Does a carbody radiate?
Lets delve into the family of self contained (vertical) dipoles.
The vertical portion of the 1/2 wave vertical dipole contributes to it's maximum potential when the other half is the exact size and shape.The second half is closer to the ground than the top half by default.
The second half can be split into many tuned elevated parts and placed from horizontally to sloped.
A mobile carbody does not and cannot equal a properly designed physically straightened downward going counterpart half.
A better understanding is found when one views the circuit from the center feed point.
In a mobile application Center feed remains the same but the halves are dramatically different.
A Ground Plane antenna is a name for when a half that is vertical and the other half is divided into 4 or more parts and symmetrically distributed about the semi circle.strictly speaking radials held in the horizontal plane.
The 4 parts (of the whole second halve)are named radials and are oriented 90 degrees or in the horizontal plane hence ground plane) but their contribution to the verticals radiation is in securing a push platform but the field strength is concentrated in the vertical axis that by a quarter wave radiator but horizontal radiation is minimal as designed properly.
The perspective of all of the family of self contained verticals is from the feed point.
The ground plane mobile antenna system exchanges tuned elevated horizontal radials for a carbody.
A vertical conductor pushing against a carbody is fed at the bottom end usually a junction;, and the horizontal? carbody is a platform or plane that also completes the antenna.
It works but presents as a weird thicker shape hump compared to horizontal radials that are elevated and tuned, that hump reduces in size compared to lower and lower frequency applied to the circuit while the plane remains unchanged the vertical must be lengthened expand..coupling through to the earth surface where the carbody is usually sitting on rubber tires an insulated semi conductor. with a capacitance to earth below.
The carbody cannot just grow wires and radials are within our service however.
Even when radials are horizontal such as a set of 4 tuned horizontal and directly next to the feed point isolated radials fashioned symmetrically they cancel horizontal radiation therefore no field strength to measure in that axis but a remnant.
A better solution is in using a sloped second halve split into equal parts elevated ans isolated from ground.
So the sloped tuned elevated radials do NOT cancel all their radiation and is measurable out in the far field. In this caseThere IS contribution yet the sloping angle does not preclude the antenna from the family of self contained verticals but is a variant that can be utilised when installed properly above a mobile.
The carbody is a solid plane that works.
Tuned, elevated, sloped, isolated radials at an angle of apx 45 degrees is not the same but is a dipole.
PS the angle may be tilted upward and lends itself to some utility for hilltop mobileering where the isolated radials do not touch the ground.
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