Cpw fed square patch antenna with ISM band.
With the development of many different wireless communication standards, it is desirable to integrate as many standards such as
GPS, WLAN, WIMAX standards as possible into a single wireless device . Because of the rapid development of ultra wide band communication systems in recent years, much research has been conducted on UWB antennas, among which printed wide aperture antennas have been regarded as popular candidates. The frequency range for UWB systems between 3.1-10.6 GHz will cause interference to the existing wireless communication systems, such as the wireless local area network (WLAN) for IEEE 802.11a operating in 5.15-5.35 and 5.725-5.825 GHz bands, WiMAX (3.3-3.6 GHz), and C-band (3.7-4.2 GHz), so the UWB antenna with single and dual band-stop performances is required. In order to satisfy IEEE 802.11 a standard, the proposed antenna should operate at 2.45 GHz. . Therefore, slotted antennas for WLAN applications become a research point  in the past decades and many different technologies for miniaturized antenna have been proposed. The 915MHz ISM band (902MHz ~ 928MHz) is a commonly used unlicensed band in the United States of America and 2.4GHz ISM band  (2.402GHz ~ 2.484GHz) is the most commonly used unlicensed band  worldwide for industrial, scientific, and medical applications. Demand for compact antennas operating in ISM bands is increasing day by day. If the antenna has low profile, it will be useful for multiband mobile communication system .
Some designs with dual band-notched property are achieved by utilizing a couple of half-wavelength parasitic elements  in an open rectangular slot, embedding dual C- shaped slots on the radiator or inserting dual quarter- wavelength stubs  However, the above designs have limited band -notched performance (VSWR < 10)  at each notched frequency or limited gain suppression (<10 dB) in the notched band. However, it had limited band  performance due to the dielectric loss of the substrate. Another method was suggested in which had introduced a substrate integrated waveguide  (SIW) cavity within the feed line of a monopole antenna  to obtain multiple band-notched functions. In constructing an implantable antenna, it is critical to place the implant in the medium in which it operates.
In order to operate the Unlicensed ISM band centered at 60 GHz(57-64GHz), High data rate (in the order of multiple of Gbps) and For the application to Transmit uncompressed HD video streaming in Wireless point to multipoint connections this type of end fire antenna can be used. High propagation loss at these frequencies makes the design of high-gain antennas crucial. For such antennas to be commercially viable, they need to be compatible with low-cost technologies. Numerous antenna designs at 60 GHz have been previously proposed and implemented using multilayer technology including low-temperature co fired ceramic (LTCC), liquid crystal polymer (LCP) , and high-end hydrocarbon ceramic printed circuit boards (PCB).
In this paper, an implantable antenna is proposed for industrial, scientific, and medical (ISM) applications. The proposed antenna is found to be compact in size and has a reasonable return loss of -10 dB to cover the ISM band, which is insensitive to the variation of the electrical properties of the human body. Only a few implantable antennas have been evaluated under the ISM band and the proposed system is mainly tested for ISM band applications. Since large implants are used to reduce the transmission range, we are forced to construct compact antennas for adequate use in the ISM band since human skin and body fluids are strong attenuators of signals. A coplanar waveguide (CPW) fabricated on a dielectric substrate was first demonstrated by C. P. Wen [4, 5, 6, 14]. Since that time, tremendous progress has been made in CPW based microwave integrated circuits (MICs) as well as monolithic microwave integrated circuits (MMICs) [15, 16. The advantages of a coplanar waveguide structures over the conventional microstrip lines  are: Firstly fabrication process is simplified in CPW-fed structures. Secondly, it facilitates easy shunt as well as series surface mounting of active devices. Third, it eliminates the need for wrap around and via holes, and fourth, it reduces radiation loss. Furthermore the characteristic impedance is determined by the ratio of the dimensions, so size reduction is possible without limit, at the cost of higher losses. Also, there exists a ground plane between any two adjacent lines; hence cross talk effects between adjacent lines are very weak. Major advantages gained in manufacturing are, first, CPW lends itself to the use of automatic pick-and-place and bond assembly equipments for surface mount component placement and interconnection of components, respectively . Second, CPW allows the use of computer controlled on wafer measurement techniques for device and circuit characterization up to several tens of GHz [19, 20]. These advantages make CPW based MICs and MMICs cost effective in large volume. As a result, CPW circuits can be made denser than conventional microstrip circuits . These features make CPW  ideally suited for Microwave integrated circuits as well as Monolithic microwave integrated circuits applications. The quasi-TEM mode of propagation  on a CPW has low dispersion and hence offers the potential to construct wide band circuits and components.
