A Compact 3.5/5.5 GHz Dual Band-Notched Monopole Antenna For Application In UWB Communication Systems With Defected Ground Structure

Transcription

1 A Compact 35/55 GHz Dual Band-Notched Monopole Antenna For Application In UWB Communication Systems With Defected Ground Structure Jyoti R Panda and Rakhesh S Kshetrimayum Department of Electronics and Communication Engineering Indian Institute of Technology Guwahati, Assam INDIA Abstract- A compact ultrawideband monopole antenna having dual band-notched characteristics with a defected ground structure (DGS) proposed Two symmetrical L-shaped slots are created on the ground plane to generate the UWB characteristics in the proposed antenna To generate the notch at 52/58 GHz band, a U-shaped slot is cut in the rectangular radiating element, which mitigate the potential interference with WLAN To have another notch band simultaneously around 30/40 GHz, which is the operating band of WiMAX (33-36 GHz) and C-band (37-42 GHz), an inverted U-shaped element is printed on the opposite side of the substrate By properly varying the dimensions of the U shaped slot and the radiating element, not only two controllable notch resonances, but also a very wide bandwidth from 191 GHz to 391 GHz (152%) with two sharp notched bands covering all the 35/55 GHz WiMAX, 4 GHz C-band and 52/58 GHz WLAN, are achieved The proposed antenna properly optimized and simulated providing broadband impedance matching, appropriate gain and stable radiation pattern characteristics I INTRODUCTION EDERAL Communication Commission's (FCC)'s ruling in FFebruary 2002 [1] for the commercial use of huge band from 31 GHz to 106 GHz has completely revolutionized the wireless and high speed data communication world This huge bandwidth from 31 GHz to 106 GHz is known as the ultrawideband (UWB) spectrum Shortly after the FCC's ruling in February 2002, research started throughout the world to design the various systems and components that will enhance the credibility of the UWB system and UWB antenna is one of them Last nine years researchers all over the world designed and proposed many UWB antennas, which are compact, low cost, less fragile, light weight and easily incorporable in the portable and hand held devices in the UWB system There are many challenges in the UWB antenna design and the notable among them are broadband impedance matching, appropriate gain characteristics and stable radiation pattern But along with the vast operating bandwidth of the UWB antenna ( GHz), there exist some narrowband wireless services, which occupy some of the frequency bands in the UWB bands The most well known among them is wireless local area network (WLAN) IEEE80211a and HIPERLAN/2 WLAN operating in 5-6 GHz band Apart from WLAN, in some European and Asian countries, world interoperability for microwave access (WiMAX) service from GHz and 4 GHz C-band also occupy in the UWB band In some antenna designs, the UWB antenna uses filters to notch out the interfering bands But the use of filters increases the complexity of the UWB system and also increases the weight Hence it is needed to design the UWB antenna with dual bandnotched characteristics both in GHz and 5-6 GHz to mitigate the interference between the narrowband wireless systems and UWB systems Till now many designs of the UWB band-notched antennas are proposed [2]-[13] to alleviate the disturbance caused by the WLAN with the UWB system The simple and most commonly used approach is to incorporate various shapes and sizes of slots into the main radiator In [2] a bell shaped patch with stair case structure is proposed Apart from that two parasitic patched are printed on the substrate to provide the band-notch characteristics A L shaped slot [3] is cut in the edges of main radiator with a C shaped in the main radiator An arc shaped slot is cut in the elliptical shaped patch [4], with a rectangular slot is cut in the ground plane A rectangular tuning stub [5] is embedded in the circular annular ring, which generates the band-notched characteristics in the UWB spectrum A split ring resonator (SRR) [6] is used in the main patch for the band notched characteristics A ring shaped parasitic patch [8] is printed within the central circular slot The central circular slot is cut from the bell shaped patch A cutting pie with the flare angle e is cut from the circular patch [9] This antenna is consists of two monopoles with a small strip bar is located in between the two monopoles [10] A simple arc [12] is cut in the circular radiating patch provides the band notch characteristic An E shaped slot is removed from the rectangular radiating element of the UWB antenna, which is fed by a triangular tapered feed line with the end having a trident shape A U-shaped slot is cut /$ IEEE

