Ok, so let's assume we have a dipole transmit antenna that is tuned for 90 Mhz, and let's assume that it operates with extremely low voltages, millivolts, for example, with AC currents in the microamps range. Now solder a diode (PN) to the distal tip of this antenna, with a wire running from the diode to ground. If the diode is forward biased with DC, then there should be a short circuit, and the antenna will be detuned. But let's assume that DC on the order of milliamps is needed to forward bias the diode. So the operating voltages and currents of the dipole antenna are below the threshold to forward bias the diode. Would the antenna then resonate, and behave as normal?
Please take at face value what I am saying - I am not saying this is practical, I just want to know if this makes sense what I am saying, in principle.

 

The diode has capacitance at any voltage so that would have to be taken into account also.
The capacitance would be large enough to make a difference at 90MHz in most cases but you could check the data sheet for the diode you would want to use. For example, a regular rectifier diode like 1N4004 would have high enough capacitance to probably shunt most of the current to ground. How much difference that makes in the radiation efficiency would have to be looked into anyway though. Depending on the length of the antenna, it may not matter or it may eat up most of the power.

 

Do some research on PIN diodes. They are used for switching RF. I have never used them. I just know of their existence.

Les.