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In this article, a novel direct analytical and exact synthesis for the multi‐section transformers with arbitrary real‐to‐real transforming ratio is proposed. Compared with the conventional small reflection theory, the proposed one features an exact solution and design flexibility. Based on the new method, the direct solution for a three‐section maximally flat transformer is presented for the first time. And the Remez iteration method is introduced to obtain the multiband Chebyshev response transformers. For validation, a tri‐band Chebyshev impedance transformer was designed and fabricated. The simulated and measured results agree with each other. [ABSTRACT FROM AUTHOR]

A novel method for a single‐feed circularly polarized (CP) loop antenna with both broad impedance bandwidth and axial ratio (AR) bandwidth is presented based on characteristic mode analysis (CMA). The circular polarization characteristics are generated by exciting two orthogonal degenerate modes (DMs) via single feeding simultaneously. The 90° phase difference is achieved by loading the lumped inductors or capacitors. The wide bandwidth characteristics are generated by splitting a pair of DMs. Consequently, the two overlapping resonance points are split. The positions of feeding and loadings are determined with the aid of CMA. Compared with conventional methods, the presented method can simplify the feeding structure and provided a compact antenna. Based on this method, a loop antenna with two inductors is demonstrated for circular polarization application. The measured results show an impedance bandwidth of 47% and 3 dB AR bandwidth of 8.3% at 2.4 GHz wireless local area network (WLAN) bands. Both the simulated and measured results agree well. [ABSTRACT FROM AUTHOR]

A power amplifier with bandwidth expansion and linearity enhancement in 130 nm complementary metal‐oxide‐semiconductor (CMOS) process is presented. A LC connected dual‐resonant network is proposed to achieve good broadband performance and high out‐band rejection capability simultaneously. Furthermore, the advanced multiple‐gated transistor technique is employed to cancel out odd‐order intermodulation and harmonic distortions. The PA is implemented in 130 nm CMOS process with an area of 1.17 mm × 0.92 mm. Measurement results demonstrate that the PA exhibits a peak power gain of 8 dB with a relative bandwidth of 38% while maintaining a low reflection coefficient of −23.2 dB, maximum saturation output power of 15.6 dBm, maximum OP1dB and OIP3 of 14.3 dBm and 19 dBm, and a peak power added efficiency of 21.3%, respectively. In addition, an out‐band rejection of 20 dB and 23.2 dB at 6.1 GHz and 14 GHz are measured. [ABSTRACT FROM AUTHOR]

The multimode orbital angular momentum (OAM) radio waves can be used to multiplex multiple transmission channels to increase the capacity of communication system without adding additional bandwidth. However, the divergence of the OAM beams and beam inconsistency escalate by increasing OAM mode number. Moreover, the worse sidelobe level (SLL) always appears along with a better convergent beam. In this article, the fruit fly optimization algorithm (FOA) is proposed to suppress the SLL in multimode OAM scenario. Based on the concentric circular array antenna (CCAA), the feeding amplitudes and the radii of the array are synthesized simultaneously to realize less than −30 dB SLL of the multimode OAM patterns. When the main lobes with different OAM modes steered to a uniform azimuth of θ = 0°, the SLLs of these OAM modes are also suppressed to less than −21 dB. The advantages of FOA used in the OAM pattern synthesis are verified by comparing it with the genetic algorithm (GA). The FOA‐based synthesis has a simpler implementation flow diagram which reduces the time of synthesis to 39.5% of GA. [ABSTRACT FROM AUTHOR]