What are limitations of conventional tubes at microwave frequencies?

What are limitations of conventional tubes at microwave frequencies?

Conventional low frequency tubes like triodes fail to operate at microwave frequencies (MF) because the electron transit time from cathode to grid becomes do large that it cannot produce microwave oscillations.

What is the frequency range of microwave?

Microwave frequencies range between 109 Hz (1 GHz) to 1000 GHz with respective wavelengths of 30 to 0.03 cm. Within this spectral domain are a number of communication systems applications that are important in both the military and civilian sectors.

Why are conventional vacuum tubes less useful signal source over 1GHz?

When frequencies are above 1GHz, the real part of the impedance becomes small enough to nearly short the signal source. Consequently, the output power is decreased rapidly.

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What is conventional tube?

The vacuum tubes that are examples of conventional tubes are triodes, tetrodes, and pentodes. Generally speaking, vacuum tubes have one cathode, one anode and one or more grids. The grids are used to control actions.

What are its limitations at high frequencies?

Answer: You can’t send a signal to a submarine underwater in high frequencies; it has to be low frequencies. UHF and VHF can’t penetrate bunkers or building materials like low-frequency signals. Low-frequency signals can, in theory, travel much further with the atmosphere acting as a waveguide.

What two problems prevent conventional electronics from working at microwave frequency?

Conventional electronic components do not work well at microwave frequencies because wavelengths approximate component sizes, distributed constants (LC) that are negligible at lower frequencies are critical at microwave frequencies, and the skin effect produces an ac resistance that is greater than the dc resistance.

What are the limitations of vacuum tube technology?

Vacuum Tubes: Disadvantages Bulky, hence less suitable for portable products. Higher operating voltages generally required. High power consumption; needs heater supply that generates waste heat and yields lower efficiency, notably for small-signal circuits. Glass tubes are fragile, compared to metal transistors.

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What is microwave tube?

Microwave tubes are electron guns for generating linear beam tubes. A microwave tube generates and amplifies higher frequencies in the microwave range of frequency spectrum. When a microwave tube is energized, the electrons are emitted from the cathode and are focused on the control grid.

What are microwave tubes?

What are O type microwave tubes?

Klystrons and TWT’s are linear beam or O type tubes in which the accelerating electric field in the same direction as the static magnetic field used to focus the electron beam. A klystron is a vacuum tube that can be used either as a generator or as an amplifier of power at microwave frequencies.