Although the perfectly circular shape is generally preferred, the resonator could be of {HEAD ~ any closed loop shape} such as {TAIL ~ an ellipse}, etc 
such as
Although the perfectly circular shape is generally preferred , the resonator could be of { HEAD ~ any closed loop shape } such as { TAIL ~ an ellipse } , etc
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH