Akademik Veri Yönetim Sistemi
INTERNATIONAL GRADUATE RESEARCH SYMPOSIUM IGRS’22, İstanbul, Türkiye, 1 - 03 Haziran 2022, ss.1
In this paper, we provide an overview of coupling matrix synthesis and
design of a microstrip bandpass filter for the 5G n77 (3700 MHz) band based on
the coupling matrix approach. 5G radio equipment strictly requires high
filtering performance to prevent adjacent channel interference. Asymmetrical
pseudo elliptic filter approximation with finite transmission zeros is
providing optimal in-band, out-band performance together with sharp cut-offs at
the passband edges. Microstrip technology may employ filter designs up to 100
GHz. Unlike waveguide and coaxial cavity filters, microstrip filters are
cost-effective and provide ease of manufacture.
The coupling matrix is a compact tool that represents a certain
topology of the bandpass filters. It represents the filter prototypes without
being required to extract reactive components’ values in advance. The coupling
matrix incorporates both inter-resonator coupling coefficients and frequency
offsets in the vicinity of center resonances. The direct synthesis approach,
mostly, ends up with physically unrealizable coupling matrices. Instead, a
realizable coupling matrix is obtained by means of successive similarity transformations
applied to the synthesized matrix. Similarity transformations may emerge in singlet,
triplet, and quadruplet topologies which comprise a finite number of prescribed
transmission zero either real or complex.
This paper begins with design specifications. In order to fulfill n77
specifications, 0.1 dB passband ripple and a decent amount of out-band
rejection is may be realized by a 3rd order filter with 1 finite transmission
zero. Next, the characteristic polynomial and filtering function is derived via
utilizing a recursive method. Once the set of polynomials is known, the 2-port
short circuit admittance matrix is defined by the ratio of certain
characteristic polynomials. Afterward, a nodal admittance matrix is formed for
the transversal low pass prototype. Coupling matrix synthesis is ended up by
equating the short circuit admittance matrix and corner elements of the nodal
admittance matrix. Diagonal elements of the coupling matrix represent the
frequency offset of each resonator section while off-diagonals are direct and
cross-couplings. Appropriate similarity transform is applied to the synthesized
matrix for reconfiguring its topology from transversal to triplet. In this
work, we deploy a square open-loop resonator. Any coupling can be implemented
by changing the orientation and distance between the resonators. A square loop
resonator may support a dual-mode of operation which is realized by adding
perturbations on the resonator rings.