With the steady improvements in tracking radar technologies over the past twenty years, the diameter requirements for the antennas has been reduced to match the improvements in transmitter power and receiver sensitivity. This has led to a need for shorter feeds for use in a cassegrain configurations.
Micro Metalsmiths has developed feeds for use at CBand which are fabricated from its own cast waveguide components and optimised to tight phase characteristics. As a long standing manufacturer of monopulse comparators, the development of an antenna feed was the next logical step in the extension of the product range. The choice of horn design was crucial to achieving a compact feed design.
Micro Metalsmith's compact comparator uses four waveguide tees connected via four extension waveguides to the central four horns. The overall waveguide section is tuned to achieve less than ±1° phase imbalance between ports. The C-Band version is capable of handling up to 1MW peak power at normal atmospheric pressure. It is designed for operation up to 30PSIA, and is recommended to be pressurised to maintain a dry atmosphere inside the waveguide. Sum, Elevation and Azimuth ports are provided as waveguide flanged interfaces. Isolation between any two ports is 35dB minimum. When fitted to an antenna Cross Polarisation ratios of 30dB minimum are achieved, and an Error channel Null stability of less than 0.1mil across the frequency range.
The auxiliary horns are connected to a power combiner network which includes the tees that are part of the central comparator. The two horizontal horns are combined with the azimuth signal from the comparator whilst the two vertical horns are combined with the elevation signal. All the interconnecting waveguide are phase matched during manufacture. A final test in an anechoic chamber allows the beam patterns from the main and auxiliary horns to be set coincident thus providing accurate combining to give the maximum possible null depth. When fitted to an antenna null depths of 35dB minimum are achieved with typical values greater than 50dB.