2 in the ground plane [13] A square shaped SRR is printed on the circular shaped radiating element [14] Two L-shaped slots are cut from the ground plane with an arc is cut from the circular radiating patch [15] A deep almost full shaped arc is cut in the annular circular ring [16] An E-shaped slot is cut from the rectangular radiating patch with a notched ground plane [17] In this antenna the circular disc is used as the radiating element, which is fed by the papered microstrip line The ground plane is round cornered, which enhance the impedance bandwidth especially at the high frequency In one structure two L-shaped slot is cut from the ground plane and in another structure a pair of square ring resonators is created in the ground plane, which provides the required the band-notch characteristic to notch out the WLAN band from the UWB spectrum [18] Based on the background of the structures of various UWB notch-antennas above, this paper proposes a simple and compact microstrip line fed planar UWB antenna with dual band-notched characteristics in 374 GHz ( GHz) and 55 GHz ( GHz) The dual band-notched characteristic in the proposed antenna can be achieved by creating two symmetrical L-shaped slots in the ground plane, then removing a U-shaped slot from the rectangular radiating element and followed by creating another inverted U-shaped radiating element on back side of the substrate It is observed that by adjusting the total length of the U-shaped slots to be approximately half the guided wavelength (Ag ) of the required notch frequency, a destructive interference takes place making the antenna non-radiating at that notch frequency The tuning of the central notch frequency can be done by suitably adjusting the total length of the U-shaped slots The optimization of the design and the subsequent simulation is done by IE3D software [20] The proposed antenna provides an impedance bandwidth of GHz with VSWR:::; 2, except the bandwidths of GHz for WiMAX system, 4-GHz C-band and GHz for IEEE80211a and HIPERLANI2 WLAN systems The appropriate gain and stable radiation patterns are also obtained In this paper, a compact UWB antenna of area 22 by 24 mm 2 is first presented having symmetrical L-shaped slots in the ground plane By removing a U-shaped slot from the rectangular radiating element, a single band-notched characteristic from 489 to 603 GHz is obtained By creating an inverted U-shaped slot on the backside of the substrate, dual band-notched characteristic for the proposed antenna is created to reduce the potential interference between the narrowband system and the UWB system Details of simulation results and the antenna designs are presented to demonstrate the performance of the proposed antenna II ANTENNA DESIGN AND RESULTS A UWB Antenna Design and Results Side View Bottom Layer \ Fig 1 Geometry and configuration ofuwb antenna Figl shows the geometry and configuration of a UWB antenna The antenna was fabricated on an h=1 mm FR4 epoxy substrate with the dielectric constant 8r=44 and loss tangent tano=o002 As shown in the figure, the shape of the radiating element is rectangular In the ground plane two symmetrical L shaped slots are created to have the bandwidth for the usage in UWB communication systems The radiating element is fed by 50-'0 microstrip transmission line, which is terminated with a sub miniature A (SMA) connector for the measurement purpose The electromagnetic software IE3D is employed to perform the design and optimization process The design parameters are given in the Figl Two symmetrical L-shaped slots are introduced in the ground plane Hence in this way defects has been introduced in the ground plane This defected ground structure (DGS) effects the current distribution in the ground plane, which helps in broadening the impedance characteristics of the antenna Introducing two symmetrical L-shaped slots in the ground plane and carefully adjusting the parameters of Mg and Ng in Figl, extra resonances can be evoked and much enhanced impedance bandwidth may be obtained The proposed antenna is simulated using method of moments (MoM) based