Switchable Coplanar Waveguide Low Pass Filter for Wireless Applications Using RF-MEMS

In this paper, a switchable linear phase coplanar waveguide (CPW) low-pass filter (LPF) is presented which is designed by using radio frequency micro-electro-mechanical systems (RF-MEMS). Traditionally schottky diode, PIN diode and point contact diodes are used for switching the transceivers from one frequency to another. It increases the insertion loss and slows down the switching speed. The RF-MEMS capacitive shunt switches were used to replace the diodes. Traditionally Butterworth and Chebyshev LPFs are used in communication systems. Those LPFs exhibits high reflection in the pass-band and it is also very difficult to achieve faster switching speed due to its poor sharper cut-off characteristics. Because of its poor cutoff and non-linear phase characteristics, it will create unwanted cross talk between microwave sub-systems. In order to overcome the above issues our proposed LPF will be ideal sub-system in future multi-standard systems. The use of RF-MEMS shunt capacitive switch gives the flexibility of tuning the cut-off frequency of the LPF. The proposed switchable LPF was designed by using surface micromachining technology with 3 GHz cut-off frequency, which enables to make simple planar structures of the filter, resulting in easy integration with other planar circuits. In addition, external switching devices for frequency selection are not required. In this filter, a precise and stable frequency-tuning ratio can be obtained because the center frequency can be changed by changing the total inductance by simply controlling ON/OFF actuation of the MEMS switch. The simulation result verifies the switching ability of the proposed design.