An automated transmit combiner monitoring system (100) for an RF radio transmitter system includes a transmitter (101) for providing a primary source of radio frequency (RF) energy and an isolator network (105,107) for isolating the output of the transmitter (101) from secondary sources of RF energy. A transmitter combiner junction (109) is used for enabling the transmitter (101) to provide RF energy to a single antenna (111) while a dummy load (113) is used for loading any unwanted RF energy from the transmitter (101) that is received from the isolator network (103,105). An RF detector (115) is then used for measuring RF energy from the dummy load and an alarm reporting device (119) then monitors the system to provide an alert based on RF energy measured outside a predetermined threshold.

A coaxial phase shifter for shifting the phase of a signal being transmitted along a transverse electromagnetic transmission line. The phase shifter is in line with the transmission line's inner conductor, such that it is very compact and such that the transmission line's outer conductor need not be modified. The phase shifter includes electrically-conductive fingers arranged in spaced, confronting relationship with each other, to capacitively couple the signal from one segment of the transmission line's inner conductor to another. In addition, the phase shifter is configured to provide an input impedance at both of its ends that matches the characteristic impedance of the transmission line.

To monitor the course signals radiated by the two-frequency glide-path station with respect to course line and course width, and to monitor the clearance signal, the signals radiated by the antennas (A1, A2, A3) and a signal extracted directly from the transmitter (1) are so combined (5, 6, 7) that the clearance signal (CL), the sideband signal (SBO), and the carrier and sideband signal are obtained. These signals are evaluated (8) for monitoring purposes in a manner known per se.

Disclosed is an improvement to Integral Monitoring of two-frequency Instrument Landing System Localizer transmitting antenna arrays, by means of which the Clearance signal can be precisely separated from the combined Course and Clearance output of an Integral Monitor recombiner and monitored as if it existed alone. A first detector detects a composite Clearance and Course signal input, and sends an output to a separation filter which does not pass frequencies of 0, 90 or 150 hertz, but does pass frequencies of the difference between Course and Clearance frequencies (.DELTA.f), .DELTA.f.+-.90 hertz, and .DELTA.f.+-.150 hertz. The output of the filter is input to a second detector which measures the difference between the percentages of 90 and 150 hertz amplitude modulations of an amplitude modulated carrier having a frequency .DELTA.f.