Power amplifiers play a critical role in wireless communication systems, where achieving desired performance metrics such as linearity, gain, and efficiency often requires careful design trade-offs. Traditional design approaches heavily rely on load-pull techniques and designer experience for output matching network topology selection, resulting in lengthy design cycles and potentially suboptimal solutions. This paper presents an automated topology exploration methodology that eliminates the need for load-pull procedures by directly optimizing the matching network topology based on performance metrics through simulated annealing and linear optimization. The effectiveness of the proposed approach is demonstrated through a 3.5 GHz power amplifier, implemented with a single CG2H40010F GaN HEMT, which achieves a power-added efficiency (PAE) of 55% and a third-order intermodulation distortion (IMD3) of -30 dBc within a 20 MHz bandwidth at an output power of 37 dBm in board-level electromagnetic (EM) simulations, while significantly reducing the design cycle to under 3 hours. The proposed design was fabricated and experimentally characterized to validate its performance.

In this paper, a novel mixed-mode-based pattern reconfigurable epsilon-near-zero (ENZ) antenna for intelligent IoT applications is presented. To flexibly manipulate the radiated wave, a new even-odd mode radiation control method is explored. Then, an aperture-shared reconfigurable metamaterial radiator is integrated by using a switchable waveguide-like ENZ resonator and a patch structure. These designs can be used to realize size reduction and beam steering. The ENZ resonator excites an even mode field distribution and radiates an omnidirectional beam. On the contrary, the patch structure excites a broadside pattern with an odd mode distribution. By mixing the even/odd modes, the field distribution of the metamaterial radiator is controlled. Thus, its radiation pattern is reconfigured. More importantly, this metamaterial radiator can adaptively switch the radiation beam in the vertical plane by creatively introducing the reconfigurable fixed-frequency ENZ resonator. Therefore, it is fully different from the conventional Yagi-type or Huygens-form reconfigurable antennas. To verify the proposed concept, a 1-D prototype is implemented. This design can achieve seven-beam switching in the vertical plane (broadside, omni., and tilted beams) by controlling the 1-bit phase / 1-bit amplitude / 1-bit aperture switching states, making it a promising candidate for intelligent IoT applications, such as smart home, digital factory, and intelligent vehicle. This work offers a new method for low-cost pattern reconfigurable adaptive antenna designs.

In this article, a novel miniaturized quad-polarized pattern reconfigurable antenna is presented for intelligent Internet of Things (IoT) applications. Different from the conventional linearly polarized (LP) antennas, dual-polarized (dual-LP) or circularly polarized (CP) pattern reconfigurable antennas must manipulate two orthogonal E-field components simultaneously. Therefore, neither the conventional Yagi-Uda method nor the Huygens principle is adequate for this task. Here, a novel hybrid radiation control concept is introduced for the first time by combining the Yagi method with the even-odd mode technique to realize multipolarized pattern switching. Due to the reflection mechanism, the Yagi structure can achieve beam steering in the H-plane. Meanwhile, the E-plane beam can be controlled by using the even-odd mode method. In short, by introducing the hybrid control designs, the radiation patterns of the dual-polarized or CP antennas can be independently switched in the same coverage region. For validation, a metasurface-based multipolarized (dual-polarized and dual-CP) pattern reconfigurable antenna is implemented. The antenna is operated in the 5G-NR band and demonstrates a peak gain of 8.0 dBi/7.5 dBic and a beam-switching range of ±35°. This work provides a new multipolarized pattern reconfiguration method. Both the method and the design case are suitable candidates for intelligent IoT communication and perception applications.

Metamaterials are materials typically engineered with novel or artificial structures to produce electromagnetic properties that are unusual or difficult to obtain in nature. Because of their promise to provide engineerable permittivity, permeability, and index of refraction, metamaterials have drawn broad interest and have led to possible utilization in many electromagnetic applications from the microwave to optical regime, especially for the radiated-wave devices. This paper presents a detailed review upon the most recent research efforts associated with those metamaterial-based small antennas. They are discussed and classified in several different categories such as the antennas based on dispersion engineering, metaresonators, and metamaterial loadings. Some practical difficulties or limitations for the development of metamaterial-based small antennas are pointed out and the possible approaches to resolve these problems are also illustrated. A wide variety of antenna examples are included to facilitate the understanding for general readers.