A Comprehensive Study of Losses in mm-Wave Microstrip Antenna Arrays

This paper presents a study of losses in mm-wave microstrip antenna arrays Methods to reduce losses in mm-wave microstrip antenna arrays are described in this paper, Microstrip antennas posses attractive features such as low profile, light weight, small volume and low production cost. In addition,the benefit of a compact low cost feed network is attained by integrating the microstrip feed structure with the radiating elements on the same substrate. However, losses in the microstrip feed network forms a significant limit to the achievable gain in microstrip antenna arrays, Conductor, dielectric and radiation losses are the major components of loss in mm-wave microstrip antenna arrays. Surface wave losses in thin microstrip substrates (compare to wavelength) are usually negligible. At frequencies ranging from 30 to 40 GHz conductor losses are around 0. 15 to 0.2 dB per wavelength, dielectric losses are around 0.04 to 0.05 dB per wavelength for a 50 ohm line on a 10 mil duroid substrate with εr=2.2. The open nature of the microstrip configuration suffer from radiation originating at various geometrical discontinuities This radiation phenomenon causes additional signal loss in the microstrip antenna feed network. These phenomena become significant in mm-wave microstrip antenna arrays, more bends, T-junctions and other discontinuities are introduced in the feed network and radiation loss increases considerably. As an example radiation loss of a right angle bend in a 50 ohm line on a 10 mil duroid substrate with εr= 2.2, is 0.1dB at 30GHz and 0.17 dB at 40GHz.