How to calculate the maglitude and bandwidth of a RF pulse?

[ShannonZ]

I use the following code to generate a 90-deg rect RF pulse.

import pypulseq as pp
system = pp.Opts(rf_ringdown_time=1e-6, rf_dead_time=1e-6,adc_dead_time=20e-6)
seq = pp.Sequence()

P1 = 100e-6     #100us
FA = 3.1416/2  # 90-deg
rf = pp.make_block_pulse(flip_angle=FA,duration=P1,delay=10E-6,system=system,use='excitation')

seq.add_block(rf)
seq.add_block(pp.make_delay(1))

seq.plot(time_range=[0,P1])
print(f'{pp.calc_rf_bandwidth(rf)}')  # return 0

What is the correct way to obtain the magnitude and excitation bandwidth of this rect rf pulse
I wanna simulate a CPMG sequence with a constant background gradient, the bandwidth of hard pulses indeed needs to be considered.