Besides all implementation details, some general properties of an electrically small antenna should be considered
- the maximum achievable directivity is that of a small dipole (cosine law)
- the smaller the antenna relative to wavelength, the higher it's resonance Q respectively the smaller it's bandwitdth, Q ~ 1/r³
- the bandwidth of an electrically small antenna can be increased by including loss elements (and reducing the gain respectively)
- instead of an impedance matched antenna, an electrical or magnetic field probe (Hertz dipole or small loop) may be used, by nature it has only low sensitivity.
The microstrip patch concept seems not well suited for the intended purpose, although in principle, a high permittivity ceramic substrate (Er ≈ 50) can be used to make a 50 mm patch resonate at 433 MHz.