II. Antenna Design:
The proposed antenna structure is shown in Figure. 1 which is printed on and Rogers 6010 (dielectric constant 10.2 and loss tangent tan [delta] = 0.0023) the antenna simply consists of low dielectric loss substrate, half-circle shaped ground plane, circle radiator, horizontal stubs and CPW feeding line. The geometry of the antennas in this section was decided by the parametric study of each element in the software. The proposed UWB antenna consists of substrate, ground, circle radiating patch and feed. The patch is connected to a feed line. The thickness of substrate is 0.635mm and Rogers 6010 (dielectric constant 10.2 and loss tangent tan [delta] = 0.0023) used as the substrate material. It has the high permittivity and low dielectric loss substrate material. The main dimensions of antenna are listed in Table I.
1. Width of the patch
C/[2f.sub.0] [square root of (2/[[epsilon].sub.r] + 1)]
[lambda] is wavelength
C is Velocity of light (3 * 108 m/s)
f0 is Operating/ Resonant frequency (in GHz)
2. Length of the patch
[[epsilon].sub.reff] = [[epsilon].sub.r] + 1/2 + [[epsilon].sub.r] - 1/2 [[1 + 12 h/W].sup.[1/2]] (2)
Where, [epsilon]r is the relative permittivity of the substrate h is the thickness of the substrate and is given by
h = 0.0606[lambda]/[square root of ([[epsilon].sub.r] (3)
The incremental length of the patch along its length has now been extended on each end by a distance AL and is given by empirical formula (Ramesh et al, 2001)
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (4)
The effective length is
[L.sub.eff] = C/[2f.sub.0] [square root of ([[epsilon].sub.eff])] (5)
The length of the patch is finally given as
L = [L.sub.eff] - 2[DELTA]L (6)
3. The fed location design
The position of the fed can be obtained by using (Dr.Max Ammnan)
[X.sub.f] = L/[square root of ([[epsilon].sub.reff])]
Where Xf is the desire input impedance to match the fed and [[epsilon].sub.reff] is the effective dielectric constant.
[Y.sub.f] = W/2 (8)
4. Ground dimension:
For practical consideration, it is essential to have a finite ground plane if the size of the ground plane is greater than the patch dimensions by approximately six times the substrate thickness all around the periphery. Hence, the ground plane dimensions would be given as (Huang, 1983) (Thomas, 2005)
[L.sub.g] = 6h + L;[W.sub.g] = 6h + L; (9)
The geometrical parameters of the length and width of patches are optimized in an attempt to achieve design goals at both the 2.4 and 5 GHz bands. For feeding, the impedance matching of the antenna can be improved by adjusting feed. The feeding structure of the square patch antenna consists of a coplanar waveguide feed with matching mode impedance of 50[OMEGA]. A CPW transmission line consisting of a single metallic layer is selected for feeding the antenna because of its easy integration on the paper substrate due to its planar structure. The proposed antenna includes vertical stubs and open ending slot. By combining the design concepts of the two single band antennas, this section will further extend and investigate these approaches to the dual band designs. The 2E-shaped slot is used for enhancing the AR bandwidth. The 2E-shaped slot is formed by extending the signal strip of the CPW in the x direction to the center of two sides of the outer geometry and the protruding into the slot at an inclined angle of parallel with respect to the x axis. The lengths of the horizontal slot extended inner to the patch are 5.6mm and width is 1.4mm respectively. The gap between the inner and outer wall in the vertical direction is 1.93mm. So, the CPW fed at center with two symmetrical E-shaped slots embedded in the center of ground plane accounts for the enhancement of the AR bandwidth. In addition, a tuning stub is embedded in the feeding structure in order to enlarge the impedance band. Hence, a CPW-fed square slot antenna with 2E-shaped CPW feedline for the circularly polarized radiation is achieved.
