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

In this paper, analysis of a class of coupled microstrip transmission lines is developed based on finite and infinite element methods. The microstrip line consists of two dielectric layers with two infinitesimally thin perfectly conducting strips clad on the dielectric layers. It is worthwhile to note that in this development the assumption that the finite transverse dimensions of the microstrip line structure are smaller than the operating wavelength resulting in the wave velocity is no longer independent of frequency and the quasi-static TEM mode approximation analysis can be provided. Coupled microstrip transmission lines have become an attractive means of microwave integrated circuits, namely filters, directional couplers, matching networks, delay lines, and equalizers. The system of coupled transmission lines has also found the use to connect electronic subsystems on modern avionics systems such as aircraft and missiles consisting of large closely coupled cable bundles. In the design of microwave integrated circuits MICs requires a knowledge to predict the electrical transmission properties of microstrip lines. These are namely characteristic impedances, eigenvectors, normal mode propagation constants, and network functions of the lines. A system of coupled microstrip transmission lines is analyzed with both the ordinary finite and infinite elements to solve for the potential and field distributions in the cross section of the microstrip line. A variational principle is applied to compute the Maxwellian capacitance or inductance matrix per unit length of the line. This analysis has the advantage of straightforwardly identifying propagation modes. The parameters of the microstrip line can be determined in terms of the capacitance or inductance matrix. The system of coupled transmission lines is assumed to be uniform along its longitudinal z-direction. The equivalent circuit for the coupled microstrip lines is developed and its application to the solution of wave propagation modes is demonstrated.

Introduction. Coupled two- or three-wire microstrip lines are often used to reduce a phase noise of voltage-controlled oscillators (VCOs). Unfortunately, the phase noise was not optimized depending on the lengths of a three-wire coupled microstrip lines.Aim. For the three-wire coupled microstrip structure, the task of determining of the optimal lengths of its stabs was set. The stabs were corresponded to the reduced phase noise of the selected VCO.Materials and methods. In the oscillator example, the resonator model with three electromagnetically coupled microstrip lines was studied. Herein the second line from the first and the third from the second line differed by the same physical length. The widths of the first and of the third lines were the same, and their coupling clearances with the second line were the same too. On the one hand, in this three-wire microstrip line short-end modes with a common ground electrode were implemented. On the other, at the ends of the first and of the third lines open-end modes were implemented. The free end of the second line is line input.Results. For the considered oscillator, the basic formulas for calculating its frequency-setting elements and resonator model parameters were obtained. By these formulas the estimation of base contours impedances for two oscillators with three-coupled microstrip lines of the same and different lengths, and also for the oscillator using a two-coupled microstrip line was given. For comparison, the proposed VCO near the optimal difference in the three-wire line microstrips lengths had the base contour impedance phase steepness 2...4 times greater, as well as its modules graphs had the width 4...10 times less.Conclusion. In comparison with the known VCOs, the possibility of obtaining lower phase noise spectrum levels at 6...10 dB/Hz in the designed oscillator with the calculated lengths of the selected three-coupled line microstrips was experimentally confirmed.

In this paper, analytical equation-based solutions are derived to allow quick and accurate calculations directly from the physical parameters of coupled, asymmetrical, lossy, and nonuniform microstrip lines with interdigital trapezoidal tabs incorporated, resulting in their corresponding scattering parameters. Capacitance and inductance matrices under a quasi-static condition are derived from the cross-sectional dimensions of asymmetrical coupled microstrip lines with unequal widths. They are converted into a frequency-dependent resistance–inductance–conductance–capacitance model, allowing complete equation-based solutions to their four-port Z-matrix, S-matrix, and ABCD-matrix. As an application example of tackling the complexity of transmission lines, the derived analytical method is applied to a transitional structure with linearly varying trace width in tabbed microstrip lines by the method of segmentation. In addition, a new concept of tab-coupling fringing capacitance is specifically introduced to compensate for underestimated mutual capacitance at tab positions, which will improve the accuracy of the proposed approach. Numerical modeling results from commercial simulation tools are compared for validation purposes. As a conclusion, the proposed method and its versatility are demonstrated with applications to practical high-speed and high-density printed circuit board designs, which renders itself effective and efficient in an optimization process.

