Introduction to the Loop Antenna
1
Antenna Engineering
Lecture 11: Loop Antennas
11.1 Introduction to the Loop Antenna
11.2 Small Loop Antenna vs. Short Dipole Antenna
11.3 Current Distribution on A Loop Antenna
11.4 Small Loop Antenna
11.5 Large Loop Antenna
2
11.1 Introduction to the Loop Antenna
Loop Antenna:
- A wire or a printed strip in a closed loop form
- Applications: communication, NFC, RFID, magentic field measurements,
radio direction finding
- Useful frequency range: 3kHz
30GHz
Figure: HF loop antenna for amateur radio (qrznow.com, J. Hallas, W1ZR)
3
11.2 Small Loop Antenna vs. Short Dipole Antenna
Duality Principle:
4
11.3 Current Distribution on A Loop Antenna
Loop Current:
- cos(
kl
), sin(
kl
) variation along the loop
5
11.4 Small Loop Antenna
Electrically Small Loop:
-
C
= 2
π
a
<
λ
/ 3
- Current: constant along the loop,
I
=
I
0
- Far-field:
6
-
Radiation resistance:
- Directivity:
7
11.5 Large Loop Antenna
Loop antennas are versatile devices used in various applications such as communication, NFC, RFID, and radio direction finding. This lecture covers the fundamentals of loop antennas, including small vs. large loops, current distribution patterns, and the comparison with short dipole antennas. Explore the principles behind loop antenna design and performance, radiation resistance, directivity, and characteristics of electrically small loops.
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Presentation Transcript
Antenna Engineering Lecture 11: Loop Antennas 11.1 Introduction to the Loop Antenna 11.2 Small Loop Antenna vs. Short Dipole Antenna 11.3 Current Distribution on A Loop Antenna 11.4 Small Loop Antenna 11.5 Large Loop Antenna 1
11.1 Introduction to the Loop Antenna Loop Antenna: -A wire or a printed strip in a closed loop form -Applications: communication, NFC, RFID, magentic field measurements, radio direction finding - Useful frequency range: 3kHz 30GHz Figure: HF loop antenna for amateur radio (qrznow.com, J. Hallas, W1ZR) 2
11.2 Small Loop Antenna vs. Short Dipole Antenna Duality Principle: 3
11.3 Current Distribution on A Loop Antenna Loop Current: - cos(kl), sin(kl) variation along the loop 4
11.4 Small Loop Antenna Electrically Small Loop: - C = 2 a < / 3 - Current: constant along the loop, I = I0 - Far-field: jkr e 2 = = ( ) sin ; H k I S E H 0 4 r 2 = = /(2 ); = = ; / k S a 5
- Radiation resistance: 2 2 8 3 P I S 3 = = r R r 2 0 2 - Directivity: D = 1.5 1.8 dB = 0 2 ( , ) = sin D D 0 6
