. 11. Standard photolithography was used for the fabrication. 5. Conclusion A compact ultra wideband monopole antenna fed by CPW and microstrip line with triple band-rejection characteristics are presented and discussed. A simple triple band rejection structure using broken ∩-slot is presented. By transforming the CPW feed to microstrip, the bandwidth and radiation characteristics are preserved. We achieved a reduction in size compared to the antennas presented in [20–36]. The effects of the various geometrical parameters on the antenna performance are studied. The experimental results show that the realized antenna with a very compact size and relatively good radiation characteristics has a wide bandwidth from 1.9 to 11.3 GHz with triple controllable notched bands centered at 2.4, 3.8 and 5.5 GHz. Acknowledgments The authors would like to thank the reviewers for their professional comments and suggestion. They also are thankful to Young Researchers Club of Islamic Urmia Azad University and Urmia University for their financial support. They are also grateful to the Lab. of Millimeter Waves of Iran Telecommunication Research Center (ITRC) for providing the testing equipment. References [1] Federal Communications Commission Revision of Part 15 of the Commission’s Rules Regarding Ultra-Wideband Transmission System from 3.1 to 10.6 GHz. In: FEDERAL Communications Commission. Washington, DC: ET-Docket, FCC; 2002. p. 98–153.
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P. Lotfi et al. / Int. J. Electron. Commun. (AEÜ) 65 (2011) 734–741 [25] Kim DZ, Yu JW. Wide-band planar monopole antenna with triple band-notched slots. J Electromagn Waves Appl 2009;23:117–28. [26] Lee WS, Kim DZ, Kim KJ, Yu JW. Wideband planar monopole antennas with dual band-notched characteristics. IEEE Trans Microw Theory Tech 2006;54:2800–6. [27] Lee WS, Lim WG, Yu JW. Multiple band-notched planar monopole antenna for multiband wireless system. IEEE Microw Wireless Compon Lett 2005;15:576–8. [28] Zhou H-J, Sun B-H, Liu Q-Zh, Deng J-Y. Implementation and investigation of U-shaped aperture UWB antenna with dual band-notched characteristics. Electron Lett 2008;44:576–8. [29] Yin K, Xu JP. Compact ultra-wideband antenna with dual bandstop characteristic. Electron Lett 2008;44:453–4. [30] Deng JY, Yin YZ, Zhou SG, Liu QZ. Compact ultra-wideband antennawith triband notched characteristic. Electron Lett 2008;44:1231–3. [31] Lee HJ, Jang YH, Kim JP, Choi JH. Wideband monopole antenna with WLAN (2.4 GHz/5 GHz) dual band-stop function. Microw Opt Technol Lett 2008;50:1646–9. [32] Bi DH, Yu ZY, Mo SG, Yin XC. Two ultra-wideband antennas with 3.4/5.5 GHz dual-band notched characteristics. Microw Opt Technol Lett 2009;51:2942–5. [33] Niu SF, Gao GP, Li M, Hu YS, Li BN. Design of a novel compact elliptical monopole ultra-wideband antenna with dual band-notched function. Microw Opt Technol Lett 2010;52:1306–10. [34] Zhang M, Zhou X, Guo J, Yin W. A novel ultrawideband planar antenna with dual band-notched performance. Microw Opt Technol Lett 2010;52:90–2. [35] Ryu KS, Kishk AA. UWB monopole antenna with single or dual band-notches for lower WLAN band and upper WLAN band. IEEE Trans Antennas Propag 2009;57:3942–50. [36] Li WT, Shi XW, Hei YQ. Novel planar UWB monopole antenna with triple bandnotched characteristics. IEEE Antennas Wireless Propag Lett 2009;8:1094–8. [37] Garg P, Bhartia P, Bahl I. Microstrip antenna design hand book. 1st ed. House; 2001. p. 794–5. Parisa Lotfy was born in Urmia, Iran, in May 1984. She received the B.S. degree in Electrical Engineering from the Urmia Azad University, in 2008. She is currently working toward the B. S degree in mathematics and M.S. degree in Electrical Engineering in Urmia University. She is a member of Iranian Society of Electrical Engineers. Her current research interests are in antenna design, numerical methods in electromagnetic.
