The design and characterization of a broadband 20–480 GHz continuously tuneable on-chip spectrometer based on non-linear transmission lines in 65-nm CMOS technology is presented. The design procedure of the sampler that detects the ultra-broadband signal from the transmitter in time and frequency domain is described in detail. It consists of a non-linear transmission line, a passive pulse differentiator and a high-speed sample and hold-circuit. The relevance of the layout of the Schottky diodes in the sampler with a maximum RC-cutoff frequency of 430 GHz is described. Time domain and frequency domain measurements are presented to characterize the 480 GHz sampler bandwidth as well as the 3.1 ps sampler rise time. A signal to noise ratio of 90 dB at 100 GHz, 70 dB at 200 GHz and more than 30 dB at 480 GHz is reached. Two implementation of the spectrometer with antennas are presented, one with an on-chip antenna and one in a hybrid package. The antenna-less on-chip implementation of the transmitter and sampler requires no external lenses and is miniaturized to an area of 3 mm2. Future applications include analysis of fluids in microfluidic packages or droplet analysis in bio-medical or pharmaceutical applications.

High-performance SiGe HBTs and advancements in packaging processes have enabled system-in-package (SiP) designs for millimeter-wave applications. This paper presents a 122-GHz bistatic frequency modulated continuous wave (FMCW) radar SiP. The intended applications for the SiP are short-range distance and angular position measurements as well as communication links between cooperative radar stations. The chip is realized in a 130-nm SiGe BiCMOS technology and is based on a fully differential frequency-multiplier chain with in phase quadrature phase receiver and a binary phase shift keying modulator in the transmit chain. On-wafer measurement results show a maximum transmit output power of 2.7 dBm and a receiver gain of 11 dB. The chip consumes a DC power of 570 mW at a supply voltage of 3.3 V. The fabricated chip is integrated in an embedded wafer level ball grid array (eWLB) package. Transmit/receive rhombic antenna arrays with eight elements are designed in two eWLB packages with and without backside metal, with a measured peak gain of 11 dBi. The transceiver chip size is 1.8 mm × 2 mm, while the package size is 12 mm × 6 mm, respectively. FMCW measurements have been conducted with a sweep bandwidth of up to 17 GHz and a measured range resolution of 1.5 cm has been demonstrated. 2D positions of multiple targets have been computed using two coherently linked radar stations.

This paper presents the design and measurement results of a high-gain D-band broadband power amplifier (PA) implemented in a 130 nm SiGe BiCMOS technology. The topology of the PA is based on four differential cascode stages with interstage matching networks. A detailed analysis of the frequency behavior of the transimpedance-gain of the common-base stage of the cascode is presented by means of small-signal equivalent circuits, when the proposed four-reactance wideband matching network is used for output matching to the subsequent stage. The effect of the size of the active devices, in achieving a desired gain, bandwidth, and output power, is investigated. The fabricated D-band amplifier is characterized on-wafer demonstrating a peak differential gain and output power of about 25 dB and 11 dBm, respectively, while utilizing a DC power of 262 mW from a 2.7 V supply. The 3-dB small-signal bandwidth of the PA spans from 100 to 180 GHz (limited by the measurement setup), making it the first SiGe-based PA to cover the entire D-band frequency range. The PA achieves a state-of-the-art differential gain-bandwidth product of around 1.4 THz and the highest GBW/PDC ratio of 5.2 GHz/mW among all D-Band Si-based PAs.

This paper presents for the first time high-efficiency W-band power amplifiers (PAs), the design of which follows the digital PA (DPA) design concept. Two DPAs with different output networks have been realized: a single-band version (S-DPA) for 95 GHz and a dual-band design (D-DPA) for signal frequencies fS of 68 GHz (first band) and 76 GHz (second band), respectively. The PAs are realized as monolithic microwave-integrated circuits (MMICs) in a 0.8 μm InP DHBT transferred-substrate process. They utilize a double-emitter-finger DHBT unit cell with an emitter area of 2 × 0.8 × 6 μm3 each. In contrast to the usual W-band PAs, the proposed single-stage amplifier MMICs do not apply any special reactive matching for the transistor, which leads to very compact chip sizes of 0.27 mm2 (S-DPA) and 0.39 mm2(D-DPA). The S-DPA includes one band-pass filter (BPF) at the output with 0.6 dB insertion loss (IL) and 24 dB input return loss (RL) at the signal frequency of 95 GHz. The dual-band BPF shows 0.7 dB IL in both bands with a RL of more than 21 dB each. Applying an overdriven sinusoidal input signal to emulate digital operation the DPAs achieve a maximum output power of 14.4 dBm and power-added efficiency of 31% when using the single-band configuration. Collector efficiencies of more than 80% and the flexible multi-band operation demonstrated prove the great potential of the digital PA concept for future high-speed communications.

