Approaching the Reflection-Bandwidth Product Limits of Multielement Arrays Using Continuous Decoupling Zeros

A systematic method for decoupling multielement antenna arrays is proposed by creating continuous decoupling zeros in a wide frequency range, which has the ability to approach the reflection-bandwidth product limits. For decoupling purposes, the admittance matrix versus frequency is adopted as the target of the study, which is fit to a rational function using vector fitting. Ideal lossless LC components are adopted for designing a four-level decoupling and matching network (DMN), and the trend of the mutual coupling curve and the suitable frequency range of DMN are discussed. The constructed DMN has a small number of elements and hence is easy to integrate with the feeding network. A prototype of the three-element array is manufactured and measured. This prototype covers the frequency band of 4–5 GHz with the isolation of over 15 dB and the return loss of over 10 dB, which achieves ~70% of the theoretical upper limit of the reflection-bandwidth product. Benefiting from the improved isolation, the realized gain of the array is also improved by ~0.5 dBi within this frequency range. The proposed method can be readily extended to N-element arrays and further to an N × N array using hybrid decoupling schemes. A 4 × 4 monopole array was selected as an example along with the DMN and decoupling elements (DEs). Owing to its lumped-circuit form, this method can be applied to other broadband arrays of similar architecture.