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The Toolbox — Symbols

RF & Microwave Symbols

Standard RF and microwave schematic symbols for antennas, transmission lines, passive components, and active devices.

Antennas

Generic AntennaGeneral antenna symbol used when antenna type is unspecified in a schematic.
Dipole AntennaHalf-wave dipole — two equal-length elements fed at the center. Most fundamental antenna type.
Vertical / Whip AntennaVertical antenna — omnidirectional in azimuth. Standard symbol for VHF/UHF mobile and marine antennas.
Yagi AntennaDirectional Yagi antenna symbol showing boom with multiple elements. Arrow indicates direction of maximum radiation.
Parabolic / Dish AntennaParabolic reflector antenna symbol. Used for satellite, microwave, and radar applications requiring high gain.
Loop AntennaSmall loop or magnetic antenna. Sensitive to magnetic field component of EM wave. Used in direction finding (ADF/NDB).

Transmission Lines

Coaxial CableCoaxial transmission line cross-section symbol. Inner conductor surrounded by dielectric and outer shield.
WG
WaveguideRectangular waveguide cross-section. Used at microwave frequencies where coaxial loss becomes excessive.
Z₀
Transmission Line (General)General transmission line symbol — two parallel lines representing the conductors of any two-wire transmission line.

Passive RF

ATT −X dB
Attenuator (RF)Fixed RF attenuator. Reduces signal power by a specified number of dB while maintaining impedance match.
ISO
RF IsolatorTwo-port device allowing signal flow in one direction only. Prevents reflections from load reaching the source. Typically 20–30 dB isolation.
Coupler Coupled Isolated
Directional CouplerFour-port device sampling forward or reverse power. Coupling factor (dB) indicates how much power is sampled at the coupled port.
P1 P3 P2
RF CirculatorThree-port device routing signals in one direction — 1→2→3→1. Used in duplexers to isolate TX from RX on a shared antenna.
÷ −3dB −3dB
Power Splitter / CombinerDivides RF power equally between outputs (splitter) or combines multiple inputs (combiner). Each split incurs 3 dB plus insertion loss.
BALUN UN BAL
BalunBalanced-to-Unbalanced transformer. Converts between balanced (differential) and unbalanced (single-ended) signals. Prevents common-mode currents on coax.

Active RF

RF AMP
RF AmplifierGeneric RF amplifier block. Triangle shape with signal flowing in direction of gain. Gain in dB noted inside or adjacent.
RF IF LO
MixerMultiplies RF and LO signals to produce IF at sum and difference frequencies. Core of superheterodyne receivers.
RF RF
PIN Diode SwitchPIN diode used as an RF switch. Low insertion loss when forward biased (ON), high isolation when reverse biased (OFF).

Measurement

SWR
SWR / Power MeterIn-line RF meter measuring forward power, reflected power, and SWR in a transmission line.
SA
Spectrum Analyzer (Block)Block symbol representing a spectrum analyzer input. Displays signal amplitude versus frequency.
Note: RF schematic symbols vary between standards (MIL-STD, IEEE, IEC) and between manufacturers. The symbols shown represent the most commonly used conventions in US electronics documentation.