Rolf Jonsson

Computational load pull simulations of SiC microwave power transistors

The design of power transistors for microwave applications requires a good understanding of their large signal behaviour in a real circuit context. The computational load-pull simulation technique ...

Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies

This paper describes the design, fabrication and measurement of two single-stage class-AB power amplifiers covering the frequency band from 0.7-1.8 GHz using a SiC MESFET and a GaN HEMT. The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32% and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4%. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34% and a power gain above 10 dB. The results for SiC amplifier are better than for GaN amplifier for the same 10-W transistor.

Self-actuation tests of ohmic contact and capacitive RFMEMS switches for wideband RF power limiter circuits

This paper presents an experimental study on the high power handling capabilities of some ohmic contact based and capacitive RF-MEMS switches (incl. self-actuation tests made up to 18 GHz). Such tests carried out on a series and shunt connected ohmic contact COTS MEMS switch show that self-actuation occurred at 29-37 dBm of RF input power (Pin) given a DC bias (Vbias) of 42-47 V. Corresponding high power tests of a capacitive MEMS switch made on quartz (at 4 GHz) show that self-actuation occurred at Pin = 24-31 dBm with Vbias = 0-19 V. The experimental results further indicate a potential usefulness of employing ohmic contact and capacitive MEMS switches to realize optimised low-loss wideband power limiter circuits.

Single-stage, high efficiency, 26-watt power amplifier using SiC LE-MESFET

This paper describes a single-stage 26 W negative feedback power amplifier, covering the frequency range 200-500 MHz using a 6 mm gate width SiC lateral epitaxy MESFET. Typical results at 50 V drain bias for the whole band are, around 22 dB power gain, around 43 dBm output power, minimum power added efficiency at P1 dB is 47% at 200 MHz and maximum 60% at 500 MHz and the IMD3 level at 10 dB back-off from P1 dB is below -45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66% PAE.

Broadband RF SiC MESFET Power Amplifiers

We have designed and characterized preliminary versions of two wideband SiC-based RF power amplifiers using SiC MESFETs from Chalmers University and Lateral Epitaxy SiC MESFETs fabricated at AMDS AB. When optimized transistors are available they will be used in the design of amplifiers for a 100 – 500 MHz multifunction EW system.

Evaluation of SiC MESFET structures using large-signal time-domain simulations

Ibis work deals with silicon carbide (SiC) metal semieonduetor field effect transistors (MESFETs) and microwave amplifiers using them. The wide bandgap (WBG) semiconductors silicon carbide and gallium nitride have a large potential for microwave power generation. The high power density combined with the comparably high impedance attainable by devices in these materials also offers new possibilities for wideband high power microwave systems. To realise these possibilities we need transistors that are well understood and optimised and amplifier designs that take advantage of the broadband possibilities offered by the transistors. We have developed and used physical drift-diffusion simulation models for SiC MESFETs. The simulation results showed a large influence of the doping and thickness of the channel and buffer layers, and the properties of the semi-insulating substrate on the DC and small signal device performance. A comparison between the physical simulations and measured device characteristics has also been carried out. A novel and efficient way to extend the physical simulations to the large signal high frequency domain has been developed. The method was used to investigate experimentally detected problems in the dynamies of the transistors during large signal operation and to further optimise the device structure. In this work a number of broadband SiC MESFET amplifiers were designed, fabricated and characterized. The packaging and charaeterisation of transistors is described and the design and characterisation of the amplifiers are presented. A 100-500 MHz amplifier showed a measured output power above 20 W and gain >15 dB across the band and a peak power of 26 W at 400 MHz, corresponding to a power density of 5.2 W/mm, with an associated power added efficiency (PAE) of 46 %. A 0.8-2 GHz feedback amplifier showed a measured output power above 5 W, gain >7 dB and PAE above 15 % across the band. A two stage 2.8-3.3 GHz amplifier had a maximum measured output power of 12.6 W with 22 dB gain and 9% PAE measured at 2.8 GHz. These results clearly show that SiC devices have a large potential for microwave power amplifiers in general and broadband amplifiers in particular.

Micro-Doppler extraction of a small UAV in a non-line-of-sight urban scenario

The appearance of small UAVs on the commercial market poses a real threat to both civilian safety and to military operations. In open terrain a radar can detect and track even small UAVs at long distances. In an urban environment with limited line-of-sight and strong static and non-static background, this capability can be severely reduced. The radar cross section of these UAVs are normally small compared to the background. However, the rotors of the UAVs produce a characteristic micro-Doppler signature that can be exploited for detection and classification. In this paper, we investigate in an experimental set-up whether it is possible in the radar non-line-of-sight to retrieve the micro-Doppler signature of the UAV rotors. This is done by exploring up to three multipath bounces in the measured signal. The measurements were made with a semi-monostatic single receiver-transmitter radar system operating at X-band in a pulsed single frequency mode. The radar response of the UAV, with plastic and metallic rotors, was measured at several positions inside a 4 m wide corridor with metallic walls. In this paper, data from one line-of-sight and two non-line-ofsight positions are presented. Results show that we are able to detect the micro-Doppler of the rotors and to retrieve the number of revolutions per minute, for both rotor types. Free space Finite-Difference Time-Domain calculations have also been performed on a CAD-model of the UAV rotor to determine the optimal choice of polarization and the short-time Fourier transform filter length.

Performance of SiC Microwave Transistors in Power Amplifiers

The performance of SiC microwave power transistors is studied in fabricated class-AB power amplifiers and class-C switching power amplifier using physical structure of an enhanced version of previously fabricated and tested SiC MESFET. The results for pulse input in class-C at 1 GHz are; efficiency of 71.4 %, power density of 1.0 W/mm. The switching loss was 0.424 W/mm. The results for two class-AB power amplifiers are; the 30-100 MHz amplifier showed 45.6 dBm (∼ 36 W) output powers at P1dB, at 50 MHz. The power added efficiency (PAE) is 48 % together with 21 dB of power gain. The maximum output power at P1dB at 60 V drain bias and Vg= -8.5 V was 46.7 dBm (∼47 W). The typical results obtained in 200-500 MHz amplifier are; at 60 V drain bias the P1dB is 43.85 dBm (24 W) except at 300 MHz where only 41.8 dBm was obtained. The maximum out put power was 44.15 dBm (26 W) at 500 MHz corresponding to a power density of 5.2 W/mm. The PAE @ P1dB [%] at 500 MHz is 66 %.