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In this article, an omnidirectional dual-polarized antenna with synergetic electromagnetic and aerodynamic properties is propounded for high-speed diversity systems. The propounded antenna comprises a probe-fed cavity for horizontally polarized radiation and a microstrip-fed slot for vertical polarization. Double-layer metasurfaces are properly designed as artificial magnetic conductor boundaries with direct metal-mountable onboard installation and compact sizes. An attached wedge-shaped block is utilized for windage reduction in hydrodynamics. The propounded antenna is fabricated for design verification, and the experimental results agree well with the simulated ones. For vertical polarization, the operating bandwidth is in the range of 2.37–2.55 GHz, and the realized gain variation in the azimuthal radiation pattern is 3.67 decibels (dB). While an impedance bandwidth in the range of 2.45–2.47 GHz and a gain variation of 3.71 dB are also achieved for the horizontal polarization. A port isolation more than 33 dB is obtained in a compact volume of 0.247λ0 × 0.345λ0 × 0.074λ0, where λ0 represents the wavelength in vacuum at the center frequency, wherein the wedge-shaped block is included. The propounded diversity antenna has electromagnetic and aerodynamic merits, and exhibits an excellent potential for high-speed onboard communication.

This letter presents a high precision wideband active vector-modulating phase shifter with high dynamic range gain control ability. Compared with conventional switching-filter phase shifter and vector-modulation phase shifter, this Δ -Σ modulated vector phase shifter can provide quasi-continuous phase and gain control capability. According to the experimental results, the dynamic range of gain control is greater than 35.5 dB. The output reflection is lower than -10 dB through the 18-50-GHz band, and the input reflection is lower than -10 dB from 18 to 45 GHz. The phase shifter occupies 700 μm x 900 μm on 0.13-μm SiGe bipolar complementary metal-oxide-semiconductor (BiCMOS) technology, and the core size is only 400 μm x 500 μm. After digital calibration, the proposed phase shifter has achieved the highest phase and gain control precision compared with the state-of-the-art digital controlled phase shifters.

This paper presents a broadband THz power amplifier (PA) operating close to the maximum oscillation frequency (fmax) with proposed power combining and stagger-tuned gain boosting techniques. A compact broadband power combiner based on the compensated three-conductor transmission line (T-line) balun is proposed to simultaneously achieve broadband matching and power combining. A 4-stage stagger-tuned gain boosting amplifier operating closely to fmax is investigated to achieve a flattened power gain. Based on the proposed techniques, a broadband 300-GHz PA is implemented in a 130-nm SiGe BiCMOS process with ft/fmax = 350/450 GHz. It exhibits a peak gain of 15 dB and 3-dB bandwidth of 67 GHz (247314 GHz) with 2.5V supply voltage. At 290 GHz, a 5-dBm maximum output power POUT-MAX was measured with a 1-dB compressed output power OP-1dB of 3.3 dBm and a maximum PAE of 1.19%. The measured output power POUT-MAX and OP-1dB of the PA are 2.25 dBm and 0.63.3 over 250300 GHz, respectively. To the best of our knowledge, this PA achieves the highest operational frequency and widest bandwidth compared with other works in SiGe/CMOS process operating closely to fmax.

In this article, a fully integrated dual-band gallium nitride (GaN) Doherty power amplifier (DPA) based on multi-resonant circuits (MRCs) is presented. A lumped T-type network in combination with the output capacitances of the main and auxiliary transistors is able to realize the quarter-wavelength transformer (QWT) in DPA, and its component values are totally decided by the operating frequency, given a certain characteristic impedance. MRCs are proposed to exhibit the required component values at two different frequencies. By replacing each component in the T-type network with an MRC, a dual-band QWT can be achieved. An integrated dual-band DPA is implemented in a commercial 0.25-μm GaN-HEMT process to validate the proposed method. The fabricated DPA shows a saturated output power of 43.8-44.7/44.4-44.8 dBm, a 6-dB back-off drain efficiency (DE) of 41%-46%/41.5%-47%, and a saturated DE of 49%-52%/56%-59% in 3.35-3.6/4.8-5.2 GHz, with a compact size of 2.8 x 3.5 mm². Applying a 100-MHz OFDM signal with a 7.8-dB peak-to-average power ratio (PAPR), an average efficiency of 37%/40% and an average power of 37/37 dBm are measured at 3.5/5.0 GHz, and the adjacent channel power ratio (ACPR) is better than -49 dBc after digital predistortion (DPD). To the best of our knowledge, the proposed DPA is the first demonstration of fully integrated dual-band GaN DPAs.

