Novel dual-band LTCC bandpass filters for microwave applications

Abstract

The idea of using a single wireless communication system for multiple frequency bands simultaneously, has directed part of wireless communication researches towards the design of dual-band microwave components. This dual functionality of components bring low power consumption, system size reduction and more efficient in cost minimizing. Beside all of these advantages, specifications such as type of circuit, Implementation platform, frequency, dimension, performance and etc. have created stringent challenges in this field. In many dual-band communication systems, one of the essential components is microwave dual-band bandpass filter (DBPF). Filtering networks allow signals to pass between two specific frequencies whereas block unwanted signals or make attenuation. In our study, we focus on design, physical realization and fabrication of very compact size of dual-band bandpass filters using low temperature co-fired ceramic technology (LTCC). Among commonly used strategies for building filters, lumped-elements are used to reach compact circuit size at frequencies less than 6 GHz. Out of different options for realizing lumped-elements, LTCC technology is highly recommended due to high circuit integration with size and loss reduction through the use of multilayer of low loss dielectrics. Initially, we present a new schematic for dual-band LTCC second-order Chebyshev bandpass filter. Using even and odd mode analysis, working mechanism of the proposed schematic is fully analyzed mathematically and a direct synthesis procedure is presented to calculate the values of the schematic elements for given center frequencies and bandwidth. This design procedure leverages as much as possible, analytical formulas. The nature of the frequency response of the circuit is established by combination of four poles and four zeros and specific sequencing between them. Four transmission zeros are generated to clean out of band frequencies and reject spurious signals. The limitations on the proposed schematic and design procedure are completely discussed and two appendixes are provided for demonstration process of analytical formulas. Then, the filter topology and synthesis technique are applied for designing of a dual-band bandpass filter (D-BPF) operating in Industrial, scientific and medical (ISM) bands 0.9 and 2.45 GHz and fabricated in LTCC technology. The measurement results show an excellent agreement between the electromagnetic (EM) simulated and fabricated prototype. Further, a new schematic of LTCC narrow bandpass filter containing two poles and two transmission zeros (TZs) is presented for industrial narrowband applications (SNBPF). The bandpass frequency response is established by the two poles, and two TZs are appointed in the both sides of passband to reject spurious signals. Due to symmetry of the network, similar to DBPF, even and mode analysis is used to explain working mechanism. Also, a design procedure is provided to apply the new topology in different frequencies of spectrum. Then, we demonstrate that the single bandpass is generalized to a dual-band frequency response (DNBPF) by manipulating the schematic of SNBPF filter. The working mechanism and design procedure of the DNBPF are provided. To validate the theory of proposed schematics, two design examples are synthesized and prototyped in LTCC. Finally, we propose a fast technique for realization of lumped-elemet values into 3D physical layout on LTCC. Depending on number of elements, physical dimension, mutual coupling and parasitic effects, the circuits require time consuming optimizations and this stage can be very frustrating for designers. In this technique, using correlation strategy between simulators Advanced Design Simulators (ADS) and High frequency structure simulator (HFSS), processing time of physical realization is reduced significantly because of elimination of tuning steps. The usefulness of this technique is demonstrated through a fully synthesized D-BPF.

Date	29 Mar 2020
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Ammar B. Kouki (Supervisor)