Receiver Antenna in SPiCE

[jdirga]

I need to include a receiver antenna in SPICE simulation. Should I model the antenna as a current source or voltage source? Does this depend on the type of the antenna(whether it's a dipole, loop, etc)? Please help. Thx.

[Rob K2CU]

The simplest, and probably the best approach would be to use a voltage source with the antenna resistance (50 Ohms) in series with it. I assume you are modeling the circuit that the antenna connect to, such as a receiver simulation, or a filter. Modeling an antenna to reflect the type of antenna, gain, etc is much more complex. For that type of modeling, I would suggest MMANA-GAL, an easy to use freebee.

I have been working on models of various vacuum tubes for evaluating circuits such as the Pullen mixer versus a 6BE6 type mixer. I have just today been working on dual plate deflection tubes such as the 7360 and have it just about done. Most Spice simulators include just a few basic tubes, if any.

If anyone else is interested, I would be happy to share the models I have collected as well as schematic symbols that I have created for LTSpice. LTSpice is a free simulator available from Linear Technologies. IT works very well and is not too difficult to learn to use if you have ever used Spice simulators. I have used it to simulate several Class E transmitters, and a 6J6 pullen mixer as well as many other circuits. It can be daunting if you have never used Spice. But it is well worth it to learn to use.

[jdirga]

Thanks for the reply. Could you give a reason why it should be modeled as a voltage source instead of a current source?

My original thought was if it were a loop antenna, it should be modeled as a voltage source because the signal is generated on the received antenna thru Faraday's law of induction, i.e. emf=change of flux. However if it were a dipole, it should be modeled as a current source because signal is generated due to lenz's law?(but I'm not confident with this).

[Rob K2CU]

Classic receiving antenna analysis bases the induced terminal voltage upon the strength of the arriving time variant electric field. A good explanation can be found at:

http://en.wikipedia.org/wiki/Antenna_measurement

Look at the section "Calculation of Antenna parameters in reception".


It provides a Thevinen equivalent circuit for an antenna based upon a voltage source and series impedance. This is why I suggested a voltage source and series impedance (or resistance) for your spice simulation. A current souce could be used by converting the voltage source and series impendance to an equivalent current source with parallel conductance.  A lot of what you do has to do with what you are trying to study with the Spice simulation.

From the referencd website:
The induced voltage is proportional to: 1. the Square root of the real part of antenna impednace times the antenna gain; 2. the wavelength; 3. the cosine of the angle between the antenna elements and the incoming wave; 4. the strenght of the incoming waves electric field; and inversly proportional to the square root of Pi times the impedance of of free space (approx 377 Ohms). This equivalent circuit is valid for all types of antennas.

I can understand the thought that a dipole would be a current source as the radiation from a dipole is derived by the integration over a length of minute current dipole elements. 

Lenz's law has to do with deriving the polarity of the induced current in a conductor. the induced current is of a polarity such that if it were appplied to the conductor, it would create a magnetic field opposite to the applied magnetic field. It sort of like the idea that if you push on a wall with a one pound force, it pushes in the opposite direction with a one pound force. it was to explain why the current polarity is what it is.