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FOCAL POINT: Add Power As You Need It

As the world’s insatiable thirst for information access continues to grow at an ever increasing rate, satellite service providers are faced with the need for power amplifiers that can deliver large amounts of linear power reliably. Today’s complex modulation and coding schemes increase the number of bits one can pack into a hertz of transponder bandwidth and when it comes to transmission, more bits requires more power. High-order modulation schemes become an inherent challenge when factors such as single-carrier spectral regrowth, multi-carrier intermodulation distortion with associated memory effect and AM/PM phase distortion are factored into the equation.

In the past, when thousands of watts of uplink power were required, earth station designers had little choice but to incorporate Klystrons or high-power TWTAs to achieve power levels of this magnitude. Klystrons, though cost effective, are bandwidth limited to a single transponder and are consequently unable to provide access to the satellite’s entire frequency resource. Though wideband TWTAs are not plagued with the bandwidth issue, they are still tube-based products that require extremely high-voltage power supplies, are subject to out-gassing and by design, have numerous single points of potential failure. These limitations are partly responsible for the enormous growth in demand for Solid State Power Amplifiers (SSPAs). As SSPAs are based on transistor technology, they are much less susceptible to the distortion effects previously mentioned. Additional benefits include the use of low voltage power supplies, the ability to achieve high linearity without the need for additional linearizers and higher Mean-Time-Between-Failure (MTBF) values. Unlike tubes that require special handling for transport, SSPAs utilize small, compact RF “modules” that can be shelf-spared without concern for out-gassing.

If asked for their proverbial “wish list”, some operators would say the ability to size the amplifier to suit their current needs and scale it up to higher power levels in the future as the need for more power arises would be a nice feature. Long term maintainability might be a key factor as a disruption in service can equate to a serious loss of revenue. The elimination of mechanical devices such as waveguide and coaxial switches as a method of gaining redundancy increases reliability as does the ability of station operators to remove and replace critical amplifier components without disrupting service.

In order to meet these demanding requirements, Paradise Datacom has introduced the latest innovation in high power, Solid State Power Amplifier design — PowerMAX, the latest in modular and scalable amplifier systems.

Modularity = Maintainability
The key to providing a truly maintainable system is through the provision of easy access and simple removal of critical components for site technicians. This includes the SSPA module, cooling fans, power supply modules, and M&C card. All active assemblies within the PowerMAX system are hot-swap replaceable either from the front or rear panel of the amplifier chassis. There is no need to pull a chassis from the equipment cabinet.

Having an inventory of lower cost replaceable subassemblies means that there is never a need to return any part of the PowerMAX system to the factory for any repair. Mean time to replace any subassembly is 10 minutes. These repairs can be made without the need to power down the entire system. Therefore there is never any down-time with the PowerMAX system.

Soft-Fail Redundancy
The PowerMAX system was designed to be used as a redundant amplifier system. The PowerMAX architecture is considered “pure parallel” by reliability engineers. This means that there are no waveguide switches or other active components in the RF path. The failure of an SSPA module results in a small decrease in total system output power capability. The amount of total output power decrease in the event of a SSPA module failure depends on the total number of RF modules in the system and is summarized below.

4 Module System
1 failed module = 3dB decrease

8 Module System
1 failed module = 1.2dB decrease

16 Module System
1 failed module = 0.6dB decrease

Another important advantage of passive power combining is that there is never any finite interruption of the signal traffic with the failure of an RF module. This is critical in systems requiring master clock resynchronization when a large decrease in signal is experienced, even for a brief period of time.

When the system is used in Gain Correction Mode, the system gain is maintained at a constant level in the presence of an amplifier module failure. Therefore, if a system is sized such that the loss of one RF module can be tolerated by the system link budget, there will be no noticeable system performance change with the loss of one RF module.

The power supply is sized to have a full spare module. Thus a failure of any power supply module means that there is no decrease in output power or any other operational characteristic of the amplifier.

Even the system Monitor and Control facility is completely parallel redundant. Each SSPA chassis has its own embedded controller with a hierarchy of system control. An entire SSPA chassis can fail and no system performance parameters will be affected. Additionally the system will maintain remote communications with a system level Monitor and Control via RS485 or Ethernet communications. This advanced hierarchy of control enables the entire parallel system to be operated as if it were a single thread amplifier. This is true of both local (front panel) control as well as remote control.

The capital investment in an installation’s High Power Amplifier is always a major expense regardless of the HPA technology. A great deal of system engineering and planning must go into the selection of an amplifier’s output power capability. It is often difficult to predict the potential growth in signal traffic and end user application of a particular HPA. The field scalability of the PowerMAX system offers a great way to protect the customer’s investment. The customer can start out with a 4 module system and later upgrade to 8 or 16 modules. The design of the system makes it extremely easy to add additional RF and power supply modules in the field.

The system uses Paradise Datacom’s proprietary 4-way waveguide combiner network that makes conversion from a 4 module system to an 8 module system very easy to perform in the field. The chassis power easily connects to the system DC bus via quick connect style connectors. Thus there is minimal nut-and-bolt assembly required when upwardly scaling the PowerMAX system.

The PowerMAX is the first HPA system to utilize “True RMS” output power detection. Legacy HPA systems have long used simple diode peak detector circuits that provide a very crude means of output power detection. These circuits only give an accurate output power indication with an unmodulated CW carrier. By utilizing RMS detection and thermistor-based sensor technology, the PowerMAX system reports accurate RMS output power regardless of the number of carriers and modulation schemes present.

As PowerMAX architecture is based upon Paradise Datacom’s wide range of high density SSPA modules, a variety of output power levels and frequency bands can be addressed simply by populating the system accordingly. At present, the system can be configured as a C-, X-, Ku-, or Ka-band SSPA with the following output power levels.

C Band
250W, 300W, 400W, 500W & 600W

X Band
250W & 500W
Ku Band
125W, 150w & 200W

Ka Band
40W & 80W

Thanks to Paradise Datacom’s proprietary RF power combining network, modules can be “scaled” in groups of four to achieve extremely high output power levels. Tables 1 through 3 summarize the available system output power capability with 4, 8, and 16 module systems.

The PowerMAX family of solid state amplifier systems provides output power levels previously obtainable only with Klystron or TWTA technology. The system engineer can now design high power earth stations with all of the advantages solid state power amplifiers bring to bear. Unlike the high power amplifiers based upon tube technology, the PowerMAX system has all of the advantages of a pure-parallel redundant system. A soft-fail, parallel redundant system with complete hot-swap modular subassemblies makes the PowerMAX architecture one of the most exciting new systems to come along in the Satcom and base station amplifier environment in quite some time.