Hi.

> Logamp is originally a peak detector used for continuous wave RF power measurement.  
> I wonder, in case input signal is multi cariers or others (CDMA, WCDMA, EDGE, GSM,...),
> can I still use logamp with some offset tuning for the output?

You mean log-envelope detector ?
If so, logamp is applicable for such signals.
But some cresto factor compensation is needed for accurate power measurements,
for example, see data sheet of AD8313 from ADI.

> Further more, anyone knows how to simulate those kinds of signal source multitone-wise in ADS,
> plz show me the way.  

There are many ways for such purpose in ADS.
For example, use V_nTone component which is valid for not only HB-Ana but also Transient-Ana.
Practical example are available in examples/Com_Sys/CATV_prj.

Or simply use signal sources in "Souce-Modulated", where various predefined moudulated signal sources such as GSM, DECT, CDMA, etc. are available.

> When using "source-modulated" signal source,
> selecting CDMA for instance,
> how can I have different frequency allocations for simulations?
> Those sources are almost non-modified except for only frequency and power.
> What if I want to compare in case of same channel power but 4, 8, or 16 sub-carriers?

CDMA(IS95) is direct sequence spread spectrum modulation which doesn't have
sub carrier but equivalently it can be expressed by multicarrier which amplitudes and phases
are random.
If you would like to express cdma signal by multicarrier, use V_nTone component.

Or your "same channel power but 4, 8, or 16 sub-carriers" means code multiplex ?