Miniaturised and reconfigurable planar filters for ultra-wideband applications

An increasing demand for electromagnetic spectrum has resulted from the emergence of feature-rich and faster throughputs wireless applications. This necessitates the developments of dynamic reconfigurable or multifunctional systems to better exploit the existing spectrum. Future wireless devices will be expected to communicate over several bands with various other devices in order to fine tune the services they provide to the user. Each band may require a separate RF transceiver and such modern wireless multi-band multi-mode communication systems call for high performance, highly integrated compact modules. Since the Federal Communications Commission (FCC) released the unlicensed frequency band 3.1-10.6 GHz for ultra-wideband (UWB) commercial communications, the development race for commercialising UWB technology has seen a dramatic increase around the world. The aim of this research is to develop reconfigurable planar microwave filters for ultrawideband applications. The project investigates some key design issues of reconfigurable filters, which are being observed constantly in the latest development and realisation of microwave filters. Both analytical and numerical methods are performed to construct a realistic and functional design. Two different types of frequency reconfigurability are investigated in this thesis: discrete (e.g. PIN diode, Optical switch) and continuous (e.g. varactor diode). Using the equivalent circuits and considering the direct coupled filter structure in most cases, several topologies with attractive features are developed for future communication systems. The proposed works may be broadly categorised into three sections as follows. The first section explores a square ring shape close loop resonator along with an opencircuited stub in the symmetry plane. To realise a reconfigurable frequency states within the same spectrum, an innovative approach is developed for this case. An optical or photoconductive switch, comprised of a silicon die activated using near infrared light is investigated as a substitute of PIN diode and performances are evaluated to compare the feasibilities. In addition, a in-band interference rejection technique via externally coupled Tshape resonator is shown. However, it is observed that both structures achieve significant size reductions by utilising the inner part of the resonators. To improve the filter selectivity, a convenient design approach generating a pair of transmission zeros between both passband edges and a single zero in the stop band for harmonic suppression is discussed in the second section. Moreover, the development of notched rejection bands are studied and several novel methods to create a single and multiple notched bands employing the square ring shape structure are proposed. On inspection, it is found that the notch structure can be implemented without deteriorating the filter performances. The discussions are supplemented with detailed design examples which are accompanied by theoretical, simulated and experimental results in order to illustrate the filter development process and showcase practical filter performance. The third section reveals a novel highly compact planar dual-mode resonator with sharp rejections characteristics for UWB applications. A bandwidth reconfiguring technique is demonstrated by splitting its even-mode resonance. Filter structure with the dual-mode resonator is shown to have a relatively wide tuning range, significantly low insertion loss and a constant selectivity along with frequency variations in comparison to similar published works. Finally, the earlier dual-mode structure are modified to realise a dual wideband behaviour. A detail analysis with comprehensive design procedures is outlined and a solution for controlling the frequency bandwidths independently according to the application interest is provided. In line with the previous section, experimental verification is presented to support and supplement the discussions

Miniaturised sharp rejection bandpass filter with reconfigurable bandwidth for UWB applications

A novel, compact and highly selective microstrip bandpass filter with bandwidth reconfigurability for ultra-wideband (UWB) applications is presented. The proposed design uses stepped impedance resonator (SIR) for realization of bandpass filter (BPF) and employs a single varactor diode (BB135-NXP) for the purpose of reconfiguring bandwidth. Additionally, to improve the selectivity between passband edges, a cross-coupling between I/O feed lines is introduced which generated pairs of attenuation poles at each side of the passband. Measurements on a fabricated reconfigurable filter confirm the accuracy of the design procedure. Measured responses show good agreement with simulation. The proposed filter is able to achieve significant size reduction (8.5 mm × 7.1 mm excluding the feeding ports) as compared to the conventional bandpass filters with reconfigurable bandwidth

