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This paper presents a novel approach to achieve a high Q series negative capacitor (NC). A stepped-impedance distributed amplifier (DA) is used to achieve the negative group delay (NGD) response. The input/output (I/O) impedance of the transistor in each stage is calculated to meet the specific voltage gain coefficient ratio. By this way, the NGD phenomenon can be observed between the input and reversed output ports of DA. A major advantage of this architecture is that the gain is configurable while maintaining a fixed NGD. By properly choosing the gain coefficient, the proposed circuit can exhibit the same S 21 as an ideal NC network. From the experimental results, it can be calculated that in 1.4-1.55 GHz the NGD circuit can exhibit the desired equivalent NC value. In addition, thanks to the active structure, the circuit shows a high quality-factor (Q) performance.

In this paper, a scalable large signal GaN HEMT model including nonlinear thermal sub-circuit is described. Only two scalable parameters are needed in the I ds scalable model by introducing a simple correction factor. The established model can predict the I-V curves at different-in-size AlGaN/GaN HEMTs devices accurately. Small signal S-parameters and large signal load pull tests with on-wafer measurement is used to further validate the proposed model. Finally, the proposed scalable model is used to design a broadband high efficiency continuous class-E power amplifier (PA). Experimental results show that this class E PA is realized from 2.5-3.5 GHz with drain efficiency of 60%-70%, over 8.2 dB gain and over 35.2 dBm output by using a GaN HEMT with 1.25 mm total gate width. The results show that the proposed model is useful for high efficiency amplifier design.

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The effects of parasitic inductance of transistor on finite dc-feed inductance type class E microwave power amplifier is analyzed in this letter. We find that the frequency bandwidth can be improved by fully consideration of the output parasitic inductance of transistor. To validate the method, a GaN power amplifier by using the proposed topology is designed for demonstration purpose. Experimental results show that the amplifier is realized from 2.5 GHz to 3.5 GHz (33.3%) with measured drain efficiency larger than 60%, which show good agreement with the simulated results.

This paper presents a GaAs double-balanced mixer (DBM) applying an improved Marchand balun. This structure is achieved by adding a frequency-tuning tail capacitor to the end of the imbalanced coil. By using this tail capacitor, the size of balun is greatly reduced and the IF bandwidth is largely extended. The equivalent circuit modeling and working principle of this structure are described in this paper. The RF bandwidth of the proposed mixer is from 6 GHz to 18 GHz. The measurement result shows that the mixer's IF bandwidth ranges from DC to 8 GHz with the conversion loss less than 10 dB. Because of the good amplitude and phase performance of the proposed balun, the LO to IF isolation is also improved. The total chip area is 950 × 600 µm 2 .

This letter presents the implementation of a 6-bit true-time-delay (TTD) transmit/receive (T/R) module in X-band. Improved phase linearity is achieved by using thin film coplanar waveguide transmission lines than traditional microstrip lines or lumped LC components of the most other TTD designs. In order to meet the requirement of the large dynamic temperature range in practice, the hybrid coupler reflective phase shifters with varactor diodes are adopted in long-time-delay units as temperature compensations for thermal phase drift. Experimental results of this TTD T/R module are carried out within a bandwidth of 1.2 GHz at X-band. The gain flatness is better than 1 dB and RMSE of the phase errors is less than 7°in all the transmitting and receiving delay states.