I am working on transceiver AX5243. I want know impedance of differential antenna pins to matching simultaneously both 868/915/433MHz (in datasheet only matching single band).
Hello, as you can see from the datasheet, for each frequency band we propose a different matching network (Fig.9 of https://www.onsemi.com/pdf/datasheet/ax5243-d.pdf).
Among these passives, while the filter and balun could be designed to be wideband (at least for 868 and 915 Mhz), the tank (LC,CC,CT,LT) is designed to optimally load the Class-E PA for a specific frequency. You could obtain a reasonably good performance for both 868 and 915, but 433 MHz is too far away.
Note 1: the radio is fully programmable and the different frequency ranges can be programmed on-the-fly. You can, with the same PCB and antenna, transmit at 868 MHz and then move to 433 MHz just by reprogramming the FREQA/B registers and re-performing the PLLRANGING. The drawback of not having a well adapted matching network is that the efficiency (current consumption and output power) and spectral performance (noise) will be not optimal.
Note 2: given that the AX5243 implements a Class E amplifier, the impedance shown at the ANTP/ANTN pins is variable depending on the frequency and output power at which the PA operates.
You can find more info on the topic here:
@georgi.gorine thank you for your support