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Depends, if the length of the coaxial on both antenna are the same then the signal will divide in both anteena provided both antenna are the same with respect to each wavelength.
The signal will still be split evenly ( at the coupler point) even if the coax lengths are different.
What will happen when the coax lengths are different between the coupler and each antenna
is that they ( the antennas) will be out of phase with each other.
This is often done by amateur radio operators for satellite work when they want to produce
circular polarisation of say a pair of yagi antennas
cheers
Dave
PS how about elaborating a bit on what you are trying to achieve so that more practical answers can
be given for your specific application
If the antennas are the same polarization and close by, you have formed a simple phased array antenna. i.e. the radiation pattern of the pair of antennas will now be more directional, with nulls at certain azimuths.
If the two antennas are different polarizations, such as omni vertical polarized of ANT1, and omni horizontal polarized for ANT2, then you have made a dual polarization omnidirectional antenna.
If you mean couple in the sense of "combiner", a tuned device where the
lengths of the couple parts are quarter-wavelength to operate as matching
transformers, with a similar arrangement to match to the output, then you have
a signal summing device.
Commonly used in phased array antennas for gain. 2 antennas gives a gain
Gain = antenna gain + 3dB
4 antennas gives Antenna Gain +6dB
8 Antennas gives Antenna Gain + 9 dB etc.
Using the spacing between two antennas to generate a null in a specific direction
to lose the signal from an interfering transmission is the next common usage.
The time delay between the signal arrival between each antenna can be used to
steer the null. Adjusting cable lengths has an identical effect, by trying to make
the signal arrive at the coupler 180 degrees out of phase from the main antenna.
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