software IE3D [20] The VSWR graphs for different values of Mg and Ng are shown in Fig2 and Fig 3 respectively From the VSWR graph of Fig2, it is clear that when there are no slots in the ground plane bandwidth is from 3 to 9 GHz, which is not adequate for the UWB communication systems So, when there are no L-shaped slots in the ground plane, poor impedance matching occurred As the length of the L-shaped slot Mg is increased, the impedance matching is improved quite a lot At one point, when the length of Mg of the L-shaped slot on the both side of the 50-Q microstrip feed line is 73 mm, wide impedance bandwidth is obtained due to the proper impedance matching between the microstrip feed line and the rectangular radiating element But when the length of Mg is increased further, again there is impedance mismatch between the feed line and radiating element resulting poor impedance matching, hence inadequate

3 impedance bandwidth for the UWB communication obtained So, from the above parametric study, it is clear that there exist a optimum length Mg for the two symmetrical L-shaped slots in the ground plane, for which wide impedance bandwidth is obtained Another important parameter is Ng which is the distance between the two symmetrical L-shaped slots in the ground plane, plays an important role in providing proper impedance matching resulting large impedance bandwidth The distance between the two slots should be large enough to reduce the coupling between the two L-shaped slots, but by increasing the distance between the two slots Ng, the excitation due to the coupling between the two L-shaped slots is weakened, which disturbs the surface current density in the central portion of the ground plane exactly below the microstrip feed line Increasing or decreasing the distance Ng between the two L-shaped slots, the impedance matching phenomenon of the antenna is degraded for the higher values of the frequency The optimum value of Ng is adjusted to be 19 mm as shown in Fig 3, for which the antenna provided the full band UWB characteristic from 344 GHz to 1355 GHz The optimum value of Ng (=19 mm) is exactly same as the width of the microstrip feed line Fig3 represents the gain in dbi verses frequency The gain increases with the frequency and the maximum at 90 GHz The maximum gain of antenna 1 is 316 dbi at 90 GHz 4 0:: 25 > 4r "," : : -Ng=O50 mm ' -Ng=190 mm : -Ng=400 mm : -Ng=450 mm 4 --L- -1- L Fig 3Simulated VSWR for different values of Ng with fixed Values of Mg=73 mm ofuwb antenna 4r----r----r----r----r ,,,,,,,,,,,,,,,,,j,,,,,,,,,,,,,, l,,,,,,,,,,! i 0! r i 1 : :! - 2,""',","",' f"" " " """,, : " """",,,, ; " ",, """ "' I""" """ "" 35! 25 > 2 -Without Slot -Mg=550mm -Mg=620mm -Mg=645mm -Mg=730mm Mg=800 mm --r- -4 """" " ""'''1'''''''''''''''''''' : '''''''''''''''''''''+ '''''''''''''''''''1''''''''''''''"" -" Fig 4 Simulated gain (dbi) vs frequency ofuwb antenna B UWB Band-Notch Antenna Design and Results,, 8 --;':1'0::----:':::-- 8 Fig 2 Simulated VSWR for different values of Mg with fixed Values of Ng=19 mm ofuwb antenna 14 Along with the UWB spectrum ( GHz), some narrowband systems operate Notable among them is IEEE 80211a and HIPERLANI2 WLAN system Hence, to mitigate the interference from the above narrowband system, bandnotch function is desirable in the UWB system Fig5 shows the geometry and dimension of the UWB antenna with band-notch characteristic from GHz band By removing an U-shaped slot from the rectangularradiating patch having two symmetrical L-shaped slots in the ground plane of UWB antenna, a band notch function is created It is noteworthy that when the band-notched structure is applied to the UWB antenna, there is no redesigning work needed for the previously taken dimensions In general, the main aim behind the design methodology of the notch function is to tune the total length of the U-shaped slot approximately equal to the half guided wavelength (Ag) of the desired notch frequency, which provides the input impedance singular At the desired notch frequency, the current distribution is around the U-shaped slot Hence, a destructive interference for the excited

