Microwave and Optical Technology Letters最新文献

This letter presents a W-band Colpitts voltage-controlled oscillator (VCO) designed in a 130 nm SiGe BiCMOS process. The proposed VCO employs a push-push harmonic extraction topology to generate the second harmonic output, while a novel optimal capacitance ratio technique is used to minimize the phase noise over the entire tuning range. The output frequency range of this VCO is 92.9 ~ 100.0 GHz, with a phase noise of −90.53 dBc/Hz at a 1 MHz frequency offset. The supply voltage is 2.5 V, and the power consumption of the VCO core and buffer is 80 mW and 32.5 mW, respectively. The chip area of this VCO is 0.438 mm².

This paper presents a 0.35–2 GHz bidirectional true time delay (TTD) transmit/receive (T/R) multifunctional chip utilizing a 0.25-μm GaAs enhancement/depletion (E/d-mode) pseudomorphic high electron mobility transistor (pHEMT) process. The chip integrates several key components: a 6-bit TTD with coverage of 945 ps and a step of 15 ps, a bidirectional amplifier (BA) featuring an improved common source-common gate structure, a 1.6-dB amplitude equalizer (AE), and seven parallel drivers (PDs) for TTD and BA control. The 6-bit TTD employs all-pass networks for the delay path and utilizes three types of reference paths to compensate for the amplitude imbalance between the delay path and the reference path. Meanwhile, the BA employs a dual-C structure combined with dual R-L feedback to mitigate process variation sensitivity significantly. Besides, the 1.6-dB AE is utilized to achieve an overall 1-dB positive gain slope in both transmit and receive modes. In transmit mode, the chip achieves a gain of 4.9–5.9 dB with output power at 1 dB compression point (OP1dB) exceeding 19.3 dBm. In receive mode, the chip achieves a gain of 5.1–6.1 dB, accompanied by a noise figure (NF) lower than 2.56 dB, and an OP1dB larger than 5.4 dBm. Both transmit and receive modes achieve 1-dB positive gain slope. Meanwhile, the transmit and receive root-mean-square (RMS) TTD errors are less than 12.7 and 12.4 ps with associated RMS amplitude errors lower than 0.52 and 0.43 dB, respectively. To the authors' knowledge, this study represents the first demonstration of a GaAs-based bidirectional TTD multifunction chip operating in the UHF band.

Optical waveguides can be used to confine and propagate optical signals. In this study, an optical waveguide was formed by helium ion implantation with an energy of 400 keV and a dose of 6 × 10¹⁶ions/cm² in the Nd³⁺-doped silicate glass. The morphology was examined using a microscope to record its shape. The dark-mode spectrum and corresponding effective refractive indices of the He⁺-implanted Nd³⁺-doped silicate glass waveguide were measured at 632.8 nm by the prism coupling technique. The energy loss, projected range, and longitudinal straggling of the irradiated helium ions were derived by the SRIM 2013 package. The near-field light intensity profile for the He⁺- irradiated Nd³⁺-doped silicate glass waveguide was measured by the end-face coupling system, which is the first observation compared with earlier works. The optical properties of the waveguide suggest that it is a promising candidate for integrated optics systems.

In this letter, a novel reconfigurable filter with multifunction of continuous tunable frequency, bandwidth (BW), and attenuation is proposed. The tunable filter is integrated designed based on a fully tunable filtering coupling structure with external quality factor (Q_e) control and a tunable attenuation unit with impedance transformation capability. The fully tunable filtering coupling structure is deigned using terminal varactor loaded half-wavelength microstrip resonator with tunable center frequency and coupling coefficient. Adjustment of Q_e is realized through the addition of a varactor at the feedline port. Tunable attenuation is achieved by loading PIN diodes through a coupling structure. To improve the efficiency of impedance transformation, an asymmetric structure is employed. The performance degradation of the bandwidth and center frequency due to the tunable attenuation can be compensated by the fully tunable filtering coupling structure. The measurements show that the reconfigurable filter can be tuned from 0.99 to 1.61 GHz with tunable attenuation and bandwidth. The attenuation can be tuned over a range of 30.6 dB at 1.4 GHz, and the fractional bandwidth (FBW) can be tuned from 10% to 30% at 1.3 GHz.