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Saber Soltani was born in Urmia, Iran, in March 1983. He received the B.S. degree in Electrical and Telecommunication Engineering from the Urmia Azad University, in 2006 and M.Sc. degree in Electrical and Telecommunication Engineering from Urmia University, Urmia, Iran, in 2008. He is currently working toward Ph.D. degrees in Microelectronics Research Laboratory, Urmia University, Urmia, Iran. He is a member of Iranian Society of Electrical Engineers and young researcher club of Urmia Azad University. He is the author or coauthor of several refereed journal articles and conference papers. His research interests include antenna miniaturization, optimization method, monopole antennas, slot antennas, hybrid antennas, circular polarization antennas, diversity antennas, mobile phone and wireless local-area network antennas, and their antenna applications. Mohammad Naghi Azarmanesh, was born in Tabriz, Iran, in 1950. He received the B.S. degree in physics from Tabriz University, Iran, in 1973, the M.S. degree in electrical engineering from the University of Paris VI in 1976, and Ph.D. degree in electrical engineering from Poly technique De Toulouse, France. In 1979 he joined Applied Physics Department in Urmia University, where he worked effectively in founding Electrical Engineering Department in 1983. In 1998 he worked with three other colleagues in developing Microelectronics Research Center in Urmia University. He is currently the head of Microelectronics Research Center. Dr. Azarmanesh is a member of Iranian Society of Electrical Engineers and member of IEEE, Institute of Electronics, Information and Communication Engineers (IEICE) of Japan. He has published a book, Electromagnetic Field Theory (Urmia: Urmia University, 1996).
Contents lists available at ScienceDirect
International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.de/aeue
Triple band-notched UWB CPW and microstrip line fed monopole antenna using broken ∩-shaped slot Parisa Lotfi a , Saber Soltani a,∗ , Mohammadnaghi Azarmanesh b a b
Young Researchers Club, Islamic Azad University, Urmia, Iran Microelectronics Research Laboratory, Urmia University, Urmia, Iran
a r t i c l e
i n f o
Article history: Received 21 January 2010 Accepted 6 November 2010 Keywords: Multiple band notches Monopole antenna UWB antenna
a b s t r a c t This paper describes a compact ultra-wideband CPW and microstrip line printed monopole antenna with multi band-rejection characteristics. The small antenna fed by CPW and microstrip line has small volume of 44 mm × 12 mm × 0.8 mm. By adding broken ∩-shaped slot on the tapered radiating patch, the antenna provides band-rejection characteristics. The center frequency of three notched bands centered on 2.4, 3.8, and 5.5 GHz can be adjusted by modifying the length and width of the inserted slot. Good agreement is achieved between the simulated and measured results. The measured impedance bandwidth of the proposed antenna ranges from 2.2 to 11.3 GHz for VSWR ≤ 2, excluding the rejection bands. The omnidirectional radiation patterns of the fabricated antenna are presented, which show that the designed antennas are good candidate for various UWB applications. The measured gain variation is less than 3 dB over the operating frequency band. © 2010 Elsevier GmbH. All rights reserved.
