); [EMAIL_ADDRESS] (F.J.); [EMAIL_ADDRESS] (W.W.); [EMAIL_ADDRESS] (M.S. ); [EMAIL_ADDRESS] (G.F.P)  
[PERSON], [PERSON], [PERSON] A Cross-Mode Universal Digital Pre-Distortion Technology for Low-Sidelobe Active Antenna Arrays in 5G and Satellite Communications. Electronics **2021**, _10_, 2031. [[https://doi.org/10.3390/electronics10162031](https://doi.org/10.3390/electronics10162031)]([https://doi.org/10.3390/electronics10162031](https://doi.org/10.3390/electronics10162031))  
Footnote 1: email: [[http://www.mdpi.com/journal/electronics](http://www.mdpi.com/journal/electronics)]([http://www.mdpi.com/journal/electronics](http://www.mdpi.com/journal/electronics))  
Received: 15 July 2021  
Accepted: 17 August 2021  
Footnote 13: email: [[http://www.mdpi](http://www.mdpi)]([http://www.mdpi](http://www.mdpi)). number of feedback paths equals the number of PAs [5]. This is acceptable for small-scale arrays with a few PAs, but it would be extremely challenging for large-scale arrays that consist of hundreds or thousands of PAs [6]. The linearization of arrays consumes abundant amounts of operation power and makes the system unnecessarily complex, since both a analog-to-digital converter (ADC) and coupler are essential components for each feedback path [7; 8], as shown in Figure 1a. Additionally, nowadays, active arrays tend to be more integrated and compact [9], making one-to-one pre-distortion of PAs infeasible. To reduce the feedback-path quantity, the average DPD system with one feedback path was proposed to linearize the active array, as shown in Figure 1b [10]. Only one ADC component remains in the average DPD system, which reduce sits ADC power consumption compared with Figure 1a. However, the linearization performance is highly dependent on the consistency of PAs, specifically the gain factor, which is used to synthesize the pre-distortion function. Moreover, a large amount of couplers is still mandatory. Various authors [11; 12; 13; 14; 15; 16] attempted to model and pre-distort the non-uniform active arrays. However, only conditions with different input power levels (leading to various operation regimes) were considered in these works, while optimizations of supply voltages and bias voltages were not covered. This means that several PAs will not operate in their compression regions. Accordingly, these PAs operating in low power levels or even linear regions cannot reach their optimum efficiency. Therefore, the power efficiency achieved by [11; 12; 13; 14; 15; 16] may be limited. Additionally, for multi-antenna systems in satellite communications, the consistency of PAs in an active array cannot be guaranteed [17]. Power amplifiers tend to operate in different modes due to their imperfections (e.g., the manufacturing tolerance) and different local environmental conditions (e.g., the operating temperature). However, the sidelobe level is an essential specification of satellite antenna arrays, as it characterizes the capability of arrays to suppress the interference. In order to realize low sidelobes while maintaining high power efficiency, PAs can be intentionally arranged to operate in different saturation modes with desired power levels [18; 19; 20; 21; 22]. However, it is infeasible to directly apply the existing DPD methods designed for signal PA or uniform power antenna arrays to linearize low-sidelobe active antenna arrays with non uniform power distribution [23; 24; 25; 26; 27; 28]. Therefore, an effective linearization technique for low-sidelobe active antenna arrays is needed. Figure 1: Block diagram of digital pre-distortion (DPD) techniques used for non-uniform amplitude excitation active antenna arrays: (**a**) one-to-one DPD [5], (**b**) average DPD [10], and (**c**) the proposed cross-mode universal digital pre-distortion (CMUDPD). In this paper, a cross-mode universal digital pre-distortion (CMUDPD) technique is proposed to linearize low-sidelobe active antenna arrays, as depicted in Figure 1c.