This letter proposes an X-band power converter for high-speed bit-stream modulation. The converter consists of a power amplifier (PA) with pulsed load modulation, which performs highly efficient dc-ac conversion for a wide range of output powers, and a switching rectifier. Power conversion was performed in the X-band, and the potential for broad bandwidth and profile minimization was demonstrated. The PA was fabricated using a discrete gallium-nitride HEMT device and it delivered 39-dBm RF output power with 57.4% drain efficiency (DE) at 9.2 GHz under class-B conditions. At 6-dB output power back-off, 38.2% DE was measured for a 4 Gb/s data rate. The switching rectifier is designed using a class-B PA strategy to demonstrate the proposed concept. The ac-dc conversion efficiency was measured to be 44.6%, and 3.05-W dc power was delivered.

Y. Song and Y. E. Wang, " X -band DC–DC Power Converter for High-Speed Bit-Stream Modulation," in IEEE Microwave and Wireless Components Letters, vol. 28, no. 1, pp. 46-48, Jan. 2018, doi: 10.1109/LMWC.2017.2779815.

Bitstream transmitters based on bandpass or envelope delta-sigma modulation promise high power efficiency for broadband communications with nonconstant-envelope modulations, but at the price of elevated quantization noise. An active noise filtering technique is proposed in this paper to address the quantization noise issue of such transmitters. The essential concept of active noise cancellation is to utilize multiple power amplifiers (PAs) with identical or similar transfer characteristics fed with the same input, but with different time delays. The difference in time delay determines whether the outputs of the PAs are combined in phase or out of phase at a certain frequency, which forms the passband or the stopband of the active filter. The active noise filtering technique can potentially replace the external high-Q passive bandpass filter typically needed for such transmitters.

Y. Song, R. Zhu and Y. E. Wang, "Active Noise Filtering for X -Band GaN Transmitters With Bitstream Modulations," in IEEE Transactions on Microwave Theory and Techniques, vol. 65, no. 4, pp. 1372-1380, April 2017, doi: 10.1109/TMTT.2016.2638813.

Mixers are frequency conversion devices that are widely used in radio applications. This article presents an in-depth theoretical study on the parametric mixing and amplification performance of the time-varying transmission lines (TVTLs) and utilizes the concept to design two TVTL parametric mixers on a commercially available InGaP HBT process. Unlike traditional passive mixers, these parametric mixers can provide a mild conversion gain and achieve a relatively low-noise figure. For the traveling-wave TVTL, the theory of the parametric mixing with the single-sideband condition is reviewed and compared with the double-sideband mixing case. The noise performance analysis shows that the noise figure of the TVTL can be made arbitrarily low to the quantum noise limit through the input reactive termination.

X. Zou, Q. Wu and Y. E. Wang, "Monolithically Integrated Parametric Mixers With Time-Varying Transmission Lines (TVTLs)," in IEEE Transactions on Microwave Theory and Techniques, vol. 68, no. 10, pp. 4479-4490, Oct. 2020, doi: 10.1109/TMTT.2020.3011116.