Thomas J. Warnagiris

Performance of a meandered line as an electrically small transmitting antenna

For antennas to radiate at maximum efficiency, their dimensions must be on the same order as the radiated wavelength. At frequencies below 30 MHz, antennas with efficient radiation are often too large for mobile and portable applications. Smaller antennas can be made to radiate efficiently by use of matching networks. For installation convenience and ease of adjustment, these networks are usually placed between the transmitter and the antenna input; but it has been found that for best radiation efficiency, matching network elements should be placed at points on the antenna structure. Unfortunately, such matching networks must be tuned for each transmitting frequency and, when mounted on the antenna, they cannot easily be tuned. A meander element antenna was found to present some electrical and mechanical properties allowing convenient placement of tuning elements when configured as an electrically small transmitting antenna. Some simplified design guidelines were derived from experimental data.

T-1028A/FPS-85 radar transmitter design

The AN/FPS-85 radar is a large, fixed-position, phased-array radar located at Eglin Air Force Base, Florida. The radar has a peak radiated power of about 32 MW generated by a 72 X 72 matrix of separate transmitter elements that are individually rated for a maximum peak power output of 10 kW. All current amplifier and mixer functions on the existing transmitters are performed by tube devices. Southwest Research Institute is currently under contract by the U.S. Air Force to redesign the transmitter units and supply three operational prototypes. The design goals of the program are to extend the performance envelope by increasing pulse width and duty cycle capabilities, and to increase the reliability of the transmitter by using solid-state components where practical. The transmitter prototype redesign is in an advanced state and has involved the design of pulsed-power modulator circuits, energy storage networks, and custom solid-state and tube cavity amplifiers. An industry search for suitable manufacturers of custom RF amplifier modules has resulted in the conclusion that an all-solid-state design is technically viable; however, the expense of the all-solid-state approach has made a combined solid-state/tube design economically attractive.

Peak power tailoring and phase nulling of the AN/FPS-85 radar

The AN/FPS-85 radar is a large, fixed-position, phased-array radar located at Eglin Air Force Base, Florida. The radar has a peak radiated power of about 32 MW generated by a 72 X 72 matrix of transmitter elements that are individually rated for a maximum peak power output of 10 kW. The current transmitter modules have no automatic phase nulling capability and no remote output power adjustment capability. The result is a randomly varying amplitude pattern across the beam aperture. Southwest Research Institute is currently under contract by the U.S. Air Force to redesign the transmitter units and supply three operational prototypes. Part of the design and performance upgrade will be an automated, remotely controlled power and phase adjustment system which will utilize a centrally located host computer to send phase and amplitude adjustments to the individual transmitters via a digital serial link.

Pulsed power management and design philosophy in the T-1028A/FPS-85 radar transmitter

The T-1028A/FPS-85 transmitter is part of the AN/FPS-85 phased-array radar system located at Eglin Air Force Base, Florida. The radar features an electronically steerable beam at a peak radiated power of about 32 MW generated by a 72 X 72 matrix of separate T- 1028A/FPS-85 transmitter elements that are individually rated for a maximum peak power output of 10 kW. The output stage RF amplifier is a cavity design that uses the YU-176 planar triode tube. The signals to modulate the tube cathode are developed within the transmitter. This departs from the original transmitter design philosophy in which all 5184 transmitter units were modulated by single-signal sources that originated from centralized equipment locations and were then fed to the transmitter elements by an extensive network of cables and feed boxes. Recent improvements in technology have made small and inexpensive switching components available which allow for individual pulsed power and modulator circuits. The proposed retrofit of the radar site with the redesigned transmitters will result in the obsolescence of the existing modulator equipment.