This paper presents for the first time a wavetable-based coding scheme to generate a high-speed binary input signal for digital RF power amplifiers. The approach maximizes the utilization of the time domain handling capabilities of the pulse forming circuit. Key features are a greatly improved output spectrum purity in comparison with common digital modulators, the ability to adjust the modulator to any given pulse forming hardware and a built-in signal correction option that comes without additional computational cost. To give a first impression on the modulators behavior and its possibilities to adapt to different hardware constraints, simulations are carried out for different parameter variations and for different baseband bandwidths. Furthermore, the proposed concept is emulated with an arbitrary waveform generator to gather additional measurement data. For a 5 MHz wideband code division multiple access (WCDMA) signal (6.5 dB peak-to-average power ratio) at 900 MHz, an error vector magnitude (EVM) of 0.26% and better than >58 dB adjacent channel leakage ratio (ACLR) were recorded. To the authors’ knowledge, these are the best values achieved so far for a single-bit coding scheme without digital predistortion that still maintains maximum power coding efficiency.

In this paper, design, implementation, and experimental results of efficient, high-power, and multi-octave gallium nitride-high electron mobility transistor power amplifier are presented. To overcome the low optima source/load impedances of a large transistor, various topologies of a broadside-coupled impedance transformer are simulated, implemented, and measured. The used transformer has a flat measured insertion loss of 0.5 dB and a return loss higher than 10 dB over a decade bandwidth (0.4–4 GHz). The transformer is integrated at the drain and gate sides of the transistor using pre-matching networks to transform the complex optima source/load impedances to the appropriate impedances of the transformer plane. The measurement results illustrate a saturated output power ranged between 80 and 115 W with an average drain efficiency of 57% and gain of 10.5 dB across 0.6–2.6 GHz.

In this work, an electromagnetic (EM) model and a small-signal (lumped-element) model of a wafer-level encapsulated (WLE) radio frequency microelectromechanical systems (RF-MEMS) switch is presented. The EM model of the WLE RF-MEMS switch is developed to estimate its RF performance. After the fabrication of the switch, the EM model is used to get accurate S-parameter simulation results. Alternative to the EM model, a small-signal model of the fabricated WLE RF-MEMS switch is developed. The developed model is integrated into a 0.13 µm SiGe BiCMOS process technology design kit for fast simulations and to predict the RF performance of the switch from a pure electrical point of view. The 0.13 µm SiGe BiCMOS embedded WLE RF-MEMS shows beyond state-of-the-art measured RF performances in D-band (110–170 GHz) and provides a high capacitance Con/Coff ratio of 11.1. The results of the both EM model and small-signal model of the switch are in very good agreement with the S-parameter measurements in D-band. The measured maximum isolation of the WLE RF-MEMS switch is 51.6 dB at 142.8 GHz with an insertion loss of 0.65 dB.

This paper presents a second-order tunable single-ended (unbalanced) bandpass filter (BPF) with continuous 0.4–3-GHz coverage and a tunable balun BPF with continuous 1.1–1.7-GHz coverage for software-defined radio transceivers with the use of band-switchable and radio frequency (RF)-micro-electromechanical systems (MEMS)-tuned resonators. The BPFs are realized with two pairs of RF switches for coarse-tuning and RF-MEMS-tunable capacitors for fine-tuning. On the one hand, for the tunable single-ended BPF, a transition between three bands is enabled using two pairs of RF switches. On the other hand, for the tunable balun BPF, a transition between two bands is enabled using one pair of RF switches. Furthermore, the three-band switchable single-ended BPF is constructed in a nested two-filter bank structure for expanding the tuning range without increasing the footprint. In addition, to complement the discrete band gaps, RF-MEMS capacitor-tuned resonators are used, and a continuous tuning range of nearly the entire ultra-high-frequency band is achieved. The filter bank is fabricated on a Duroid substrate with εr = 3.5 and h = 0.787 mm. The filter bank has an insertion loss of 3.2–6.8 dB and a 1-dB bandwidth of 65–450 MHz with a continuous tuning range of 0.4–3 GHz.

Different configurations of leaky-wave antennas (LWAs) based on graphene metasurfaces are studied. The electronic properties of a graphene metasurface in the low THz range are investigated in details in order to discuss the reconfigurability features of the presented structures. Simple exact formulas for evaluating the ohmic losses related to the surface plasmon polariton (SPP) propagation along a suspended graphene sheet, and the relevant figures of merit of SPP propagating over a generic metasurface are given. Such formulas allow us to explain the low efficiency of reconfigurable antennas based on SPPs along graphene metasurfaces. Then, the radiative performance and relevant losses of graphene Fabry–Perot cavity antennas (FPCAs) based on non-plasmonic leaky waves (LWs) are investigated and compared with previous solutions based on SPPs. In particular, a single-layer structure, i.e. a grounded dielectric slab covered with a graphene metasurface, and a multilayered structure, i.e. a substrate–superstrate antenna in which the graphene metasurface is embedded at a suitable position within the substrate, are considered in detail. The results show that the proposed LW solutions in graphene FPCAs allow for considerably reducing the ohmic losses, thus significantly improving the efficiency of the proposed radiators.

