Author Topic: Investigation on Octagonal Microstrip Antenna for RADAR & Space-Craft applicatio  (Read 2921 times)

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Author : Krishan Kumar, Er. Sukhdeep Kaur
International Journal of Scientific & Engineering Research Volume 2, Issue 11, November-2011
ISSN 2229-5518
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Abstract : In this paper octagon shape planar microstrip antenna is presented. Octagonal antenna can find applications in Radar  and Space-crafts. The antenna is fed by a 50 Ω microstrip line and printed on a dielectric Fr4 substrate of  dimension (22mm X 22 mm) permittivity εr =4.4 and height h = 1.6 mm. The optimization on the planar octagonal microstrip has been done to accomplish an -10 dB return loss bandwidth. Moreover, in comparison with a simple rectangular shaped antenna, the proposed design enhances the bandwidth and improves input return loss. Better than 83.54 % radiation efficiency has been achieved in the range 3.1 to 15 GHz. The parameters like substrate dimension, feed size and ground plane which affect the performance of the antenna in terms of its frequency domain and time domain characteristics are investigated.

Index terms: Directional patterns, finite ground plane, microstrip line feed, microstrip antenna, omni-directional patterns, ultra wideband (UWB).

1   Introduction                                                               
MICROSTIP antenna technology has progressed a lot and is still emerging in the field of radar , space-craft ,wireless & mobile communication. It has created increased interest in the planar forms of the MSA antennas can also be integrated between the radio frequency (RF) front end circuitry and the radiating structure. The simplest way to implementing planar forms of the antenna is using the microstrip feeding technology, which is widely used in radar & Space-craft applications.
Microstrip antenna in its simplest form consists of a radiating patch on one side of a dielectric substrate and a ground plane on the bottom side of the substrate. However, many other shapes, such as the square, circular, triangular, semicircular, hexagonal, and annular ring shapes are also used. Microstrip antennas are popular because of its compact size, light weight, low cost, low profile, high efficiency and economical fabrication features [1], [2]. Out of the different forms the simplest form of the microstrip antennas is the microstrip slot antenna, which radiates omni-directional radiation patterns. Microstrip slot antennas fed by a microstrip line have shown wideband and ultra wideband performances [3][4].The simulation results of antenna design were obtained by employing the Ansoft Corporation High Frequency Structure Simulator (HFSS) v11.0 tools, which are finite element method (FEM), based commercial full wave analysis programs [5].

    A. Antenna Geometry: Fig. 1 illustrates the evolution of the proposed Microstrip Antenna on the Fr4 substrate.
Fig. 1 The proposed Octagonal Microstrip antenna (a) Simulation Model Fig.2.The reflection coefficient (S11, dB) versus frequency (GHz) plot for antenna design.

From the simulations & measurements of the microstrip antenna the optimized dimension are 22 mm x 22 mm (l x b) and thickness of 1.6mm. The offset feeding strip is generally 1.6 mm thick.  Fig.1 (a) shows the microstrip antenna with octagonal structure and finite system ground plane. However the Efficiency Vs Frequency characteristics of microstrip antenna vary for the different frequency of simulation.  In order to further reduce the overall size of the microstrip antenna structure a slot can be cut at the octagonal radiator. As an example the microstrip antenna fabricated on a Fr4, εr=4.4 & 1.6 mm in thickness. The position of feed point to the antenna structure can be varied to vary the result. The microstrip antenna substrate is enclosed in a radiation box. The radiation box of the antenna is generally larger in dimension (lxb)   and it is approximate four times larger in height. The antenna structures are then assigned with the analysis set-up which encloses solution frequency, start & stop frequency of simulations, step size, Max. no. of passes etc..It should be noted that in the simulation process the microstrip antenna design structure was feed by a microstrip feeding with a 50 ohm internal resistance which is provided without any RF feeding cables. The ground plane size selection is also based on the study presented in [6], [7] on the microstrip slot antennas.
The electric field distributions of the octagonal microstrip antenna at the different frequency of simulation (5 GHz, 10 GHz & 15 GHz) are demonstrated as below:
At 5 GHz

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