ceramic antennas

[Jamie Morken]

Hi,

Why is ceramic used in antennas, such as surface mount chip antennas and
GPS passive antennas? What is the internal structure of these antennas?
I am guessing there is a metal conductor inside the ceramic?

cheers,
Jamie

 

[Guy Macon]

Jamie Morken wrote:

Why is ceramic used in antennas, such as surface mount chip antennas and
GPS passive antennas? What is the internal structure of these antennas?
I am guessing there is a metal conductor inside the ceramic?

The ceramic antennas are generally dielectric antennas, not the
conducting antennas we all know and love. I am not a RF wizard,
but I can take a shot at explaining the differences as I understand
them (comments/corrections welcome!).

As I understand it, there are two basic types of ceramic antenna,
but both kinds can be combined in one structure.

The first type is basically a standard conducting antenna using metal
conductors on ceramic with a very high dielectric constant. The
dielectric pretty much contains the near field, which greatly reduces
the user's hand detuning the circuit. It also makes it a lot easier
to put multiple antennas close together and allows for a smaller
antenna (IIRC, wavelength is proportional to the square root of the
dielectric constant).

In the second type - often called a dielectric resonator antenna - the
dielectric resonates and becomes a source of radiation. This mode can
be combined with the mode above, and parasitic elements can be added
to make absolutely sure that old-school engineers such as myself can't
figure out what is going on without going back to school.

In addition, the dialectic can act as a lens. For an interesting
discussion on how this works with grapes in a microwave, see
[ http://128.252.223.112/posts/archives/dec97/882909591.Ph.r.html ].
also see [ http://www.edn.com/contents/images/268486f1.pdf ].

All of which pretty much explains why I would hire someone who
knows what he is doing rather than attempt such a design myself.
This stuff is a Black Art. <grin>

 

[Joerg]

Hello Jamie,

Why is ceramic used in antennas, such as surface mount chip antennas and
GPS passive antennas? ...

Predictable material properties, such as dielectric coefficient and
loss. Also, there is a good lot to lot correlation.

BTW, the wireless card I for my PC has the antenna on plain old FR4.
Cheap, but it works.

... What is the internal structure of these antennas? ...

All I have seen it's all on either surface.

I am guessing there is a metal conductor inside the ceramic?

That would be pretty expensive to do.

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hello Guy,

This stuff is a Black Art. <grin

Nah. Just a wee bit of Maxwell, some 12 year old single malt and RF lab
gear will do.

Regards, Joerg

http://www.analogconsultants.com

 

[Guy Macon]

[ http://elecdesign.com/Articles/ArticleID/9987/9987.html ]
has a detailed description of one type of ceramic antenna.