In order to calculate the full three-dimensional electromagnetic field inside a structure and the corresponding S-parameters, HFSS employs the finite element method (FEM). The basic approach of this method is to divide a complex structure into smaller sections of finite dimensions known as elements. These elements are connected to each other via joints called nodes.
After the optimization, the geometric dimensions of the proposed antenna are as follows in Table I. The basic approach of this method is to divide a complex structure into smaller sections of finite dimensions known as elements. These elements are connected to each other via joints called nodes. Each unique element is then solved independently of the others thereby drastically reducing the solution complexity. The final solution is then computed by reconnecting all the elements and combining their solutions. These processes are named assembly and solution respectively in the FEM. In order to design the high performance broadband CP square patch antenna, a detailed parametric study of the antenna is made.
RESULT AND DISCUSSION
The characteristics of the proposed CP antenna have been simulated by Ansoft High Frequency Structure Simulator (HFSS) software. Antenna design and simulation with ANSYS HFSS, the industry leading 3D electromagnetic (EM) simulation tool for high frequency and high speed electronic components. With multiple simulation technologies and powerful automated adaptive mesh refi nement providing gold standard accuracy, HFSS can help antenna designers who are constantly challenged with implementing designs across more and more frequency bands inside a smaller and smaller footprint. HFSS provides automatic, accurate, and effi cient solutions to overcome these challenges, making it the ultimate tool of choice for antenna simulation. Basic performance characterization such as return loss, input impedance, gain, directivity and a variety of polarization characteristics can be analyzed in HFSS. It was fabricated on 10 x 10 x 1 [mm.sup.3 FR4 epoxy substrate with dielectric constant [[epsilon].sub.r]=4.4 and loss tangent tan[delta]=0.02. Two symmetrical E-shaped slits embedded in the center of square patch are constructed, which can introduce more resonant branches. Novel symmetrical E-shaped slits introduce more resonant branches. Moreover, the antenna can be easily fabricated on PCB. Simulated results are illustrating that the optimum 3-dB bandwidth can be completely covered by the VSWR < 2 impedance bandwidth.
Fig. 2 shows the fabricated structure of proposed antenna. The fabricated design was simulated using EM simulator software HFSS and tested for scattering parameters using an Agilent network analyzer. The simulated return loss graphs shown in following figures. After parameters sweep and structure optimization, the return loss is shown in Fig. 3. The operate bands can cover 2GHz only. It is therefore important to refine at a frequency for which the return loss is high and hence the mesh refinement can produce accurate results.
Various cases were simulated in order to investigate how this parameter affects the results in HFSS. The value of delta S, which was common to all of them, was specified as 0.02. From return loss curves it is observed that the proposed antenna has prominent resonance with peak return loss of -26.25dB which occurs at 2.41GHz frequency. The simulated impedance bandwidth for 10-dB return loss is from 1540 to 3567GHz, which shows about 1173 GHz bandwidth. The antenna performs a wide bandwidth due to the two resonant modes which are excited by the 2E-shaped in square patch having CPW fed at center having 50 ohm impedance. It is evident that the simulation result shows the resonant frequency and bandwidth of the antenna with a reasonable accuracy. It is seen experimentally that the CPW fed strip monopole is resonating at 2.47GHz covering the impedance band from 1.53GHz to 2.46GHz. There should be maximum power transfer between the transmitter and the antenna to perform efficiently for any application.
The VSWR plot for CPW fed antenna is shown in Figure 4. Ideally, VSWR must lie in the range of 1-2 near the operating frequency value. The optimum VSWR of the proposed antenna at 2.45 GHz is 1.01 as shown in Fig.4. The desirable VSWR value from 1.1 to 1.9 has been achieved in the ISM band from 1.53GHz to 2.46GHz. It satisfies the 2:1 VSWR bandwidth, which is sufficient for the antenna operation.
