02-06-2012, 01:20 PM
Experimental and Theoretical Investigation on Plasma Antennas
Experimental and Theoretical Investigation on Plasma Antennas.pdf (Size: 94.84 KB / Downloads: 96)
Introduction
A plasma antenna is constructed from insulating tubes filled with low pressure gas; the gas inside the tube
can be ionized applying bursts of power, so that plasma can be rapidly generated and destroyed; it is well known that
a surface wave propagating along the tube length can create and sustain a plasma column [1]. The plasma element
can be used instead of metal wires or surfaces as a conducting medium for the radiated signal. Two different signals
are needed in such antennas: the “pump or excitation signal”, which supply to the tube the power needed to ionize
the gas, and the “radiated signal”, which support information to be transmitted.
The main peculiarities related to this antenna follows from the possibility of changing the electric parameters
of plasma. When the pump signal is switched off, the gas inside is not ionized and the tube is simply a dielectric
with a very small radar cross section. On the contrary, when the pump signal is applied, the gas is ionized and the
tube behaves like a metallic antenna. Because of this characteristic, plasma antenna was firstly studied for military
applications; however, it can be also used in many civil applications to realize smart antennas, circular scan arrays,
reconfigurable antennas, time and space selective shielding, frequency selective shielding [2].
Experimental Investigation
A commercially available tube designed for lightning purpose has been used to create plasma column; the
tube has been inserted in a metallic box placed under a ground plane and fed by a single electrode (fig.1): the intense
field between a copper ring placed around the tube and the ground plane provide the pump signal that propagates
along the columns creating and sustaining the plasma. A second copper ring can be placed near the first one to apply
the signal to be radiated. Thus, two different networks are needed: the excitation network and the signal one. The
set-up used [4] allows to determine the efficiency of the antenna with respect to the radiated field as a function of the
pump power delivered to the plasma column. The signal radiated when a copper tube replaces the plasma element
was used as a reference for the efficiency calculation.
Conclusion
Preliminary experimental and theoretical investigations of plasma antennas have been conducted: the
experimentally activity highlighted how the main physical properties of a plasma antenna are strongly affected from
the variation of the input parameters involved. A numerical 1-D model was developed to conduct a parametric
investigation of the interaction between electromagnetic field and plasma. It has been shown that the model is valid,
reliable and helpful for understanding the complex phenomena concerning plasma antenna physics. Future work will
concern the implementation of a more realistic cylindrical geometry.