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Hi,
I'm trying to obtain a directional beam using two antennas of the WARP board. When two antennas are placed at half wavelength (~6 cm apart), and along x axis, the radiation pattern should be an '8' pattern along y axis if the input to both the antennas is in-phase. If the input is 180 degrees out of phase, it should be an '8' pattern along x axis.
But when I take measurements by placing a receiver along x axis (I'm transmitting a sinusoid), the amplitude is high when the inputs to the antennas are in-phase (ideally there should be nulls along x axis) than when inputs are in anti phase. Similarly, when I place the receiver along y axis, the amplitude is high when the inputs are out of phase as compared to input in-phase. I'm wondering if there is a 180 degree phase shift between the two transmitting antennas in-built in the system. Can you please clarify if I'm missing something and if you have tested directional beams.
Thanks
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You're describing a kind of beamforming, which in this form requires the carriers of each transceiver be frequency and phase aligned. Each WARP radio board implements in independent transceiver. If they're clocked by the same clock board, their carriers will be frequency matched, but there will always be a phase offset between their carriers. And because each radio's PLLs re-lock with every power cycle, the phase offset will be random (per power cycle, but fixed once the radios lock). In order to realize the kind of beam pattern you describe, you will need to build some kind of inter-radio phase estimator/corrector.
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