Welcome to Masayoshi Tanaka  Website  

Research activities of wireless & satellite communications in the following laboratories.
-  College of Industrial Technology, Nihon University, 
     Department of Electrical and Electronic
     Engineering.​
-  NTT Electrical Communications Laboratories.
  

     Multiport amplifier

 

The use of an MPA configuration was proposed for the power amplifier system of multi-beam communications. MPA is a special configuration composed of a power divider, a power combiner and an array of high power amplifiers (HPAs), and can overcome these problems with maximum flexibility and minimum hardware.

 

The MPA is composed of multiple input/output ports and multiple HPAs and is employed as a last-stage, high-power amplifier shared by multiple ports as shown in Fig. 3.

 

Figure 4 shows an example of an eight-port MPA with eight HPAs. The power divider (DIV) and the power combiner (COMB) are composed of a large number of hybrid circuits (HYBs).

DIV splits the input signal into multiple equal-amplitude signals, which have a unique phase distribution determined by the input used.

 

After amplification by the HPAs, COMB recombines the signals into a single signal, which is then passed to a single output that is determined by phase distribution. Since it is possible to install more HPAs than the number of ports in an MPA, power amplifiers with less output power such as MMICs can be used to construct an MPA.

 

Since signals from multiple ports share the HPAs in an MPA, it is possible to use power efficiently in case of traffic imbalance among ports, traffic variation due to access terminal movement, and so on.

 

In addition, communications for every port are maintained even if some HPAs fail.

Degradation of beam isolation due to variation among HPA characteristics and HPA arrangement methods that effectively improve beam isolation have been already investigated.

 

The multiport amplifier that we developed for the first time in the world was installed and operated on the ETS-VI satellite in 1994. (Ref.8, 9,11, 12) , (detail) 

 

Further developments are being made toward delivering higher output power and utilizing higher frequency bands.

 

We are studing the following issues to improve the MPA performance.

1. Design and configuration of enhancing beam isolation

2. High efficicent power amplifier configuration

3. Highly reliable configuration

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Design and configuration of enhancing beam isolation and reliability

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The degradation of MPA beam isolation due to HPA failures is a major problem, because for satellite application it is of great importance to maintain performance for long periods of time in space.

 

Thus, it is particularly desirable to develop a design method and an operation algorithm that is effective for achieving a reliable MPA with higher output power in higher frequency bands at reasonable cost . However, these issues have not yet been sufficiently investigated.

 

To address these issues, we investigated MPA performance degradation due to HPA failures and showed that it is possible to improve beam isolation by re-configuring on/off conditions of HPAs in the event of HPA failures.

 

Based on the results we obtained, we propose a new type of MPA we call the Self-redundant, Re-configurable MPA (SRRC-MPA). In a conventional system, a failed unit is replaced with a spare one through switch circuits. However, this new MPA does not require any additional spare HPAs or switch circuits.

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Improving the power efficiency of power amplifiers

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Improving the power efficiency of power amplifiers is another concern because power resources are limited for satellite on-board equipment.

 

It is particularly desirable therefore to develop a high-power amplifier system effective in achieving high efficiency at a reasonable cost.

 

In general, HPAs are highly efficient near the nonlinear saturation region. HPA linearization technology is often used for increasing efficiency. However, this requires additional complex circuits and time-consuming adjustments.

 

We investigated the intermodulation (IM) performance of MPA due to the HPA nonlinearity and showed the effective configuration that makes it possible to improve the signal to the third order IM product ratio (C/IM3) and improve the power efficiency of power amplifiers .