Recent Development of Microwave Devices for Wireless Communications
Hong, Jia-Sheng; Goussetis, George; Record, Paul
Heriot-Watt University

Filter technologies Emerging UWB technology has a great potential for future wireless systems. This has pushed for the development of new UWB microwave devices including filters. To this end, we have developed several novel UWB filters including those using low-cost and low-loss LCP materials, which will be presented at this workshop. Some developed UWB filters can also produce a notch within its passband for suppressing unwanted interference, and an example is shown in Fig. 1(a).

As materials which can produce frequency agility in microwave applications, in addition to semiconductor varactors and PIN diodes, ferroelectrics have been giving a great interest for the development of electrically tuned microwave circuits. We will report our recent R&D results on electronically tunable devices such as tunable dual-mode bandpass filters and DGS band reject filters.

We have also developed high-Q and miniature microwave resonators and filters based on the concept of folded-waveguide. For example, a new miniature triangular folded-waveguide resonator filter has only one-eighth of the footprint of conventional TE101 cavity. Fig. 1(b) depicts a developed miniature triangular folded-waveguide resonator.

The unique ability of high temperature superconducting (HTS) materials to conduct current with negligible resistance at RF/microwave frequencies can be employed to provide components and communication systems with vastly increased efficiency. We have developed novel narrow-band HTS bandpass filters with extremely high performance as illustrated in Fig. 1(c).

Periodic structures An ongoing activity in the area of periodic structures is focusing on the analysis, design and application of 2D periodic metamaterial surfaces. Recent findings include the strong bi-anisotropy (strong electric-to-magnetic field coupling) produced by perturbed 2D periodic metallodielectric planar arrays. This effect has been utilised in the realisation of improved planar absorbers. Currently we are looking to fabricate and test prototypes at IR (~10THz). In another application, metamaterial surfaces have been employed for the linearisation of the propagation in waveguides, which has direct application in reducing the dispersion of pulses with short time-domain profile.

In addition, we have investigated far field manipulation using heterogeneous on dielectri cs for microwave dielectric resonator antennas . We have achieved some good results visualising the field forming ( by Finite difference modelling) which is commensurate with our measurements on physical models. These antennas allow 360 deg. rotation of the radiated field. We are looking at periodic dielectric structures to enhance and dynamically tune the effective dielectric constant within the antenna dielectric.

RF MEMS RF MEMS switches have recently emerged as enabling devices for improving the cost-effect performance of microwave switching networks and systems. We have carried out a preliminary investigation of micromachined RF MEMS switches that are capable of handling high power. This development is based on the concept of power dividing /combining. Fig. 1(d) shows a prototype.