What physical effect or device is capable to generate strong radio interference on relatively short distance (around 2-3 m) and in wide spectrum (30MHz-10 GHz or wider)?

Could some near-field effects work? Similar to those which work in transformers?

At 10GHz and 3m it can't be near field. This implies that some adverse effects will be felt at a longer distance.

 

Many possibilities exist, depending on whether you seek interference, destruction of weak equipment, destruction of purposely shielded equipment. 30MHz-10GHz in one equipment is a bit ambitious, I'd split it over 2 or 3 generators+antennas.

 

This is standard warfare technology for decades, well-known but not very public. Armed forces are equipped and use it, especially to destroy radars at the beginning of a war to get the control of the sky.

 

Range exceeds 10m by much. Consider 100m for a luggage-sized weapon, much more for a weapon installed in an aeroplane or in a bomb.

This would probably do the job

https://en.wikipedia.org/wiki/Spark-gap_transmitter

but they are illegal essentially everywhere because they cause a lot of interference.