Microwave devices and components. Phase delay and propagation velocity. The propagation constant. Transmission line distortion. Wave reflection and the reflection. coefficient. Standing wave ratio. Fundamental waveguide characteristics. Microwave passive components. The directional coupler. Waveguide junctions. Cavity resonators. Circulators and isolators. Microwave active devices. Solid-state devices. Microwave tubes. Multicavity magnetrons.
Microwave tubes are lamps that produce microwaves. 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. The emitted electrons are focused by a low positive voltage. To accelerate the electron beam, a very high positive DC voltage in equal amplitude is applied at the accelerator and buncher grid. The buncher grids superimpose AC voltage on DC voltage, which generates an electrostatic field between the buncher grids. The direction of the generated electrostatic field is governed by the frequency present in the microwave tube cavity. The continuous change in an electrostatic field accelerates and deaccelerates the electron beam. There are many types of microwave tubes. Examples include Klystrons, two-cavity Klystron, and crossed-field amplifiers. Two-cavity Klystron or Klystrons are velocity-modulated tubes. Two-cavity Klystrons are widely used as communication equipment and radar. Klystrons require a strong electrostatic field for efficient emission of an electron beam. Crossed-field amplifiers are vacuum electron devices and are generally used in master oscillator power amplifiers. Other microwave tubes are commonly available.
There are several ways in which microwave tubes function. A microwave tube works on the principle of velocity modulation. A velocity modulation principle generally avoids the problem of frequency limitation that often occurs in microwave tubes. The size of microwave tubes should range from 0.25 mm to 200 mm. An electron beam generated by a microwave source works well in the operating temperatures ranging from 910 to 1200 °C. Microwave sources are made up of materials such as tungsten, nickel, rhenium, and stainless steel. Osmium Ruthenium coating should be present on a microwave source tube. In addition, microwave sources should also have a machined tolerance of +/- 0.005mm. Microwave tubes are designed and manufactured to meet most industry standards.
Microwave tubes are used in many applications. Examples include coil formation in helical resonators and supporting resistors in high power combiners. In addition, Microwave tubes are also used in transistors and diode bases, high frequency resistor cores, conduction power tubes, and as a substrate in hybrid microelectronics. Microwave tubes should adhere to Institute of Electrical and Electronics Engineers (IEEE) 802.16 specification standards.