Dual band FSS with fractal elements

Abstract

Computer simulation: Fig. 2 shows a turbocoded W-CDMA reverse link transmission model. The single mobile user is assumed to continuously transmit information data at 64kbit/s. The data are divided into a sequence of 5120bit data frames. Frame data are frst 16bit CRC encoded and then turbo encoded with coding rate of 1/3 and generator polynomials of 1, 517, 5/7 in octal notation (the two RSC encoders are the same and have a constraint length of 3 bits (see Fig. la). A multistage interleaver (termed MIL) [4] realises turbo internal interleaving and channel interleaving. At the W-CDMA transmitter, the coded binary data sequence is transformed into a quaternary phase shift keying (QPSK)-modulated symbol sequence after some non-information bearing data have been appended. Four pilot symbols are appended to the resultant 128 ksymboVs QPSK-modulated symbol sequence every 0.625ms (the time interval beginning with four pilot symbols followed by 76 data symbols is called the time slot) and is QPSKspread using a 4.096 Mchip/s complex long pseudo-random spreading sequence (spreading factor 32) to be transmitted over a frequency-selective fading channel [l]. The fading channel is modelled as a frequency selective Rayleigh channel having an ITUspecified vehicular B power delay profile [5]. Two spatially separated antennas and a four-finger (two fmgedantenna) coherent RAKE combiner are assumed at the base station receiver. Channel estimation for coherent RAKE combining is performed by averaging eight received pilot symbols of two consecutive slots. The RAKE combiner output sample sequence is de-interleaved and turbo decoded as described previously. Signal-to-interference plus background noise power ratio (SIR) measurement based fast transmit power control (TPC) described in [6] is assumed; the power up/down step size is 1dB and the power-control rate is 1600Hz.We measured the average bit error rate (BER), average received EJZo per antenna (since the single user is assumed in the simulation, Zo is equal to the background noise spectrum density No), and average number of decoding iterations for various values of target SIR for fast TPC. The measured average BER and the average number of decoding iterations are plotted in Fig. 3 against the average EJNo per antenna for the fading maximum Doppler frequency fD = 5 and 80Hz. The maximum number of decoding iterations is eight (in our simulation, after eight iterations, the improvement in BER performance is saturated). It can be clearly seen from Fig. 3 that the introduction of CRC decoding into the turbo decoding iteration process does not degrade the BER performance at all, while the average number of decoding iterations can be reduced by half at average BER = 1 P and by 75% at average BER = 1W. Similar results were gained under slow fading rates, i.e. fD = 5Hz. Conclusions:A method for reducing the average number of iterations has been addressed in this Letter. To reduce the average number of decoding iterations, the CRC error check is incorporated into the decoding iteration proce...

Fractal FSS: a novel dual-band frequency selective surface

“…10 the response of the FSS computed as indicated in (13) is shown. The results show that for values (14) the transmission loss at 13.27 GHz is less than a fraction of decibels, while the transmission loss at the stop frequency of 14.08 GHz is greater than 25 dB. These values are obtained for an incident angle of less than 17 from broadside.…”

“…This paper will present the numerical and experimental results obtained from an FSS designed and built by arraying a two-iteration Sierpinski dipole. While some preliminary results were discussed by the authors in [14], this paper will provide an in depth insight to the behavior of the fractal FSS, and the possible ways to modify its response to match it to given specifications. In Section II the main properties of the Sierpinski dipole are reviewed and the design of the FSS is presented.…”

The Nature of Electromagnetic Waves in Metamaterials and Metamaterial-inspired Configurations

“…Due to the coupling between the unit cells, the conventional closed element FSSs are often single-band which displays only one dip in the reflection and transmission spectrums. Dual band FSSs, as a breakthrough to the conventional single-band ones, have already realized by fractal elements [34]. And multi-layer structures or complex resonator units are often employed in order to achieve multi-band band-pass or band-stop characteristics of FSS [35,36].…”

Analysis of frequency selective structures with fractal elements

“…The ratio of upper frequency of a rejection to the lower frequency is equal ý = 2,25. It is important to notice, that as against [3], in the given example the dipoles are located in knots of a grid with a rectangular cell. In a paper [3] the case has been considered, when the similar fractal dipoles locate in knots of a grid with a triangular mesh.…”

“…Such antennas can operate at once on several frequencies [2]. In a paper [3] the frequency selective structure, which is composed from the fractal elements, is represented. The elements of this frequency selective structure have the shape of Sierpinski gasket.…”