Abstracts:Undersampling is an effective way to reduce the cost of digital predistortion (DPD), but it poses challenges for signal alignment, especially for fractional delay alignment. In this letter, a Taylor expansion-based method for fractional delay approximation solution is proposed. To verify the proposed alignment algorithm, the basis manifold regularization (BMR) is introduced to ensure that the DPD can converge to a satisfactory performance even at an ultralow sampling rate. Simulations and experimental tests demonstrate that the proposed method not only has high alignment accuracy but also low complexity in comparison with traditional methods.

Abstracts:In this letter, a broadband rectifier with a wide-incident-angle (WIA) property is proposed. The circuit is composed of a broadband quadrature coupler (BQC) and two broadband subrectifiers (RectA and RectB). Here, RectA and RectB are connected to the two output ports of the BQC and combined by a direct current (dc) power combiner. Then, the obtained dc power is transmitted to the load resistor. Besides, two RF sources (RF1 and RF2) with identical input power and a phase difference (<inline-formula> <tex-math notation="LaTeX">$Delta varphi$ </tex-math></inline-formula>) are connected to the input and isolated ports of the BQC. A detailed theoretical analysis is carried out. To validate the proposed scheme, we design a broadband (1.6&#x2013;2.8 GHz) WIA rectifier. Measurement results show that the power conversion efficiency (PCE) exceeded 60&#x0025; in the frequency range from 1.6 to 2.8 GHz at 13.1 dBm of the input power. Additionally, at 2.45 GHz, the PCE varies in the range of 60.8&#x0025; and 72.6&#x0025; within the entire <inline-formula> <tex-math notation="LaTeX">$Delta varphi $ </tex-math></inline-formula> range (0&#x00B0;&#x2013;360&#x00B0;). Thus, the obtained PCE variation (<inline-formula> <tex-math notation="LaTeX">$Delta eta$ </tex-math></inline-formula>) is 11.8&#x0025;. Considering its excellent broadband and WIA features, it is very suitable for high-efficiency radio-frequency (RF) energy harvesting (RFEH) systems.

Abstracts:In this letter, a 10&#x2013;43-GHz low-noise amplifier (LNA) monolithic microwave integrated circuit (MMIC) is designed in a commercial 0.15-<inline-formula> <tex-math notation="LaTeX">$mu text{m}$ </tex-math></inline-formula> GaAs E-mode pseudomorphic high electron mobility transistor (pHEMT) technology. In the proposed LNA circuit, a novel coupled-line (CL)-based positive feedback structure is employed with the bandpass characteristic. By carefully tuning its coupling factor and arm length, the center frequency <inline-formula> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> and the intensity of the feedback can be controlled, respectively. Subsequently, targeting <inline-formula> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> at the higher cutting edge of the working band leads to compensated gain roll-off and extended bandwidth. Incorporating three-stage common-source (CS) architectures, an LNA prototype is fabricated with a size of 1.05 mm2 including pads. Under 2-V voltage drain drain (VDD), good performance is obtained, including 24.6-dB peak gain with 3-dB bandwidth of 33 GHz, 2.4&#x2013;3.0-dB noise figure (NF), 54.5 &#x00B1; 13.8-ps group delay, and 12.3/21.5-dBm best output power at 1 dB gain compression (OP1dB)/output third order intercept point (OIP3). The total dc power is 110 mW.

Abstracts:The theory, design, and implementation of a millimeter-wave (mm-wave) two-stage common-emitter (CE) low noise amplifier (LNA) using a 130-nm silicon-germanium (SiGe):C Bipolar CMOS technology is presented. The LNA was optimized for wideband performance from 62 to 110 GHz for both mm-wave radar/sensing and wireless communication applications. A two-stage broadband noise and impedance matching technique is used to obtain a relativity flat gain (13.5 dB) and noise figure (NF) (4.5 dB) across the E-/W-band. Low-voltage <inline-formula> <tex-math notation="LaTeX">$(V_{text {CC}}=0.7,,text {V})$ </tex-math></inline-formula> and low-power (5.9 mW) operation is achieved by forward biasing the base&#x2013;collector junction, while the wideband capability is further improved by a T-type input matching network utilizing constant quality factor curves. To the best of authors&#x2019; knowledge, the presented LNA has the widest 3-dB bandwidth with the lowest power consumption in the literature for silicon-based E-/W-band LNAs.