1. Introduction Monopole antennas have advantages of small size, ease of fabrication, low cost, and compatibility to the rest of the RF front ends. Therefore a lot of researchers have been attracted to the development of the monopole antennas. The Federal Communication Commission (FCC) has allocated 3.1–10.6 GHz for commercial ultra-wideband (UWB) communication systems [1]. Several planar UWB monopole antennas, which have the potential to meet such requirements, were reported in [2–5]. Due to the overlap of the currently allocated UWB frequency band with the communication systems such as: WLAN1 (2400–2484 MHz), WLAN2 (5.2 GHz (5150–5350 MHz) and 5.8 GHz (5725–5825 MHz)), WiMAX (3400–3690 MHz) and C-band (3.7–4.2 GHz). Therefore, it is necessary for UWB antennas performing band-notched function in those frequency bands to avoid interferences. Generally, there are few ways for monopole planar antennas to achieve band-notched characteristics. One way is cutting a proper slot (such as a U-shaped slot [6,7], an arc-shaped slot [8], a V-shaped slot [9], square-slot [10], defected ground structure (DGS) [11], a bent slot or C-shaped slot [12]). Putting parasitic elements near or rear the printed monopole [13,14], C-shaped attachment element in patch [15], are acting as filter to reject a sub-band. By using
∗ Corresponding author. Tel.: +98 441 3452807; fax: +98 441 3452807. E-mail addresses: ps.lotfi@gmail.com (P. Lotfi), st [email protected] (S. Soltani), [email protected] (M. Azarmanesh). 1434-8411/$ – see front matter © 2010 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2010.11.001
simple open-end slits, which are usually quarter-wave-length long, frequency notches can also be obtained [16]. An advanced antenna design with steep fall-off rate and sufficient bandwidth at the rejection band has been demonstrated in [17]. However, these methods have some weakness that the notch frequency cannot be easily adjusted after fabrication. Recently, the use of rectangular resonant slot and inserting quarter-wavelength stubs with varactor diodes has been proposed in [18,19], respectively. However, all of these monopole antennas mentioned above have concerned no more than one notched band. A triple frequencynotched antenna is obtained in [20], but the performance of the notches deteriorates at the same time. In [21], instead of integrating the band notched element with the radiating element, half mode substrate integrated waveguide cavity is used to create multiple stop-bands. By combining two methods, inserting split ring slots and two arc slots or special feed line coupled by SRRs and split ring slot or cascading several pairs of SRRs to the monopole antenna, triple notched frequency bands are achieved in [22,23]. Then, researchers changed the conventional SRR structure to reverse split rings into the two sets of the co-directional square split rings [24]. Although the antenna in [25–27] can perform two or three notched bands using three kinds of slots in the interior of the radiating element, it only covers a frequency band from 2 to 6.5 GHz. Moreover, it has been designed on a non-planar configuration with large size that could not meet the demand of integrating with planar printed circuits nowadays. In [27–34], multiple bandnotch characteristic is obtained by hybrid method. UWB monopole antenna with single or dual band-notches for lower WLAN band and upper WLAN band is presented in [35]. Recently, in [36] triple
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generate a stronger resonance than any other shape due to the current distribution concentration at the edge of the patch. Furthermore, in our antenna due to patch shape restriction, we cannot change position of slots. The etched slots would resonate in certain frequencies upon which the antenna performs band-notched characteristics. Details of design to generate triple notched bands with central frequency of 2.4 and 3.8, and 5.5 GHz will be studied in this section.
Fig. 1. Schematic diagram of CPW-fed monopole antenna.
notched bands are obtained by using a -shaped slot in the radiating patch, a semi-octagon-shaped resonator on the backed side, and a defected grounded structure. However, it is difficult to create multiple frequency notches in all of the antennas shown above. In this paper, we present a simple novel planar UWB monopole antenna with multiple notched bands using CPW and microstrip line. Three band interferences are considered to be notched, frequency bands centered on 2.4, 3.8, and 5.5 GHz. The proposed antenna has three broken ∩-shaped slots etched on the patch to generate multiple notched bands. Note that using these inverted U-shaped slots instead of three split ring resonator presented in [22] decreases the area to be occupied by slots on the patch. Unlike [27–34], in our antenna, multiple band-notch characteristic is obtained by one simple method. The antenna with triple notched bands is fabricated and experimentally verified. Good agreement is achieved between the measured data and simulated results which are obtained using HFSS v10 (method of finite-element by Ansoft). The configuration of the CPW-fed antenna is firstly introduced in Section 2. The proposed antenna were fabricated and measured, and the corresponding measured results are shown in Section 3. Radiation patterns and gain are also presented in that section. The guideline and results of the microstrip line fed antenna are presented in Section 4. The conclusion is made in Section 5.
