Lab-05: Loop Antenna, Theory

1. Loop Antenn Examples

Smartphon Loop Antenna

Credit Card NFC Loop Antenna

AM Receiving Ferrite Loop Antenna, Circuit Exchange International

qrznow.com HP Loop Antenna for Amateur Radio, Joel Hallas, W1ZR

Cytony DF-A0097A Crossed Loop/Monopole Watson Watt DF Antenna, 2-m Loop, VLF/LF/MF

13.3-30MHz Amateur Radio Fractal Loop Antenna

FM Radio Receiving Loop Antenna

HF Loop DF Array at Penhale Sands Tx Station, Cornwall, UK

HF Vehicle Loop Antenna for NVIS Communication, Harris Corp.

2. A Small Loop Antenna

-

- Current: constant along the loop

I = I₀

- Farfield

- Radiation resistance

- Directivity:

- Multi-turn: N = number of turns

Electric and magnetic fields: N times

Radiation resistance: N² times

- Equivalent circuit with a tuning capacitor

R_r : radiation resistance

R_l : conductor loss resistance

L_A : loop external inductance

L_i : loop internal inductance, due to H inside the conductor

Thin wire (b<<a)

Thick wire: formulas by R. Dengler, Advanced Electromagnetics, 5(1), Jan. 2016

: quality factor

3. Large Loop Antennas

Radiation pattern

Input impedance

Large impedance when C = 0.5λ

Resonance at C = 1.0, 1.5, 2.0, 2.5 wavelengths

4. Loop antenna impedance matching

1) Small loop antenna impedance matching

2) NFC tag impedance matching