Absorptive K-Band Bandpass Filter Using a Balanced Recursive Structure

Seong-Mo Moon,Han Lim Lee,Moon-Que Lee

doi:10.3390/electronics9101633

Abstract

This article presents a new K-band absorptive bandpass filter (ABPF) based on a microwave balanced recursive architecture. The proposed structure was configured using two passive microwave hybrid couplers, two conventional bandpass filters (BPFs), and a recursive path control module consisting of a phase shifter and an optionally variable gain amplifier. Using the proposed structure, stable return characteristics that were insensitive to the output load variation in the passband, a reduction in standing wave due to absorption in the stopband, and potentially high reliability could be achieved. Furthermore, since the same BPFs were reused, the electrical filtering order within the given physical BPF stages could be increased effectively. The proposed architecture was verified by comparing it with the performance of the conventional two-stage cascaded BPF. The measured results showed a 3 dB passband at 280 MHz with the center frequency at 19.9 GHz and improved roll-off characteristics. Furthermore, the stopband showed the reflectionless characteristic with the return loss being better than 7 dB.

Highlights

With the rapidly increased demand for high data rate services, high-throughput satellite (HTS)systems have recently been considered as the key technology in the satellite industry
Conventional filters are only matched in the passband and are fully reflective in the stopband and transition band, resulting in unwanted interferences in multi-channel operations of HTS radio frequency (RF) chains configured with complicated nonlinear devices
There have been previous studies on reflectionless filters based on lumped elements or microstrip resonators [4,5,6,7], these techniques need to be investigated more to be adopted for K-band applications since the self-resonance characteristics of lumped components and requirements for high Q-factor increase the difficulty of realization

Summary

Introduction

With the rapidly increased demand for high data rate services, high-throughput satellite (HTS)systems have recently been considered as the key technology in the satellite industry. Absorptive (reflectionless) filters are highly desirable to avoid possible problems caused by out-of-band reflection combined with nonlinear devices, such as intermodulation products, gain ripple, and instability [4,5]. There have been previous studies on reflectionless filters based on lumped elements or microstrip resonators [4,5,6,7], these techniques need to be investigated more to be adopted for K-band applications since the self-resonance characteristics of lumped components and requirements for high Q-factor increase the difficulty of realization. For K-band filters, several structures based on microstrip line resonators [8], RF-MEMS [9] and GaAs MMIC [10]

Methods

Results

Conclusion