non-Foster Circuits Research Articles

A 44–64-GHz mmWave Broadband Linear Doherty PA in Silicon With Quadrature Hybrid Combiner and Non-Foster Impedance Tuner

The proliferation of millimeter-wave (mmWave) bands across 24–90 GHz and the strict spectral efficiency requirements demand future transmitter front ends to operate across multiple bands with simultaneously back-off efficiency and high linearity—characteristics that typically trade off strongly with each other. In this article, we propose a simultaneously broadband, back-off efficient and linear mmWave Doherty power amplifier (PA) architecture with a quadrature hybrid, and a non-Foster inspired impedance tuner on-chip. The combination of transformer-based hybrid and the quasi-non-Foster tuner allows the architecture to synthesize optimal impedances to the PA across the 2-D variations of power back-off and frequency, enabling high back-off efficiency across a broad frequency range. In addition, the unique location of the tuner at the isolation port of the hybrid allows us to exploit its benefits while shielding the architecture from effects of tuner non-linearity, power losses, and typical stability concerns of traditional non-Foster circuits. For high linearity, we implement an emitter follower-based class-C bias network with boosting effect. The PA is implemented in a 130-nm SiGe BiCMOS process. Across 44–64 GHz, the PA achieves 18.5–21.5-dBm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {sat}}$ </tex-math></inline-formula> , the peak collector efficiency of 26%–34.7% and 14%–23.2% at 6-dB back-off, maintaining back-off enhancement ratio of 2.77/2.53/2.37 (1.39/1.27/1.19) at 46/52/62 GHz compared to the class-A (class-B) operation. It supports 6-gigabit-per-second (Gb/s) 64-QAM signal with −26.5-dB/−28.3-dBc error vector magnitude (EVM)/adjacent channel leakage ratio (ACLR) at average <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {out}}$ </tex-math></inline-formula> /power added efficiency (PAE) of 14.6 dBm/15% at 54 GHz. This work achieves the state-of-the-art bandwidth among silicon-based mmWave PAs where higher than class-B back-off efficiency is achieved.

On the Design of Ultralow-Profile Broadband Absorber Based on Non-Foster Circuit

In this letter, a novel and effective method for non-Foster active absorber with ultralow profile and wide absorption band is proposed. The three-layer absorber consists of a square loop frequency selective surface array printed on the FR-4 dielectric substrate, a non-Foster matching layer, and a backed metal plane.Equivalent circuit model for the active absorber is proposed and analyzed, providing great insight into the effect of non-Foster matching layer on breaking the Rozanov limit effectively. A 1×10 absorber absorbing structure sample is fabricated.It is shown by measurement that the absorber has a fractional bandwidth of 36.0%, with a total thickness of only 0.008 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> (wavelength at the lowest absorption frequency). The simulation and experimental results are in good agreement in the operating band, which verifies the accuracy of the design method.

Non-Foster acoustic radiation from an active piezoelectric transducer

The quality factor of a passive, linear, small acoustic radiator is fundamentally limited by its volume normalized to the emitted wavelength, imposing severe constraints on the bandwidth and efficiency of compact acoustic sources and of metamaterials composed of arrangements of small acoustic resonators. We demonstrate that these bounds can be overcome by loading a piezoelectric transducer with a non-Foster active circuit, showing that its radiation bandwidth and efficiency can be largely extended beyond what is possible in passive radiators, fundamentally limited only by stability considerations. Based on these principles, we experimentally observe a threefold bandwidth enhancement compared to its passive counterpart, paving the way toward non-Foster acoustic radiation and more broadly active metamaterials that overcome the bandwidth constraints hindering passive systems.

Bandwidth and gain enhancement of composite right left handed metamaterial transmission line planar antenna employing a non foster impedance matching circuit board

The paper demonstrates an effective technique to significantly enhance the bandwidth and radiation gain of an otherwise narrowband composite right/left-handed transmission-line (CRLH-TL) antenna using a non-Foster impedance matching circuit (NF-IMC) without affecting the antenna’s stability. This is achieved by using the negative reactance of the NF-IMC to counteract the input capacitance of the antenna. Series capacitance of the CRLH-TL unit-cell is created by etching a dielectric spiral slot inside a rectangular microstrip patch that is grounded through a spiraled microstrip inductance. The overall size of the antenna, including the NF-IMC at its lowest operating frequency is 0.335λ0 × 0.137λ0 × 0.003λ0, where λ0 is the free-space wavelength at 1.4 GHz. The performance of the antenna was verified through actual measurements. The stable bandwidth of the antenna for |S11|≤ − 18 dB is greater than 1 GHz (1.4–2.45 GHz), which is significantly wider than the CRLH-TL antenna without the proposed impedance matching circuit. In addition, with the proposed technique the measured radiation gain and efficiency of the antenna are increased on average by 3.2 dBi and 31.5% over the operating frequency band.

