INTRODUCTION TO MICROWAVES

Microwave

An electromagnetic wave with a relatively short wavelength and high frequency, classified as radio waves.

Frequency Division Multiple Access (FDMA)

Each user is assigned a separate frequency band within the available spectrum, used in satellite communication and analog cellular networks.

Time Division Multiple Access (TDMA)

Users share the same frequency but transmit in different time slots, used in GSM cellular networks.

Code Division Multiple Access (CDMA)

Users share the same frequency and time, but each is assigned a unique code to separate signals.

Skin Effect

The phenomenon where high-frequency energy travels only on the surface of a conductor, not penetrating deeply.

Characteristic Impedance

The inherent opposition that a transmission line offers to the flow of an electromagnetic wave.

Return Loss (RL)

Measures how much power is reflected back from the load in decibels.

Voltage Standing Wave Ratio (VSWR)

Describes how much standing wave interference occurs due to reflections.

Directional Coupler

A device that consists of two transmission lines placed close to each other, allowing energy transfer in one direction.

Quadrature Hybrid

A specialized coupler that takes an input signal and equally divides it between its two outputs, maintaining 90° phase difference.

Matched Detector

A detector designed to convert an RF signal into a video or DC signal efficiently.

Power Divider

Divides an input signal into two or more output signals, often maintaining amplitude balance.

Attenuator

A device that reduces the strength of a signal without distorting its waveform.

Band Pass Filter

Passes a specific band of frequencies and rejects frequencies below and above that band.

Low Pass Filter (LPF)

Passes frequencies below a certain cutoff frequency and attenuates frequencies above that frequency.

High Pass Filter (HPF)

Passes frequencies above a specific cutoff frequency while attenuating signals below that frequency.

Cavity Resonator

A closed metal structure that confines electromagnetic fields in the microwave region.

Klystron

A microwave vacuum tube using cavity resonators to produce velocity modulation of an electron beam for amplification.

Magnetron

A microwave tube that generates high levels of microwave power using built-in cavity resonators.

Traveling Wave Tube (TWT)

An RF power amplifier that can generate hundreds to thousands of watts with extremely wide bandwidth.

Waveguide

Hollow metal conducting pipes designed to carry and constrain microwave signals.

Coaxial Cable

A transmission line with one conductor completely surrounding another, used for RF signals.

VSWR (Voltage Standing Wave Ratio)

Indicates how well the impedance of a load matches the characteristic impedance of a transmission line.

Return Loss

The measure of how much power is reflected back due to impedance mismatches.

S-band

Microwave frequency range from 2 to 4 GHz, used for radar and Wi-Fi communication.

Ka-band

Microwave frequency range from 27 to 40 GHz, used for high-frequency satellite communications.

Microwave Diode

A semiconductor device that can amplify, oscillate, mix, detect, attenuate, and switch high frequency signals.

Schottky Diode

A diode that consists of an N-type semiconductor and metal, used for RF applications due to its fast switching speed.

PIN Diode

A diode with a layer of intrinsic semiconductor between two doped regions, acts as a variable resistor at microwave frequencies.

Gunn Diode

A microwave device that exhibits negative resistance and is primarily used as an oscillator.

Varactor Diode

Acts like a variable capacitor when reverse-biased, mainly used in frequency multiplier circuits.

Heterojunction Bipolar Transistor (HBT)

A transistor that utilizes two different types of semiconductor materials to achieve high speed and efficiency.

Amplifier

A device that increases the level of a signal to produce the required amount at the output.

Oscillator

A device that provides a sustained unstable signal for frequency reference or generating specific tones.

Fixed Attenuator

An attenuation device providing a constant level of signal reduction.

Variable Attenuator

An attenuation device that allows users to adjust the amount of signal reduction as required.

Reflection Coefficient

Quantifies the fraction of an incident wave that is reflected at an interface due to impedance mismatch.

Decibel (dB)

A logarithmic unit used to express the ratio of two values, often used in measuring power or intensity.

Isolation

The measure of how well a directional coupler prevents reverse energy transfer from occurring.

