Coupled Microstrip Research Articles

Design and application of D‐band bandpass filter based on 0.18 μm complementary metal oxide semiconductor process

AbstractThis paper designs a bandpass filter for D‐band and 0.18 μm complementary metal oxide semiconductor (CMOS) process. The bandpass filter is composed of an inverted L‐shaped coupling microstrip line and a cross‐coupled resonator, and is coupled to produce two controlled transmission zeros. A defected ground structure is used to make a good impedance match. The designed filter has a 3 dB impedance bandwidth of 52 GHz (149–201 GHz) with a center frequency of 175 GHz and an insertion loss of 3.23 dB. The design of this paper is a CMOS 0.18 μm process capable of applying the D‐band bandpass filter with the advantages of lower insertion loss, broadband, and compact size.

Compact multi‐band eight‐element MIMO antenna with decoupled antenna pairs for 5G mobile terminal applications

AbstractThis paper presents a novel design method for a tri‐band multiple in multiple out (MIMO) antenna. The antenna consists of four sets of identical antenna pairs arranged on the two side frames. Three resonant modes can be obtained using a microstrip coupling feed structure by employing different branches in antenna unit design. The working frequencies of the modes can be adjusted independently. Moreover, in each pair of antennas, two antenna units were closely arranged and a decoupling grounding branch was employed between the adjacent antennas to ensure good isolation. The tri‐band eight‐element MIMO antenna operates at 3.5, 4.9, and 5.6 GHz and the isolations were better than 14 dB. The proposed antenna had a low profile of 0.06 and good isolation so it has potential applications in 5G mobile terminals.

Iterative synthesis method for high‐directivity symmetrical stepped‐impedance microstrip parallel‐line coupler

AbstractTraditional quarter‐wavelength parallel‐line couplers (QWPLC) in microstrip form suffer heavily in low directivity because of unbalanced even‐mode and odd‐mode phase velocities. Related schemes to improve directivity lead to complex structures and large dimensions. This study derives and validates an iterative synthesis method to design a high‐directivity microstrip coupler adopting a symmetric stepped‐impedance microstrip coupled line (SSIMCL). Given that the even‐mode and odd‐mode effective dielectric constants (EDCs) vary with the characteristic impedances, the authors take the EDCs of traditional QWPLC as the initial values for an SSIMCL, and the characteristic impedances and EDCs can be computed and converged in several iterations, resulting in good phase delay balance and high coupler directivity. A 20‐dB microstrip coupler working at 1 GHz with high directivity is designed, fabricated, and measured. The obtained maximum directivity is 47 dB and approximately 1 GHz, while the relative bandwidth with a directivity higher than 20 dB and a return loss better than 20 dB is larger than 70%. The novel microstrip coupler also features a compact, simple structure shorter than λg/4.

A High Directivity Microstrip Coupler Based on Reflective Resistors

A High Directivity Microstrip Coupler Based on Reflective Resistors

A compact all-frequency absorptive dual-band bandpass filter with T-shaped transmission line absorption branches

Multi-band and all-band absorptive filters can greatly promote the miniaturization of radio frequency (RF) communication systems. However, the existing absorptive multi-band filters have problems such as large size, narrow passband, high insertion loss, and low RF signal absorption capacity. Herein, a new all-frequency absorptive dual-band bandpass filter (BPF) is proposed by combining an N-shaped microstrip coupler with T-shaped transmission line absorption branches. The N-shaped microstrip coupler can flexibly implement the dual-band bandpass filtering of RF radio frequency (RF) signals in a compact structure. The T-shaped transmission lines can effectively absorb the stopband signals reflected from the N-shaped coupler at full frequency. The theoretical and experimental results show that the 3-dB fractional bandwidths (FBWs) of the proposed BPF with a size of 0.41 λg × 0.20 λg are 60.5 % at 1.3 GHz and 13.3 % at 4.1 GHz, respectively, and the return losses in all frequency are greater than 10 dB, indicating that the filter has the characteristics of wide passband, small size, and all-frequency absorption of reflected bandstop signals. In short, the combination of N-shaped coupler and T-shaped transmission line provides a way to achieve an all-frequency absorptive dual-band BPF with a small size, wide passband and low return loss.

