Dependence of modern telecommunication signals transmitter with components separation output signal distortion level on the envelope path filter parameters

Abstract

The article investigates the dependence of the envelope elimination and restoration (EER) transmitter out-of-band emissions on the parameters of its envelope path LPF. LPFs of the sixth order with the Cauer structure, having the same degree of clock frequency unwanted products suppression, unilaterally and bilaterally loaded, and optimized LPFs with a smooth transition of the frequency response from the passband to the stopband are considered. It is shown that when the transmitter is operating at a nominal load (broadband antenna), a sharp transition from the passband to the stopband in the envelope path LPF leads to an increase in out-of-band emissions that are separated from the center frequency of the transmitter by the LPF cutoff frequency. The minimum envelope path allowable bandwidth is at least 5 transmitted signal bandwidths when using a Cauer-type LPF with a standard approximation and at least 3.5 bandwidths for an optimized LPF with a smooth transition. For the case of a transmitter operating on a resonant antenna with a limited bandwidth, the dependences of the minimum envelope path filter required bandwidth on the antenna bandwidth and the VSWR value at the edges of the amplified signal band are revealed. It is shown that the use of two-sided loaded filters in the envelope path allows the transmitter to work on antennas with half the bandwidth and reduce the antenna SWR requirements from 1.03 to 1.07. The use of smooth transition filters allows you to reduce the minimum required bandwidth of the LPF by 20% compared to standard filters. The most preferable is the use of a two-sided loaded LPF of the 6th order with a smooth transition, which ensures the operation of the transmitter to the antenna with VSWR = 1.07 at the edges of the transmitted signal band with a minimum LPF bandwidth equal to 5.8 signal bands.