|Institution:||University of New Mexico|
|Keywords:||Aluminum Nitrode, microresonators, kt2, temperature compensated, filter coupling|
|Full text PDF:||http://hdl.handle.net/1928/23623|
There is currently a gap in the technologies available for realizing miniature, temperature compensated RF filters with fractional bandwidths of ~1%. This presentation will cover the development of miniature filters based on temperature compensated aluminum nitride microresonators that have fractional bandwidths exceeding the microresonator coupling coefficient, kt2, limit of 0.3%. A method is presented that offers the flexibility of using low Q reactive components to couple temperature compensated aluminum nitride microresonators with bandwidths ranging from extremely narrow (0.05%), as limited by the Q of the resonators, to fairly wide (~1.5%) depending on the coupling network topology. This method overcomes the limiting effect on filter bandwidth due to piezoelectric resonators’ kt2 material property and makes possible full, on-chip integration of an RF filter’s resonators, coupling networks, and matching networks. This coupling method maintains the benefits of series-cascaded resonator filters such as simplicity of design, out of band rejection, and single-ended port architecture. The filter synthesis method is demonstrated in a 3-pole, temperature compensated AlN microresonator filter that achieves a fractional bandwidth of 1.2% at a center frequency of approximately 500 MHz and an insertion loss of 5.4 dB. Based on the measured temperature coefficient of frequency of the resonators that comprise the filter, the center frequency of the filter will drift by 240 kHz from -55 to 125 ○C, which is less than 0.05% of the filter 3 dB bandwidth. The narrow bandwidth and excellent temperature stability will lead to RF systems with improved sensitivity and that are more robust to out of band jammers.