Below is a simple Arduino GSM Jammer (900 MHz)
For 1800 MHz another VCO can be used.
The square wave from Arduino pin 10 fed to VCO tuning volt input which will almost cover the Required input voltage from 0.5 to 5 volts to cover the frequency range from 870 MHz to 980 Mhz
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Arduino code for generating square wave
void setup(){ }
void loop()
{
tone(10, 15000); // generate square wave
}
Click for video:
Arduino SIM800L IMEI change
https://obaidkakar.blogspot.com/2022/05/arduino-sim800l-imei-chaging.html?m=1
1).MVCO944 (870 Mhz – 980 Mhz)
2). BFG591 or SXA389 RF Transistor 4-7GHz ,1.5 Watts 
1).The transistor used in this project must be working on high frequencies , any other type transistor can be used.
Power supply must be 5vdc
Components used:
KSF Electronics 
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