loop antenna
DESCRIPTION
A loop antenna has simple structure but its analysis is not easy to perform. Since a loop antenna is a dual pair of a dipole antenna, we can adopt the analysis of a dipole for a loop based on the duality theorem. By stacking a number of loops, we can increase the antenna gain and radiation resistance very easily.TRANSCRIPT
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