Michael Gadringer

Predistortion of Digital RF PWM Signals Considering Conditional Memory

The trend in transmitter systems is to move the digital domain closer towards the antenna using digital modulators and drivers to reduce circuit complexity and to save power. A common assumption made is that they are capable of generating ideal pulses and thus do not suffer from analog imperfections. But the output signals of real drivers for high frequency operation are not perfectly rectangular anymore, which leads to distortion lowering the signal quality. In this paper the general properties of high frequency digital driver circuits operating at 2.6 GHz are analyzed and the impact of the different effects is presented. The predistortion of such drivers in the context of digital discrete time RF PWM modulators is studied. It has been found that conventional sample based predistortion can only correct the driver nonlinearity from -29 dBc to -49 dBc for the example considered using a 40 MHz bandwidth signal at 2.6 GHz. Therefore a special predistortion scheme considering the impact of pulses adjacent to the other samples is proposed. The mitigation of effects due to the discrete time nature of the signal is considered and discussed in detail. The capabilities of the proposed predistortion scheme are verified by extensive simulations as well as by measurements. By applying the proposed predistortion concept the spectral quality can be further improved to -66 dBc. In addition different scenarios with limited resolution and a carrier frequency offset are analyzed.

Virtual reality for automotive radars

Car manufacturers spend quite a lot on the development of driver assistance systems and subsequently on autonomous driving functionality. To ensure the safety and reliability of these functions meet industrial standards it is necessary to verify and validate their functionality. While tests on the road are still the ultimate evidence of correct operation they are associated with huge efforts and risks. Therefore, they have to be complemented by other means like simulations and tests on specialised testbeds. For the latter the car’s sensors have to be stimulated in a way that they perceive a desired – but only virtual – environment. An important type of sensor in cars is the radar due to its various advantages. This article describes the development of a stimulator generating virtual radar targets in order to enable the testing of autonomous driving functions.ZusammenfassungAutohersteller investieren eine hohe Summe in die Entwicklung von Fahrerassistenzsystemen und in autonomes Fahren. Es ist daher notwendig, die sichere und zuverlässige Funktion dieser Systeme zu verifizieren und zu validieren. Dies kann mit Testfahrten auf der Straße erfolgen, was aber mit großen Kosten und hohem Aufwand verbunden ist. Es wird daher daran gearbeitet, zumindest Teile dieser notwendigen Tests mit Simulationen auf Prüfständen durchzuführen. Das Radar ist ein wichtiger Sensor für die erwähnten Systeme, deshalb ist dessen Stimulation von entscheidender Bedeutung. Dieser Beitrag beschreibt die Entwicklung eines Stimulators zur Erzeugung von virtuellen Radarzielen, um autonome Fahrfunktionen auf dem Prüfstand zu testen.

A preliminary result on development of analog broadband tapped delay line for L-band applications

This paper presents a brief comparison of delay line elements to develop a tapped delay line system. The comparative study includes surface integrated waveguide (SIW)-based delay line elements and coaxial cables. For SIW-based delay line elements, we divide the analysis into two scenarios based on the used transition line configuration, namely microstrip-to-SIW transition and grounded coplanar waveguide (GCPW)-to-SIW transition. This transition line is required to ensure impedance matching between transmission line and SIW component. Based on numerical analysis, it can be seen that the return loss of a SIW-based delay line with microstrip-to-SIW transition is better than the one with GCPW-to-SIW transition. Furthermore, the time delay of SIW-based delay line with microstrip-to-SIW transition is longer than the one with GCPW-to-SIW transition. In addition, for the whole design of 6-taps delay line system, a flat time delay of around 1 ns is achieved which reasonable insertion loss and isolation between two neighboring taps.

A common drain parallel amplifier in GaN using baseband PWM and direct filter connection for efficiency enhancement

To cope with the increasing demand for bandwidth in wireless communications coding schemes with high crest factors are employed. As a result the power amplifier (PA) is operated far below maximum output power for most of the time leading to low average efficiency in traditional designs. Therefore PA concepts providing efficiency enhancement in back off are key for efficient transmitters. Baseband PWM operated PAs in combination with direct filter connection are possible candidates. Due to the constant current of the used filters special PA structures are required. The proposed parallel common drain amplifier offers this properties. Its general operational principle is explained and an implementation study in a GaN MMIC process is presented. The designed PA operates at 2.65 GHz delivering a maximum output power of 3 W. To get optimum performance of the direct filter connection a codesign of the PA and the cavity filter included in the output matching network was done, resulting in a compact solution.

Frequency dividers in radar target stimulator applications

More and more driver assistance systems are integrated into modern vehicles. This development results in a continuous rise in the complexity of these vehicles, as the functions have to comply to the corresponding safety standards. Testing and validating these functions on an automotive test bench instead of driving tests at closed proving grounds requires comprehensive stimulation of the involved sensors. In this article we are focusing on an approach for stimulating short-range radar sensors of a vehicle located on such a test bench. Coping with the requirements imposed by these types of sensors we investigate the usage of frequency multipliers and dividers in the frequency translation section of the radar stimulator. For this purpose, we provide an overview on different concepts for these multipliers and dividers. After reviewing the advantages and disadvantages of these devices, we provide measurement results of a stimulator setup applying this type of frequency translation.ZusammenfassungFahrassistenzsysteme spielen eine immer größere Rolle in modernen Fahrzeugen. Die Integration dieser Systeme und die damit verbundene Einhaltung der nötigen Vorschriften und Sicherheitsstandards erhöhen die Komplexität der Fahrzeuge enorm. Um die Funktionsprüfung von Fahrassistenzsystemen auf dem Prüfstand durchführen zu können, ist eine umfassende Stimulation der Sensoren des Systems notwendig.Dieser Beitrag behandelt einen Zugang zur Stimulation automotiver Radarsensoren für den Nahbereich auf einem Prüfstand. Dabei wurde die Verwendung von Frequenzmultiplikatoren und Dividierern im Frequenzumsetzungspfad des Radar-Stimulators untersucht. Der Artikel gibt einen Überblick über verschiedene Konzepte zur Realisierung dieser Funktionsblöcke. In der Folge werden die Vor- und Nachteile der in Verbindung mit einem Radar-Target-Stimulator verwendeten Konzepte aufgezeigt und Messergebnisse präsentiert.

