Article Preview
Top1. Introduction
In the communication field, Wireless communication is the most vibrant and fastest growing technology, in which information is transmitted from one end device to other end without making physical connections (David & Viswanath, 2005). Interestingly, in every communication system, to transfer information transmitter and receiver play quintessential role and can be deployed between few meters to thousands of kilometers like T.V remote and Satellite communication respectively. As, no guided medium is used, so transmission and receptions of signals is achieved using Antennas. Antenna is the device that converts electrical signal into radio waves on transmitter side and vice versa on receiver side (Alejandro, 2008). Also, it is one of the crucial parts in circuit designing to achieve compactness. Nowadays, in communication systems different types of antennas are available like Horn antenna, dipole antenna, PIFA, and micro strip patch antenna etc. as shown in figure 1. Also low profile antennas are desired to achieve high performance over wide range of frequencies. Due to such reasons micro strip patch antenna are gaining much attention in this field and used widely because of their numerous advantages like low profile, low cost, planar, robustness, and conformability to curved surfaces, ease of installation and fabrication simple and inexpensive to manufacture using modern printed circuit technology (Balanis, 2016).
Figure 1. Different types of antennas for wireless communication
1.1 Patch Antenna
Concept of patch antenna came in existence in 1953 and patented in 1955 but antenna gain attraction for various applications in 1970’s (Girish Kumar, 2002). Patch antennas as shown in figure 2 consist of radiating patch on one side of dielectric substrate and ground plan on other side. Antenna radiating patch can be triangular, circular, square, rectangular, ring etc. as reflected in figure 3 below. The radiating patch and feed line is photo etched on the dielectric substrate.
Figure 2. Generalized structure of a Patch antenna
Figure 3. Different shapes available of patches for application
For patch antenna, length of rectangular patch taken is between 0.3333λ0 to 0.5 λ0; here λ0 is the wavelength of free-space. Thickness of radiating element patch is taken (h<< λ0). Dielectric substrate thickness (t) is considered between 0.003 λ0 and 0.05λ0 with dielectric (εr) constant of 2.2 to 12. Antenna patch is selected so that its radiation pattern remains maximum to the patch and can be achieved by properly exciting the mode of antenna (Balanis, 2016). Patch antenna dimensions depend upon frequency of operation, proper selection of dielectric substrate material, and dielectric constant value of material used. To get better efficiency of antenna, dielectric material with high thickness and low value of dielectric constant is needed. But it increase the antenna size, so to design compact antenna, substrate material with high dielectric constant can be used but these are less efficient and give less bandwidth. So, there is always compromise between antenna size and performance efficiency. Dielectric constant with small thickness and high εr value can be used for microwave circuits because tightly bound magnetic fields are needed to reduce effect of unwanted radiations and coupling and to achieve more compactness. Path antenna analysis is done using transmission line, cavity or full wave methods. Among all methods transmission method is easy but less accurate and cavity model method is more accurate but difficult to analyze and more complex. Most accurate method is full wave methods of analysis (Balanis, 2016). Due to finite dimensions of patch, antenna goes under fringing effect from the edges. The amount of fringing is mainly function of antenna dimensions and substrate height. In antenna for xy- plane, fringing is function of L/h and εr of substrate. Instead, of various advantages patch antennas has some shortcomings in terms of gain and bandwidth. Researchers are mainly focusing on different techniques used to improve antenna gain and bandwidth.