Helmut Leier

20W GaN HPAs for Next Generation X-Band T/R-Modules

High power amplifiers for a next generation of T/R-modules for future X-band active array antennas are realized on the bases of novel AlGaN/GaN HEMT structures, which are epitaxially grown on SiC wafer substrates. Both, hybrid and monolithically integrated circuits are designed and realized as key elements for transmit chains. Based on hybrid designs excellent peak power levels of 23 W (43.6 dBm) with an associated power added efficiency (PAE) of 29% are realized. Over a bandwidth of 2 GHz (X-band) the output power levels are above 20 W. In a more sophisticated approach first monolithically integrated circuits (MMICs) are designed, simulated and fabricated using a novel via-hole microstrip technology. Output power levels of 20 W (43 dBm) with an associated PAE of 30% are measured on small size 12 mm2 chips. Highest ever reported maximum power added efficiency values of up to 36.5% are achieved

A Compact 24 GHz Sensor for Beam-Forming and Imaging

A compact 24 GHz sensor setup for experimental verifications of radar imaging and digital beam-forming has been designed and realized. The sensor consists of a FM-CW radar front-end and a remote radar electronic unit. The front-end consists of a switched antenna array of 25 linearly arranged elements fed by one transmitter and two parallel homodyne receivers connected to separate receive antenna elements. The remote radar electronic unit includes the base-band signal generation, analog inputs for data acquisition and programmable digital circuitry for measurement control, data storage and interface handling. The sensor can be operated from a notebook computer via standard PC interfaces, thus forming a compact imaging radar system well suited for field tests. The sensor addresses primarily short and medium range automotive applications, but its flexibility in signal generation, sampling and coherent signal processing makes it interesting for many other application fields. In this article, a detailed description of the total system is given and exemplary signal processing methods for imaging and beam-forming are introduced and demonstrated with measurement results

Architecture and interconnect technologies for a novel conformal active phased array radar module

Highly integrated transmit/receive modules are key components for modern active phased array radar systems. This paper describes architecture and related interconnect technologies for a novel transmit/receive module with integrated radiating element and circulator for X-band applications. It allows the realization of future planar or conformal active antenna arrays with low installation depth as well as high maintainability performance.

Coplanar AlGaN/GaN HEMT power amplifier MMIC at X-band

A power amplifier MMIC based on AlGaN/GaN HEMTs was fabricated and measured. The coplanar balanced amplifier consists of two 8/spl times/100/spl mu/m transistors. Wilkinson splitters were used to divide and combine the power. BY biasing the amplifier at V/sub DS/=30V a maximum CW output power of 39dBm corresponding to 5W/mm with a maximum power added efficiency (PAE) of 33.8% was achieved at 10GHz. Biasing the amplifier at V/sub DS/=20V resulted in 36.7% PAE with 37.2dBm CW output power at 10GHz. To the authors knowledge these results represent the highest output power density so far achieved for GaN-based MMICs at X-band in CW mode.

Reduction of base-collector capacitance in InP/InGaAs HBT's using a novel double polyimide planarization process

The parasitic base-collector capacitance (C/sub BC/) in InP/InGaAs heterojunction bipolar transistors (HBTs) has been reduced using a novel double polyimide planarization process which avoids damage of the extrinsic base layer. The extrinsic base metal outside the base-collector mesa is placed on the polyimide by polyimide coating and etch-back to the base layer. We obtained f/sub T/ of 81 GHz and f/sub MAX/ of 103 GHz with a 2/spl times/10 /spl mu/m emitter. Performance comparison between two devices with the same area of 2/spl times/2 /spl mu/m but with different base-collector mesa area showed 56% reduction of C/sub BC/ and 35% increase of f/sub T/ and f/sub MAX/.

Power handling limits and degradation of large area AlGaN/GaN RF-HEMTs

We investigate the influence of the device geometry of large scale RF power AlGaN/GaN-HEMTs on the RF output power density. Multifinger-RF-HEMTs with different device geometries were fabricated on comparable epilayers grown on both sapphire and SiC substrates. Thermal impedances of the different FETs were measured and simulated. We discuss the correlation between the thermal device impedance and the RF output power, measured at 2 GHz. Degradation phenomena under high temperature and high current conditions are reported. As a result, we show that the thermal device impedance can be used as a design rule for the optimization of AlGaN/GaN-RF-HEMTs. 2002 Published by Elsevier Science Ltd.

Signal Integrity Analysis of a 1.5 Gbit/s LVDS Video Link

Future applications in luxury class cars may require digital video transmission with data rates as high as 1.5 Gbit/s. The signal integrity of an LVDS Serializer/Deserializer video link was investigated in this work from the viewpoint of the car manufacturer. Physically consistent simulation models for the driver, receiver, connectors, and cables were developed which are valid up to 3 GHz. Simulated and measured eye diagrams are compared and evaluated to obtain the maximum cable length as a function of data rate. Finally, the effect of pre-emphasis on the maximum cable length for various data rates was investigated.

24-27 GHz dielectrically stabilized oscillators with excellent phase noise properties utilizing InP/InGaAs HBTs

We report on the design, fabrication, and RF performances of 24-27 GHz dielectric resonator oscillators (DROs) using InP/InGaAs HBTs. The employed HBT devices yield f/sub T/ values of 70 GHz and f/sub max/ values of up to 180 GHz, respectively. The measured phase noise of -107 dBc at 100 kHz offset is significantly lower than that of comparable DROs using GaAs based HBTs. To our knowledge, this is the first demonstration of phase noise results on InP/InGaAs HBT DROs.

Worst case signal integrity analysis for in-vehicle data transmission via UTP cables

Future luxury car applications require reliable data transmission at higher data rates over copper cables. The unshielded twisted pair (UTP) cable is well proven for low data rates and is considered as a cost effective candidate for high speed data transmission. In this paper, the impedance of a UTP cable as a function of the distance to the car body is analyzed and a worst case impedance profile is identified. Resonances in frequency domain were measured and simulated, and their effect on time domain signals was analyzed for different bit patterns at various data rates.

Odd-mode impedance-controlled shielded flat flexible cables for in-vehicle data transmission

The application of flat flexible cables (FFCs) for data transmission in cars is investigated. Measurements and simulations of commercial unshielded FFCs indicate possible signal integrity problems for the transmission of high data rates. Newly designed shielded FFCs were fabricated in a cost effective extruding process with different dielectrics and various shielding concepts. They were characterized using time domain reflectometry to compare measured and simulated odd-mode impedances. The different shield types are evaluated with emission measurements of a high speed CAN connection