Abstracts:In this letter, we report the near quantum-limited performance of a 230 GHz endfire superconductor-insulator-superconductor (SIS) mixer utilizing a Nb/Al-AlOx/Nb trilayer. An important feature of this mixer is its use of a unilateral finline for the waveguide-to-planar circuit transition, which allows for a wide radiofrequency (RF) bandwidth, a simple waveguide structure with easy alignment, and for the mixer chip to be aligned along the optical axis. Each of these factors is beneficial in the construction of large-format focal plane arrays. We tested the new finline mixer from 210 to 260 GHz in a liquid helium cryostat at &#x007E;4 K. The best recorded noise temperature was approximately twice the quantum limit, which is comparable to conventional radial probe mixers. This suggests that endfire SIS mixers can be used in large format arrays, comprising 100s or even 1000s of SIS mixing elements, while retaining state-of-the-art quantum mixing performance.

Abstracts:A millimeter-wave (MMW) variable-gain power amplifier (VGPA) with <inline-formula> <tex-math notation="LaTeX">$P_{mathrm {1,dB}}$ </tex-math></inline-formula> improvement technique is proposed. The proposed VGPA consists of a postdistortion power amplifier (PDPA) and a variable-gain amplifier (VGA), for realizing high output power 1-dB compression point (<inline-formula> <tex-math notation="LaTeX">$P_{mathrm {1,dB}}$ </tex-math></inline-formula>) and variable gain, respectively. To improve the <inline-formula> <tex-math notation="LaTeX">$P_{mathrm {1,dB}}$ </tex-math></inline-formula> performances, a postdistortion technique with peaking-mode gain response shaping is proposed. This new approach has less amplitude-to-amplitude (AM&#x2013;AM) distortion. Fabricated in 65-nm CMOS process, the proposed VGPA achieves 16-dBm output <inline-formula> <tex-math notation="LaTeX">$P_{mathrm {1,dB}}$ </tex-math></inline-formula> with 29.5&#x0025; power added efficiency (PAE) and 16.7-dBm saturated output power (<inline-formula> <tex-math notation="LaTeX">$P_{mathrm {sat}}$ </tex-math></inline-formula>) with 34&#x0025; peak PAE. The maximum gain reaches 33.1 dB with 3-dB bandwidth from 23.1 to 29 GHz and 31.1-dB dynamic range of gain adjustment.

Abstracts:This letter presents a novel miniaturized dual-band bandpass filter (BPF) using a dual-mode dielectric waveguide resonator (DWR). The DWR is a cylinder dielectric block with the surface being silver-coated. The two modes are TM010 and TM011 modes, which are used to construct the two passbands. The frequency of them can be adjusted by changing the radius and the height of the cylinder DWR and the frequency space can be controlled independently. The BPF is composed of three cylindrical cavities, which are arranged in an equilateral triangle. The three cavities construct a cascaded trisection (CT) unit, which creates a transmission zero (TZ) at the upper side of the two passbands. Finally, a dual-band BPF using DWR is simulated, manufactured, and measured to exhibit the feasibility of the proposed design. Their results are in good agreement, showing good performance, such as miniaturization, good return loss (RL), and upper stopband selectivity.

Abstracts:This letter presents a novel vertical waveguide-to-microstrip self-diplexing transition for dual-band applications. The transition is realized with standard printed circuit board (PCB) manufacturing processing, making it suitable for mass production and practical applications. A standard waveguide is screwed on the topside of the stack-up. Dual-band self-diplexing operation is achieved by coupling two microstrips (one for each band) to two radiating patches through H-shaped slots. The operating bandwidth has been enhanced by adding two parasitic patches above the radiating ones. Metalized via holes are used to form a cage around the rectangular waveguide and the microstrips to prevent power leakage. A prototype has been fabricated to operate at K/Ka frequency band. The experimental results show a &#x2212;10 dB matching bandwidth of 20&#x0025; and 14&#x0025; for the lower and upper bands, respectively. Within these ranges, the maximum measured insertion loss is about 0.6 and 0.7 dB, respectively.

Abstracts:In this letter, a broadband waveguide magic-T with compact size is presented. A grounded suspended stripline has been used to obtain broadband isolation characteristics and increase power capacity. The inner ridge-matching structure is used to achieve broadband matching. The method and design process of the demonstrated magic-T are described in detail. The measured 15-dB bandwidth is about 30.3&#x0025;, almost for waveguide BJ-320 waveguide operating bandwidth. The measured isolation between sum and deference ports is above 37.5 dB; 20-dB measured isolation is achieved between collinear ports. The measured and simulated results are in good agreement. It has advantages in high-power applications.

Abstracts:In this letter, the current source implementations are presented for the hybrid implicit&#x2013;explicit finite-difference time-domain (HIE-FDTD), the improved HIE-FDTD, and the leapfrog HIE-FDTD methods. The asymmetry and the field errors of these HIE-FDTD methods are investigated for all possible values of the time index parameters. The proposed implementations give very low asymmetry and field errors for all the three HIE&#x2013;FDTD methods. The field errors given by these HIE-FDTD methods are lower than those given by the alternating direction implicit finite-difference time-domain (ADI-FDTD) method.