Hanyang University 1/24 ANTENNA THEORY ANALYSIS AND DESIGN Chapter.2 Sungjoon YOON

Hanyang University 2/24 Contents Antennas & RF Devices Lab. 2. Fundamental Parameters Of Antennas 2.13 Input Impedance 2.14 Antenna Radiation Efficiency 2.15 Antenna Vector Effective Length And Equivalent Areas 2.16 Maximum Directivity And Maximum Effective Area 2.17 Friss Transmission Equation And Radar Range Equation 2.18 Antenna Temperature

Hanyang University 3/24 Figure 2.27 Transmitting antenna and its equivalent circuits. The impedance presented by an antenna at its terminals or the ratio of the voltage to current at a pair of terminals or the ratio of the appropriate components of the electric to magnetic fields at a point. = antenna impedance at terminal a-b (ohms) = antenna resistance at terminal a-b (ohms) = antenna reactance at terminal a-b (ohms) Loss resistance Radiation resistance = Generator impedance (ohms) = Resistance of generator impedance (ohms) = Reactance of generator impedance (ohms)

Hanyang University 4/24 To find the amount of power delivered to for radiation and the amount dissipated in as heat Power delivered to the antenna for radiation. Power that dissipated as heat. Conjugate matching

Hanyang University 5/24 Power that dissipated as heat in the internal resistance of the generator = power for radiation + power that dissipated as heat in the antenna If the antenna is lossless and matched to the transmission line half of the total power supplied by the generator is radiated by the antenna during conjugate matching, and the other half is dissipated as heat in the generator.

Hanyang University 6/24 Conjugate matching ( to remove imaginary components) Power delivered to the load Power that scattered of ( reradiated) Power that dissipated as heat through

Hanyang University 7/24 The conduction-dielectric efficiency is the ratio of the power delivered to the radiation resistance to the power delivered to and The antenna efficiency takes into account the reflection, conduction, and dielectric losses If the skin depth of the metal is very small compared to the smallest diagonal of the cross section of the rod, the current is confined to a thin layer near the conductor surface. Therefore the high-frequency resistance can be written, based on a uniform current distribution, as P : the perimeter of the cross section of the rod : the conductor surface resistance : the angular frequency : the permeability of free-space : the conductivity of the metal.

Hanyang University 8/24 An antenna in the receiving mode is used to capture (collect) electromagnetic waves and to extract power from them. Equivalent quantities are used to describe the receiving characteristics of an antenna Figure 2.29 (a)Dipole antenna in receiving modeFigure 2.29 (b) Aperture antenna in receiving mode

Hanyang University 9/24 The vector effective length (effective height) is used to determine the voltage induced on the open-circuit terminals of the antenna when a wave impinges upon it It is a far-field quantity and it is related to the far-zone field radiated by the antenna, with current in its terminals It is particularly useful in relating the open-circuit voltage of receiving antennas =vector effective length =incident electric field =open-circuit voltage at antenna terminals “the ratio of the magnitude of the open-circuit voltage developed at the terminals of the antenna to the magnitude of the electric-field strength in the direction of the antenna polarization.

Hanyang University 10/24 the ratio of the available power at the terminals of a receiving antenna to the power flux density of a plane wave incident on the antenna from that direction, the wave being polarization-matched to the antenna. effective area (aperture) With each antenna, we can associate a number of equivalent areas. These are used to describe the power capturing characteristics of the antenna when a wave impinges on it. = effective area (effective aperture) = power delivered to the load = power density of incident wave Figure 2.29 (b) Aperture antenna in receiving mode

Hanyang University 11/24 (conjugate matching) Scattering area is defined as the equivalent area when multiplied by the incident power density is equal to the scattered or reradiated power Loss area is defined as the equivalent area, which when multiplied by the incident power density leads to the power dissipated as heat through

Hanyang University 12/24 Capture area is defined as the equivalent area, which when multiplied by the incident power density leads to the total power captured, collected, or intercepted by antenna Capture area = Effective area + Scattering area + Loss area Aperture efficiency of an antenna, which is defined as the ratio of the maximum effective area of the antenna to its physical area For a lossless antenna ( ) the maximum value of the scattering area is also equal to the physical area.

Hanyang University 13/24 Figure 2.30 Two antennas separated by a distance R directive properties The power transferred to the load or If antenna 2 is used as a transmitter, 1 as a receiver maximum effective areas (directivities) If antenna 1 is isotropic, then = 1 the maximum effective area of an isotropic source is equal to the ratio of the maximum effective area to the maximum directivity of any other source

Hanyang University 14/24 Figure 2.30 Two antennas separated by a distance R If conduction-dielectric,reflection and polarization losses are also included, then the maximum effective area

Hanyang University 15/24 The analysis and design of radar and communications systems often require the use of the Friis Transmission Equation and the Radar Range Equation. Figure 2.31 Geometrical orientation of transmitting and receiving antennas for Friis transmission equation. (Power density of Isotropic radiator for distance R) (Power density of non Isotropic radiator for distance R)

Hanyang University 16/24 the amount of power collected by the receiving antenna can be written Receiving effective area (Power density of non Isotropic radiator for distance R) or (the ratio of the received to the input power) If reflection loss and polarization loss are included For reflection and polarization-matched antenna aligned for maximum directional radiation and reception

Hanyang University 17/24 Figure 2.32 Geometrical arrangement of transmitter, target, and receiver for radar range equation. Radar cross section or echo area (σ ) : the area intercepting that amount of power which, when scattered isotropically, produces at the receiver a density which is equal to that scattered by the actual target = radar cross section or echo area =Observation distance from target =incident power density =scattered power density =incident (scattered) electric field =incident (scattered) magnetic field

Hanyang University 18/24 The power captured by the target is reradiated isotropically, and the scattered power density can be written as The amount of power delivered to the receiver load Receiving effective area

Hanyang University 19/24 If reflection loss and polarization loss are included polarization-matched for maximum directional radiation and reception

Hanyang University 20/24 The radar cross section, usually referred to as RCS, is a far-field parameter, which is used to characterize the scattering properties of a radar target. For achieve low RCS Round corners Avoid flat and concave surfaces Use material treatment in flare spots

Hanyang University 21/24 Figure 2.35 Antenna, transmission line, and receiver arrangement for system noise power calculation. Every object with a physical temperature above absolute zero (0 K = −273 ) radiates energy Equivalent temperature (Brightness temperature) = brightness temperature (equivalent temperature; K) = emissivity (dimensionless ) = molecular (physical) temperature (K) = reflection coefficient of the surface for the polarization of the wave

Hanyang University 22/24 Figure 2.35 Antenna, transmission line, and receiver arrangement for system noise power calculation. Antenna noise temperature Antenna Noise Power Assuming no losses or other contributions between the antenna and the receiver

Hanyang University 23/24 Figure 2.35 Antenna, transmission line, and receiver arrangement for system noise power calculation. The effective antenna temperature at the receiver terminals System Noise Power(include receiver) = antenna temperature at the receiver terminals (K) = antenna noise temperature at the antenna terminals (K) = antenna temperature at the antenna terminals due to physical temperature(K) = antenna physical temperature (K) α = attenuation coefficient of transmission line (Np/m) = thermal efficiency of antenna (dimensionless) l = length of transmission line (m) = physical temperature of the transmission line (K) = system noise power (at receiver terminals) = antenna noise temperature (at receiver terminals) = receiver noise temperature (at receiver terminals) = effective system noise temperature (at receiver terminals) Noise Power(Include antenna,transmission loss)

Hanyang University 24/24 Thank you for your attention Antennas & RF Devices Lab.