How to Improve Local Oscillator Purity for Radar and Defense Systems

+ Pro XG7 Analog Signal Generator

Control Local Oscillator Contributions

Characterizing radar and electromagnetic spectrum operations (EMSO) receivers and frequency converters requires a local oscillator (LO) reference with suitable frequency, drive level, and spectral purity. Engineers can substitute an external radio frequency (RF) source for the system LO to establish controlled measurement conditions. The substitute source must meet the frequency-conversion stage's input requirements while contributing sufficiently low phase noise, broadband noise, spurious signals, and harmonics. These characteristics are evaluated at the frequency offsets and bandwidths relevant to the measurement. Engineers also account for signal-path losses, impedance requirements, and the LO power delivered to the mixer or converter. In systems with multiple conversion paths, independently controlled sources may be needed to provide appropriate LO references for each path.

A typical configuration connects a low-noise signal generator to the receiver's LO input or frequency-conversion stage. Engineers select the required LO frequency, establish the drive level, and verify the source's spectral characteristics before interpreting the resulting intermediate-frequency (IF) or receiver response. Phase noise and unwanted spectral components can propagate through the conversion chain, potentially appearing as measurement artifacts or elevated noise. Engineers assess these contributions against the expected signal levels and measurement bandwidth, adjusting source settings or signal-path connections as needed. For multi-path architectures, separate RF outputs can support independent LO conditions across receiver or converter channels. The objective is to establish a sufficiently clean and controlled reference so that subsequent characterization reflects the behavior of the receiver or converter.

Low-Noise Local Oscillator Substitution Solution

Establishing a clean LO reference requires an external RF source with appropriate frequency coverage, drive power, phase noise, and spectral purity. The Keysight Pro XG7 analog signal generator provides a low-phase-noise source for substituting the LO in radar and EMSO receiver or converter measurements. Engineers configure the required LO frequency and level, account for signal-path losses, and connect the source to the appropriate mixer or frequency-conversion input. Low broadband noise and unwanted spectral content help minimize measurement artifacts that could obscure the response of the device under test. For architectures with multiple signal paths, independently controlled RF sources can support separate LO references. Engineers evaluate source phase noise, spurious signals, harmonics, and delivered power against the requirements of the measurement. This solution focuses on selecting and configuring a suitable external LO reference for accurate receiver and converter characterization.

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