Comparison of rf characteristics
| Download this article in .PDF format |
This file type includes high resolution graphics and schematics when applicapable.
A variety of packages for both point-contact and Schottky diodes is available, including cartridge, coax, picomin, and MQM. Various packages have different impedances. For comparison, the same MQM package configuration for point-contact and Schottky diodes was used. This package was chosen because of its inherent broadband capabilities which emphasize semiconductor differences.
A cross section of the diode, as it appears when packaged, is shown in Fig. 9. The unit consists of two metal ends and a glass body. The glass is sealed to the kovar ends, thus making a true hermetic seal. Length is approximately 0.2 in., body diameter, 0.08 in. and metal-end diameter 0.062 in.
For test purposes, each diode was placed in a holder matched to the diode’s impedance at spot frequencies. Although the MQM package is suitable for strip-line and miniature packages, the holders used for testing were selected to mate with standard test equipment. Holders for S-band and X-band are shown in Fig. 10.
The test set-up for measurements at both S- and X-band is shown in Fig. 11. A low-noise klystron was used. Since the measurements were made in a single-diode mixer, it was essential to have a narrow band-pass filter to ensure rejection of the LO sideband noise. The 30-Mc amplifier was matched to the resistance and capacitance presented by the diode holder combination.