J. Marimuthu

PLANAR MICROSTRIP BANDPASS FILTER WITH WIDE DUAL BANDS USING PARALLEL-COUPLED LINES AND STEPPED IMPEDANCE RESONATORS

A dual-band bandpass filter with wide and highly attenuated stopbands is designed using parallel coupled microstrip line (PCML) and stepped-impedance-resonators (SIRs). The proposed filter is composed of a pair of highly coupled PCML-SIR structure and a central resonator using a low impedance rectangular microstrip. Initially, the wide dual-band performance is achieved by creating a transmission zero between those two bands using a tightly coupled PCML-SIR with a suitable impedance ratio. Then, a low impedance resonator is placed between the pair of PCML-SIR to generate multiple resonant frequencies for a broadband performance. The simulated and measured results of those filters agree very well. The bandwidth of the first band in the developed filters extends from 1.75 GHz to 3.75 GHz with less than 0.3 dB insertion loss at the center of the band. The second band has a bandwidth that extends from 6.95 GHz to 8.75 GHz with less than 0.5 dB insertion loss at the center of that band. The stopband separating those two passband has more than 30 dB attenuation with transmission zero at 5.85 GHz.

Software-Defined Radar for Medical Imaging

A low-cost reconfigurable microwave transceiver using software-defined radar is proposed for medical imaging. The device, which uses generic software-defined radio (SDR) technology, paves the way to replace the costly and bulky vector network analyzer currently used in the research of microwave-based medical imaging systems. In this paper, calibration techniques are presented to enable the use of SDR technology in a biomedical imaging system. With the aid of an RF circulator, a virtual 1-GHz-wide pulse is generated by coherently adding multiple frequency spectrums together. To verify the proposed system for medical imaging, experiments are conducted using a circular scanning system and directional antenna. The system successfully detects small targets embedded in a liquid emulating the average properties of different human tissues.

Stepped frequency continuous wave software defined radar for medical imaging

Software defined radar (SDRadar) is investigated as a possible transceiver for microwave-based medical imaging applications. In radar-based microwave imaging, wideband pulses are synthetically created using a stepped frequency continuous wave (SFCW) varying over the entire wideband frequency range. Although the resolution is typically low compared with other tools, such as X-ray, microwave imaging is gaining popularity due to low health risk, and low-cost compared to conventional medical imaging systems. Recent works show the feasibility of this technique by employing commercial vector network analysers (VNA); however, using VNA results in a rigid, bulky and expensive system. To realize a mass screening diagnostic tool, a low-cost portable system based on SDRadar as a transceiver is proposed. The SFCW-SDRadar prototype is implemented using both open source software and hardware. The software part of the radar is realized using GNU Radio, whilst the hardware part is implemented using bladeRF.

Reconfigurable Software Defined Radar for medical imaging

A low-cost, portable and reconfigurable Software Defined Radar (SDRadar) based is proposed for medical imaging. The proposed system can replace the commercial VNA, which is currently used in experimental microwave imaging systems. The proposed SDRadar has the capability to produce synthetic stepped-frequency continuous wave, frequency modulated continuous waveforms (FMCW) and pseudo random noise waveforms that can be used for non-linear and time variant medium. This will lead to a vital opportunity to improve the time, resolutions and accuracy in microwave-based medical imaging. Furthermore, the proposed device with hybrid waveforms can be designed for better imaging of complex human tissues.

Biomedical imaging system using software defined radio

Microwave medical imaging is an attractive complement to current diagnostic tools for medical applications due to its low-cost, portability and non-ionization radiation. In this paper, generic software defined radio (SDR) technology is used to perform biomedical measurements, paving the way for low-cost, compact and reconfigurable imaging systems. SDR technology is capable of wide band instantaneous spectrum capture, in our case 20 MHz at a time in the 0.3 - 3.8 GHz band. To provide the resolution required in medical imaging, it needs to combine multiple frequency spectrums together. Using this as the basis of the system, a cylindrical scanning system and directional antenna are used to measure a biological phantom with multiple targets inside. The system is able to detect the two targets with varying spacing.