This letter presents a novel frequency-reconfigurable aperture-coupled circular patch antenna based on substrate-integrated suspended line (SISL) technology, designed for single-/dual-band switching and frequency tuning in the C-band. The proposed antenna consists of an aperture-coupled circular patch with a sectoral slot and a biasing circuit to control a single PIN diode or a pair of varactor diodes. The characteristic mode analysis (CMA) was instrumental in the design of the reconfigurable patch and the feeding. The first antenna configuration can switch between single and dual-band operation, with a single band operating at 5.6 GHz with 11.62% fractional bandwidth (FBW) and a peak realized gain of 9.01 dBi, and a dual-band at 5.3/6 GHz with 6.04%/6.17% FBW and 8.57 dBi peak realized gain. The second antenna configuration (with the same physical structure) can tune the operational frequency between 4.84 and 5.89 GHz based on varactor diode reverse bias voltage with a frequency ratio (FR) of 1.22 and achieve a peak realized gain of 9.44 dBi within the tuning range. Both antenna configurations exhibited stable broadside radiation. The total antenna size is $��0.8�\; �{\lambda }_0�\; �\times �\; �0.8�\; �{\lambda }_0�\; �\times �\; �0.06�\; �{\lambda }_0�$, where $��{\lambda }_0�$ is the free space wavelength corresponding to the lowest operating frequency. This study provides a comprehensive solution for next-generation wireless systems by combining a compact platform, innovative feeding mechanisms, and state-of-the-art analysis techniques.

A wideband dual-polarization magneto-electric (ME) dipole antenna for mobile communications is presented. A crossed-dipole feed mechanism is used to inspire the ME dipole antenna for achieving a wide frequency band. The radiation arm of the electric dipoles is developed by two square patches having different dimensions, thus enhancing the impedance matching at the higher frequency range. To enhance the isolation, two metal pillars are used and embedded between the cross-dipole feed mechanism and ground plane. By using above-detailed scheme, a wideband ME dipole antenna was designed, analyzed and measured. Our antenna has a broad bandwidth of 65.38% (1.39–2.74 GHz), and high isolation beyond 28.5 dB over the operating band. It achieves stable unidirectional radiation pattern and the gain is 9.3 ± 1.3 dBi within the operating band. These characteristics make the proposed design a promising candidate for mobile communication systems.

In this study, we propose a novel all-dielectric metasurface polarization converter to realize interconversion of linear and circular polarization in inter-satellite laser communication systems, which function as a quarter-wave plate (QWP). The metasurface exhibits a high transmittance (> 0.8) over the 1500–1600 nm wavelength range, with a peak value exceeding 0.9 at 1550 nm. Additionally, the reflectance is maintained below 0.1 throughout this spectral region. It efficiently transforms y-polarized light into left-handed circularly polarized (LCP) light with an ellipticity exceeding 0.99 and converts right-handed circularly polarized (RCP) light into x-polarized light with a linear polarization degree approaching unity, thereby achieving near-perfect polarization conversion efficiency. Furthermore, we investigate the effects of structural parameters, polarization, and incidence angle on the polarization conversion performance of the metasurface. The results demonstrate that the proposed all-dielectric metasurface achieves dual functionality: efficient interconversion between linear and circular polarization states, while simultaneously enhancing laser communication system efficiency through effective stray light suppression. These results suggest broad applicability of the all-dielectric metasurface in advancing inter-satellite laser communication technologies.

A novel filtering antenna based on spoof surface plasmon polaritons (SSPPs) is presented. The antenna has high suppression performance and tunable radiation nulls. The proposed antenna mainly consists of four parts, a metal ground, an SSPP-based transmission line etched with slots, two driving elements on the upper and bottom surfaces, and three parasitic elements on the upper surface. By using the proposed SSPP-based transmission line, good out-of-band suppression performance is achieved. Moreover, the out-of-band resonances are suppressed by etching slots in the SSPP structure. Besides, the radiation nulls of the antenna can be tuned by adjusting the key geometrical dimensions, which would be useful to fit different interference. The measured operating band is 2.130–2.606 GHz (20.1% at f₀ = 2.368 GHz), the in-band average gain of the proposed antenna is 8.89 dBi with the peak realized gain of 10.55 dBi. The upper out-of-band suppression level is larger than 23.708 dB over 3.2–7.4 GHz band, while the gain response decreases rapidly from the maximum value (10.55 dBi at f = 2.52 GHz) to the minimum value (−67.315 dBi at f = 3.4 GHz).

We propose a novel and robust bias control method for Mach–Zehnder modulators that enables precise stabilization using low-amplitude pilot tones without requiring the detection of second- or higher-order harmonics. The technique relies on the ratio of the partial derivative of the direct current component to that of the first-order pilot tone with respect to the bias voltage, serving as a high-sensitivity feedback signal. Simulation and experimental results verify that the method significantly lowers the required pilot tone power, mitigates intermodulation distortion, and improves system linearity. Furthermore, it ensures stable and accurate bias control even under optical power fluctuations, making it particularly well-suited for microwave photonic links that demand high signal-to-noise ratios.