SILICON CRYSTAL RECTIFIERS 



25 



fixed tuned basis they would result in an increase in the apparent loss be- 

 cause of the mismatch of the radio frequency circuits. 



While the conversion loss is degraded by increasing the contact area, the 

 power handling ability^ of the rectifiers is improved, as shown in Fig. 13. 



1 2 3 4 5 6 7 8 



SPRING DEFLECTION IN THOUSANDTHS OF AN INCH 



Fig. 12 — Relationshi]) between sjjring deflection and conversion loss in 

 silicon crystal rectifiers. 



This is not surprising because the larger area contact gives a wider current 

 distribution and thus minimizes the localized heating effects near the con- 

 tact. Generally, therefore, in the development of units for operation at a 



*The measurement of power handling ability of crystal rectifiers by application of 

 radio freciuency jwwcr is comi)licated by the fact that the impedance of the unit under 

 test varies with power level. If a unit is matched in a converter at a low-power level 

 and ]iower at a higher level is then applied, not all of the j^ower available is absorbed by 

 the unit but a portion of it is reflected (due to the change in impedance). This factor 

 has been called the self protection of the unit and it necessitates the distinction between 

 the powei absorbed hy and the power available to the unit under test. The data for 

 Fig. 13 were acquired by first matching the unit in converters at low powers (about 0.3 

 milliwatts CW 30C0 mc's) and then exposing it for a short period to successively higher 

 levels of pulse power cf sc[uare wave form of 0.5 microseconds width at a rei:)etition rate 

 of 20CO pulses per seccnd, measuring the loss and noise ratio after each power application. 

 The power handling ability is then expressed as the available peak power required to 

 cause a 3 db impairment in the conveision loss or the receiver noise figure. This method 

 was employed because in ladar receivers the units are matched for low-power levels. In 

 this lespect the method simulates field operating conditions, but the "spike" of radar 

 pulses is absent. 



The increase in power handling abilit\' with increasing area shown in Fig. 13 is confirmed 

 by similar measure ments with radio frequenc>- pulse power with the unit matched at 

 high-level powers, b\- direct-current tests, and by simple 60-cycle continuous wave tests. 

 The magnitude of the increase depends, however, upon the particular method employed 

 for measurement. 



