DESIGN AND ANALYSIS OF MICROSTRIP PATCH ANTENNA FOR WHITE SPACE TV BAND

Abstract

Federal Communications Commission regulates the radio spectrum with designation of three bands (54 -88 MHz, 174-216MHz and 470-806MHz) for broadcasting terrestrial television. Television stations are often operated in geographically separate areas to avoid interference. Furthermore, all television stations are not used in some parts of the nation due to population density. The frequency designated to these unused television stations and the spectrum between TV stations are called white spaces. Many researchers have been investigated and demonstrated that this untapped spectrum may be utilize to deliver broadband Internet access while getting along with nearby TV channels. White space is an important possibility in the context of our evolving wireless mobile environment. This portion of the spectrum is primed for experimentation and innovation. Due to introduction of 4G, 5G and IoT services the frequency spectrum above the 806 MHz becomes very crowded. White space TV band frequencies fascinate researcher because of large available spectrum, good propagation characteristics, excellent penetration, and of course no cost. As the frequency of TV band is small as compared to the most of the available wireless devices, the biggest challenge at this frequency is the largest physical size of the antenna. Planar antenna is the one of the solutions to reduce size of TV band antenna. There is some disadvantage of planar antenna like low gain, narrow bandwidth etc. Various bandwidth and gain enhancement techniques are available in literature to overcome the disadvantages of planar antennas. In this thesis, microstrip patch antennas are designed to operate in white space TV band. The gain and bandwidth enhancement techniques are used to achieve ultra-wide band and high gain antennas. Fractal geometry is used to further reduce the size of the antenna with multiband characteristics. The different applications of these antennas are RFID, IEEE 802.11, ‘Super Wi-Fi’ and for long distance communication in the presence of obstacles such as wall, hill, mountains etc. The thesis is organized into six chapters as described below. In the first chapter, a brief introduction of white space TV band and its spectrum is explained with the availability of TV band for different applications. Antennas were designed for high gain and bandwidth. This introduction lays the foundation that is needed to appreciate the work performed in this thesis. In the second chapter, circular patch antenna is designed for RFID application. In India, the frequency band used for RFID applications is 865–867 MHz with 2MHz bandwidth. In xi comparison to the currently existing RFID antenna, the proposed antenna is compact in dimensions. Four concentric rings are sliced from a circular microstrip patch, and a shorting pin is used to connect the patch to the ground. The design was done on FR4, which is a fairly common and durable substrate. The antenna design's gain and directivity are 7.6dBi and 9.9 dB, respectively. The antenna may operate on two bands in the intended frequency spectrum, namely 479- 492 MHz and 643 -653MHz. The bandwidth obtained in these bands are 13 MHz and 10 MHz, individually, that is higher than commercially available UHF RFID antenna. The bands have a return loss of -29dB and -14dB, respectively. Parameters of design antenna have been compared with the commercially available RFID antenna. The proposed antenna is having the lowest VSWR of 1.07 as compared to 1.4 for all compared antennas. Bandwidth is also increased from 3MHz to 13MHz. It was observed that the proposed design has a compact size with a good agreement of gain, bandwidth, VSWR, and front-to-back ratio and limited ground size Extending the work performed in second chapter, again circular microstrip patch antenna with three circular rings is designed. In 1st design we are able to achieve desirable gain and multiband, but the bandwidth is small. After changing the position of rings and size of ground plane proposed antenna can be used in complete TV band with a compromise in gain. In the presented paper a novel application of microstrip circular patch antenna with three rings on patch is proposed. The bandwidth and efficiency of the proposed antenna can be compared with the work already published in the white space TV band. It was observed that the proposed antenna is having good bandwidth and efficiency with considerable gain. In the fourth chapter, inverted stacked parasitic patch antenna with two layers is explored. In this design, two layers are stacked on each other with coaxial feed at the lower circular patch. The two top circular patches are placed in an inverted position and electromagnetically coupled with a lower patch. The substrate used is FR4. The proposed antenna can operate between 499- 650MHz frequency band with 5.6dBi gain. The proposed antenna is having an efficiency of 98%. A parametric analysis is done to cater to the requirements of the antenna size, gain, and radiation pattern. The parametric study found that when both top patches are elliptical, the lowest size with the largest gain is achieved. After variation of the eccentricity of top two patches, it was concluded that for compactness of antenna top patch eccentricity should be 0.5 with increased gain of 5.6dBi. Depending upon the requirement, the proposed antenna can be xii used for base station and as user terminal. These low frequencies allow signals to penetrate things like walls, trees, etc., better than higher frequencies, and they can be used for various purposes, such as IEEE 802.11, in the 470–806 MHz band between TV channels. In the fifth chapter, fractal patch antenna is designed. The effect of fractal slots on patch and cross slots in ground are investigated. In the proposed design 4 iteration Koch snowflakes patch is used to get dual band. 4th iteration Koch snowflake patch is placed 18mm above the air. FR4 is placed 65mm above the ground plane as superstrate. As no of iteration increased size of antenna is going to reduce. Further 4th iteration Koch snowflakes slots have been created in patch to get three bands. Last two bands have been combined to get higher bandwidth by creating 4th iteration cross slots in the ground plane. The antenna is working in multi polarization in the received bands. The physical size of antenna is reduced by 38 mm with a gain of 4.5dBi In the end, the sixth chapter consists of the overall conclusion and future scope of the thesis. In this thesis, we designed circular microstrip patch antenna with circular rings, inverted stacked parasitic circular patch antenna and Koch fractal patch antenna to achieve high gain and considerable bandwidth in white space TV band with reduced size. These antennas can be used as RFID application, IEEE 802.11, super wide band and any application which requires TV band frequency. In this way, this thesis will discuss size reduction, bandwidth and gain enhancement techniques by using slots, stacking and fractal shapes.