4 surface current will occur, which causes the antenna to be nonresponsive at that frequency The input impedance closer to the feed point, changes abruptly making large reflections at the required notch frequency Side Viow Top Layer Bottom Layer ' Il I oi Fig 5 Geometry and configuration ofuwb notch antenna The guided wavelength of a slot line is approximately given by [19] it =it 2 g 8 +1 r where Ag is the guided wavelength, A is the free space wavelength and 8r is the permitivity of the substrate According to Cohn [19], a half wavelength slot can be served as a resonator, because in the air regions of the slot, the magnetic field lines make curve and return to the slot region at half the guided wavelength interval Hence to generate a resonance at a desired frequency, the physical length of the slot should be half the guided wavelength In our case the shape of the slot is U and its physical length (L) should be approximately equal to A- L == --2 (2) 2 The guided wavelength (Ag) can be expressed in terms of the notch frequency (f,,) and is given by it =!: 2 (3) g i n 8 r + 1 The notch frequency (f,,) can also be expressed in terms of the physical length (L) of the U-shaped slot and is given by (1) f :: 2 = (4) n 2L 8 r + 1 where c is the speed of light in vacuum Fig6 depicts the simulated VSWR of the UWB notch antenna for the different N As observed, the adjustment of the band-notched frequency can be done by varying the length (N) of the U-shaped slot By decreasing N from 715 to 57 mm, the tip of the notched band shifted from 50 GHz to 60 GHz The total simulated length L for the UWB notch antenna is denoted as L=2N The performance of the simulated VSWR of the UWB notch antenna, which provides the desired center notch frequency of 55 GHz, is shown in the Fig6 From the figure it is very clear that, the desired filtering property is achieved by introducing an U-shaped slot Compared to UWB antenna design, the single band-notched UWB antenna effectively blocks out the 5-6 GHz and still performs excellent impedance matching at other frequencies of UWB band The tip of the desired notch band is exactly at 55 GHz at the VSWR value of 689, which is the center frequency of the WLAN band The notch band stretches from 489 GHz to 603 GHz, in which whole of the WLAN band is immersed The antenna gain of UWB notch antenna, compared to UWB antenna in the entire UWB is presented in the Fig7, which shows a sharp decrease in gain at 55 GHz, which is the center frequency of the WLAN band and good performances at other frequencies of the UWB band The value of gain at 55 GHz is -783 dbi 7---a'--- == 8 f S f : II : II : I '/', I Fig 6 Effect of length (N) on the VSWR of the UWB notch antenna _ :::t: 4,r----r---r----r---r--- t:: -- "we Ante, iii : : -UWB Notch Antenna -2! C) -4 j ) : -8 1 y l + _) i : T t ( ; : 8l---':-----'-----::O----:'::-----:-' Fig 7 Simulated gain (dbi) vs frequency of UWB notch antenna, compared to UWB antenna

5 C Side View UWB Dual Band-Notch Antenna Design and Results Bottom Layer \' 22 Y J W I I Fig 8 Geometry ofuwb dual band-notch antenna Apart from WLAN, WiMAX occupies band from GHz and that is within the UWB frequency band of operation and this interferes with the operation of the UWB systems Apart from WiMAX, 4 GHz C-band also operates at around 4 GHz Hence to mitigate the potential interference between the narrowband systems, in this paper a new design of dual bandnotched UWB antenna is presented By introducing an inverted U shaped radiating element on the back side of the substrate of the UWB notch antenna, a dual band notch characteristic is obtained whose first notch band is extended from 296 GHz to 478 GHz having the center notch frequency at 374 GHz and the second notch band is extended from 518 GHz to 635 GHz having the center notch frequency at 55 GHz Fig8 depicts the geometry of the UWB dual band-notched antenna whose one U-shaped slots is created in the rectangular radiating element and other inverted U-shaped radiating element is introduced in the back side of the substrate The U-shaped slot in the rectangular radiating element provides the band-notch whose center frequency is at 55 GHz The inverted U-shaped radiating element in the backside of the substrate is responsible for crating a band notch whose center frequency is at 374 GHz, each of the total length of the U-shaped slot is obtained by using the expression (2) Fig9 shows the simulated VSWR of the UWB dual band-notch antenna compared to antenna UWB antenna The VSWR graph of the UWB dual band-notch antenna provides two notches centered at 374 GHz and 55 GHz The frequency band at center frequency at 374 GHz extends from 296 GHz to 478 GHz, which is the operating band of WiMAX and 4 GHz C-band