Conventional digital predistortion (DPD) techniques are facing the challenge of complexity in the fifth generation (5G) and beyond concurrent dual-band terminal transmitters. This article proposes novel low-complexity behavior models for the DPD of terminal power amplifiers (PAs). Derived from the conventional memory polynomial (MP) model, the new models utilize magnitude-selective affine (MSA) functions as nonlinear basis functions to greatly decrease the model complexity. The proposed paralleled envelope indexed 2-D MSA (PI-2-D-MSA) model and combined envelope indexed 2-D MSA (CI-2-D-MSA) model take both the in-band intermodulation and cross-band modulation into account and can well compensate for nonlinear distortion in dual-band terminal PAs. Moreover, the proposed models are extended to nonuniform sampling rate (NSR) scenarios, where the aliasing effect for the low sampling rate band is analyzed. Simulations and experimental measurements under the uniform sampling rate and the NSR scenarios were carried out on a 1.7–2.8-GHz wideband Doherty PA and a 4.4–5.0-GHz class-AB terminal PA and demonstrated the linearization performances of the proposed models. The total numbers of floating-point operations (FLOPs) of the PI-2-D-MSA and the CI-2-D-MSA models were 11% and 8% of that of the prior 2-D-MP model, respectively. Even though their linearization accuracy deteriorated, the relaxed linearization standard for terminal transmitters can still be achieved.

In this article, a novel broadband millimeter-wave (mm-wave) front end (FE) based on the asymmetric switch network structure is proposed for multistandard fifth-generation (5G) applications. The asymmetric switch network consists of a bidirectional impedance transformation network and a T-type topology single-pole single-throw (SPST) switch. In the TX-mode, the bidirectional impedance transformation network serves as an output matching network to achieve a continuous-mode Class-F−1 power amplifier (PA) to expand the bandwidth. In the RX-mode, the OFF impedance of the PA can be transformed into a high-impedance region by the bidirectional impedance transformation network. Based on the proposed structure, a broadband mm-wave front end is implemented in the 0.13- $\mu \text{m}$ SiGe BiCMOS process, which occupies $906\,\,\mu \text{m}\,\,\times 997\,\,\mu \text{m}$ including pads. In the TX-mode, the −1-dB $P_{\mathrm {sat}}$ bandwidth of the FE covers 21–44 GHz with the maximum output power of 18.1–19 dBm and the peak power added efficiency (PAE) of 20.2%–26.8%. In the RX-mode, the FE achieves an 84.6% and −3-dB small-signal gain fractional bandwidth from 20.2 to 49.8 GHz with 38-mW power consumption. It achieves a measured noise figure (NF) of 7.62–11.64 dB over the frequency range of 24–48 GHz. To the best of our knowledge, this is the first FE that covers all the present 5G mm-wave bands without reconfiguration.

