Sharp-rejection microstrip bandpass filters with multiple transmission zeros

A simple design of a sharp-rejection microstrip bandpass (BPF) filter is presented. By creating multiple transmission zeros in the lower and upper stopbands, sharp rejection characteristics are obtained. The basic filter unit consists of a single parallel coupled-line section and an open-ended stub. A lossless transmission line model approach is used to derive the design equations for frequency responses and transmission zero positions. The bandwidths are controllable by the zero locations that in turn are controlled by varying the impedances of the configuration. To validate theoretical predictions, two prototype BPFs operating at lower band 2.4 GHz of WLAN are fabricated in microstrip form.     

Dual‐Transmission‐Line Microstrip Equiripple Lowpass Filter with Sharp Roll‐Off

A novel application of a dual‐transmission line is proposed to design a lowpass filter (LPF). The proposed structure uses only transmission line elements to produce an equiripple LPF response with sharp roll‐off. Design equations are derived using a lossless transmission line model. Controlling the electrical lengths, three transmission‐zeros are realized in the stopband to obtain a sharp roll‐off rate and wide stopband bandwidth. A single unit microstrip LPF with a 3‐dB cut‐off frequency at 1.0 GHz having a roll‐off of 135 dB/GHz along with a stopband bandwidth of 69.5% is designed for validation.     

Microstrip Coupled-Line Lowpass Filter with Wide Stopband for RF/Wireless Systems

We present the design of a compact microstrip lowpass filter with a wide stopband which is up to ten times the cutoff frequency. The filter is based on a coupled-line configuration and shunt open stubs. The open stubs create additional transmission zeros, which are used to extend the stopband of the filter without any additional components or cascaded units. A prototype lowpass filter with a 3 dB cutoff frequency of 0.428 GHz and a 15 dB stopband extended up to 4.77 GHz is fabricated to validate the theoretical predictions.     

Harmonics and size reduced microstrip branch‐line baluns using shunt open‐stubs

This article presents the design of harmonic suppressed compact microstrip balun, using shunt open‐stubs. Two approaches using Π‐shaped and T‐shaped open‐stub configurations are investigated. Because of the stopband effect of the open‐stubs, the harmonic passband responses are suppressed effectively. A compact‐size balun is realized because both kinds of structures have slow wave characteristics. To validate theoretical predictions, two prototype baluns operating at f₀ = 1 GHz, showing size reduction up to 75% and no spurious passband up to 4f₀ compared with the conventional design are fabricated in microstrip form. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

High‐rejection wide‐stopband lowpass filters using signal interference technique

A design of compact, sharp rejection microstrip lowpass filters (LPF) with wide‐stopband is presented by using signal interference technique. The filter parameters can be easily controlled by the characteristic impedances of the configuration. Explicit design equations with graphs are presented. To validate the theoretical prediction, two prototype LPFs are fabricated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Compact Planar Dual‐Wideband Bandstop Filters with Cross Coupling and Open‐Ended Stepped Impedance Resonators

This letter presents the design of a compact bandstop filter (BSF) operating at two frequencies. The proposed BSF consists of open‐ended stepped impedance resonators (OSIR) and an end‐shorted parallel‐coupled microstrip line (E‐PCML). The OSIRs are used to achieve the impedance‐controlled stopband positions. The wide BSF bandwidths are achieved through enhanced coupling of the E‐PCML. Explicit design guidelines are derived using a lossless transmission line model. To validate theoretical predictions, a prototype dual‐band BSF operating at 900 MHz and 2,100 MHz with fractional bandwidths of 72% and 36% respectively, is implemented in microstrip.     

On symbol synchronization of MPPM sequences

We investigate the synchronization properties of slot-synchronized multipulse pulse position modulation (MPPM) sequences. We derive a bound on the probability of MPPM symbol synchronization and identify synchronizable MPPM symbols, which, when periodically inserted in the data stream, can remove an observed performance floor     

Harmonic suppressed compact wideband branch‐line coupler using unequal length open‐stub units

In this article, the design of a broadband branch‐line coupler (BLC) with reduced size and suppressed harmonic passband response is presented. The proposed approach can be used to replace the low impedance λ/4 lines of the conventional BLC by an equivalent structure almost λ/12 in length. The main advantage of the proposed BLC is that, it has approximately the same bandwidth as that of a conventional BLC. A prototype broadband coupler having fractional bandwidth >50% at 1.1 GHz and of size less than one third of a conventional three‐section wideband BLC topology is realized. In addition, at least 20 dB suppression of up to fourth harmonics is achieved. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Optimization of flame stabilization methods in the premixed microcombustion of hydrogen–air mixture

The premixed combustion of a lean hydrogen–air mixture is analyzed in this study to examine various properties and flame stabilization. A two-dimensional (2D) analysis of a microscale combustor is performed with various shapes of bluff bodies (e.g., circular and triangular). Nine bluff bodies are placed at the entrance of the microscale combustor and solved with 2D governing equations. The analysis is performed with the three velocities of 10, 20, and 30 m/s, but the equivalence ratio is fixed in all cases. The various characteristics of the microscale combustor are studied such as the temperature of the wall, difference in peak temperature, the mean velocity at the outlet, and temperature of the exhaust gases. Flame stabilization depends on various factors such as bluff body shape and size, and the velocity of the fuel–air mixture at the inlet and recirculation zone. In comparison to all bluff body cases, we observe that the wall blade bluff body is the most efficient (low exhaust gas temperature, large recirculation zone, low mean velocity at the outlet of the microcombustor, and high wall temperature) compared with all eight other bluff body cases. Combustion efficiency is directly proportional to the wall temperature, meaning that the microcombustor with wall blade bluff bodies is more efficient with a stabilized flame. The simulation results are compared with published data on an L/D ratio of 15.