WOBBLifa trace antenna

Does the trace antenna resonate at 2.4 GHz, and what is its S11 and gain?

Antenna report
2026-10-15 22:33
FAILS

The antenna resonates at 2640 MHz (+10.0% from 2400 MHz), with 37.5 - j40.1 ohm and S11 of -7.2 dB against 50 ohm at 2400 MHz. Peak gain 1.92 dBi toward theta 32 and phi 75 degrees.

resonance
2640 MHz
S11
-7.2 dB
impedance
37.5 - j40.1 ohm
gain
1.92 dBi
mesh
72624 unknowns

Confidence medium

  • a fast run skips the finer mesh and the farther boundary, so the discretization error is not measured

Simulation

S11 over the sweep
S11 over the sweep
Input impedance
Input impedance
Radiation pattern cuts
Radiation pattern cuts
Field strength near the antenna
Field strength near the antenna

Checks

statuscheckresult
passpower balancethe power flowing out through a sphere around the antenna matches the power fed in less the dielectric loss to 1.3% or better at all 8 frequencies (worst at 1800 MHz, 11.9 W out against 11.2 W for 1 A at the port), and the far field carries 16 W at 2400 MHz (5.3% apart)
inforun timepredicted 10 min from the 11,053 node mesh before any solve, took 5 min for 8 frequencies. It gave up 2 fewer frequencies in the sweep; a coarser mesh (the 'fast' quality); no verification solves on finer or larger meshes to fit the 15 min budget

How to fix it

Scale the resonant length by 1.100
Make the part that sets the resonance 10.0% longer, since resonance scales inversely with length.

Assumptions

  1. Fed by a lumped port, a 0.5 mm wide strip across the 0.6 mm gap from (-9, 3.6, 1.583) to (-9, 3, 1.583) mm carrying 1 A. The impedance is the voltage across the gap over that current, so it holds the gap's capacitance and the strip's inductance.
  2. Metals and copper sheets are perfect conductors, so conductor loss is left out. Dielectric loss comes from each material's loss tangent.
  3. Free space around the antenna, closed by a sphere of 108 mm radius that absorbs outgoing waves (a second order boundary condition). The far field comes from the fields on a sphere of 66.7 mm.
  4. First order edge elements no larger than a tenth of the shortest wavelength in air, one mesh for the whole sweep with 72624 unknowns.
  5. 'board' is board laminate, relative permittivity 4.4, loss tangent 0.02.
  6. Solved in 3D. The antenna is the geometry in ifa.kicad_pcb, which no closed form describes.
  7. The antenna is net ANT. Ground is GND.
  8. The board is a slab of relative permittivity 4.4 and loss tangent 0.02, 1.6 mm thick (kicad stackup).
  9. Vias are not modeled and copper is a perfect conductor of zero thickness.