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

[Magnus Danielson]

On 07/07/2012 06:21 PM, Dr. David Kirkby wrote:
> 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.

We had this straighten out about a month ago, and me posting more or 
less as I landed from a transatlantic flight wasn't optimum (tired and 
waving hands didn't help, as I got it wrong).

RHCP should match RHCP and LHCP should match LHCP.

Cheers,
Magnus