I think you are referring to antennas such as are used on MF ADF antennas on aircraft. A pair of ferrite rods with wound resonant inductors, placed at right angles. Each antenna has a figure-8 radiation pattern and for ADF the output of one loop at a time is summed with an E-field antenna which has an omni-directional pattern. The result is a cardioid pattern.
The same principal applies with any pair of magnetic loops at right angles.
Hi
Thanks for the reply.
I am working at 100 Khz hence i cannot use E field antenna (size issues). Is it possible that I use two H field antennas placed at right angles and get a near omnidirectional radiation pattern.
How do I sum the outputs of these two antennas. I am thinking of using a combiner but would there be any phase problems.
Does an omnidirectional H field antenna exist.
You can use an E-field antenna. The theory indicates that an isotropic antenna (dimensionless point in space) has only about 2.2dB less gain than a half wave dipole. Trouble is that it's feed impedance has close to zero ohms real impedance and near infinity capacitive reactance so it's difficult to connect to a feed line.
For a receive only antenna, a short whip connected to an amplifier having a very high input impedance (which tends to swamp out the Xc component), can achieve very useful gain. These are sold as Voltage Probe or Active Antennas and are readily available. I saw one on a European car which used the side mirror as the antenna, but most use whips.
As for combining loop antennas, the simplest thing is an input transformer with two primary windings. Otherwise two preamps having the same gain and combined same as you would do a mic mixer. Phase is not an issue unless your application has some special need.
nbucska - It sounds like you're referring to Circular Polarization (CP); crossed antennas fed 90-degrees out of phase. Orcus had mentioned 100kHz. CP isn't used much at LF.
