A Compact Coupled-Line Multiband Microstrip Antenna

Transcription

1 29 A Compact Coupled-Line Multiband Microstrip Antenna Md. Rokunuzzaman 1, M. T. Islam 1, Baharudin Yatim 1 and Mhd Fairos Asillam 2 1 Institute of Space Science (ANGKASA),Universiti Kebangsaan Malaysia, UKM Bangi, Selangor, Malaysia 2 National Space Agency of Malaysia (ANGKASA), Lot 2233, Jalan Turi, Kpg. Sg. Lang, Banting, Selangor, Malaysia robelhk@yahoo.com Abstract - A multiband microstrip antenna is proposed in this paper. By using a circular slot at the ground plane, the circular radiation at the antenna frequency resonances has been achieved. A patch is designed with a coupled U-shaped line. To gain resonance at the lower frequency, a microstrip line is introduced at the middle of the circular slot. The assessment of the proposed antenna shows good agreement for gaining circular radiation pattern. Index Terms - Circular, microstrip, radiation, multiband, slot. I. INTRODUCTION Modern wireless communication system is getting more into multiband antennae due to their response in different desired frequencies and a desired type of applications can be entertained using a single multiband antenna. By using different shapes of slot and multiple passive patch, multiband is achievable for different applications. The communication in different frequencies for applications within one gadget is increasing. To improve the size compatibility of the gadgets and increase the gain of the antenna, multiband antennae are becoming popular day by day. In [1] a method is described to reduce size and enhance the performance for suspended plate multiband antennae. Also in [2] by using fractal Sierpinski Gasket antenna, the multiband behaviour is explained. Several multiband antennae aiming for different applications are focused in [3]. Also the antenna structure described in [3] follows Chebyshev distribution rule for the slot arrays combined with another triangle passive patch element. Using this Chebyshev distribution, the multiband response with decreased size of the antenna is achieved. Also for the feeding of the probe, a place between 2 slots (triangle and rectangular Chebyshev slots) has been chosen after optimization. For different functions to be introduced of the antenna, switches have been used in the rectangle patch slots in [4]. The functionalities such as similar radiation pattern, most importantly frequency selectivity gives vast advantage by reducing jamming and rough effects of co-site interference. Also antenna applications such as UMTS (Universal Mobile Telecommunication System; MHz), WIMAX (Worldwide Interoperability for Microwave Access; GHz), and WLAN (Wireless Local Area Network; MHz) can be entertained using the antenna in [4]. A triangle shaped patch antenna covered with another triangle shape and in the middle of the two patch (active and passive) a triangle shaped slot is demonstrated in [5] with dual-band resonance response. A rectangular shaped slot is cut in the middle of the ground plane to have tuning property between the 2 resonance frequencies. Different type of wideband antenna is shown in [7, 8]. In [9] a coplanar waveguide fed metamaterial inspired patch antenna is shown. [10-18] shows antenna designed in different substrates with different shapes to achieve UWB band, UHF RFID band and so on. In this paper, a multiband antenna design is proposed with multiband response at the frequencies 6.18 GHz, 8.52 GHz, 14.7 GHz and GHz. By changing the gap between the coupled lines in the patch of the antenna, input impedance can be varied. The ground plane of

2 30 the antenna with a circular slot in the middle and a small microstrip line in the middle of the circular slot plays an important role in finding the resonance responses mentioned above. The lowest resonance frequency achievement is done using the small microstrip line in the ground plane as mentioned. The antenna design and experimental results are presented with details using important parametric figures. (a) (b) II. ANTENNA STRUCTURE FORMULATION The coupled structures even (Z oe ) and odd (Z oo ) mode impedance can be evaluated by using coupled line microstrip structure impedance formulation technique described in [6]: (1) (2) Slot antennae designed in different antenna designs operates between 300 MHz to 24 GHz. The circular slot in the ground plane of the proposed antenna plays a very important role in finding the resonance in the specified frequencies. Slot antennae are classified as aperture type antenna. In Babinet s principle, it is stated that the far field radiation of an aperture slot antenna can be related with the complementary of the same structure. Figure 1 shows the antenna along with its complementary structure. The relation between the slot antenna and its complementary structure can be formulated with the equations: (3) (4) (5) (c) (d) Fig.1. (a) and (c) are the patch and ground plane, where (b) and (d) are their complementary respectively. Here, η 0 =Intrinsic impedance of free space, = Electric field of circular patch, =Magnetic field of circular patch, =Electric field of the complementary patch and =Magnetic field of complimentary patch. The formulation agrees with the current distribution and radiation pattern at the resonant frequencies. III. RESULTS AND DISCUSSION The multiband antenna is designed using the EM simulation software HFSS (High Frequency Structure Simulator) which is quite popular nowadays for antenna design with complicated shapes and substrate. For the multiband antenna design, a 20 mm by 20 mm glass-reinforced epoxy laminate printed circuit board is chosen. Originally known as FR-4 substrate is quite popular nowadays due to its durability, chip price and water absorption rate of close to zero. The permittivity of the FR-4 substrate used for the proposed antenna design is Ɛ r =4.6 with a thickness of H=1.6 mm. Figure 1 shows the geometry of the proposed antenna. The antenna current distribution is shown in Figure 2. (6)

