Glossary
Glossary
| Term | Definition |
| Admittance | The combination of capacitance and conductance in a transmission line. |
| Attenuation Loss | The loss that occurs due to the absorption of the signal in the transmission line. |
| Avalanche Transit Time Devices | Devices that utilize the delay between voltage and current in an avalanche, along with transit time, to exhibit negative resistance. Examples include IMPATT, TRAPATT, and BARITT diodes. |
| BARITT Diode | BARrier Injection Transit Time diode. A device where carrier injection is caused by forward-biased junctions, resulting in less noise than impact ionization. |
| Bolometer | A device used for low microwave power measurements, whose resistance changes in proportion to the applied microwave power. |
| Capacitance | The effect arising from the voltage difference between phase conductors, which creates an electric field. |
| Cavity Klystron | A microwave tube that uses cavity resonators and an electron beam to amplify microwave signals. |
| Cavity Magnetron | A cross-field tube where the anode is made of resonant cavities. The interaction between a radial electric field and an axial magnetic field causes it to produce high-power oscillations. |
| Characteristic Impedance () | The ratio of the amplitudes of voltage and current for a wave traveling in one direction along a uniform lossless transmission line with no reflections. |
| Co-axial Lines | A transmission line consisting of an inner conductor surrounded by a concentric cylindrical insulating material and a concentric outer conductor. |
| Conductance (G) | The inverse of the leakage current that flows between a transmission line and the ground, or between phase conductors. |
| Coupling Factor (C) | In a directional coupler, the ratio of incident power to the forward power, measured in dB. |
| Directivity (D) | In a directional coupler, the ratio of forward power to the back power, measured in dB. |
| Directional Coupler | A 4-port waveguide junction that samples a small amount of microwave power for measurement purposes. |
| E-H Plane Tee (Magic Tee) | A 4-port junction formed by attaching both a series (E-arm) and parallel (H-arm) waveguide to a main waveguide. Also called a Hybrid or 3dB coupler. |
| E-Plane Tee (Series Tee) | A T-junction where the side arm axis is parallel to the electric field. The outputs from the main ports are 180° out of phase with each other. |
| Gunn Effect Devices | Also known as Transfer Electron Devices (TEDs), these rely on the transfer of electrons between two different energy valleys in the semiconductor’s conduction band. |
| H-Plane Tee (Shunt Tee) | A T-junction where the side arm axis is parallel to the magnetic field, causing the magnetic field (current) to divide between the arms. |
| Hybrid Wave (HE) | A mode of propagation where neither the electric nor the magnetic field is purely transverse to the direction of propagation. |
| IMPATT Diode | IMPact ionization Avalanche Transit Time diode. A high-power semiconductor diode that uses impact ionization and transit time effects to produce a dynamic RF negative resistance. |
| Impedance | The combination of resistance and inductance in a transmission line. |
| Impedance Matching | The process of making the load impedance equal to the source impedance (resistance equal, reactance equal and opposite) to achieve maximum power transfer. |
| Inductance (L) | A parameter representing the opposition to a shift in current, caused by a varying magnetic field inducing an EMF in the opposite direction of the current flow. |
| Insertion Loss | The loss that occurs due to energy transfer using a transmission line compared to the energy transfer without a transmission line. |
| Isolation | In a directional coupler, the ratio of incident power to the back power, measured in dB. It defines the directive properties. |
| Micro Strip Lines | An unsymmetrical parallel plate transmission line with a dielectric substrate, a metallized ground on the bottom, and a thin conducting strip on top. |
| Microwaves | Waves that radiate electromagnetic energy with shorter wavelengths. |
| Monolithic Microwave Integrated Circuit (MMIC) | An integrated circuit where all active and passive circuit elements are fabricated on a single semiconductor substrate, used for microwave applications. |
| Phase Velocity () | The rate at which the wave changes its phase, or the velocity of the wave components of a sine wave when modulated. |
| Rat-race Junction | A four-port microwave device, formed as an angular ring, used to combine two signals with no phase difference or to split a signal into two halves. |
| Reflection Co-efficient () | The ratio of the reflected voltage to the incident voltage at the load terminals, expressing the amount of reflected energy due to impedance mismatch. |
| Reflection Loss | The loss that occurs due to the reflection of a signal because of an impedance mismatch. |
| Reflex Klystron | A single-cavity Klystron that operates based on reflections and oscillations. It provides low power and has a variable frequency. |
| Return Loss | The measure of the power reflected by the transmission line. |
| Scattering Matrix ([S] Matrix) | A square matrix that gives all combinations of power relationships between the various input and output ports of a microwave junction. Its elements are the scattering coefficients. |
| Schottky Barrier Diode | A simple diode with a metal-semiconductor junction that exhibits non-linear impedance, primarily used for microwave detection and mixing. |
| Skin Effect | The tendency of a high-frequency alternating current to flow through only the outer layer (surface) of a conductor, rather than through the center. |
| Slotted Line | A measurement device consisting of a slotted section of waveguide and a movable probe used to measure standing wave patterns and determine VSWR and impedance. |
| Strip Lines | A planar transmission line consisting of a central thin conducting strip placed inside a dielectric substrate between two wide ground plates. |
| Stub Matching | A method to achieve impedance matching by connecting sections of open or short circuit lines (stubs) in shunt with the main transmission line. |
| TRAPATT Diode | TRApped Plasma Avalanche Triggered Transit diode. A high peak power microwave generator where a high-field avalanche zone propagates through the diode, trapping a plasma of electrons and holes. |
| Transverse Electric Wave (TE) | A mode of propagation where the electric field is purely transverse to the direction of propagation, but the magnetic field is not. |
| Transverse Electromagnetic Wave (TEM) | A mode of propagation where both the electric and magnetic fields are purely transverse to the direction of propagation. |
| Transverse Magnetic Wave (TM) | A mode of propagation where the magnetic field is purely transverse to the direction of propagation, but the electric field is not. |
| Travelling Wave Tube (TWT) | A broadband microwave amplifier that operates through the prolonged interaction between an electron beam and an RF field propagating along a slow-wave structure, such as a helix. |
| Varactor Diode | A semiconductor device whose junction capacitance can be varied as a function of the reverse bias voltage applied to it. |
| Voltage Regulation | The change in the magnitude of the voltage between the sending and receiving ends of a transmission line. |
| Voltage Standing Wave Ratio (VSWR) | The ratio of the maximum voltage to the minimum voltage in a standing wave pattern, used to measure the magnitude of an impedance mismatch. |
| Waveguide | A hollow metallic tube of uniform cross-section for transmitting electromagnetic waves by successive reflections from the inner walls of the tube. |