Jayaseelan Marimuthu

Equivalent J - Inverter Network Parameters Analysis and Cancellation of Spurious Response of Parallel Coupled Microstrip Line

In this paper, the frequency-dispersive characteristic of a two-port parallel coupled microstrip line (PCML) is presented using equivalent J-inverter network parameters which were obtain from its admittance parameters. The extracted J-inverter parameters, J-susceptance and electrical line length, were used to obtain the transmission zero frequency, fundamental response frequency and harmonic response frequency of the PCML. The transmission zero frequency can be realigned by varying a centrally located single groove size to suppress the first spurious harmonic passband of the filter. A technique was identified by using J-inverter parameters to cancel the spurious response. It was found that the transmission zero of J-susceptance null of the PCML can be realigned to cancel the first harmonic resonance. This was done by using a single groove with specific dimension. The proposed technique was justified by two single-stage bandpass filter of PCML with tight coupling characteristic

Wideband and harmonic suppression method of Parallel Coupled Microstrip Bandpass Filter using centered single groove

In this paper, a single grooved wideband Parallel Coupled Microstrip Bandpass Filter (PCMBF) with improved passband response and first harmonic suppression is described. The suppression of first harmonic spurious response was done by using a transmission zero frequency realignment method. The realignment was done by using a single groove with specific dimensions. The transmission zero and first harmonic frequencies can be realigned by varying a single groove size which is located at the center of the Parallel Coupled Microstrip Line (PCML). The wideband with harmonic suppression is achieved in three- stage PCMBF by using two single-stage bandpass filter of identical tight coupler with optimized grooved.

Harmonic cancellation of parallel-coupled bandpass filter with transmission zero realign method

This paper presents the harmonic cancellation of a 3/sup rd/ order Butterworth response parallel-coupled bandpass filter by introducing periodical grooves. The cancellation was obtained by aligning the transmission zero of the tight coupling (TCg) coupler with the harmonic of the weak coupling (WCg) coupler. The alignment of transmission zero and harmonic was carried out by introducing square grooves periodically at the TCg and WGc couplers. Various numbers of grooves were introduced at the TCg and WCg couplers. By varying the number of grooves at the TCg coupler, the first transmission zero was obtained. Then similar method was used to align the harmonics of the WCg coupler with transmission zero of the TCg coupler. When three stage bandpass filter design with transmission zero of the TCg coupler is aligned with the harmonic of the WCg coupler, the overall the performance of filter improved in terms of suppression of the harmonics and cutoff frequencies.

Experimental performance of harmonic suppressed Bandpass Filter

In this paper, the experimental performance of a fabricated single grooved broadband parallel coupled microstrip bandpass filter (PCMBF) with improved passband response and first harmonic suppression is presented. The suppression of the first harmonic spurious response is possible through transmission zero frequency realignment method. A single groove of specific dimensions located at the center of the parallel coupled line has been employed for the realignment of the transmission zero and first harmonic frequencies. An implemented single-stage bandpass filter with various coupling gaps showed harmonics suppressions with optimized groove. Then, two-stage bandpass filters of different operating bandwidth were designed for optimized groove. It was then implemented and tested. The measured results validate real harmonics suppression performance with controllable single groove parameters.

Second harmonic suppression characteristic of a grooved bandpass filter

In analysing the performance of any communication system, degradation is usually caused by unwanted signals. Filters are hence placed at desired locations to filter out these unwanted frequencies. However, the presence of significant harmonic signals that can be generated by devices such as mixers can easily contribute to the unwanted frequencies. Special attention has to be given in suppressing the second harmonic present in the filter output. This paper presents the design of a parallel-coupled bandpass filter having grooved structures. The chosen frequency of operation is 2.5 GHz, suitable for wireless communication system. The proposed design improvements were investigated for Chebyshev response filters. The filters consist of several filter orders, each having different number of grooves. Experimental investigations revealed that as the number of grooves increases, the second harmonic signal decreases. However, it is interesting to note that the behaviour changed with the presence of seven grooves.

Single-stage parallel coupled microstrip line bandpass filter using weak coupling technique

The frequency-dispersive characteristic of a two-port parallel coupled microstrip line (PCML) can be obtained using equivalent J-inverter network parameters. The latter is obtained from its corresponding admittance parameters. Hence, the behaviour of transmission zero frequency, fundamental response frequency and harmonic response frequency of the PCML can be shown. The former is realigned by varying a centrally located single groove size to suppress the first spurious harmonic passband of the filter. Using the J-inverter parameters, the transmission zero of J-susceptance null of a PCML can be realigned by employing a single groove with specific dimension. This simultaneously cancels the first harmonic resonance. In this paper, the behaviour of the J-inverter parameters with varying coupling gaps is presented. The effect of having weak coupling characteristic is then presented. The proposed technique is then justified by two single-stage bandpass filters of PCML with weak coupling characteristic.

Compact broadband PCML bandpass filter with broad upper stop band

A simple broadband parallel coupled microstrip line (PCML) bandpass filter with compact design is proposed. A PCML structure with two feeding network of various widths is characterized by an equivalent J-inverter network. The extracted parameters indicate that the normalized J susceptance and equivalent electrical length are frequency dependent. A pair of PCML structure with middle resonator, without ground plane aperture at PCML structure and capacitive open-ended stub at the middle resonator, is proposed. The proposed design is further optimized by adjusting the length and width of the middle resonator. Three broadband bandpass filter with PCML structure of various coupling strengths have been designed. The simulated and measured insertion and return loss responses show good agreement with bandwidth of over 80%, return loss of better than -16 dB and 250% broad upper stopband.

Microwave filter research in Universiti Teknologi Malaysia

This paper describes four microwave filter configurations that have been recently developed over the past five years. These are a direct coupled cavity waveguide filter, an internally- coupled hairpin-line filter, a meander-gap hairpin line filter and a three-element parallel-coupled filter.

Triggered Spark Gap Command Charger for High Repetition Rate Applications

A normal dc resonant charger was transformed into a command-mode charger by connecting a spark gap at its output terminal, prior to the load circuit. This charging spark gap was triggered by a transformer connected in series, pulsed by a fast spark gap circuit. Noise suppression schemes were implemented throughout the command charger, in particular around the charging spark gap to order prevent misfiring. The ringing noise and spikes from the capacitor discharge and those of the stray capacitance of coaxial cable were strongly suppressed by a simple LCR circuit so that these would not induce self-breakdown in the charging spark gap. This triggered spark gap command charger was tested to 2 kHz and < 10 kV with a resistive load. A transversely excited atmospheric CO2 laser was operated up to 300 Hz and (10-15) kV that was limited only by the flow rate of the laser gas mixture