Antenna Design and NanoVNA

Introduction

NanoVNA is a simple but powerful tool to analyze antennas.

VNA: Vector Network Analyzer

SWR: Standing Wave Ratio measures the degree of mismatch between a transmission line and its load. SWR is a measure of what is happening to the forward and reflected voltage waveforms and how they compare in size.

Theory

Main Screen

• Start/Stop frequency at the bottom
• Marker
• Calibration status on the right side.
  • C0-C4: Corresponding calibration data is loaded
  • c0-c4: Corresponding calibration data is loaded, but the frequency range has been changed.
  • D direcitivity error
  • R Error correction is applied: Reflection
  • S Error correction is applied: Source
  • T Error correction is applied: Transmission
  • X Error correction is applied: Isolation/ Crosstalk
• Reference position. Yellow Horizontal line. (DISPLAY -> SCALE -> REFERENCE POSITION)
• Trace status. Trace formats are following
  • LOGMAG: Logarithm of absolute value of measured value
  • PHASE: Phase in the range of -180 ° to + 180 °
  • DELAY: Delay
  • SMITH: Smith Chart
  • SWR: Standing Wave Ratio
  • POLAR: Polar coordinate format
  • LINEAR: Absolute value of the measured value
  • REAL: Real number of measured value
  • IMAG: Imaginary number of measured value
  • RESISTANCE: Resistance component of the measured impedance
  • REACTANCE: The reactance component of the measured impedance

• Battery status

Calibration

NanoVNA should be calibrated always when the frequency range is changed.

• CAL RESET
• Connect OPEN standard to port 1 (CH0) and execute CAL CALIBRATE OPEN.
• Connect SHORT standard to port 1 (CH0) and execute CAL CALIBRATE SHORT.
• Connect the LOAD standard to the port 1 (CH0) and execute CAL CALIBRATE LOAD.
• Connect the LOAD standard to port 1(CH0) and port 2 (CH1) and execute CAL CALIBRATE ISOLN. If there is only one load, connect the LOAD standard to port 1 (CH0), the port 2 (CH1) can be left unconnected.
• Connect cables to the port 1 (CH0) and port 2 (CH1), connect the cables with the through connectors, and execute CAL CALIBRATE THRU.
• End calibration and calculate error correction information CAL CALIBRATE DONE
• Specify the data number and save. CAL CALIBRATE SAVE SAVE 0

Antenna Measurements

Use Port 1 when measuring one port devices.

NanoVNA draws the measurement result on the screen as a graph of the measured quantity versus frequency or on the Smith Chart.

M1: Marker position

Before each measurement:

• which traces we want to display (up to four or three plus Smith Chart)
  • DISPLAY -> CHANNEL -> CH0 Reflect for antennas.
• trace channel (CH0 REFLECT or CH1 THROUGH) for each trace separately
  • DISPLAY -> TRACE. Click multiple times.
  • Active Trace.
• trace format (unit of measurement of each format)
• scale (how many units of measurement per each horizontal line, for each trace separately)
• reference position for each trace separately
• sweep frequency (stimulus frequency range)
• calibrate the NanoVNA