How to design antenna to maintain stable phase center?

[fly_fish]

My teacher asks me to research on antenna phse center. How to design an antenna to maintain stable phase center ? Trimble and Novatel have produced such antennas. But how to analysis and simulate them?

 

[Lupin]

antenna phase centre definition wiki

Do you have to design an antenna with stable Phase Center?

What articles are you considering? I work on it as well.

Regards

Lupin

 

[eirp]

antenna phase center definition

I'm also interested in phase center problematic..
You mean stable with what variable?

I think main problems (not discussed a lot) is that the excited wave isn't spherical thus the phase center isn't simple a point.

Appreciate more comments!

Cheers
eirp

 

[Lupin]

zephyr 2 phasen centre

I consider it stable respect to the edge of view.. I mean the Teta Angle (considering a spherical coordinate reference).

Do you have the same assumption?

Your consideration is correct.

Lupin

 

[fly_fish]

phase centre gps antenna

Nominally, the GPS receiver antenna phase center is located at the center of this square patch, that is, at the mechanical enter of the antenna. However, in practice the effective electrical center of the antenna moves around in three dimensions.

This is a function of the apparent azimuth and elevation of the satellite being tracked, and the way that the antenna is fed, that is, how it is electrically connected to the rest of the circuit. Because multiple satellites are tracked at any time,and each one has a different azimuth and elevation, each measurement is taken from a slightly different location in space, somewhere near the mechanical center of the antenna. Thus, although surveyors require a measurement at a single point in space
at any point in time, their antennas take measurements from a group of electrical phase centers that are all at slightly different locations.

The space in which these electrical phase centers may vary is something like an error ellipsoid; consequently, if an antenna’s variation is large, then its ellipsoid is also large.

An ideal GPS antenna for surveying would take all measurements from an exact, physically defined, mechanical location, regardless of satellite
elevation angle or azimuth, or any other factor. Such an antenna would be said to have extremely good phase center stability.

In high-performance antennas, the variation of the phase center in the horizontal plane is limited to values of less than 1 millimeter, regardless of the direction from which the signal is received, or the rotation of the antenna. vertical phase center variations as a function of satellite elevation angle in an absolute sense are highly consistent, even across different antennas of the same type.

If an antenna phase center moves very predictably as a function of satellite elevation, regardless of the azimuth of the satellite, and if this consistent behavior is held within very fine tolerances across all antennas of its type (even if thousands of them are produced), then the antenna has very good phase center repeatability.

 

[fly_fish]

variation of phase center with field of view

Articles concering on antenna phase center are too few. I have only 2 papers about Novatel's GPS600 antenna and 2 papers about the Trimble Zephyr Geodetic Antenna.

Do you have any other articles, Lupin?

I consider the symmetrically placed feed points are critcal to maintain stable antenna phase center. The reason is not clear yet.
The key problem is to analysis this kind of antenna and design the feeding network.

 

[tmau]

Re: Antenna Phase Center

Please check out the ARRL QEX - Practical Microwave Antennas, Part 1 - Antenna Fundamentals & Horn Antenna.

Are u doing the reflector design? If the polarization is linear and the phase centers of E- & H -plane are difference, therefore the efficiency will be lower.

 

[satellite]

Re: Antenna Phase Center

Dear friends,

please find attached a good paper on navigation antennas with a section dedicated to the phase center problem.

bye,

Satellite

 

[juppydu]

Re: Antenna Phase Center

Hello !

First of all to define a phase centre you have to define the coverage area, since the phase centre varies with the the coverage area! (an antenna can have several phase centre !!)

Second you have to define the bandwidth over you are looking for the phase centre ! large bandwidth generally produce a large phase centre variation!

Then a stable phase centre means a phase centre that has very little varition in space with respect to a fixed point (not necessary phase centre location is equal to the mechanical centre !). On other hand a variable phase centre produce, in frequency, over the coverage area a phase variation since any observer see different "phase centre".

A good idea to control the phase centre at over the specified field of view and over the operative bandwidth is to synthetise a pattern with "flat phase" i.e. a pattern that doesn't phase variation in the field of view!
This can be done with a software that is able to consider phase pattern constraint.

Bye, bye. :wink:

 

[fly_fish]

Antenna Phase Center

My task is to resarch on microstrip antenna with stable phase center. It maybe a patch antenna or slot antenna.
It seems that symmetrical feeds lead to symmetrical pattern in the horizontal plane ,thus producing stable phase center.

 

[satellite]

Re: Antenna Phase Center

Dear juppydu,

could you provide some reference material?

 

[juppydu]

Re: Antenna Phase Center

Hello,

the last sentence of fly_fish is partially correct ! it is true that an antenna with "central symmetry layout" and "fed" in central symmetry way produce a phase pattern with rotationally suymmetrical pattern with respect to the boresight axis, anyway this doesn't mean that the phase centre is "stable", it means only that the phase centre is moving only along to the boresigth axis, but doesn't says anything about how much is the movement in the frequency band considered !

unfortunately, satellite, I doesn't have any dedicated material about the phase centre definition. What I know is coming from my direct experience on the antenna field.

The question can be summarized in the following example : Suppose you have a an antenna locate in a black box and you cannot see where the antenna is in the box, but you can measure the radiated field of the antenna, and a people ask you where is the antenna in the box ?
Now if you walk around the box along a semi-circle with the centre (that you choiced) somewhere in the box, you have the following possibilities:

-you see a fixed phase value => there is a spherical wave source locate in the centre of your circle, this presumably is the antenna you are looking for !

- you see a phase with a convex shape (positive of negative) => there is a spherical wave source locate before or after the centre of your circle.

- you see a phase centre with a slope (positive or negative) => there is a spherical wave source on the left or on the right of the centre of your circle.

-you can have a mixed situation of the two last cases !

In every cases you can compute the coordinate correction to recover the centre of the equivalent spherical wave source (the phase centre) of the antenna in the black box !
(PS: in the real world the measured phase pattern is affected by measurements errors and the computation of phase centre is slightly complicated).

In conclusion what you can found is the antenna phase centre position, on other hand the equivalent spherical wave source of your antenna in the black box, not the true antenna position, theortically the phase center can be at several meter of distance from the antenna (Think also to the mirror effect, it a virtual point)! anyway in the real cases the "electrical centre" (the phase centre) is close to the "mechanical centre" ! we can say that the phase centre is the electrical equivalent of mechanical gravity center ?!

let me know any comments about that !

 

[Kit-the-great]

Antenna Phase Center

I'm faces the challenge of phase center when I'm develop the off-axis short-focus mm-wave Cassegrain antenna. I'm found only one way to solve the problem of horn phase center: design the sub-reflector of special shape to correct the non-spherical wavefront from horn.