Frequency Reconfigurable Log Periodic Microstrip Dipole Antenna Array for Wideband Applications

Transcription

1 IJIRST International Journal for Innovative Research in Science & Technology Volume 4 Issue 3 August 2017 ISSN (online): Frequency Reconfigurable Log Periodic Microstrip Dipole Antenna Array for Wideband Applications B. Siva Prasad M. G. Sumanth Associate Professor Department of Electronics & Communication Engineering Department of Electronics & Communication Engineering A.U. College of Engineering, Andhra University, Baba Institute of Technology & Sciences,Visakhapatnam, Visakhapatnam, Andhra Pradesh Andhra Pradesh Prof. P. Mallikarjuna Rao Department of Electronics & Communication Engineering A.U. College of Engineering, Andhra University, Visakhapatnam, Andhra Pradesh Abstract The concept of reconfigurable antenna is widely used as an additional feature of reconfigurable ability for future wireless communication systems especially for cognitive radio applications, radar system and multi-frequency communications. There are various configurations of reconfigurable antenna such as monopole, dipole and log-periodic wideband antenna. This paper describes the design and simulation of frequency reconfigurable log periodic microstrip dipole array (FRLPMDA) using dipole patch elements with an useful frequency range for C band (4-8 GHz), X band ( 8-12 GHz ) and Ku band (12-18 GHz ). The integration of reconfigurable antennas with radio frequency (RF) switches are needed to perform the switchable ability [3-6]. In this paper, a frequency reconfigurable LPMDA has been designed to perform a wideband frequency operations by connecting fifteen dipole antennas using coaxial feed line technique. Then, the diversity in frequency is achieved by switching ON and OFF of the PIN diodes connected at every transmission line. It is compact in size and useful to support on board Radar and many wireless applications where they can reduce the size of front circuitry in communication systems. Keywords: Reconfigurable, Log Periodic Antenna, Microstrip, Wideband I. INTRODUCTION Design of the modern microwave communication systems and on board radar equipment for air craft and war ships EW/ECM needs a proper technical solution for small size broadband antennas.the main goal of designing this antenna is to obtain frequency diversity. A single antenna can be operated over three different sub bands. Suppose an enemy is jamming our present frequency band with noise signal, then we can shift our present operating frequency band by using same antenna as before, without changing its physical design by controlling of the switches at the transmission line of patch.the required frequency band could be achieved for three sub bands by controlling a group of switches as shown in table 2. For this purpose, reconfigurable log periodic microstrip dipole array is used for broad operating bandwidth of 14 GHz. Here ANSYS HFSS 13.0 v is used to carry out the simulation process. The antenna is analyzed based on several parameters such as Return loss, Gain and VSWR. It is a low cost multiband printed circuit board (PCB) antenna and it can be fabricated on Arlon AD 250 substrate with Relative Dielectric Constant ϵr = 2.5 and thickness h = 0.51mm. II. ANTENNA DESIGN The standard approach for the design of LPDAs proposed by carrel[1] can be used with suitable modifications.the geometrical structure of the proposed frequency reconfigurable log periodic microstrip dipole array antenna is shown in Figure.1 with fifteen dipole patches which are developed on Arlon AD 250 substrate with thickness of 0.51mm and dimensions of mm.the design principle of log periodic microstrip dipole array antenna requires scaling of dimensions from period to period so that the performance is periodic with logarithm of frequency. Scaling of dimensions of patch dipole elements from one dipole element to another is given by scaling factor 'τ' which determines the antenna angle apex 'α'. spacing factor 'σ ' which is also known as " Relative Spacing constant ". Patch length (L n), width (W n) and distance between elements (d n,n+1 ) are calculated [2] and they are presented in table 1. For this design f h = 18 GHz, f l = 4 GHz. 1) STEP 1: The Scale Factor τ = and Spacing Factor σ = 0.14 All rights reserved by 86

2 2) STEP 2: The apex angle can be obtained as, (1 τ) tan (α) = 4σ α = ) STEP 3: The number of elements in an array is given by N = 1 + logb s log( 1 τ ) Length of the largest dipole B s = Length of smallest dipole τ = Number of elements N = 15 4) STEP 4: Calculation of lengths of dipole The length of last dipole, L 15 = c 2 f l ϵ e = mm Where, c = 3x10 8 and ϵ e-effective dielectric constant ϵ e = = distance between dipole elements is given by d n,n+1 = L n+1 L n 2 tan (α) The length and distance between elements of other dipoles is computed as L n = d n 1,n = τ L n+1 d n,n+1 5) STEP 5: The width of the largest dipoles is computed as W n = π a n Frequency Reconfigurable Log Periodic Microstrip Dipole Antenna Array for Wideband Applications Z n = η π [ln L n/2 a n 2.5] For Zn to be 50Ω,we calculate corresponding a n,where a n is the radius of cylindrical dipole and 'η' is the characteristic impedance of substrate. then, W n = π a n For longest dipole L n = mm W 15 = 1.95 mm Width of the 50Ω transmission line is 1.91 mm. Fig. 1: Proposed Antenna Top View Table 1 Geometry of the designed printed FRLPMDA. Dipole Ln [mm] Wn[mm] d n,n+1 [mm] All rights reserved by 87

