Power amplifier (PA) models, such as the neural network (NN) models and the multilayer NN models, have problems with high complexity. In this article, we first propose a novel behavior model for wideband PAs, using a real-valued time-delay convolutional NN (RVTDCNN). The input data of the model is sorted and arranged as a graph composed of the in-phase and quadrature ( $I/Q$ ) components and envelope-dependent terms of current and past signals. Then, we created a predesigned filter using the convolutional layer to extract the basis functions required for the PA forward or reverse modeling. Finally, the generated rich basis functions are input into a simple, fully connected layer to build the model. Due to the weight sharing characteristics of the convolutional model’s structure, the strong memory effect does not lead to a significant increase in the complexity of the model. Meanwhile, the extraction effect of the predesigned filter also reduces the training complexity of the model. The experimental results show that the performance of the RVTDCNN model is almost the same as the NN models and the multilayer NN models. Meanwhile, compared with the abovementioned models, the coefficient number and computational complexity of the RVTDCNN model are significantly reduced. This advantage is noticeable when the memory effects of the PA are increased by using wider signal bandwidths.

In this article, an artificial neural network (ANN)-based large-signal model (LSM) of AlGaN/GaN high electron mobility transistors (HEMTs) with accurate buffer-related trapping effects characterization and modeling is proposed. A hybrid small-signal parameter-extraction method for AlGaN/GaN HEMTs is used to acquire the parasitic parameters. To simplify the modeling procedure of the drain-source current Ids, an ANN-based model associated with the empirical equations taking into account the trapping effects, self-heating effects, and breakdown issue is developed. The low-frequency dispersions related to the buffer-related trapping effects have been well modeled by using a new empirical equation, which has been verified by small-signal S-parameters. Also, a new thermal factor KT and an improved Shockley diode equation are given in the proposed model as well. The developed LSM has been fully verified by a 2 × 100 μm AlGaN/GaN HEMT with the pulsed I-V, small-signal S-parameters, power sweep, and load-pull measurements.

A compact Ka-band monopulse Cassegrain antenna based on the reflectarray elements is presented in this letter. The proposed antenna consists of a main-reflectarray, a sub-reflectarray, a SIW comparator and a monopulse feed to achieve good sum-difference characteristics. Compared with traditional monopulse Cassegrain antenna, the total length of the proposed antenna is shrinked to 67.85%. The results of measurement agree with that of simulation very well. The measured SUM beam gain of the proposed antenna is 29.4 dBi by eliminating the loss of Ka-band comparator, the 3-dB beamwidth is 3.85°, the first sidelobe level is under -12 dB, the cross-polarization level is better than -20 dB, and the gain ratios between the SUM and DIFF are about 3 dB and 5 dB in azimuth and elevation plane, respectively. The measured results show that the proposed antenna is a good candidate for the low-cost multi-mode tracking system with limited space, especially for that working at high frequency.

This article presents a generalized theory and new design methodology for reverse-load-modulated dual-branch (RMDB) power amplifiers (PAs), which uses a current-biased transistor in the main branch to realize optimal load modulation without using the impedance transformers at the output of the PAs. Consequently, this topology offers a proper load modulation mechanism over a wider frequency bandwidth. Besides, smaller output matching network (OMN) footprint and lower loss are suitable features for monolithic microwave integrated circuit (MMIC) designs. The proposed theory can be applied for symmetrical and asymmetrical designs to realize different output power back-off (OPBO) ranges. The theory and design methodology were used to design the first MMIC RMDB PA. The broad bandwidth of this design (2.6-3.8 GHz) allows it to cover multiple bands in 4th-generation (4G) Long Term Evolution (LTE) and 5th-generation (5G) New Radio (NR) standards. Under continuous wave (CW) excitation, the experimental results show a drain efficiency (DE) higher than 58% at peak output power (POP) and 37% at 9 dB OPBO, over the whole frequency band.

An improved ferrite nonlinear (NL) loss theory is developed for polycrystal ferrite microstrip limiters upon the high-power microwave (HPM) environment. The NL critical threshold equation and equivalent loss model are derived from the field coupling mechanism between spin waves and microwave pulse. Thus, the equivalent NL loss behavior with the microwave waveform parameters (pulse duration and power) is implanted in the ferrite limiter model to perform the numerical simulation through the commercial electromagnetic tool. The measured limiting data at pulse duration with 60, 80, 100, and 200 ns are in good agreement with the equivalent simulation results.