Small RF Tunable Inductor

[Antenna (^.^)]

I am trying to make a tunable impedance matching circuit for a reconfigurable patch antenna.
Does anyone know where to find an rf tunable inductor, maybe in chip or smd form? (small enough for a PCB)

Or maybe a digitally tunable LC filter?

Thanks!!

 

[jiripolivka]

I am trying to make a tunable impedance matching circuit for a reconfigurable patch antenna.
Does anyone know where to find an rf tunable inductor, maybe in chip or smd form? (small enough for a PCB)

Or maybe a digitally tunable LC filter?

Thanks!!

How can anyone offer you ideas without any specifications?
Try a plastic straw and wind a coil on it. To tune, use a screwdriver to set coil length. Or insert an aluminum core and move it to set inductance.

 

[FvM]

Electrically tunable inductors are huge devices, requiring considerable DC current for control. The only suitable small solution seems to be a combination of multiple inductors and analog switches.

You should mention the intended frequency and inductance range.

 

[vfone]

Because is about tuning the impedance of a patch antenna, I assume the working frequency is greater than 500MHz.
At those relative high frequencies tuning the inductors is practically impossible, due to their low values and small dimensions.
But there are many approaches of antenna tuners used in the latest mobile phones, using switched capacitors and inductors.

go to page 22:
**broken link removed**

 

[Warpspeed]

Tunable inductor has been around for at least a couple of hundred years, methods include:

Variometer.
Roller inductor.
Permeability tuning by a slug mounted on a screw.
Saturate inductor.

All work, and all are physically quite large.

 

[Borber]

For HF let us say above 0.1GHz inductors are made variable by mechanic deformation. Coil of few turns of thick wire can be stretched and it's inductance decreased and vice versa. Inductance of straight wire can be decreased if shorted loop is placed close to it. Closer the loop is lower is the inductance.

 

[mtwieg]

. If you need smaller size then you're better off using a varactor or trimcap in combination with a fixed inductor.

 

[biff44]

you can transform a variable capacitance on one side of a transistor into a variable inductance on the other side. in other words come up with a "virtual" inductance. Its just a matter of using the right embedding reactances or feedback to swing from one half of the smith chart into the other.

For that matter, a variable capacitor placed at the end of a length of transmission line can certain look "inductive" at the far end of the line

 

[D.A.(Tony)Stewart]

If you work with a good MEMS supplier, it is possible using polysilicon varicap to tune the patch.
**broken link removed**

 

[kripacharya]

Electronic tuning of an inductor is probably not the direction to go. Since your impedance match circuit is bound to have capacitors also, a better bet is to use varactors in creative ways. If for some reason this is not feasible, then the next best approach imho would be to switch in/out combinations of fixed inductors using PIN diodes. Or switch in/out an entire matching network depending on the application...