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ssrs 2014 barcode Six z in Software
Six z Scanning QR Code 2d Barcode In None Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications. Make QR Code 2d Barcode In None Using Barcode creator for Software Control to generate, create Denso QR Bar Code image in Software applications. g( , ) Recognizing QR Code In None Using Barcode decoder for Software Control to read, scan read, scan image in Software applications. Generating QR Code JIS X 0510 In Visual C#.NET Using Barcode generator for Visual Studio .NET Control to generate, create QR Code ISO/IEC18004 image in VS .NET applications. 0.5 0.5 QR Code Encoder In Visual Studio .NET Using Barcode printer for ASP.NET Control to generate, create QR Code image in ASP.NET applications. QR Code Drawer In .NET Framework Using Barcode printer for Visual Studio .NET Control to generate, create QRCode image in .NET applications. Figure 6.6 (a) A radiation pattern. (b) The beamwidth in the Hplane. (c) The beamwidth in the Eplane. QR Code 2d Barcode Maker In Visual Basic .NET Using Barcode generation for .NET framework Control to generate, create QR Code ISO/IEC18004 image in .NET framework applications. Making Code 128C In None Using Barcode creator for Software Control to generate, create Code 128B image in Software applications. Because the radiation pattern is defined in terms of radiated power, the normalized electric field strength pattern will be given by 2g( , ). 6.8 Beam Solid Angle and Directivity Plane angles are measured in radians, and by definition, an arc of length R equal to the radius subtends an angle of one radian at the center of a circle. An angle of radians defines an arc length of R on the circle. Drawing Bar Code In None Using Barcode generator for Software Control to generate, create barcode image in Software applications. Print ANSI/AIM Code 39 In None Using Barcode creator for Software Control to generate, create Code 3 of 9 image in Software applications. Antennas
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(b) Figure 6.7
(a) Defining the radian. (b) Defining the steradian.
This is illustrated in Fig. 6.7a. The circumference of a circle is given by 2 R, and hence the total angle subtended at the center of a circle is 2 rad. All this should be familiar to the student. What may not be so familiar is the concept of solid angle. A surface area of R2 on the surface of a sphere of radius R subtends unit solid angle at the center of the sphere. This is shown in Fig. 6.7b. The unit for the solid angle is the steradian. A solid angle of steradians defines a surface area on the sphere (a spherical cap) of R2 . Looking at this another way, a surface area A subtends a solid angle A/R2 at the center of the sphere. Since the total surface area of a sphere of radius R is 4 R2, the total solid angle subtended at the center of the sphere is 4 sr. The radiation intensity is the power radiated per unit solid angle. For a power Prad radiated, the average radiation intensity (which is also the isotropic value) taken over a sphere is Ui Prad 4 W/sr (6.7) Six
From the definition of directivity d, the maximum radiation intensity is Umax
(6.8) The beam solid angle, A, for an actual antenna is defined as the solid angle through which all the power would flow to produce a constant radiation intensity equal to the maximum value. Thus Umax Prad (6.9) Combining Eqs. (6.7), (6.8), and (6.9) yields the important result
(6.10) This is important because for narrowbeam antennas such as used in many satellite communications systems, a good approximation to the solid angle is > HPBWE
HPBWH
(6.11) where HPBWE is the halfpower beamwidth in the E plane and HPBWH is the halfpower beamwidth in the H plane, as shown in Fig. 6.6. This equation requires the halfpower beamwidths to be expressed in radians, and the resulting solid angle is in steradians. The usefulness of this relationship is that the halfpower beamwidths can be measured, and hence the directivity can be found. When the halfpower beamwidths are expressed in degrees, the equation for the directivity becomes 6.9 Effective Aperture
41253 HPBW8E 3 HPBW8H
(6.12) So far, the properties of antennas have been described in terms of their radiation characteristics. A receiving antenna has directional properties also described by the radiation pattern, but in this case it refers to the ratio of received power normalized to the maximum value. An important concept used to describe the reception properties of an antenna is that of effective aperture. Consider a TEM wave of a given power density at the receiving antenna. Let the load at the antenna terminals be a complex conjugate match so that maximum power transfer occurs and power Prec is delivered to the load. Note that the power delivered to the actual receiver may be less than this as a result of Antennas
feeder losses. With the receiving antenna aligned for maximum reception (including polarization alignment, which is described in detail later), the received power will be proportional to the power density of the incoming wave. The constant of proportionality is the effective aperture Aeff which is defined by the equation Prec Aeff (6.13) For antennas which have easily identified physical apertures, such as horns and parabolic reflector types, the effective aperture is related in a direct way to the physical aperture. If the wave could uniformly illuminate the physical aperture, then this would be equal to the effective aperture. However, the presence of the antenna in the field of the incoming wave alters the field distribution, thereby preventing uniform illumination. The effective aperture is smaller than the physical aperture by a factor known as the illumination efficiency. Denoting the illumination efficiency by I gives Aeff

