GaN microwave monolithic integrated circuit (MMIC) power amplifiers (PAs) technologies for millimeter-wave (mm-wave) applications are reviewed in this paper. In the mm-wave band, GaN PAs have achieved high-output power as much as traveling wave tube amplifiers used in satellite communications. Additionally, GaN PAs have been integrated enough to be used for 5G and Beyond-5G. In this paper, a high accuracy large-signal GaN-HEMT modeling technique including the trapping effects is introduced in mm-waves. The prototyped PAs designed with the novel modeling technique have achieved RF performance comparable to that of the state-of-the-art GaN PAs in mm-wave.

This paper reports on X-band Gallium Nitride (GaN) chipsets for cost-effective 20W transmit-receive (T/R) modules. The chipset components include a GaN-on-Si monolithic microwave integrated circuit (MMIC) driver amplifier (DA), a GaN-on-SiC high power amplifier (HPA) with GaAs matching circuits, a high-gain GaN-on-Si HPA with a GaAs output matching circuit, and a GaN-on-Si MMIC switch (SW). By utilizing either combination of the DA or single high-gain HPA, the configurations of two T/R module types can be realized. The GaN-on-Si MMIC DA demonstrates an output power of 6.4-7.4W, an associate gain of 22.3-24.6dB and a power added efficiency (PAE) of 32-36% over 9.0-11.0GHz. A GaN-on-SiC HPA with GaAs matching circuits exhibited an output power of 20-28W, associate gain of 7.8-10.7dB, and a PAE of 40-56% over 9.0-11.0GHz. The high-gain GaN-on-Si HPA with a GaAs output matching circuit exhibits an output power of 15-30W, associate gain of 27-30dB, and PAE of 26-33% over 9.0-11.0GHz. The GaN-on-Si MMIC switch demonstrates insertion losses of 1.1-1.3dB and isolation of 10.1-14.7dB over 8.0-11.5GHz. By employing cost-effective circuit configurations, the costs of these chipsets are estimated to be about half that of conventional chipsets.

High power amplifier technologies for base transceiver stations (BTSs) for the 5th generation (5G) mobile communication systems and so-called beyond 5G (B5G) systems are reviewed. For sub-6, which is categorized into frequency range 1 (FR1) in 5G, wideband Doherty amplifiers are introduced, and a multi-band load modulation amplifier, an envelope tracking amplifier, and a digital power amplifier for B5G are explained. For millimeter wave 5G, which is categorized into frequency range 2 (FR2), GaAs and GaN MMICs operating at around 28GHz are introduced. Finally, future prospect for THz GaN devices is described.

A methodology for obtaining semi-custom high-power amplifiers (HPAs) is described. The semi-custom concept pertains to the notion that a selectable output power is attainable by replacing only transistors. To compensate for the mismatch loss, a new output matching network that can be easily tuned by wiring is proposed. Design equations were derived to determine the circuit parameters and specify the bandwidth limitations. To verify this methodology, a semi-custom HPA with GaN HEMTs was fabricated in the S-band. A selectable output power from 240 to 150 W was successfully achieved while maintaining a PAE of over 50% in a 19% relative bandwidth.

It is known that in the selected mapping (SLM) scheme for orthogonal frequency division multiplexing (OFDM), correlation (CORR) metric outperforms the peak-to-average power ratio (PAPR) metric in terms of bit error rate (BER) performance. It is also well known that four times oversampling is used for estimating the PAPR performance of continuous OFDM signal. In this paper, the oversampling effect of OFDM signal is analyzed when CORR metric is used for the SLM scheme in the presence of nonlinear high power amplifier. An analysis based on the correlation coefficients of the oversampled OFDM signals shows that CORR metric of two times oversampling in the SLM scheme is good enough to achieve the same BER performance as four times and 16 times oversampling cases. Simulation results confirm that for the SLM scheme using CORR metric, the BER performance for two times oversampling case is almost the same as that for four and 16 times oversampling cases.

Compact and planar active integrated antenna arrays with a high power multi-stage amplifier were developed with effective heat sink mechanism. By attaching an aluminum plate to the backside of the creased amplifier circuit board, effective cooling can be achieved. The nonlinear behavior of the amplifier agrees well with the simulation based on the Angelov model. The high power amplifier circuit consisted of the three-stage amplifier and operated with an output power of 4 W per each element at 5.8 GHz. The 32-element active integrated antenna array stably operated with the output power of 120 W under the effective heat sink design. With a weight of 4 kg, the weight-to-output power ratio and the volume-to-output power ratio of the antenna array are 33.3 g/W and 54.5 cm3/W, respectively. Wireless power transmission was also successfully demonstrated.

A Ka-band 0.5 W monolithic amplifier using a novel tandem FET has been developed. The tandem FET consists of two FET cells connected in series through a short transmission line. The features of the tandem FET are high gain, flat gain response and miniaturized size. The tandem FET is very useful for obtaining high gain, high power amplifiers operating in millimeter-wave region where combining and matching circuits' losses are significantly large. By combining four tandem FETs, a linear gain of 4.5 dB, a 1 dB compressed power of 26.3 dBm and a saturated output power of 27.3 dBm (0.54 W) have been achieved at 37 GHz. The size of the amplifier is 1.73.20.03t mm.