Transmission Line Resistance Compression Networks and Applications to Wireless Power Transfer

Abstract

Abstract-Microwave-to-dc rectification is valuable in many applications including rf energy recovery, dc-dc conversion, and wireless power transfer. In such applications, it is desired for the microwave rectifier system to provide a constant rf input impedance. Consequently, variation in rectifier input impedance over varying incident power levels can hurt system performance. To address this challenge, we introduce multi-way transmissionline resistance compression networks (TLRCNs) for maintaining near-constant input impedance in rf-to-dc rectifier systems. A development of TLRCNs is presented, along with their application to rf-to-dc conversion and wireless power transfer. We derive analytical expressions for the behavior of TLRCNs, and describe two design methodologies applicable to both single and multi-stage implementations. A 2.45-GHz 4-way TLRCN network is implemented and applied to create a 4-Watt resistancecompressed rectifier system that has narrow-range resistive input characteristics over a 10-dB power range. It is demonstrated to improve the impedance match to mostly-resistive but variable input impedance class-E rectifiers over a 10-dB power range. The resulting TLRCN plus rectifier system has >50% rf-to-dc conversion efficiency over a >10-dB input power range at 2.45 GHz (peak efficiency 70%), and SWR <1.1 over a 7.7-dB range, despite a non-negligible reactive component in the rectifier loads.

Theory and Implementation of RF-Input <newline/>Outphasing Power Amplification

“…The implementation described in this work and used for the experimental prototype is based on an all-transmissionline approach as described for the power combining system in [10], and for resistance compression networks (RCNs) in [27], but we note that versions are also possible using discrete components, microstrip techniques, or a combination of those, related to the lumped-element [7], [8], microstrip with shunt reactive element [9], and all-transmission-line [10] variations of the four-way outphasing power combiner. Likewise, the approaches described in this work may be applied two-way (Chireix) outphasing, including its relatively wideband variations [4], [5].…”

“…An analogous inverse-RCN approach can be seen in the relationship between the transmission-line combining network [10] and transmissionline resistance compression network (TLRCN) [27]. As described in detail in [27], a TLRCN may be constructed as a binary tree of transmission-line sections, with the two branch lengths at the nth branch point a deviation ±∆ n from a base length (typically λ/2 or λ/4). The ends of the final branches are typically terminated in identical loads, and a quarter-wave transmission line may also be employed before the initial branch point to provide impedance matching into the TLRCN.…”

Design of Class E resonant rectifiers and diode evaluation for VHF power conversion

“…Applications for these circuits include very-high-frequency dc-dc converters [1][2][3][4][5][6][7][8], wireless power transfer systems [4,9,10], and energy recovery circuits for radio-frequency systems [5,6]. In many of these applications, it is desirable for the rectifier to appear as a resistive load at its ac input port.…”

“…For example, in some very-high-frequency dc-dc converters, proper operation of the inverter portion of the circuit can depend upon maintaining resistive (but possibly variable) loading in the rectifier stage. In still other applications it is desired to have an input impedance that is resistive and approximately constant across operating conditions [5,6]; this can be achieved by combining a set of resonant rectifiers having variable resistive input impedances with a resistance compression network [5,[7][8][9][10]. In all these systems, however, it is desirable to maintain resistive input impedance of the rectifier as the operating power varies.…”

“…Resonant rectifiers have been explored in a variety of contexts [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The traditional design of a class E rectifier, or shunt-loaded resonant rectifier, utilizes a (large) choke Figure 1.…”