The design and development of novel ultra-wide band (UWB) antenna and filter units for RF front-end applications

RF Front-end is the term basically used to refer to the parts in an RF receiver that comprise the initial stage before the intermediate frequency or base-band section. It is usually meant to cover the antenna, filter, mixer with local oscillator and amplifier units in a typical superheterodyne receiver. RF Front-end design is a prominent issue within the RF system design as it is closely linked to the system architecture and performance. Since it has a direct impact on the system performance, its design has always been an important task for the industry as well as attractive for the academia to study. Recent scientific studies on the RF Front-end design indicates two mainstream trends; either the design, development and manufacturing of RF Front-end circuitry in the form of "System-on-a-Chip" architectures i.e increased integration or the application of various optimization algorithms on the design of RF Front-end sub-units like antenna and filter as well as the overall system design to obtain a better performance. In this study, we followed the second trend and studied "Ultra Wide Band - UWB" RF Front-end design issues in terms of design, implementation and concatenation of novel UWB antenna and filter units as they are common to all kinds of RF Front-end system architectures. Other parts that are used to complement and test the design are commercially (readily) available equipment with known electrical characteristics and performance. The designed antenna is a compact (miniaturized) version of a "Vivaldi Shaped Partially Dielectric Loaded (VS-PDL) Transverse Electromagnetic (TEM) Horn antenna". It was specifically designed to achieve high gain levels around 10dBi over the UWB band of 1.5-10.6 GHz. Vivaldi antennas as well as the TEM Horn antennas are good candidates for UWB applications as they both have relatively simple geometry and high gain over a wide bandwidth. The idea is to make use of combined respective advantages of Vivaldi and TEM horn antennas to achieve the desired goals by shaping the TEM horn antenna to look like a Vivaldi antenna. The antenna structure is further modified by a partial dielectric load in the center to increase the gain bandwidth. It is placed in a surrounding box made of a Perfect Electric Conductor (PEC) material to reduce the undesired side lobes and to obtain more directive radiation pattern. The results are promising and the Vivaldi Shaped Partially Dielectric Loaded (VS-PDL) TEM horn antenna is proposed as a compact UWB antenna for systems using the newly established UWB (3.1-10.6 GHz) band and also for various applications including the RF Front-End parts of the communication systems using the popular bands like ISM, Wi-Fi and GSM. Regarding the filter, a new methodology using a 3D Electromagnetic (EM) simulator-based Support Vector Regression Machine (SVRM) models of base elements is presented for band-pass filter (BPF) design. SVRM models of elements which are as fast as analytical equations and as accurate as a 3D EM simulator, are employed in a simple and efficient Cuckoo Search Algorithm (CSA) to optimize an ultrawideband (UWB) microstrip BPF. CSA performance is verified by comparing it with other Meta-Heuristics such as Genetic Algorithm (GA) and Particle Swarm Optimization (PSO). As an example of the proposed design methodology, an UWB BPF that operates between the frequencies of 3.1 GHz and 10.6 GHz is designed, fabricated and measured. The simulation and measurement results indicate in conclusion the superior performance of this optimization methodology in terms of improved filter response characteristics like return loss, insertion loss, harmonic suppression and group delay. The concatenation of the antenna and the filter (as if they were part of a complete RF Front-end circuitry) without seeking any certain application is verified by the simulations using the CST STUDIO SUITE Electromagnetic (EM) Simulation software program first and then by the system level measurements within the laboratory environment. It has been observed that there were no significant waveform dispersion on the received pulse shape. This is an important issue in the UWB design and hence the measurement results are concluded as very satisfactory and in agreement with the simulation results indicating a successful UWB performance of the units under test.