Flat Gain Research Articles

Adjoint Equations for Beam-Wave Interaction and Optimization of TWT Design

By formulating and solving the adjoint equations governing the beam–wave interaction in a traveling-wave tube (TWT), we show the partial derivatives with respect to design parameters of various TWT figures of merit (FoMs) may be efficiently calculated. FoMs include average gain, gain flatness, and gain–bandwidth product, and design parameters include beam voltage and circuit geometry. We use these derivatives in an optimization algorithm that finds parameter values that minimize or maximize the desired FoM. We show that a 1-D large-signal simulation code, such as CHRISTINE, may be easily modified to compute the adjoint solutions. We further show that only three runs of the modified code suffice to compute the partial derivatives of the output power and phase at a specified frequency with respect to an arbitrary number of parameters, resulting in potentially large savings in computing time compared with direct, finite difference calculation of the partial derivatives. We illustrate the method by optimizing the beam voltage and gap spacing of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band folded-waveguide (FWG) TWT. The formulation given here applies only to TWT slow wave structures, such as coupled-cavity and FWGs, and to klystrons, composed of discrete gaps followed by drift spaces; it does not apply to helix structures, which may be the subject of a future paper.

On Sparse Gain Flattening in Pump-Constrained Submarine Links

Having in mind the capacity optimization of power-constrained submarine links, by following the work in (Cho <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2020) we first compare the achievable information rate (AIR) of gain-flattened and un-flattened short links (called here blocks) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_{b}\leq 12$</tex-math></inline-formula> spans with span loss 16.5 dB and with end-span single-stage co-pumped erbium-doped fiber amplifiers (EDFA) when the transmitted wavelength division multiplexed (WDM) channels all have the same transmitted power. All EDFAs have the same pump power and the same physical parameters. In the flattened case, each EDFA is followed by an ideal gain-flattening filter (GFF) that chops off the EDFA gain exceeding the span loss. No GFFs are used in the un-flattended case. We show that, for block length <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_{b}&gt;7$</tex-math></inline-formula> , at large-enough input power the AIR of the GFF block exceeds that of the no-GFF block, while for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_{b}\leq 7$</tex-math></inline-formula> at large input power the AIR is about the same. We next build a long submarine link by concatenating many <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_{b}$</tex-math></inline-formula> -span no-GFF blocks, and placing a GFF at the last EDFA of each block in order to flatten the block gain down to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_{b}$</tex-math></inline-formula> -span loss, and calculate the AIR of the resulting sparse-GFF submarine link, accounting also for nonlinear interference. For a 287-span case-study link with span loss 9.5 dB, we show that the best power efficiency is achieved by blocks of size <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N_{b}=6$</tex-math></inline-formula> (i.e., one GFF every 6 spans) when the pump is around 11 mW. When the GFF excess loss is 0.3 dB the top-AIR gain over the standard all-GFF system is 9.5%, a value that decreases to 4% when the excess loss is zero. Considering that modern submarine-grade GFFs have almost zero excess loss, and that the most efficient pump power is likely too low to operate with, we conclude that sparse-GFF links offer little advantage in practice over the current design.

A triple path noise cancellation LNA with transformer output using 45 nm CMOS technology

Abstract A triple path dual resistive feedback noise cancellation (TP-DRNC) low noise amplifier (LNA) with transformer output presented which provides high gain, low noise figure (NF), and high figure of merit (FM). The analysis of triple path, dual resistive, gain, and NF have been discussed. The effect of various components used in the circuit have been analyzed and their optimized values are obtained which resulted in the high (FM). The combination of dual resistive feedback with triple path NC transformer output allowed for low NF and high gain. The proposed GPDK 45 nm complementary metal oxide semiconductor (CMOS) technology-based LNA offers a flat gain curve of 10.81 dB over the range of 1.6 GHz to 4.3 GHz, or 2.7 GHz bandwidth, and S11 less than −9 dB. The input third order intercept point (IIP3) for the given bandwidth has value of 5.7 dBm, while the minimal NF achieved is 2.7 dB; (FM1) is 14.026 and (FM2) is 12.48. The proposed LNA’s layout with an o -chip transformer has an area of 0.01985 mm2

Novel Integration Techniques for Gap Waveguides and MMICs Suitable for Multilayer Waveguide Applications