Complex Impedance Transformation Using Symmetric Coupled Microstrip Lines of Adjusted Electrical Lengths

Complex Impedance Transformation Using Symmetric Coupled Microstrip Lines of Adjusted Electrical Lengths

High isolation MIMO antenna designed with tightly coupled microstrip patch pairs

This paper proposes an array antenna with high isolation for MIMO application. Two tightly coupled microstrip patch pairs are proposed as array element with two rectangular stubs connected. By adjusting the position and width of the stubs, good resonant frequency matching can be achieved, and isolation can be effectively improved across the operating frequency band. Furthermore, 1 × 2 and 1 × 4 arrays with only 0.04 wavelength space between the edges are constructed for MIMO application. By adding an open-loop resonators (OLR) and slots in the metal reflector, the isolation between adjacent ports can be improved to 26 dB. In order to verify the feasibility of the proposed array antenna, the array antenna has been simulated, processed and tested, respectively. The simulation and measurement agree well and show the isolation more than 25 dB for all ports. The proposed structure has great potential in practical MIMO applications.

A Compact Coupled line Microstrip Band Pass Filter for Wireless Receiver Applications

A Compact Coupled line Microstrip Band Pass Filter for Wireless Receiver Applications

A Novel Ultra-Compact Microstrip Coupler With Low Imbalance Magnitudes and Phases for Wireless Networks

A Novel Ultra-Compact Microstrip Coupler With Low Imbalance Magnitudes and Phases for Wireless Networks

Implementation of an LNA Using a Microstrip Coupler as a DC-Block for Sub-6 5G Communication Systems

Implementation of an LNA Using a Microstrip Coupler as a DC-Block for Sub-6 5G Communication Systems

POWER SUPPLY OF RING ANTENNA USING DIRECTIONAL COUPLERS

Context. The circular polarization of radio waves is used in various electronic systems. This includes, for example, space communications stations, some radio relay communication systems, radar stations, data transmission systems and others. The characteristics of radio wave propagation are studied by using electromagnetic waves separated by circular orthogonal polarization in radiomonitoring and radiocontrol systems. Compared to other antenna types, circularly polarized antennas, such as rings, have superior design simplicity and excellent electrodynamics properties.
 Objective. The objective of this study is to analyse the characteristics and application of directional microstrip couplers for supplying power to ring antennas.
 Method. To better the performance of microstrip ring antennas, the reasons for their limited operating frequency range are analysed. These causes include the frequency-dependent parameters of the coupler, errors in calculating the directional coupler circuit, and radiation from asymmetric strip lines. To understand how supply lines, affect antenna characteristics, correlations between radiation fields determined in both its coordinate system and that of the primary axis are taken into account.
 Results. An analysis of the dependence graphs of the main characteristics of ring microstrip antennas with intricate power supply circuits for directional couplers and comparison with similar characteristics for simple circuits revealed that the shape of the radiation pattern in the higher radiation hemisphere became symmetrical about the axis, especially when symmetrically supplying the ring with branch-line couplers. The frequency band has also widened, at which there was an acceptable degree of deviation in the ellipticity coefficient from unity.
 Conclusions. The simulation results of microstrip ring antennas with power lines connected to directional couplers of different types showed that supplying the ring antenna with electricity via the directional coupler ensures circular polarization for the emitted electromagnetic waves. Additionally, the range of operating frequencies where there is only a small discrepancy in ellipticity coefficient remains at an acceptable level of –3 dB is quite broad. By utilizing directional branch-line couplers to power a ring antenna, it is possible to simultaneously emit both right and left circularly polarized waves with the same antenna.

