Multi band RF bandpass filter design
Abstract
RF Band Pass filters are at the front end of a wireless system enabling pre-selection of the desired band as well as rejection of interferers. As wireless systems become more multifunctional, it will be increasingly important to have miniaturized filters that can select more than one band at a time. This can be achieved by having multi-band filters that can select more than one band at the same time and/or using tunable band pass filters that can cover large frequency ranges. By using the vertical integration capability of LTCC (Low Temperature Co-fired Ceramic) technology, novel dual band filters up to fourth order have been demonstrated in a form factor as small as 6mm by 4mm by 0.5mm. The filters utilize the mutual couplings inherently present in a high-density technology like LTCC to create a dual pass band response using only a single set of lumped components. Another aspect of bandpass filter design is achieving a tunable passband response, having a flexible center-frequency as well as controllable bandwidth. This has been achieved for high-Q evanescent-mode cavity filters that can be tuned in center frequency over more than an octave while still maintaining low insertion loss. The bandwidth of a band pass filter varies as a function of its center frequency, and can be quite significant over large tuning ranges. In order to address this issue, bandwidth compensation networks have been designed for these filters that reduce this variation, without degrading the performance of the filters. It will be shown that an almost constant bandwidth can also be achieved using this technique over an octave tuning range, while maintaining less than 3 dB insertion loss for second order filters having almost exactly 25 MHz bandwidth. Subsequently, up to six of these tunable filters have been integrated in parallel to allow simultaneous selection of multiple bands that can be spaced as close as the individual filter bandwidth.
Degree
Ph.D.
Advisors
Chappell, Purdue University.
Subject Area
Electrical engineering
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