This letter presents a compact hexa-mode microstrip resonator which is originated from a traditional stub-load resonator (SLR). Stub in SLR isreplaced by a couple of square-loops in the proposed resonator. The advantage of this replacement is that six modes emerge to realize a compact size, and more transmission zeros are generated in its application on filter to enhance the frequency selectivity. For demonstration, a compact dual-band microstrip filter using the proposed resonator is designed in 2.4 GHz/5.2 GHz of WIFI channel, and six transmission zeros are generated to enhance the frequency selectivity.
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