DESIGN OF WEARABLE MULTIBAND CIRCULAR MICROSTRIP TEXTILE ANTENNA FOR WIFI/WIMAX COMMUNICATION

In proposed design the wearable circular microstrip antenna of radius of patch is 14 mm and the top of patch consist of two square slits of dimensions 5x5 mm2 and 10x10mm2 and the ground structure is made partial of 28mm x 86mm. Due to the properties of jeans fabric as low cost, flexible the antenna is made wearable. In the proposed study, circular microstrip textile based antenna has been designed for the ISM band of resonating frequency of 2.4GHz. The proposed structure provided the triple band as the radiating frequencies of 2.4GHz for WiFi, 6.4GHz for WiMAX and 12GHz for 5G communication applications. The simulated and fabricated results such as return loss, VSWR and gain - directivity etc. are analyzed and compared for the frequencies of 2.38GHz, 6.4GHz and 12GHz. In this proposed antenna, the bandwidths of antenna are obtained of the order 700MHz, 3.43GHz & 2.75GHz and gain of antenna are of the order 1.89 dBi, 3.98 dBi & 4.86 dBi.

802.11 to 16, the WiMAX is used in broadband wireless communication. The frequency band allocated to WiMAX IEEE 802.16a is varying from 10 -16GHz and for IEEE 802.16d or IEEE802.  varies from 2-11GHz. This frequency band is implemented to interface with OFDM or OFDMA for broadband wireless communication. Nikhil Kumar Singh. et al. (2016) observed that proposed antenna operating at three frequency bands of 3.42GHz, 9.73GHz & 11.17GHz and it has been used for multiband application. The wearable antenna has been designed on jeans material and used for on human body communication [1]. H.K. Bhaldar. et al. (2020) studied the microstrip textile antenna for Wi-Fi communication and antenna has been resonating at frequency of 2.45GHz & provided return loss of -15.76dB with directivity of 8.05. The antenna is designed with rectangular shape & jean as dielectric material to get wide bandwidth [2]. Carlos. et al. (2018) designed on body wearable antenna designed at ISM band of frequency 2.45GHz & radiated at -18dB of return loss & also a robust snap on button textile antenna designed at 2.45GHz and provided return loss of -25dB [3,4]. Pranita Manish et al. (2018) observed and analyzed the microstrip textile antenna simulated at 2.45GHz with different dielectric fabric materials such as Cotton, Polyester, Cordura and Lycra. The values of return losses at 2.45 GHz frequency for respective textile material have studied -32dB, -35dB,-29dB and -31dB [5]. Anurag Saxena. et al. (2018) designed the antenna operating at the multiple frequencies from 5.3GHz to 10.15GHz and provided the bandwidth of 62.78%, return loss of -25dB at 5.44GHz & -24db at 8.05GHz. The author used the moon strip line structure of patch [6]. Idellyse and Rama Reddy. et al. (2018) proposed the circular polarized textile antenna and U slot conical antenna which is designed at ISM band of frequency range 2.4GHz to 2.45GHz, the values of S11 parameter -35dB & -20dB are observed at resonating frequency [7][8]. Sweety Purohit. et al. (2014) simulated the light weight wearable antenna using jeans material at the resonant frequency of 2.45GHz. When antenna used for on body communication, the SAR is very important parameter considered for wearable application and the standard SAR value used is of 1.6 W/kg of tissue [9]. Jiahao Zhang et.al (2017) observed the miniature feeding network for aperture coupled antennas designed at frequency of 2.4GHz -2.483GHz with gain of 5.6dBi. The author have studied various shapes of coupling aperture such as ring, H-shaped, rectangular, E shaped, cross etc. at various frequencies in ISM band [10]. The Yiye Sun. et al. (2014) designed the circular patch with thin feed line and has rectangular ground plane. The bandwidth of designed antenna has been enhanced due to use of tapered feed line. The proposed antenna used at ultra-wide band application for frequency range of 2.8GHz to 16GHz [11]. Punith S. et al. (2020) studied and the implemented the multiband antenna resonating at 23.9GHz, 35.5GHz and 70.9 GHz and used for 5G communication. The antenna has been analyzed to achieve the return losses of -19.97dB, -22.73dB and -21.96dB for the above mentioned operating frequencies [12]. S. Kumar. et al. (2018) analyzed and implemented the co-planar fed antenna at ISM band for implantable on the body with bio sensor for on body communication. The proposed antenna designed with loop structure and it is radiating with return loss of -37dB [13]. Seyed Mohsen. et al. (2019) designed the multiband CPW fed microstrip wearable antenna for operating frequency of 3.2GHz to 16.3GHz for ultra-wide band application. The compact antenna is implemented on the body and in the air; the efficiency observed on the body is greater than in the air located antenna [14]. Sandeep Singh Sran. et al. (2020) studied and analyzed the wearable fractal antenna operating at 2.53GHz, 4.9GHz and 7.6GHz for S, C, and X band application. The proposed antenna improved the gain and bandwidth at these resonant frequencies [15]. A. Deviovanni. et al. (2018) proposed the high gradient linacs for hadron therapy for the frequency range of 3 to 5.7GHz. The proton beams are radiated by using hadron therapy with energies 70 and 230Mev [16].
After doing the literature survey, the proposed antenna design focused on the improvement of the gain and bandwidth of antenna.

