P. Gardner

Band-Notched UWB Antenna Incorporating a Microstrip Open-Loop Resonator

Ultrawideband (UWB) systems require band notch filters in order to prevent sensitive components, within the front-end of the receiver, from being overloaded by strong signals. Recently, it has been shown that these filters can be integrated into the UWB antenna, to great advantage. This communication presents a new method for forming a notch band within the frequency response of a UWB antenna. An open loop notch band resonator is located on the back of the substrate, used to support the UWB monopole. The act of separating the resonator from the antenna means that they can now be designed in isolation, using the standard approach described in the literature, and then combined. A prototype was constructed and good agreement has been obtained between simulation and measurement. The radiation patterns are consistent over the frequency range of interest.

Vivaldi Antenna With Integrated Switchable Band Pass Resonator

A novel reconfigurable wideband to narrowband Vivaldi antenna is presented. A single pair of ring slot resonators is located in the Vivaldi to realize frequency reconfiguration, maintaining the original size unchanged. The proposed antenna is capable of switching six different narrow pass bands within a wide operating band of 1-3 GHz, offering added prefiltering functionality. A fully functional prototype has been developed. PIN diode switches were employed at specific locations in the resonator to change its effective electrical length, hence forming different filter configurations. Antenna performance obtained from simulation and measurement results shows good agreement, which verifies the proposed design concepts. The antenna is potentially suitable for applications requiring dynamic band switching such as cognitive radio.

Antenna Requirements for Software Defined and Cognitive Radios

Antenna requirements for software defined radio (SDR) and cognitive radio (CR) systems are reviewed and the resulting challenges are discussed. Both concepts imply capabilities for operation over very wide bandwidths, of the order of one decade in some cases. This then becomes the main challenge for antenna designers. However, as the concepts evolve, some systems will work over limited bandwidths and existing or extended bandwidth antennas will be used. In the Paper the concepts are explained. As bandwidth is a major concern, the fundamental limits of performance are restated. For handheld radio antenna bandwidth and efficiency at low frequencies is the main problem. Both in the terrestrial fixed infrastructure and in space communication the difficulty of designing very wideband arrays to give the pattern control necessary for interference minimization is significant. In defence applications external handset antennas are seen to be necessary and extension to very wide bandwidths is also seen to be challenging. It is concluded that there is steady progress towards the realization of both SDR and CR, and this is throwing up very significant antenna challenges.

Small H-shaped antennas for MMIC applications

A small short-circuited H-shaped GaAs monolithic microwave integrated circuits (MMICs) patch antenna is presented. Resonant at 5.98 GHz, it is the lowest frequency MMIC patch antenna reported that we are aware of and is intended for short-range communications (e.g., vehicular). Initial experimental and theoretical characterization of the proposed structure has been carried out on soft microstrip substrates. It has been shown that the size of an H-shaped patch antenna can be reduced to as low as one tenth of that of a half wavelength patch antenna resonant at the same frequency, saving valuable substrate space. The resonance frequency, radiation patterns and gain have been investigated. Ground plane truncation effects, which are important for MMIC applications, have been examined using the finite-difference time-domain (FDTD) method.

Active Integrated Antenna Design Using a Contact-Less, Proximity Coupled, Differentially Fed Technique

A novel contact-less, differential feeding technique suitable for integrated active antenna design is demonstrated. This technique utilizes an odd mode signal to generate fringing fields on either side of a microstrip gap under the antenna. This allows electromagnetic energy to be efficiently coupled from the transmission lines to the radiating antenna. In a balanced integrated antenna amplifier configuration, the proposed non-contact feeding method removes the need for any balun or power combining network. Hence in theory, a compact RF front-end design with lower losses can be realized. This feeding method has been successfully applied to the design of simple passive microstrip patch antennas and active integrated antennas (AIA). Simulated and measured results are also included to validate the proposed feeding concept and antenna designs. The performance of the proposed differential feeding technique on a simple microstrip patch antenna has been systematically studied. The study suggests that the proposed proximity method is broadband in nature, allowing antennas operating at different resonant frequencies to be swapped without the need to change the feed dimensions and without degrading the matching performance