2.1.1. The effect of variation of the ground plane length Lg Fig. 2(a) gives the simulated VSWR of the antenna as a function of frequency for different values of length Lg of the two symmetric ground planes. From Fig. 2, one can find that a greater Lg has more significant effects on the bandwidth of the proposed antenna. This is due to the capacitive and inductive effects caused from the electromagnetic coupling effects between the patch and ground planes. Therefore, that region plays an important role in impedance matching. From the simulation results in Fig. 2(a), it is observed that the impedance bandwidth at the upper operating frequency increases as Lg increases. In turn, additional resonances occur at 8 GHz, while the lower operating frequency remains almost unchanged. The size of the ground plane is an important parameter of the E-plane radiation pattern. Fig. 2(b) shows that the changes of Lg have significant effect on the co-pol/cross-pol ratio at normalized E-plane radiation patterns at 4 GHz. At the other frequencies over the bandwidth, increase in Lg has positive effect on the reduction of cross-pol level at normalized E-plane radiation patterns, but co-polar is almost fixed. In the H-plane, co-pol/cross-pol ratio is insensitive to changes in Lg . When the size of the ground plane is increased to a certain value (20.3 mm × 2 mm), optimum radiation patterns can be obtained. However, if the size of the ground
2. Antenna design The proposed UWB monopole antenna geometry with a 50 CPW-fed, having a fixed signal strip thickness Wf = 2.8 mm and gap of distance g = 0.3 mm between the signal strip and the finite coplanar rectangular ground plane is depicted in Fig. 1. The feed of antenna that fabricated on a FR4 epoxy substrate with thickness of 0.8 mm and relative permittivity εr of 4.4 and loss tangent of (around 0.02) is designed using standard design equations [37]. The use of low-cost FR4 as substrate introduces some additional complexity on the antenna design. This additional complexity is due to the inaccuracy of the FR4 relative permittivity and its high loss tangent. Variations in the FR4 electrical permittivity can shift the operating frequency. The antenna consists of a tapered-shape patch. Nevertheless, the slot’s width and first slot’s (L1 ) distance from patch edge and distance between slots are set to 0.5 mm due to the manufacturing tolerance. It is known that the equivalent L–C components of slots give rise to form a band rejection characteristic. 2.1. Parametric analyze A parametric study of the proposed monopole antenna was carried out in order to achieve UWB and band rejection operation. To decrease the complexity of the design, some of antenna parameters are fixed as shown in Fig. 1. To achieve band-notched characteristics, broken ∩-shaped slots have been etched on UWB antenna patch. Through full-wave EM simulation, we have found that, in particular, a slot with the similar shape of the antenna patch can
Fig. 2. Variations of Lg with fixed other optimized dimensions of the UWB CPW-fed antenna (L1 = L2 = L3 = 0 mm): (a) VSWR; (b) normalized E-plane radiation patterns at 4 GHz.
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Fig. 3. Relations between the VSWR and variations of L1 with fixed other optimized dimensions of the UWB CPW-fed antenna (L2 = L3 = 0 mm). Fig. 4. Relations between the VSWR and variations of L2 with fixed other optimized dimensions of the UWB CPW-fed antenna (L1 = 39.7 mm, L3 = 0 mm).