A Balanced Symmetrical Branch-Line Microstrip Coupler for 5G Applications

Symmetry in designing a microstrip coupler is crucial because it ensures balanced power division and minimizes unwanted coupling between the coupled lines. In this paper, a filtering branch-line coupler (BLC) with a simple symmetrical microstrip structure was designed, analyzed and fabricated. Based on a mathematical design procedure, the operating frequency was set at 5.2 GHz for WLAN and 5G applications. Moreover, an optimization method was used to improve the performance of the proposed design. It occupied an area of 83.2 mm2. Its harmonics were suppressed up to 15.5 GHz with a maximum level of −15 dB. Meanwhile, the isolation was better than −28 dB. Another advantage of this design was its high phase balance, where the phase difference between its output ports was 270° ± 0.1°. To verify the design method and simulation results, the proposed coupler was fabricated and measured. The results show that all the simulation, design methods, and experimental results are in good agreement. Therefore, the proposed design can be easily used in designing high-performance microstrip-based communication systems.

Improved Empirical Formula Modeling Method Using Neuro-Space Mapping for Coupled Microstrip Lines.

In this paper, an improved empirical formula modeling method using neuro-space mapping (Neuro-SM) for coupled microstrip lines is proposed. Empirical formulas with correction values are used for the coarse model, avoiding a slow trial-and-error process. The proposed model uses mapping neural networks (MNNs), including both geometric variables and frequency variables to improve accuracy with fewer variables. Additionally, an advanced method incorporating simple sensitivity analysis expressions into the training process is proposed to accelerate the optimization process. The experimental results show that the proposed model with its simple structure and an effective training process can accurately reflect the performance of coupled microstrip lines. The proposed model is more compatible than models in existing simulation software.

A Filtering Switch Made by an Improved Coupled Microstrip Line

A Filtering Switch Made by an Improved Coupled Microstrip Line

High-directivity and compact microstrip coupler for RF power applications.

A microstrip coupler was designed, fabricated, and tested to monitor the power of the 500MHz kW-level amplifier modules currently installed in an 80-kW solid-state transmitter. The proposed coupler consists of multi-section coupled lines and employs a reverse-coupling scheme, achieving a very compact structure. The dual-side configuration with good termination enables the coupler to have high directivity and wide bandwidth without using any lump components for better temperature stability. Under a low-power test, the measured coupling is 37.69 dB with high directivity from 82 to 700MHz. The coupling is almost independent of the power at 499.65MHz, while the directivity slightly decreases to 33.85 dB at the input power of 1 kW. The maximal insertion loss of 0.08 dB was observed at 1-kW input power. The proposed directional coupler suits many high-power applications, especially in low-frequency regimes.

Phased Array Antenna With Self-Calibration Network and Improved Scanning Performance

In this paper, a phased array antenna with a self-calibration network and improved scanning performance is proposed. For the online calibration, the phased array antenna requires a self-calibration network, which occupies the space between the antenna elements. Besides, the coupling suppression structure for improving the scanning performance of the phased array also needs to be placed between antenna elements. To place these two structures with different functions at the same time, it is a good method to reuse the self-calibration network as the coupling suppression structure. In this work, one side of metallic vias of the substrate integrated waveguide (SIW) cavity to suppress the element coupling is replaced by a coupling microstrip line. Such a hybrid structure can not only realize the online calibration function but also improve the scanning performance of the phased array. Moreover, to reduce the dynamic range of the coupling coefficient between the antenna element and the coupling end of the self-calibration network, reactance regulator blocks are employed on the coupling microstrip line. The coupling coefficient is between –17.2 dB and –24.5 dB in the operating frequency band from 15 GHz to 17 GHz. With the self-calibration network, the gain of the 8×8 patch antenna is increased by 1.95 dB, and the sidelobe level (SLL) is decreased by about 4.20 dB when scanning at –50° in E-plane.

An Ultra Compact Microstrip Branch Line Coupler with Wide Stopband Using LCL Filter and Meandered Stubs for Microwave Applications

