PROJECT 245 : SOME KEY ACHIEVEMENTS

Working Group III: Active Antenna Architectures and Components

One key achievement of COST Project 245 in the field of active antenna architectures has been the development and consolidation of the new transmit antenna concept of semi-active multi-matrix antennas, originally introduced in COST Project 223 for multibeam mobile communication satellites. The principle is illustrated in fig. 13.

Fig. 13 Block diagram of a multi-matrix semi-active reflector antenna (Courtesy ESA-ESTEC)

Amplifier modules are separated from radiating elements by microwave "matrices", which allow to run all amplifiers at maximum efficiency for all traffic to beam distributions. Multimatrix antennas, now operating on board the INMARSAT III mobile communication satellite series, are considered worldwide for other satellites.

Under COST project 245, the semi-active antenna concept has been successfully extended to planar arrays for generation of contoured beams with low sidelobes and also to conformal arrays, in particular for use in future base stations for mobile telephony.

Fig. 14 Vehicle mounted SATPHONE antenna (Courtesy VTT, Finland)

The Technical Research Center of Finland (VTT) and Ylinen Electronics Co., have developed under contracts to the European Space Agency an L- band satphone antenna for land vehicles (fig. 14). The work is related with the development of the European Mobile Satellite System (EMSS). employ Italsat-1 (F2) and Artemis satellites. The EMSS system, will comprise two communication systems the Prodat-2 system and the MSBN (Mobile Satellite Business Network) system. The Prodat-2 system, is a message store and forward system. An omnidirectional antenna is used in a Prodat-2 terminal. The MSBN system offers higher bit rates providing voice, data and telefax services. In a MSBN terminal a directional antenna with a tracking system is needed. This new MSBN antenna subsystem is based on mechanical beam steering and consists of an antenna unit and a control unit. The antenna acquires and tracks automatically a geostationary satellite when the vehicle is in motion and changes its direction. The tracking system includes an electric angular rate sensor, which improves the tracking performance especially in cases when the truck turns fast or when fading is encountered on the satellite link. Two versions of the antenna unit are available. The larger one has a gain around 11 dBi. The more compact one provides a gain of around 8 dBi.

There is a considerable interest in the use of adaptive antennas for mobile communication systems. The incorporation of spatial diversity provided by adaptive array antennas offers a new dimension to the reduction of interference and to higher spectral efficiency. The adaptive antenna system adjusts to the electromagnetic environment as it changes and dynamically alter the signal patterns to optimize the performance of the radio channels. Complex signal processing algorithms continuously distinguished between desired signals, multipath and interfering signals as well as determine their direction of arrival. The ability to track users with main beams and interferers with nulls insures that the link budget is constantly maximized. The fig. 15 shows a three-sector base station antenna arrangement in microstrip technology. The up link is covered by a number of narrow fixed beams with high antenna gain to fill the entire area of one hexagonal cell. Dual polarization is employed to create enough beams with a minimum of antenna columns. Each receive beam has its own low noise amplifier located at the antenna to reduce the effect of cable losses. The down link is handed by conventional 120=83 sector antennas on either side of the array antenna. Power amplifiers are integrated in the sector antennas to give balance between the up and the down link performance. Future wireless networks will provide multimedia services requiring high as well as low data rate transmission for mobile users. Study of efficient exploitation of the spatial domain by the use of array antennas is needed due to the limited capacity of current wireless access techniques. Interdisciplinary research related to array antennas, radios and signal processing algorithms is needed.

Fig. 15 Adaptive antennas in mobile communication systems (Courtesy Ericsson Microwaves, Sweden)

Fig. 16 Microwave phased array in microstrip technology (Courtesy University of Wroclaw, Poland)

The MC-8 microstrip phased array, under study during COST Project 245, has a wide range of beam steerability and generates linear polarization around 5.0 GHz. A specific feature of the MC-8 is its low sidelobe level achieved by an amplitude taper generated in the beam former. The potential application of antennas operating in this frequency band is in Microwave Landing System (MLS) and Synthetic Aperture Radar (SAR). The key parameters of these system antennas are high gain, low sidelobe level and scanning capability in one or two directions. MLS antennas must have a wide beam scanning range. The MC-8 array was measured by a far-field technique in an anechoic chamber (fig. 16).

Fig. 17 Active Ku-band satellite antenna for fixed communications (Courtesy Alcatel Espace & France Telecom)

In the area of fixed satellite communications, annular ring elements elements developed during the COST project 245, have had applications at L-band and at Ku-band. At L-band they have been exported to equip the Nippon Star satellite.

At Ku-band, they have been developed in dual linear polarisation and interfaced with filters, power amplifiers and a low level beam former with MMIC components. A complete array breadboard has been demonstrated (fig. 17). This technology will fly on the French telecommunication satellite STENTOR.

Fig. 18a Active array breadboard for satellite TV reception (Courtesy University of Paderborn, Germany)

Due to the rising number of TV and radio programs distributed via satellite, direct satellite reception will gain an increasing importance in the next years. Since the early days of satellite-TV, research activities at the University of Paderborn concentrated on active phased array antennas for quasi-mobile and mobile satellite reception. The advantage of adaptive phased arrays is to provide operation continuously adapted to a specific signal situation (e.g. multipath fading environment, interferences) by proper control of the main beam and the sidelobes. An active antenna for mobile DBS-reception has been built up and presented during COST Project 245. Fig.18a illustrates an active phased array antenna for multiple orbital positions which has been developed and realized at University of Paderborn and presented during COST 245. The array is designed for satellite reception in the Ku-band. It consists of 64 Rampart-line columns arranged alternately for left- and right-hand circular polarization. The phase of the column signals is weighted by subsequent 4-bit phase shifters. A processor system controls the phase shifters in order to optimize the picture quality of the received signal by adapting the position of the main beam as well as the polarization (WS Proc. p 263)

Fig. 18b shows the RF-components for each column, that have been developed at University of Paderborn during COST Project 245. A two-stage12 GHz low-noise amplifier is provided for each column as well as a 4-bit phase shifter.

Fig. 18b

Fig. 19 Low noise amplifier for satellite TV reception active array (Courtesy Chalmers University)

Layout of a low noise 12 GHz one stage amplifier for Satellite TV reception (fig. 19). The design, evolved under COST Project 245, is adapted for multi-element antenna arrays, each antenna element having its own amplifier. The output of the amplifier is DC isolated by use of a dB coupler.

Quasi-optical techniques offer many advantages in developing microwave and millimeter wave radars and high power communication transmitters. Recent developments in microstrip antennas and solid-state devices have made it possible to combine the active devices with planar antennas to form active antenna elements. Active devices are usually integrated directly into the patch structure. A novel design of an X-band patch antenna integrated with a Gunn diode has been developed. The Gunn diode has been placed into the rectangular opening formed by removing the central part of the patch. Proposed geometry (fig. 20) offers three degrees of freedom by changing the position, width or length of the inverter. Very good E and H far-field co-polarization and cross-polarization patterns have been measured. Nearly linear frequency dependence with bias voltage and a low parasitic AM make this active antenna very suitable for FM applications. A relatively high EIRP, acceptable noise levels are observed throughout the tuning range. Injection locking experiments have shown a wide locking range and allowed the determination of the Gunn diode loading conditions. Such a miniaturized wide-band VCO antenna can be efficiently used for microwave and millimeter-wave spatial power combiners. (WS Proc. p 281)

Fig. 20 Voltage controlled self oscillating planar antenna (Courtesy University of Zagreb, Croatia)

COST-245 Summary report

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Mars 1997 Content Responsible : Technical Manager : Webmaster@lema.epfl.ch