Ultra Performance Requirement For A Digital Attenuators in MIMO Applications

Posted by Blaise Yen on June 6, 2017

Introduction

        Digital Programmable Attenuators are routinely used in radio performance testing to simulate path loss. MIMO technology enables the use of multiple streams of data to boost throughput. The number of streams is also increasing from the 2×2 of only a few years ago to 8×8 and soon to be even higher. Multiple channel attenuators offer a compact package with a single digital interface to control multiple channels. For most applications, a 63dB of total amount of attenuation and chain to chain isolation is sufficient to provide excellent performance on the system level.  In some very special cases, these parameters need to be further improved. This article will outline this requirement and how AdauraTech’s new AD-USB4AR2 will enable the users to achieve this ultra-performance.

Typical Test Setup

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Figure 1 This diagram illustrates a typical chamber test set up for measurement of throughput performance.

 

RF Leakage Paths

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Figure 2 This diagram shows the RF leakage paths where chain to chain isolation is defined.  The ADUSB4A offers a typical of 70dB isolation.

Typical Signal Levels

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Figure 3 The RF signal is reduced by the radiated path or by fixed attenuators to a realistic level of -30dBm to prevent saturation of most radio front end.  An RF signal of -30dBm will appear as -100dBm (-30dB-70dB) at another chain.  -100dBm is typically below receive sensitivity of most radios. 

Special Case

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Figure 4 illustrates a case where the RF signal is much higher at 0dBm level.  The Chain to chain isolation of 70dB will not suppress the leakage below sensitivity level.

Special Case with AD-USB4AR2

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Figure 5 shows the special case with ADUSB4AR2 where 100dB of chain to chain isolation will provide ultra performance to suppress the leakage level to below receive sensitivity.

 

Conclusion

        In summary, AdauraTech continually provide cost effective high performance test products for the wireless industry.  The new ADUSB4AR2 is an example of another addition to our product portfolio to enable compact form factor with ease of computer control and ultra-high RF performance.

 

Posted in Blog, RF Test Engineering, USB 4-Channel RF Attenuator.