help on design of backscattering modulation circuit

Dear all,
I am now doing a project on a simple RFID system....I need to design a backscattering modulation circuit to modulate the carrier signal from the reader(about 3GHz). The modulating signal are the pulses from a pulse generator.
Can anyone give me resources or ideas on how to design it? Thx

Here it is:
http://autoidlab.eleceng.adelaide.ed...l/backscat.pdf

I also find a pdf describe a simple block diagram of the backscattering tag..
it first mixed the pulse sequence with a IF oscillator ,then collect the output of the mixer to a varicap and then connect it to a matching circuit and antenna...

I want to know if my understanding is right?
The varicap give two different states of impedance when the sequence is "1" and "0" respectively and then the matching circuit matched the antenna impedance to the load impedance of state "0" so that little RF power is reflected when state is "0" and more power is reflect at state "1"...