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:Uploaded on FRIDAY 28th OCT 2016

ANALYSIS OF ANTENNA RADIATION PATTERNS OF DUAL BAND MICROSTRIP PATCH ANTENNA

In this article, We are going to analyse the results for the Antenna Radiation Patterns for the fabricated Dualband rectangular Microstrip patch antenna by Chemical etching method.

Antenna radiation plots can be quite complex because in the real world they are three-dimensional. However, to simplify them a Cartesian coordinate system (a two-dimensional system which refers to points in free space) is often used. Radiation plots are most often shown in either the plane of the axis of the antenna or the plane perpendicular to the axis and are referred to as the azimuth or "E-plane" and the elevation or "H-plane" respectively.

Many plotting formats or grids are in use. Rectangular grids as well as polar coordinate systems are in wide use. The principal objective is to show a radiation plot that is representative of a complete 360 degrees in either the azimuth or the elevation plane. In the case of highly directional antennas, the radiation pattern is similar to a flashlight beam.

The antenna radiation plot shows the relative field intensity in the far field (at least 100 feet or 30 meters distant from typical antennas) in free space at a distant point. Ground reflections are usually not a factor at these frequencies so they are often ignored. The antenna supplier either measures the radiation pattern by rotating the antenna on its axis or calculates the signal strength around the points of the compass with respect to the main beam peak. This provides a quick reference to the response of the antenna in any direction. Note that the antenna radiation pattern is reciprocal so it receives and transmits signals in the same direction.

For ease in use, clarity and maximum versatility, radiation plots are usually normalized to the outer edge of the coordinate system. Furthermore, most of us are not accustomed to thinking in terms of signal strength in volts, microvolts etc. so radiation plots are usually shown in relative dB (decibels).

For those not familiar with decibels, they are used to express differences in power in a logarithmic fashion. A drop of 1 dB means that the power is decreased to about 80% of the original value while a 3 dB drop is a power decrease of 50% or one-half the power. The beamwidth specified on most data sheets is usually the 3 dB or half-power beamwidth.

Another reason for using dB is that successive dB can be easily added or subtracted. A doubling of power is 3 dB while a quadrupling is 6 dB. Therefore, if the antenna gain is doubled (3 dB) and the transmitter power is quadrupled (6 dB), the overall improvement is 9 dB. Likewise, dB can also be subtracted.

Three types of plotting scales are in common usage; linear, linear logarithmic and modified logarithmic. The linear scale emphasizes the main radiation beam. Some would argue that this plotting system makes the radiation pattern look better than it really is since it suppresses all side lobes. The linear logarithmic scale is preferred when the level of all sidelobes is important. The modified logarithmic scale emphasizes the shape of the major beam while compressing very low-level (>30 dB) sidelobes towards the center of the pattern. This plotting scale is now becoming quite popular.

How to interpret Aantenna Radiation Plots?

An antenna plot is like a road map. It tells you where the radiation is concentrated. Patterns are usually referenced to the outer edge of the plot which is the maximum gain of the antenna. This makes it easy to determine other important antenna characteristics directly from the plot.

Most antenna users are interested in the directivity or beamwidth of the antenna. As mentioned earlier, this is usually referred to as the "half-power" or 3 dB beamwidth, the points between which half the power is radiated or concentrated, and specified in degrees. As an example, the typical half-power beamwidths of a 3, 6 and 10 element Yagi are 60, 40 and 30 degrees respectively.

Another popular antenna specification is the "front-to-back" (F/B) ratio. It is defined as the difference in dB between the maximum gain or front of the antenna (usually 0 degrees) and a point exactly 180 degrees behind the front. The problem with specifying only the F/B ratio is that it does not account for any lobes in the rear two quadrants.

How to use Antenna Radiation plots?

Antenna plots are the road map for the antenna user. Plots tell you where power is being radiated or received (since they are reciprocal). They also tell you how much degradation you can expect if the antenna is not aimed properly. Sometimes it is desirable to communicate with more than one station. Antenna plots will assist in the proper aiming of the antenna for optimum performance on all the desired signals. The narrower the beamwidth, the greater the difficulty in properly aiming the antenna. Remember that weather phenomenon such as wind may also affect antenna performance or dictate the type of antenna mounting.

If there are interfering signals, they may be picked up by the antenna. When you have a radiation plot, you can determine the actual level of such signals. Finally, if there are interfering signals, the radiation plot can be used to minimize them by placing such signals in a null or low sidelobe position.

PATTERN ANALYSIS

Simulated results
HelpShareideas- DESIGNED MICROSTRIP DUAL BAND PATCH ANTENNA image

Fig 1. Simualted Radiation Pattern for MICROSTRIP DUAL BAND PATCH ANTENNA


Practical results
HelpShareideas- View of FABRICATED PATCH ANTENNA AS PER OUR DESIGN image

Fig 2a. Practical Radiation Pattern for MICROSTRIP DUAL BAND PATCH ANTENNA


HelpShareideas- View of FABRICATED PATCH ANTENNA AS PER OUR DESIGN image

Fig 2b. Practical Radiation Pattern for MICROSTRIP DUAL BAND PATCH ANTENNA

APPLICATIONS

We have designed a Patch antenna for ISM ranging from 2.4GHz to 2.5GHz ,S-Band (2GHz -4GHz) and C-Band ( 4GHz-8GHz) .

INDUSTRIAL, SCIENTIFIC AND MEDICAL (ISM BAND) :

  • The Industrial, Scientific And Medical (ISM) radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial, scientific and medical purposes other than communications. In general, communications equipment must accept any interference generated by ISM equipment.


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