Leopold Reiter

SDARS - Antennas: Environmental Influences, Measurement, Vehicle Application Investigations and Field Experiences

According to the challenging antenna performance requirements for the reception of the Satellite Digital Audio Radio Services (SDARS), environmental influences are playing an important role for the practical design and application of such an antenna. This paper will report about remarkable influences on the performance of SDARS – Antennas with respect to ground plane conditions for measurements in anechoic chambers, as well as for vehicle mounting conditions. Results of field tests will show, what this means for reception.

Concept Studies of Scanning and Combined Scan/Phase Antenna Diversity Systems for SDARS

Several concepts of antenna diversity for satellite digital audio radio systems (SDARS) are investigated. A comparison is made regarding the improvement of reception quality. Special attention is paid to easy realisation in an automotive environment. Proof is shown that for critical reception scenarios for example underneath dense foliage or in multipath situations between high buildings an antenna diversity system yields a significant reduction of the total duration of mutes. The concept of a new scan diversity and a combined scan/phase antenna diversity system are investigated, realised in hardware and evaluated in real scenarios. Full diversity function is achieved with only minor or even without modifications of the receiver and no additional effort in mounting and required space for the antenna modules. As in single arm reception systems only one tuner is used. There is only one antenna cable between antenna module and the receiver. Index Terms – SDARS, Antenna Diversity, Mobile Reception, Multipath Propagation

Antenna-Diversity Techniques in Cars for FM-Radio, TV and Cellular Phone

Car producers prefer multi antenna scanning diversity systems to improve FM and TV reception quality. These systems are highly efficient and cost effective to reduce distortions going along with multipath propagation. A criterion for the diversity effectiveness of a multi-antenna arrangement on a car is derived. This number of equivalent decorrelated antennas being effective is evaluated by turntable antenna measurements as a basis for computer simulated virtual drives in a Rayleigh wave propagation scenario. The comparison of different antenna arrangements shows that even compact antenna systems integrated on one single car window provide high diversity effectiveness. Even mobile phone reception quality for GSM can be increased.

SDARS-Antenna-Diversity-Schemes for a better Radio-Link in Vehicles

The most challenging task for digital mobile satellite broadcast reception is to satisfy a variety of combined requirements for automotive applications. According to the US satellite digital broadcast system (SDARS) the antenna parameters according to the SDARS-Antenna Specification have to be met [1]. There is a great desire for a low profile design or even hidden antenna systems according to styling conditions given by the Automotive Industry. For the time being there are strong recommendations for a specific mounting location of a SDARS-antenna in order to meet the required radiation pattern on a vehicle. For many vehicle models this location is considered as inconvenient and there is a strong demand to design more inconspicuous antennas. This design constraint for the SDARS antennas would cause intolerable high bit-error-rates resulting in too many interruptions in poor signal areas even though up to two QPSK-modulated satellite signals and a terrestrial OFDM-modulated signal of the digital data stream are made available at a time however with an offset of time between each other. The intention of this paper is to present research results with respect to the additional obtainable improvement by means of a fast switching antenna-diversity system in addition to the SDARS combined satellite-and-terrestrial-channel-diversity-system. Error correcting codes by principle are applied in any digital communication system but due a different character cannot be a substitute for the satellite-and-terrestrial-channel-diversity and antenna-diversity as well.

High-impedance amplifier enabling an easy implementable interface for a diversity system of window-printed antennas

For FM radio reception in cars a high-impedance amplifier concept represents a lean interface between antennas and the radio, enabling an easy integration of different antenna structures with low development effort. Results of the frequency responses in the European and Japanese FM band of an optimized high-impedance amplifier in combination with several measured window antennas with different impedance behavior are presented. In order to highlight the advantages of the high-impedance amplifier concept, the results are compared to those of a standard 50-Ohm amplifier using the same antennas. In contrast to the 50-Ohm amplifier, which requires a matching network for each antenna structure, it is possible to apply just one single high-impedance amplifier for various window-printed antennas occurring in a diversity system. The investigations show the great flexibility and applicability of the high-impedance amplifier, since the number of conditions to be met is significantly reduced.

High-impedance amplifier in combination with coated FM windscreen diversity antennas

For the European FM frequency range, a set of four active diversity antennas with high-impedance amplifier is investigated, which are realized in terms of different connections to the conductive coating of a car windscreen. A comparison between simulation and measurement of the screen antennas is carried out and the active frequency responses of all antennas in combination with an optimized high-impedance amplifier circuit are shown. The investigations demonstrate a very powerful performance of the coated screen antenna structures in combination with the high-impedance amplifier compared to a passive quarter wavelength reference antenna. It can be shown that even though the antenna ports offer different impedances, the same amplifier circuit can be used for all these structures. Hence, the use of the high-impedance amplifier concept enables an easy interface, which offers high flexibility in choice of the antenna structures and low development effort for their design.

A New Antenna Principle for Satellite Radio Reception including the Option for Diversity and Multiband Application

The new Satellite Digital Audio Radio Service (SDARS) has already started in USA. The circularly polarized satellite signals are supported by terrestrial transmitters in built-up areas using vertical polarization [1]. Therefore the receiving antenna has to meet both requirements. Due to automotive aspects for reception of this service low profile antennas are required. In this paper such an antenna is presented which meets both the SDARS-specifications and the requirements for SDARS-antenna diversity application due to multipath reception even with satellite signals. The design principle allows in a further upgrading multiband application for cellular phone e.g. GSM or UMTS.

Dynamik und Linearität von Hochfrequenzgegentaktmischstufen

The most important characteristic of a balanced mixer is the dynamic range which is determined by the sensitivity and the distortion performance in regard to intermodulation and crossmodulation. Balanced mixers with ideal bipolar transistors with an exponential current-vojtage behaviour would not generate any non-linear distortions. In practice, the suppression of undesired intermodulation products is limited exclusively to the influence of parasitic circuit elements, such as base series resistances, emitter resistances, source resistances of the oscillator signal and the source admittance of the signal current source. Best sensitivity and linearity as well are obtained in the switching mode of the transistors. Therefore, in this mode of operation, the dynamic is maximum and is only a function of the bias current, signal source admittance and the IF-bandwidth. Für die Dokumenta t ion: Gegentaktmischer / Intermodulation / Kreuzmodulation / Dynamik / Hochfrequenztechnik

Rauscheigenschaften und Empfindlichkeit von Hochfrequenzgegentaktmischstufen

For evaluation of the sensitivity of balanced mixers the noise contributions of bipolar transistor noise sources and the noise sources of the mixer network are investigated as a function of the amplitude of a sinusoidal and a rectangular oscillator wave function. It is shown that the noise sources in the oscillator input circuit of the mixer contribute only negligibly to the total noise if a rectangular oscillator wave function is applied. Therefore, in this mode of operation, optimum sensitivity is obtained which is only a function of the transistor bias current and the IF-bandwidth. Für die Dokumenta t ion: Gegentaktmischer / Empfindlichkeit / Rauschen / Hochfrequenztechnik