In this brief, a 24–29.5 GHz millimeter-wave (mm-wave) voltage-combined Doherty power amplifier (DPA) based on compact low-loss combiner is proposed for the fifth-generation (5G) applications. By maximizing the use of parasitic parameters in the circuit, a compact low-loss combiner is proposed to achieve the required impedance transformation with only one additional series capacitor. A detailed design procedure is also introduced in the brief. Based on the proposed combiner, a fully integrated Doherty PA is implemented in 0.13- ${\mu }\text{m}$ SiGe BiCMOS process with a core area of only 0.29 mm2. The DPA achieves a 27% −3-dB small-signal gain fractional bandwidth and a 15.9 dB small signal gain at the center frequency of 27 GHz. The −1-dB Psat bandwidth covers 24–29.5 GHz (20% fractional bandwidth), and the maximum output power is 20.8 dBm ± 0.4 dB. From 24 to 29.5 GHz, the designed DPA provides 23.2% to 28.4% power-added efficiency (PAE) at saturated output power, and 18.3% to 21.9% PAE at 6 dB of output power back-off (OPBO).

This article presents a fully integrated distributed efficient power amplifier (DEPA) for fifth-generation (5G) massive multiple-input multiple-output (MIMO) applications. In conventional DEPA, an individual input matching network (IMN), power splitter, and phase compensation line are used for each auxiliary power amplifier (PA) unit, resulting in a large overall size. To facilitate integration, an energy-efficient and compact DEPA with modified input matching and power splitting network is proposed, where a distributed input matching network (DIMN) is used for the auxiliary PA. A broadband input matching, reasonable power splitting, and phase alignment can be achieved simultaneously by adjusting the dimensions of gate transmission lines (TLs) between different auxiliary PA units. An integrated DEPA is implemented in a commercial 0.25- $\mu \text{m}$ GaN-HEMT process to validate the proposed architecture. The fabricated DEPA shows a saturated output power of 40.4–41.7 dBm, an 8-dB back-off drain efficiency (DE) of 35%–50%, and a saturated DE of 46%–56% from 3.2 to 5.2 GHz, with a compact size of $3.4\times3.0$ mm2. Applying a 100-MHz orthogonal frequency division multiplexing (OFDM) signal with a 7.8-dB peak-to-average power ratio (PAPR), an average efficiency of 35.7%–47% is measured over the entire bandwidth, and the adjacent channel power ratio (ACPR) is better than −46 dBc after digital predistortion (DPD). To the best of our knowledge, the proposed DEPA demonstrates the widest bandwidth among all reported fully integrated back-off efficient PAs without using digital techniques or reconfiguration.

High-frequency (HF) transmitter implemented with the multioctave power amplifier (PA) is faced with the problem of high-order harmonics owing to the nonlinearity of the PA. In this letter, a complexity-reduced harmonic-cancellation digital predistortion (CR-HC-DPD) is proposed and a narrow pulse sampling (NPS) method is adopted for model identification. Compared with the previous HC-DPD scheme, the proposed CR-HC-DPD approach greatly decreases the number of sampling points used for modeling and, in turn, reduces the computational complexity. Measurement results on a class-AB GaN PA with a 600-Hz two-tone signal demonstrated that the CR-HC-DPD scheme canceled all the harmonics for being below −60 dBc with less than 5% complexity compared with the HC-DPD scheme.

High frequency (HF) transmitter implemented with the multioctave broadband power amplifier (PA) enables long-distance communication and has strong survivability. However, it is faced with the problem of harmonics because of the nonlinearity of the PA. We first consider canceling the harmonics using a harmonic cancellation digital predistortion (HC-DPD) technique, instead of lossy and bulky analog filter banks. A uniform complex-valued Hilbert transform-based polynomial (HTBP) function is proposed for the modeling of the harmonics, as well as the fundamental component in the real-valued input and output signals. In order to validate this idea, detailed experiments were performed for carrier frequencies located at 5 and 10 MHz, respectively. After the proposed HC-DPD, the harmonics were all canceled to satisfy the linearization requirements. In particular, the improvement of the second harmonic is more than 40 dB, which is nearly 20 dB better than that of the memoryless polynomial (MLP) model. Furthermore, the experimental results demonstrate that the proposed technique is scalable, in which the model coefficients extracted at a specific power level, signal bandwidth, and carrier frequency can be extended to other scenarios. Both the second and third harmonics were canceled for being below −45 dBc after the HC-DPD.

