Ralf Leberer

A 76 GHz multiple-beam planar reflector antenna

A multiple-beam antenna based on the principles of a folded reflectarray antenna and a bifocal antenna is presented. Experimental results are given for a 76.5 GHz antenna with 90 mm diameter, a height of 26 mm, and a scanning range of ±13.5 as well as for an antenna with 130 mm diameter, a height of 30 mm, and a principle scanning range of ±30°. With its low height and potentially low fabrication cost, this antenna is an interesting candidate for next generation automotive radars.

A dual planar reflectarray with synthesized phase and amplitude distribution

A quasi-planar reflector arrangement for generating an arbitrary phase and amplitude distribution in the antenna aperture and thus a wide range of far field patterns is presented. A parallel pair of reflectarrays is used. One is implemented as a standard reflectarray using rectangular patches on a microwave substrate with metallized backside. The other reflectarray is provided with a polarizing grid, which acts as a ground plane for one polarization and is transparent for the orthogonal polarization. An offset rectangular feed horn is embedded in the lower reflectarray to illuminate the upper reflector. A design procedure for a linear polarized antenna with a sector beam in the azimuth and a narrow beam width in the elevation is presented and is verified with measurement results.

Folded multilayer microstrip reflectarray with shaped pattern

A folded multilayer printed reflectarray with shaped pattern is demonstrated. The configuration consists of a multilayer twister reflectarray, a centered feed embedded in its structure and a polarizing grid, which acts as reflector and radome for each polarization, respectively. A design procedure, valid for obtaining any arbitrary shaped pattern, has been implemented. In order to achieve the pattern specifications along a frequency band, initially a multifrequency pattern synthesis method, which relies on a phase-only synthesis, is applied to obtain the required phase-shift on the reflectarray surface. Afterwards, each stacked patch is individually optimized to generate the required phase-shift previously synthesized. The method has been successfully applied to a LMDS base station antenna, characterized by a sectorial cosecant squared beam in the band 24.5-26.5 GHz. A breadboard consisting of a folded 3-layer circular reflectarray is presented. Measurements show a good concordance with theoretical patterns at 25 GHz, and good shaping of the beam along 24-26 GHz.

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

An AlGaN/GaN class-S amplifier for RF-communication signals

A Gallium-Nitride (GaN) current switched class-S amplifier for 450 MHz RF-signals is presented. A FPGA board is used to generate a band-pass delta sigma sequence with 1800 Mbit/s. This quasi digital signal is amplified to the required gate voltage swing for the HEMTs using a commercial available preamplifier. The AlGaN/GaN-HEMTs are driven in a high efficient switch mode. Linearity is preserved using the class-S architecture. Limits of this classical amplifier architecture are shown and discussed. Simulation results are presented and the realized class-S demonstrator is shown.

GaN MMIC based T/R-Module Front-End for X-Band Applications

Amplifiers for a next generation of T/R-modules in future active array antennas are realized as monolithically integrated circuits (MMIC) on the bases of novel AlGaN/GaN HEMT structures. Both, low noise and power amplifiers are designed for X-band frequencies. The MMICs are designed, simulated and fabricated using a novel via-hole microstrip technology. Output power levels of 6.8 W (38 dBm) for the driver amplifier (DA) and 20 W (43 dBm) for the high power amplifier (HPA) are measured. The measured noise figure of the low noise amplifier (LNA) is in the range of 1.5 dB. A T/R-module front-end with mounted GaN MMICs is designed based on a multilayer LTCC technology.

A folded 3-layer printed reflectarray with shaped pattern for LMDS central station sectored antenna

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Linear broadband GaN MMICs for Ku-band Applications

AlGaN/GaN-based HEMT MMICs on s.i. SiC wafer substrates are designed and realized for linear broadband amplifiers. Electrical performance data and assembly technology issues are presented in this paper. The linear broadband amplifier MMIC operates in the frequency range from 9 GHz to 19 GHz and is fabricated in microstrip technology including via-holes. The measured small signal gain is about 13 dB and the output power at 1dB compression is in the range of 27dBm. Two-tone measurements show good linearity. Up to 26dBm output power the IM3 value is better than 30dBc. A reliable assembly process for the MMICs is necessary in order to achieve good thermal conductivity between the underlying SiC wafer substrate and the heatspreader beneath

Folded reflectarray antennas for shaped beam applications

Folded reflectarrays in general consist of a feed, a reflectarray, and a second substrate with printed structures in front of feed and reflectarray, acting as polarizing filter. In this way, compact and possibly lowcost antennas can be designed. This contributions demonstrates the possibilities of this approach for shaped beam antennas using a phase-only design approach and extending the polarizer with additional phase-adjusting elements to allow all types of dual reflector approaches. As examples, two sector antennas, a multibeam antenna, and a multibeam antenna with sector-shaped lobes are presented.

Design and Realisation of a Compact 38 GHz Radiometer

Architecture, design, assembly and performance data of a 38 GHz radiometer are presented in this article. The radiometer is intended to serve as a demonstrator in microwave system education and as a platform to demonstrate novel RF structures and design techniques. Among other components, it includes a folded planar reflect array antenna, a mechanically sealed transition from circular waveguide to microstrip and several monolithic microwave integrated circuits (MMIC). With an internal reference and various analog and digital compensation circuits, the radiometer is able to measure absolute noise temperatures within a considerable operating temperature range. Adjustable data integration parameters allow the radiometer to be used for many different scenarios. The overall performance of the radiometer is verified by system measurements and some exemplary field tests. Übersicht In diesem Artikel werden Architektur, Entwicklung und Aufbau eines Radiometers bei einer Frequenz von 38 GHz beschrieben. Das Radiometer stellt sowohl ein Demonstrationsobjekt in der Lehre als auch eine Experimentierplattform für neue Hochfrequenzstrukturen und Entwurfstechniken dar. Es enthält unter anderem eine gefaltete planare Reflektorantenne, einen mechanisch dichten Übergang von Rundhohlleiter auf Mikrostreifenleitung und verschiedene MMIC-basierte Millimeterwellenund Hochfrequenzschaltungen. Da das Radiometer über eine interne Referenz und verschiedene analoge und digitale Kompensationsnetzwerke verfügt, ist die Messung von absoluten Rauschtemperaturen innerhalb eines beträchtlichen Gerätetemperaturbereichs möglich. Über einen weiten Wertebereich einstellbare Integrationszeiten erlauben es, das Gerät für verschiedene Meßszenarien zu verwenden. Die Leistungsdaten des aufgebauten Radiometers wurden durch die Ergebnisse von Systemmessungen und durch beispielhafte Feldtests verifiziert. Für die Dokumentation Radiometry / Radiometer / Folded Reflect Array Antenna /Circular Waveguide-to-microstrip Transition