Adaptive neuro-fuzzy inference system (ANFIS) digital predistorter for RF power amplifier linearization

This paper describes an adaptive digital predistorter (ADP) for RF power amplifier (PA) linearization using an adaptive neuro-fuzzy inference system (ANFIS). The ANFIS predistorter (PD) employs the advantage of real-time modeling of the PAs responses in determining the PDs functions. The amplitude and phase corrections for the PD are represented in an easy-to-understand fuzzy if-then rule, while the parameters involved in the fuzzy representation are trained using neural networks algorithms, namely gradient-descent and least squares estimate (LSE). Experimental results show that a 26.3-dB improvement in linearity for a two-tone signal is obtained, while a distorted WCDMA signal is suppressed by at least 12 dB. The adaptability of the ANFIS PD to instantaneous variation in PA responses through time is also demonstrated, and results show that the ANFIS PD is capable of adapting to simulated environmental changes, which is a topic often omitted by researchers in this area. Further testing demonstrated that the tuning parameters involved in the training could be reduced by more than half for a fairly nonlinear PA without significantly degrading the suppression capability.

Multi-band antennas

Two different types of novel dual band antennas suitable for a data communicator device are reported. The first antenna is a dual frequency, dual polarization microstrip patch antenna, capable of generating two distinct frequencies with different polarization characteristics and radiation patterns. This antenna has been intended for coverage of the GSM/Iridiums satellite frequencies. The second antenna modified bent folded monopole antenna having two resonant frequencies, with a frequency separation of 1.9. This antenna could be used in the GSM/DCS1800 frequencies. The limitations of both antennas are also briefly mentioned.

The design of nine element quasi microstrip log periodic antenna

This paper described the design, simulation and fabrication of the inset feed log periodic antenna with nine elements. The antennas have been modeled using microstrip lines and S parameter data from an individual single element. The data is extracted from the simulation and combined with the microstrip transmission line. The properties of antennas such as bandwidth, gain, cross-polar isolation and half power beamwidth have been investigated and compared between simulation and measurements. A bandwidth up to 51% is achieved by using nine-element arrays. The cross-polar isolation of the log periodic antenna is in the range of 10 to 30 dB. The typical half power beamwidth (HPBW) of the log periodic antenna is 40/spl deg/ for E plane and 60/spl deg/ for H plane. The gain of the antenna relative to the dipole antenna ranges from -3 dB to 5 dB.

Integrated antenna/power combiner for LINC radio transmitters

This paper presents integrated antennas, which can fulfill both the functions of an antenna and a power combiner, thus reducing the circuit loss. This will be useful for linear amplification using nonlinear components systems, where the circuit-level power-combiner losses degrade overall efficiency. Two antennas, which use a single-layer structure and a multilayer structure, respectively, are designed. Both antennas achieve good impedance-matching characteristics under both even- and odd-mode excitations. The single-layer antenna has a narrow bandwidth, and the even-mode radiated power at boresight is 33 and 26 dB lower than that of the odd-mode radiated power at the E- and H-plane, respectively, thus demonstrating the effective suppression of even-mode radiation. The other antenna using multilayer structure achieves a broad-band bandwidth (S/sub 11/<-10 dB) of 15.5% and 8% under the odd- and even-mode excitation, respectively. Across the bandwidth, broadside radiation patterns with low cross-polar levels (<-21 dB) are achieved under the odd-mode excitation, while the even-mode radiation is also suppressed.

A novel digital predistorter technique using an adaptive neuro-fuzzy inference system

This letter presents a novel digital predistorter technique using an adaptive neuro-fuzzy inference system (ANFIS). The proposed approach employs real-time input and output signals of a nonlinear power amplifier as inputs to the ANFIS, so as to approximate the inverse functions of the power amplifier. The antecedent and consequent parameters of the FIS constructed by the ANFIS are tuned using backpropagation and least squares algorithms. Simulation shows that this novel technique has improved the linearity of a WCDMA signal by a further 4 dBc compared to a conventional look-up table (secant) approach. Moreover, this proposed technique is capable of adapting to instantaneous variation in the power amplifier response through time, which is a topic often omitted by researchers in this area.