Sir,
I am unable to get your question. When antenna is fed with particular signal (which needs to be transmitted) it generates EM radiation of certain frequency for which it is designed.
If you are looking for dynamics of the antenna with co-axial feed, like how S-parameters are matched, what power value signal possessed, etc then reply back and let us know in this thread. Or you can refer to C. Balanis's book (on Antenna Theory). It is given nicely in this book.
An antenna, as a conductor of electric charge, will have certain electrical impedance characteristics. Electrical impedance (Z) is comprised of both 'real' (resistance R) and 'complex' (reactance X, capacitive and inductive) components expressed as Z=R+iX. The reactance, due to capacitance and inductance, is frequency dependent and themselves consist of both self- and externally coupled, ex. self-capacitance vs. capacitive coupling with environment, and space. As an electric signal is supplied to the antenna, electric charge flows into and out of the antenna structure creating an electrical potential distribution along the antenna (E-field). This charge flow, or electric current, produces a magnetic field B. Thu, due to the excitation sources, and the antenna characteristics, these fields are coupled in space and time, typically 90 degrees out-of-phase (see phasor diagram). These field of course extend out into space. Then comes the discussion of Near-Field vs. Far-Field energy. The oscillatory nature of the fields and the impedance characteristics of space will always the production of E-M fields which are both closed as well as waves which can partially radiate. The Near-Field component is not radiated (beyond ~2-3 lambda) and is the portion of the antenna energy stored in the 'imaginary', Reactance X properties of the antenna's capacitance and inductance. The Far-Field is that portion of the antenna energy which is radiated. The Resistance R mentioned above is comprised of both the ohmic resistive losses of the antenna, AND the Radiated (Far-field) portion of the E-M energy from the antenna. In general, maximum antenna radiation occurs at/near the antenna's self-resonance frequency(s). ALSO, you mentioned COAXIAL CABLES...A coaxial cable is a form of an Un-Balanced transmission line. As such, in order to achieve optimum energy transmission, its self impedance properties should be properly transitioned (matched) to that of the antenna which is often a balanced load. If you do not, then the impedance mismatch will cause internal signal reflections, and some current from inside the coax will flow over to the exterior of the coaxial cable shield and then the shield itself will also become a E-M radiator, similar to your antenna. Various methods to do this include use of baluns and Gamma-match, 1/4 lambda stubs, etc.
You need a balun. And then it works like an antenna!
I think I don't understand your question and this is my answer :)
Happy new 2015 year.
Thanx boone sir,
You have given physical interpretation.
happy new year 2015.
The co axial feed carrying energy in the electrical form which is fed to antenna with a proper matching (To ensure no reflection - no energy back). The electrical energy is a time varying quantity and hence the energy (Charge) accelerates and decelerates while flowing through antenna elements. The phenomena generates electric field or line of force between two separated element (of antenna) ends. same time it generates magnetic field or line of force around the elements. As it is time varying (positive and negative) and zero crosses lines it has a line of force clockwise as well as anticlockwise. Thus the electrical energy gets converted into electro magnetic wave energy and released in a space
- Badges
- Science topic
- Similar topics
- Engineering
- Telecommunications Engineering
- Antennas and Propagation