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Design >> RF Design >> why is this inductor necessary for dipole antenna?
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Message started by liletian on Apr 17^th, 2011, 7:59pm

Title: why is this inductor necessary for dipole antenna?
Post by liletian on Apr 17^th, 2011, 7:59pm

Hi Guys
In TI CC2430 product, their chips have a differential output. They provides two solution for dipole antenna and monopoly antenna each.
For the dipole antenna, I am wondering why L321 in the attached pic? What is the purpose? ALso, why do they also need L331 to connect DC and middle of the dipole?

Second, for the monopoly antenna solution, can anyone explain the matching network? Basically I am wondering how can they get the network?

Finally, in those day, people are unlikely to use off-chip discrete components, what is the reason for that?
I am thinking it is because of the price. Also, even off-chip discrete component has better electrical quality , but it will be hard to model the connection parasitics. Are those the two reasons people try to avoid off-chip components?
Thanks

Title: Re: why is this inductor necessary for dipole antenna?
Post by dfury on Apr 25^th, 2011, 1:53pm

Hi,

What i think is that these inductors and capacitive networks are used to remove the imaginary part of the impedance of the dipole or monopole antennas and match it to the real output impedance of the I.C. pins. It also can be catering for the imaginary part of the impedance at the output of the I.C. pins which are also not purely resistive loads.

The discrete off-chip components today are very accurate but always prone to size issues .As the frequency of the circuit operation increases the connecting strip-lines or microstrip lines are becoming smaller and smaller and hence the off-chip components are way too large in size and prone to parasitic effects. Hence we can use microstrip based inductive and capacitive networks for impedance matching which can take much more area than a discrete component.But in majority applications values of capacitance and inductance are only realistically achievable by using off chip discrete components.

Regards