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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.

Increasing the efficiency of transmitters, as the largest consumers of energy, is relevant for any wireless communication devices. For higher efficiency, a number of methods are used, including envelope tracking and envelope elimination and restoration. Increasing the bandwidth of used frequencies requires expanding envelope modulators bandwidth up to 250–500 MHz or more. The possibility of using amplifiers with input signal quantization (AISQ), as an alternative to the most common hybrid envelope tracking modulators, is considered. An approach has been developed for optimizing AISQ characteristics according to the criterion of minimum loss when amplifying modern telecommunication signals with Rayleigh envelope distribution. The optimal quantization levels are determined and the energy characteristics of AISQ are calculated. AISQ loss power is shown to decrease by 1.66 times with two-level quantization, by 2.4 times with three-level quantization, and by a factor of 3.0–3.7 for four–five quantization levels compared to a class B amplifier. With these parameters, AISQ becomes competitive with respect to hybrid envelope tracking modulators but does not have electromagnetic interference from the pulse width modulation (PWM) path.

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To amplify modern high crest factor telecommunication radio signals with high efficiency, switching operation modes of transistors and synthetic amplification methods are used. The most common of these are the Kahn method (EER – envelope elimination and restoration) and the outphasing method. However, application of these methods has a number of technological (in terms of element base capabilities) limitations on the bandwidth and dynamic range of amplified signal. To expand high-efficiency RF power amplifiers field of application, the possibilities of combination several different synthetic amplification techniques are being considered. Expressions are obtained for the theoretically achievable efficiency when combining the outphasing method with a bridge power combiner and pulse-step modulation of supply voltage. The dependence of average efficiency on the number of supply voltage levels is determined. RF amplified signal bandwidth and its dynamic range determine the minimum required pulse width of the PWM modulator for the EER amplifier. Variants of these characteristics dependence on the number of supply voltage levels are discussed with combined use of PWM and pulse-step modulation of the supply voltage. Directions for further research are formulated.