loop antenna

Loop Antenna

Antenna Antenna EngineeringEngineering

CHO, Yong HeuiCHO, Yong Heui

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab2

Small loop antenna

1. Loop antenna

Duality theorem Electric dipole antenna

JEjH

MHjE

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab3

Magnetic dipole moment

1. Loop antenna

Electric dipole moment vs. magnetic dipole moment

nISmdQp ˆ

zIzI m

zQdt

dzQ

dt

dm

mp HMEP me 0

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab4

Near field components

1. Loop antenna

Constant current Duality theorem:

ISjzIm

ˆsin1

4

rjk

r

zeIE

jkrm

ˆsin1

4

ˆcos12

2

2

kr

j

rjk

r

zeI

rkr

j

r

zeIH

jkrm

jkrm

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab5

Far field components

1. Loop antenna

Observation point: infinity

ˆsin4

jkr

zeIE

jkrm

ˆsin4

jkr

zeIH

jkrm

*Re2

1HES

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab6

Radiation power and resistance

1. Loop antenna

Effective antenna: # of turns N

rr RIISkP2222

2

1

12

2

2

322

3

8

6

S

SkRrSingle turn

2

2

322

3

8

6

NS

NSkRrMultiple turns

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab7

Loop-stick antenna

1. Loop antenna

Ferrite core and multiple turns Large radiation resistance AM receiver

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab8

One-wavelength loop antenna

1. Loop antenna

Continuous current distribution- Not uniform current- Compared with standing wave antenna- Traveling wave antenna

Square loop antenna: gain = 3.09 dB

lder

lIA rrkj

loop

)(

4

)(

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab9

Crystal loop antenna

1. Loop antenna

Efficient antenna: multiple turns Direction of current, feeding point

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab10

Circular loop antenna

1. Loop antenna

Gamma matching: variation of T-matching Tuning: capacitor, resonant frequency

Gamma matching part

Tuning part

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab11

Gamma matching

1. Loop antenna

Folded dipole antenna Capacitor needed

Antenna Antenna EngineeringEngineering

EM Wave LabEM Wave Lab12

Tuning: capacitor

1. Loop antenna