what is the meaning of balanced and unbalanced feedings????

salam

what is the meaning of balanced and unbalanced feedings of antennas and how it affects their behavior??? plz explain and if there is articles plzzz upload.

Truth.

Re: what is the meaning of balanced and unbalanced feedings?

Hi Truth -- Whenever electrical current flows in one direction, an equal amount (over time) must flow in the opposite direction, back to the source. For balanced transmission line, both paths have very nearly, or even exactly, the same geometry. Two parallel wires ("Twin Line" is an example) are balanced. Coax is unbalanced because one current path (the shield) is physically different from the other current path (the center conductor).

One problem comes when we want to attach an unbalanced line (like coax) to a balanced load (like a dipole). RF on the antenna can induce current on the outside of the coax shield. The outside of the coax shield becomes a stub hooked onto the dipole feed point. This disrupts the antenna pattern and the input impedance. To overcome this problem, a balun (balanced-to-unbalanced) is added. There are many forms for a balan. The idea is to open circuit the connection between the coax shield and the dipole. It can be as simple as winding a few turns of the coax into a small loop at the dipole feed point. The loops of coax form an RF choke for the RF trying to flow on the outside of the coax shield. Other forms of a balun resemble a transformer, usually with a torroidal ferite core. The net effect is the same.

There is a good book on baluns, the ARRL (American Radio Relay League) publishes it, go to https://www.arrl.org/catalog/ and search for "balun". The baluns described there are for HF and VHF. They are temporarily out of stock, they hope to get more copies in June. You might be able to get it in your libary, or contact an amateur radio club in your area. Very likely someone has a copy near you.

thanks for your reply u r so kind , I understand now, so a balun is used to do an impedance maching between two devices one unbalunced like a coax line and another balanced like a dipole antenna.

i m intrested in microwave baluns (not HF or VHF) and i m working on microstrip antennas (UWB) so if u have any papers or ebooks downloadable from the net plzzzzzzz help me .
thanks again rautio.

Truth