why do not we use the loop(magnetic) antenna?

[xuexucheng]

we usaully use the electric antenna such as dipole.
why do not we use the loop(magnetic) antenna?
Is it radiating inefficient? why?

 

[RCinFLA]

Back in the days of pagers, many used loop antenna's through UHF frequencies. Commercial AM radio always used, and still uses, loop antennas.

A loop antenna, by itself, does not have very good performance. Loop antennas can improve performance by coupling into a nearby conductive surface. In the case of pagers, they coupled into the human body to improve performance.

Pager did not have transmitters so there was not any health issue questions with radiation absorption.

 

[Syncopator]

We sold tuned horizontal h.f. loop antennas for use with tactical radios more than 20 years ago. Their advantage is a high radiation angle and worked very well.

 

[sezgyno]

the impedance of loop antennas inductive so they are losly from impedance mismatch

 

[RCinFLA]

the impedance of loop antennas inductive so they are losly from impedance mismatch

You can impedance match to just about anything. Question of antenna is how much of what you are matching to is radiation resistance and how much is dead dissipative resistance. Radiation resistance of small loop is generally low (fraction of ohm).

If the loop is loaded into a larger structure its radiation resistance can increase.

Think of a vertical antenna like an AM broadcast antenna. It can be impedance matched by tapping into the antenna close to the bottom grounded end. Now instead of tapping the antenna directly, put an impedance matching loop that inductively couples into the larger vertical antenna near the bottom grounded end where the RF currents are high.

 

[ferdows]

hi sezgyno
inductive impedance in some time can make problem but i think in low frequency is not problem
dipole and mono pole use more because of them easy design and easy array but loop antenna array* not common and specially loop with out core didn't have merit to dipole and usually it take more place
*(see the handbook of antenna of Johnson for more information about yagi -uda with loop)