A high gain, compact active disc-cone antenna based on non-foster matching circuit

The conventional passive matching technology of antenna is limited by the gain-bandwidth constraints. The antenna miniaturization can be only achieved in a very narrow frequency band with a low gain in the high frequency (HF) and very high frequency (VHF) bands. In order to realize the broadband matching and high gain design of the miniaturized disc-cone antenna, a non-Foster matching circuit, which consists of a negative impedance converter, a transformer and a current buffer, is proposed for impedance matching of the miniaturized disc-cone antenna. It is different from the conventional non-Foster matching circuit, which is merely composed of a negative impedance converter. Compared with the classical design, the size of the miniaturized antenna loaded with the proposed circuit is reduced by 60.9%. The S11 parameter of the antenna is less than −15 dB in the frequency range of 150–250 MHz, and the gain improvement of the non-Foster matching circuit to the miniaturized disc-cone antenna is more than 10 dB. Therefore, the matching circuit proposed in this research has better impedance matching performance and gain improvement compared to the conventional design. The results from the experiments validate the feasibility and effectiveness of the new design scheme.

A Non-Foster UWB Electrically Small Planar Monople Antenna (ESPMA)

Electrically small antennas (ESAs) may be employed instead of full-size antennas in a limited space for many communication networks such as the very high-frequency (VHF) band applications and ultra high-frequency (UHF)band applications. However, ESAs can not simultaneously achieve high gain and broadband by passive matching due to the gain-bandwidth theory. This paper presents a ultra wide-band (UWB) transmit electrically small planar monople antenna (ESPMA) with a non-foster impedance matching to bypass the restriction of the gain-bandwidth theory. The proposed antenna is composed of a planar monopole antenna with a height of 10 cm in profile and a non-Foster circuit. The plane monople antenna is chosen because of its better impedance performance than a cylindrical monople. The proposed antenna can operate in the band range of 80 MHz - 500 MHz (145%, VSWR<2.5) much greater than the maximum bandwidth of 0.285% in the theory of matching with the conventional passive circuit. The transmission efficiency of the antenna is improved by as much as 31dB compared with the same antenna without the proposed matching network. Besides, the stability of the proposed matching network is remained within the operating band.

Chu limit and non-Foster radiation for sound

We show that the quality factor of a small passive acoustic radiator is fundamentally limited by its volume normalized to the emitted wavelength, imposing important constraints on the bandwidth and efficiency of compact acoustic sources. We overcome this bound, known in electromagnetics as Chu’s limit, by realizing a piezoelectric transducer loaded with a non-Foster circuit, showing that its radiation bandwidth is fundamentally limited only by stability considerations. Based on these principles, we experimentally observe over a threefold bandwidth enhancement compared to its passive counterpart, paving the way towards non-Foster acoustic elements and metamaterials that overcome the bandwidth constraints of passive systems.

Design and Characterization of VHF Band Small Antenna Using CRLH Transmission Line and Non-Foster Matching Circuit

In this paper, we propose an electrically small antenna consisting of a composite right/left-handed (CRLH) transmission line (TL) and a non-Foster matching circuit. An interdigital capacitor (IDC) and spiral inductor are used to fabricate the very high frequency (VHF) band antenna based on CRLH TL. The size of the proposed antenna is as small as 0.025 × 0.014 × 0.0008 λ at 145.5 MHz using the zeroth-order resonant generated by the CRLH TL. The antenna operation bandwidth is extended by the non-Foster circuit (NFC) consisting of a pair of transistors in a cross-coupled manner. An antenna prototype is fabricated and the input impedance, the received power, and gain of the proposed antenna are measured. The results show that the broadband characteristic is maintained while the form factor is extremely small compared to the wavelength. The average received power enhancement and increased bandwidth of antenna are 17.3 dB and 335.5 MHz (from 249.2–268.2 to 145.5–500 MHz), respectively. The calculated gain of the proposed antenna with the non-Foster is about −45 dBi at 155 MHz. The proposed antenna can be considered as a potential candidate of a low-profile antenna for military ground communications at the VHF band.

