A circular polarization (CP) and mode reconfigurable wideband orbital angular momentum (OAM) patch array antenna is presented. The proposed design is based on a reconfigurable feed network (RFN), a direct current (DC) bias circuit, and a 2×2 patch array. By changing the DC bias voltages of PIN didoes, the operating state of the antenna can be reconfigured between the left-hand circular-polarization (LHCP) with a mode l=+1 and right-hand circular-polarization (RHCP) with a mode l=−1, over the wide impedance bandwidth of 21%. For the two states, the measured peak gains are larger than 5.3 dBi and 5.2 dBi, and the axial ratios in half-power main beam directions are lower than 1.29 dB and 1.05 dB, respectively. Different from existing OAM antennas, the diversities of polarization, frequency, and mode as well as the circular polarization with inherently high cross-polarization discrimination, are simultaneously integrated in the proposed antenna, which serves as a good basis for improving the capacity and spectral efficiency of radio systems. In addition, the antenna features single external input port, a simple RFN occupying a small number of diodes, and compact size of 1.28×1.28×0.07 λ03 (λ0 is the free-space wavelength at centre frequency), all of which ease implementation and reduce fabrication cost. Therefore, the proposed antenna is very promising for modern high-speed and large capacity wireless communication systems.

A circularly polarized (CP) patch array antenna is proposed for ultrawideband operation by introducing weak-coupling mechanism into feeding network, feeding unit, and radiation structure, respectively. As an example, a wideband 2×2 patch array antenna consists of a weakly coupled-line four-feed network, a coupled feeding unit, and four weakly coupled sequentially rotated symmetric hexagonal patches is designed for verification. Measured results show that the proposed antenna exhibits the 10-dB impedance bandwidth of 98% (2-5.92 GHz), 3-dB axial ratio bandwidth of 96.3% (2.15-6 GHz), and 3-dB gain variation bandwidth of 82.5% (2.65-5.95 GHz) with the peak gain of 9.5 dBic at 5.15 GHz and the maximum efficiency of 88%. By the weak-coupling method, the design achieves not only the largest CP bandwidth and the symmetric radiation patterns without any beam squint over the whole band, but also the smaller volume of (1.13 × 1.13 × 0.15) λ ³ ₀ (λ ₀ is the wavelength at 4 GHz) compared with the reported patch array antennas. Therefore, the proposed CP patch array antenna is very promising for modern wireless applications such as WiFi, global navigation satellite system, and radio frequency identification systems.

A compact ultra‐wideband 90° phase shifter based on a short‐circuited stub and a weak coupled line (WCL) is proposed. The circuit configuration and derivation of S ‐parameters and phase difference are presented. The analysis result indicates that the phase deviation (PD) bandwidth can be extended to 200% by adjusting the coupling coefficient of the WCL. The fabricated phase shifter exhibits a bandwidth of 118% from 0.66 to 2.56 GHz for return loss >10 dB, insertion loss (IL) <0.5 dB and a PD of ±3.9°. Comparison shows that the proposed phase shifter not only has the most compact size with single‐layer structures but also achieves the largest bandwidth and lowest IL. The design features low‐cost, good design portability and convenient installation. Thus it is a good candidate for wideband and ultra‐wideband applications.

In this paper, a dual-band complex impedance transformer is proposed and applied to design a concurrent high-efficiency power amplifier (PA) with a widely spaced frequency. The transmission line parameters of the PA, including dual-band harmonic control network, and dual-band fundamental matching network, are obtained using the derived analytical design formula, which avoids the time-consuming numerical optimization. In addition, the proposed transformer can reduce the probability to use the transmission line with extremely high or low impedance. Simulation and measurement verified that the fabricated dual-band PA achieves the peak power-added efficiency (PAE) of 78.8% and 73.1% with the output power of 42.5 and 40.2 dBm at 0.88 and 2.4 GHz, respectively.

A methodology for designing a dual-band (DB) high-efficiency power amplifier (PA) with adjustable transmission zero (TZ) is proposed in this paper. For achieving a compact topology, the circuit for constructing the adjustable TZ is merged into the output matching network (OMN), and an open stub is shared by the harmonic control network (HCN) and the OMN. For verifying the proposed design method and structure, a prototype operating at 2.1 and 3.5 GHz is designed. The adjustability of the TZ is analyzed, and the frequency range of the TZ is between 2.3 and 3.2 GHz. For verification, the TZ is set to be 2.4 GHz and the DB PA is fabricated and measured. The result shows that the PA achieves the maximum power-added efficiency (PAE) of 68.5% and 64.8% with the output power of 41.0 and 40.4 dBm at 2.1 and 3.5 GHz, respectively. Moreover, the power gain at the TZ of 2.4 GHz is -26.9 dB, which shows a good suppression effect. Therefore, the proposed PA has a good application prospect in wireless communication systems.