On-board AJ enhancement using adaptive nonlinear processing: practical aspects of Smart AGC implementation

Abstract

This study verified the capability of a new anti-jam approach (proprietary trademark name: Smart AGCY that could be used for. MILSATCOM transponders; it assessed performance in controlled jamming scenarios, and surveyed the capability of current technology to support near-term implementation. Smart AGCTM employs time-dependent, RF "center stripping", the size of which is determined by a fast measurement of the jammer's amplitude. Results with constant envelope (CE) and slowly varying jamming confirm that the output jammer-plus-intermod-to-noise ratio, (J+IM)/S, can be reduced to several dB above the combination of background noise level and wanted signal level. With Smart AGCW, a pure unmodulated carrier (CW) jammer at the center of the band would no longer be the optimum jammer for direct sequence spread spectrum modulation (DSSS), nor could a CE signal produce 6dB small signal suppression, nor could it capture the transponder's EIRP. Smart AGCm does not employ radically new technology. RF delay, on the order of a few hundred nanoseconds, needed to compensate for delay in the tracker filters, is not new technology for spacecraft. The center stripping function, while new, employs variable back-biased diodes or the equivalent (such as GaAs MESFETs), but these have been deployed in transponders before. The use of a wide dynamic range linear driver amplifier is the same technology used in current hard limiting transponders. 1 INTRODUCIION OBJECrrVE OF STUDY Beginning in 1989, Comsat implemented a new technique for nonlinear analysis called the Z M Microscope [l] which simplifies solutions for intermodulation distortion and power division in piece-wise linear, time-varying nonlinearities. It was essential to analyzing the capabilities of Smart AGCW. Preliminary analytical results were published in MILCOM '91 [2] and results of the R&D investigation were presented at the AIAA conference in Washington, D.C, March 1992 131.The basic Smart AGCm concept, described is shown in Figure 1. In response to a measurement on the envelope, the null zone is activated. Th of this RF nonlinearity is to strip the center fr input signal, as the inset shows for a simplified case: one large and one small sine wave.The objective of this study was to verify AJ capability through simulation tests of the output (J + IM)/S performance vs. input J/S of Smart AGCTM under controlled jamming scenarios including the following: -CONSTANT ENVELOPE: CW AND PHASE MODULATED -TWO SINE WAVES ("BEAT FREQUEN -ADDITIVE WHITE GAUSSIAN NOISE (A In the course of the study, sev alvorithms were investigated including: -ORIGINAL TRACKER (Figure 1 and 4) -RMS TRACKER (Figure 6) -LOW PASS AND BANDPASS -ABOVE, WITH "BYPASS Not all combinatio suppression provided the in about 6 dB [41. For am a hard limiting transponder. Thus for example two CWs having an average J/S of 20 dB, if converted to a CW with the same average power, would have a benchmark performance of (J + IM)/S of 26dB. CHARACTERISTICS OF THE SIMULATION, THE TRACKERS, AND TEST SIGNALS SIMULATION A N D TE...

A 915 MHz 175 $\mu \text{W}$ Receiver Using Transmitted-Reference and Shifted Limiters for 50 dB In-Band Interference Tolerance

“…In the worst case, if is higher than − , the transfer function with respect to will become a typical limiter which will degrade the SIR. To obtain an accurate ∆ , one possible solution is a feedforward control path [16], but this uses too much power. In this work, we design a feedback control loop (figure 9(a)), which consists of a SL and an envelope tracker.…”