Inductive window band-pass filter using integrated waveguide substrate technology for WLAN applications

Subject Areas : Multimedia Processing, Communications Systems, Intelligent Systems

Mahdi Jalali ¹ , Reza Khajeh Mohammad Lou ²

1 - Assistant Professor, Department of Electrical Engineering, Naghadeh Branch, Islamic Azad University, Naghadeh, Iran
2 - Assistant Professor, Department of Electrical Engineering, Miandoab Branch, Islamic Azad University, Miandoab, Iran

Received: 2024-04-04 Accepted : 2024-05-10 Published : 2024-08-18

Keywords: Band-pass filter, transition line, return loss, induction window, waveguide complex substrate,

Abstract :

In this article, a 5.5 GHz inductive window filter based on SIW waveguide structure on FR4 substrate is introduced for use in the WLAN band. This filter, together with the transition step microstrip line for connecting the waveguide to the 50-ohm microstrip line, has a return loss (S11) of less than -10 dB, a bandwidth of 700 MHz, and a low transmission loss (S21), which is 98% of the WLAN application band. covers The parameters of the filter are obtained by using the induction window by modeling in the form of a T network and the K inverse transformation method. The induction window intermediate filter has been analyzed using HFSS software, and the return loss of 25 dB and suitable bandwidth have been obtained. The filter proposed in this article is light in weight and volume, and the cost of its construction is very low and can be implemented and integrated into many communication and microwave systems.

Introduction: Filters are widely used in modern telecommunication systems and satellites. The general requirements for these filters are low loss, high power transmission, small size, and high trace bandwidth with low implementation cost. Compared to flat transmission lines, rectangular waveguides have low loss and high-quality factors. Despite this high cost and the difficulty of using them in plate circuits prevent their use in low-cost and high-size users. Recently, a new concept of integrated waveguide substrate (SIW) has been proposed. Many telecommunications devices such as antennas, power dividers, filters, and separators have been reported based on the integrated waveguide technology. This technology is a suitable choice for the design of microwave and millimeter wave filters, which provide a low profile, the ability to be implemented on cheap printed circuit boards, and low weight with good performance.

Method: A fourth-order filter with a bandwidth of about 700 MHz at a central frequency of 5.5 GHz is designed in this section. The usual method for calculating the length and width of each induction window cavity is as follows: 1- Obtaining the dimensions of conventional rectangular waveguide and SIW waveguide 2- Modeling each induction window cavity as a T network using Marcuvitz theory to calculate the reactance and susceptance of the T network 3- Convert T network to K inverter

Results: A four-order SIW induction window filter with a transition line at a center frequency of 5.5 GHz was designed and demonstrated. The designed filter has a return loss and an adjustable loss in the WLAN application band. And it is easily integrated with microstrip circuits. The filter in the WLAN band has a smooth transmission coefficient with -8 dB loss.

Discussion: It can be seen from the figure that the return loss of the filter in the WLAN band is in the range of -10 to -28 dB and the transmission coefficient in 80% of the WLAN band has a smooth response and in the rest with an acceptable transmission coefficient.

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