Design of an Ultra-Wideband Using the Stub Q-Factor Technologies, Ended by Short-Circuit Configurations

Abstract

An Ultra-WideBand (UWB) bandpass filter is presented in this paper, using the maximally-flat principle through the stubs (resonators), terminated by a short circuit. The global stubs’ quality factor Q is determined to control the filter’s bandwidth from the line-section sizes, placed along the transmission line as I-shaped. The Q-factor is related to an operating frequency  to mismatch the system thereabout. This approach allowed determining the filters’ parameters: insertion loss (IL), return loss (RL), bandwidth (BW), and attenuation coefficient in two frequency ranges: (5.76 – 12.241) GHz. All stubs are terminated by a short-circuit and are quarter-wavelength. The technique uses parallel admittance, which is pairwise identical according to the number of resonators. Each circuit’s section is represented by its  chain matrix before using the Cascading Chain Matrix (CCM) to determine the filter’s parameters. With the entire circuit board Q-factor, it’s possible to control the bandwidth size, fixed at -10 dB of the return loss. The prototypes have been fabricated and validated for five resonators in the scanned frequency (3 – 13) GHz. A 1-mm thickness of FR4 HTG-175 has been used to validate the new approach. The filter’s size is 27.51x7.6172 mm2, determined at GHz. Experimental results have shown a UWB of 6.481 GHz with 0.947 of IL at 9 GHz (the central frequency) and 72% of the fractional bandwidth. Two feedlines of 10 mm have been added to solder SMA connectors to link the prototype and the vector network analyzer (VNA). The results have been compared with the Agilent Design System (ADS) software.

Keywords: Chain matrix, maximally-FlatMicrowave bandpass filterResonatorShort-circuited lineTransmission-lineUltra-wideband (UWB)