SNR Enhancement of an Electrically Small Antenna Using a Non-Foster Matching Circuit

A non-Foster circuit (NFC) is known as an active broadband matching technique to improve the impedance matching bandwidth of an electrically small antenna (ESA). There has been a vast amount of papers that report the generation of negative impedance using an NFC and its effectiveness on broadband antenna matching. However, only a few discussed its impact on the signal-to-noise-ratio (SNR), which is one of the most important figures-of-merit for a wireless communication system. In this paper, the SNR enhancement due to an NFC was measured and discussed. An NFC was carefully designed to have a low dissipation loss and to meet the stability conditions. The optimized NFC design was fabricated and applied to an ESA length of λ⁄15 at a frequency range of 150 to 300 MHz. The measured results showed that the NFC enhanced the received power of the antenna system by more than 17 dB. However, due to the noise added by the NFC, the SNR enhancement was not guaranteed for some frequency points. Nevertheless, an average of 7.3 dB of SNR improvement over the frequency band of interest is possible based on the experiment result.

Optimization of loosely coupled inductive data transfer systems by non-Foster impedance matching

Abstract. Wireless energy transfer is often used in industrial applications to power actors or sensors, for example in rotating applications as replacement for mechanical slip rings. In addition to the energy transfer, we have developed inductively coupled data transfer systems to expand the range of possible applications. The data transfer is accomplished by using loosely coupled coils on both sides of the power transfer system. In pure energy transfer systems, resonant coupling is used, meaning that the power transfer coils are both tuned to a common frequency to compensate the relatively small coupling factor between power transmitter and receiver and to achieve an impedance matching between both sides by compensating the inductive component of the transfer coils. In this case, capacitors can be connected in series or in parallel to the coils, leading to a sharp, narrow band resonance peak in the transfer function. In inductively coupled data transfer systems, this approach is often not useful because not just a pure sine wave has to be transferred but more likely a signal of a certain bandwidth. In one of our applications, a 100 Mbit s−1 Ethernet stream is transferred with an occupied bandwidth of 62.5 MHz. The coil structures used so far in our data transfer applications were intrinsically unmatched to the data transfer systems. Additionally, due to the small coupling factor between the data transfer coils, transfer losses in the range of up to 15 dB or worth had to be accepted. This is especially critical regarding the high noise level in vicinity of the energy transfer system and the cross coupling between the two transfer channels. For passive, lossless circuits, Foster's theorem states that the reactance increases monotonically with frequency. Subsequently, the inductive part of a circuit can just be exactly compensated with a capacitance for one single frequency. In contrast, active circuits like a negative impedance converter (NIC) can be used to achieve a non-Foster behaviour, for example a negative inductance can be realized. In theory, an inductance in series or parallel to a negative inductance of the same magnitude would be cancelled out for every frequency applied. For low power level applications like active receiving antennas, this approach has already been successfully used in the past to achieve improved matching of simple antenna structures over a comparably large bandwidth. We make use of non-Foster circuits, namely negative impedance converters, to compensate the inductive part of two loosely coupled inductors to achieve smaller transfer losses and better impedance matching, which should lead to a decreased transfer signal loss and higher signal to noise ratio. The results of this paper serve as a basis for this development. So far, we achieved almost complete cancellation of the reactive part introduced by the loosely coupled data transfer inductors. Unfortunately, the circuits active device used to form the negative impedance converter introduced a highly resistive element, greatly increasing the signal transfer losses. Nevertheless, the theory of loosely coupled inductors is shown in a compact form and a strategy to cancel the reactive part is presented. Simulations and measurements of a transfer system are carried out, both showing good agreement regarding the reactance cancellation. Based on this, optimised implementations will be developed in the future.

비-포스터 회로가 결합된 UHF 대역 CRLH 전송선 안테나 설계

In this paper, we propose an ultra high frequency(UHF) band military antenna using composite right/left handed(CRLH) transmission lines and non-Foster circuits. The antenna uses the zeroth-order characteristic of the CRLH transmission line in order to miniaturize the antenna. The non-Foster circuit’s negative capacitance can offset the input reactance of the antenna to improve bandwidth. The size of the CRLH transmission line antenna is 20.9×13.2×1.6 mm3 and the size of the non-Foster circuit is 20×14.4×1.6 mm3. The measured received power of the antenna is improved by an average of 19.96 dB at 250～500 MHz.

