RF design glossary

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

This glossary defines the core terms of radio-frequency design. Each definition links to a full article with formulas and sources.

What do the key RF terms mean?

ACLR / ACPR: Ratio of in-channel power to power leaking into an adjacent channel. More
Axial ratio: Ratio of major to minor axis of the polarization ellipse; 0 dB is perfect circular polarization. More
Balun: Device converting between balanced (differential) and unbalanced (single-ended) signals. More
Barkhausen criterion: Oscillation condition: loop gain magnitude of one with total phase a multiple of 360°. More
Bias tee: Network that combines DC bias and RF on one port while isolating them on the others. More
Bode–Fano limit: Fundamental bound on the bandwidth over which a reactive load can be matched. More
Characteristic impedance (Z0): Ratio of voltage to current of a single traveling wave on a transmission line. More
Circulator: Non-reciprocal three-port routing power 1→2→3→1. More
Conversion loss: Ratio of mixer RF input power to IF output power. More
Coplanar waveguide (CPW): Transmission line with signal conductor between coplanar grounds. More
dBc: Decibels relative to the carrier power. More
dBi: Antenna gain in decibels relative to an isotropic radiator. More
dBm: Power in decibels relative to 1 milliwatt. More
De-embedding: Mathematically removing fixture effects from measured network data. More
Digital predistortion (DPD): Applying the inverse of a PA's nonlinearity to the baseband signal. More
Directivity (antenna): Ratio of radiation intensity in a direction to the average over all directions. More
Directivity (coupler): Isolation minus coupling, in dB; ability to separate forward and reverse waves. More
Doherty amplifier: Main and peaking amplifiers with load modulation for high back-off efficiency. More
Duplexer: Filter network letting a transmitter and receiver share one antenna at different frequencies. More
Dynamic range: Span between the smallest and largest signals a system handles. More
Effective aperture: Ae = Gλ²/4π, the equivalent capture area of an antenna. More
EIRP: Effective isotropic radiated power: transmit power plus antenna gain minus feed losses. More
ENR: Excess noise ratio of a calibrated noise source. More
EVM: Error vector magnitude: rms constellation error relative to the ideal. More
Far field: Region beyond about 2D²/λ where the pattern no longer depends on distance. More
Fractional-N synthesizer: PLL whose average divide ratio has a fractional part, set by a delta-sigma modulator. More
Free-space path loss (FSPL): (4πd/λ)², the spreading loss between isotropic antennas. More
Fresnel zone: Ellipsoid around a line-of-sight path in which path differences are below λ/2. More
Friis equation: Pr = Pt·Gt·Gr·(λ/4πd)² for free-space links. More
Gilbert cell: Active double-balanced multiplier used as a mixer. More
Group delay: Negative derivative of phase with respect to angular frequency. More
Harmonic balance: Frequency-domain method for periodic steady state of nonlinear circuits. More
Image frequency: Second RF frequency that mixes to the same IF, 2·f_IF from the wanted signal. More
Insertion loss: Reduction in power transmitted caused by inserting a component. More
IP3 (third-order intercept): Extrapolated power where third-order IM equals the fundamental. More
ISM bands: Bands designated for industrial, scientific and medical RF energy uses. More
Jitter: Timing variation of a clock edge; integrated phase noise in time units. More
K factor (Rollett): Stability factor; K > 1 with |Δ| < 1 indicates unconditional stability. More
Link budget: Accounting of gains and losses from transmitter to receiver. More
LNA: Low-noise amplifier; the first gain stage of a receiver. More
Load-pull: Large-signal measurement varying load impedance to find optimum PA terminations. More
Microstrip: PCB transmission line: strip over a ground plane with dielectric between. More
Mismatch loss: Power lost to reflection: −10·log10(1 − |Γ|²). More
Mu factor (μ): Edwards–Sinsky single-parameter stability test; μ > 1 means unconditionally stable. More
Noise figure: Degradation of SNR by a device, in dB, referenced to 290 K. More
Noise temperature: Equivalent temperature representing a device's added noise; Te = 290(F − 1). More
P1dB: Power at which gain has dropped 1 dB from its small-signal value. More
PAE: Power-added efficiency: (Pout − Pin)/PDC. More
PAPR: Peak-to-average power ratio of a signal. More
Phase noise: Random phase fluctuation of an oscillator, specified in dBc/Hz at an offset. More
PLL: Phase-locked loop: feedback system locking an oscillator to a reference. More
Q factor: 2π × stored energy / energy dissipated per cycle; f0/BW for resonators. More
Radiation resistance: Resistance representing power radiated by an antenna. More
Reciprocal mixing: Blocker mixing with LO phase noise into the wanted channel. More
Reflection coefficient (Γ): Ratio of reflected to incident voltage wave: (ZL − Z0)/(ZL + Z0). More
Return loss: −20·log10|Γ| in dB. More
S-parameters: Scattering parameters relating incident and reflected waves of a network. More
Self-resonant frequency (SRF): Frequency at which a component's parasitics resonate with its intended reactance. More
Sensitivity: Minimum input power giving the required SNR or error rate. More
SFDR: Spurious-free dynamic range: span from noise floor to the level where spurs reach it. More
Skin depth: Depth at which current density falls to 1/e: δ = 1/√(πfμσ). More
Smith chart: Polar plot of reflection coefficient overlaid with impedance or admittance circles. More
Stripline: Conductor centered between two ground planes in a homogeneous dielectric. More
Superheterodyne: Receiver that converts the signal to a fixed intermediate frequency. More
Touchstone file: Text format (.sNp) for network parameter data. More
Transducer gain: Power delivered to the load divided by power available from the source. More
TRL calibration: Thru-reflect-line VNA calibration method. More
VCO: Voltage-controlled oscillator. More
VNA: Vector network analyzer: instrument measuring magnitude and phase of S-parameters. More
VSWR: Voltage standing wave ratio: (1 + |Γ|)/(1 − |Γ|). More
Wilkinson divider: Matched, isolated in-phase power divider using λ/4 lines and a resistor. More
Zero-IF: Direct-conversion architecture translating RF straight to baseband. More

