A bandwidth optimization model for a novel equivalent 90° transmission-line section is proposed in this paper. Furthermore, the structure of 3-D compact 3-dB branch-line directional coupler and its equivalent-circuit model are presented. They can achieve both excellent isolations between each branch and high-density integration by using equivalent 90° transmission-line sections and coaxial through-silicon via technology in 3-D integrated circuits. Finally, a 3-D coupler is designed with the center frequency of 100 GHz, as well as the bandwidth and size reach 20 GHz and 174 × 236.9 × 208.7 μm ³ , respectively. The results of the 3-D full-wave field solver High-Frequency Structure Simulator and the proposed model are well matched, showing that the proposed model can be used to quickly evaluate the electrical performance of the 3-D coupler before manufacture, thus effectively promoting the design efficiency and quality.

In this brief, a substrate integrated waveguide (SIW) bandpass filter (BPF) with wide out-of-band rejection is researched and fabricated with the center frequency of 45.8 GHz and 3-dB FBW of 2.18%. Due to the exploitation of electronic excitation, higher order modes mismatch and orthogonal transmission, the simulated and measured out-of-band rejection is better than 20 dB with frequencies up to 7.6f0 and 2.4f0, respectively. Diplexer with stopband suppression better than 30 dB up to 1.87f0 is proposed based on the theory of the proposed filter. Dual-mode resonator operating with TE301 mode (43.8 GHz) and TE103 mode (45.8 GHz) has been designed to provide the transition of two filter channels. High isolation better than 27 dB over the whole band can be achieved. Transmission zeros (TZs) are generated by spurious resonances under electrical excitation, resulting in high selectively of the passbands. Good agreements between simulations and measurements can be observed.

This letter presents a novel $W$ -band compact wideband triple-mode bandpass filter (BPF) using multistub resonator. The resonator is loaded both by T-shaped stepped impedance stub (TSIS) and symmetrical open stub pair (SOSP) to generate three resonant modes and two transmission zeros for improving the bandwidth and enhancing the stopband rejection ability. Moreover, the characteristic admittance ratio has the ability to flexibly adjust the bandwidth and the transmission zero. The proposed BPF is fabricated in 65-nm CMOS technology with a core area of 444 $\times$ 192 $\mu$ m $^{2}$ . The measurement results show that the 3-dB bandwidth is 30.7 GHz at the center frequency of 94 GHz, the minimum insertion loss is 4.3 dB, and the stopband rejection is better than 20 dB.

Closed-form expressions for the optimized number and size of repeaters in multi-walled carbon nanotube (MWCNT) interconnects are presented. The contact resistance and inductive effects are taken into account. It is found that the propagation delay of MWCNT interconnects can be reduced effectively by inserting repeaters. However, the contact resistance has a significant influence on the optimized number and size of repeaters. Moreover, it is found that both the optimal number of repeaters and the minimum propagation delay are kept almost unchanged with the variation of carbon nanotube (CNT) kinetic inductance. The optimal number of repeaters in the MWCNT interconnect is much smaller than that in its Cu counterpart, thus saving chip area and power consumption.

A wideband, compact, digitally-assisted variable gain phase shifter (VGPS) in a 65-nm CMOS process is presented for Ka-band applications. A digitally-assisted variable gain amplifier (VGA) architecture with a wide gain-control dynamic range and minimal input/output impedance variations is proposed by combining bias and digital control. Using only a one-stage digitally-assisted VGA, the VGPS achieves orthogonal phase and gain control with low RMS gain and phase errors in a compact size. Theoretical analysis is explored to provide physical insight into the working mechanism of the VGPS. In this design, the proposed VGPS leverages 3 bits for 18-dB gain tuning and 4 bits for 360° phase control. Measurements show that the VGPS exhibits an average peak gain of 0.6 dB at 28.4 GHz with a 3-dB bandwidth from 25.4 to 35.6 GHz. The measured RMS gain and phase errors is below 0.37 dB and 3°, respectively, from 25.4 to 34 GHz. It is implemented in a 65-nm CMOS process with the core area of 0.19 mm2 excluding the pads.

This paper presents a novel compact wideband quadruple-mode bandpass filter (BPF) with four resonant modes and five transmission zeros (TZs). Two T-shaped stepped impedance stub loaded resonators are coupled in parallel to the input and output feed lines to form the entire BPF. To provide a wideband and outstanding rejection in upper stopband, the two TZs are introduced by the stepped impedance stub as well as the designed coupling capacitor, and the two inherent TZs produced by the coupling between the resonators and feed lines are used and carefully tuned. The proposed BPF is fabricated in 65 nm CMOS technology with a core area of 0.072 mm ² (7.1×10 ^-3 λ ₀ ² ). The measurement results show that the 3-dB bandwidth is 24.2 GHz at the center frequency of 94 GHz as well as the minimum insertion loss is 4.6 dB. Meanwhile, the stopband extends to 170 GHz with a stopband rejection above 25 dB.