Conventional Coupled Lines Research Articles

Design method of Dual-Band Wilkinson power divider with designable length and high design freedom

A new theory of designing dual-band power divider (PD) based on Wilkinson structure is presented in this paper. Because of the utilization of coupled lines, the proposed PD is with a high design freedom that many transmission line (TL) combinations can be used for a fixed frequency ratio k (ƒ2/ƒ1). Meanwhile, since the lengths of the conventional coupled lines used are extremely long, the slow-wave structure is introduced, which configuration results in a property of designable length and compact size because of the improved space efficiency. After analysing the even- and odd-mode circuits, precise design formulas are derived and further verified for the frequency ratio from 1.5 to 6.0 using NI AWR simulator under the consideration of the largest realizable TL impedance as 128 Ω. For verification, two PDs with the same centre frequency of 1.0 GHz and 4.0 GHz but different TL configurations are designed based on the proposed design theory. According to the experimental results, both fabricated PDs have good performances as expected, such as low in-band insertion loss (S21), wide isolation, and relatively better out-of-band rejection than majority of previous studies that the maximum S21 between the two passbands is larger than 6 dB, while previous studies are around 4 dB.

Quasi-Reflectionless Microstrip Bandpass Filters With Improved Passband Flatness and Out-of-Band Rejection

High-order quasi-reflectionless bandpass filters with improved passband flatness and good impedance matching both in-band and out-of-band are proposed in this work. The proposed design consists of conventional coupled-lines bandpass sections loaded with the presented absorptive stubs at the input and output. Analysis shows that the absorptive stub is equivalent to a 2-pole bandstop filter. Compared to the prior art, the higher-order nature of the presented absorptive stub enables a flatter passband and better out-of-band rejection. The overall filter stopband attenuation can be readily improved by increasing the number of coupled-lines sections without altering the passband responses. Furthermore, cross-coupling between the two absorptive stubs can be used to improve the out-of-band rejection by introducing two transmission zeros without affecting the absorption characteristics. The proposed design concepts are experimentally validated by the design and fabrication of a set of 2.4-GHz 1-, 2-, and 3-pole microstrip quasi-reflectionless bandpass filters. Measured frequency responses of these filters closely match those of the simulation.

Planar Single/Dual-Band Crossovers With Large- Frequency Ratios Using Coupled Lines

Compact planar crossovers with large-frequency ratios using coupled lines for single-band and dual-band are proposed in this letter. Conventional coupled lines with different transmission lines are used to realize the single and dual passband. The center frequency of the single-band crossover and frequency ratio for the dual-band can be easily changed by changing the characteristic impedance of the coupled and transmission lines. Two compact planar crossovers located at 1.35 and 1.31/2.69 GHz are designed and measured. The measured results are in good agreement with the simulated ones.

LTCC Wideband Bandpass Filters With High Performance Using Coupled Lines With Open/Shorted Stubs

Two compact low-temperature co-fired ceramic (LTCC) wideband bandpass filters using coupled lines with open/shorted stubs are proposed in this paper. Two conventional coupled lines with open/shorted stubs are used to increase the passband order for the wideband filters. Two independent transmission zeros realized by the open/shorted coupled lines are used to further improve the passband selectivity and harmonic suppression. Due to the 3-D LTCC circuit, the coupled lines and stubs can be located at different layers to overcome the large circuit size. Two fifth-order wideband LTCC bandpass filters centered at 3.1 GHz with multiple transmission zeros are designed and fabricated for verification. The theoretical and measured results are in good agreement and show good in-band performances.

Dual-Band Microstrip Bandstop Filter With Multiple Transmission Poles Using Coupled Lines

A novel dual-band microstrip bandstop filter with multiple poles using open/shorted coupled lines is proposed in this paper. Nine transmission poles near the two stopbands can be easily realized by conventional coupled lines and transmission lines. The two center frequencies of the dual-band bandstop filter can be adjusted flexibly by only changing the even/odd-mode of the coupled lines. The planar microstrip dual-band bandstop filter ( $\varepsilon r = 2.65$ and $h = 0.5$ mm) with nine transmission poles is designed and fabricated. High selectivity and good in-band performances can be achieved in the proposed filter.

Compact Single-/Dual-Band Planar Crossovers Based on Strong Coupled Lines

Three compact planar crossovers based on strong coupled lines loaded with open stubs are proposed in this paper. Two conventional coupled lines loaded with different electrical wavelength open stubs are used to realize the single/dual passband. The center frequencies of the three planar crossovers can be adjusted over a wide frequency band by changing the even-/odd-mode characteristic impedance of the coupled lines and the characteristic impedance of the open stubs. Three compact planar crossovers located at 1.78, 1.88, and 1.02/2.98 GHz are designed and fabricated for verification. The theoretical and measured results are in good agreement and show good in-band performances.

