Design and realisation of low loss air‐filled rectangular coaxial cable with bent quarter‐wavelength supporting stubs

A new type of rectangular coaxial cable, operating from 28 to 48 GHz, was designed and fabricated with thick SU8 photoresist technology. Two pairs of bent quarter‐wavelength supporting stubs were proposed to reduce the lateral dimension of the structure. A size reduction of 40% was achieved by using the bent supporting stubs design as compared with a similar one with straight supporting stubs design. An average insertion loss of 0.36 dB across the bandwidth of 28‐48 GHz was achieved, with return loss of better than − 14 dB. The use of bent supporting stubs did not compromise its microwave performance. The component is, therefore, particularly appealing for integrated components such as complex couplers or Butler matrix, where overall size reduction (with no loss of performance) and cost saving can be substantial.