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.

See more info at https://nanovna.com/

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

For antenna measurements:

• Traces
  • CH0/ S11 (Yellow), refl: LogMax
  • CH0/ S11 (Green), refl: Smith
  • CH0/ S11 (Yellow), refl: SWR
  • CH1 (Purple): Nothing
• Frequency Range
  • STIMULUS: Start/ Stop.
• Calibrate
  • CALIBRATE -> RESET
  • CALIBRATE: OPEN, SHORT, LOAD and DONE. SAVE to location.
• MARKER -> SEARCH -> MINIMUM

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

Antennas: 433 MHz

Monopole

• 

  18.8 cm; Resonances at 220MHz and 484 MHz.

• 

  18.8 cm; Closer look at 220 MHz resonance.

• 

  18.8 cm; Closer look at 484 MHz resonance.

• 

  20.8 cm; Small resonances at 244MHz and 484 MHz.

• 

  20.8 cm; Closer look at the other resonance.

• 

  16.8 cm; Other resonance.

Quarter wave wire antenna; $L=fc/4=3\times 1084\times 434\times 10^{6}=0.173m$

The resonances of quarter wave monopole antennas measured with NanoVNA and using its black short cable. Calibrated first to 100-900 MHz and to the two resonances.

Length	Resonance 1	Resonance 2
16.8 cm	236 MHz -> 229 MHz	524 MHz -> 516 MHz
17.3 cm	237 MHz -> 232 MHz	516 MHz -> 508 MHz
18.8 cm	220 MHz -> 216 MHz	484 MHz -> 496 MHz
20.8 cm	244 MHz -> 237 MHz	484 MHz -> 487 MHz

Dipole

https://www.electrical4u.com/dipole-antenna/ - Folded Dipole Antenna - Two-Wire Folded Dipole Antenna - Three Wire Folded Dipole Antenna (Folded Tripole)