Questionnaires Antennas CH 1 & 2

Questionnaires “Antenna Theory” Constantine Balanis Chapter One 1. An antenna, in addition to radiating or receiving energy, it is also used to accentuate energy in some directions and suppress in others. 2. An antenna is a device that, in the transmitting mode, converts guided waves to free-space waves. 3. An antenna is a device that, in the receiving mode, converts free-space waves to guided waves. 4. Constructive and destructive interference patterns inside transmission lines connected to antennas, formed by reflections from impedance mismatches between the transmission lines and the antennas, are referred to as: standing waves. 5. An aggregate of individual discrete radiating elements (antennas) in an electrical and geometrical arrangement is referred to as an array. 6. To create radiation, there must be a time-varying current. 7. To create radiation, there must be an accelerating charge. 8. To create radiation, there must be a decelerating charge. 9. Radiation can be created by discontinuous wires. 10. Radiation can be created by bent wires. 11. The distance between two half-period free-space waves is lambda halves. 12. The length L (in wavelengths) of a wire/dipole antenna fed at the center whose current maximum occurs at the feed is equal to lambda-halves. Assume 0 < L < lambda. Chapter Two

1. A radiator having equal radiation in all directions is referred to as a: isotropic radiator. 2. A pattern having an essentially nondirectional pattern in a given plane and a directional pattern in any orthogonal plane is referred to as: omnidirectional. 3. A radiator having the property of radiating or receiving electromagnetic waves more effectively in some directions than in others is referred to as a: directional antenna. 4. The plane that contains the electric-field vector and the direction of maximum radiation is referred to as the: E-Plane. 5. The plane that contains the magnetic-field vector and the direction of maximum radiation is referred to as the: H-Plane. 6. A portion of the radiation pattern bounded by regions of relatively weak radiation is referred to as radiation lobe. 7. The radiation lobe containing the direction of maximum radiation is referred to as the: Major. 8. The region most immediate to the antenna where the reactive field predominates is referred to as the: Reactive near-field region. 9. The region of an antenna where the angular field distribution is essentially independent of the distance from the antenna and where the real power density predominates is referred to as the: Far-field region. 10. The region of an antenna between the reactive near-field and the far-field is referred to as the: Radiating near-field region. 11. In MKS, the units of power density are: Watts / meter squared. 12. In MKS, the units of power density are: Watts/unit solid angle. 13. The radiation intensity is related to the radiation density by: r^2.

14. The

ratio of the radiation intensity of an antenna to the

radiation intensity of an isotropic source is defined as the: Directivity. 15. The ratio of 4 Pi over the beam solid angle is defined as the: Directivity. 16. The ratio of the gain to the directivity of an antenna is defined as the: Radiation efficiency. 17. The directivities D_theta and D_phi are referred to as the: Partial Directivities. 18. The total maximum directivity is also defined as Do = 4*Pi/WA where WA is referred to as the: Beam solid angle. 19. The angular separation between two identical point on an amplitude pattern of an antenna is referred to as the: Beamwidth. 20. The range of frequencies within which the performance of an antenna, with respect to some characteristic, conforms to a specific standard is referred to as the: Bandwidth. 21. The figure traced, as a function of time, of the extremity of a time-varying electric field vector at a fixed location in space on a plane perpendicular to the direction of propagation is referred to as the: Polarization. 22. The polarization of an electric field with two components orthogonal to each other and to the direction of propagation, of the same amplitude, and with a 90 degrees phase difference is: Circular. 23. The polarization of an electric field with two components orthogonal to each other and to the direction of propagation, of the same amplitude, and with a 90 degrees phase difference is: Linear.

24. The

polarization of an electromagnetic wave two orthogonal

components transverse to the direction of propagation, the components are of equal magnitude and the phase difference between the two field components is 45 degrees is: Elliptical. 25. The factor that accounts for the polarization mismatches between an incident wave and a receiving antenna is referred to as the: Polarization Loss Factor. 26. The maximum effective area of a small finite length dipole, with an idealized triangular current distribution, is typically greater than the physical area of its cross section. 27. The maximum effective area of a lambda/2 dipole, with an idealized sinusoidal current distribution, is typically greater than the physical area of its cross section. 28. The real parts of the input impedance of an antenna are referred to as the: Radiation Resistance.

29. The

ratio of the radiation resistance over the sum of the

radiation resistance and loss resistance is defined as the: Radiation Efficiency. 30. For a linear wire antenna, its maximum effective length is typically smaller than the physical length. 31. For an aperture antenna, its maximum effective area is typically smaller than the physical area. 32. The ratio of the maximum effective area to the physical area of an antenna is defined as the: Aperture Efficiency. 33. The ratio of the available power at the terminals of a receiving antenna to the power density of a plane wave incident on the antenna is referred to as the: Effective Area.

34. The

scattering characteristics of a radar target are usually

represented by the: Radar Cross Section. 35. The equation that relates the received power to the transmitted power of two antennas, separated by a large distance R, is referred to as the: Friis Transmission. 36. The equation that relates the received power to the transmitted power of two antennas, after the signal has been scattered by a radar target, is referred to as the: Radar Range.