KiCad Design: 13.56 MHz HF RFID Loop Antenna Tile (A6) - RF Engineering

Project Overview: I am developing a modular RFID reader surface and require a 2-layer PCB design for a single passive HF RFID planar loop antenna (A6 size, ~105 x 148 mm) operating at 13.56 MHz (ISO 15693). Target Application: - The antenna must couple reliably with miniature 10 mm ISO 15693 wet inlays (NXP ICODE SLIX2) resting on or up to 25 mm above the surface. - The antenna is fed via a 50-ohm SMA connector from a standard transceiver (NXP PN5180 / ST25R3916 family). Technical Scope & Requirements: 1. Coil Geometry: - 2-layer FR4, 1.6 mm board thickness, 1 oz copper. - Rectangular outer dimensions: approximately 105 mm x 148 mm. - Calculate and simulate optimal trace width, spacing, and turn count to target an inductance (L) around 1.0 uH to 1.3 uH with minimal parasitic capacitance. 2. Passive 50-Ohm Matching Network: - Match the balanced/unbalanced coil to a 50-ohm unbalanced SMA female edge connector. - Standard capacitive matching topology (pads for series Cs, parallel Cp, and Q-damping resistor Rdamp). - Use standard 0805 SMD footprints to allow manual hand-soldering and bench tuning with a NanoVNA. 3. Component Calculation: - Calculate theoretical starting values for Cs, Cp, and Rdamp assuming an antenna Quality Factor (Q) target of 15–20. Deliverables: - Complete KiCad project (schematic and PCB layout files). - Production Gerbers, drill files, and BOM formatted for JLCPCB fabrication. - A brief simulation note/calculation sheet showing calculated L, Q, and starting passive component values. Future Work: Successful delivery of this passive antenna tile will lead directly to a follow-up contract to design a 4-channel RF multiplexer daughterboard (SP4T / ADG904) to drive multiple tiles. This is the longer term aim, this first test is getting to a confidence level to commit more funding (i.e. convincing my wife it is possible with a prototype)