Complex coaxial rotating joint shipborne long-range radar system

Link Microtek has designed and produced a complex 700mm-long eight-channel coaxial rotating joint for use in an L-band shipborne long-range radar system. Allowing microwave signals to be fed to and from the radar antenna, the rotating joint offers six PSR channels, each with a frequency range around 1400MHz, and two SSR channels covering frequencies between 1000MHz and 1100MHz. According to Link Microtek’s managing director, Steve Cranstone, the design team faced some challenges in meeting the required specifications, not least in keeping the rotating joint to an overall length of just over 700mm. “This may seem like a large assembly, but, in fact, 700mm was quite a tight constraint,” he said. “Each of the channels had to be able to handle microwave pulses with a maximum peak power of 5kW, and, crucially, the channels had to be phase matched, which meant incorporating various lengths of fairly substantial cable within the body of the rotating joint.” The design also had to deliver key performance specifications such as a VSWR of less than 1.3:1, maximum insertion loss of 1dB, maximum insertion loss WOW of 0.1dB and phase variation WOW of +/-2 degrees. “WOW figures are absolutely critical on a radar system,” commented Cranstone. “They show how the performance varies as the device rotates, and you simply can’t have the specifications leaping all over the place.”