2156-3950 (c) 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TCPMT.2019.2918478, IEEE Transactions on Components, Packaging and Manufacturing Technology > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract— In this paper, a wideband bandpass filter is proposed with three transmission zeros which are created using immittance inverters. Impedance- (K-) and admittance- (J-) inverters are integrated with the highpass section and lowpass sections, respectively, and both the sections are integrated to obtain a bandpass response. Controllable transmission zeros are created near the passband for improving the skirt factor (SF). For the theoretical investigation and validation, a lumped equivalent circuit model of the proposed bandpass filter is extracted with the quasi-lumped element techniques. The simulation results of EM/distributed model, equivalent lumped circuit model, and measured results of fabricated prototype bandpass filter are in good agreement. Fabricated EM/distributed bandpass filter has center frequency 2.17GHz, with fractional bandwidth 67.3% (1.4-2.9GHz). The measured insertion loss and group delay at the center frequency are 0.57dB and 5.91ns, respectively. A high skirt factor of 0.97 is achieved at both the cutoff frequencies with compact physical size of circuit 20.5mm×28mm and normalized circuit size 0.24λg×0.33λg. Index Terms— Wideband bandpass filter, immittance inverters, interdigital capacitor, stepped impedance resonator. I. INTRODUCTION N a new era of high-speed microwave wireless communication system, especially in mobile and satellite applications, a microstrip wideband bandpass filter (BPF) is an indispensable element to reject out-of-band spurious and image frequencies. Numerous wideband microstrip bandpass filters, applying various techniques to wideband operation with good rejection rate have been presented in [1]-[24]. Various good designs of wideband bandpass filter with high skirt factor, wide stop band rejection characteristics, and controllable transmission zeros (TZs) were demonstrated in [1-4]. In [1], a wideband bandpass filter was designed by cascading two sections and each section has one or two transmission line (TL) for controlling the selectivity. In [2], a dual-band lowpass-bandpass filter (DB-LPBPF) is presented with four potential transmission zeros (TZs), one zero-value transmission pole (TP), and three non-zeros TPs using lumped element structure. In this work, DB-LPBPF transformed into the dual-band bandpass filter using a pair of a capacitor to block zero-value TP. A dielectric loaded strip resonator is used to design bandpass filters [3]. In [4], quarter wavelength The authors are with the Department of Electronics and Communication Engineering, Indian Institute of Information Technology, Design and Manufacturing(IIITDM) Jabalpur, India (e-mail: lalit.biet@gmail.com; mparihar@iiitdmj.ac.in ). long stepped impedance resonators (SIRs) and interdigital capacitor are used to obtain a wideband bandpass response. In [5-8], wide out-of-band rejection bandwidth is achieved using different designs. In [5] and [6] parallel-coupled dual- mode resonator and cross-shaped resonator are used, respectively. A BPF with improved stopband bandwidth and attenuation using open/short-circuited stub has been demonstrated in [7]. In [8], a dual-band wideband BPF using short-circuited stepped impedance stub loaded with lowpass is illustrated for wide stopband rejection bandwidth. Wideband bandpass filter with high skirt factor presented in [9-15]. A wideband 5 th order Chebyshev bandpass filter was realized in [9], using multimode behavior of the SIR. In [10], a wideband bandpass filter is presented using a dual-path resonator to create the dual mode and transmission zeros near the lower cutoff frequency. In [11], a dual‐mode wideband bandpass filter is realized using tuning stubs and passband was created inside the wide stopband. A cascaded-quadruplet BPF design using quarter-wave resonator is presented in [12]. Here, two distinct coupling mechanisms are discussed and employed in the filter topology to achieve good selectivity. In [13-14], a hexagonal shaped SIR is used in diverse ways to realize the different kind of filtering operations (dual-band BPF and LPF). In [15], a compact and highly selective wideband– balanced BPF has been developed using two half wavelength transmission lines, one stepped impedance stub, and two coupled lines. The differential- transmission and common– mode suppression bandwidths and transmission zeros positions could be controlled by varying the physical dimensions of stubs and transmission/coupled lines. Wideband bandpass filter with high skirt factor and wide stop band characteristics in a signal design demonstrated in [16-24]. In [16], two transmission zeros are created using cross-coupling paths and coupling matrices used to design a compact bandpass filter with high selectivity and wide stopband. The work reported in [17], demonstrates the synthesis of a general sequentially coupled wideband bandpass filter with n-transmission zeros. A narrowband BPF is design with high skirt factor and wide stop bandwidth using hexagonal shaped SIR is presented in [18]. A wideband microstrip line bandpass filter with modified parallel coupled- line has been reported in [19], which offers high selectivity due to the presence of transmission zeros around the passband. In [20], the design method of wideband BPF is demonstrated which was based on the conversion of the LC circuit to its equivalent transmission line circuit using generalized unit element (GUE). In [21], a seventh order wideband bandpass filter with enhanced selectivity was illustrated using the coupled lines and open/short stubs. In [22], a bandpass filter Quasi-Lumped Analysis of Wideband Bandpass Filter with High Out-of-Band Rejection Rate Lalit Kumar, Member, IEEE, Manoj Singh Parihar, Senior Member, IEEE I