Low-cost microwave biomedical imaging

Microwave biomedical imaging has the potential to be a future complementary diagnostic technique for cost-critical situations. The accessibility and portability of diagnostic imaging can mean accurate information is available where it is needed. The feasibility of microwave imaging has been demonstrated by using lab equipment such as vector network analyzers, which, whilst they are accurate, they are also large and expensive. Capturing the required signal responses can instead be performed by using software defined radio (SDR) technology, which due to its high manufacturing volumes can have a cost which is several orders of magnitude lower than a VNA. Although the performance of such a system might be lower than that of a full-sized VNA, the performance is still adequate for biomedical imaging applications. In this paper, an SDR-based systems performance is analyzed and shown to accurately detect an abnormality within a head phantom.

Compact bandpass filter with multiple harmonics suppression using folded parallel-coupled microstrip lines

A compact bandpass filter with wide stopband and multiple transmission zero is presented. The device uses a low impedance feeding network, folded parallel coupled microstrip lines (FPCML) with stepped impedance and two capacitive coupled open stubs. The low impedance feeding network is utilized to enhance the coupling of the PCML structure and to achieve sharp lower and upper cut-off frequencies, while the folded open stub embedded with high/low impedance at end of PCML structure able to extend the upper stopband. Meanwhile, the two capacitive coupled open-ended stubs are able to produce multiple transmission zeros at the stopband to enhance the rejection response and achieve harmonic suppression. The proposed filter with a centre frequency of 2.45 GHz is designed and optimized using ADS Momentum. The filter shows excellent performance with 0.1 dB insertion loss and more than 15 dB attenuation in the wide stopband, with 20% fractional passband.

Broadband bandpass filter with multiple spurious suppression for microwave-based head imaging

Broadband bandpass filter with compact size, wide stopband and sharp upper cut-off band is presented. The filter is designed to cover the band that can be used in microwave-based head imaging for stroke detection. The proposed filter uses a low impedance feeding network, a pair of folded parallel coupled microstrip line, a rectangular microstrip resonator, and cross coupled open-ended stubs. A prototype is designed with bandwidth 1.9 GHz (centered at 2.45 GHz) and more than 15 dB attenuation at the stopband that extends up to 20 GHz. The rate of the upper cutoff frequency is more than 140 dB/GHz.

Wideband bandpass filter with wide stopband for microwave imaging system designed for stroke detection

A broadband bandpass filter with wide stopband for microwave imaging system aimed at stroke detection is proposed. The filter is designed using three different types of quarter wavelength resonators. The three resonators are low impedance feeding network, a coupled line with moderate even and odd-mode impedances and a rectangular middle resonator. The low impedance feeding network enhances the bandwidth and improves the performance at the resonant condition of the moderate mode impedance coupled structure. To suppress the harmonics and obtain wide stopband, a two-stage bandstop resonator and open-ended stubs are embedded within the design. Finally, a prototype bandpass filter of dimensions 28 mm× 28 mm is designed with fractional bandwidth 55% (850 MHz) at 1.5 GHz with more than 20 dB of attenuation across a wide stopband extending up to 4.5 of the frequency at the center of the passband.

Wideband bandpass filter with sharp cutoff and wide stopband for microwave imaging system designed for heart failure detection

A broadband bandpass filter for microwave imaging system aimed at heart failure detection is proposed. The filter is designed using the following three different types of resonators; low impedance feeding network, parallel-coupled microstrip lines and a rectangular middle resonator. To suppress the harmonics, widen and increase the attenuation at the stopband, multiple open-ended stubs are embedded within the resonators arms. ABCD matrices are used to derive the required values of the design parameters for the proposed filter. To meet the frequency requirements of microwave-based heart failure detection system, a filter is designed with fractional bandwidth 67% (500 MHz) centered at 0.75 GHz and more than 20 dB of attenuation at the stopband that extends up to four times the center frequency.