This article discusses three integration and packaging techniques for gap waveguides and monolithic microwave integrated circuits (MMICs) suitable for multilayer waveguide applications. Two vertical transitions between microstrips and ridge gap waveguides (RGWs) are presented. The first vertical transition connects RGW to a microstrip line from the top where a rectangular patch has been used. Measured results of the transition in a back-to-back structure show that the reflection coefficient is better than −10 dB from 75 to 83 GHz, and the insertion loss for a single transition over the frequency band is 0.65–0.85 dB. The second vertical transition connects RGW to a microstrip line from the back by a slot in the ground plane. Measured results of the transition in a back-to-back structure show that the reflection coefficient is better than −10 dB from 69 to 86 GHz, and the insertion loss for a single transition is 0.65–1 dB over the frequency band. Commercially available E-band MMIC amplifiers are integrated with RGWs using the two proposed transitions. Moreover, for the very first time, the integration of MMIC with inverted microstrip gap waveguide (IMGW) is realized by a compact packaging structure that utilizes bond wires and capacitive pads. All the three active integrations are consistent with the passive measurements in terms of operational bandwidth, losses, amplifier gain flatness, and unwanted resonance suppression.

An Ultra-Wideband Image-Reject Up-Conversion Mixer With a Sandwich-Coupled Transformer for 5G mm-Wave Communication

This letter presents an ultra-wideband 20–42 GHz image-reject up-conversion mixer with low dc-power consumption implemented in 55 nm CMOS technology for multiband mm-Wave 5G systems. A sandwich-coupled transformer (SCT) is adopted to expand the operation bandwidth. The proposed SCT demonstrates good performance in enhancing the coupling coefficient and quality factor, which enables wideband impedance matching. Moreover, a quadrature signal generator composed of a transformer and a polyphase filter (PPF) is utilized to generate wideband high-precision I/Q signals without any calibration. With only 24 mW dc-power consumption, the mixer exhibits excellent conversion gain flatness of 1.2±1.5 dB from 20 to 42 GHz. The measured image reject ratio (IRR) is better than −30 dBc within the entire operation band. The measured output 1-dB compression point (OP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 dB</sub> ) is −2.57 dBm at 28 GHz and −3.96 dBm at 38 GHz. The proposed mixer exhibits good broadband characteristics, which can sustain multiband operation.

A 18–44 GHz Low Noise Amplifier With Input Matching and Bandwidth Extension Techniques

This letter presents a low noise amplifier (LNA) with a 3-dB gain bandwidth (3-dB BW) of 18–44 GHz in 65-nm CMOS technology. By deriving an analytical equation of input impedance, a co-design methodology for the first two stages of LNA that can simultaneously achieve broadband input matching and low noise figure (NF) is implemented. Weakly coupled asymmetric transformers that introduce a section of reverse parallel winding in the primary coil are designed to realize broadband interstage matching, optimize the gain flatness and boost the transconductance. The proposed LNA achieves a measured peak gain of 19.5 dB with a fractional 3-dB gain bandwidth (FBW) of 83.8%, covering the whole <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 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Ka$ </tex-math></inline-formula> -band. The measured NF is 2.6–3.5 dB from 20 to 43 GHz. To the best of our knowledge, the proposed LNA achieves the highest 3-dB BW and FBW with competitive NF. The measured input 1-dB gain compression point ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {IP}_{\mathrm {1\,dB}}$ </tex-math></inline-formula> ) ranges from −23 to −18.5 dBm over the entire 3-dB gain bandwidth.

Analysis and design of a 1.7‐ to 27.1‐GHz low‐noise amplifier

AbstractThis letter illustrates a 1.7‐ to 27.1‐GHz single‐stage cascode low‐noise amplifier (LNA) with high and flat gain response. In the presented LNA, to obtain high and flat gain response in the broad bandwidth, the Micro‐strip type pHEMT is utilized as the common‐source stage so as to alleviate the gain bandwidth degradation caused by parasitic parameters. Meanwhile, multiple inductive‐peaking inductors are employed to enhance the gain. By optimizing the combination of several bandwidth extension techniques, the experimental results indicate that the exhibited LNA achieves high average gain up to 14.6 dB with ±1.5 dB variation, 2.4 dB typical noise figure, and 14‐dBm OP1dB in the frequency range from 1.7 to 27.1 GHz. Fabricated by using 0.15‐μm GaAs pHEMT process, the presented LNA occupies a chip area of 0.96 mm2.

