Electrical　modeling　of　vehicular　antennas　is　required　for　design　of　modern　vehicle-to-everything　communication　networks.　However,　full-wave　modeling　and　the　existing　equivalent　source　methods　still　ask　for　long　computation　time.　To　address　this　issue,　a　fast　simulation　method　is　proposed　in　this　paper:　a　sparse　equivalent　source　model　is　developed　based　on　Huygens＇　principle　where　a　vehicular　antenna　is　made　equivalent　to　magnetic　current　placed　on　a　finite　conducting　plate.　The　image　theory　and　the　uniform　theory　of　diffraction　are　then　applied,　a　modified　Green＇s　function　is　derived,　and　the　sparse　equivalent　source　model　is　constructed　to　replace　the　original　vehicular　antenna.　Because　of　its　simple　geometry　and　material,　in　comparisons　with　the　existing　methods,　the　proposed　model　uses　significantly　less　expenditures　for　simulation　of　vehicular　antennas　while　has　better　accuracy　due　to　the　consideration　of　the　finite　conducting　plate.　Simulations　are　performed　to　demonstrate　the　effectiveness　and　advantages　of　the　proposed　method,　and　a　real-world　experiment　is　designed　and　conducted　to　demonstrate　the　superiority　of　the　proposed　method　with　real　measurement　data.　It　is　shown　that　the　proposed　method　can　save　simulation　time　by　four　times,　with　less　than　1-dB　error　compared　to　measurement.