Satellite Antenna Redundancy (White Paper)

Redundancy solution for multiple antennas serving an n+1 configuration

Executive Summary

High uptime is critical for most satellite ground station signals. Failure of a single device in the transmission chain can disrupt large arrays of service. This creates the need for a smart, automated, backup protection system.

To meet application-specific requirements for satellite earth stations and L-band distribution systems, redundancy switches offer important advantages for operators. A single motorized antenna can serve an entire dish farm as a backup antenna protecting multiple primary dishes. Signal monitoring, control and switching of a backup antenna can be offloaded to a redundancy switch to secure a cost-effective, simple-to-use solution offering a highly robust redundancy system.

Fig.1: Satellite Earth Stations in Raisting, Germany

Introduction

Satellite ground stations demand high uptime. Spare devices in “hot standby” are thus used to ensure system uptime. In rare cases, 1:1 redundancy may be required for each antenna in the system array. However, for most requirements, several antennas may share a single redundancy antenna.

One common setup comprising six Ku-band antennas, each with four L-band signals (Horizontal High, Horizontal Low, Vertical High, Vertical Low) is backed up by one redundant antenna. This arrangement called “4*6+1” protects six primary signal paths using a single redundancy antenna path (6+1). Four of these channel redundancy units, one for each polarization (4*), are configured within a single switch.

DEV has developed a single switch to handle all of these features. Up to four redundancy units each serving 16 signal channels are possible (4*16+1).

The DEV 1993 is specified for frequencies up to 2.45 GHz and is available in 50 ? with SMA connectors or in 75 ? with precision F connectors. High isolation separating the distinct service channels from the redundancy channel is attained to ensure optimal signal quality.

Local setup and control for the device is implemented by a web interface for configuring, switching and monitoring the device.

This product can also be expanded to set up and steer a motorized backup antenna via controller to create an operator-free backup system switching signals from any failed antenna to the spare path.

Operation of the redundancy switch

In normal operating mode where antennas function fully, each signal is delivered to its chosen output. When an antenna fails, the backup dish recovers the feed of the failed antenna. Signals from the redundancy antenna should thus be routed to the output ports of the replaced dish to provide a hot-standby recovery of service.

Fig.2: Using a Motorized Redundancy Antenna

During normal operation, the signals of the redundancy antenna are routed to Output R (Figure 2) where the signal can be monitored. This is especially necessary when the redundancy antenna is motorized to adjust to the positions of each satellite serving the fixed antennas. Here, signal strength can be assessed before switching to redundancy.

Figure 2 shows a 4+1 antenna system utilizing a DEV 1993 configured for 4*4+1. Note that the bias supply for the redundancy antenna is provided by the DEV 1993.

Monitoring & Control of a Motorized Antenna

To significantly improve the uptime of a facility having multiple fixed satellite antennas, one or more motorized steerable antennas can be used as a redundant spare. When a fixed antenna fails, the steerable antenna restores signal by pointing at the satellite(s) normally served by the failed antenna.

If a fixed antenna’s L-band signal fails, the backup antenna must be commandeered to the satellite position of the lost feed, typically via its Antenna Control Unit (ACU). In addition, a redundancy switch must engage so that the signal captured by the redundancy antenna will reach its proper destination. Manual recovery is typically slower than automatic switching and requires continuous attendance by a human operator. Furthermore, in most cases, an ACU cannot be easily served by a redundancy switch.

The objective behind DEV Systemtechnik’s development of its antenna monitoring and control option has been to provide a comprehensive and powerful automatic solution for n+1 redundancies. Here, a system needs the ability to aim a motorized redundancy antenna automatically to specific satellite positions stored within the DEV 1993. Another requirement involves switching redundant signals to the same outputs fed by a primary stationary antenna.

Fig.3: Azimuth, Elevation and Polarization Angel

The position of an antenna, especially a motorized one, can be described by three angles. The azimuth (AZ) sweep of the whole antenna about its vertical axis starts clockwise at geographical North (0 deg.) to end at 360 deg. Elevation (El) refers to the angle between the satellite beam and horizontal plane. Finally, the polarization angle (Pol) – not to be confused with the mere polarity of a received signal – marks the rotation of the LNB away from its normal position, ranging from -90 deg. (counterclockwise) to 90 deg. (clockwise). Notably, not all ACUs support control of the LNB polarization angle.

Figure 4 illustrates the components of an antenna system with four stationary antennas backed up by one motorized redundancy antenna. The RF outputs (four signals per antenna) of all antennas are connected to the redundancy switch. The motion of the motorized antenna in terms of azimuth, elevation, and (possibly) the polarization is controlled by the DEV 1993 through an ACU.

Fig.4: Backup system using a Motorized Redundancy Antenna

Using the global position of the antenna site, the DEV 1993 can calculate the distinct antenna positions (AZ, El and Pol) for each different satellite as shown in Figure 5. The position of each stationary antenna is then stored for commanding the ACU to position the motorized redundancy antenna. Switched inputs are finally fed by the redundancy antenna to the corresponding outputs.

Fig.5: Satellite Position stored within the DEV 1993

Figure 4 shows Output 4 of the DEV 1993 being fed by the Motorized Redundancy Antenna after the failure of primary Satellite Antenna 4. Here, the system has already positioned the Motorized Redundancy Antenna to the coordinates required to back up primary Antenna 4, having switched the four signals to the redundant routing.

Note: The applied antenna controller needs to be connected to the CPU module.

Note: The signals of Satellite Antenna 4 are not routed to Output R when the device is switched to the redundant mode, as may be implied by Figure 4.

Dual Band Redundancy

Consider, for example, a satellite ground station having 10 Ku-band antennas using all four polarizations plus six C-band antennas with two polarizations. The goal here is to ensure antenna redundancy enlisting only one additional motorized antenna.

To fulfill this requirement, the redundancy antenna is equipped with a dual-band feedhorn system to handle Ku- and C-band signals of both frequency ranges and is motorized for quick positioning.