An omnidirectional filtering dielectric resonator antenna based on metal patches

A novel filtering dielectric resonator (DR) antenna (DRA) is designed in this article. By using a single-layer planar feed structure, the TM01δ and TM011+δ modes of a cylindrical DR are excited. The proposed filtering DRA achieves a good omnidirectional radiation performance and a flat gain response. By loading a crossed patch with four shorting pins on the feed structure, the lower edge of the passband obtains a steep roll-off rate. By plating four metal patches on the side wall of the DR, a radiation null (RN) is successfully introduced at the upper sideband of the DRA. The suppression levels of the proposed filtering DRA in the lower and upper stopbands are above 18 dB. Therefore, the proposed filtering DRA achieves filtering function without additional circuits. For demonstration, a prototype DRA is fabricated and measured. The simulated and measured results are basically consistent.

An Extensive Large Signal Equivalent Circuit Model of GaAs-PIN Photodiode

Based on the variation trend of the depletion layer of GaAs-PIN photodiode (PD) under different optical power and reverse bias voltages, an extensive large-signal equivalent circuit model that characterizes PD in non-punch-through and punch-through states is proposed in this article. According to the analysis of the PD’s depletion layer variation, the nonlinear parameters of the model are described by exponential function and Gaussian function. To verify the reliability of equivalent circuit model, on-chip measurements were performed on PIN-PD fabricated by commercial GaAs process, and the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </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">${V}$ </tex-math></inline-formula> and reflection coefficient agree with the proposed model simulation results well. Furthermore, using the proposed model for simulation with CAD tools shows that reducing junction capacitance has potential in improving PD output power and gain flatness. At the same time, the model provides a certain reference for selecting bias condition in the design of the PD matching network and fabricating PD with high power output.

A self-biased GaN LNA with 30 dB gain and 21 dBm P1dB for 5G communications

Abstract We present a self-biased three-stage GaN-based monolithic microwave integrated circuit low-noise amplifier (LNA) operating between 26 and 29 GHz for 5G mobile communications. The self-biasing circuit, common-source topology with inductive source feedback, and RLC negative feedback loops between gate and drain of the third transistor were implemented to achieve low noise, good port match, high stability, high gain, and compact size. Measurement results show that the LNA has a high and flat gain of 30.5 ± 0.4 dB with noise figure (NF) of 1.65–1.8 dB across the band. The three-stage topology also achieves high linearity, providing the 1 dB compression point output power (P1dB) of 21 dBm in the band. To our knowledge, this combination of NF, gain, and linearity performance represents the state of art of self-biased LNA in this frequency band.

A Wideband Filtering Dielectric Resonator Antenna Based on the HEM 11δ Mode

In this letter, a wideband filtering dielectric resonator antenna (DRA) based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">HEM</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11δ</sub> mode is proposed with high roll-off rate and flat gain response in the whole passband. The proposed filtering DRA is excited by a simple feed structure composed of a driven ring, a parasitic ring and a driven arc. Each of them can excite the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">HEM</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11δ</sub> mode at different resonant frequencies, thus enlarging the impedance bandwidth of the proposed filtering DRA. Since the three resonant frequencies belong to the same mode, stable radiation pattern can be achieved simultaneously. In addition, two radiation nulls are generated near the lower and upper edges of the passband by the feed structure, making the proposed DRA obtain high frequency selectivity. All the three resonant frequencies and two radiation nulls are independently adjustable. A prototype has been fabricated and measured for demonstration, and the measured results are coincided with the simulated ones.

Demonstration of a Broadband W-Band Microwave Power Module With Improved Gain Flatness

A broadband W-band microwave power module (MPM) is demonstrated. It provides a continuous wave (CW) output power of 65 W from 91 to 97 GHz with a constant driving power of 0 dBm. The MPM consists of a miniaturized folded-waveguide traveling-wave tube (TWT), an integrated power conditioner (IPC), and a gain equalizing solid-state amplifier (GE-SSA). The overall efficiency exceeds 20 % and the saturation gain fluctuation is lower than 0.8 dB. It has dimensions of 380 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$ </tex-math></inline-formula> 180 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$ </tex-math></inline-formula> 45 mm and a weight of 5.5 kg.