A methodology is presented to predict odd-mode instability in power amplifiers under output mismatch effects, as in the case of amplifiers connected to an antenna. This kind of instability is often observed in multi-device configurations, due to their symmetry properties. Unlike the single-ended situation, there is a cancellation of odd multiples of the oscillation frequency at the circuit output, so there is no impact of the load-impedance values at the sideband frequencies. The odd-mode instability only depends on the impedance terminations at the fundamental frequency and its harmonic terms, and can only be detected within the circuit unstable loop, instead of the antenna-connection terminals. The possible unstable modes are related with the eigenvectors of an outer tier conversion matrix accounting for the symmetry properties of the circuit topology. Under sufficient low-pass filtering of the amplifier output network, the analysis parameters can be limited to the magnitude and phase of the reflection coefficient at the fundamental frequency. This analysis involves a computationally efficient graphical technique to detect potential instabilities and a bifurcation-detection method to determine the instability boundaries in the Smith chart. The two main types of instability from periodic regime are considered, respectively associated with incommensurable and subharmonic oscillations. Results have been validated through pole-zero identification and experimental measurements.

A dedicated hyperthermia (HT) system was designed for tumors in intact breast extending beyond the heating depth of our superficial 434 MHz antennas, consisting of a treatment bed fitted with a 50 cm × 40 cm × 16 cm temperature controlled open water bolus. The patient lies in prone position with the breast immersed in the water positioned in front of a 34 cm × 20 cm 70 MHz waveguide operating in the TE10 mode. E-field patterns were measured in a tissue-mimicking phantom. HT was applied once a week with the 70 MHz applicator for six patients treated with thermoradiotherapy for deep lesions of recurrent breast cancer or melanoma. Two 14-sensor thermocouple thermometry probes were placed in catheters to monitor the invasive temperature. Results: Phantom measurements showed sufficient penetration depth up to 10 cm depth. The combination of 300–900 W antenna power and a water temperature of 42°C was well tolerated for the entire session of 1 h and resulted in good tumor temperatures with T90 = 39.8°C, T50 = 41.1°C, and T10 = 42.2°C. No toxicity or complaints were associated with the heating. A water mattress and other measures were needed to assure a comfortable position throughout the treatment. Conclusion: the 70 MHz breast applicator system performed well and tumor temperatures were good.

Bitstreams, square wave digital signals, enable flexible radar implementations in modern digital technology. By using bitstreams in place of analog sinusoidal waveforms, we can realize continuous-wave (CW), stepped-frequency CW, frequency-modulated CW, or even pseudo random noise-sequence and pulsed radars, all with a single bit of amplitude resolution. The building blocks are a programable waveform generator, a sweep threshold quantizer, digital delay, and a digital XOR gate as a mixer. This gives us a novel, almost fully digital (requiring only a comparator) system, as previously proposed and which is extended here. The flexibility of the transmitter allows for easy switching between waveforms and the bitstream signal can be processed with single-bit digital gates. Single-bit signals allows for exploration of novel continuous time non-clocked digital implementations to maximize speed and energy efficiency. Mixing frequencies with a digital XOR gate creates harmonics, which are explored for multiple solutions utilizing digital delay. Analytical as well as simulation results are presented. Initial measurements from a 90 nm CMOS chip is provided for the transmitter and the full system, proving the feasibility of a digital future in radar.

Air target recognition is a critical step in the radar processing chain and reliable features are necessary to make a decision. The number and position of jet engines are useful features to perform a pre-classification and give a list of possible targets. To extract these features, a sparse decomposition framework for inverse synthetic aperture radar (ISAR) images is presented. With this framework different components of the target can be detected, if signal models for these parts are available. To use it for the detection of jet engines, a review of a signal model for air intakes, which was developed by Borden, is given. This model is based on the common assumption that the propagation of electromagnetic waves inside jet engines has the same dispersive behavior as inside waveguides. With this model a decomposition of a real ISAR image, measured with the tracking and imaging radar system of Fraunhofer FHR, into point-like scattering centers and jet engines is presented.

In this paper, we propose an effective waveform diversity scheme that can be applicable to synthetic aperture radar (SAR) operations affected by interfering signals. A novel approach is taken to achieve fully adaptive SAR waveform diversity that generates sufficient number of orthogonal signals with modest performance trade-off. To this purpose, multiple phased-code waveforms are arbitrarily generated with mutually low cross-correlations. They exhibit a highly flexible characteristic as their code lengths are not limited and Doppler tolerance is well preserved throughout SAR imaging. Various SAR jamming simulations are carried out to demonstrate that the proposed waveform diversity has a good potential for electronic counter-countermeasures applications.