Claims:claims:
1. A design structure of Co-ax fedMicrostrip Antenna has been fabricated.
2. The antenna has been simulated for different resonant frequencies for di-electric constant 2.4.
3. The experimental data have been collected using the fabricated antenna. Similar return loss plot found experimentally proves legitimacy of the work.
4. The proposed approach can be carried to fabricate co-ax fed antenna with any di-electric and any resonant frequencies with adequate success. , Description:Background of invention:
Coupling of power through a probe is one of the elementary mechanisms for the transfer of microwave power. In case of coaxial
feed, the probe is the inner conductor of a coaxial line. The location of the feed point is determined for the given mode so that the best impedance match is achieved.
Advantages of Coaxial feed
1. Simplicity of the design through the positioning of the feed point to adjust the input impedance level.
2. Compatibility to coax output from source modules & measuring instruments.
Disadvantages of Coaxial feed
1. Coaxial feeding of an array requires a large number of solder joints, which makes fabrication difficult and compromises reliability.
2. For increased bandwidth of a patch antenna, a thicker substrate is used and therefore requires a longer probe. This gives rise to an increase in spurious radiation from the probe, increased surface wave power and increased feed reactance.
Impedance matching in case of co-axial feed patch antenna is computationally very tedious work. It is more complicated when the designer tries to design an antenna for a specific resonant frequency and a specific desired return loss value that is low enough to be considered as a good matching condition. Application of evolutionary algorithms like genetic algorithm is one way to eliminate this problem. But it has been seen that more often than not Genetic Algorithm fails to produce satisfactory output in a reasonable time.
The present work introduces application of Particle Swarm mization1,2 in designing co-axial fed microstrip antenna for
different resonant frequencies. The method is computationally efficient, less time consuming and produces better designs than
other popular algorithms.

Summary of the Invention:
Co-axially fed patch antenna has received a lot of interests among the researchers and also in many industrial and communication applications. The present work describes an efficient method to design a co-ax fed microstrip antenna using Particle Swarm Optimization algorithm. The objective of the work is to design antennas that will resonate at a desired resonate frequencies.It consists of a rectangular patch of dimensions a x b (a is the length of the patch and b is the width) fabricated on a substrate of thickness h and dielectric constant er. The patch is fed by a co-axial transmission line which has a characteristics impedance of 50 O. For fabrication dimension of the ground plane was kept minimum five times the size
of metallic patch. The simulated and experimental results show that this is a very efficient method to design antenna for any desired frequency as a particular target return loss can be achieved for any frequency by this method.The authenticity of the work is verified by the measured result obtained experimentally which are very similar to the simulated results.

Detailed description of the proposed approach:
The investigation is made at different microwave frequency ranges (3-18 GHz) for dielectric constant 2.4. The dimensions of the antenna in the simulated results for resonant frequency 6 GHz are coming out to be length=14.7 mm, width=25.4 mm and feed position= 4.0 mm. The input resistance and reactance at this frequency in simulation comes out to be 50.13 O and -0.9065 O respectively. It can be seen that the resistive part of antenna impedance is very close to 50 ohm and the reactive part is close to zero. The structure of co-ax fed Microstrip Antenna has been fabricated for this desired frequency and its result is showing the convergence of return loss at exactly the same target frequency. Due to the consideration of the effect of mathematically approximated feed reactance in case of coaxial fed microstrip patch antenna there is a possibility that the resonant frequency may deviate from the desired results. Efforts have been made to minimize such deviations.