Lakshman Athukorala

Compact Dual-Mode Open Loop Microstrip Resonators and Filters

A novel compact microstrip dual-mode resonator and filter are proposed. The characteristics of the dual mode resonator are investigated. It is found that the filter response exhibits a desirable stopband response where the first spurious passband naturally occurs at 3f0. Finally, methods of miniaturizing such resonators and filters are discussed. The proposed structure was able to achieve 60% size reduction.

Compact Second-Order Highly Linear Varactor-Tuned Dual-Mode Filters With Constant Bandwidth

This paper presents a compact highly linear tunable second-order quasi-elliptic filter with constant 3-dB bandwidth. The proposed filter is thoroughly analyzed to clearly describe the filter equivalent circuit and the tuning mechanism involved. In addition, the tunable resonator configuration employed is shown to improve filter linearity, especially for low bias voltages where distortion is normally stronger. A quasi-elliptic tunable filter was designed, built, and tested for illustration and verification. With a 3-dB bandwidth variation of only 4.6%, the filter had a frequency coverage from 1.45 to 1.96 GHz, an insertion loss better than 2.5 dB, and measured IIP3 >; 43 dBm throughout. The experimental results are in excellent agreement to theory and simulations.

Design of Compact Dual-Mode Microstrip Filters

This paper presents a novel filter design technique for the compact microstrip dual-mode filters. An equivalent circuit for the single dual-mode filter section is derived to show that a single unit behaves as a pair of coupled synchronously tuned single-mode resonators. The equivalent circuit was linked to the inverter-coupled bandpass prototype network to allow higher order filters to be realized. A complete design example (from design to realization) of a fourth-order Chebyshev bandpass filter is presented. It is shown that the dual-mode resonator may be employed to design cross-coupled filters with finite frequency zeros. Two filters are designed using optimized coupling matrix method, fabricated and tested. Experimental and simulation results are presented to validate the argument. Finally, it is shown that more compactness may be achieved with narrowband filters by employing folded resonators.

Compact Filter Configurations Using Concentric Microstrip Open-Loop Resonators

This paper presents two highly compact filter configurations using concentric open-loop resonators. A description of each filter configuration is presented, where a linkage between structural features and coupling coefficients is outlined. A third order trisection and a fourth order source-load coupled filter were designed and fabricated at 1.0 GHz, and each filter was shown to occupy an area of just 18 by 18 mm. The measured insertion loss of the third and fourth order filters was 0.83 and 1.20 dB, respectively. Moreover, these structures may also be cascaded to produce higher order compact filters.

Design of open-loop dual-mode microstrip filters

This paper presents the design of compact second-order bandpass ¯lters based on dual-mode open-loop resonator. A ¯lter design procedure is provided to facilitate the design process. The paper also describes the nature of the inherent transmission zero associated with the structure and presents a method of generating two additional zeros for improving stop-band performance. Finally, a ¯lter design example is presented to validate the argument.

Optically reconfigurable microstrip UWB bandpass filters

This paper presents an optically reconfigurable microstrip ultra-wideband filter. A single optical switch comprised of a silicon wafer is activated using near infra-red light to select between either a bandpass or bandstop response. With the switch in the ON state, the circuit behaves as a bandpass filter while in the OFF state, the circuit behaves as a bandstop filter in the same frequency band. The proposed filter was designed, fabricated and tested. Its performance was evaluated through simulation and measurements.

Tuneable EBG phase shifters for antenna applications

This paper investigates the concept of using optically controlled Electromagnetic Band Gap (EBG) phase shifters for antenna applications at microwave frequencies. Optically activated switches, and EBG based - phase shifters offer the benefits of continuous, quick and low interference characteristics. In addition, the rapidly growing communication market demands for compact and low cost antenna systems operating at micro/mm-wave frequencies and even beyond. Such smart antenna systems have the capability of targeting the following applications due to their unique advantages (size, weight, speed of operation, robustness and EMC issues) over existing/traditional products: (1) military communications (RF equipment, global position infrastructure), (2) networking (matrix switching systems and router technologies), (3) communications (RF devices, such as optically activated switches, antennas and filters), (4) medical imaging (Terahertz imaging technology), and security (screening).

Simulation of reconfigurable WLAN notch for UWB filters

This paper presents a third order ultra-wideband filter (3.1 GHz – 10.6 GHz) with a reconfigurable WLAN notch at 5.8 GHz. Filter reconfiguration in practice may be achieved by a switching element such as RF MEMs, a PIN diode or an optical switch. The switching element was modeled in simulation as a variable conductance line. The filter response shows a sharp rejection of the WLAN band and very low pass-band insertion loss. The quasi-elliptic nature of the bandpass response also contributes towards excellent lower and upper skirt selectivity.

Enhanced WirelessTransmitters using an inter-stage notch filter

This paper proposes a new technique in suppressing nonlinear distortion in nonlinear wireless transmitters. Several interfering signals with high power levels can cause unwanted nonlinear distortion of the poweramplifiers. A simple cascade system of a notch filter and the power amplifier is presented which potentially suppresses the interfering signals and also minimises third order intermodulation products. The proposed method is simulated in Agilent ADS using a commercial nonlinear class-ABbasestationpower amplifier model. A two tone test was carried out at 761 MHz and 763 MHz. The simulated results show an suppression of distortion by about 8 dB. The proposed technique is experimentally verified for a QPSK signal in the presence of a single interfering tone, where distortion suppression of around 10 dB have been measured.

Optically switchable microstrip resonators for RF/Microwave multifunctional systems

This papers presents the optically switchable microstrip ring resonators for RF/microwave multifunctional systems. Tunability is achieved by increasing the power of the laser applied to the highly resistive silicon wafer and changing the properties of silicon under optical illumination. Tunable ring resonators with and without the optical switches have been design and simulated. Simulation results indicate that one may achieve a maximum frequency switching range of 310 MHz.