A wideband omnidirectional planar filtenna for 5 GHz WLAN application

This paper presents a wideband planar filtenna based on the filter synthesis technique. The proposed filtenna consists of a third order hairpin line resonator filter coupled with an elliptical antenna. One arm of the last resonator of hairpin line resonator along with the extended feed arm of an antenna constitute an admittance inverter, which provides better integration between filter and antenna. The measured results show that the proposed filtenna exhibits a filtering response with impedance bandwidth of 26.5% (4.19–5.47 GHz), flat passband gain, good selectivity at band edges and omnidirectional radiation pattern well suited for WLAN application.

Mitigating end-to-end nonlinearity in LED-based VLC transceivers via an optical intensity feedback.

This Letter proposes a novel, to the best of our knowledge, intensity-modulation transmitter equipped with an optical intensity feedback (OIF) loop, which mitigates the holistic nonlinearity on both sides of intensity modulation and direct detection (IM/DD) transceivers from solely the transmitter side. In contrast to the recent effort on pre-distortion, we construct a negative feedback loop bridging the optical intensity of light-emitting diodes (LEDs) toward a sensor for nonlinearity perception to suppress the nonlinearity among all physical devices. In the meantime, we propose an analytical model for the feedback loop and an implementation scheme. The experimental results demonstrate a significant linearity improvement in the total harmonic distortion (THD) and the power gain flatness. More specifically, the average THD of the bipolar junction transistor (BJT)-based OIF transceiver is -49.4 dB (0.37%) and the minimum power gain variance is 0.0005, 0.0025% of the control group. As for the transceiver using a metal-oxide-semiconductor field-effect transistor (MOSFET), its average THD is -52.42 dB (0.25%) and the minimum power gain variance can reach 0.0026. Not only that, since the method only takes advantage of the negative feedback feature and dose not rely on any particular module, it has lower complexity and better applicability.

Design of compact highly matched broadband balanced low‐noise amplifier at X‐band using CRLH transmission lines

This article presents broadband balanced low-noise amplifier (LNA) operating at X-band, which uses composite right/left-handed (CRLH) transmission lines as input–output matching networks. Proposed LNA eliminates lumped DC-blocking capacitors and is combined with a hybrid coupler to achieve better stability and matching. Presented CRLH matching technique enhances the matching quality, reduces the overall size and considerably improves the bandwidth and noise performance. The matrix analysis of the CRLH structure is provided to determine the exact dimension of microstrip lines for the highest stable gain and the lowest noise figure (NF). The LNA structure uses a HJFET technology as an active device, which is simulated using an ADS momentum and small-signal scattering parameters provided by the manufacturer. This LNA offers an improved impedance matching and measured the 20 dB S11 band-width of 16% (8.3–9.7GHz), which is in good agreement with simulation. Total area occupied by the fabricated LNA is only 1.7 λ 0 × 0.9 λ 0 @ 8.3GHz. The LNA also provides <1.8 dB NF based on the IEEE standard temperature (16.85 Celsius), and 1 dB gain flatness throughout the entire band along with a 1 dB compression point of −1 dBm and an output third point intercept point of 19.5 dBm. The proposed CRLH-based LNA can be a good candidate for compact receivers and sensors.

Temperature-Dependent Study on L-Band EDFA Characteristics Pumped at 980 nm and 1480 nm in Phosphorus and Aluminum-Rich Erbium-Doped Silica Fibers

