Load-modulation technique without using quarter-wavelength transmission line

Ahmed M. Abdulkhaleq*, Maan A. Yahya, Naser O. Parchin, Yasir Al-Yasir, Maryam Sajedin, Issa Elfergani, Neil J. McEwan, Raed A. Abd-Alhameed, Ashwain Rayit, Jonathan Rodriguez

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


A proposed method for achieving active load-modulation technique without using a quarter-wavelength transmission line is discussed and evaluated. The theoretical analysis shows that the active load-modulation can be achieved without using a quarter-wavelength line, where the main amplifier sees a low impedance when the input signal level is low, and this impedance increases in proportion to the amount of current contributed from the peaking amplifier. The peaking amplifier sees an impedance decreasing from infinity to the normalized impedance. To validate the method, a circuit was designed, simulated and fabricated using two symmetrical gallium nitride (GaN) transistors (6 W) to achieve a peak power of 12 W and 6 dB output backoff efficiency. The design operates with 400 MHz bandwidth at 3.6 GHz and showed an average efficiency of 50% at 6 dB backoff and an efficiency of 75% at peak power. The designed circuit was tested with CW and modulated signals, the amplifier showed an Adjacent Channel Power Ratio (ACPR) of 31-35.5 dB when tested with a wideband code division multiple access signal of 6 dB peak-average-power ratio (PAPR) at 35.5 dBm average power. Additional 20 dB of linearity improvement was achieved after adding a lineariser.

Original languageEnglish
Article number0957
Pages (from-to)1209-1215
Number of pages7
JournalIET Microwaves, Antennas and Propagation
Issue number11
Early online date12 Jun 2020
Publication statusPublished - 9 Sept 2020
Externally publishedYes


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