second axis a 2 the main body 401 is mounted on the ground plane 20 over a contact area ac and the second axis passes through the central part of the contact area fig2 is a plan diagram illustrating the size of different parts of the present invention furthermore sizes of different parts of the dra 1 of the preferred embodiment are given as follows in which the main body 401 has a length a a width b and a height d the well 402 has a length a 1 a width b a height d 1 and the distance from the lower side of the well 402 to the base of the main body 401 is s wherein a 21 2 mm b 7 7 mm d 7 25 mm d 1 2 9 mm and s 3 3 mm the hollow portion 201 has a length wa and a width l a wherein wa 2 mm and l a 13 mm both of the substrate 10 and the ground plane 20 have a length w g and a width l g and the thickness of the substrate 10 is t in which w g l g 60 mm t 0 6 mm and the dielectric constant of the substrate is.