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It will reduce the effects of impedance mismatch, but not eliminate them entirely. You should get about 20dB of isolation.
If you use a circulator don't forget to terminate the unused connector
Gain is cheap (at low powers) so you are better off using a 10 dB pad + 10 dB gain and you'll easily get 30 dB of isolation, cheaper & smaller than a circulator.
I'm sorry what do you mean with a "gain" ? I'm not familiarized with RF lab accesories.
In ADS there is a circulator and a isolator. What should I fill out in the fields Z1, Z2, Z3 or what are the most important parameters ? My intention is to place one of these devices between a VCO and a 50Ω load.
I didn't know you were talking about simulation. An isolator would be ideal, just leave the default values; 100dB is plenty of isolation.
For a real VCO circuit an isolator is impractical so one would use an isolation amplifier, which is just attenuator+amplifier+attenuator. The goal is high reverse isolation, however not much foward gain is needed.
I beleive just leave tham blank and it will default to 50 ohms. If you are just doing a simulation then you don't need an isolator if you are just terminating the VCO with 50 ohms.
well, actually with a capacitive load there is no problem but with a 50Ω load emulating a spectrum analyzer there is no output signal. I do not have an output buffer that's why I'm looking for a device that allows the circuit not to be charged.
OK, I assumed the VCO could drive 50 ohms. You can use a VCVS with high input impedance (1E9), a gain of 2, and a 50 ohm output impedance. That should give you a frequency independant, unity gain buffer with high input impedance and 50 ohm output impedance.
Sounds like you need a high impedance probe. I have one of these and it works well, but may be too big for your application if it is an IC.
**broken link removed**
For ICs I have made a poor man's high impedance probe. I took a tugnsten needle probe and clipped the tip off about 1mm from the end. Then took a 1k ohm SMT resistor and silver epoxied it between the tip and probe. This was primarly for DC probing of RF traces. It may be usefull to a few GHz. There will be lot's of inductance and loss but considering a spectrum analyzer has 100 dB dynmaic range it may be usefull for simple measurements.
I'm sure there are high impedance active probes for IC use but they are probably expensive.
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