RF Carrier Suppression

Definition

When the information signal in the upconversion stage of a transmitter modulates a radio-frequency (RF) carrier, some of the RF carrier signal leaks through the mixer and appears at the transmitter output. RF carrier suppression is the measure of the RF carrier leakage relative to the modulated output signal.

To perform this measurement, set the resolution bandwidth (RBW) to 100 kHz. Then, measure the channel center frequency level, relative to the maximum output level of the resulting sin(x)/x output waveform. The measurement must be done with scrambling disabled, when transmitting a "01" test pattern, and when using DQPSK modulation (see graphic #1).

Standards

• IEEE Std 802.11b-1999 16 September 1999 Paragraph 18.4.7.7 RF carrier suppression
• ANSI/IEEE Std 802.11 First edition 1999-00-00 Paragraph 15.4.7.8

Measurement Subtleties

You can measure the RF carrier suppression by placing a reference marker at the channel center frequency and a delta marker on the peak output signal. An example measurement was performed using a PSA series spectrum analyzer and is shown in graphic #2.

The 802.11b standard does not specify if the "01" test pattern signal is framed or unframed. Some type of measurement triggering, or time gating, may be required for a framed signal.

Test Tools

For 802.11a, time gating is needed to isolate the portion of the burst that contains the center carrier. The 802.11a is multicarrier, so using time-gating on the burst allows you to see the center carrier leakage in the frequency domain. The center carrier should be nulled, so any power that shows up at this point is due to leakage. You can use either the 89600, or the PSA, since both have time-gating capabilities. For 802.11b, no time gating is needed so you can perform the measurement with the 89600 VSA, the PSA spectrum analyzer, or the ESA spectrum analyzer.

You can use the 89600 Series vector signal analyzer standalone, in conjunction with the ESA-E and PSA series Spectrum analyzers, and with several of Keysight's Infiniium family of oscilloscopes.

You can use the ESA or PSA Series spectrum analyzers as down-converting front ends for the 89600 (with specific options). This provides vector signal analysis capabilities up to 50 GHz. You can also use 89600 as standalone. This provides vector signal analysis up to 6 GHz, with one or two channel inputs, for IQ, IF, and RF measurements.