Miniaturised Microstrip Dipexers for WiMAX Applications

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Introduction
Wireless RF and microwave communication systems are a rapidly expanding
market. Such systems commonly employ filters and diplexers in RF and
microwave transceivers as channel separators. Hence there is an increasing
demand for low cost, low loss, small size and light weight bandpass filters and
diplexers [1]. At present most microstrip diplexers at RF and microwave
frequencies are produced in planar technologies such as microstrip, suspended
substrate stripline and coplanar waveguide. Several approaches of design of
microstrip diplexers were proposed [2]-[5].




Simulation Results
In order to validate the argument made the proosed bandpass filter and diplexer
structures have been designed and simulated. The bandpass filters and diplexer
were simulated by using Agilent ADS Momentum simulator [8]. Fig. 4. shows the
simulated insertion losses (S21-parameters) of the lower channel and upper
channel proposed filters.


Conclusion
Miniaturised microstrip diplexer and bandpass filters using single ring resonators
with good transmission and reflection characteristics on each channel for WiMAX
applications have been presented. The size of the proposed diplexer is reduced.
The diplexer is easy to manufacture and the results are easily reproducible. The
improvement of the performance of diplexer through introduction of additional
transmission zeros is under investigation.