Highly adaptive, instinctively interference-tolerant radio frequency (RF) receivers are in high demand today. To achieve high-interference robustness at low average power, receivers need to be dynamically configured to operate in low-power mode in the absence of interference and a high-power interference-tolerant mode as an “instinctual” response to the blocker. In this letter, we present an interference-adaptive receiver with a control loop and on-board commercial off-the-shelf (COTS) components that adapt a 2–6-GHz low-noise amplifier (LNA) from a low-power mode (−10-dBm $P_{\text {1 dB,IN}}$ and $\approx 280$ -mW power) to high-linearity mode (1.5-dBm $P_{\text {1 dB,IN}}$ and $\approx 1.4$ -W power) where the linearity is increased by 11.5 dB ( $> 14\times $ ) with a $5\times $ increase in consumed power. With no interference, the control loop automatically brings the LNA back to the low-power mode.

Instinctual Interference-Adaptive Low-Power Receiver With Combined Feedforward and Feedback Control

A pulse Doppler radar is the result of combining Doppler sensing techniques with pulsed radar operation. Such radars offer the powerful scope for direct measurements of both target range and velocity, even in the face of large clutter returns and even in the presence of chaff or other interference. To radar, the measurement of a time delay is tantamount to range, whereas the measurement of a (Doppler) frequency shift is tantamount to velocity. Thus, one must consider the design of suitable waveforms in both the time and frequency domains. However, there is a complex interplay between the waveform parameters, particularly when it comes to the selection of the radar pulse repetition frequency (PRF). All too often, the requirements for the measurement of range clash with those for the measurement of velocity. The result is that multiple waveforms may be required which depend on the nature of the targets and clutter conditions. The study of pulse Doppler radar is thus inextricably bound up with issues of waveform design and their associated processing methods whilst always maintaining a watchful eye on the target scenario and radar environment. Before tackling these waveform and processing issues, it is necessary to establish several fundamental radar concepts, which are covered in the ensuing chapters.

Historical Justification for Pulse Doppler Radar

We propose a statistical procedure to characterize and extract features from a waveform that can be applied as a pre-processing signal stage in a pattern recognition task using Artiﬁcial Neural Networks. Such a procedure is based on measuring a 30-parameters set of moments and cumulants from the waveform, its derivative, and its integral. The technique is presented as an extension of the Statistical Signal Characterization method existing in the literature. As a testing methodology, we used the procedure to distinguish a pulse-like signal from diﬀerent versions of itself with frequency spectrum alterations or deformations. The recognition task was performed by single feed-forward back-propagation networks trained for the case Sinc-, Gaussian-, and Chirp-pulse waveform. Because of the success obtained in these examples, we can conclude that the proposed extended statistical signal characterization method is an eﬀective tool for pattern-recognition applications. In particular, we can use it as a fast pre-processing stage in embedded systems with limited memory or computational capability.

Extended method for Statistical Signal Characterization using moments and cumulants: Application to recognition of pattern alterations in pulse-like waveforms employing Artificial Neural Networks

The ever-increasing requirements for high device performance and compact size drive the communications industry to lookfor new materials, technologies, and integration concepts. This simulation-based study investigates the thermal properties of a compact, heterogeneously integrated gallium nitride on silicon carbide (GaN-on-SiC) and silicon (Si) assembly. Thermal simulations and parametric studies are used to determine how the heat spreading and temperature levels in the lateral and vertical directions are affected by the thickness of the SiC layer and the distribution of the thermal interconnects. Results show that a SiC layer thinned down to 100 µm shows more pronounced differences in its thermal characteristics compared to thicker ones, especially in terms of its backside heating. Aspects related to practical implementations are also considered.

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Thermal Analysis of GaN/SiC-on-Si Assemblies: Effect of Bump Pitch and Thickness of SiC Layer

One of the major challenges in communication, radar, and electronic warfare receivers arises from nearby device interference. The paper presents a 2-6 GHz GaN LNA front-end with onboard sensing, processing, and feedback utilizing microcontroller-based controls to achieve adaptation to a variety of interference scenarios through power and linearity regulations. The utilization of GaN LNA provides high power handling capability (30 dBm) and high linearity (OIP3= 30 dBm) for radar and EW applications. The system permits an LNA power consumption to tune from 500 mW to 2 W (4X increase) in order to adjust the linearity from P\textsubscript{1dB,IN}=-10.5 dBm to 0.5 dBm (>10X increase). Across the tuning range, the noise figure increases by approximately 0.4 dB. Feedback control methods are presented with backgrounds from control theory. The rest of the controls consume $\leq$10$\%$ (100 mW) of nominal LNA power (1 W) to achieve an adaptation time<1 ms.

