Roomcap -Introduction                                                                             
31st July 2014 a                                                                                   
Felix Meyer HB9ABX                                                                                    


          Introduction to Roomcap

The Roomcap is a very different antenna.

Yet are nearly all constructions are made by wire, where the wire mostly is
leading up (vertical)or a horizontal wire going to both sides (at dipole),
or a long wire let to one side.

My new antenna is a plane (or surface), which works as radiator.
In the beginning I was working with aluminium foil (and copper foils), but
the wind resistance was very high, therefore now I work with wire grid, which
behaves like metallic foil, but have nearly no wind resistance. 

An antenna has the purpose to radiate the transmitter power as EM wave
in efficient way into space - and to capture wave from the space.

A comparison:
One wants to produce wind from mechanical power, you can waggle with
a knittle needle (20 cm to 150 cm long), or you waggle with a cardboard
(10cm x 10cm size). You see cleary, that with a cardboard you obtain
a stronger wind that with a knittle needle.

The same applies for electric use:
If you bring an electric oscillation to a plane, you will obtain a stronger
EM radiation, than when you bring oscillation to a wire.
From the transmitter you obtain power as current and voltage (in phase).
The antenna should radiate the power as a EM wave. The radio wave
consists of two components: E field and H field.
(electric field and magnetic field).

In order to radiate real power, both fields have their maximum
strength at the same location. Both components have to be in phase.

See your wire antenna, you note, that the current want to fly to the end of
the wire. There, the current stops, and therefore the current flow comes
to 0 at the end.
Therefore, the voltage reaches a maximum at the end of the wire, because
the current has to "reverse" of the direction, and there we have a jam
of the charge carriers, where we have a current flow of 0.

The speed of the wave will cause, that at 1/4 wave length distance from the
end of the wire we obtain a current maximum. At this point we have a null
of the voltage. 

Correspondingly we have a null of the E field, where we have a null
of the voltage; therefore we have a maximum of the H field at this point.
1/4 wave longth beside we have a null of the H field, and there we have
a maximum of the E field.
(See the current/voltage diagram of the half wave dipole).

A real power occurs, when the product of the both fields is not null.
However, there is always one factor is 0 ...
Therefore, this field is NOT radiating. This applies to the near-field.

Only on distance, a far-field emerges, where the E field und H field
are in phase, then this field is radiating.
This range, where the near-field converts to the far-field, this range
is called transition zone.

Here the new idea:
Use of a plane instead of a wire.
AND:
The length of the plane have to be short in relation to the wave length,
otherwise, the same would occur as wrote above, because at 1/4 length
of the plane we would get a voltage drop, and we would obtain a
no radiating near-field.

Therefore:
A short length of the plane, in order that the voltage over the length
of the plane remains nearly at the voltage maximum (corresponding
to the cos function for Roomcap).
The current flows at the beginning of the plane, and flows then
over the full length into the space, according to the Maxwell's equations,
as I describe it in the theory part, you can see it in the picture there.
(A plane forms a open capacitor).

Through this new constellation of the planes we obtain:
At the same location the both E field and H field consist from the beginning,
and therefore results the high efficiency of the antenna.

Correspondingly, the far-field begins at the antenna !  

                                                                  

ory                                                  
Theory