Abstract
AbstractIn this paper, different techniques for the generation of additional transmission zeros (TZs) in planar waveguide filters are investigated. In the classical theory, TZs are generated only by destructive interference of non-adjacent cavities, limiting the available number of TZs to the filter order itself. However, more approaches for the generation of TZs are known, including bypass-coupling in oversized cavities, frequency-dependent coupling apertures as well as dispersive/resonant TZs which can be realized by the direct source to load cross-coupling. The aim of this paper is to combine several of the strategies in one physical filter set-up to increase the maximal number of TZs beyond the filter order. Different Ku-band fourth-order filter set-ups are presented, showing in total between six and eight real as well as complex TZs. Three filters are manufactured as a proof of concept and compared with the simulation, showing very good agreement.
Highlights
Due to the high number of mobile and satellite communication services, the electro-magnetic spectrum is getting more crowded and the resource “bandwidth” is becoming scarce
Based on the initial design, which is able to realize seven Transmission zeros (TZs) in the useful Ku-band frequency range, three additional set-ups are investigated in this paper
The first set-up shows the versatility of the proposed configuration as by small changes a phase-equalized filter can be implemented. This filter is able to realize in total up to six TZs, while two of which are complex
Summary
Due to the high number of mobile and satellite communication services, the electro-magnetic spectrum is getting more crowded and the resource “bandwidth” is becoming scarce. The performance of the filters especially at the output stage after amplification is very important to fulfill the stringent out-of-band rejection requirements of a transmitter system. Depending on the application of the filter to be designed, requirements in terms of near-band rejection, losses, and volume/weight are often in the focus of interest. Transmission zeros (TZs) are important in the filter design process as the near-band selectivity of the filter can drastically be improved without increasing the filter order n and the associated losses [1]. Real- and complex TZs might be realized by destructive and constructive interference, respectively. The importance of complex pairs of TZs is mainly defined by the phase linearity constraints
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