Thank you very much everyone, all the replies were very helpful for me.
What you are describing would be an end loaded dipole and the presence of the 'plates' would modify the impedance, increase the current in the wires. So I don't know how that relates to what you say. The composite antenna would have a higher radiation resistance (one way of looking at it). More power would be radiated. Is this another of those "what is really happening?" questions? Is it only the current in a dipole that is the radiating agent?I was trying to obtain agreement that the dipole radiation comes from the wires, not from the capacitance. The electric field on the ends is not the radiated electric field. It will vary with the Q of the system, and its role is to provide the accelerating force for the electrons in the wire.
Of course, I realise that a few molecules of air make little difference, I just suggested vacuum to eliminate a point of argument. I have been an RF experimenter for 60 years incidentally.
no, there is still a metal antenna element behind them see drawingsI think the rods and cones of the eye are dielectric antennas. The incoming radiation causes electrons in them to create a chemical reaction directly, without the need for any metal.
well for a start a dielectric DOESNT conduct current (RF or otherwise) You cannot put the 2 conductors of the coax cable onto one end of the dielectric rod and hope that RF is generated ... it wont be. And that is what makes the difference between the radiator and the beam forming sectionIn your model, what is the difference between the feed of a dielectric antenna and the feed of an antenna with conventional metal parasitics? Plus, are you sure that the dielectric structure (particularly the parts right next to the drive) must not be considered to be part of the 'radiator'?
of course it does ... repeat my above commentIn particular, in the case of a resonator antenna, does your model still hold.
I really shouldn't have got so involved in this because Does it really matter what we call the radiator? Any hard rule is bound not to fit all cases and it can only confuse the innocent.
Yes, of course that's right. The waves have to be matched into the dielectric just as with any antenna. If it's a dielectric resonator antenna, the impedance to match to could be very relevant.You cannot put the 2 conductors of the coax cable onto one end of the dielectric rod and hope that RF is generated
It might pay to consider if there is a transducer, something that transforms one form of energy into another form. A transmit antenna is a transducer that adapts one end of a non-radiating feedline into an EM wavefront. A receive antenna is a transducer that performs the reciprocal conversion.Which part of a regular antenna do you call the 'radiator' and which part do you call the beam-former?
That's one way of looking at it. To my mind, the only transducers involved are the transmitting output device and the receiver front end. They actually do change the 'form' of energy. Wires, wave-guides, antennae are only constraining and directing EM Power that's already been generated elsewhere.A receive antenna is a transducer that performs the reciprocal conversion.
My take on this is based on experiments which I undertook as an amateur scientist. There are some imperfections still in understanding. The inductance and capacitance are not part of the radiation mechanism. They store reactive energy and create induction fields which are in quadrature. At switch-on, these fields charge up over a few cycles and at switch-off they similarly decay. The L-C resonance makes it easy to drive a current into the antenna, only the Radiation Resistance being involved if losses are small.I would like to buy an argument. Consider a resonant half-wave dipole in free space. Model it as an inductive wire in the middle with capacitance between the ends. The current at the centre will be a maximum as the voltage between the ends passes zero. V and I are therefore in quadrature. But since the intrinsic impedance of free space is real, with a value of about 377 ohms, an EM wave in space has the E and H components in phase.
The current in the element seems to generate the magnetic component. That H then creates the perpendicular E electric field which permits the wave to proceed through space. It seems the voltage on the dipole is irrelevant.
What is all this sinusoidal stuff with λ and 2π ? Ever since Sir Oliver Lodge, back in 1897, wandering the gas-lit streets of London, to invent frequency tuning, we have been fighting an uphill battle to spread the spectrum. Only the designers of cheap λ/2 dipole antennas need sinusoidal waves. The few of us who are over tuned circuits, are content to get it right by launching the radiant energy at the first attempt. We do not have to tune everything to resonance, then hope that maybe a little bit more will leak out next time, with the inevitable progressive loss of signal coherence. Who in their right mind would stick with inefficient radiators, sinewaves and limited bandwidth.The inductance and capacitance are not part of the radiation mechanism. They store reactive energy and create induction fields which are in quadrature.
To run me must first walk. As any waveform may be decomposed into sinusoidal components; this seems good starting point.What is all this sinusoidal stuff with λ and 2π ? Ever since Sir Oliver Lodge, back in 1897, wandering the gas-lit streets of London, to invent frequency tuning, we have been fighting an uphill battle to spread the spectrum.
That is OK, until you try to make a broadband quarter wave transformer for many different sinewaves.To run me must first walk. As any waveform may be decomposed into sinusoidal components; this seems good starting point.
Marconi stole everything from everywhere to make a system that worked. He took out patents on inventor's techniques to stop others commercialising them.The concept of frequency tuning was proposed by Marconi in 1901 in his famous UK 7777 patent.
I think you are referring not to John, but to David Edward Hughes, Professor of Music, discoverer of the bad electrical contact, and inventor of the microphone, & etc.Prof. John Hughes made tests with a mobile receiver in 1879 in Portland Place, London.
https://worldwide.espacenet.com/pub...=GB&NR=189711575A&KC=A&rnd=1530989643124&FT=D#GB Patent said:No. 11,575 A.D. 1897
Date of Application, 10th May, 1897
Complete Speciﬁcation Left, 5th Feb., 1898 Accepted, 10th Aug., 1898
Improvements in Syntonised Telegraphy without Line Wires.
I, Oliver Joseph Lodge, D.Sc., F.R.S.; of 2, Grove Park, Liverpool, in the County of Lancaster, Professor of Physics, do hereby declare the nature of this invention to be as follows :–
The object of my invention is to enable an operator to transmit messages across space to any one or more of a number of different individuals in various localities, each of whom is provided with a suitably arranged receiver.
The method consists in utilising certain processes and apparatus for the purpose of producing and detecting rapid electric oscillations, and in so arranging them that the excitation of a particular frequency of oscillation at the sending station may cause a Morse or any other telegraphic instrument to respond at a distant station, by reason of being associated, through a relay or otherwise, with a subsidiary circuit actuated by electric oscillations of that same particular frequency, or by some multiple or sub-multiple of that frequency. Another distant station will similarly be made to receive messages by exciting at the sending station alternations of a different frequency, and so on: and thus individual messages can be transmitted to individual stations without disturbing the receiving appliances at other stations which are tuned or timed or syntonised to a different frequency. Each station will usually be provided with both sending and receiving apparatus, and messages can travel simultaneously in opposite or in cross directions without the least confusion or interference. ...