Abstract
Differentially driven devices represent a highly promising research field for radio frequency (RF), microwave (MW), and millimeter-wave (mmWave) designers and engineers. Designs employing differential signals are essential elements in low-noise fourth-generation (4G) and fifth-generation (5G) communications. Apart from the conventional planar MW components, differential–fed balanced microstrip filters, as promising alternatives, have several advantages, including high common-mode rejection, low unwanted radiation levels, high noise immunity, and wideband harmonic suppression. In this paper, a comprehensive and in-depth review of the existing research on differential-fed microstrip filter designs are presented and discussed with a focus on recent advances in this research and the challenges facing the researchers. A comparison between different design techniques is presented and discussed in detail to provide the researchers with the advantages and disadvantages of each technique that could be of interest to a specific application. Challenges and future developments of balanced microstrip bandpass filters (BPFs) are also presented in this paper. Balanced filters surveyed include recent single-, dual-, tri-, and wide-band BPFs, which employ different design techniques and accomplish different performances for current and future wireless applications.
Highlights
In recent years, fourth-generation (4G) and fifth-generation (5G) wireless applications have been experiencing fast development [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
To obtain cascaded short-path TE20δ-mode resonators, a differential-fed substrate integrated waveguide (SIW) bandpass filters (BPFs) loaded with transverse slots on the top layer of the structure is presented by Shen et al [50]
Differential-fed BPFs based on substrate integrated waveguide techniques can be used for mmWave applications to obtain lower losses and higher quality factors and more power handling capability when compared with traditional planar BPFs [47,48,49,50]
Summary
Fourth-generation (4G) and fifth-generation (5G) wireless applications have been experiencing fast development [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. Arbelaez-Nieto et al [36] reviewed and studied some basic concepts related to microwave balanced bandpass filter structures and discussed some alternative methods to design, simulate, and measure differentially fed microstrip BPFs. To simplify the design procedure for other researchers, the paper has presented the step by step developments of planar differentially driven BPFs. To fully describe differentially driven devices, mixed-mode reflection coefficients were presented and discussed generally and this can be applied whenever a designer has a multiport circuit. The dual-mode ring resonator circuits can offer more compact sizes by employing multilayer techniques [38], and this will lead to the development of a high suppression of the common-mode noise for high data rate transmission and high-frequency applications. Our paper aims to survey and compare several design techniques of differential-fed microstrip BPFs by focusing on recent advances and challenges.
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