3 Here coaxial feeding technique is used. Outer conductor of the coaxial cable is connected to bottom layer of the antenna and the inner conductor is connected to the top layer of the antenna via a hole inside the substrate material. We have selected the characteristic impedance Z n of the feeding line equals to 50 ohm so as to obtain an easy matching with the coaxial cable. Here the Ku band operation is achieved by switching ON the first five PIN diodes and remaining all are OFF. While X band is attained when only 6-10 switches are ON and C band operation can be possible if switches are ON and remaining OFF. In this simulation process the ohmic losses assumed to be zero by using ideal substrate and perfect electric conductor (PEC) for patch as well as PEC pad representation shown in Figure.2. PEC pad is a small metal strip, ON state is represented by the metal strip and absence of the metal strip represents OFF state. Wide band operation is achieved when all switches are ON. Fig. 2: (a) PIN diode ON state (b) PIN diode OFF state Table 2 Switching Combinations PIN diodes ON PIN diodes OFF Band of operation Ku and X C Ultra-wide band III. SIMULATION RESULTS The proposed frequency reconfigurable log periodic microstrip dipole antenna array is simulated using ANSYS HFSS 13.0 v to analyze the performance characteristics like VSWR, Return Loss and Gain of the antenna. Figure.3 (a), (b), (c) shows the VSWR of Ku, X, C bands of operation while Figure.4 (a), (b), (c) shows Return loss for Ku, X and C bands respectively. Figure.5 (a), (b) and (c) shows 2D Radiation patterns for different sub bands. Figure.6 (a), (b) and (c) shows that simulated Gain and 3D radiation patterns for different bands of frequencies. The corresponding performance characteristics are evaluated and they are tabulated in table 3. VSWR: Fig. 3(a): for Ku Band All rights reserved by 88

4 Fig. 3(b): for X Band Fig. 3(c): for C Band Return Loss: Fig. 4(a): for Ku Band All rights reserved by 89

5 Fig. 4(b): for X Band Fig. 4(c): for C Band 2D Radiation Pattern: Fig. 5(a): for Ku Band All rights reserved by 90

6 Fig. 5(b): for X Band Fig. 5(c): for C Band Gain and 3D Radiation Pattern: Fig. 6(a): for Ku Band All rights reserved by 91

7 Fig. 6(b): for X Band Fig. 6(c): for C Band Table 3 Performance Characteristics of FRLPMDA Operating band VSWR Return Loss (db) Max Gain (db) Resonant frequency (GHz) Ku X C IV. CONCLUSION The frequency reconfigurable log periodic microstrip dipole array operated over C,X and Ku bands has been designed and simulated by ANSYS HFSS 13.0v.The simulation results shows that the proposed antenna array can be successfully used as ultrawide band antenna over frequency range from 4 GHz to 18 GHz. In terms of gain and VSWR, this antenna array shows it's best performance in the X band.it shows better performance in terms of VSWR and Returnloss in C band frequency range. Also, it shows that good performance in Ku band in all aspects. Here the required frequency band can be easily selected by choosing various switching combinations as shown in table 2. REFERENCES [1] Carrel,R., " the design of log-periodic dipole antennas ", IRE International Convention Record, Vol.9, 61-75, 1961 [2] Isbell, D. E., Log periodic dipole arrays," IEEE Transactions on Antennas and Propagation, Vol. 8, pp , [3] B. Z. Wang, S. Xiao, J. Wang, Reconfigurable patch-antenna design for wideband wireless communication system, IET Microwave Antennas Propagation, Vol. 1, Issue 2, pp , [4] Y. J. Sung, T. U. Jang, and Y.-S. Kim, A Reconfigurable Microstrip Antenna for Switchable Polarization IEEE Microwave And Wireless Component Letters, VOL. 14, No. 11, Nov [5] Kim, D., Q. Chen, and K. Sawaya, Microstrip log-periodic dipole antenna array, Proceedings of ISAP, Fukuoka, Japan, 2000 [6] M. R. Hamid, P. Gardner, P. S. Hall, Reconfigurable log periodic aperture fed microstrip antenna Loughborough Antenna & Propagation Conference, Loughborough, pp , All rights reserved by 92