RF View

RF library

Concepts, tutorials and component guides, written from handset RF experience.

22 articles

Concepts 14

What the numbers mean: short, exact explanations with the formulas.

  • TRL Calibration Explained: Thru, Reflect and Line2026-10-26TRL needs only the line impedance and line length to be known. The reflect can be any high-reflection device, equal at both ports. The line must be longer than the thru by 20° to 160° of phase, so one line covers about an 8:1 frequency band.
  • VNA Dynamic Range and Noise Floor in Stop-Band Measurements2026-10-26Transmission dynamic range is the source power minus the receiver noise floor, in dB. Raising the source power by 10 dB or narrowing the IF bandwidth by a factor of 10 each gains 10 dB, until the receiver compresses.
  • How a Vector Network Analyzer Measures S-Parameters2026-10-25A VNA measures complex wave ratios: S11 = b1/a1 and S21 = b2/a1 when a2 = 0. Because it reports ratios, S-parameters do not depend on source power while the receivers stay linear, and a magnitude of 0.1 reads -20 dB.
  • The 12-Term Error Model: What VNA Calibration Corrects2026-10-25A full two-port VNA calibration solves 12 error terms, 6 forward and 6 reverse. A one-port calibration needs 3. Measuring known standards lets the VNA solve these repeatable errors and remove them, but not noise or connector repeatability.
  • Amplifier Stability: How to Read the Rollett K Factor2026-10-18An amplifier is unconditionally stable at a frequency when K is greater than 1 and |delta| is less than 1. With S12 = 0.1 and S21 = 2, K is 1.256 and the amplifier passes; with S12 = 0.15 and S21 = 4, K falls to 0.519 and it does not.
  • dB and dBm in a Signal Chain: Adding Gains and Losses2026-10-18A gain or loss in dB is added to a level in dBm to give the new level in dBm. A -10 dBm signal through a 20 dB amplifier and a cable with 3 dB loss ends at +7 dBm, about 5 mW.
  • SMA Connectors: Frequency Limits, Torque and Reflections2026-10-18SMA connectors are 50 ohm and commonly specified up to 18 GHz, and 5 in-lb (about 0.56 N*m) is a common torque for repeatable results. Two connectors with 30 dB return loss each can combine into a reflection of up to 0.063 (about -24 dB), seen as ripple in S11.
  • VSWR Explained: Reflection Coefficient and Mismatch Loss2026-10-17VSWR = (1 + |G|) / (1 - |G|), so a VSWR of 2 means |G| = 0.333, a return loss of 9.54 dB, 11.1 % of the power reflected and 0.512 dB of mismatch loss. SWR and VSWR are the same number.
  • How to Measure RF Power: Power Meters, Analyzers and Losses2026-10-16A reading of -12.3 dBm after 10 dB of attenuator and 1.5 dB of cable means the source is -0.8 dBm, because losses in dB are added back. Mismatch with a VSWR of 1.2 at both ends adds up to about ±0.07 dB of uncertainty.
  • RF Matching Networks: L, Pi and T Compared2026-10-15An L-network has its loaded Q fixed by the resistance ratio: Q = sqrt(R_high / R_low - 1), which is 1.73 for 50 ohm to 200 ohm. Pi and T networks add a third part so you can choose a higher Q and a narrower, more selective match.
  • Smith Chart Basics: How to Read Impedance and Reflection2026-10-15The Smith chart plots the complex reflection coefficient inside a unit circle, with the center as a perfect match. A load of 100 + j50 ohm in 50 ohm gives z = 2 + j1, a reflection coefficient of 0.447 at 26.6 degrees and a VSWR of 2.62.
  • S11, S21, S12 and S22 Explained for a Two-Port2026-10-14In Sxy the first number is the port where the wave comes out and the second is the port where it was applied, so S21 is transmission from port 1 to port 2. A magnitude of 0.5 is about -6.02 dB, and a passive cable or plain filter has S21 equal to S12.
  • Return Loss vs Insertion Loss: What Each Number Tells You2026-10-13Return loss, from S11, tells you how much power bounces back. Insertion loss, from S21, tells you how much fails to arrive. A 10 dB return loss reflects 10 % of the power, yet a matched 10 dB attenuator still has 10 dB of insertion loss.
  • What S21 and S11 of a Low-Pass Filter Look Like2026-10-13At the -3 dB cutoff a Butterworth low-pass filter transmits half the power and reflects half, so S21 and S11 are both -3.01 dB. Above the cutoff S21 falls and S11 climbs towards 0 dB, because a lossless filter reflects what it cannot pass.

Tutorials 7

Step-by-step guides for S-parameters, Smith charts, matching and measurement.

  • VNA IF Bandwidth and Averaging: Noise vs Sweep Time2026-10-26Each 10 dB of noise reduction costs about 10 times the sweep time, whether you cut the IF bandwidth by 10 or average 10 sweeps. Averaging cannot remove drift, systematic errors or crosstalk, so check those first.
  • SOLT Calibration Step by Step: Short, Open, Load and Thru2026-10-25A SOLT calibration measures an ideal short (reflection coefficient -1), an open (+1) and a load (0), then a thru between the ports. The result holds only for the frequency range, IF bandwidth, power level and cable setup used.
  • L-Network Matching: Low-Pass or High-Pass Version?2026-10-20Matching 50 ohm to 200 ohm needs Q = sqrt(3) = 1.732. The low-pass version uses 13.78 nH and 1.378 pF, the high-pass version 1.838 pF and 18.38 nH, and the choice depends on the DC path and the filtering you want.
  • Microstrip Width for 50 Ohm on a 1.6 mm FR-4 Board2026-10-19On FR-4 (er 4.4) a microstrip line reaches 50 ohm at a width-to-height ratio of about 1.9, which is about 3 mm on a 1.6 mm board. Wider strips lower the impedance and narrower strips raise it.
  • When to Put an Attenuator Pad in an RF Chain2026-10-19A fixed pad of A dB passes 10^(A/10) of the power, so a 10 dB pad passes 0.1 and turns the other 0.9 into heat. It can improve return loss by up to twice its attenuation, but it costs signal level and, in front of a receiver, noise figure.
  • How to Read One Line of an S2P File (MA, DB and RI Formats)2026-10-14A two-port S2P data line holds nine numbers: the frequency, then the pairs for S11, S21, S12 and S22 in that order. The option line tells you whether each pair is MA, DB or RI, and a magnitude of 0.9975 is about -0.022 dB.
  • How to Open an S2P (Touchstone) File: 6 Ways and a Free Viewer2026-10-13An S2P file is a plain-text Touchstone file holding the two-port S-parameters of a device at many frequencies. You can plot it right here in your browser (the file never leaves your computer), read it in a text editor, or open it in RF View, Python, MATLAB or a spreadsheet.

Components 1

How real parts behave: inductors, capacitors, filters and cables.