Compact Coaxial Filters for BTS Applications
A new class of coaxial cavity filters with low-profile suitable for base transceiver station applications is proposed. The benefits of the technology are volume reduction, high performance, and superior spurious-free response. An equivalent lumped element circuit allows for a fast and efficient initial design of the resonators. Full-wave optimization is required to produce the final configuration of the filters. Experimental results demonstrate the high performance of the proposed filters. The electrical length of the experimental resonators is as low as  $\lambda _{0}/16$ . The measured insertion loss of the five-pole filter is 0.92 dB at 722 MHz. Experimental results show a spurious-free response of the order of 7.6 times.
Low-Profile and Low-Volume Split-Distributed Resonators and Filters
A new class of low-profile resonators, named split-distributed resonators is introduced in this paper. The newly proposed resonator family features high quality Q-factors and relies not only on the coupling among the constituent resonant elements, but the constituent elements themselves are also made in the distributed form. This, in comparison with the standard distributed resonator, caters for extremely low profiles, while allowing for a more uniform distribution of the electromagnetic fields inside the resonant cavity and hence higher unloaded quality factors. Furthermore, a uniform distribution of the electromagnetic fields facilitates a tremendous reduction of the resonator volume. As an experimental verification, two 5-pole band-pass filters using different realizations of individual resonant elements are designed and fabricated. The filters operate at a centre frequency of 1.8 GHz with a percentage bandwidth of 2%. The individual split-distributed resonator of these filters consists of 9 resonant elements, where each element is a distributed resonator of the second order and fourth order respectively. The measured insertion losses of the filters are in a good agreement with the values predicted by the simulations.
Novel wideband bandpass filter design based on two transformations of coupled microstrip line
This paper presents a novel wideband bandpass filter with wide stop-band. The filter is realized by using two transformations of coupled microstrip line and four dumbbellshaped defected ground structures. The stub loaded coupled microstrip line with two dumbbell-shaped defected ground structures is used to generate wide pass-band, and the endconnected coupled microstrip line with dumbbell-shaped defected ground structure is employed to implement low-pass and wide stop-band. The equivalent circuit of end-connected coupled microstrip line with dumbbell-shaped defected ground structure is derived. A wideband bandpass filter with wide stop-band using coupled microstrip line with defected ground structure has been designed, fabricated and tested. The filter has 2.76GHz bandwidth centered at 4.89GHz, and 56.4% relative bandwidth has been achieved. It is also illustrated by measured results that the filter possesses a wide stop-band from 0GHz to 2.3GHz and from 6.73GHz to 20GHz, in which the insert loss is more than 20dB. Moreover, the measured insert loss is more than 28dB from 6.97GHz to 19.03GHz. Finally, it can be found that the measured results are in agreement with the simulated results.