METHODOLOGY 2.1 Microstrip Antenna
Microstrip antenna is most preferred antenna among all printed antenna due to its properties such as light in weight, low cost & ease of installation. In today's era microstrip patch antenna widely used for wireless communication. The geometry of microstrip patch antenna consist of top patch & bottom ground plane separated by dielectric materials such as FR4, Rogger etc. as shown in figure 1. In case of wireless applications, the various structures of microstrip patch antenna are used such as square, rectangular, circular and triangular etc.

Proposed Model
The proposed circular microstrip textile antenna has been designed for Wi-Fi communication at the frequency of 2.4 GHz with radius of patch 14mm is calculated as shown in equation 1.The figure 2a shows geometry of designed circular antenna which consist of top patch with two square slits of dimensions 5mm x5mm and 10mm x10mm provide the extra frequency band. The one more extra frequency band have been achieved by using partial ground of partial ground of 86mm x 28mm which is shown in figure 2b. The circular microstrip textile antenna has made with copper foil of thickness 35micron and the dielectric substrate used as jean material with relative permittivity of 1.7 & height of material 1mm. The designed antenna is excited with voltage source connected to microstrip feed line of impedance 55 ohm. The study of microstrip antenna stated that, the inverse relation between the bandwidth and the dielectric constant ɛr. When the dielectric constant value is decreasing, the bandwidth of antenna is increasing. So this method is implemented proposed study of antenna design.
It has been observed that the proposed geometry of antenna radiating at two extra bands of frequencies 6.4GHz & 12GHz which is used for WiMAX and 5G communication. The 5G communication band can be used from 3.5GHz to 300GHz & the WiMAX frequency band used from 2GHz to 8GHz. So proposed antenna have provided the three frequency bands 2.32GHz, 6.4GHz & 11.95GHz used for Wi-Fi, WiMAX & 5G communication. The designed antenna is compact in size and provided enhanced bandwidth which is requirement of wearable application.
The proposed microstrip textile antenna has been simulated in CST microwave studio software and the various antenna parameters have been analyzed. The figure 3 shows geometry of fabricated microstrip textile antenna and it is tested using VNA of 20GHz frequency.

I) Return Loss:
For the perfect radiation the value of return loss must be maintained at minimum -10dB. From figure 4, it has been observed that designed antenna have provided the triple bands & the values of return losses are -31.827dB at a frequency of 2.3268GHz, -20.227dB at a frequency of 6.47GHz and -14.42 dB at a frequency of 11.952GHz. The bandwidths observed at these frequency bands are 0.7GHz, 3.43GHz and 2.75GHz at -10dB of the return loss plot. The above said bandwidths have been enhanced by using low value of dielectric constant of jean and partial ground structure. The simulated and fabricated results are also achieved same which is shown in figure 5 and table no.

V)
Efficiency: The efficiency of antenna calculated by the ratio of power radiated by an antenna to the total input power fed to antenna. The total efficiency differs from radiation efficiency due to losses takes place because of impedance mismatch. = * eq (3) Where ηt = total effeciency, ηr = radiation effiecincy, ZI = Impendace mismatch loss. From figure 9, it has been observed that the proposed antenna radiated at 3 frequancy bands. So the radiation and total efficiecy at three frequency bands are 78.83% & 76.61 at a frequency of 2.32GHz , 97. 98% & 95.63% at a frequency of 6.47GHz and 97.88% & 94.21% at 11.95GHz. provides one extra band in comparison with simulated results. In fabricated results also the bandwidth is improved due to use of low dielectric constant, jeans as textile material and partial ground structure. The fabricated antenna is tested with Anthrusu VNA of 20GHz.

Figure 10: Return Loss of the fabricated antenna
The

CONCLUSION
In the proposed design, the circular microstrip textile antenna with edge feed has been designed at 2.4GHz frequency & provided return loss of -31.827dB. The designed antenna also provided the 2 additional bands of frequencies 6.47GHz & 11.95GHz due to use of 2 square slits and partial ground. The radiated efficiencies of antenna are 78.83%, 97.98% & 97.88 and total efficiencies are 76.61%, 95.63 & 94.21 at the frequency bands 2.32GHz, 6,47GHz & 11.95GHz. So it has been concluded that the proposed antenna is radiating with efficiency around 90% at multiple bands.
From the simulated and fabricated results, it is concluded the proposed antenna provided bandwidth improvement from 0.7GHz to 2.75GHz and both simulated & fabricated results are validated.