Indonesian Journal of Electrical Engineering and Informatics (IJEEI) Vol. 8, No. 4, December 2020, pp. 696~705 ISSN: 2089-3272, DOI: 10.11591/ijeei.v8i4.2466  696 Journal homepage: http://section.iaesonline.com/index.php/IJEEI/index Circuit Modelling of Bandpass/Channel Filter with Microstrip Implementation Augustine O. Nwajana School of Engineering, University of Greenwich, United Kingdom Article Info ABSTRACT Article history: Received May 10, 2020 Revised Dec 12, 2020 Accepted Dec 21, 2020 This paper presents a step-by-step approach to the design of bandpass/channel filters. A 3-pole Chebyshev bandpass filter (BPF) with centre frequency of 2.6 GHz, fractional bandwidth of 3%, passband ripple of 0.04321 dB and return loss of 20 dB has been designed, implemented, and simulated. The designed filter implementation is based on the Rogers RT/Duroid 6010LM substrate with a 10.7 dielectric constant and 1.27 mm thickness. The BPF was also fabricated using the same substrate material used for the design simulation. The circuit model and microstrip layout results of the BPF are presented and show good agreement. The microstrip layout simulation results show that a less than 1.8 dB minimum insertion loss and a greater than 25 dB in-band return loss were achieved. The overall device size of the BPF is 18.0 mm by 10.7 mm, which is equivalent to 0.16λg x 0.09λg, where λg is the guided wavelength of the 50 Ohm microstrip line at the filter centre frequency. Keyword: bandpass/channel filter coupling hairpin resonator microstrip Copyright © 2020 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Augustine O. Nwajana School of Engineering, University of Greenwich, ME4 4TB, UK. Email: a.nwajana@ieee.org 1. INTRODUCTION A channel filter, also known as bandpass filter (BPF) passes frequencies within a single band and rejects all other frequencies outside the band [1]. This type of filter is widely used as the building block in the design of complex and multi-port circuits and systems. Some of the more complex devices that can be formed from BPFs include filtering antennas [2,3], multi-band filters [4–6], filtering power dividers [7,8], diplexers [9,10], etc. Figure 1 shows the response from a bandpass filter that passes all signal components between a lower frequency limit, f L and an upper frequency limit, f H , while attenuating and rejecting all other signal components that fall outside the f L and f H band. A bandpass filter can be formed by combining a lowpass filter with a highpass filter. Bandpass filters are widely used in radio frequency (RF) front end of cellular radio base station transceivers. Its main function in the transmitter is to limit the bandwidth of the output signal to the band assigned for the transmission. By this, the transmitter is prevented from interfering with other stations. In the receiver, a bandpass filter permits signals within a certain band of frequencies to be received and decoded, while stopping signals at undesirable frequencies from getting through. Many authors have reported BPFs designed and implemented using various transmission line technologies including waveguides [11–13], microstrip [14–17] and substrate integrated waveguide [18–20]. The BPF presented in this paper is based on the microstrip technology. The filter relies on the microstrip hairpin resonator to achieve compact size. It is also of high selectivity and sharp roll-off. Some filter design characteristics such as selectivity, cost, size, sensitivity to environmental effects, power handling capacity, in- band and out-of-band performance metrics, are critical specifications in the development of RF and microwave communication front end devices. Filter developers are often required to make compromise between several conflicting requirements as it is rather difficult or even physically and/or electrically impossible to