소형 안테나의 광대역 정합 및 수신전력 개선을 위한 비-포스터 회로 설계

소형 안테나의 광대역 정합 및 수신전력 개선을 위한 비-포스터 회로 설계

Parametric Optimization of a Non-Foster Circuit Embedded in an Electrically Small Antenna for Wideband and Efficient Performance

In this paper, we present the design of a small, wideband antenna with an embedded non-Foster circuit. The design procedure is based on modeling the antenna in the presence of the EM model of the negative impedance converter (NIC) and trying to optimize the components and location of this active circuit inside the antenna. The EM modeling of the circuit provides the possibility to identify the key parameters that mostly affect the performance of the antenna in terms of bandwidth and efficiency. These parameters are then optimized accordingly. This procedure is applied on a monopole antenna, which has its natural resonance at 2.2 GHz. With an embedded non-Foster circuit, the antenna is miniaturized to cover wideband frequencies around 900 MHz. Two examples are considered for different NIC topologies, after optimizing the components of the NIC, the best performance was given by the second antenna, which exhibits an impedance bandwidth of 50% (0.84–1.45 GHz) and total efficiency of 25%. The measurement results of both antennas are in good agreement with simulations showing a significant enhancement with respect to the passive antenna.

Linearity Improved Doherty Power Amplifier Using Non-Foster Circuits

In this paper, linearity improved Doherty power amplifier (DPA) is proposed for linearity improvement by modifying the input capacitor value of peaking amplifier. The non-foster circuits are substituted for the conventional λ/4 transmission line in front of peaking amplifier, which the 90° phase shifter and impedance matching can be performed by the proposed structure. Furthermore, the input capacitor value of peaking amplifier FET can be modified through modifying bias voltage and match resistance of non-foster circuits. Therefore, the AM-PM distortion of peak amplifier is suppressed, and the linearity of total DPA is improved. Compared to a conventional DPA, the third-order inter-modulation distortion of proposed DPA is reduced by 12 dB without cutting efficiency.

Wideband, Non-Foster Impedance Matching of Electrically Small Transmitting Antennas

Electrically small antennas (ESAs) can be passively matched only over very narrow bandwidths and the resulting antennas have low gains. These are the major limiting factors for ESAs used in transmit applications, especially at high-frequency (HF) and lower Very HF frequency bands. This paper discusses the challenges of transmit ESA matching circuit design and the design process of a new non-Foster transmit matching architecture for electrically small monopole antennas that achieves wide bandwidth, high transmission efficiency (transducer power gain), and stability at the same time. The proposed circuit is composed of a current buffer (for high isolation), a transformer (for real-part matching), and a negative impedance converter (for imaginary-part matching). The measured −6 dB (−10 dB) $|S_{11}|$ fractional bandwidth of the proposed non-Foster transmitting system is 110% (39%), while the maximum bandwidth that can be achieved is 0.076% (0.047%) when matched with the conventional passive matching. The transmission efficiency of the system is improved by as much as 34.4 dB compared to the same antenna without the proposed non-Foster matching circuit, and it retains an enhanced efficiency over the entire frequency band of operation (26–89 MHz). The system remains stable within this frequency band. The measurement results of the compact and broadband transmitting antenna prototype verify the design concept.

High‐power broadband graphene non‐Foster circuit enabled class‐J GaN HEMT power amplifier

AbstractThis paper presents high‐power broadband graphene non‐Foster circuit (NFC) enabled Class‐J GaN HEMT power amplifier (PA). A graphene resonant‐tunneling diode (RTD) NFC is proposed to provide negative differential resistance characteristics and to create an effective negative capacitance. The NFC is integrated in the input matching network of the Class‐J GaN HEMT PA to cancel out the transistor input parasitic capacitance so as to enhance PA bandwidth, efficiency, output power, and gain. The PA design is based on Cree's packaged GaN HEMT CGHV40030F biased with drain supply voltage of 50 V at quiescent drain‐to‐source current of 44 mA. The PA operates from 3.4 to 4.0 GHz with center frequency of 3.7 GHz. The effective negative capacitance of the NFC from 3.4 to 4.0 GHz stands at −3.3 to −6.0 pF. An effective capacitance of −3.7 pF has been obtained at 3.7 GHz. The PA has small signal gain of 16.1 dB at 3.7 GHz. Large signal simulation input power sweep from 1 to 33 dBm at 3.7 GHz, indicates that the PA has 57.8% drain efficiency, 54.7% power added efficiency (PAE), 44.6 dBm (28.8 W) output power and 11.6 dB transducer power gain at input power of 33 dBm.