3 31 (a) (b) (c) (d) Fig.2. Current distribution of the antenna at (a) 6.18 GHz, (b) 8.52 GHz, (c) 14.7 GHz and (d) GHz. From the current distribution pattern, it can be seen that at the frequency 6.18 GHz, the current distribution over the strip line situated in the middle of the circular slot at the ground plane is high which also indicates a better result in that frequency. Minor perturbations can be seen at the patch of the antenna. By adjusting the length of the strip line in the ground plane, the resonance at 6.18 GHz can be tuned. For the frequency 8.52 GHz, the current distribution is showing variation at the coupled microstrip lines at the patch. The same can be seen at the frequency 14.7 GHz. At this frequency, there is an effective current distribution at the ground plane surrounding the circular slot. The same can be observed for the frequency GHz but with less current density. The radiation pattern of the antenna at the specified frequencies is showed in Figure 3. The current distribution shown in Figure 2 (a) achieves the radiation pattern shown in Figure 3 with a circular pattern. E-plane H-plane Fig.3. Radiation pattern at (a) 6.18 GHz, (b) 8.52 GHz, (c) 14.7 GHz and (d) GHz. Almost all the resonance frequency has the circular radiation plane at E-plane cause of the circular slot in the ground plane. The irregularity of the circular radiation pattern occurs due to the microstrip line situated in the middle of the circular slot. The co and cross polarizations are shown in both E and H-plane by using orange dotted line and black filled line respectively. The

4 32 results for the resonance and directivity are shown in Figure 4 and Figure S11 (db) Fig.4. S 11 response of the proposed multiband antenna Directivity (db) Fig.5. Directivity of the proposed multiband antenna From Figure 5 it is seen that the directivity at the frequency 6.18 GHz is 4.31 db. The responsible region for that frequency can be seen from the current distribution pattern in Figure 2(a) which is the strip line in the middle of the ground plane. The directivities in other frequencies are tabulated in Table 1. Table 1: Peak gain at the resonant frequencies Directivity (db) IV. CONCLUSION In this paper, the circular radiation pattern for multiband antenna is achieved by using circular slot in the ground plane and described using the Babinet s principle. The coupled line structures are formulated using the coupled line formulas used for microstrip line structure. The results shown in this paper with the resonance response in Figure 4 can be used for applications such as Mobile, Fixed-Satellite (Earth-to-space), Radiolocation. Throughout the multiband, circular radiation pattern was achieved. REFERENCES [1] Nga, G.J., A method for the design of miniaturized suspended plate multiband antennas, Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, pp , Oct [2] Xinbo Qu, Zhaoxiang He, Wei Shi, Yunzhi Liu, Zuping Qian, Multiband analysis of Sierpinski Gasket antenna with an iterative method, Wireless Communications & Signal Processing, WCSP International Conference on, pp. 1-4, Nov [3] J. Costantine, K.Y. Kabalan, A. El Hajj, C.G. Christodoulou, New Multi_Band Design for a Microstrip Patch Antenna, Antennas and Propagation, EuCAP, The Second European Conference on, pp. 1-4, Nov [4] J. Costantine C.G. Christodoulou, S.E. Barbin, A new reconfigurable multi band patch antenna, Microwave and Optoelectronics Conference, IMOC, SBMO/IEEE MTT-S International, pp , Oct [5] L. Liu, S. Zhu, R. Langley, Dual-band triangular patch antenna with modified ground plane, Electronics Letters, Vol. 43, Issue. 3, pp , Feb [6] D.M. Pozar, Microwave Engineering, Edition. 4, John Wiley & Sons, Inc., pp [7] R. Azim, M. T. Islam and N. Misran, Dual Polarized Microstrip Patch Antenna for Ku-Band Application, Informacije MIDEM, vol. 41, no. 2, pp , [8] R. Azim, M.T. Islam, J.S. Mandeep, A.T. Mobashsher, A planar circular ring ultra-wideband antenna with dual band-notched characteristics, Journal of Electromagnetic Waves and Applications, Vol. 26, pp , [9] M.A. Wan Nordin, M.T. Islam, N. Misran, A compact wideband coplanar waveguide fed metamaterial-inspired patch antenna for wireless application, Applied Physics A, Vol. 109, Issue. 4, pp , Dec

5 33 [10] R. Azim and M.T. Islam, Compact planar UWB antenna with band notch characteristics for WLAN and dsrc, Progress In Electromagnetics Research, Vol. 133, pp , [11] A.T. Mobashsher, M.T. Islam, N. Misran, Triple band RFID reader antenna for handheld applications, Microwave and Optical Technology Letters, Vol. 53, Issue. 7, pp , Jul [12] M. Habib Ullah, M. T. Islam, Design of a modified W-shaped patch antenna on Al2O3 ceramic material substrate for Ku-band, Chalcogenide Letters, Vol. 9, No. 2, pp , Feb [13] M.N. Shakib, M.T. Islam, N. Misran, Stacked patch antenna with folded patch feed for ultra-wideband application, IET Microwaves, Antennas & Propagation, Vol. 4, Issue. 10, pp , Oct [14] M.T. Islam, A.T. Mobashsher, N. Misran, Design of microstrip patch antenna using novel U-shaped feeding strip with unequal arm Electronics Letters, Vol. 46, Issue. 14, pp , Jul [15] M. Habib Ullah, M. T. Islam, J. S. Mandeep, N. Misran, A new double L-shaped multiband patch antenna on a polymer resin material substrate, Applied Physics A, Vol. 110, Issue. 1, pp , Jan [16] L. Liu, S.W. Cheung, R. Azim, M. T. Islam, A compact circular-ring antenna for ultra-wideband applications, Microwave and Optical Technology Letters, Vol. 53, Issue. 10, pp , Oct [17] M.S. Alam, M.T. Islam, N. Misran, A novel compact split ring slotted electromagnetic bandgap structure for microstrip patch antenna performance enhancement, Progress In Electromagnetics Research, Vol. 130, pp , [18] M.N. Shakib, M.T. Islam, N. Misran, High gain W- shaped microstrip patch antenna, IEICE Electronics Express, Vol. 7, No.20, pp , 2010.