Rcs measurement calibration of an anechoic chamber and rcs

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Rcs measurement calibration of an anechoic chamber and rcs

  1. 1. International Journal of Electronics and Communication Engineering & Technology (IJECET), INTERNATIONAL JOURNAL OF ELECTRONICS AND ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online) Special Issue (November, 2013), pp. 103-109 © IAEME: www.iaeme.com/ijecet.asp Journal Impact Factor (2013): 5.8896 (Calculated by GISI) www.jifactor.com IJECET ©IAEME RCS Measurement: Calibration of an Anechoic Chamber and RCS Measures of Specific Targets Neha Rohilla1, Ishani Khanna2, Supreet Kaur Sidhu3 Electronics & Communication Engineering, BKBIET, Pilani, Rajasthan, India 1neharohilla4@gmail.com, 2ishanikhanna@gmail.com, 3supreetkaursidhu28@gmail.com ABSTRACT: In the following paper, we intend to take the RCS measurements of various objects like plate, sphere, dihedral and reflect array dihedral and get the calibration coefficient of the anechoic chamber. Here we work on an apparatus that consists of following:  Vector network analyzer (VNA)- ROHDE & SCHWARZ, ZVB-14 (10 MHz- 14GHz)  Anechoic chamber with a turntable.  Transmitting and Receiving antennas (A duplexer that serves as a switch between the antenna and the transmitter or the receiver for the signal when the antenna is used in both situations.)  Lab view software.  MATLAB software. Various objects i.e. Sphere of different diameters, plates with different dimensions, dihedral and reflect array dihedral with different angle. KEYWORDS: RCS-radar cross section I. INTRODUCTION A. Anechoic chamber An anechoic chamber (an-echoic or non-echoing) is a room designed to stop reflections of either sound or electromagnetic waves. The size of the chamber depends on the size of the objects to be tested and the frequency range of the signals used, although scale models can sometimes be used by testing at shorter wavelengths. An anechoic chamber is a room, where International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 103
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME the target is placed on a rotating pillar in the center, and the walls, floors and ceiling are covered by stacks of radar absorbing material. These absorbers prevent corruption of the measurement due to reflections. A compact range is an anechoic chamber with a reflector to simulate far field conditions. B. Radar Radar is an object detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter. RADAR gained importance during World War II. The term RADAR is basically an acronym for Radio Detection And Ranging. A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity—especially by most metals, by seawater, by wet land. Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either toward or away from the transmitter, there is a slight equivalent change in the frequency of the radio waves, caused by the Doppler Effect. Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, they can be strengthened by electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars, except when their detection is intended. C. Radar cross section (RCS) Radar cross section (RCS) is a measure of how detectable an object is with radar. A larger RCS indicates that an object is more easily detected. An object reflects a limited amount of radar energy. A number of different factors determine how much electromagnetic energy returns to the source such as:  material of which the target is made;  absolute size of the target; International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 104
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME  relative size of the target (in relation to the wavelength of the illuminating radar);  the incident angle (angle at which the radar beam hits a particular portion of target which depends upon shape of target and its orientation to the radar source);  reflected angle (angle at which the reflected beam leaves the part of the target hit, it depends upon incident angle);  the polarization of transmitted and the received radiation in respect to the orientation of the target While important in detecting targets, strength of emitter and distance are not factors that affect the calculation of a RCS because the RCS is a property of the target reflectivity. II. OBSERVATIONS A. Plate (0.0999*0.1845) Fig. 1: Frequency vs RCS using VNA Fig. 2: Frequency vs RCS using lab view software Fig. 3: Theta vs RCS using lab view software International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 105
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME Blue line – measurement Green line – theoretical graph Calibration coefficient at 9GHz = -30.906 Theta Range = -30 to 30 Delta Theta = 0.5 B. Plate (0.115*0.106) m Fig. 4: Frequency vs RCS using VNA Fig. 5: Frequency vs RCS using lab view software Fig. 6: Theta vs RCS using lab view software International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 106
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME C. Reflect array dihedral –a Fig. 7: Frequency vs RCS using lab view software Fig. 8: Theta vs RCS using lab view software D. Sphere Diameter = 88.3 mm Fig. 9: Frequency vs RCS using VNA Fig. 10: Frequency vs RCS using lab view software International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 107
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME III. COMPARISON BETWEEN H-H(HORIZONTAL) AND V-V(VERTICAL) POLARIZATION Blue- VV polarization Green-HH polarization Fig. 11: PLATE (0.1845*0.0999) m Fig. 12: Dihedral IV. RESULT 1. Here we observe that the calibration coefficient calculated by VNA and Lab view software is different. 2. The graphs obtained for H-H and V-V polarization is almost the same besides the depth of lobes. 3. Calibration coefficient obtained through Lab view software for sphere and plates of different dimensions are different. V. CONCLUSION 1. Here we observe that the calibration coefficient calculated by VNA and Lab view software is different. 2. The graphs obtained for H-H and V-V polarization is almost the same besides the depth of lobes. 3. Calibration coefficient obtained through Lab view software for sphere and plates of different dimensions are different. REFERENCES [1] Inverse synthetic aperture Radar imaging with MATLAB algorithms, First edition [2] Chapter 1: Basics of Fourier analysis [3] Chapter 2: Radar fundamentals International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 108
  7. 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME BIOGRAPHY ISHANI KHANNA was born in Delhi, India in 1992. She is pursuing B.tech in electronics and communication from B K Birla institute of engineering and technology, Pilani, Rajasthan. Did internship from IETR Lab, INSA, RENNES, FRANCE. SUPREET KAUR SIDHU was born in Bathinda, Punjab, India in 1992. She is pursuing B.tech in electronics and communication from B K Birla institute of engineering and technology, Pilani, Rajasthan. Did internship from IETR lab, INSA, RENNES, FRANCE. NEHA ROHILLA was born in Ratangarh, Rajasthan, India in 1992. She is pursuing B.tech in electronics and communication from B K Birla institute of engineering and technology, Pilani, Rajasthan. Did internship from IETR lab, INSA, RENNES, FRANCE. International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 109

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