Sub-1ms Instinctual Interference Adaptive GaN LNA Front-End with Power and Linearity Tuning

This paper shows how the signal-to-noise and distortion ratio (SNDR) for low noise amplifiers (LNA) can be derived from the commonly specified parameters noise figure, gain, third order output intercept point and 1 dB compression point. The parameters dependency of the biasing of the amplifier are also incorporated which enables the possibility to study how SNDR can be optimized for different operating conditions by dynamically change the gate- and drain voltage. An experimental verification shows that improvements in SNDR can be achieved by selecting gate- and drain voltage of the LNA according to the level of the input signal power.

Optimizing the Signal-to-Noise and Distortion Ratio of a GaN LNA using Dynamic Bias

The introduction of gallium nitride (GaN) power amplifiers (PAs) in the transmitter chain of pulsed radar architectures has proved to be advantageous compared to the previously used gallium arsenide (GaAs) PAs. However, it has also introduced new challenges in the system design due to thermal and electrical memory effects which leads to transients in the amplitude of the PA output. It is therefore of interest to pre-compensate for the memory effects such that a desired shape of the pulse is maintained. This thesis evaluates the possibilities to use an iterative learning control scheme (ILC) to improve the shape of the pulse. The research is built upon measurements the PA output, where the PA is turned on and off in between the RF pulses. Two different pulse widths (PW) are evaluated, 10 μs and 100 μs. Black box modelling are performed to be able to test the algorithm offline, but also to understand the behaviour of the transients. Thereafter the ILC algorithm is implemented both in simulation and experiments. Measurements showed that there were mainly two behaviours to compensate for in the PA output, first one oscillating transient and thereafter a decaying behaviour. Black box modelling showed that different model structures were needed for pulses of different duration. When implementing the ILC algorithm, it was possible to fully compensate for all undesired effects in simulation. In experiments the oscillating transient was not possible to fully compensate for whereas the decaying behaviour was eliminated.

Pulse shaping of radar transmitters - Compensation of memory effects through digital pre-distortion

This paper presents a study of the lateral heat propagation in an aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure grown on a silicon carbide substrate The study is enabled by the design of a temperature sensor that utilizes the temperature-dependent $I$ – $V$ characteristic of a semiconductor resistor, making it suitable for integration in GaN monolithic microwave integrated circuit technologies Using the sensor, we are able to characterize the thermal transient response and extract lateral thermal time constants from the measurements Time constants in the range from 25 $\mu \text{s}$ to 12 ms are identified Furthermore, the heat propagation properties are characterized for heat source-to-sensor distances of 86– $484~\mu \text{m}$ , resulting in delay times from 35 to $111~\mu \text{s}$  It is shown that both the time constants and propagation delay increase with temperature An empirical model of the sensor current versus temperature and voltage is proposed and used to predict the junction temperature of the sensor The study provides knowledge for heat management design and proposes an integrated temperature measurement solution for future highly integrated GaN applications

Analysis of Lateral Thermal Coupling for GaN MMIC Technologies

This paper investigates the possibilities of using a dynamic bias control scheme for a low noise amplifier to compensate for performance degradation due to thermal effects. The study was performed by characterization of bias voltage and temperature dependence between −25°C to 75°C of a GaN MMIC LNA. The performance, in terms of gain, linearity and noise, degraded, at elevated chip temperatures. Nonlinear behavioral models were developed and used to predict performance for different bias and temperature conditions. Bias conditions to achieve constant gain and noise figure versus temperature are determined. Enhanced RF performance, with improved gain and linearity is demonstrated and is shown to require increased power and involves a trade-off between improving noise figure and gain.

Lowisa Hanning

Papers

Optimizing the Signal-to-Noise and Distortion Ratio of a GaN LNA using Dynamic Bias

Pulse shaping of radar transmitters - Compensation of memory effects through digital pre-distortion

Analysis of Lateral Thermal Coupling for GaN MMIC Technologies

Compensation of Performance Degradation due to Thermal Effects in GaN LNA Using Dynamic Bias