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