What is the Principle of antenna control module?

[John_li]

Hi friends,
I want to make my antenna shorter for location limitation,someone introduced me to use ACM(antenna control module) that embedded LNA(shorter antenna+ACM) to get shorter antenna ,wideband and impedance broader.What is the Principle of antenna control module?

 

[WimRFP]

Normally spoken, making an antenna smaller reduces useful bandwidth. So your antenna control module should be something like a matching circuit that can be controlled from another device to enable changing of tuning components when frequency changes.

Best is to contact the person who told you about ACM. It may also means: "Antenna Coupler Module".

 

[biff44]

A good example is a CB radio antenna mounted on a car. Ideally, you would have a quarterwave long whip, and the car body would act as a ground plane. However, a quater wave whip at 27 MHz would be 2.8 meters high (9 feet) and you would be hitting stuff as you drive around. So they put an inductive coil at the base of the whip antenna, right near the ground plane. After that, the whip part can be made smaller. I am sure you have seen this type of antenna. Is works out that the bandwidth is just wide enough to cover the cb radio band. But, if you look at the coil, it is a honkin big one with very high Q. If you tried to do the same thing with a small coil with low Q, you would end up with a very lossy antenna.

So lets say you had a whip type antenna of a fixed length, but you wanted it to efficiently work at many frequencies. You could use that whip, but switch in different inductor values. If you had 5 inductor values, you could tune that antenna to at least 5 frequencies. If you used the fact that if the whip is longer than quarterwave, you can actually use it at higher multiples than the first resonance, and maybe get 10 or 15 usable frequencies out of those 5 inductors.

If you needed to retune the resonant frequency a little to "peak" the antenna, some sort of variable capacitance in series or parallel with the big tuning inductor can pull the frequency a little higher or lower.

To complete the circuit, you may need to add some additional tuning elements to match the impedance of the antenna at the resonance frequency.