ekS - Instytut Agrofizyki im. Bohdana Dobrzańskiego PAN w Lublinie ...

The basic element of one prototype is GaAs MMIC SPDT switch from
Stanford Microdevices, type SSW-308 [85] in a small 8-pin surface mounted
enclosure. It is used for switching signals in the frequency range from DC to
3 GHz with insertion loss lower than 1.2 dB. The prototype was constructed on
double sided epoxy resign PC board of 0.7 mm width connecting the individual
elements by 50 Ω strip lines.
The other prototype was constructed using RF reed relays [16] characterized
by insertion loss of 0.3 dB at the frequency 0.5 GHz. It is suited for installation on
50 Ω transmission lines. The switch was mounted on 1.6 mm width epoxy resign
PC board using strip lines of appropriate width of 50 Ω.
The testing measurements were done with the sampling oscilloscope
HP54121T equipped with 20 GHz sampling head and a needle pulse generator of
proprietary construction, which produces a needle pulse of 200 ps rise and fall
times. The two-rods TDR probe (10 cm length rods, 1.5 mm in diameter and
15 mm distance between the rods) was applied for tests in the soil.
10.4.2. SP8T fully integrated switch
The basic element of the prototype microwave switch is the integrated circuit
HMC253QS24 from Hittite Microwave Corporation [42]. It is supplied from a
single +5V voltage, has an built-in decoder controlled from standard TTL signals
to chose one from eight available channels. It is sold in a cheap and surface mount
package (QSOP type). The operation of the circuit is guaranteed in the frequency
range 0-2.5 GHz. The basic parameters of the integrated circuit HMC253QS24, ie
insertion loss of the selected channel and isolation are presented in Fig. 45.
Fig. 45.
Insertion loss and isolation between channels related to frequency for the MMIC device
HMC253QS24 implemented in the prototype TDR switch
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