I don't know about antenna size changes for windshear WX systems.
One of the main functions of EGPWS or TAWS (Terrain Awareness Warning Systems) is windshear recognition and warning.
Through the use of Air Data, Radio Altitude, Accelerometers, and IRS..... the systems sense actual deteriration of horizontal vs vertical flight performance. Once the downward envelope theshold has been breached, the system warns the crew.
It is "reactive". The aircraft must be "in" a windshear situation for warnings to occur.