A Compact Coupled-Line Butterworth Bandpass Filter for Sub-6 GHz Applications

Abstract

This paper presents the design, fabrication, and experimental validation of a compact microstrip bandpass filter operating at 3.5 GHz for sub-6 GHz 5G wireless communication systems. The proposed filter is realized using a fourth-order Butterworth response implemented through a parallel coupled-line topology, aiming to achieve a maximally flat passband response, low insertion loss, and sufficient selectivity within the n77 frequency band (3.3-3.8 GHz). The design procedure starts with the synthesis of a normalized low-pass Butterworth prototype, followed by bandpass transformation and its implementation as an equivalent distributed microstrip structure. Electromagnetic analysis and parametric optimization are employed to accurately model coupling effects, transmission line behavior, and fabrication constraints. The filter is fabricated on a low-cost FR-4 substrate with a dielectric constant of 4.3 and a thickness of 0.8 mm using standard printed circuit board manufacturing techniques. Experimental characterization is performed using a vector network analyzer to evaluate the frequency response. Measurement results demonstrate a center frequency of 3.5 GHz with an impedance bandwidth of approximately 300 MHz, showing good agreement with the predicted performance. The proposed bandpass filter offers a compact footprint, simple geometry, and reliable frequency response, making it a suitable candidate for integration into 5G radio-frequency front-end modules and other modern wireless communication systems.

Keywords

• Butterworth response
• Coupled-line topology
• Microstrip bandpass filter
• Sub-6 GHz 5G systems

Sub-6 GHz Uygulamaları için Kompakt Kuplajlı Hat Butterworth Bant Geçiren Filtre

Abstract

Bu çalışmada, sub-6 GHz 5G kablosuz haberleşme sistemleri için 3.5 GHz merkez frekansta çalışan kompakt bir mikroşerit bant geçiren filtrenin tasarımı, üretimi ve deneysel doğrulaması sunulmaktadır. Önerilen filtre, maksimum düz geçiş bandı cevabı, düşük ekleme kaybı ve n77 frekans bandı (3.3–3.8 GHz) içerisinde yeterli seçicilik sağlamak amacıyla paralel kuplajlı hat topolojisi kullanılarak dördüncü dereceden Butterworth tepkisiyle gerçekleştirilmiştir. Tasarım süreci, normalize edilmiş bir alçak geçiren Butterworth prototipinin sentezi ile başlamakta, bunu bant geçiren dönüşüm ve eşdeğer dağıtılmış mikroşerit yapı olarak gerçekleştirilmesi izlemektedir. Kuplaj etkileri, iletim hattı davranışları ve üretim kısıtlarını doğru şekilde modellemek amacıyla elektromanyetik analiz ve parametrik optimizasyon çalışmaları yapılmıştır. Filtre, dielektrik sabiti 4.3 ve kalınlığı 0.8 mm olan düşük maliyetli FR-4 alttaşı üzerinde standart baskılı devre kartı (PCB) üretim teknikleri kullanılarak üretilmiştir. Deneysel karakterizasyon, frekans cevabını değerlendirmek üzere bir vektör ağ analizörü kullanılarak gerçekleştirilmiştir. Ölçüm sonuçları, yaklaşık 300 MHz empedans bant genişliğine sahip 3.5 GHz merkez frekans elde edildiğini ve ölçülen sonuçların öngörülen performansla iyi bir uyum gösterdiğini ortaya koymaktadır. Önerilen bant geçiren filtre; kompakt boyutları, basit geometrisi ve güvenilir frekans cevabı sayesinde 5G radyo frekans ön uç modülleri ve diğer modern kablosuz haberleşme sistemlerine entegrasyon için uygun bir aday sunmaktadır.

Keywords

• Sub-6 GHz;
• bant geçiren filtre
• kuplajlı hat
• Butterworth filtre
• mikrodalga filtre
• RF devreleri

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