1. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna and Microwave Laboratory Babol Noshirvani University of Technology, Iran In the name of God Introduction

2. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Research Projects: Numerical Experiments or Numerical Lab Laboratory Experiments On-Site(field) Experiments Antenna Lab

3. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Electromagnetics Spectrum

4. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Electromagnetics Spectrum

5. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Electromagnetics Spectrum

6. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Electromagnetics Spectrum

7. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Fundamental Parameters of Antenna

8. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 8 1. Radiation Mechanism

9. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 9 2. Radiation Pattern (Directivity) So, based on what application we are dealing with, an appropriate radiation pattern is selected. dipole( λ /2) antenna (omnidirectional pattern) reflector antenna (pencil-beam pattern)

10. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 3. Reflection Coefficient (S11) Vinc Vref S11= Vref / Vinc Vref=0 then log(S11)=-inf db Vref=1 then log(S11)=0 db  S11 plot  fr-antenna  BW-antenna

11. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 4. Farfield Criteria

12. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 5. Pattern Lobes

13. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 6. Half Power Beamwidth E pattern P pattern 10log (P pattern )

14. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 6. Polarization

15. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 7. Input Impedance Zin= RL +Rr + jXA Zin= input impedance RL= loss resistance Rr= radiation resistance XA= antenna reactance At a given frequency all these parameters are controlled by antenna geometry

16. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements

17. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements  Many antennas, because of complex configuration & excitation, cannot be investigated analytically.  Experimental results are often needed to validate theoretical data.  It is usually most convenient to perform antenna measurements with test antenna in its receiving mode.  By reciprocity, receiving mode characteristics are identical to TX mode.  Ideal condition for measuring is incidence of a plane waves having uniform amplitude and phase.  Although this ideal condition is not achievable, it can be approximated by separating test antenna from illumination source by a large distance on an outdoor range.  At large radii, curvature of spherical phase front produced by source antenna is small over test antenna aperture.  If separation distance is equal to inner boundary of far-field region, 2D 2 /λ, then maximum phase error of incident field from an ideal plane wave is about 22.5 o, as shown in:  In addition to phase front curvature, reflections from ground and nearby objects are possible sources of degradation of test antenna illumination.

18. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements  Experimental investigations have a number of drawbacks:  1. For pattern measurements, distance r>2D 2 /λ is too long even for outside range.  2. It also becomes difficult to keep unwanted reflections from surrounding objects.  3. In many cases, it may be impractical to move antenna from operating environment to measuring site.  4. For some antennas such as phased arrays, time required to measure may be enormous.  5. Outside measuring systems provide an uncontrolled environment, and they do not possess an all- weather capability.  6. Enclosed measuring systems usually cannot accommodate large antenna systems such as ships, aircraft.  7. Measurement techniques are expensive.  Some of above shortcomings can be overcome by using special techniques such as:  Indoor measurements.  Far-field pattern prediction from near-field measurements.  Scale model measurements.  Automated commercial equipment specifically designed for antenna measurements.  Utilizing computer assisted techniques.

19. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements  Because of accelerated progress made in aerospace/defense related systems, more accurate measurement methods were necessary.  Accurate measurement methods are:  Tapered anechoic chambers.  Compact and extrapolation ranges.  Near-field probing techniques.  Improved polarization techniques.  Swept-frequency measurements.  Automated test systems.  A more extensive and exhaustive treatment of these and other topics can be found in:  IEEE Standard Test Procedures for Antennas [7].  A summarized journal paper [8].  A book on microwave antenna measurements [6].

20. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements  Reflection Ranges:  There are two basic types of antenna ranges:  The reflection ranges.  The free-space ranges.  Reflection ranges for a judiciously design, can create a constructive interference in region of test antenna which is referred to as the “quiet zone.”  This is accomplished by designing ranges so that specular reflections from ground as shown:  Usually it is desirable for illuminating field to have a small and symmetric amplitude taper.  This can be achieved by adjusting transmitting antenna height while maintaining constant that of receiving antenna.  They are used for systems operating in the UHF to 16GHz frequency region.  Free-space ranges, designing to suppress contributions from surrounding environment, include as:  Elevated ranges.  Slant ranges.  Anechoic chambers.  Compact ranges.  Near-field ranges.

21. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Rectangular Tapered Antenna Measurements  Anechoic Chambers:  Anechoic chamber is an alternative to outdoor testing.  To provide a controlled environment, indoor anechoic chambers have been developed.  In general, as operating frequency is lowered, thickness of RF absorbing material must be increased to maintain a given level of reflectivity performance.  There are two basic types of anechoic chamber designs:  Rectangular chamber.  Tapered chamber.  Design of each is based on geometrical optics techniques.  Each attempts to reduce or to minimize specular reflections.  The rectangular chamber is designed to simulate free-space conditions and maximize volume of quiet zone.  Its design takes into account pattern and location of source, frequency and isotropic antenna.  Reflected energy is minimized by the use of high quality RF absorbers.  Despite use of RF absorbing material, significant specular reflections can occur.

22. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements  Tapered anechoic chambers take form of a pyramidal horn.  They begin with a tapered chamber which leads to a rectangular configuration at test region.  Source is usually placed near apex so that reflections from side walls occur near source antenna.  For such paths, phase difference between paths are very small by properly locating source antenna near apex.  Thus direct and reflected rays near test antenna provide a relatively smooth amplitude illumination taper.  This can be illustrated by ray-tracing techniques.  By increasing f 0, it becomes increasingly difficult to place source sufficiently close to apex that phase difference between direct and secularly reflected rays can be maintained below an acceptable level.  For such applications, reflections from walls of chamber are suppressed by using high gain source antennas whose radiation toward walls is minimal.  In addition, source is moved away from apex, and it is placed closer to end of tapering section so as to simulate a rectangular chamber.

23. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements  Compact Range antennas:  Microwave antenna measurements require a uniform plane wave.  Requirement of an ideal plane wave illumination can be achieved by utilizing a compact range.  A Compact Antenna Test Range (CATR) is a collimating device which generates nearly planar wave fronts in a very short distance.  Distance is typically 10–20m compared to the 2D 2 /λ.  Some attempts have been made to use dielectric lenses as collimators [15].  Name CATR refers to one or more curved metal reflectors which perform collimating function.  CATR are very large reflector antennas designed to optimize planar characteristics.  CATR are designated according to their analogous reflector antenna configurations: parabolic, Cassegrain, Gregorian.  Major drawbacks of compact ranges are :  Aperture blockage.  Direct radiation from source to test antenna.  Diffractions from edges of reflector.  Feed support.  Depolarization coupling between two antennas.  Wall reflections

24. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements  CATR Performance: Amplitude and phase ripple in quiet-zone fields produced by a CATR caused by phasor sum of reflected and diffracted rays from reflector

25. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Measurements Two common CATR reflector edge treatments that are used to reduce diffracted fields in quiet zone.  CATR Performance:

26. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir Antenna Room

27. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 1) Chamber Geometry a) Rectangular Chamber

28. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir b) Taperd Chamber

29. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir 1) جاذب دی الکتریک : 2) جاذب مغناطیسی : - جذب موج الکترومغناطیسی به خاطر وجود قسمت تلفاتی در Permittivity دی الکتریک می باشد - ساختار اصلی این نوع جاذب پلیمر urethane و خرده ریزهای کربن است - فرم فیزیکی آن ها ابر مانند بوده، پس سبک می باشند، اما پایداری کمتری دارند -Tune ترند، اما پهنای باند کمتری دارند - جذب موج الکترومغناطیسی به خاطر وجود قسمت تلفاتی در Permeability ساختار مغناطیسی می باشد - ساختار اصلی این نوع جاذب مواد مغناطیسی موسوم به فریت می باشد - فرم فیزیکی آن ها بصورت لایه ای و ورقه ای بوده، سنگین ترند، اما پایداری بیشتری دارند - کمتر Tune اند، اما پهنای باند بیشتری دارند 2) Radar Absorbing Material

30. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir شرکت های ارائه کننده جاذب مایکروویوی 1. شرکت Telemeter Electronic 2. شرکت FRD EMI Shielding Materials 3. شرکت Laird Technology 4. شرکت Emerson and Cuming Microwave 5. شرکت MAJR Product Corporation 6. شرکت Eeonyx Corp.

31. Antenna and Microwave Laboratory Babol Noshirvani University of Technology zakeri@nit.ac.ir