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.

In this publication, we present the design and realization of a tunable bandpass filter utilizing a cascaded parametric amplifier architecture, configured in a way that increases the tunable bandwidth and produces gain. The filter is based on a two-stage design comprised of an upconverter and a downconverter in series with each other. The mixing is done using varactor diodes, known for high conversion gain and low-noise capabilities. The amplifiers are used to upconvert the signal to a fixed resonant idler and then downconvert the signal back to its original frequency, resulting in a narrow passband and out-of-band rejection. The prototype is configured using a hybrid MMIC-PCB approach and is demonstrated over the tunable frequency range of 1.1∼2.1GHz, with an up to 5dB gain at the passband, a noise figure of 3.8dB, and over 30dB suppression out-of-band

S. C. Chen, L. K. Yeung, S. -M. Huang and Y. E. Wang, "Design of Cascaded Parametric Mixers for Tunable Bandpass Filtering—Theory and Implementation in L-Band," in IEEE Access, vol. 13, pp. 199267-199276, 2025, doi: 10.1109/ACCESS.2025.3636080.

Performing correlation directly at the first stage of RF front-end provides secure communication and immunity to jamming through coding/decoding, which may increase the dynamic range of the receiver by providing additional isolation from the leakage of the transmitter. In this paper, two tunable, chip-scale time-domain RF correlators based on the monolithi-cally integrated time-varying transmission line (TVTL) are designed. Both frequency domain and time-domain correlation are tested. The results demonstrated the low loss, broadband and high power handling performance of the proposed chip-scale RF correlator.

Q. Wu, X. Zou, R. Zhu and Y. E. Wang, "Chip-Scale RF Correlator with Monolithically Integrated Time-Varying Transmission Line (TVTL)," 2018 IEEE/MTT-S International Microwave Symposium - IMS, Philadelphia, PA, USA, 2018, pp. 431-434, doi: 10.1109/MWSYM.2018.8439846. keywords: {Correlators;Frequency shift keying;Frequency measurement;Correlation;Radio frequency;Power transmission lines;Integrated RF correlator;Tunable filter;Spread Spectrum Communication;time-varying transmission line (TVTL)},

In this article, we present a parametric downconverter that may be used in a mixer-first receiver front end. In such a receiver, the first mixer should offer a satisfactory low-noise figure (NF), high conversion gain (CG) to suppress the noise contribution of the next stages, and high linearity to avoid receiver saturation in the presence of interferences. Parametric mixers are known to offer parametric CG for frequency upconversion with no fundamental noise penalty due to its parametric amplification nature. This work is the first experimental demonstration of a parametric downconverter that achieves positive gain and low NF. The proof-of-concept mixer with a center input frequency of 1.9 GHz and an output frequency of 1.45GHz is designed and implemented on PCB. The mixer achieves a measured peak CG of 10 dB and a 1-dB compression point of +7 dBm. Furthermore, the fabricated mixer achieves a minimum NF of 2.8 dB over its bandwidth.

M. Hedayati, L. K. Yeung, M. Panahi, X. Zou and Y. E. Wang, "Parametric Downconverter for Mixer-First Receiver Front Ends," in IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 5, pp. 2712-2721, May 2021, doi: 10.1109/TMTT.2021.3058214.

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.

In-band jamming/interference could be alleviated by performing direct correlation at the RF front-end through coding and decoding. In this paper, a chip-scale RF correlator is designed utilizing the monolithically integrated time-varying transmission line (TVTL). The proposed correlator is low-loss, has low noise figure and can handle large power. Both correlation and correlation/demodulation tests are carried out.

Q. Wu, X. Zou and Y. E. Wang, "Jamming Resilient Spread Spectrum Receiver with Time-Varying Transmission Line (TVTL) RF Correlator," 2020 IEEE Radio and Wireless Symposium (RWS), 2020, pp. 20-23, doi: 10.1109/RWS45077.2020.9050035.

The Sequentially-Switched Delay Lines (SSDL) consists of a set of RF switches and transmission lines of equal length which provides magnetless nonreciprocity with no theoretical bandwidth limit. SSDL circulator architectures are presented in this paper on a GaN MMIC. The SSDL circulators presented here demonstrate nonreciprocity from 10 MHz to 1.2 GHz with isolation between the transmitter and receiver which is greater than 20 dB for most of the measured frequency range. The insertion loss of the GaN MMIC SSDL circulator is reduced to below 3 dB from 10 MHz to 800 MHz, by using matching circuits at the gates of the switching transistors. The spurious-free operation of the SSDL circulator is also verified from 10 MHz to 1 GHz. It is also demonstrated that with passive bootstrapping, SSDL insertion loss is further reduced to about 2 dB and P1 dB performance can be significantly enhanced by an additional 10 dB. The time-modulation/switching strategy to achieve broadband magnetless nonreciprocity has the potential to be used in future STAR and full duplex communication systems.

M. Biedka, Y. Li and Y. E. Wang, "Ultra-Wide Band On-Chip Circulator With Sequentially Switched Delay Lines (SSDL)," in IEEE Access, vol. 11, pp. 69033-69045, 2023, doi: 10.1109/ACCESS.2023.3268060.