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Rf And Microwave

Micro-strip Filters for Multiplexer applications

Date : 18/11/2013

Author Information

Faheem

Uploaded by : Faheem
Uploaded on : 18/11/2013
Subject : Telecommunications

A multiplexer is a network that separates signals from a common port to other ports, sorted according to their frequency. Multiplexers are constituted from filters, and on-board Ku-band input multiplexer for a satellite communications system is traditionally implemented using waveguide components in order to achieve low insertion loss and high selectivity of the filter response. As in conventional filter design, rejections between channels are usually improved by increasing the order of cross-coupled channel filters. The extra rejection provided by addition poles in a high order filter allows for the bandwidth of the channel filter to be expanded. At the same time, satisfactory filter rejection is maintained. However, extra resonators required to realize additional poles in high order filters typically increases the weight and size of the multiplexer, which is not a preferable solution for extremely weight sensitive satellite applications.

In a multiplexer, channel filters are usually connected through a common waveguide manifold. Interactions among channel filters need to be taken into account in order to achieve channel performance close to a stand-alone filter. In conventional design, the manifold is merely considered as part of a matching network for each channel and any resonances generated by the interconnecting transmission line are to be avoided. However, it has been shown that manifold resonances can be utilized to form additional resonances for channel filters. Using the conventional manifold coupled multiplexer configuration, the distance between channel filters and the distance between each channel filter and the manifold are determined to ensure that a pole is formed causing an additional real reflection zero to be brought into the passband of the multiplexing network. The channel filter order is therefore increased by one without additional resonators. As shown in the technique is applicable to both contiguous and non-contiguous multiplexers and there is no impact on the overall dimension compared to a conventional design.

Recently, several methods of designing diplexers triplexers and multiplexers have been presented. The article presents the common-resonator structure where the first resonator of the bandpass filters is shared and the channel passband frequencies have to be chosen at the resonant frequencies of the common resonator. Therefore the freedom in choosing passband frequencies is restricted and because of the limited available coupling area, only a small number of channels are possible. In a triplexer based on stepped-impedance resonators with high isolation and large circuit size caused by the extra matching network is proposed. In planar triplexers were presented by properly locating the attenuation poles near the passbands of the triplexer. References provide other development in the art.

The objective of multiplexers is to generate two duplicates of the received signal, filtered within the band of interest, in order to apply a different treatment to each one. More precisely, one of the outputs is used to separate the even channels, while the other corresponds to the odd channels. This division of the signal allows the multiplexer channel filters to have lower selectivity and be simpler, since the channel-to-channel guard bands are greatly increased. This type of design also covers the more general possibility of two different input signals from two receivers. However, waveguide technology elements are typically heavy, bulky, and difficult to integrate with other elements such as amplifiers. The objective of this project is to develop a lower cost equivalent device using microstrip technology.

This resource was uploaded by: Faheem