Insertion Loss

The amount of signal loss that occurs when a coupler or other device is inserted into a transmission line.

Atmospheric Attenuation

The gradual loss of signal strength due to the atmosphere, significant in microwave communications.

Transmission Line

A conductor or conductor system that carries electromagnetic waves from one point to another.

Coaxial Transmission Line

A type of transmission line consisting of a central conductor surrounded by an insulating dielectric and a conductive shield.

Microstrip Antenna

An antenna made with microstrip technology, often mounted directly on a printed circuit board.

Patch Antenna

A type of microstrip antenna that is small, easy to fabricate, and can be integrated with other electronic components.

Helical Antenna

A type of antenna that consists of a helix, known for radiating circularly polarized waves.

Parabolic Reflector Antenna

An antenna that uses a parabolic dish to focus energy from a horn antenna into a narrow beam.

Bicone Antenna

An omnidirectional antenna that radiates signals equally in all directions, made up of two conical structures.

Printed Circuit Board Antenna

An antenna manufactured directly on a printed circuit board for compactness and integration.

Slot Antenna

An antenna made by creating a slot (or dipole) in a metal sheet, functioning similarly to a dipole antenna.

Dielectric Lens Antenna

An antenna that uses a dielectric lens to collimate or focus microwave signals.

Smart Antenna

An adaptive antenna that adjusts its performance based on incoming signals and environmental conditions.

Adaptive Beam Forming

Technique used by smart antennas to adjust reception patterns for improved signal targeting.

Frequency Hopping

A method in communication systems where the frequency changes rapidly to avoid interference.

Multiple Access Techniques

Methods to allow multiple users to share the same communication channel while minimizing interference.

Amplitude Balance

A comparison of power levels between two output ports in a hybrid circuit.

Phase Balance

The degree to which the phase difference between two outputs tracks over the range of operation.

Impulse Response

The output signal of a system when stimulated by an impulse, used for characterizing linear systems.

Working Principle of a Waveguide

Waveguides operate by confining electromagnetic waves within their hollow structure for transmission.

Input Coupling Network

The component that combines RF and LO signals in a mixer.

Electromagnetic Waves

Waves that propagate through space carrying electromagnetic radiant energy.

Waveguide Mode

The specific patterns of electric and magnetic fields inside a waveguide.

Coupled-Cavity TWT

Uses a slow wave structure of cavities coupled to amplify signals using velocity modulation.

Ring-Loop TWT

A traveling-wave tube that uses ring-like structures to achieve high power amplification.

Waveguide Cutoff Frequency

The frequency below which a waveguide cannot propagate electromagnetic energy.

Probe and Loop Coupling

Techniques used to inject signals into or extract signals from a waveguide.

Heterojunction Technology

A technology that utilizes two different semiconductor materials to enhance performance.

GaAs/AlGaAs Structure

A highly efficient structure used in high electron mobility transistors (HEMTs).

Broadband Communication systems

Systems that utilize a wide range of frequencies for transmitting data.

Cutoff Frequency

The minimum frequency at which a waveguide can propagate an electromagnetic wave.

Waveguide Dimensions

The physical size of a waveguide, which affects its bandwidth and the cutoff frequency.

Rectangular Waveguide

A type of waveguide with a rectangular cross-section used for microwave transmission.

Circular Waveguide

A type of waveguide with a circular cross-section, often used for higher modes and greater bandwidth.

Mode of Propagation

The specific way in which electromagnetic waves propagate within a waveguide, including TE, TM, and TEM modes.

TE (Transverse Electric) Mode

A mode of propagation where the electric field is entirely perpendicular to the direction of wave propagation.

TM (Transverse Magnetic) Mode

A mode of propagation where the magnetic field is entirely perpendicular to the direction of wave propagation.

TEM (Transverse Electromagnetic) Mode

A mode of propagation where both the electric and magnetic fields are perpendicular to the direction of travel.

Waveguide Losses

The attenuation of signal strength in a waveguide due to dielectric losses and conductor losses.

Phase Velocity

The speed at which a wave phase propagates through a medium, varying based on the waveguide's characteristics.