[time-nuts] Antenna question about RHCP/LHCP I'm sure a time-nut can answer

[Dr. David Kirkby]

On 06/ 5/12 12:26 AM, Magnus Danielson wrote:
> On 05/06/12 00:30, Dr. David Kirkby wrote:
>> This is not exactly a time related question, but I'm sure the subject
>> must be of interest to time-nuts using GPS.
>>
>> If one transmits from an antenna such as a helical one, RHCP, can the
>> same antenna be used for reception, or does the helix need to be wound
>> the other way?
>>
>> If you google this topic, there seems to be a lot of confusion about
>> whether the TX antenna and RX antenna need to both have RHCP or whether
>> one needs to be LHCP and the other RHCP.
>>
>> Given GPS uses circular polarization, I'm hoping someone here will know.
>>
>> It would appear there are different definitions of "circular
>> polarization", with one considering it from the point of view of the
>> source, and the other considering it from the point of view of the
>> receiver. The IEEE apparently uses the former, and others (especially
>> optics) use the opposite.
>>
>> http://en.wikipedia.org/wiki/Circular_polarization
>>
>> My aim was to make a gain measurement of two circular polarized
>> antennas. I have two identical antennas, but are unsure if the signals
>> should be received strongly, or whether theoretically no signal would be
>> received. (Of course in practice, one never achieves perfect
>> polarization, so there will always be a signal detected, even if
>> cross-polarized.
>
> They would have to have opposite rotation.
>
> The waveform rotation will follow the transmitter antenna into the
> receiver antenna. The receiver antenna follows the same rotation that
> the transmitter antenna has, it's just that the face each other, so when
> you turn one of the 180 degrees such that they face the same direction
> you would see that they are in fact rotated in opposite directions.
>
> I'm sure the sat folks can confirm this.
>
> Cheers,
> Magnus

I can confirm that I'm 100% sure that the polarization of the two antennas needs 
to be the same - i.e. both RHCP or both LHCP. I built two of them for RHCP, and 
got appreciate gain.

Despite what other may say, there does seem to be a lot of confusion about this 
issue, but I've satisfied myself by building them and testing the gain using a 
VNA as the signal source and detector.

Dave