Design of a Multiband Octagonal Patch Antenna

Department of E and I Technology, Acharya Nagarjuna University, Guntur – 522510, Andhra Pradesh, India; sharmilad@gmail.com Department of System design, Andhra University, Visakhapatnam – 530003, Andhra Pradesh, India; raomp17@gmail.com Departmen of Physics, Andhra University, Visakhapatnam – 530003, Andhra Pradesh, India; raopsvs@rediff.com Departmen of ECE, Acharya Nagarjuna University, Guntur – 522510, Andhra Pradesh, India; kishore.ece.anu@gmail.com


Introduction
The growth in usage of electronic devices in day to day life made changes in wireless communication systems. Increased usage of radars for communication purpose causes demand in small, multi band antennas. Due to this requirement patch antenna technology used widely even though they have narrow band radiation, poor polarization purity, low efficiency, low gain and limited power capacity. Apart from this disadvantages the patch antennas having following advantages. They are low cost, low volume structures, less weight and easy to fabricate. In Some special applications the communication systems such as radars, satellites and GPS (Global Positioning System) are going to be operated in multi frequency applications 1 . At this time the usage of number of different single band antennas can be eliminated by using single micro strip patch antenna.
The design of multiband patch antenna is simple as compared to multi frequency and broad band patch antennas. Due to this a Multiband Octagonal Patch Antenna has been designed for working in six different frequencies presented in multi band (C, Ku, K, Q and U bands). Main applications of these bands are used in terrestrial microwave communications such as radar, satellite, aircraft, mobile and space craft communications and for radio astronomy 2,3 .

Methodology
In General, micro strip patch antenna consists of three layers: 1. Ground, 2. Substrate and 3. Patch. The ground and patch are metallic plates where the radiation occurs. Serrated structure is a method used to change the shape and size of the patch in terms of length, width and height of the substrate 4 . Serrated structures are useful to make the antenna compact and to be operated in multiple bands 5,6 . The dimensions of the proposed serrated structure are calculated by using following mathematical model 3 .
( ) And ( ) where, ƒr =resonant frequency (in Hz), L=length of patch (in mm), W=width of patch (in mm), h=height of substrate (in mm) and εr=relative dielectric constant. Basically h/w << 1for better gain and bandwidth 7,8 . With the calculated dimensions, the octagonal shape is proposed as the serrated structure as shown in Figure 1.

Roposed Antenna Design Parameters
The

Simulation Results and Discussion
The Designed Octagonal micro strip patch antenna is simulated and analyzed by FEM method HFSS software.  To achieve better performance, slot should be introduced into patch. The slot is of 0.5 mm wide which is inserted into the patch as shown in the figure. Single slot was arranged to improve the overall performance in the proposed design as shown in Figure 3. The overall performance is good at some individual frequencies 7.6GHz, 12.0GHz, 24.5GHz, 37.7GHz, 43.2GHz and 47.9GHz with return loss (<-10db) and VSWR(<2), Gain 8.6db. The recorded Schematics of return loss, VSWR and overall gain pattern have been recorded. The Designed octagonal patch antenna is applicable to multi band operations without any modification based on the HFSS simulated results.
This antenna is planned and optimized by HFSS. The return loss of the planned antenna is exposed in the Figure  4 and it covers C, Ku, K, Q and U-bands with frequencies of 7.6GHz, 12.0GHz, 24.5GHz, 37.7GHz, 43.2GHz and 47.9GHz and a return loss of -12.2dB, -14.0dB, -17.4dB, -17.8dB, -20.5dB and -10.9dB respectively.
The VSWR of the antenna at the frequencies 7.6GHz, 12.0GHz, 24.5GHz, 37.7GHz, 43.2GHz and 47.9GHz is 1.6, 1.4, 1.3, 1.2, 1.1 and 1.7 respectively and shown in the Figure 5. The planned antenna haves a stable gain of 8.98dB shown in Figure 6.

Conclusion
A multi band octagonal patch antenna is presented in this study. This antenna has a close size of 24 x 21 x 1 (in mm), which is informal to be integrated in tiny devices. Results show that the planned antenna covers C, Ku, K, Q and U-bands transmission at 7.6GHz, 12.0GHz, 24.5GHz, 37.7GHz, 43.2GHz and 47.9GHz respectively and return loss calculated at corresponding frequencies obtained are -12.2dB, -14.0dB, -17.