choke ring antenna question

[senmeis]

Hi,

A choke ring antenna is typically used in GNSS receivers. What’s the radiating element inside? A dipole?

 

[neetugw]

Hi,


A choke ring antenna is commonly used in GNSS applications to minimize multipath interference. The radiating element inside is typically a microstrip patch antenna or a quadrifilar helix, rather than a dipole. Patch antennas are widely used due to their compact size, circular polarization, and good impedance matching with GNSS signals.


Let me know if you’d like more details!

 

[D.A.(Tony)Stewart]

The signal is for RHCP antenna not linear. The ring has concentric groves to attenuate stronger lateral ground signals. The Helix is used to capture a wider sky view.

Are you sharing your wisdom ? got another question?

 

[senmeis]

Thanks.

 

[senmeis]

Can I replace this radiating element with a pair of perpendicular dipoles which can receive circular polarized signals?

 

[vfone]

Two perpendicular dipoles do not give you circular polarization.
Still get 3dB polarization loss, as it is between linear and circular polarizations.

 

[senmeis]

Two signals which are perpendicular, linear polarized and in-phase can create a circular pol. Signal. Is it correct?

 

[vfone]

If you have two perpendicular dipoles (vertical and horizontal), the field vector turns a right-hand sense or a left-hand sense?

 

[volker@muehlhaus]

If you have two perpendicular dipoles (vertical and horizontal), the field vector turns a right-hand sense or a left-hand sense?

That depends on the phase offset, 90° or -90°

 

[D.A.(Tony)Stewart]

- For right-hand circular polarization (RHCP), if the wave is coming toward you (propagating along the z-axis), the electric field rotates clockwise. In this case, the horizontal dipole’s signal leads the vertical dipole’s signal by 90 degrees in time.
- For left-hand circular polarization (LHCP), the field rotates counterclockwise, and the vertical dipole’s signal leads the horizontal dipole’s signal by 90 degrees.

 

[vfone]

I think there is a confusion between Cross Linear Polarization and Circular Polarization, which are different concepts in the context of electromagnetic wave polarization.
Cross Linear Polarization refers to two orthogonal linear polarization states, when Circular Polarization occurs when the electric field vector rotates in a circular motion as the wave propagates.
Therefore, while cross linear polarization involves two linear polarization states that are perpendicular to each other, circular polarization involves a specific phase relationship and MOTION of the electric field vector that results in a circular pattern.

 

[senmeis]

This description is taken from the attached book page:

Changing the phase difference between two linearly polarised waves gives a variety of resultant polarisations. When the phase difference is 0 or pi, the result is another
linearly polarised wave. Phase differences of pi/2 and 3pi/2 both result in circular polarisations, but with opposite handedness. Phase differences in between these special cases results in the generalised elliptical polarisation.