Multiplier diodes

A wide range of products is available as passive diode frequency multipliers, here are the differences and the main applications:

STEP-RECOVERY or SNAP-OFF: certainly the most widely used, for low power applications, for high multiplications > 3, broadband comb generation, for very steep and fast pulses . The choice of step-recovery diode empirically can be defined with the following rules: diode lifetime > input frequency period ( τ > 1/Fin ) , transition time < output frequency period ( Trr < 1/Fout ), example with MaCom diode MA144769 / MA44769:
τ typ. = 35 ns, 1/35ns = 28 MHz therefore applicable for input frequencies greater than approx. 30 MHz, Trr = 150 ps, 1/150ps = 6.6 GHz therefore applicable for output frequencies up to approx. 6 GHz, for higher frequency applications it is necessary, as usual, to use devices with ceramic cases therefore having low residual capacitance. With step-recovery it is possible to obtain very high multiplication factors and output frequencies up to 26 GHz and beyond, in fact they are used in the HP 33004 type Comb-Generator... for instrumentation, radar, microwave multipliers with very low phase noise etc., the price range varies from medium/high for ceramic case diodes to low cost with modern SMD devices such as the Macom MA144769 / MA44769 described in the example above.
Step-recovery diodes had a remarkable development in the 60s and 70s, indispensable for the nascent microwave applications, then with the advent of GaAsFet they suffered a slow and gradual decline. Now they have been rediscovered and if with a significant advantage in applications as low phase noise multipliers as they are passive devices, moreover with the presence of low cost SMD devices they are becoming increasingly accessible even for mass production.

VARACTOR: generally used for medium and high power multiplications, x2 , x3, max x4 and with high output efficiency, typical 50/60% x2 up to 25/40% x4 , they are available in an output frequency range from 300 MHz to 18 GHz. Typically they are medium to large sized devices and made of ceramic due to the fact that they have to withstand higher powers, therefore sufficient thermal dissipation is required due to the power lost in the output which manifests itself as power to be dissipated, often the cathode is connected to the rheophore with a thread to facilitate mounting on a heatsink or directly on the cavity case.

COMB-GENERATORS: these are devices often already connected to SMA and ready to use, which use a step-recovery diode, for stumenzione military receivers frequency meters etc., suitable for generating a very wide RF comb to microwaves and beyond. To achieve a high multiplication factor and good efficiency, they are tuned to the input frequency, so they should only be used on a specific input frequency, e.g. 500 MHz ±10 MHz for maximum efficiency, while the output comb will be every 500 MHz up to microwaves. Such devices are high cost and therefore only to be used for professional applications.

Various diodes, PIN, Varicap and Schottky: in addition to these 2 families of diodes specially developed as frequency multipliers, there are other diodes created for other applications, i.e. with lower performance than step-recovery, but at very low cost. For multiplications within 100 MHz - 5 GHz and where multiplication efficiency is less important, varicap and PIN diodes or selected pairs of Schottky RF for frequency duplicators and also ultra fast switching silicon diodes but with Cj < 1pF and Trr 18 GHz, Schottky diodes in beam-lead technology are also used.
There are several HP application notes, VHF Communications Q3 - 1978 and much more interesting in VHF Communications Q3 - 2006 and many articles in Dubus magazine for millimetric.

Anwendungshinweise:

Application note HP n. 1054: Low Cost Frequency Multipliers Using Surface Mount PIN Diodes