Frequently asked questions

What is the difference between return loss and VSWR?

Both describe reflection magnitude: return loss in dB, VSWR as a ratio of standing-wave maxima to minima.

What is the difference between dBi and dBd?

dBi is relative to an isotropic radiator; dBd is relative to a half-wave dipole, 2.15 dB higher than isotropic.

What does IP3 mean?

The third-order intercept point, a linearity figure of merit.

Categories: Reference

Articles on RF Design Wiki

Start here	Main page What is RF design Learning path Design workflow
Fundamentals	Decibels and dBm RF power Wavelength and frequency Thermal noise Noise figure Noise temperature SNR and Eb/N0 Skin effect Q factor Nonlinearity and harmonics Intermodulation and IP3 P1dB compression Dynamic range and SFDR
Transmission lines	Transmission line theory Characteristic impedance Γ, VSWR and return loss Input impedance of a line Quarter-wave transformer Microstrip Stripline Coplanar waveguide Coaxial cable Waveguides RF connectors
Matching and S-parameters	Impedance matching Maximum power transfer Smith chart L-network matching Pi and T networks Stub matching Bode–Fano limit S-parameters Touchstone files Z, Y, ABCD parameters De-embedding Mixed-mode S-parameters
Filters and passives	RF filter basics Filter approximations LC filter design Microstrip filters Cavity and dielectric filters SAW and BAW filters Diplexers and duplexers Wilkinson divider Couplers and hybrids Baluns Circulators and isolators RF attenuators Passive components
Amplifiers	Gain definitions Amplifier stability LNA design Power amplifier basics PA classes Efficiency and PAE Doherty amplifier Linearization and DPD Load-pull Transistor technologies Transistor biasing ACPR and EVM
Mixers and frequency generation	RF mixers Mixer specifications Image frequency I/Q modulators Oscillator basics Crystal oscillators VCO design Phase noise Jitter from phase noise PLL basics PLL loop filter Fractional-N synthesis Direct digital synthesis Multipliers and dividers
Antennas and propagation	Antenna fundamentals Gain and directivity Dipole antenna Monopole antenna Patch antenna Arrays and beamforming Small antenna limits Polarization Friis equation Free-space path loss Link budget Multipath and fading Atmospheric and rain loss Path loss models Fresnel zones
Receivers and systems	Receiver architectures Superheterodyne Direct conversion Low-IF receiver Software-defined radio Receiver sensitivity Blocking and selectivity Transmitter architectures Modulation ADCs for RF Radar basics
PCB layout and materials	RF PCB layout RF PCB materials Grounding and vias Controlled-impedance stackup Decoupling RF shielding Thermal design
EMC and EMI	EMC and EMI basics FCC Part 15 CISPR standards Immunity and ESD EMI filters and ferrites Precompliance testing RF exposure limits
Test and measurement	Vector network analyzer VNA calibration Spectrum analyzer Noise figure measurement Phase noise measurement RF power measurement Signal generators TDR Antenna measurement Oscilloscopes for RF
Simulation	Simulation overview Harmonic balance EM simulation EM solver methods SPICE for RF
Standards and bands	Frequency bands Radar band letters ISM bands 5G NR bands Wi-Fi and Bluetooth RF GNSS frequencies Amateur radio bands Spectrum regulation
Reference	Formula cheat sheet Textbooks and references Glossary FAQ All sources
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