This article presents a pattern-reconfigurable saber-like antenna with low wind drag for the onboard communication application, under the requirement of upper hemispherical coverage. The compact antenna mainly consists of a segmented loop and a $\Pi $ -shaped polygon, which are closely integrated for compact size. By controlling the OFF/ON states of a p-i-n diode embedded in the segmented loop, the proposed antenna can be operated at dipole/monopole modes. An upper hemispherical coverage area can be achieved since broadside and omnidirectional patterns are obtained at dipole and monopole modes, respectively. To validate the design strategy, a prototype was fabricated and tested. A good agreement between the simulated and measured results is achieved. The measured −8 dB reflection coefficient common bandwidth of two modes is from 2.16 to 2.63 GHz with the relative bandwidth of 19.6% while keeping a smaller size of $30.5\times 32.5\times 0.6$ mm3 ( $0.24\,\,\lambda _{0} \times 0.26 \lambda _{0}\times 0.005 \lambda _{0}$ , $\lambda _{0}$ is the free-space wavelength at the center frequency). We portend that the proposed design scheme, with merits of low wind drag, metal ground compatibility, and upper hemispherical coverage, has the potential for airborne application.

In this letter, a broadband millimeter-wave (mm-wave) continuous-mode Class-F power amplifier (PA) based on the deembedded transistor model is proposed for the fifth-generation (5G) applications. To design the output matching network at the intrinsic current-generator plane, an $S$ -parameter fitting method is proposed to extract the parasitic parameters of nonpackaged transistors over a wide frequency range. The PA is implemented in the 0.13- $\mu \text{m}$ SiGe BiCMOS process, which occupies only 0.42 mm2. By controlling the even and odd harmonics impedance, the PA achieves a 78.2% −3-dB small-signal gain fractional bandwidth from 21.1 to 48.2 GHz. The −1-dB $P_{\mathrm {sat}}$ bandwidth covers 21–43 GHz (68.8% fractional bandwidth) and the saturated output powers are 17.2–18.1 dBm. Meanwhile, the designed PA provides a 24.1%–32.1% peak power-added efficiency (PAE) over the band.

A positive feedback gain-enhanced technique for power amplifiers has been introduced in this Letter. With the proposed circuit design method for optimal inductive feedback, a 180 GHz high-gain single-stage cascode power amplifier in a 130 nm SiGe process is implemented. The measurement results show a power gain of 10 dB and 20 GHz bandwidth with 110 mW dc power are achieved, and 6.5 dBm of output power referred to P 1dB and 3.5% collector efficiency are attained. The chip area of the power amplifier is only 0.50 × 0.48 mm2.

This article presents a wideband orthogonal-mode dual-antenna pair with a shared radiator for fifth-generation (5G) multiple-input multiple-output (MIMO) metal-rimmed smartphones. The wideband decoupling property of the dual-antenna pair is realized by the combination of the orthogonal monopole/dipole modes in the lower band and the orthogonal slot/open-slot modes in the higher band. With the orthogonal-mode design scheme, the dual-antenna pair shows a wide impedance bandwidth of 3.3–5.0 GHz and a high isolation of more than 21.0 dB across the entire band without using any external decoupling structures. By arranging four such dual-antenna pairs at two side edges of the smartphone, an $8 \times 8$ MIMO system is fulfilled. Both the simulation and measurement results show that the proposed $8 \times 8$ MIMO system could offer an isolation of better than 12.0 dB and an envelope correlation coefficient of lower than 0.11 between all ports. The measured average antenna efficiencies are 74.7% and 57.8% for the two antenna elements of the dual-antenna pair. We portend that the proposed design scheme, with merits of shared radiator, wide bandwidth, and metal rim compatibility, has the potential for the application of future 5G smartphones.