In this project, the efficient design of circular-shaped microstrip patch array antenna for Ultra Wide Band applications is been proposed. In the recent era, microstrip patch antenna plays a vital role as they are found to be immensely useful due to its compact nature, easy integration and its lightweight. UWB systems are popular because of their larger bandwidth and power management efficiencies but the design of UWB based applications requires low profile antennas. It has been found that circular antenna gives better return loss, good directivity and radiation pattern.
The inset feed technique, used in the proposed model provides good impedance matching, which further improves the characteristics of the antenna.
The latest growth in the field of wireless technology requires the antenna which can perform multiple capabilities and functions.Hence, Ultra Wide Band (UWB) communication systems achieve huge attention in both academics and industrial fields. Ultra Wide Band has a number of boosting advantages that are reasons why it presents more powerful solution to wireless broadband than other technology.
Ultra Wide Band (UWB) has been chosen extensively due to larger bandwidth range proposed by the FCC (Federal Communications Commission) in 2002 by United States of America (USA). According to the commission the bandwidth allotted for the wireless communication ranges from 3.1GHz to 10.6GHz. UWB is preferred mostly because of its high data rate i.e., hundreds of Mbps (Megabits per seconds) or several Gbps (Gigabits per seconds) with distance coverage of 1 to 10 meters and also for its low power utilization.
So, many researchers are paying more attention in this field because the FCC has released commercial use of UWB for indoor applications.
Microstrip Patch Antennas plays a vital role in the field of wireless communication due to its less weight, compact size, ease of fabrication and low cost. This antenna basically consists of a dielectric substrate.There is more number of substrate available for the design of micro-strip patch antenna and its dielectric constant ranges from 1.17 to 2.5. The top layer of the antenna is called as the metallic patch which can be made of Gold or Copper and the lower layer is the ground plane which has to be infinite theoretically. The efficiency of the patch antenna depends on its patch shape and size, substrate thickness and its dielectric constant, and also depends on the feed point location and type.In certain applications such as microwave imaging, or radar applications,high gain is needed.
Circular microstrip patch antennas are one particular configuration of the antenna, which has more potential in the applications of low profile antennas while considering its geometry. There are many shapes available for constructing microstrip patch such as Dipole, Square, Rectangular, Triangular, Circular, Circular Ring, and Disc sector in which Circular patch has more advantages like flexibility in design and has largest bandwidth in terms of GHz and also it can give better return loss, radiation pattern and good directivity.
Typically, the Ultra wide band single antenna element has relatively low gain of 2-3dBi, which can be improved by using antenna arrays.Antenna arrays are widely used in many practical systems to improve gain and provide beam scanning capability.
The basic design model of the proposed ultra wide band antenna is given in the introduction. Section I specifies the antenna dimensions and configuration using the conventional design formula. The last section deals with the result analysis of the depicted model.
The proposed model of the antenna consists of a perfectly conducting patch with the FR4 substrate.The FR4 substrate has a relative permittivity of 4.4 and a loss tangent of 0.02. The thickness of the dielectric substrate used is of 1.6 mm. the upper radiating part comprises of a circular patch of radius of 12 mm calculated using the formula (3) given below for the resonant frequency of 3.5 GHz.
The feeding technique given for excitation to the circular patch is inset feed. The width of the line feed is calculated using (5), and a value of 25.88 mm is determined for the resonant frequency of 3.5 GHz. Due to the design constraints, the width is slightly adjusted to 20.59 mm. The length of the line feed used is of 3 mm and is calculated using the formula from (5) to (7). The obtained result from the formula  has a dimension value of 19 mm. But for better resonant characteristics, only 1/6 times of the above-obtained value is considered.
The design of UWB antenna element is presented in Fig.1. A single patch antenna element consists of a circular patch with inset feed printed on FR4 substrate having relative permittivity 4.4 with the loss tangent 0.02.
Fig 1:Single element antenna
Return Loss is the plot of Reflection Coefficient in dB vs. frequency in GHz; Return Loss plot for the single element antenna is shown in the Fig 1.1.The obtained graph shows that, the antenna resonates under the following three frequencies i.e 3.5GHz,6.4GHz and 9.5GHz.The Return loss at this frequencies is -12.2dB,-23dB,-14.3dB.
Fig 1.1:Return loss for single element
Gain is an important parameter of an antenna that defines the total power which is radiated in a particular direction. The unit of gain is dBi. Fig 1.2 shows the graph of gain v/s frequency. The gain of 3dBi, 2.2dBi,and 6dBi at 3.5 GHz, 6.4GHz and 9.5GHz respectively.
Fig 1.2:Gain of single element antenna
Fig 1.3: Antenna efficiency of single patch UWB antenna
In this study we now consider 2×1 array UWB antenna as shown in Fig 2.This antenna array is designed by using two identical antennas.
Fig 2: Two Element UWB Array
Return Loss plot for the two element array is shown in the Fig 2.1.And the obtained graph shows that the antenna resonates under four frequencies i.e 2.1GHz,4.1GHz and 7.5GHz and 9.1GHz.The Return loss at this frequencies is -10.8dB,-14.2dB,-17dB and -18dB respectively.
Fig 2.1:Return loss for two element array
Fig 2.2:Gain of two element array
The above figure shows the graph of gain v/s frequency. The gain of 7dBi, 5.8dBi,and 7.2dBi and 8.1dBi at 2.1GHz, 4.1GHz and 7.5GHz and 9.1GHz respectively.
Fig 2.3: Antenna efficiency of two-element array
We have employed IE3D software for simulating the designed antenna. As we know that gain, bandwidth and centre frequency characterizes any antenna. A graphical representation of the single patch and 2×1 arrays, gain, return loss and antenna efficiency is shown. Thus, the 2×1 array results in good gain compared to that of the single patch and also it covers the entire UWB frequency range.
Thus, the circular microstrip patch antenna with single patch and 2×1 arrays is designed and simulated for UWB application. The obtained return loss plot covers the range from 2GHz to 11GHz that includes the UWB range of 3.6 to 10.6 GHz. The other antenna parameters like gain, antenna efficiency and return loss are obtained for the depicted model gives a satisfactory performance. The antenna array designed improves the gain as compared to that of the single patch. Hence, the circular microstrip patch antenna designed with 2×1 arrays can be used for multi-band wireless communication.
I would like to thank my internal guide, Prof. Palhavi Kerkar, Assistant Professor , ETC Department , for allowing me to carry out this project under her supervision and for her valuable suggestions , encouragement and constructive criticism. I would also like to express my gratitude to Dr.H.G.Virani, Head of Department , Electronics and Telecommunication Engineering.
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