Mini-Circuits’ frequency multipliers offer a new degree of freedom in designing frequency multiplier chains. Their multi-octave band width and excellent rejection of fundamental and third harmonics enable a significant reduction in filter requirements. In addition, they operate with 50Ω impedances at input and output ports and are not very sensitive to input power. They perform well from 0 dBm to +20 dBm input. The frequency doubler may be operated as a quadrupler. Referring to the figure, the fourth harmonic will be approximately 12 dB less than the second. When filtering and power level considerations are made, there may be situations where operating the doubler as a quadrupler is a practical alternative to two successive stages of doubling. Mini-Circuits’ frequency doublers are economically priced while covering the very broad frequency range from 5 KHz to 3000 MHz. They offer a very low conversion loss, from 11 dB, and high spurious rejection 40 dB. These doublers give exceptional unit-to-unit matched performance.
Frequency Doubler Measurements
Frequency doublers generate the second harmonic of an input signal, while suppressing fundamental and odd harmonics. One test determines the conversion loss as the dB-difference between the fundamental input power and the second harmonic output power. Another test measures the output power of the “spurious” spectral components: the fundamental, and the third and fourth harmonics, each relative to the desired second harmonic output. The Figure below shows the setup for both tests. The amplifier and attenuators ahead of the DUT are chosen to drive it at the specified fundamental input power, typically in the +5 to +15 dBm range, as well as to ensure a matched source impedance. Mini-Circuits amplifier model ZHL-2 is suitable for testing the lower-power DUT’s, and ZHL-1000-3W or ZHL-5W-1 for the higher power ones. The filter can be low-pass or band-pass; its purpose is to present a harmonic free input signal to the DUT. For wide-band testing, different filter cut-off frequencies have to be used according to the frequency being applied.
For the conversion loss test, replace the DUT with a “through” connection, and obtain a 0 dB reference on the spectrum analyzer. Then reconnect the DUT and measure the second harmonic with the analyzer. Calibrate the spectrum analyzer at the fundamental and second harmonic, to account for its flatness, using a power meter. For the spurious output test, obtain a 0 dB reference on the spectrum analyzer, tuned to the second harmonic, with the DUT in place. Then tune to the fundamental, and third and fourth harmonics, and measure each on the analyzer relative to the 0 dB reference.
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