We have recently introduced a new class of cavity resonators and filters, termed distributed resonators [1] and [2]. The distributed resonator allows a major reduction in the resonator profile while maintaining an excellent electrical performance. In [1], an individual distributed resonator consists of a number of low-profile resonant posts arranged in a grid, where the resonant posts on the vertical and horizontal axes of the grid mainly couple to their immediate neighbors. The substantial reduction in the filter profile, comes – to a degree – at the price of the footprint, mainly due to the fact that the individual distributed resonator consists of a number of resonant posts.
In this paper, the concept of [1] and [2] is further generalized by realizing the individual resonant element in a distributed form. The new resonator is termed split-distributed resonator since the individual resonant post is effectively split in order to better exploit mutual coupling. Due to their split configuration, the individual distributed resonant posts no longer strongly couple only to their neighbors on the vertical and horizontal axes, but to their diagonal elements as well. This has a profound effect on the reduction of resonator footprint, while maintaining the low resonator profile and excellent electrical performance. As a practical demonstrator, a 5-pole is designed and fabricated, and its performance tested. The filter is made to operate at a frequency of 1.8 GHz, with an absolute bandwidth of 40 MHz. Each resonator of the proposed filter consists of 9 split-distributed resonant elements, placed in close proximity. The chamber size of each resonator is 30 mm x 30 mm x 7 mm, with an unloaded quality factor of over 1700. The measured insertion loss of the filter is 0.94 dB, which is in excellent agreement with the theoretically predicted value of 0.76 dB.
[1] S. Bulja and M. Gimersky, “Low-Profile Distributed Cavity Resonators and Filters,” IEEE Trans. Microw. Theory Techn., vol. 65 issue 10, pp. 3769-3779, 2017.
[2] S. Bulja, E. Doumanis and D. Kozlov, “Concentric distributed resonators and filters”, in Radio and Wireless Symposium (RWS), Anaheim, CA, USA, 2018, pp.267-269.
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