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Six QR Code Scanner In None Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications. QR Code JIS X 0510 Drawer In None Using Barcode creator for Software Control to generate, create QR Code JIS X 0510 image in Software applications. 6.13. What is the effective aperture of an isotropic antenna operating at a wavelength of 1 cm 6.14. Determine the halfpower beamwidth of a halfwave dipole. 4l, Reading Quick Response Code In None Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications. QR Code JIS X 0510 Encoder In Visual C#.NET Using Barcode generator for .NET Control to generate, create QR Code JIS X 0510 image in .NET applications. 6.15. A uniformly illuminated rectangular aperture has dimensions a b 3l. Plot the radiation patterns in the principal planes. Generate QRCode In .NET Framework Using Barcode printer for ASP.NET Control to generate, create QRCode image in ASP.NET applications. Paint QR Code In Visual Studio .NET Using Barcode creator for Visual Studio .NET Control to generate, create QR image in .NET framework applications. 6.16. Determine the halfpower beamwidths in the principal planes for the uniformly illuminated aperture of Prob. 6.15. Hence determine the gain. State any assumptions made. 6.17. Explain why the smoothwalled conical horn radiates copolar and crosspolar field components. Why is it desirable to reduce the crosspolar field as far as practical, and state what steps can be taken to achieve this. 6.18. When the rectangular aperture shown in Fig. 6.9 is fed from a waveguide operating in the TE10 mode, the farfield components (normalized to unity) are given by Quick Response Code Generation In VB.NET Using Barcode encoder for .NET framework Control to generate, create Denso QR Bar Code image in Visual Studio .NET applications. Making Barcode In None Using Barcode encoder for Software Control to generate, create bar code image in Software applications. p Eu su, fd 5 2 sin f 2 cos X sin Y p 2 Y X2 2 a b 2
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6.25. 6.26. Determine the depth of the reflector specified in Prob. 6.23. A 3m paraboloidal dish has a depth of 1 m. Determine the focal length. 6.27. A 5m paraboloidal reflector works with an illumination efficiency of 65 percent. Determine its effective aperture and gain at a frequency of 6 GHz. 6.28. Determine the halfpower beamwidth for the reflector antenna of Prob. 6.27. What is the beamwidth between the first nulls 6.29. Describe briefly the offset feed used with paraboloidal reflector antennas, stating its main advantages and disadvantages. 6.30. Explain why doublereflector antennas are often used with large earth stations. 6.31. Describe briefly the main advantages to be gained in using an antenna array. 6.32. A basic dipole array consists of five equispaced dipole elements configured as shown in Fig. 6.26. The spacing between elements is 0.3l. Determine the current phasing needed to produce an endfire pattern. Provide a polar plot of the AF. 6.33. What current phasing would be required for the array in Prob. 6.32 to produce a broadside pattern 6.34. A fourelement dipole array, configured as shown in Fig. 6.26, is required to produce maximum radiation in a direction 0 15 . The elements are spaced by 0.2l. Determine the current phasing required, and provide a polar plot of the AF. 6.35. A rectangular patch antenna element has sides a 9 mm, b 6 mm. The operating frequency is 10 GHz. Plot the radiation patterns for the 0 and 90 planes. 6.36. For microstrip line, where the thickness t of the line is negligible compared to the dielectric thickness h, and the line width W h the effective dielectric constant is given by ee > er 2 1 2 er 1 1 12 h W
er is the dielectric constant of the dielectric material. The characteristic impedance is given by
Z0 120 2ee c W h 1.393 0.667 ln a W h 1.444b d
Six
(see Chang, 1989). Calculate the characteristic impedance for a microstrip line of width 0.7 mm, on an alumina dielectric of thickness 0.7 mm. The dielectric constant is 9.7. 6.37. For the microstripline of Prob. 6.36, calculate (a) the line wavelength (b) the phase shift coefficient in rad/m, and in degrees/cm. The frequency of operation is 10 GHz. 6.38. The dielectric constant of polyguide dielectric is 2.32. Calculate the characteristic impedance and phase shift coefficient for a microstrip line of width 2.45 mm, and dielectric thickness 1.58 mm. 6.39. The effective dielectric constant for a microstripline is 1.91. Design a switchedline phase shifter (see Fig. 6.35) to produce a phase shift of 22.5 at a frequency of 12 GHz. Show how switching might be achieved using PIN diodes. 6.40. Calculate the power required to drive a MEM switch, which has to operate at a frequency of 8 kHz. The switch capacitance is 0.5 pF, and the drive voltage needed for switching is 75 V. (Hint: The energy stored in a capacitor is 1/2 CV2 and power is J/s.)

