Z. Ismail Khan

Achievable bandwidth of a quarter wavelength side-coupled ring resonator

Studies on the achievable range of bandwidth of a side-coupled ring resonator bandpass filter are presented. The elements of the resonator susceptible on varying the filter bandwidth are identified and design solutions are given in order to push the bandwidth to its minimum and maximum values. Based on the side-coupled ring resonator topology, two microstrip filters were designed at 10 GHz to achieve the narrowest and widest bandwidth with respect to insertion losses and technological limitation. Results of the studies with the given technology show that the ring resonator is suitable to address bandwidth from narrow (3.6%) to wide (31%). These concepts are validated through simulations and experiments for filters implemented on alumina substrate.

Clutter modeling for forward scatter radar (FSR) micro-sensor network with ultra high frequency (UHF) band

The clutter model for ultra high frequency (UHF) band for forward scatter radar (FSR) is developed in this paper using Log-Logistic distribution. The model follows maximum likelihood estimation (MLE) approach in finding the parameters for the distribution as well as root mean square error (RMSE) of the data between the clutter signal and statistical model as the goodness of fit (GOF) test. The model is then compared to four different distribution models, which are Log-Normal, Gamma, Weibull and Nakagami. The results of the comparisons show that Log-Logistic model best fits the clutter signal.

Single-mode ring resonator for microwave bandpass filter applications

Topologies of two microwave bandpass filters are presented. The first topology comprises of a single mode ring resonator which is fed along one of its quarter-wavelength sides. The second topology is constructed based on the first topology whereby two series cascaded ring resonators with a quarter wavelength coupled line in the middle of the structure to obtain a 4th order bandpass filter with a good out-of-band rejection level. Observation on the controlling parameters of the 4th order bandpass resonator is conducted to investigate the effect of each parameter in terms of bandwidth, matching level and the transmission zeros. The proposed concept is demonstrated using microstrip technology with operating frequency at 2 GHz. The substrate used in this simulations is Tachonic with characteristics of: εr = 4.5, h = 1.63 mm, tan δ = 0.0035. The filter layout is presented in this paper along with the simulation results to show its feasibility.

Dual-band bandpass ring filter

A topology of a dual-band filter is presented based on a series-combination of two identical ring resonators. The circumference of each ring is equal to one wavelength taken at the center frequency between the two chosen operating frequencies. The control of the filter response in terms of bandwidth and separation between the operating frequencies can be done by varying the impedances of the filter elements which are the ring line impedance and the even- and odd-mode impedances of the coupled lines. The proposed concept is demonstrated through a design of a microstrip dual-band filter operating at 0.9 GHz and 1.8 GHz on epoxy substrate with ɛr = 5.4 and substrate thickness of 1.6-mm. Experimental results show good agreement with the theoretical analysis.

Compact coplanar waveguide pseudo-elliptic filter at microwave frequencies

Microwave filter with pseudo-elliptic response is realized using coplanar waveguide technology. Based on the quarter-wavelength side-coupled ring topology, the filter presents a second order bandpass response with transmission zeros in its out-of-band frequencies. The inter-ground distance of the coplanar waveguide (CPW) lines is set to be 3.4 mm which is about twice the thickness of the substrate while the inter-ground distance for the coupled-sections is equal to 3.71 mm. Both sides of the ground plane of the CPW are short-circuited to eliminate the odd-mode and to allow only the even-mode propagation along the lines. The measured passband response is centered at 2.4 GHz with a relative bandwidth of 12.5% and 3 dB minimum loss. Explanations on the filter design are given in the paper along with its simulation and measurement results.

Miniaturized microstrip ring filter

Miniaturized microstrip ring filter is presented. Four lumped capacitors are added in the initial ring resonator topology to shift the resonant frequency to about 50% of its nominal value, leading to size reduction of the filter. The required value of the capacitors is calculated using tuning synthesis equations of the ring resonator. The passband response of the filter is improved by modifying the line impedance of the ring. The final layout of the miniaturized filter centered at 2.76 GHz is compared to its counterpart showing a size reduction of about 67%.

Measurement, processing and modeling of a tropical foliage clutter using Forward Scatter Radar micro-sensor network with VHF and UHF bands

This paper starts with description of a tropical foliage clutter measurements conducted at Forest Research Institute Malaysia (FRIM) using Forward Scatter Radar (FSR) with very high frequency (VHF) and ultra high frequency (UHF) bands. A clutter model is developed based on the characteristics of the measured clutter signal. This model will be used as a reference clutter signal in order to eliminate the effect of clutter during detection and classification process. Five types of statistical distribution are used to model the clutter signal namely Gamma, Log-Normal, Log-Logistic, Weibull and Nakagami. The models are then being compared and tested using root mean square error (RMSE) method to find the best distribution model that satisfies to represent the clutter signal. Gamma distribution model is found to be the best model for tropical foliage clutter.

Frequency shifting of microstrip ring filter using open stubs

Dual-mode microstrip ring filter whose center frequency is shifted to a lower frequency using four additional open stubs is presented. Nevertheless, the shifted dual-mode ring filter has to face an in-band matching problem in its passband response. A possible solution to the problem is proposed by modifying the line impedance of the ring filter. In this paper, a frequency shifting of about 33.33 % of its 3 GHz initial value is implemented for a microstrip ring filter on FR4 substrate. All the filter layouts are presented along with the comparison between the simulation and measured results.

Miniaturization of microstrip ring filter using lumped capacitors

Microstrip ring filter with reduced size is designed by adding four lumped capacitors to its initial topology. Depending on the value of the capacitors, the center frequency of the initial filter can be shifted to about 50% of its initial value and result in a smaller filter as compared to the one realized directly at the desired frequency. However, the shift in frequency has to face the matching level problem in the filter passband response. As a solution, the impedance of the quarter wavelength transmission line is proposed to be modified. The value of the lumped capacitor and the required line impedance of the ring are calculated using the synthesis of tunable ring filter. Implemented on FR4 substrate, the layout and simulation results of miniaturized ring filter are presented in this paper, showing a size reduction of about 66% with 2.5 GHz center frequency.