plane is further increased, the radiation patterns start deteriorating. Moreover, the ground plane affects the operating bandwidth of the proposed antenna. A larger ground plane deteriorates operating bandwidth. 2.1.2. The effect of first slot length (L1 ) to generate band notched in WLAN1 of 2.4 GHz Fig. 3 shows simulated VSWR characteristics with the optimum values of other dimensions and L2 = L3 = (0 mm) for different values of L1 . As the length L1 increases from 25.3 to 39.7 mm, the center frequency of notched band is varied from 3.6 to 2.5 GHz. It can be seen that the bandwidth of notch remains almost fixed and the notch intensity varies between 3.5 GHz and 5.5 GHz. From this result, one can conclude that the intensity and frequency of notched band is controllable by changing length L1 . It is also seen that by increasing L1 , the total electrical length of the antenna is increased and hence the lowest frequency of the antenna is markedly decreased from 3 to 2.2 GHz. The relation between central notched frequencies and Lnotch1 can be expressed approximately based on the results of Fig. 3 as follows: Lnotch1 (mm) = (0.09(L1 − 24)2 − 0.61(L1 − 24) − 4.7) + 24 c = d = √ 2 2fnotch εr
(1)
where d is the dielectric wave length, fnotch is the center of the undesired band base as shown in Fig. 3, c is the speed of light in free space, and εr is the dielectric constant.
where d is the dielectric wave length, fnotch is the center of the undesired band base as shown in Fig. 4, c is the speed of light in free space, and εr is the dielectric constant. 2.1.4. The effect of third slot length (L3 ) to generate band notched in WLAN2 of 5.5 GHz The simulated VSWR curve with different values of L3 is plotted in Fig. 5. As the L3 increases from 12 to 15.2 mm with other fixed dimensions and L1 = (39.7 mm), L2 = (28.9 mm), the center frequency of notched band varies from 5.2 GHz to 5.8 GHz. Of course this variation is very regular. It can be seen that bandwidth of notch remains almost fixed. On the other hand, the filtering frequency of notch at 3.8 GHz and bandwidth of notch at 2.4 GHz is insensitive to the changes of L3 . The relation between central notched frequencies and Lnotch3 can be expressed approximately based on results of Fig. 5 as follows: Lnotch3 (mm) = (−0.1(L3 − 14)2 + 0.36(L3 − 14) − 0.55) + 14 =
d c = √ 2 2fnotch εr
(3)
where d is the dielectric wave length, fnotch is the center of the undesired band base as shown in Fig. 5, c is the speed of light in free space, and εr is the dielectric constant. Table 1 shows comparison data between central notched frequencies in Figs. 3–5 and Eq. (1–3). Good agreement is achieved between these data. The optimized dimensions of antenna using parametric analysis and designer’s experience for antenna can be summarized as follows: Lg = 20.3 mm, L1 = 39.7 mm, L2 = 28.9 mm, L3 = 13 mm.
2.1.3. The effect of second slot length (L2 ) to generate band notched in WiMAX of 3.5 GHz and C band Fig. 4 indicates the simulated VSWR results for proposed antenna in terms of length L2 . For L2 = 21, 24.4 and 28.9 mm with other fixed dimensions and L1 = (39.7 mm), L3 = (0 mm), the notch frequencies decrease from 4.2 to 3.5 GHz. It can be seen that tuning the length L2 has significant effects on shifting notch frequency. Of course this variation is very regular. It can be seen that intensity of filtering frequency and bandwidth of notch remains almost fixed. On the other hand, the filtering frequency and bandwidth of notch at 2.4 GHz is insensitive to the change of L2 . The relation between central notched frequencies and Lnotch2 can be expressed approximately based on results of Fig. 4 as follows: Lnotch2 (mm) = (−0.02(L2 − 20)2 + 0.64(L2 − 20) − 3.62) + 20 =
d c = √ 2 2fnotch εr
(2)
Fig. 5. Relations between the VSWR and variations of L3 with fixed other optimized dimensions of the UWB CPW-fed antenna (L1 = 39.7 mm, L2 = 28.9 mm).
