Design of microstrip tri‐mode balun bandpass filter with high selectivity

Abstract

A new microstrip tri-mode balun bandpass filter (BPF) with good filtertype and balun-type functions is presented. To realise the tri-mode BPF performance, the multimode stepped-impedance resonator is introduced and parallel coupled to both the balanced and the unbalanced ports. To achieve 180°phase difference, two types of transition structures, i.e. the microstrip-coplanar waveguide-microstrip transition and the microstrip-coplanar stripline-microstrip transition, are adopted for the two balanced output ports design, respectively. A balun BPF operating at 2.6 GHz is designed and fabricated to validate the feasibility of the new approach. Results indicate that the proposed balun BPF exhibits not only high selectivity with two transmission zeros locating at 1.7 and 3.7 GHz but also good balance performance with 0.5 dB magnitude imbalance and 5°phase imbalance between the balanced outputs.Introduction: The ever increasing demand for compact and low-cost wireless communication systems leads to the requirement for high the integration of microwave circuits especially for the passive components. The development of a balun bandpass filter (BPF) that can properly integrate both the functions of balun and the BPF turns out to be a necessary way to reduce the size and cost of systems. The balun BPF, in other words, is a multi-function embedded passive component, as it can not only convert an input unbalanced single-ended signal into its balanced differential one but also make the desired signals to be transmitted smoothly over a certain frequency band while blocking other undesired signals. Over the past few years, much effort has been focused on this area [1][2][3][4][5].To reduce circuit dimensions, a balun BPF using the low-temperature co-fired ceramic technology was proposed in [1], yet the multilayer process increases the complexity and the cost of the circuit. By combining the topology of the coupled-line and the stepped-impedance resonator (SIR), a good performance microstrip balun filter was introduced in [2]. On the other side, microstrip dual-mode patch resonators have been receiving much attention to design a balun BPF with dual-mode response [3,4]. Moreover, to further reduce circuit size and the improve harmonic suppression performance of the dual-mode balun filter, a dual-mode patch resonator with capacitive loading was proposed in [5]. The dual-mode balun filters mentioned above are all designed based on the loop-type resonator. However, to the best of our knowledge, there is no report on the design of a microstrip multimode balun BPF by using the widely used open-type microstrip multimode resonator.The primary motivation of this Letter is to design a new wideband tri-mode balun BPF with an open-type microstrip multimode resonator. By utilising the first three modes of the multimode SIR resonator and the electric filed distribution characteristic of the transition structures, a new design method of a microstrip tri-mode planar balun BPF is presented. For demonstration, a tri-mode balun BPF is designed, fabr...

Wideband balun filter on slot‐line resonator with intrinsic balanced performance in magnitude and phase

“…Over the past few years, as increasing demand for today's communication RF‐fronds to be compact, low cost, multi‐functionality, balun bandpass filter (BPF), simultaneously maintain a function of a balun converting unbalanced signal to a balanced one and frequency selectivity of a bandpass filter (BPF), shows its promising to meet such requirement and in practical application as one multi‐function circuits blocks. In recently years, a great mount of works has been devoted to developing and realizing of such kind of high performance balun filters . Among them, the substrate integrated waveguide (SIW) has been used to design a class of low‐loss balun filter with good filtering response and out‐band rejection .…”

“…Next, a microstrip triple‐mode wideband balun with high selectivity and balun‐type function was presented in Ref. , but it needs to install two dissimilar types of wideband transitions, resulting in the complicated geometry and extra circuit area. In Ref.…”

“…In recently years, a great mount of works has been devoted to developing and realizing of such kind of high performance balun filters. [1][2][3][4][5][6] Among them, the substrate integrated waveguide (SIW) has been used to design a class of low-loss balun filter with good filtering response and out-band rejection. 1,2 Owing to its narrow bandwidth, it is not suitable for wideband application.…”

Ultra-wideband coplanar waveguide-to-asymmetric coplanar stripline transition from DC to 165 GHz

“…In communication systems, CPW in a ground-signal-ground (GSG) configuration is normally used for designing amplifiers [2][3][4][5], frequency doublers [6,7], mixers [8,9], power DACs (PDACs) [10,11] and interposer connections between different components [12,13]. Being different from CPW, CPS as well as ACPS are in a ground-signal (GS) configuration and they are used for designing baluns [14][15][16][17], antennas [18][19][20], and the electrodes of Mach-Zehnder modulators (MZMs) [21][22][23].…”

Using Open Stubs and Tuning the Width of Output Microstrip Lines of a Balun Diplexer to Obtain the Matching Output Impendence With Rf Output Transceiver

“…Compared with conventional single-ended circuits, balanced circuits can easily meet and even exceed requirements. Balunselectrical devices that convert between a balanced and unbalanced signal and thereby enable the transition from unbalanced circuits to balanced ones -are used as interface devices [1][2][3]. Baluns can take many forms and may include devices that transform impedances.…”