KULLIYYAH OF ENGINEERING DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING ANTENNA AND WAVE PROPAGATION LABORATORY (ECOM 4101) EXPERIMENT NO 2 “EFFECTS OF PARASITIC ELEMENTS ON YAGI- UDA ANTENNA ARRAY” INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA KULIYYAH OF ENGINEERING ECOM 4101 ANTENNA LAB EXPERIMENT NO: __ NAME OF EXPERIMENT: _____________________________ Student Name : __________________________ Matric Number : __________________________ Submission date : __________________________ Mark obtained : __________________________ EXP NO: 2 EFFECTS OF PARASITIC ELEMENTS ON YAGI-UDA ANTENNA ARRAY OBJECTIVE You are given half wave length dipole antenna with various lengths of parasitic elements. By using this half wave dipole antenna fed by 9.45 GHz signal generator and other sizes of parasitic elements, propose an experimental procedure to achieve the following objectives: To become familiar with the Yagi-Uda Antenna and its structure and various electrical lengths with locations. To investigate the effects of the number of elements to the radiation pattern characteristics. MATERIAL 1 Rotating antenna platform 737 400 1 Gunn power supply with SWR meter 737 021 1 Gunn oscillator 737 01 1 Isolator 737 06 1 Pin Modulator 737 05 1 Large Horn Antenna 737 21 2 RF cable, L = 1 m 501 02 2 Supports for waveguide components 737 15 2 Stand base MF 301 21 1 Set of microwave absorbers 737 390 1 Set of 10 thumb screws M4 737 399 1 Remote control for rotating antenna platform 737 401 1 Dipole antenna kit 737 410 BRIEF THEORY The Yagi-Uda antenna was invented in Japan at Tohoku Imperial University by Hidetsugu Yagi and Shintaro Uda in 1926 and published his research in English in 1928. Yagi arrays were used widely in the Second World War because they were simple to build and directional. Yagi-Uda antenna, named after its developers, is widely used for TV reception. A dipole (or folded dipole) is used as the only 1 active element to intercept radio waves and transfer the electromagnetic energy to a transmission line in the form of electric current and voltage. An antenna with a driven element and one, or more, parasitic element is generally known as a “yagi”, after on of its inventors (Mssrs Yagi and Uda). With the length of the second dipole (the un-driven or “Parasitic” element) shorter then the driven dipole (the driven element) the direction of maximum radiation is from the driven element towards the parasitic element. In this case, the parasitic element is called the “director”. With the length of the second dipole longer than the driven dipole the direction of maximum radiation is from the parasitic element towards the driven element. In the case, the parasitic element is called the “reflector”. All other elements are considered as parasitic radiators without any feedline or matching network; thus making the realization considerably cheaper. The parasitic elements influence both the input impedance of the active element as well as the radiation pattern of the overall antenna system. An element longer than λ/2 behind the active element will act as a reflector, which reflects the approaching waves in the major lobe toward the dipole. Conversely, a shorter element in front of the active element will act as a director, which concentrates the received waves in the major lobe and reradiates toward the dipole. The directivity of the antenna system is greater with an increased number of parasitic elements, particularly the directors. Practically, there is a limit beyond which very little gain is obtained by the addition of more directors. The length of the directors (0.30λ0.45λ) and the spacing between them (0.30λ0.4λ) must be properly selected to optimise the front-to-back ratio of the antenna. On the other hand, it has been concluded numerically and experimentally that the reflector spacing and size have negligible effects on the forward gain, but large effects on the backward gain (front-to-back ratio) and input impedance. The major role of the reflector is played by the first element next to the active one (~0.25λ) away). Increasing the number of reflectors will only contribute slightly in the performance of Yagi- Uda antenna. The input impedance of the dipole, which acts as the active element, is lower compared to an isolated dipole. In order to make the matching easier, a 2-element folded dipole is often used to replace the single dipole. This will give impedance step-up by a factor of 4. 