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Table 1 Center frequency of rejection band. L1
L2
L3
fnotch (Fig. 3)
fnotch (Eq. (1))
Lnotch (Fig. 3)
Lnotch (Eq. (1))
39.7 32.5 25.3
0 0 0
0 0 0
2.41 3.0 3.6
2.4137 3.0046 3.6055
29.626 23.8 19.8333
29.6166 23.7970 19.8333
L1
L2
L3
fnotch (Fig. 4)
fnotch (Eq. (2))
Lnotch (Fig. 4)
Lnotch (Eq. (2))
39.7 39.7 39.7
21.0 24.4 28.9
0 0 0
4.2 3.8 3.5
4.2065 3.8058 3.5054
17.0 18.7895 20.4
17.1 18.7898 20.4013
L1
L2
L3
fnotch (Fig. 5)
fnotch (Eq. (3))
Lnotch (Fig. 5)
Lnotch (Eq. (3))
39.7 39.7 39.7
28.9 28.9 28.9
12 13 15.2
5.8 5.5 5.2
5.8089 5.5084 5.2080
12.3103 12.9818 13.7308
12.3102 12.9818 13.7307
3. Results and discussion 3.1. Impedance bandwidth The dimensions of CPW-fed monopole antenna geometry parameters used in measurement are based on optimized dimensions using parametric analysis in Section 2. Fig. 6 shows the measurement, simulation frequency response of the voltage standing wave ratio (VSWR) and return loss for the proposed CPW-fed monopole antenna. The VSWR and return loss was measured by an Agilent 8722ES network analyzer. The measured impedance bandwidth (VSWR < 2) is about 9.4 GHz starting from 1.9 GHz to 11.3 GHz including the notched bands of the IEEE 802.11a in the US and the HIPERLAN/2 in Europe and WiMAX and C-band and WLAN1 . It can be seen that measured notched frequencies and bandwidths for each of the notches are very suitable to suppress the disturbances from WLAN and WiMAX systems. Very low VSWR is observed in the measurement between notches. Comparison between simulated results and the measured results show reasonable agreement at lower frequencies. This may be due to little differences of the FR4 substrate between the practical and simulated models. In addition, the dielectric constant and dissipation factor are not stable when the frequency increases.
normalized E and H planes radiation patterns and simulated current distribution at the three resonance frequencies at 3.2, 4.5, 6.2, and 10.2 GHz and three center stop-band frequencies at 2.4, 3.8, and 5.5 GHz for two state with and without slots in Fig. 7(a)–(g). The gain and radiation patterns were measured using the ETS 3115 system. Errors in the measured bandwidth, radiation pattern, and antenna peak gain can be expected owing to the feed cable placed in the near field of the antenna. The co and cross-polarized components of the field are different in the x–z (H plane) and y–z (E plane) planes. In the H plane, the co-polarized component is EФ , the cross-polarized component is E . It is the contrary in the E plane. The radiation characteristics for the proposed antenna in the two principal planes, E plane and H plane at the pass-band frequencies are dipole-like patterns and are about the same due to the same current distribution at two states as shown in Fig. 7(b, d, f, and g). In the case of the stop-band frequency as shown in Fig. 7(a, c, and e), comparison between states with and without slots show that cross-polar level is increased and dipole like pattern is eliminated. The reason of these phenomena is that high density of surface current around the broken ∩-shaped slots of L1 , L2 , and L3 was observed at 2.4, 3.8, 5.5 GHz, which implies that the slots resonate near center frequency of WLAN1, WiMAX, C, and WLAN2 bands, respectively. 4. Microstrip-fed monopole antenna design
3.2. Radiation pattern and gain results For complete study of far field performance of proposed antenna, from return loss results in Fig. 6, we present measured
Fig. 6. Measured and simulated VSWR and return loss of the triple band-notched CPW-fed monopole antenna.
