AN2731 Freescale Semiconductor / Motorola, AN2731 Datasheet - Page 9

• Manufacturer Part Number: AN2731
• Description: Compact, Integrated Antennas: Designs and Applications for the MC13191 and MC13192
• Manufacturer: Freescale Semiconductor / Motorola

4.1.4
If a quarter wavelength is coiled up, a very compact antenna can be made which still has reasonable
efficiency. Some experimentation may be required to find resonance, because the length of the wire is not
exactly related to a quarter wavelength. This type of antenna is very popular at lower frequencies.
4.1.5
A spiral antenna, with the windings in one plane like a pancake, is well suited to be implemented on a PCB.
Performance is similar to the helix.
4.1.6
The meander antenna or meander pattern, is an antenna with the wire folded back and forth where
resonance is found in a much more compact structure than can otherwise be obtained.
The meander, spiral, and helix antennas are similar in that resonance is obtained in a compact space by
compressing the wire in different ways. In all three cases, the radiation resistance, bandwidth, and
efficiency drops off as size is decreased, and tuning becomes increasingly critical. Impedance matching
can be implemented by tapping, as in the F-antenna. The meander and helix antenna, or a combination of
these two, are easily implemented in a PCB, and many chip antennas are based on these types of antenna.
Freescale Semiconductor
The Helix
The Spiral
The Meander Antenna
Figure 8. Meander Pattern (Tapped for Impedance Match)
Compact Integrated Antennas, Rev. 1.2
Impedance Matching
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