ence ▁it ▁is ▁focused ▁into ▁a ▁narrow ▁col lim ated ▁beam . ▁Ref lect ed ▁energy ▁from ▁the ▁environment ▁follows ▁the ▁reverse ▁path ▁and ▁is ▁focused ▁by ▁the ▁reflect or ▁onto ▁the ▁feed ▁horn ▁where ▁it ▁travel s ▁back ▁to ▁the ▁receiver . ▁The ▁reflect or ▁must ▁be ▁built ▁to ▁a ▁precision ▁determined ▁by ▁the ▁w avel ength ▁used . ▁For ▁a ▁one ▁cent imeter ▁w avel ength , ▁a ▁reflect or ▁precision ▁of ▁one ▁or ▁two ▁mill im eters ▁would ▁be ▁ade qu ate . ▁ ▁A ▁sl otted ▁wave guide ▁has ▁no ▁reflect or ▁but ▁em its ▁directly ▁through ▁the ▁sl ots . ▁The ▁spacing ▁of ▁the ▁sl ots ▁is ▁critical ▁and ▁is ▁a ▁multiple ▁of ▁the ▁w avel ength ▁used ▁for ▁transmission ▁and ▁reception . ▁The ▁effect ▁of ▁this ▁geometry ▁is ▁to ▁form ▁a ▁high ▁gain ▁anten na ▁that ▁is ▁highly ▁direction al ▁in ▁the ▁plane ▁of ▁the ▁anten na . ▁Without ▁augment ation ▁a ▁sl otted ▁wave guide ▁is ▁not ▁as ▁efficient ▁as ▁a ▁par abol ic ▁reflect or , ▁lack ing ▁an ▁ability ▁to ▁focus ▁in ▁the ▁vertical ▁plane , ▁but ▁is ▁much ▁more ▁dur able ▁and ▁is ▁less ▁expensive ▁to ▁construct . ▁The ▁anten na ' s ▁vertical ▁focus ▁is ▁usually ▁en hanced ▁by ▁the ▁application ▁of ▁a ▁mic row ave ▁l ens ▁attached ▁to ▁the ▁front ▁of ▁the ▁anten na . ▁As ▁this , ▁like ▁the ▁companion ▁sl otted ▁wave guide , ▁is ▁a ▁one - dimensional ▁device , ▁it ▁too ▁may ▁be ▁made ▁relatively ▁cheap