In this paper, we propose a new filtering switch with excellent working performance made using an optimized coupled microstrip line. Upon analyzing the RF (radio frequency) front-end’s system structure, the switching device was simplified to a diode, which was connected to the microstrip circuit we designed to become a filter switch with both filtering and shutdown functions. First, we obtained an equivalent schematic of this filtering switch based on the relevant microstrip line theory. This switch consists of two coupled microstrip circuits, parallel-coupled feed lines and coupled-line stub-load resonators (CLSs), and a PIN diode. Second, the operating principle is described by the switching of the operating states, with ideal shutdown performance in the off state and considerable selectivity and excellent out-of-band rejection performance in the filtered state. Finally, a prototype filtering switch with a center frequency of 0.8 GHz was designed and tested. After subsequent optimization and improvement, the simulation and test performance results were noticeably consistent, consequently verifying the performance requirements of this filtering switch in two operating states in the center frequency band.

Knowing the elements of capacitance matrices for coupled microstrip lines, we are able to obtain the characteristics of coupled or meander lines by application of a matrix theory. The elements of the capacitance matrice a previously computed from geometrical dimensions of the lines can now be obtained directly by analytical formulas in a large domain of values of omega , s, h and epsilon/sub r/.

Three wideband transitions from Substrate-Integrated Waveguide (SIW) to Coupled Microstrip (CMS) lines are presented. It is demonstrated that a transition from the fundamental SIW mode to the even quasi-TEM mode of the CMS is straightforward, whereas dominant coupling to the odd mode is only realizable by removing parts of the ground plane. Asymmetric transitions maintaining the ground plane excite a hybrid mode which includes both quasi-TEM modes of the CMS. For this hybrid mode, the excitation ratios between the even- and odd-mode components can be varied, and an unequal power divider is obtained. Performances of the individual transitions and power divider are verified by commercially available field solvers. Dimensional parameters are provided.

Coupled microstrip lines are used to suit a wide variety of circuit applications like directional couplers and filters. Another coupled line variety called corrugated coupled microstrip modifies the phase velocities of the two eigen-modes in the direction of propagation. This property can be used in the design of fase shift couplers, i.e., the coupled wave is phase shifted with respect to the input wave, and in the design of filters with suppression of spurious response at twice the frequency center. The property cited above is used here to discuss other important feature of the corrugated coupled microstrip lines that doesn't appear in the conventional literature: frequency shift. The simulations performed in an appropriate software show that the idea works very well and can be useful in microwave devices like duplex, diplex and multiplex.

In this paper, a electrical field distribution of planar parallel coupled microstrip line has been proposed at different frequencies. Electromagnetically induced electric field has been studied with the help of HFSS software. The influence of frequency on microstrip field characteristics has been examined. A simple structure with shifted and partially coupled microstrip transmission line excited by external source has been simulated on silicon substrate. This gives us the clear indications for circuit layouting in an integrating environment so that EM interference and thus cross talk can be minimized.

In this paper, we investigate the influence of the excitation of improper radiating modes (leaky modes) in the propagation characteristics of coupled microstrip transmission lines. We calculate the crosstalk noise excited in the victim line and evaluate the impact of the presence of a metallic top cover due to the circuit packaging. The time domain propagation of pulses of different widths and rise times are computed in order to study the effect of the separation between the coupled strips on the crosstalk noise currents. We show that both even and odd leaky modes can be simultaneously excited on the covered microstrip structure at low frequencies. This can seriously compromise the signal integrity on the line because of the appearance of effects such as radiation, power loss, and interference, which are usually found in microstrip transmission lines at high frequencies. Our results are compared with those provided by a conventional analysis based on the quasi-TEM approximation and transmission line theory. For an open microstrip structure, we have found that the transmission line model accounts properly for the crosstalk current on the victim line. However, on covered coupled microstrip lines with a sufficiently low top-cover height, the crosstalk noise is higher than expected and cannot be accurately predicted by the transmission line model, even at frequencies where the cross section of the line is much smaller than the wavelength.

This paper introduces a new compact broad band branch line coupler (BLC) using coupled lines. The bandwidth of this new 3 dB BLC is about 25% at 2 GHz and the size of it is about 19% of conventional broad band 3 dB micro-strip BLC with two quarter wavelength lines in each port.

In this paper, closed-form expressions are presented which model the frequency-dependent even- and odd-mode characteristics of parallel coupled microstrip lines with hitherto unattained accuracy and range of validity. They include the effective dielectric constants, the characteristic impedances using the power-current formulation, as well as the open-end equivalent lengths for the two fundamental modes on coupled microstrip. The formulas are accurate into the millimeter-wave region. They are based on an extensive set of accurate numerical data which were generated by a rigorous spectral-domain hybrid-mode approach and are believed to represent a substantial improvement compared to the state-of-the-art and with respect to the computer-aided design of coupled microstrip filters, directional couplers, and related components.

A compact parallel coupled line microstrip bandpass filter (BPF) for sub-6 GHz fifth generation (5G) applications is designed operating between edge frequencies of 3.40 and 3.80 GHz. The design is designed and simulated by means of the Advanced Design System (ADS) software using the flame retardant-4 (FR-4) board as the substrate. The BPF design applies the insertion loss method (ILM) to generate a parallel coupled line filter structure that performs passband permission and unwanted noise attenuation below 3.40 GHz and above 3.80 GHz, respectively. Consistent and relevant performances in terms of matching impedance, return loss (S11), insertion loss (S21), voltage standing wave ratio (VSWR), far field radiation pattern, gain, directivity, and radiated efficiency promise the microstrip BPF design has a potential for sub-6 GHz 5G applications.

Design of an all-optical analog-to-digital converter (AOADC) is presented here based on a leaky waveguide deflector in electro-optic (EO) polymers driven by a coupled microstrip (CMS) line. In particular, back-to-back transitions from grounded coplanar (GCPW) to microstrip line (MS) and from microstrip to CMS line, permitting to connectorize and characterize the EO deflector, are presented. The best achieved bandwidth is over 53 GHz with a remarkably lower cutoff frequency of only 2 GHz. This transition, without via-hole, using electromagnetic coupling between the bottom and top ground planes simplifies the manufacturing and facilitates the characterization of component by means of coplanar probes.

A filter is a key and critical component for all types of wireless communication receivers, which are used to reject the noises (unwanted frequencies) in accordance with the applications. Band pass filters enable operation of any given module in a particular frequency range. In this paper, a compact microstrip band pass filter is proposed with operating range from 2.7 to 10.7 GHz for Ultra-Wide band (3.1 to 10.6 GHz) applications. The Chebychev elliptic function filtering method is employed. Two open circuited stubs are used to achieve the upper transmission loss and coupled micro strip structure is used to reduce transmission loss. The designed filter has insertion loss greater than -1 dB and return loss lower than -10 dB in pass band. The filter is designed with dimensions of 10mm x 9mm x 1.6mm on FR4 (er = 4.3) substrate. The sharp cut-off at lower and upper stop bands has been achieved by proper tuning of the widths and lengths of the open circuited stubs. Bandwidth of about 8 GHz and a flat group delay in the pass band have been achieved. In view of its compactness, this filter can be easily integrated with all communication devices. The designed band pass filter has potential and promising application in UWB (Wi-Fi, Wi-Max, WLAN and ITU) applications.

The design of multi-hole back-to-back microstrip couplers is described, combining standard design methods initially developed for rectangular waveguide multi-aperture couplers and full wave spectral domain techniques for the planar circuits. The couplers consist of two microstrip lines on different sides of a common ground plane. Coupling is achieved through a number of holes (slots) in the ground plane between both microstrip lines. Theoretical and experimental results of a 8-hole coupler with a coupling value of 3 dB for 5 GHz are presented. >