Wireless power transfer (WPT) to the implantable medical devices (IMDs) often suffers from antenna radiation direction and polarization misalignments, which degrades the wireless power link efficiency. Although increasing the incident power density is able to solve the power hunger of IMDs, it poses safety issues to the human tissue. In this paper, an antenna alignment method using intermodulation is proposed to address WPT antenna misalignment in a safe way. Two-tone (2T) waveform excitation is employed to enhance the rectification as well as to generate intermodulation. The intermodulation power is fed back via a magnetic resonant coupling link. Due to the monotonic relation between the intermodulation power and the degree of antenna misalignments, the receiving antenna (in body) can be aligned with the transmitting one (out body). Such a scheme has the advantages of less harm to human tissue and less interference between the 2T waveform excitation and the magnetic resonant coupling link. The whole system is theoretically analyzed and experimentally validated.

A novel compact quintuple-mode stub-loaded resonator and ultrawideband (UWB) bandpass filter (BPF) are proposed in this letter. The proposed resonator can generate two odd modes and three even modes in the desired band. The odd-mode resonance frequencies are exclusively correlated to the modified triple-mode resonator; even-mode resonance frequencies can be flexibly controlled by the impedance-stepped open and short stub at its central plane, whereas the odd-mode ones are fixed. The open stubs in pairs at two sides of the low-impedance line are mainly applied to adjust the high resonant modes (f_m4, f_m5) into desired passband. The short stub can generate two transmission zeros near the lower and upper cutoff frequencies, leading to high rejection skirt. A quintuple-mode UWB filter is simulated, fabricated, and measured. The EM simulated and measured results are presented, and an excellent agreement is obtained.

Differential-mode and common-mode chokes (DMC and CMC) are key components of electromagnetic interference (EMI) filters. Accurate impedance knowledge of these chokes allows optimal EMI filter design to meet the conducted emission requirements. An impedance analyzer (IA) or vector network analyzer (VNA) with a fixture adapter is commonly adopted for impedance measurement of a passive component. Usually, the non-standard terminals of both DMC and CMC make them incompatible for direct mounting on commercially available fixture adapters. Relying on additional interconnects to the fixture adapters introduce inherent parasitic effects that limit measurement accuracy up to several megahertz. This paper proposes a design method of customized fixture adapters which are specifically tailored for impedance measurement of single-phase DMC and CMC. Through a systematic parasitic de-embedding process, the choke impedance can be extracted with excellent accuracy up to 120 MHz.

In this paper, a 2-stage compact wideband low-noise amplifier (LNA) monolithic microwave integrated circuit (MMIC) with multiple resistive feedback (MRFB) is presented. From the DC point of view, the proposed MRFB functions as a self-biasing structure to bias transistors in the optimal condition, improving the noise figure (NF) and linearity. Meanwhile, by employing MRFB with source degeneration and input inductor, the proposed LNA achieves wideband flat gain at the AC side. In comparison with traditional topologies, a wide bandwidth of more than 11.5 GHz with low noise figure of less than 2.5 dB can be achieved. To verify the proposed LNA structure, a chip prototype is fabricated in a 0.15- $\mu$ m GaAs E-mode pHEMT process with a compact die size of only 0.75 mm $^2$ including all the testing pads. From the measurement results, the proposed LNA circuit features a 1.0 to 12.5 GHz 3-dB working bandwidth (172% fractional bandwidth), 23.6 peak gain, 1.51 dB minimum NF, 66.7 $\pm$ 15 ps group delay, and 24.3/12.6 dBm best OIP3/OP1dB, respectively. The total DC power is around 87.5 mW from a single 2.5-V power supply.

This article presents a 3-stage millimeter-wave low-noise amplifier (LNA) monolithic microwave integrated circuit (MMIC) design for broadband applications. The proposed structure consists of cascading common-source (CS) LNA with coupled interstage feedback (CIF) paths at the second and third stages. By tuning the coupling factor and the inductance of the CIF, enhanced overall gain and extended working bandwidth can be achieved simultaneously. The proposed CIF formed by a simple on-chip edge-coupled parallel metal-lines features small size and high flexibility. To facilitate circuit design and optimization, an equivalent circuit for the proposed CIF structure is developed. Besides, to address the trade-off between impedance matching and noise performance, a noise matching strategy focusing more on higher frequencies is presented to achieve good noise performance. With the proposed techniques, an LNA prototype is demonstrated in a commercial 0.15- $\mu$ m GaAs E-mode pHEMT process. The fabricated LNA has a die size of 1.15 mm $^2$ and DC power consumption of 109 mW. The measurement results show a peak gain of 25.6 dB with a 3-dB bandwidth of 9 $\sim$ 42 GHz, the minimal noise figure (NF) of 1.91 dB, a group delay of 68.7 $\pm$ 20.5 ps, and 20.8 dBm best OIP3 under 2.0-V VDD.