Array Antennas for mmWave Applications: A Comprehensive Review

The demand for wide bandwidth has driven us to focus on the higher spectrum, the millimeter wave (mmWave) spectrum. The mmWave offers several advantages, such as wide bandwidth, low latency, and higher data rate, but the signal at these frequencies significantly suffers high atmospheric attenuation and path loss. To overcome these issues, array antennas are used as it provides high gain, better directivity, and bandwidth. This paper presents a detailed review of array antennas based on feeding methods and discusses reconfigurable arrays. The series-fed array results in a narrow bandwidth, high return losses, and low gain that can be resolved with tapered structures, coplanar waveguide (CPW), and SIW technique. Similarly, transmission losses, coupling losses, and high side lobe-levels in parallel-fed arrays can be addressed with multilayer structures, coplanar strips with CPW, pill-box transmission, ridge gap waveguide (RGWG), graphene material, and magnetoelectric dipoles. The merits of series and parallel feed methods are availed with the hybrid feed method. These feeding methods with arrays are extended to reconfigurable array along with active RF switch with stubs, continuous or discrete phase shifter, butler matrix, and/or graphene nanoplates. The parameter performance metrics of these arrays are summarized and concluded with the future scope.