VHF 및 UHF 대역 소형 안테나 매칭성능 개선을 위한 비 포스터 정합회로 설계

Herein, a non-Foster matching circuit is designed to improve the impedance matching characteristics of small antennas in the VHF and UHF bands. The proposed non-Foster circuit is designed to operate with negative capacitance in a wide frequency band from 50 MHz to 1,000 MHz for use in various communication bands. To ensure the stability of the non-Foster circuit with conditional stability, the open-circuit stability condition of Linvill was satisfied, and the circuit was fabricated using the FR-4 substrate. The fabricated non-Foster circuit was combined with a small antenna to verify its performance by measuring the return loss and received power in the FM, DMB, and GSM bands. The measured return loss was improved from −6 dB to −30 dB, and the measured received power was improved from 0.5 dBm to 5.2 dBm.

The Observation of Dispersionless Superluminal Propagation in a Non-Foster Loaded Waveguide and Its Fundamental Limitations

Superluminal pulse propagation has been observed in past investigations. Conventional methods rely on resonance-based gain/absorption line materials, inevitably inducing significant pulse distortion. Motivated by the negative reactance slope of the non-Foster circuits, we investigated superluminal propagation based on a non-Foster loaded waveguide. Superluminal square-wave pulse transmission with negligible distortion has been observed in time-domain measurements. In addition, the propagation distance limitation for a non-Foster-based superluminal waveguide is derived by analyzing the distortion of the transmitted waveform. We conclude that a distortion-limited superluminal output pulse cannot emerge more than the original pulse duration ahead of the same pulse transmitted in vacuum, in agreement with causality. This investigation provides an alternative solution to the gain/absorption approaches, and is directed toward a more comprehensive understanding of superluminal propagation.

Theoretical design and analysis of wideband active hard electromagnetic surfaces using non-Foster circuit loaded anisotropic metasurfaces

The electromagnetic (EM) hard surface which can both support transverse electric and transverse magnetic surface wave modes has the important ability to reduce the EM blockage of metallic obstacles. We propose a method to design an electrically thin hard surface with wide bandwidth by loading with non-Foster elements. The wideband hard surface composed of an anisotropic impedance coating can be considered as a kind of active metasurface. We develop a method to determine the values of the loading non-Foster circuit which can minimize the dispersion of the unit cells. For this method, we derive accurate values for the loading non-Foster elements through theoretical analysis. We also determine the fundamental limitations on the bandwidth due to stability requirements. To verify our theoretical design, we simulate the transmission performance between the two ports on opposite sides of a metallic rhombus-shaped obstacle coated with the non-Foster based metasurface. The simulated results show that the blockage has been largely reduced over a broad bandwidth from 0.2 GHz to 1.5 GHz. Finally, we provide a discussion on how the resistive part of the non-Foster circuit can affect the performance of the wideband hard surface coating.

Robust stability characterizations of active metamaterials with non-Foster loads**Project supported by the National Natural Science Foundation of China (Grant No. 61701349), the Natural Science Foundation of Shandong Province, China (Grant Nos. ZR2017QF012 and ZR2017MF042), and the Program for the Top Young Innovative Talents, China (Grant No. Q1313-03).

Active metamaterials incorporating with non-Foster elements have been considered as one of the means of overcoming inherent limitations of the passive counterparts, thus achieving broadband or gain metamaterials. However, realistic active metamaterials, especially non-Foster loaded medium, would face the challenge of the possibility of instability. Moreover, they normally appear to be time-variant and in unsteady states, which leads to the necessity of a stability method to cope with the stability issue considering the system model uncertainty. In this paper, we propose an immittance-based stability method to design a non-Foster loaded metamaterial ensuring robust stability. First, the principle of this stability method is introduced after comparing different stability criteria. Based on the equivalent system model, the stability characterization is used to give the design specifications to achieve an active metamaterial with robust stability. Finally, it is applied to the practical design of active metamaterial with non-Foster loaded loop arrays. By introducing the disturbance into the non- Foster circuit (NFC), the worst-case model uncertainty is considered during the design, and the reliability of our proposed method is verified. This method can also be applied to other realistic design of active metamaterials.