The microstrip-fed antenna module is derived from the CPW-fed antenna configuration by transferring the feeding network from CPW to microstrip line, as seen in Fig. 8. We have chosen a 50 impedance line to feed the tapered patch, whereas the rest of the dimensions are kept the same as for the CPW-fed model as presented in Section 2. The monopole antenna using a mictrostip line termination not only has similar ultra-wideband with multi band-rejection characteristics compared to the CPW-fed antenna, but also the two metallization layers used are very easy to construct in single or multi-substrate PCB boards, therefore making this antenna structure suitable for direct integration with UWB circuitry. Fig. 9 shows the measured and simulated VSWR results for the fabricated band-notched microstrip-fed monopole antenna and excellent agreement between them is observed. It can be seen that measured notched frequencies and bandwidths for each of the notches has very suitable to suppress the disturbances from WLAN and WiMAX systems. Very low VSWR is observed in the measurement between notches. Fig. 10 shows the measured gain and simulated radiation efficiencies for proposed antenna fed by CPW and microstrip line from 2 to 11 GHz. The figure indicates that the realized triple bandnotched antenna has good gain flatness except in three notched bands. As desired, three sharp gains decrease in the vicinity of
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Fig. 7. Simulated results of the surface current distributions and measured radiation patterns for the antenna at (a) 2.4 GHz; (b) 3.2 GHz; (c) 3.8 GHz; (d) 4.5 GHz; (e) 5.5 GHz; (f) 6.2 GHz; and (g) 10.2 GHz.
2.4, 3.8 and 5.5 GHz. This figure shows that the antenna gain values of the proposed antenna with only three slots (without triple band-notch) are similar to those without them (simple monopole). Therefore, these slots will not have negative effect on the radiation performance of the antenna, in UWB band. On the other hand, the simulated radiation efficiencies of the proposed triple band-
notched antenna, at 2.4, 3.8 and 5.5 GHz, are only about 48, 35 and 57%, respectively. We see again that the radiation efficiency plots of the antenna with and without triple stop-bands structures are similar to each other, except at the notch frequencies. From the measured VSWR and simulated surface current distribution, measured gain and radiation pattern and simulated radiation effi-
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Fig. 7. (Continued. )
Fig. 8. Schematic diagram of microstrip-fed monopole antenna.
Fig. 9. Measured and simulated VSWR of the triple band-notched microstrip-fed monopole antenna.
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Fig. 10. Simulated radiation efficiency and measured gains values of the proposed triple band-notched UWB CPW and microstrip-fed monopole antenna monopole antenna.
Fig. 11. Photograph of the fabricated antennas. Top view: Right, CPW-fed monopole antenna; Left, microstrip-fed monopole antenna.
ciencies for proposed antenna, we conclude that the slots structure can help resonate at three given frequencies which play a role as band-notched filters. The photograph of the proposed antenna fed by CPW and microstrip line printed on FR4 substrate is shown in Fig. 11. Standard photolithography was used for the fabrication. 5. Conclusion A compact ultra wideband monopole antenna fed by CPW and microstrip line with triple band-rejection characteristics are presented and discussed. A simple triple band rejection structure using broken ∩-slot is presented. By transforming the CPW feed to microstrip, the bandwidth and radiation characteristics are preserved. We achieved a reduction in size compared to the antennas presented in [20–36]. The effects of the various geometrical parameters on the antenna performance are studied. The experimental results show that the realized antenna with a very compact size and relatively good radiation characteristics has a wide bandwidth from 1.9 to 11.3 GHz with triple controllable notched bands centered at 2.4, 3.8 and 5.5 GHz. Acknowledgments The authors would like to thank the reviewers for their professional comments and suggestion. They also are thankful to Young Researchers Club of Islamic Urmia Azad University and Urmia University for their financial support. They are also grateful to the Lab. of Millimeter Waves of Iran Telecommunication Research Center (ITRC) for providing the testing equipment. References [1] Federal Communications Commission Revision of Part 15 of the Commission’s Rules Regarding Ultra-Wideband Transmission System from 3.1 to 10.6 GHz. In: FEDERAL Communications Commission. Washington, DC: ET-Docket, FCC; 2002. p. 98–153.
