A circular polarized wave radiates energy in both the horizontal and vertical planes and all planes in between. Non linear polarized wave forms are said to be elliptically polarized. Here the proposed antenna is circularly polarized and it can be used in terrestrial communications the link margins are much better than space borne signal mainly due to the distances involved. The ideal methods for analysis microstrip antenna are Transmission line model, cavity model and Methods of moment techniques.
In this model microstrip antenna is represented by two slots of width W and height h, separated by a low impedance transmission line of length L. Some electric field lines are travelling outside the substrate resulting fringing effect that is changing effective dielectric constant. It is a function of the dimensions of the patch and the height of the substrate.
Transmission line model is easy to design but it is having less accurate. Transmission line model ignores field variations along the radiating edges. This model provides a better way to model the radiation patterns and is closer in the physical interpretation of the antenna characteristics. The normalized fields within the dielectric can be found more accurately by treating the region as a cavity bounded by electric conductors above and below and by magnetic walls along the perimeter of the patch.
The disadvantage of this method is complex in nature. In this method, the surface currents are used to model the microstrip patch and the volume polarization currents are used to model the fields in the dielectric slab. The basic form of the equation to be solved by the Method of Moment is. The aim here is to find g, when F and h are known. Here we used ADS software for analysing proposed antenna.
Microstrip topology is analysed quickly and accurately with momentum using ADS. The simulator is based on the Method of Moments MoM technology that is particularly efficient for analysing planar conductor and resistor geometries. The implemented antenna is having FR4 substrate with dielectric constant 4.
Thickness of the Substrate is taken as 1. Operating frequency has chosen as 2. A radius of circular patch antenna can be calculated by using the following equations. The simulation of circular microstrip antenna is done on ADS software and we get simulation results of return loss, Gain, 3D E- fields. Figure 7 depicts the resonating frequency of proposed patch antenna is 2.
This low value of return loss yields higher efficiency in WLAN applications. Figure 7 and 8 shows the return loss characteristic of simulated and fabricated antenna, both are in a good agreement. The antenna is having best impedance matching at 2. Radiation pattern in figure 10 represents the directional properties of microstrip antenna.
Antenna gain and Directivity for frequencies within the bandwidth is presented in figure 11, maximum gain is approximately 6. The simulated and measured results satisfy the requirements of wireless communication.
In this paper, dual fed circular polarization microstrip antenna was chosen. The patch is generally made of conducting material such as copper or gold and can take any possible shape.
Fig 1 Microstrip antenna For good antenna performance,a low dielectric constant with thick dielectric substrate is desirable,as it provides better radiation,better efficiency and larger bandwidth. Transmission line model depicts the microstrip antenna by two slots of width W and height h seprated by transmission line of length L.
The microstrip is a non homogeneous of two dielectrics,typically,substrate and the air. Most of the electric field lines reside some part in the air and rest in the substrate. This results that transmission line. So,dominant mode of propogation will be the quasi-TEM mode. The coordinate axis was selected as the height along z direction , length along x direction and width along y direction. The microstrip patch antenna is represented by two slots, separated by a transmission line of length L and open circuited at both the ends as shown in Fig 4.
Fig 4 Rectangular microstrip antenna The voltage is maximum along the width of the patch and due to the open ends,the current is minimum.
With respect to the ground plane the fields at the edges can be resolved into tangential and normal components. The normal components of the electric field at the two edges along the width are in opposite directions and thus out of phase as seen in Fig 5.
The tangential components which are in phase, means that the resulting fields combine to give maximum radiated field normal to the surface of the structure. The fringing fields along the width can be modeled as radiating slots and electrically the patch of the microstrip antenna looks greater than its physical dimensions.
Fig 5 side view of antenna. We have designed an array of rectangular patch antenna of the center frequency 2. Gain required as We have employed a hybrid structure where we are using rogers RT duroid as a substrate. The three essential parameters for the design of microstrip patch antenna are: 1 Frequency of operation f 0 : The resonant frequency of the antenna must be selected appropriately.
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