Ceramic patch antennas are usually measured on top of metal ground board upper surface and each size and shape of patch printed on genetic corpuscle image have different impedance values and resonant frequencies.
Change in the impedance values and resonant frequencies of the ceramic patch antennas also depend on thickness, width and material of the measuring ground plane as well.
When boundary condition within the air compared to when mounted to a device, special features of antennas also change due to the change in the boundary condition.
With considerations of the special features, the impedance values of patch antennas should be matched in order to minimize reflection loss and, therefore, a tuning work is required to resonate within 1575.42MHz of L1 frequency.
When measuring 25x25mm ceramic patch antennas on 70x70mm ground plane, the resonant frequency is generally 1575.42MHz.
However when the same ceramic patch antennas are measured within 28x28mm size of PCB for LNA, the resonant frequency is around 1565-1570MHz.
Furthermore, when this is mounted to the set device, its resonant frequency gets reduced even more to 1555-1565MHz.
Each set has different conditions due to the special features of mounted device such as the materials used for the case and the affects generated from its functional features.
Therefore, in order to resonate the ceramic patch antennas within 1575.42MHz, a tuning work is needed to increase the frequency.
Furthermore an impedance matching should be conducted once again due to the patch antennas and changes in its impedance values.
In case of RFID reader antennas, the same impedance matching is also required and the matching technology, thus, can be regarded as its own beneficial values and long recognition distance used for the transmission single ports.