HIGHLIGHTED-Microwave-Communications.pdf

B prevent cathode back heating c ensure bunching d

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b) prevent cathode back-heating c) ensure bunching d) improve the phase-focusing effect 329. Signal propagation in a waveguide is by a) electrons b) electric and magnetic fields c) holes d) air pressure 330. The dominant mode in most waveguides is a) TE 0,1 b) TE 1,2 c) TM 0,1 d) TM 1,1 331. Periodic permanent-magnet focusing is used with TWTs to a) allow pulsed operation b) improve electron bunching c) avoid the bulk of electromagnet d) allow coupled-cavity operation at the highest frequencies 332. A popular microwave mixer diode is the a) Gunn b) Varactor c) Hot carrier d) IMPATT 333. A magnetron whose oscillating frequency is electronically adjustable over a wide range is called a a) coaxial magnetron b) dither-tune magnetron c) frequency-agile magnetron d) VTM 334. The main benefit of using microwave is a) lower-cost equipment b) sampler equipment c) greater transmission distances d) more spectrum space for signals 335. Which diode is a popular microwave oscillator? a) IMPATT b) Gunn c) Varactor d) Schottly 336. Which of the following is not a disadvantage of microwave? a) higher cost equipment b) line-of-sight transmission c) conventional components are not usable d) circuits are more difficult to analyze
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337. Which of the following is a microwave frequency? a) 1.7 MHz b) 750 MHz c) 0.98 MHz d) 22 GHz 338. In a TWT, the electron beam, is density- modulated by a a) Permanent magnet b) Modulation transformer c) Helix d) Cavity resonator 339. Which of the following is not a common microwave application? a) radar b) mobile radio c) telephone d) spacecraft communications 340. Indicate the false statement. Transit time in microwave tubes will be reduced if a) the electrodes are brought closer together b) a higher node current is used c) multiple or coaxial loads are used d) the anode voltage is made larger 341. Coaxial cable is not widely used for long microwave transmission lines because of its a) high loss b) high lost c) large size d) excessive radiation 342. The main advantage of the TWT over a klystron for microwave amplification is a) lower cost b) smaller size c) higher power d) wider bandwidth 343. A magnetic field is used in the cavity magnetron to a) prevent anode current in the absence of oscillations b) ensure that the oscillations are pulsed c) help in focusing the electron beam, thus preventing spreading d) ensure that the electrons will orbit around the cathode 344. A waveguide has a cutoff frequency of 17 GHz. Which of the signals will not be passed by the waveguide? a) 15 GHz b) 18 GHz c) 22 GHz d) 25 GHz 345. When the electric field in a waveguide is perpendicular to the direction of wave propagation, the mode is said to be a) vertical polarization b) transverse electric c) horizontal polarization d) transverse magnetic 346. The TWT is sometimes preferred to the magnetron as a radar transmitter output tube
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