In this paper, wepresent a comparative study on temperature-dependent spectroscopic characteristics and L-band amplifier performance for aluminum-rich erbium-doped fiber (EDF) and in-house fabricated phosphorus co-doped EDF. Different pumping configurations were studied to conclude that the pump wavelength of 980 nm with unequal forward/backward pump powers exhibited better temperature stability. Phosphorus EDF provided 19.4±1.4 dB gain and 4.6±0.2 dB noise figure (NF) from 1575–1615 nm at room temperature (RT), for a multi-channel input signal of −25 dBm in each channel, whereas the aluminum-rich EDF provided 20.3±5.1 dB gain and 5.3±0.8 dB NF. Using a single-channel input signal of −25 dBm at 1625 nm, phosphorus EDF maintained >10 dB gain with a 9.6 dB and 12 dB gain increment than aluminum-rich EDF at RT and −60 °C, respectively. The temperature-dependent gain (TDG) coefficient from 1575–1615 nm was in the range −0.006 to −0.044 dB/°C for phosphorus EDF and 0.011 to −0.023 dB/°C for aluminum-rich EDF, over the temperature range −60 to +80 °C. We propose a hybrid L-band amplifier concatenating aluminum-rich EDF with phosphorus EDF, to suppress the temperature dependence of phosphorus EDF and improve the gain bandwidth restriction of aluminum-rich EDF. The hybrid EDF exhibited multi-channel 20.9±3.9 dB gain and 3.7±0.6 dB NF from 1575–1615 nm at RT. The TDG coefficient of the hybrid EDF remained almost constant from 1585–1615 nm, contributing to a temperature-insensitive gain flatness.

Analysis and Demonstration of Mm-Wave Distributed Amplifiers With Modified Artificial Transmission Line Model

In this article, we analyze the mm-wave distributed amplifiers (DAs) with a modified artificial transmission line (M-ATL) model which includes the parasitic inductance and capacitance of the transistors. The characteristic impedance and the cutoff frequency are analytically derived with the M-ATL model. It is found that the parasitic inductance reduces the cutoff frequency, thus limiting the DA bandwidth and can be optimized for the group-delay equalization. To confirm the accuracy of the M-ATL model, two mm-wave DAs – ultra-wideband DA (UWDA) and variable-gain DA (VGDA) – were demonstrated using a 250-nm InP DHBT process. The on-chip bias network and group-delay equalization of the DAs are analyzed to improve the bandwidth and gain flatness. The measurement shows that the UWDA exhibits an average gain of 11 dB over the frequency from 6 to 261 GHz. The VGDA shows an average gain variation from 1.5 to 11.1 dB over the frequency from 6 to 200 GHz.

Integration Design of Millimeter-Wave Bidirectional Endfire Filtenna Array Fed by SIW Filtering Power Divider

In this letter, a millimeter-wave (mmW) substrate integrated waveguide (SIW) filtering power divider (FPD) with differential outputs is proposed and used as a feeding network for bidirectional endfire filtenna array. By using theoretical design rule based on coupling coefficient and external quality factor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q_e</i> ), the proposed FPD combines multiple functions such as filtering, power divider, and unbalanced-to-balanced (balun) conversion into one single circuit. Meanwhile, the FPD is insensitive to the load impedance so that it can be seamlessly connected to the back-to-back quasi-Yagi antenna array for bidirectional radiation. For demonstration, an mmW bidirectional endfire filtenna array centered at 27.5 GHz fed by three-order FPD is designed and fabricated. The measured results exhibit that the proposed filtenna array owns an impedance bandwidth (| <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | < −10 dB) of 3.4%, flat passband gain with a peak gain of 5.4 dBi, and good selectivity (the stopband gain roll-off is up to 25 dB/GHz. Good agreement is observed between the simulated and measured results.

Design of a V-band low noise amplifier for passive millimeter wave imaging application

This paper presents a design methodology for wideband low noise amplifier (LNA) with flat gain and low noise figure (NF). A parallel RC network loaded stub circuit is proposed to enhance simultaneous noise and impedance matching. Moreover, the same structure is applied to compensate for transistor gain roll-off with frequency. By properly selecting the stub lengths for different stages, flat gain and low NF are obtained in wideband. The method is verified by designing a V-band 4-stage LNA based on 0.15 μm GaAs pHEMT process. The LNA features 15.2 dB average gain within 45–61 GHz bandwidth. In the required band of 51–57 GHz, the LNA achieves flat gain of 14.9 ± 0.3 dB and low NF of 2.6–4.2 dB. It consumes 30 mA current from 3 V supply and occupies area of 2 mm × 1.3 mm. Although the LNA is inherently multipurpose design, it is particularly suited for passive millimeter wave imaging due to its characteristic of high sensitivity.

Design a Broad-band High flatness Gain Low Noise Amplifier for radar Applications

Design a Broad-band High flatness Gain Low Noise Amplifier for radar Applications