Highly selective reconfigurable filter for UWB systems

A novel highly selective compact reconfigurable filter with a switchable notched band for ultrawideband (UWB) systems is presented. The proposed filter exhibits two distinct features by altering switching device such as PIN diode (BAP65-02) in this case. First, a switchable notched band is generated which facilitates a rejection at 3.5 GHz to avoid interferences from the WiMAX systems. Later, a reconfigurable filter is developed which changes from bandpass to bandstop at the same UWB (3.1-5.2 GHz) spectrum. The filter shows very low pass-band insertion loss and five transmission zeros are created between passband edges to enhance the signal selectivity and broad rejection at the stopband. A filter sample is fabricated to provide an experimental verification on the proposed filter. The proposed filter is able to achieve significant size reduction as compared to an conventional reconfigurable filters and bandpass filters with notched band

Miniaturized dual-mode microstrip bandpass filters with a reconfigurable notched band for UWB applications

A novel, compact, and highly selective dual-mode microstrip bandpass filter with a switchable notched band is presented. A notched band is developed by employing an open-circuited stub which can be switched by a pin diode to avoid WLAN interferences (5.8 GHz) within the spectrum. The proposed filter achieves a significant size reduction (8.5 mm × 7.1 mm) as compared to conventional dual-mode filters with notched band. Simulated and experimental results of the designed filter were presented

Optically reconfigurable CPW filters for UWB applications

A miniature optically reconfigurable ultra-wideband CPW bandpass filter is proposed. With the optical switch in the ON state (200W), the circuit behaves as a bandpass filter while in the OFF state (0W), the circuit behaves as a bandstop filter within the same frequency band. The simulation results of the proposed bandpass/bandstop filter are presented

High linearity microstrip bandpass filter with electronically tunable notch

A high linearity reconfigurable bandpass filter embedded with a tunable notch structure has been presented for future wideband wireless communication applications. A single varactor diode (BB135-NXP) is used for the purpose of tuning the notch. The linearity of the varactor-tuned bandpass filter is also evaluated. The proposed filter is able to achieve a good linearity with IIP3 of 37, 46, and 45 dB at 2.3, 2.4, and 2.5 GHz, respectively, and with no significant loss. Simulations have been verified by the measurements of a fabricated prototype. A good agreement has been achieved simulated and measured results

Highly linear microstrip wideband bandpass filter with switchable notched band for wireless applications

This article presents a highly linear reconfigurable bandpass filter embedded with a switchable notch structure to get a band-notched characteristic at a specified frequency.A single PIN diode (BAP65-02) is used for the purpose of switching the notch. An optical switch, comprised of a silicon dice activated using near infrared light is also investigated as an alternative to the PIN diode. While the PIN diode or the optical switch is in the ON state this reconfigurable filter behaves as a bandpass filter with a notch at 2.4 GHz in order to reject WLAN interference while a full band response is obtained in the OFF state. The proposed filter is able to achieve good linearity using PIN diode with IIP3 of 47 dBm and there is no significant loss. A prototype is fabricated, and measured results are compared to simulations. A good agreement has been achieved between simulated and measured results

Compact UWB bandpass filter with reconfigurable notched band

A compact bandpass filter is presented for ultra-wideband (UWB) applications with a reconfigurable notched band to reject unwanted signals from the WiMAX systems. A single pin diode is used for the purpose of switching the notch. An optical switch, comprised of a silicon dice activated using near infrared light is also investigated as an alternative to the pin diode. While the switch is in the ON state this reconfigurable filter behaves as a bandpass filter with a notch at 3.5 GHz and a full band response is obtained in the OFF state. The filter offers excellent performance for the lower-band frequency of a UWB system, ranging from 3.1 to 5.0 GHz and exhibits very low passband insertion loss. Also, transmission zeros are generated at the passband edges to enhance the signal selectivity. A filter sample has been designed and fabricated to provide experimental verification on the proposed filter. A good agreement has been achieved between simulated and measured results with both the pin diode as well as the optical switch. The proposed reconfigurable filter with notched band was able to achieve 40% size reduction as compared to an embedded open-circuited stub