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P. Lotfi et al. / Int. J. Electron. Commun. (AEÜ) 65 (2011) 734–741 [25] Kim DZ, Yu JW. Wide-band planar monopole antenna with triple band-notched slots. J Electromagn Waves Appl 2009;23:117–28. [26] Lee WS, Kim DZ, Kim KJ, Yu JW. Wideband planar monopole antennas with dual band-notched characteristics. IEEE Trans Microw Theory Tech 2006;54:2800–6. [27] Lee WS, Lim WG, Yu JW. Multiple band-notched planar monopole antenna for multiband wireless system. IEEE Microw Wireless Compon Lett 2005;15:576–8. [28] Zhou H-J, Sun B-H, Liu Q-Zh, Deng J-Y. Implementation and investigation of U-shaped aperture UWB antenna with dual band-notched characteristics. Electron Lett 2008;44:576–8. [29] Yin K, Xu JP. Compact ultra-wideband antenna with dual bandstop characteristic. Electron Lett 2008;44:453–4. [30] Deng JY, Yin YZ, Zhou SG, Liu QZ. Compact ultra-wideband antennawith triband notched characteristic. Electron Lett 2008;44:1231–3. [31] Lee HJ, Jang YH, Kim JP, Choi JH. Wideband monopole antenna with WLAN (2.4 GHz/5 GHz) dual band-stop function. Microw Opt Technol Lett 2008;50:1646–9. [32] Bi DH, Yu ZY, Mo SG, Yin XC. Two ultra-wideband antennas with 3.4/5.5 GHz dual-band notched characteristics. Microw Opt Technol Lett 2009;51:2942–5. [33] Niu SF, Gao GP, Li M, Hu YS, Li BN. Design of a novel compact elliptical monopole ultra-wideband antenna with dual band-notched function. Microw Opt Technol Lett 2010;52:1306–10. [34] Zhang M, Zhou X, Guo J, Yin W. A novel ultrawideband planar antenna with dual band-notched performance. Microw Opt Technol Lett 2010;52:90–2. [35] Ryu KS, Kishk AA. UWB monopole antenna with single or dual band-notches for lower WLAN band and upper WLAN band. IEEE Trans Antennas Propag 2009;57:3942–50. [36] Li WT, Shi XW, Hei YQ. Novel planar UWB monopole antenna with triple bandnotched characteristics. IEEE Antennas Wireless Propag Lett 2009;8:1094–8. [37] Garg P, Bhartia P, Bahl I. Microstrip antenna design hand book. 1st ed. House; 2001. p. 794–5. Parisa Lotfy was born in Urmia, Iran, in May 1984. She received the B.S. degree in Electrical Engineering from the Urmia Azad University, in 2008. She is currently working toward the B. S degree in mathematics and M.S. degree in Electrical Engineering in Urmia University. She is a member of Iranian Society of Electrical Engineers. Her current research interests are in antenna design, numerical methods in electromagnetic.
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Saber Soltani was born in Urmia, Iran, in March 1983. He received the B.S. degree in Electrical and Telecommunication Engineering from the Urmia Azad University, in 2006 and M.Sc. degree in Electrical and Telecommunication Engineering from Urmia University, Urmia, Iran, in 2008. He is currently working toward Ph.D. degrees in Microelectronics Research Laboratory, Urmia University, Urmia, Iran. He is a member of Iranian Society of Electrical Engineers and young researcher club of Urmia Azad University. He is the author or coauthor of several refereed journal articles and conference papers. His research interests include antenna miniaturization, optimization method, monopole antennas, slot antennas, hybrid antennas, circular polarization antennas, diversity antennas, mobile phone and wireless local-area network antennas, and their antenna applications. Mohammad Naghi Azarmanesh, was born in Tabriz, Iran, in 1950. He received the B.S. degree in physics from Tabriz University, Iran, in 1973, the M.S. degree in electrical engineering from the University of Paris VI in 1976, and Ph.D. degree in electrical engineering from Poly technique De Toulouse, France. In 1979 he joined Applied Physics Department in Urmia University, where he worked effectively in founding Electrical Engineering Department in 1983. In 1998 he worked with three other colleagues in developing Microelectronics Research Center in Urmia University. He is currently the head of Microelectronics Research Center. Dr. Azarmanesh is a member of Iranian Society of Electrical Engineers and member of IEEE, Institute of Electronics, Information and Communication Engineers (IEICE) of Japan. He has published a book, Electromagnetic Field Theory (Urmia: Urmia University, 1996).