RF and microwave PCB work has a vocabulary that outsiders find dense and insiders find efficient — the terms compress entire design decisions into two or three words. This glossary organizes the working vocabulary into four layers: frequency and signal terms, material and impedance terms, manufacturing and test terms, and system-level terms. Each entry states what the term means and the decision it usually drives.
Frequency and Signal Terms
- RF (Radio Frequency): signals from 3 kHz to 300 GHz; the umbrella term for wireless, radar and sensing electronics.
- Microwave: the 300 MHz to 300 GHz subset where PCB design becomes transmission-line engineering.
- Millimeter-wave (mmWave): 30 to 300 GHz, where wavelengths shrink to millimeters and every tolerance tightens.
- Insertion loss: signal energy lost passing through a trace or component; the budget every RF design negotiates.
- Return loss: energy reflected back from an impedance mismatch; -20 dB is a common quality bar.
- VSWR: standing-wave ratio expressing match quality; 1.2:1 or better indicates a healthy transmission path.
- S-parameters: the measured language of RF networks — S11 for reflection, S21 for transmission — read on a VNA.
- Crosstalk: unwanted coupling between adjacent traces, managed with spacing and ground guards.
Material and Impedance Terms
- Dielectric constant (Dk): how much a substrate slows and shapes fields; sets trace geometry and velocity. The property landscape is surveyed in the RF and microwave material landscape.
- Dissipation factor (Df): the fraction of signal energy the substrate absorbs per cycle; the loss-budget number.
- Characteristic impedance (Z0): the impedance a transmission line presents, typically 50 ohms; controlled through the controlled impedance design rules.
- Microstrip / stripline / CPW: the three canonical transmission-line geometries — outer layer, buried between planes, and coplanar with side grounds.
- PTFE and hydrocarbon laminates: the two dominant high-frequency dielectric families, trading loss against processability.
- TCDk: the temperature coefficient of Dk — how much tuning drifts as the board heats and cools.
Manufacturing and Test Terms
- Controlled impedance: fabricating traces to a specified impedance window, verified by coupon and TDR.
- LDI (laser direct imaging): digital exposure that achieves the fine-line precision RF boards demand; the step is detailed in the high-accuracy pattern transfer guide.
- Plasma desmear: PTFE hole-wall preparation that wet chemistry cannot perform.
- Back-drilling: removing unused via barrel to kill stub resonance above roughly 10 GHz.
- ENIG: the flat, corrosion-resistant finish that dominates RF assembly; alternatives are compared in the surface finish guide.
- AOI / flying probe / ICT: the optical and electrical screening hierarchy defined in the inspection types overview.
- VNA: vector network analyzer — the instrument that measures S-parameters and turns electrical claims into data, per the high-frequency PCB testing workflow.
- Coupon: a surrogate structure processed with the panel to prove impedance and plating without sacrificing product.
System-Level Terms
- Phased array: an antenna of many elements whose PCB requires amplitude and phase consistency across channels — the engineering is walked through in the 64-channel phased array case study.
- mmWave radar: 24/60/77 GHz sensing boards combining antenna integration, low-loss material and tight registration.
- EMI/EMC: electromagnetic interference and compatibility — the regulatory frame that shielding and grounding disciplines serve.
- Insertion-loss ripple: passband variation caused by resonances and impedance wobble; a symptom reviewers read like a fingerprint.
- Impedance tolerance: the accepted deviation window, commonly ±5% for RF production and tighter for demanding chains.
