A novel class of Butler matrix with inherent bandpass filter (BPF) transfer functions is presented in this paper. The Butler matrix is the fundamental network to split and recombine the signal in multi-port power amplifiers, however, to suppress spurious frequencies generated by the amplifiers or to provide nearband rejection in order not to interfere with other transmission/receiving bands separate filtering is often required. Here, the traditional power division and phase distribution of the Butler matrix are included together with filtering selectivity into one single device based only on coupled resonators. An analytical synthesis procedure of the coupling matrix for 2 2 networks is presented here for the first time. The proposed solution has shown significant advantages in terms of size reduction compared to the traditional baseline consisting of a distribution network plus a bank of BPFs. The synthesis and design of a 2 2, 180 hybrid coupler at 10 GHz and a 4 4 Butler matrix with an equal-ripple four-pole Chebyshev bandpass characteristic centred at 12.5 GHz with 500-MHz bandwidth are described, confirming the synthesis technique proposed. Two models of the 4 4, one built with additive manufacturing and the other with milling, are also presented and compared. Experimental measurements are in good agreement with both simulations and theoretical expectations.Index Terms-Bandpass filters (BPFs), Butler matrix, circuit synthesis, multi-port power amplifier (MPA), power distribution.
This paper presents a monolithic 3D-printed ceramic X-shaped dual-mode microwave filter. The filter is manufactured utilizing a lithography-based ceramic manufacturing (LCM) process, allowing the realization of the resonator as well as the housing in one single piece. Therefore, contact as well as alignment problems, usually arising between a ceramic in T M mode operation and a metallic enclosure, can conveniently be avoided. A fourth order dual-mode filter with a designed center frequency of 6 GHz and a bandwidth of 279 MHz is realized in alumina material. Practical design rules to be considered in the filter layout process as well as limitations imposed by the LCM approach are discussed. The outer surface of the ceramic cavity is subsequently metallized using a silver spray-coating. Advantageously, the metallization is only a few micrometers thick, wherefore the weight of the component can be reduced. The measurement results are compared to the simulation and reveal good agreement. A temperature stability measurement shows a center frequency downward shift of 0.22%.INDEX TERMS 3D-printed ceramic filter, additive manufacturing, alumina 3D printing, dielectric TM dualmode filter, monolithic ceramic filter.
A dual-band passband filter with ellipsoidal cavities is presented in this paper. The filter exploits the ellipsoidal cavity fundamental mode for obtaining one of the two bands and its degenerate for obtaining the other band. The basic building block of the filter is the ellipsoidal cavity with input-output irises rotated with respect to the cavity axes. This cavity produces two poles and one transmission zero (TZ). One pole is exploited in the lower band and the other in the upper band. The rotation angles of input-output irises are used for the fine positioning of the TZ, either in the lower stopband, in the middle stopband (between the two passbands) or in the upper stopbands. Filters with two N-order bands and N TZs are obtained in a modular design by cascading N cavities. Each of the N TZs can be independently positioned in each of the three stopbands. The filter presents an inline geometry and doesn't require the use of internal elements such as posts for controlling the frequency band separation. To validate the proposed approach, a 6-pole dual-band filter with TZ in the middle band has been designed, fabricated with a 3-D printer, and measured.
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