Design of MF RC500 Matching Circuits and Antennas

EXAMPLE DESIGN OF MF RC 500 ANTENNAS
The following examples are PCB antennas without a ferrite shielding. If ferrite is used, the values for the capacitors will change due to the detuning effects of the ferrite. It is recommended to place a metal plate behind the ferrite, connect this metal plate to ground and tune the antenna with that metal plate in place and connected. In this case there will be no difference if the antenna is placed in metallic or non-metallic environment. This metal plate should be connected to the shield of the triax-cable or to the ground shield if a coax cable is used.

Tuning must be done after assembling the complete antenna or after mounting the antenna to it’s final position respectively!

General Layout Hints
EMC FILTER AND RECEIVING CIRCUIT
L0 and C0 are used for filtering of the output signal of the MF RC500 and must be placed very close to the TX1 and TX2 pin of the MF RC500. For satisfying EMC results the layout of these components is critical. The ground connection of C0´s should be very short and should have very low impedance to the TGND pin of the MF RC500 (ground plane with multiple vias for connection). The narrow placement of these components is essential for suppression of higher harmonics of the carrier frequency.
The layout of the receiving circuitry is less critical and special requirements are not needed.
Figure 6-1 shows a part of an layout for the MF RC500 with the critical components.

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Figure 6-2. Layout Example for EMC Filtering and Receiving Circuit

Layout of the Antenna and the Matching Circuit
The antenna layout depends on the used shielding and the matching itself. For direct matched antennas it is recommended to use a centre tap to achieve a better EMC performance.

Example for a Directly Matched Antenna
SHIELDED AND COMPENSATED RECTANGULAR ANTENNA
Size of turn = 115 x 115mm, Drawing not in scale
Component values: to be calculated

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Figure 6-3. Example of rectangular antenna

RECTANGULAR ANTENNA
Size of turn = 78,5 x 67mm, Drawing not in scale
Component values: to be calculated

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Figure 6-4.Example for rectangular antenna

SHIELDED RECTANGULAR ANTENNA
A layout example is given in Figure 6-5.

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Figure 6-5. Shielded rectangular antenna

Example for an 50 W Matched Antenna
COMPENSATED RECTANGULAR ANTENNA
Size of turn = 115 x 75mm. Drawing not in scale.
Component values:

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Figure 6-6. Example of compensated rectangular antenna

COMPENSATED CIRCULAR ANTENNA
Diameter = 15cm. Drawing not in scale
Component values:

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Figure 6-7. Compensated circular antenna

SHIELDED CIRCULAR ANTENNA
Diameter = 15cm; 3-layer PCB. Drawing not in scale
Component values:

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Figure 6-8. Shielded circular antenna