With the increasing demand for channel capacity, higher data rate, and wider bandwidth for wireless communication and sensing, the focus of millimeter-wave technology development is moving toward higher frequencies. For example, the 5G standard maps the FR2 bands into 24.25–52.6 GHz to satisfy the need for higher bandwidth, while the upcoming 6G communications is considering W-band, D-band, and even G-band as the targeted operating frequencies. This evolution is driving mmWave systems toward the miniaturization of devices and components. This trend advocates the need for integrating compact passive and active components into the package, leading to complex heterogeneous integration platforms.

This article presents an automated design method for nonuniform transmission lines (NTLs) for broadband complex impedance matching. In contrast to tapers like the Klopfenstein, the presented method enables matching between complex impedances, such as required in interstage matching circuits for multistage amplifiers. A microstrip implementation of a NTL matching network is likely to require bending in circuit layout, which is not usually done for tapers. Therefore, an analytical technique is demonstrated for meandering microstrip lines with a continuously varying impedance, allowing compact integration in a circuit, particularly useful in monolithic microwave integrated circuits (MMICs).

Over the past few decades, microwave electronics have been advancing toward higher levels of miniaturization and integration, accompanied by a continual increase in operating frequencies. In this work, we review the impact of surface roughness on the microwave performance of transmission lines, investigate the underlying physical mechanisms, and address conflicting findings in existing literature. We also compare three categories of surface roughness models - topological, phenomenological, and fractal - emphasizing the role of correlation factors in phenomenological models and discussing the strengths and limitations of each approach.

An ultrabroadband Wilkinson power divider employing a single-folded inductor is presented. Unlike conventional designs with discrete inductors, this work utilizes a multisection topology with a symmetric inductor that leverages mutual inductance to significantly extend the fractional bandwidth (FBW). The divider achieves over 10-dB return loss and isolation across 2.2–82 GHz, corresponding to a 190% FBW. Plus, custom-designed metal-oxide–metal (MOM) shunt capacitors and resistors are embedded at the crossing section of the inductor paths to reduce parasitic inductance and additional loss, achieving 2.2-dB insertion loss at 80 GHz.

This letter introduces a compact 3-D stacked chip design for a four-channel RF TRx beamformer, emphasizing its innovative structure and performance attribute. The design leverages two layers of bonded Au micro-bumps and incorporates isolation piers between devices and channels, which are facilitated by the use of Au micro-bumps and GaAs through substrate via. The 3-D stacked chip is formed through the vertical stacking of a CMOS chip, GaAs carrier, and GaAs MMIC. This proposed 3-D stacked MMIC achieves a high level of integration within compact dimensions of 5.8×5.8×0.4 mm. Across 32–38 GHz, the transmitted signals reach an output power of 27 dBm, while the receiving channel demonstrates a noise figure of 3.5 dB.