VSWR is a measure of how well matched antenna is to the cable impedance. A perfectly matched antenna would have a VSWR of 1:1. This indicates how much power is reflected back or transferred into a cable. VSWR obtained from the simulation is approximately ero at two resonating frequencies. This considers a good value as the level of mismatched is very low because high VSWR implies that the port is not properly The elevation pattern and azimuthal pattern gain display is presented. For better performance o f any antenna, the radiation pattern should be in the shape of eight. For the proposed antenna, the radiation pattern is almost symmetrical and in the shape of eight. The height (h) of the radiating element from the ground has a major influence on the performance of the antenna, as it modifies the radiation pattern and the impedance of the antenna. Increasing it, guided waves of the antenna are transitioning more efficiently into free--space waves and the impedance become more capacitive.
Figure 5 presents the simulated radiation efficiency of the antenna. The radiation efficiency of the antenna is about 50% to 60%. It can be seen that although the efficiency shows some level of decrease with the improvement of impedance bandwidth, it is acceptable for the circularly polarized antenna. Another important parameter to understand the antenna characteristics 2D radiation pattern which is shown in figure 6 for the proposed antenna. Radiation pattern shown in below figures presents the graphical representation of radiation properties of antenna as a function of space co- ordinates taken in xy plane.The proposed antenna has bi-directional radiation patterns in E-plane at 9.5 GHz resonant frequency. In H-plane, the antenna has Omni-directional radiation patterns, which indicates that it can receive the signals in all directions.
The different parameters of proposed antenna for biomedical at 2.4GHz has been compared with simulated & measured results as given in the table 2 below.
In this paper, we presented the design of a rectangular patch antenna covering the 1.5GHz-3.5 GHz frequency spectrum. The resonant frequency of 2.45 GHz It has been shown that this design of the rectangular patch antenna produces insertion loss of -26 db Bluetooth application.. The design antenna exhibits a good impedance matching of approximately 50 Q. This antenna can be easily fabricated on substrate material due to its small size and thickness. The simple feeding technique used for the design of this antenna makes this antenna a good choice in many communications.
We are grateful to referees for their valuable comments.
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(1) S. Suganthi, (2) M. Noorjahan, (3) P. Thiruvalar selvan
(1&3) Professor, Department of Electronics and Communication Engineering,
(2) Assistant Professor, Departmen t of Electronics and Communica tion Engineering,
(1&2) K.Ramakrishnan College of Technology, Tiruchirappalli, Tamilnadu, India.
(3) TRP Engineering College, Tiruchirappalli, Tamilnadu, India.
Received 28 March 2017; Accepted 7 June 2017; Available online 12 June 2017
Address For Correspondence:
S. Suganthi, Professor, Department of Electronics and Communication Engineering, E-mail: firstname.lastname@example.org
Caption: Fig. 1: Schematic diagram of proposed antenna
Caption: Fig. 2: Fabricated structure of proposed biomedical antenna
Caption: Fig. 3: Simulated return loss S11 of antenna
Caption: Fig. 4: VSWR of the proposed antenna
Caption: Fig. 5: Simulated radiation efficiency of proposed antenna
Caption: Fig. 6: Simulated radiation patterns of Antenna at
Caption: Fig. 7: Simulated radiation patterns of Antenna at 2.4GHz
Caption: Fig. 8: Simulated 2D gain of Antenna at 2.4GHz
Table I: Dimensions Of The Proposed Antenna Parameter Dimension(mm) Parameter Dimension(mm) L1 10 G 5.2 W1 10 X 6.2 L2 0.3 Y 1.93 L3 10 W2 0.4 L4 5.6 W4 14.6 Table II: Comparison Different Parameters Of The Proposed Antenna Parameters Simulated Measured Return loss -26 -24 Radiation efficiency 98.79 97 Frequency(GHz) 2.42 2.4 Bandwidth 80% 76%
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|Author:||Suganthi, S.; Noorjahan, M.; Selvan, P. Thiruvalar|
|Publication:||Advances in Natural and Applied Sciences|
|Date:||Jun 1, 2017|
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