Yagi Uda Antenna Analysis

In this assignment, we are required to design an antenna which is capable of transmitting and receiving electromagnetic waves operating at 433MHz. Our aim is to maximize the gain of the antenna and achieve impedance matching between load impedance and transmission line’s impedance. Among a wide range of different antennas, our group decide to build up a Yagi Uda antenna to fulfill this assignment for two main reasons.
Firstly, the gain that Yagi Uda antenna provides is very high. Hence for transmission, Yagi Uda antenna makes sure all the transmitted wave to be directed to required area and for reception, it can receive maximum signal from the required area.
Secondly, Yagi Uda is widely used as high-gain antenna on High Frequency (3-30MHz),
Reflectors and directors are parasitic elements which are not connected to the radio receiver or transmitter through the feed line. The reflector absorbs the radio waves from the driver dipole and re-radiates with a different phase. The waves from different directors interfere with each other and strengthening the antenna’s radiation in the desired direction, and cancelling out waves in the undesired directions.

The ideal dipole antenna’s radiation pattern is as shown in Fig 1. Dipole Antenna Radiation Pattern below. The reflector and directors of Yagi Uda antenna cancels the radiation to the back and sides, and direct the wave to the forward direction. As the simulation result (Fig 2. 3D Polar Plot) shows, our antenna almost direct all wave to forward direction (positive y) and the level of backward lobe is very low. Fig 1. Dipole Antenna Radiation Pattern

Fig 2. 3D Polar Plot

Impedance
The real value suggests how the power is radiated or absorbed by the antenna during transmitting and receiving; the imaginary part shows how much the power stored in the near field of the antenna. To ensure a proper match, the real part of the antenna impedance must equal to the real part of the source impedance, which is 50 Ohm; and the imaginary part must cancels the imaginary part of the source impedance. Since the imaginary part of the source impedance is 0, the imaginary part of the antenna impedance must also be 0.

After running a few simulations and making adjustments on the length and relative position of the antenna elements, the best result that we obtained is that the real part of impedance is 52.9 while the imaginary part of impedance is 0.33 at 433MHz. Fig 3. Antenna Impedance.

Reflection coefficient is ratio of the complex amplitude of the reflected wave to that of the incident wave. Specifically for load, the reflection coefficient is determined by its impedance ZL and the impedance towards the source Zs. The smaller reflection coefficient indicates smaller percentage of the total power being reflected back to the source. In our simulation, the reflection coefficient we obtain is -30.9 at 433MHz. Fig 4. Reflection