we want to design a single antenna for all three bands which are 315MHz, 433MHz, and 868MHz. However, in the application note, its stated that the differential impedance for the bands are:
1) Zout@315MHz = 122+j31 ohm
2) Zout@433MHz = 116+j41 ohm
3) Zout@868MHz = 86.5+j43 ohm
in the same application note, design of 315/433MHz matching circuit and 868/915MHz matching circuits are given separately! does this means we cannot design single antenna to cover all three bands? single antenna can only cover 315/433MHz or 868/915MHz?