To quantify the effect of air gap on the dielectric constant measurement of low-loss materials, this letter presents the first quantitative study of the effect of five different shapes on the dielectric constant measurement using three low-loss materials as examples. The experimental results show that if low-loss materials’ dielectric constant measurement error is controlled within 5%, the air gap cannot exceed 4%. The results of this letter can provide effective guidance and reference for improving the measurement accuracy of electromagnetic parameters of low-loss materials.

This letter reports a new theoretical analysis of third-order intermodulation (IM3) reduction in nonlinear communication amplifiers by signal injection. On the basis of well-known Volterra series analysis, we put forward a general model that can analyze both the qualitative and quantitative effects of injected signal parameters on output IM3s, which previous literatures failed to achieve. Our theory can directly calculate the optimal amplitude and phase of single injected signal and points out the duality for some dual-signal injections which can help reduce their parameter scanning complexity from 4-D to 2-D. These conclusions are in good agreement with the simulation of two traveling wave tube (TWT) amplifiers by 3-D-FDTD-PIC code and CST and MTSS. Our work proposes an original analysis about how to adjust injected external signals to obtain best IM3 cancellation in communication systems, and boosts the research efficiency for new signal injection techniques from a novel perspective.

In this letter, we design a magnetically coupled resonant wireless power transfer (MCR-WPT) system on the conformal cylindrical surface based on the flexible printed circuit (FPC) coils. The coil has the advantages of small size, lightweight, and high bendability. We combine mathematics and simulations to explore the relationship between the self-inductance/mutual inductance of the flexible coil and the bending radius of the conformal cylindrical surface. Both theoretical and simulation results show that as the bending radius decreases linearly, the self-inductance and mutual inductance of the coil also decrease nonlinearly. In addition, as the bending radius decreases, the transmission efficiency (TE) decreases, and the resonant frequency shifts to a higher range. Finally, measured and simulated results agree well, which further validates the conclusions.

This letter presents an accurate magnetic coupling coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> ) model for a through-silicon via (TSV)-based 3-D transformer. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> factor can be precisely derived from the self-inductance and mutual inductance, which are calculated by various analytical formulas based on physical geometries. The results of this model correspond well with those of Q3D extractor and high-frequency structural simulator (HFSS), with maximum errors of 3.8% and 4.4%, respectively. An equivalent circuit model of a TSV-based transformer is used for further verification. The S-parameters obtained by the circuit model match well with the measurements.

In a frequency-domain chipless RFID system, the backscattered signal from a tag is directly obtained in the frequency domain over limited bandwidth. However, to reduce the parasitic reflections, it is crucial to obtain the backscattered signal in the time domain. This letter proposes a precise quasi-analytic method, known as the model-based vector fitting (VF) technique, to provide the closed-form equation of the backscattered response in the time domain. The proposed method successfully recovers a tag’s identification (ID) among parasitic reflections using a single tag measurement without requiring prior knowledge about the tag.

In this letter, the modified flat-roofed sine waveguide slow-wave structure (FRSWG-SWS) is proposed for the wideband high-power sub-terahertz traveling-wave tube (sub-THz TWT), which possesses the advantages of wide operating bandwidth, low loss, minimal reflection, and ease of fabrication. The simulation results demonstrate that the transmission parameter is more than −5.0 dB in the frequency range between 210 and 250 GHz. The beam–wave interaction results indicate that the modified FRSWG can provide over 50 W of output power and 30 dB of gain from 205 to 250 GHz with sheet electron beam with a voltage of 20.8 kV and a current of 150 mA. Finally, we use high-speed milling to fabricate the modified FRSWG by the nano-Computer Numerical Control (CNC) technology. The cold test results demonstrate that the modified FRSWG has low loss and good reflection characteristics.

A microfluidically reconfigurable slow wave phase shifter (MRPS) with integrated actuation is introduced. MRPS is based on a selectively metalized plate (SMP) repositionable within a microfluidic channel placed in close proximity to a microstrip line. SMP repositioning creates a variable capacitive loading to alter the speed of the propagating wave. The device exhibits < 2 dB insertion loss (IL) and a reconfiguration time of 50 ms. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$|S_{21}|$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$|S_{11}|$ </tex-math></inline-formula> , and phase performances are characterized to be stable with respect to gravity by no more than 0.16 dB, 3.02 dB, and 7.73° variations, respectively. Vibration test shows 0.08 dB in IL, 1.72 dB in return loss (RL), and 4.23° in phase variations. The device is expected to handle 5.2 W of continuous RF power.

This work introduces a new topology for designing low-phase noise (PN) dual-band voltage-controlled oscillator (VCO) by proposing orthogonally located inductors in 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS. The inductors are implemented using five metal layers keeping the lowest layer empty to maximize the quality ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> ) factor. The first inductor is two halves shunted octagonal loops using the top layer (M6) and utilized in cross-coupled VCO, while the second inductor is formed by four C-shaped shunted inductors using the lower four layers <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{M}_{\mathrm {5-2}}$ </tex-math></inline-formula> and used in current-reuse (CR) VCO. The M6 inductor improves the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor by more than 25%over one loop inductor in the frequency band of interest, while the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{M}_{\mathrm {5-2}}$ </tex-math></inline-formula> inductor uses four shunt layers to boost the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor by 28% in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -band compared to the single-layer inductor. The VCO oscillates from 22.36 to 23.4 GHz with PN of −112.4 dBc/Hz at 1 MHz and figure of merit (FoM) of −188.8 dBc/Hz, while the CR VCO has tuning range from 23.8 to 25.7 GHz with a PN of −107 dBc/Hz at 1 MHz and FoM −185.8 dBc/Hz.

In this letter, a low-profile dual-band frequency selective surface (FSS) is designed as a polarizer for satellite communication. This single-layered FSS with a meandered open loop intersected by a metallic strip behaves as a dual sense polarizer. It converts linearly polarized (LP) EM waves of frequency range 2.01–2.64 GHz into left-hand circularly polarized (LHCP) EM waves. Similarly, the LP waves in the frequency range of 3.26–3.68 GHz are converted into right-hand circularly polarized (RHCP) EM waves. The unit cell dimension of the compact polarizer is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.075\lambda _{0} \times 0.075\lambda _{0} \times 0.005\lambda _{0}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> stands for free space wavelength at the lowest cut-off frequency. This study explores the structural design evolution of the proposed polarizer and verifies the frequency behavior of the structure using a circuit model. The simulated performance of the dual-band polarizer is experimentally tested. Good concordance is observed between the simulated and measured results.