A branch line coupler (BLC) with ultra-compact size and harmonic suppression ability using an LCL filter and meandered stubs is proposed in this paper. There are some important factors in microstrip coupler design, including size reduction, harmonic suppression, and low insertion loss. Thus, improving each of these factors will contribute to a more efficient design. In the proposed circuit, for the first time, LCL filters, including four T-shaped circuits and four meandered line open-ended stubs, were used together to reduce the circuit size and suppress unwanted harmonics. The proposed LCL filters, incorporated in the BLC branches, resulted in superior size reduction and harmonic suppression for the presented BLC. The proposed BLC correctly worked at 900 MHz with 300 MHz operating bandwidth, which showed 33% fractional bandwidth (FBW). Additionally, a wide suppression band from 1.4 GHz to 8.8 GHz, with more than 20 dB attenuation level was obtained, which suppressed the second to ninth unwanted harmonics. The overall size of the proposed 900 MHz coupler was only 11 mm × 10.4 mm (0.044 λ × 0.042 λ) while the size of the conventional 900 MHz coupler was 61.5 mm × 62.5 mm (0.25 λ × 25 λ). The proposed BLC had a very small size and only occupied 3% of the size of the conventional coupler, which corresponded to a 97% size reduction. To the best of the authors’ knowledge, to date, the best size reduction has been obtained among the published couplers. Furthermore, the experimental results verified the simulated and analyzed results of the proposed technique and demonstrate its potential for improving the performance and miniaturizing the size of other similar BLCs.

Rapid and reliable re-design of miniaturized microwave passives by means of concurrent parameter scaling and intermittent local tuning

Re-design of microwave passive components for the assumed operating frequencies or substrate parameters is an important yet a tedious process. It requires simultaneous tuning of relevant circuit variables, often over broad ranges thereof, to ensure satisfactory performance of the system. If the operating conditions at the available design are distant from the intended ones, local optimization is typically insufficient, whereas global search entails excessive computational expenses. The problem is aggravated for miniaturized components, typically featuring large numbers of geometry parameters. Furthermore, owing to their tightly-arranged layouts, compact structures exhibit considerable cross-coupling effects. In order to reliably evaluate electrical characteristics under such conditions full-wave electromagnetic (EM) analysis is mandatory. Needless to say, EM-driven design over broad ranges of operating frequencies is an arduous and costly endeavor. In this paper, we introduce a novel procedure for rapid and reliable re-design of microwave passives. Our methodology involves concurrent scaling of geometry parameters interleaved with local (gradient-based) tuning. The scaling stage allows for low-cost relocation of the operating frequencies of the circuit, whereas the optimization stage ensures continuous (iteration-wise) alignment of the performance figures with their target values. The presented framework is validated using several miniaturized microstrip couplers, re-designed over extended ranges of the center frequencies. For all considered structures, satisfactory designs are successfully identified despite the initial designs being distant from the targets, whereas local tuning turns out to be demonstrably inferior. Apart from its efficacy, one of the most important advantages of the proposed framework is its simplicity, and the lack of problem-dependent control parameters.

A high‐performance microstrip bandpass filtering coupler with low‐loss and compact size

AbstractIn this letter, novel spiral‐coupled transmission lines are used to obtain a high‐performance microstrip coupler. The advantages of the proposed microstrip coupler are novel structure, filtering frequency response, suppressed harmonics up to second harmonics, transmission poles, low losses, compact size, and good phase balance. The proposed structure is novel and different from the previous coupler designs such as rate‐races, rings, and branch‐lines types. It is presented for the first time in this work with a very small size and good performance. The size of this coupler is only 82.6 mm2 (0.004 λg2). The common port return loss is 33 dB and the insertion losses at port 2 and port 3 are 2.2 and 2.7 dB, respectively. To prove the accuracy of the design method and simulation results, the proposed coupler is fabricated and measured where the measurement results confirm the simulation results and the proposed design method.

A novel configuration of microstrip coupler with low loss and suppressed harmonics

This work presents a novel structure to design a microstrip coupler. The best values of S21 and S31 are 0.65 dB and 0.83 dB, respectively, in the passband of the proposed coupler. Another significant advantage of this coupler is its filtering frequency response, where it can suppress the harmonics below the passband from DC and above the passband, from 1st up to 7th harmonics. The phase difference between S21 and S31 is 90°±0.1°, which indicates a high phase balance. Beside these features, a compact size of 0.01 λg2 is achieved using the proposed novel configuration of the microstrip coupler. A perfect mathematical design method is introduced to show how the insertion loss (IL) can be reduced. Two BPFs are designed, analyzed and placed in the coupler structure. Finally, the designed coupler is fabricated and measured to verify the simulation results, where the experimental results are close to the simulated results.