  A novel sparse array (SA) structure is proposed based on the maximum
inter-element spacing (IES) constraint (MISC) criterion. Compared with the
traditional MISC array, the proposed SA configurations, termed as improved MISC
(IMISC) has significantly increased uniform degrees of freedom (uDOF) and
reduced mutual coupling. In particular, the IMISC arrays are composed of six
uniform linear arrays (ULAs), which can be determined by an IES set. The IES
set is constrained by two parameters, namely the maximum IES and the number of
sensors. The uDOF of the IMISC arrays is derived and the weight function of the
IMISC arrays is analyzed as well. The proposed IMISC arrays have a great
advantage in terms of uDOF against the existing SAs, while their mutual
coupling remains at a low level. Simulations are carried out to demonstrate the
advantages of the IMISC arrays.
