Slotted log periodic fractal koch antenna for ultra high frequency digital television application

Abstract

The Ultra High Frequency (UHF) band has long been used for voice, data and video communications. For the terrestrial television broadcasting, the lower frequency band of the UHF is used which ranges between 470 to 890 MHz. The conventional UHF antennas for receiving TV signals are quite large. One method that can be utilized is by using a compact and directional antenna that can be easily fabricated. The geometry used in this antenna design is Koch curve fractal structure. The advantage of using fractals in designing the antenna is to minimize the antenna size. The Log Periodic Antenna (LPA) is chosen because it had a wide bandwidth. This thesis describes the design of the planar fractal Koch antenna with slots for the UHF band. Four different iterations which is 0th iteration, 1st iteration, 2nd iteration and series iteration have been designed and simulated. The simulation process was done using Computer Simulation Technology (CST). The antenna has been fabricated on the Flame Retardant 4 (FR4) laminate microstrip board with dielectric constant of 5.4 and thickness of 1.6 mm. The simulation results show that the Koch curve technique can be used to minimize the length of the arm LPA, but the lower frequency tends to shift to the higher frequency as the number of iterations increases. Thus, a slot is introduced at each of the element of the Log Periodic Antenna in order to avoid the lower designed frequencies from shifting to higher band. A 28.7% reduction of the antenna size has been achieved by using slotted fractal Koch technique at the 2nd iteration. All antennas have been tested and measured in terms of reflection coefficient, radiation pattern and its realized gain. The simulation and measurement results have been compared and analyzed. A good agreement was achieved with reflection coefficient, S11< -10 dB for the entire UHF digital television band frequency design, directional radiation patterns with beamwidth of 75°, wide bandwidth up to 95% and an average gain of 6 dBi along the frequency range. This proposed antenna suitable for the intended application.