The frequency band at center frequency at 55 GHz extends from 518 GHz to 635 GHz, which is the operating band of WLAN Hence it can be concluded that the two notch bands for the UWB dual bandnotch antenna are created by two U-shaped slots, one on the rectangular radiating element and other at the back side of the substrate, effectively notch out the operation bands of WiMAX, 4 GHz C-band and WLAN respectively, mitigates the potential interference between the narrowband systems and UWB system The overall UWB band extends from 191 GHz to 1391 GHz o 9r--'--======c===== i --UWB Antenna 8 j -UWB i Dual Bad-notch ntenna 7 ' ; ; ; ; 8 ; : : : ; """""'''''''''r ''''''''''''''''''; '''''''''''''''''': '''''''''''''' '' 1 :::::::::1::::::::::::::::: 5 1! i i! : 4 \ "'--1-' 1 ;, [ i 3 \" + ',i C= ; Frequency(G Hz) i ::/ Fig 9 Simulated VSWR of UWB dual band-notch antenna, compared to UWB antenna Fig10 shows the variation of gain in db with the frequency for the UWB dual band-notch antenna compared to UWB antenna From the Fig1 0 it is clear that there is sharp dip in the gain at around 39 GHz and 55 GHz, which confirms the effective operation of the UWB dual band-notch antenna in the two-narrowband systems However, for the other frequencies outside the notched band, the antenna gain is appropriately varying and almost stable in the whole of the UWB band The gain of UWB dual band-notch antenna at 39 GHz is dbi and the gain of UWB dual band-notch antenna at 55 GHz is dbi respectively 4r----r----r----r----r----- : r;;::j:::::t ::1 =- -2 i -" " ; -UWB Dual Band-notch Antenna In,' i i i i 4, a ;:+!1:: i Fig 10 Simulated gain (dbi) vs frequency of UWB dual band-notch antenna, compared to UWB antenna Figll shows the E-plane (yz-plane) radiation pattern of the UWB dual band-notch antenna at 35, 55, 75 and 105 GHz respectively and Fig12 shows the H-plane (zx-plane) radiation pattern of the UWB dual band-notch antenna at 35, 55, 75 and 105 GHz respectively The H-plane radiation pattern is purely omni-directional at all the simulated frequencies In the E-plane, the radiation pattern is like a small dipole leading to a bi-directional radiation pattern The E-plane radiation pattern is directional along _90 and 90 respectively

6 at simulated frequencies of 35 GHz and 105 GHz At 55 GHz the E-plane is tilted left side upward and directed along _60 and 120 At 75 GHz the E-plane is tilted left side downward and directed along -150 and 30 There is almost no change in the shape of E-plane radiation pattern at all the simulated frequencies Hence the UWB dual band-notch antenna exhibits stable and constant radiation pattern at all the frequencies o (,) o (1J) 7H-1"""' '''- ''_' ''''' '_,--,,,17O ) 1>; :co 1c: :''J «) (d) Fig 12 Simulated H-plane (zx-plane) radiation patterns of UWB dual band-notch antenna at (a) 35 GHz, (b) 55 GHz, (c) 75 GHz and (d) 105 GHz,,, ;r----' «) (d) Fig 11 Simulated E-plane (yz-plane) radiation patterns of UWB dual band-notch antenna at (a) 35 GHz, (b) 55 GHz, (c) 75 GHz and (d) 105 GHz III CONCLUSION A compact microstrip line fed monopole antenna with single and dual band-notched function for the application in UWB communication system has been presented and analyzed Two symmetrical L-shaped slots are introduced in the ground plane of the antenna, which are responsible for the proper impedance matching, thus provides the full operating band for the UWB systems Creating a U-shaped slot in the rectangular radiating element and introducing an inverted U-shaped radiating element in the rear of the substrate, a single and dual bandnotch characteristics are created, which alleviates the potential interferences with existing WiMAX, C-band and WLAN operating bands respectively Stable radiation pattern and appropriate gain in the UWB bands are obtained The antenna presented in this paper is expected to find future application in UWB system REFERENCES [I) First Report and Order, "Revision of Part 15 of the Commission's Rule Regarding Ultra-Wideband Transmission systems FCC 02-48," Federal Communication Commission, 2002 [2) K -"- Kim, Y -J Cho, S -"-Hwang and S -D Park, "Band-notched UWB planar monopole antenna with two parasitic patches," ElectronLett vol 41, no14, pp , Jul, 2005 [3) W Choi, KChung, JChung and JChoi, "Compact ultra-wideband printed antenna with band-rejection characteristics," ElectronLett vol 41, no18, pp , Sep, 2005

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