Answer Key
- Microwaves are electromagnetic waves with shorter wavelengths that radiate energy. They are not reflected by the ionosphere, travel in a straight line, are reflected by conducting surfaces, and are easily attenuated over shorter distances. Microwave currents can also flow through a thin layer of a cable.
- Characteristic Impedance (Z_0) is the ratio of the amplitudes of voltage and current for a wave traveling in one direction along a uniform line with no reflections. For a lossless line, where resistance and conductance are zero, the formula simplifies to R_0 = \sqrt{L/C}, where L and C are the inductance and capacitance per unit length.
- In TEM (Transverse Electromagnetic) mode, both the electric and magnetic fields are purely transverse to the direction of propagation. In TE (Transverse Electric) mode, the electric field is purely transverse, but the magnetic field is not. In TM (Transverse Magnetic) mode, the magnetic field is purely transverse, but the electric field is not.
- A waveguide is a hollow metallic tube of uniform cross-section used for transmitting electromagnetic waves via reflections from its inner walls. The main difference is that a waveguide is a one-conductor structure that cannot support a TEM wave, while a transmission line is a two-conductor structure that can.
- A Varactor diode is a semiconductor device that functions as a voltage-variable capacitor. When the junction is reverse-biased, mobile carriers deplete, creating a capacitance. The junction capacitance can be varied as a function of the applied reverse bias voltage, decreasing as the reverse bias increases.
- An E-H Plane Tee is a four-port microwave junction formed by attaching both a series (E-Plane) and a parallel (H-Plane) waveguide to a main rectangular waveguide. It is also commonly known as a Magic Tee, Hybrid, or 3dB coupler.
- A Directional Coupler is a 4-port device that samples a small amount of microwave power for measurement purposes, such as incident and reflected power. Its Coupling Factor (C) is the ratio of the incident power to the forward coupled power, measured in dB.
- A two-cavity Klystron amplifies a signal by modulating an electron beam. An input signal creates an electromagnetic field in the first cavity, which varies the speed of electrons passing through it, causing them to form bunches in the drift space. These electron bunches then induce a much stronger field in the second cavity, resulting in an amplified output signal.
- A Cavity Magnetron is a cross-field microwave tube in which the electric and magnetic fields are perpendicular to each other. It uses resonant cavities as part of its anode structure to provide high peak power oscillations and is primarily useful in radar applications.
- A slotted line is a measurement device consisting of a slotted section of transmission line with a movable probe. It is used to measure the standing wave pattern inside the waveguide, from which values like Voltage Standing Wave Ratio (VSWR), impedance, and reflection coefficient can be determined.