Exercise :: Microwave Communication - Section 4
| 31. | Which of the following modes of transmission will not be supported by a rectangular waveguide? |
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| 32. | In a circular waveguide with radius r, the dominant mode is |
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Answer: Option B Explanation: Some applications require dual polarization capability. Circular waveguide has this capability. These analysis uses cylindrical coordinates. In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode. If D is diameter of waveguide λc = 1.706 D for TE11 mode λc = 1.029 D for TE21 mode λc = 0.82 D for TE01 mode λc = 1.306 D for TM01 mode. |
| 34. | A parametric amplifier uses |
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Answer: Option B Explanation: In a parametric amplifier the non-linear element is varactor diode or inductor. |
| 35. | Assertion (A): Impatt diode can be used in both amplifiers and oscillators. Reason (R): Impatt diode has a low resistance. |
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Answer: Option B Explanation: An Impatt diode has n+ - p - i - p + structure and is used with reverse bias. It exhibits negative resistance and operates on the principle of avalanche breakdown. Impatt diode circuits are classified as broadly tunable circuit, low Q circuit and high Q circuit. The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode. The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%. Its applications include police radar systems, low power microwave transmitter etc. |