Compact microstrip bandstop resonator for dual-band wireless communication

This paper proposes a concept for design and fabrication about a compact microstrip bandstop resonator for dual-band wireless communication. This proposed microstrip bandstop resonator is constructed from 2 open-circuited quarter wave-length transmission line stubs and J-inverter which are used to separate widely between low and high frequency bands by using transmission lines theory and admittance inverter. The low frequency band of 800–900 MHz can be served the CDMA mobile networks of CAT Telecom Public Company Limited in Thailand, and the high frequency band of 2.3–2.7 GHz can be served the wireless networks both WiFi-2.45 GHz and WiMA-2.5 GHz. The experimental results have been shown that the measured return losses are in good agreement with the simulated ones both the entire higher and lower frequency bands. Refer to considering the return loss of 20 dB, the bandwidth of a measured microstrip bandstop resonator is close to the simulated bandwidth for the lower frequency band, but it is wider than the simulated bandwidth for the higher frequency band. Moreover, the measured insertion losses are high, but those are in good agreement with the simulated ones. The advantages of this proposed microstrip bandstop resonator are as follows: the return losses are good and acceptable, the wide rejection band can be owned, and the compact size can be achieved.