The 4503A-03 from Narda-MITEQ is a RF Detector with Frequency 10 MHz to 18 GHz, Max Input Power 20 dBm, Frequency Flatness ±0.6 dB, Voltage Sensitivity 500 mV/mW, VSWR 1.60:1. Tags: Connectorized, Diode Detector. More details for 4503A-03 can be seen below.