2 (a) (b) Figure 1 : (a) typical Yagi Antenna; (b)Yagi-uda viewed from left to right Geometry of Yagi Antennas Figure 2: Geometry of Yagi- Uda antenna. Dipole Two conductors of length /4 One connected to signal, the other to ground The only driven element in the system, no electrical connection to directors or reflector Directors Lengths smaller than dipole, continuously decreasing Excited by the field of the dipole Make antenna directional Reflector Larger than dipole Prevents antenna from sending backwards PROCEDURES Initial Setting (Based on Experiment 1) 1. The antenna measurement system is set-up according to Figure 3. 2. Switch on the rotating antenna platform. 3. Switch on the computer and run the antenna measurement software. 4. Rotate the transmitting horn antenna to produce the required wave polarization for E- plane and H-plane pattern measurements. 3 r=170cm Figure 3 Yagi Uda Antenna Configurations 5. Construct a Yagi antenna using the dipole antenna kit provided with the experiment set. 6. Investigate the E-plane patterns for the configuration with a reflector, a director, a director plus a reflector, and 4 directors plus a reflector. The transmitted waves must be horizontally polarized. 7. Arrange the set to produce vertically polarized waves. Measure the H-plane patterns for the configuration with a reflector, a director, a director plus a reflector, and 4 directors plus a reflector. 8. Analyze the E- and H-plane radiation pattern of the all the Yagi antenna. Deduce the 3-dB beamwidth for each of the plane patterns. 9. Replace the type 2 with the type 3, 4 and 5 of the Yagi-Uda antenna kit respectively (please see the appendix) 10. Repeat from step 5 to 8 to complete the experiment. 11. Comparison of the differences among all types of the Yagi-Uda antennas should be included in the discussions. 4 RESULTS 1. Manual Procedures for Plotting Radiation Pattern (A) Element 1: ______________________ Table 1: Directional Diagram Types of Test Antenna: Polarization: Type of Source Antenna: Polarization: Distance Between Source & cm Test Antenna: Detector Bias Current: µA WR Meter Range: dB Frequency: Angle [º] SWR Meter Level [dB] Angle [º] SWR Meter Level [dB] 0 0 -10 10 -20 20 -30 30 -40 40 -50 50 -60 60 -70 70 -80 80 -90 90 -100 100 -110 110 -120 120 -130 130 -140 140 -150 150 -160 160 -170 170 -180 180 5 (B) Element 2: ______________________ Table 1: Directional Diagram Types of Test Antenna: Polarization: Type of Source Antenna: Polarization: Distance Between Source & cm Test Antenna: Detector Bias Current: µA WR Meter Range: dB Frequency: Angle [º] SWR Meter Level [dB] Angle [º] SWR Meter Level [dB] 0 0 -10 10 -20 20 -30 30 -40 40 -50 50 -60 60 -70 70 -80 80 -90 90 -100 100 -110 110 -120 120 -130 130 -140 140 -150 150 -160 160 -170 170 -180 180 6 (C) Element 3: ______________________ Table 1: Directional Diagram Types of Test Antenna: Polarization: Type of Source Antenna: Polarization: Distance Between Source & cm Test Antenna: Detector Bias Current: µA WR Meter Range: dB Frequency: Angle [º] SWR Meter Level [dB] Angle [º] SWR Meter Level [dB] 0 0 -10 10 -20 20 -30 30 -40 40 -50 50 -60 60 -70 70 -80 80 -90 90 -100 100 -110 110 -120 120 -130 130 -140 140 -150 150 -160 160 -170 170 -180 180 7 (D) Element 2: ______________________ Table 1: Directional Diagram Types of Test Antenna: Polarization: Type of Source Antenna: Polarization: Distance Between Source & cm Test Antenna: Detector Bias Current: µA WR Meter Range: dB Frequency: Angle [º] SWR Meter Level [dB] Angle [º] SWR Meter Level [dB] 0 0 -10 10 -20 20 -30 30 -40 40 -50 50 -60 60 -70 70 -80 80 -90 90 -100 100 -110 110 -120 120 -130 130 -140 140 -150 150 -160 160 -170 170 -180 180 2. After plot manually, then change the device in order plot by computer. Attach the output from the computer generated result(s). 8 a ( ) – Diagram a / dB Directional Diagram in Polar Coordinates: R-Axis – Relative Amplitude (Log) 9 a ( ) – Diagram a / dB Directional Diagram in Polar Coordinates: R-Axis – Relative Amplitude (Log) 10 a ( ) – Diagram a / dB Directional Diagram in Polar Coordinates: R-Axis – Relative Amplitude (Log) 11 a ( ) – Diagram a / dB Directional Diagram in Polar Coordinates: R-Axis – Relative Amplitude (Log) 12 QUESTIONS 1. What are the different elements in a Yagi-Uda antenna? Mention the use of each. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 2. What you can be observed to the radiation patterns when the number of element changes? Compare for each plot. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… 3. From the experiment done, which element has the better radiation pattern in term of directivity? …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ……………………………………………………………………………………………………………