In this paper, a bandstop to allpass reconfigurable filter technique is proposed in Single Pole Double Throw (SPDT) switch design. Proof of concept of the bandstop to allpass reconfigurable filter is presented. It is physically realized using transmission line and radial stub in 3.5 GHz band (3.4 to 3.6 GHz). The isolation, insertion loss and return loss of the SPDT switches are analyzed and to validate this technique the prototypes are fabricated using FR4 substrate with a thickness of 16 mm. A very good agreement is shown between the simulated and measured results. Using this technique, it is able to produce more than 30 dB isolation with minimum number of PIN diodes, thus reducing 42.7 of the total circuit size compared with conventional design. Besides, additional 22.9 of isolation bandwidth can be obtained with the use of radial stub compared with transmission line stub. The potential application of this SPDT switch is Time Division Duplex (TDD) switching for WiMAX and LTE communication system in the 3.5 GHz band.