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Design Notes

VSS Phased Array Signal Splitter for Receivers (PHARRAY_RXSIG)

This project demonstrates:

1. The use of the VSS PHARRAY_RXSIG block

2. The use of VSS RFB measurements

3. How to measure Gain-to-System-Temperature-Ratio

The built-in G/T measurement computes the ratio of isotropic antenna gain to system equivalent noise temperature. The Gain is measured directly from output port of antenna, and the noise at output of system is referred back to this antenna output port.

To measure G/T of the entire phased array, the noise and gain must be measured separately and G/T computed using equations since we cannot directly access the gain of single antenna.

Because every noise contribution is multiplied by the amplifier gains g > 1 and the attenuation coefficient e, and the signal contribution likewise, then the S/N (and antenna G/T) is constant throughout the cascaded graphs. This means we can measure G/T from any reference point.

In the system diagram Test,

which consists of single cascade of antenna and amp models, the built in G/T measurement referenced to the output of antenna, is compared to budget measurement of SPWR_node and T_node at output

G/T calculated as:


G/T agrees with the built-in measurement.

This method was then applied to the complete array. The input source was split using the PHARRAY_RXSIG block. The input signal is passed as-is to all the channels. This is akin to defining a multipath channel to all the arrays. This ensures that the gains of the antennas add correctly.

The source and the PHARRAY_RXSIG are made noiseless and an antenna temperature is added to each antenna. This means that the antenna temperatures Tant are uncorrelated. If the noise were instead added to the source (making each antenna noiseless and due account taken of antenna gain by scaling source temp by factor 10^(-antgain/10)) to give same noise temperature at output of each antenna, then in this case the antenna noise would be fully correlated. This is because of the action of the PHARRAY_RXSIG - noise generated outside of the PHARRAY_RSSIG emerges correlated. Noise generated internal to the element emerges uncorrelated.

Correlation of the antenna noise gives a higher Tsys and worse G/T.