Digitally Frequency-Controllable Dual-Band WLAN Filters Using Micromachined Frequency-Tuning Elements

This paper demonstrates two types of dual-band bandpass filters for wireless local area network (WLAN) applications. The two filters (contact-type and capacitive-type) are focused on their digital-mode operations in order to alternatively select the operational frequency-band of the WLAN having two frequency bands of 2.4 and 5.1 GHz. Different types of micromachined frequency-tuning elements having only two states are implemented on each filter in order to control the center frequencies of the filters. The filters are fabricated using a surface micromachining technology, which enables to make simple planar structures of the filters, resulting in ease integration with other planar circuits. Also, external switching devices for frequency-selection are not required, since they are already implemented on the filter own structures. Measured center frequencies of the contact-type filter were 2.55 and 5.1 GHz (50 % tuning-ratio), and the insertion loss and return loss were 4.2 dB and 21.5 dB at 2.55 GHz, and 5.2 dB and 21 dB at 5.1 GHz, respectively. The initial center frequency of the capacitive-type filter was measured to be 5.3 GHz and it was shifted to 2.6 GHz (49 % tuning-ratio) with the applied voltage of 60 V. The total insertion loss and return loss were 2.9 dB and 24.4 dB at 5.3 GHz and 3.3 dB and 20.1 dB at 2.6 GHz, respectively.