PCB RF probe landing pads for multiline deembedding

The interface between a probe station and an active or passive component on a printed circuit board is of great importance for RF systems operating in the mm-wave frequency range. The landing pads provide the transition between a coplanar measurement device and a microstrip interface. This paper addresses the design issues of such landing pads focusing on finding the optimal design enabling multiline deembedding with a measurement error better than 0.1dB.

mm-Wave RFID for IoT applications

The internet of things (IoT) and its applications demand for solutions for small and low-power communication devices. Overcoming the drawbacks of UHF radio frequency identification (RFID) a shift of the backscatter communication principle to mm-wave frequencies is desirable. With the significant reduction of the transponder size and wider communication bandwidth, many new applications become possible. Demonstrating the feasibility, we implemented a fully functional MMID system in the E-band. Both, the base station and the transponder are investigated and their performance is presented in a system context.

EMC performance measurements for professional wireless microphone systems

With shrinking spectral bandwidths and more intense use of the remaining frequency areas, the importance of good electromagnetic compatibility (EMC) performance of professional wireless microphone systems, as used by broadcasters, is increasing. A wireless microphone system consists of one or more pocket or handheld transmitters and usually the same amount of receivers. Both have to be immune against disturbances, and on the other hand they should not produce interferences.This paper deals with electromagnetic compatibility (EMC) performance tests of three analogue professional wireless microphone systems. The authors describe the complete measurement procedure using two different setups. These setups employ the pocket transmitter or the receiver as device under test (DUT). Different disturbance signals are used utilizing amplitude modulation (AM), frequency modulation (FM) or digital video broadcast-terrestrial (DVB-T). The audio quality of the transmission system is rated with the total harmonic distortion plus noise (THD+N). Additionally, the authors investigate intermodulations (third harmonic) caused by the transmitter. The results of all performance tests are extensively discussed.ZusammenfassungMit den kleiner werdenden verfügbaren Spektren und der intensiveren Nutzung der verbleibenden ist ein gutes EMV-Verhalten von professionellen Funkmikrofonsystemen ein immer wichtiger werdendes Kriterium. Diese Funksysteme bestehen aus einem oder mehreren Taschen- und Handsendern und der gleichen Anzahl von Empfängern und werden oft bei Fernseh- und Rundfunkanstalten eingesetzt. Beide, sowohl Sender als auch Empfänger, müssen störfest gegenüber äußeren Einflüssen sein und sollen selbst keine Störungen produzieren.Dieser Beitrag handelt von den Prüfungen der Elektromagnetischen Verträglichkeit von drei professionellen analogen Funkmikrofonsystemen. Die Autoren geben eine Einführung in die aktuelle Situation und beschreiben das komplette Messverfahren mit zwei Messaufbauten. Mit diesen Aufbauten werden jeweils der Sender oder der Empfänger getestet. Dabei werden Störsignale mit unterschiedlichen Modulationsarten, Amplitudenmodulation (AM), Frequenzmodulation (FM) und Digital Video Broadcast-Terrestrial (DVB-T) verwendet. Die Qualität des übertragenen Audiosignals wird mit dem Total Harmonic Distortionxa0+ Noise-Kriterium (THD+N) bewertet. Zusätzlich werden die Intermodulations-Störungen, die vom Sender unter gewissen Umständen erzeugt werden, gemessen. Die Ergebnisse der Prüfungen werden anschließend ausführlich diskutiert.

Numerical characterization of a SIW-based time delay line element with meandered slots structure

This paper presents a delay line element with meandered slots being part of a substrate integrated waveguide (SIW) structure and its numerical analysis. The proposed delay line element is designed by using a coplanar waveguide (CPW) configuration due its low dispersion compared to other transition configurations. The proposed delay line element is designed on a substrate of Rogers RO4360 with a thickness of 1.524 mm. Its numerical characterization is conducted in terms of return loss, insertion loss and group delay time. By numerical analysis and synthesis, the optimum delay line element can be designed and the desired characteristics can be achieved for operation in the frequency range of 1.4-2.8 GHz with a return loss up to 40 dB at a frequency around 1.75 GHz. Additionally, an almost flat insertion loss with values around 0.5 dB and a likewise nearly constant time delay around 1 ns is achieved over the desired frequency band.

A mm-Wave RFID system based on the EPC-Gen2 protocol

The importance of radio frequency identification (RFID) is expressed by the vast amount of commercial applications using this approach. Worldwide, billions of the RFID systems are operated in the HF (13.56 MHz) and UHF (868 and 915 MHz) frequency range. These RFID implementations suffer from rather large antennas required for a reliable and efficient operation. Increasing the operating frequency overcomes this physical constraint.