One application of signals in the 300 MHz – 3 GHz range is ina.air traffic controlb.maritime radioc.police radiod.Cellular telephony

The range of 300 MHz to 3 GHz is used particularly for various communication applications. Here’s a brief analysis of the given options:

1. Air Traffic Control: Typically utilizes VHF and UHF bands, including frequencies in the 108 MHz to 137 MHz range, and sometimes extends into the GHz range.

2. Maritime Radio: Commonly operates in HF, VHF, and some UHF bands. VHF maritime communication operates typically around 156 MHz – 174 MHz, but also engages in higher frequencies not usually encompassing 3 GHz.

3. Police Radio: Generally employs frequencies that are variably located within the UHF range; however, some police communications can fall within the 300 MHz to 3 GHz range.

4. Cellular Telephony: Uses frequencies starting from around 400 MHz to downlink bands over 2 GHz, making it a prime candidate within the specified range.

Conclusion:

Among the options provided, the most fitting application within the 300 MHz – 3 GHz range is d. Cellular telephony.