수직 장착된 결합선로를 이용한 광대역 90° 쉬프만 위상천이기

본 논문에서는 수직으로 장착된 결합 선로를 이용한 광대역 쉬프만 위상천이기를 제안하고자 한다. 제안된 쉬프만 위상천이기는 일반적인 결합 선로와 결합 선로 바로 위에 별도의 결합선로를 수직으로 장착한 구조로 이루어졌다. 전체 결합 선로의 두 독립적인 전송 모드인 우 모드와 기 모드 각각에 대한 임피던스와 위상 특성을 계산하여 제안된 쉬프만 위상천이기의 위상 특성을 해석하였다. 이를 기반으로 일반 결합 선로로는 구현이 어려운 높은 임피던스 비를 갖는 <TEX>$90^{\circ}$</TEX> 쉬프만 위상천이기를 제작하였다. 동작 중심 주파수는 2.4 GHz로 하였다. 실험 결과, 오차 <TEX>${\pm}5^{\circ}$</TEX>를 만족하는 최대 대역폭은 1.5~3.2 GHz로 70.8 %의 대역폭을 얻었다. 또한, 측정 반사 특성은 동작 대역에서 13.3 dB 이하이며, 삽입 손실은 1.2 dB 이하로 측정되었다. In this paper, an broadband Schiffman phase shifter is proposed using vertically installed coupled lines. It consists of the typical coupled lines and a extra coupled lines which is installed vertically on the original coupled lines plane. Phase responses of Schiffman phase shifter with vetically installed coupled lines are analyzed in consideration of the phase velocity of two independent transmission modes and the characteristic impedances. The <TEX>$90^{\circ}$</TEX> Schiffman phase shifters with high impedance ratio is realized at 2.4 GHz, which cannot be implemented with the conventional coupled lines. The measured results show that the bandwidth is 1.5~3.2 GHz(70.8 %) within the phase errors <TEX>${\pm}5^{\circ}$</TEX>. The measured return loss is found to be better than 12.4 dB and insertion loss is less than 1.2 dB over the operating frequency band.

Wide-Stopband Bandpass Filters Using Asymmetric Stepped-Impedance Resonators

This letter presents novel bandpass filters (BPFs) with a wide stopband using asymmetric stepped-impedance resonators (SIRs). An uncoupled section located within conventional coupled lines functions as a means of achieving additional transmission zeros between each existing zeros, created by the conventional coupled lines. Designing two types of resonators, which have the same fundamental resonant frequency f1 with different spurious harmonic resonances, results in extending the stopband bandwidth with the better suppression level. Embedded inserted feeder structure is also designed to create supplementary transmission zeros at about 9.0 and 13.0 GHz. Measured results of the proposed filter show the suppression level of -23.7 dB up to 10.6f1 with the FBW of 8.9%.

슬롯-결합 선로를 이용한 광대역 90° 쉬프만 위상천이기

본 논문에서는 슬롯-결합 선로를 이용한 개선된 쉬프만 위상천이기를 제안하고자 한다. 제안된 쉬프만 위상천이기는 일반적인 결합 선로와 결합 선로 바로 밑에 단순한 직사각형 모양의 슬롯으로 이루어졌다. 슬롯과 결합된 결합 선로의 두 독립적인 전송 모드인 우 모드와 기 모드의 임피던스와 위상 특성을 계산하여 제안된 쉬프만 위상천이기의 위상 특성을 해석하였다. 본 논문에서는 일반 결합 선로로는 구현이 어려운 높은 임피던스 비를 갖는 <TEX>$90^{\circ}$</TEX> 쉬프만 위상천이기를 제작하였다. 동작 중심 주파수는 2.4 GHz로 하였다. 실험 결과, 대역폭은 위상 오차 <TEX>${\pm}5^{\circ}$</TEX>의 위상천이기에서 약 74.2 %의 밴드폭을 얻었다. 또한, 측정 반사 특성은 동작 대역에서 15.0 dB 이하이며, 삽입 손실은 1.5 dB 이하로 측정되었다. In this paper, an improved Schiffman phase shifter is proposed using slot-coupled lines. It consists of the typical coupled lines and a simple rectangular slot which is placed in the ground plane underneath the coupled lines. Phase responses of the slot-coupled Schiffman phase shifter are analyzed in consideration of the phase velocity of two independent transmission modes and the characteristic impedance of slot-coupled line. The <TEX>$905^{\circ}$</TEX> Schiffman phase shifters with high impedance ratio is realized at 2.4 GHz, which cannot be implemented with the conventional coupled lines. The measured results show that the bandwidth is around 74.2 % within the phase errors <TEX>${\pm}5^{\circ}$</TEX>. The measured return loss is found to be better than 15.0 dB and insertion loss is less than 1.5 dB over the operating frequency band.

Design Elliptic Lowpass Filter with Inductively Compensated Parallel-Coupled Lines

This paper presents a simple technique to design an ellicptic transfer fuction microstrip lowpass filter based on a ection of doubly inductive compensated parallel-coupled lines. The proposed lowpass filter has the suppression performance to suppress the signal transmission in transition and stopband better than the filter based on the conventional coupled lines. The proposed design procedures are convenient with the closed form design equation. To emonstrate the techniques performance, simulated and measured results at 0.9GHz cut off frequency LPF with ncompensated and the compensated structures are compared. The measured results obtained from the proposed LPF exhibit 0.2dB insertions, less than 20dB return loss and more suppression performance than 35dB at 1.8GHz.

Design of a Compact Hairpin Filter with Spurious Suppression

In this paper, a new method for suppressing the first spurious passband in microstrip hairpin filter is proposed. For this purpose, meandered shaped coupled lines are used instead of conventional coupled lines. Furthermore, by using this method, a size reduction of 50% is achieved. Simulated and measured results show that the modified bandpass hairpin filter presents a rejection level exceeding 35 dB in the first spurious passband.