 The need for multi @-@ band antennae arises with mobile devices that need to roam between countries and networks where the frequency bands used can often be different . Perhaps the most conceptually simple design , first reported in 1997 , is to nest two PIFA patch antennae one inside the other . Another technique is to insert one or more spur lines into the patch , which has the effect of coupled resonators broadening the band . Other techniques rely on multiple modes being generated , which makes for a more compact design . Examples of this are the C @-@ slot pattern , which is a similar pattern to the interdigital filter , and the tightly meandered pattern shown as , respectively , C and D in the diagram . 
