Phase nonlinearity reduction of a complex receiver having multiple phase correlators

Abstract

AbstractThis article analyzes and describes phase nonlinearity reduction techniques in detail for ultra wideband complex receivers to qualify airborne system requirements. Phase nonlinearity directly affects the final frequency resolution coming from unknown threats. Thereby, the reduction of phase nonlinearity of all radio frequency (RF) channels including phase correlators is very essential. A simple phase nonlinearity calculation step has been shown in this article without taking the help of any coding (software). A detail excel sheet–based phase nonlinearity calculation has been explained and estimated with examples. Power and phase corrections are especially done to keep the RF response flat over a wide frequency spectrum to enhance better phase linearity. This is done by designing various equalizers with different slope gradients and adjusting power levels by using attenuation pads or reducing feeds by other means. Phase nonlinearity has been kept under control by tracking the phase of mixers, other passive/active components within ±5°, and all the RF channels within ±15°. The power level has been adjusted within P1dB or just beyond the P1dB to keep the harmonic level less, which in turn controls phase nonlinearity in all the active devices. The performance of phase correlators against various power levels has been analyzed to finalize uniform RF and LO power levels (feed) at the input of the phase correlators. The level of uniform feed has been decided after reviewing phase nonlinearity responses of the correlators. Thus, the final resolved frequency become accurate (<3 MHz root mean square). Finally, four receivers have successfully been developed and evaluated over temperature (−40°C to +71°C) and vibration to establish the method for mass production.