Browse Prior Art Database

A SELF TUNED LOOP ANTENNA

IP.com Disclosure Number: IPCOM000008366D
Original Publication Date: 1997-Dec-01
Included in the Prior Art Database: 2002-Jun-11
Document File: 2 page(s) / 85K

Publishing Venue

Motorola

Related People

Peter Miller: AUTHOR

Abstract

A loop or coil antenna, in particular for use on means that an RF tag can be built more simply and such items as RF tags normally needs to be tuned at lower cost than at present. by a separate component to make the circuit resonate at the frequency of interest to obtain maxi- A conventional tuned circuit consists of a parallel mum efficiency. The technique disclosed here L-C circuit (using 2 components) as shown below. avoids the need for this extra component. This To manufacture this circuit as shown using a "printed" coil requires at least a two layer structure, as clearly to connect the capacitor between the two ends of the "spiral" is not possible while still tracking on a single layer.

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MOTOROLA Technical Developments

A SELF TUNED LOOP ANTENNA

by Peter Miller

  A loop or coil antenna, in particular for use on means that an RF tag can be built more simply and such items as RF tags normally needs to be tuned at lower cost than at present.
by a separate component to make the circuit
resonate at the frequency of interest to obtain maxi- A conventional tuned circuit consists of a parallel mum efficiency. The technique disclosed here L-C circuit (using 2 components) as shown below. avoids the need for this extra component. This

  To manufacture this circuit as shown using a "printed" coil requires at least a two layer structure, as clearly to connect the capacitor between the

two ends of the "spiral" is not possible while still tracking on a single layer.

D

The above geometry can be modeled as an inductor with a low internal resistance and a small stray capacitance.

*' Motoroh. Ix ,997 19 December 1997

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MOTOROLA Technical Developments

INDUCTANCE

The inductance of this geometry can be calcu- lated by the following equation.

  Clearly, this is effectively identical to that required (the resistance would be present in any coil structure) and thus can be used as a conventional tuned circuit with no need for a separate tuning capacitor.

  In this structure, the self capacitance is relative- ly high (due to the tracks being close). It is also rel- atively immune to production tolerances-in...