IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 52, NO. 7, JULY 2004 1739 Considerations for Source Pulses and Antennas in UWB Radio Systems Zhi Ning Chen, Member, IEEE, Xuan Hui Wu, Student Member, IEEE, Hui Feng Li, Student Member, IEEE, Ning Yang, and Michael Yan Wah Chia, Member, IEEE Abstract—This paper addresses two vital design considerations in ultrawide-band radio systems. One is that radiated power density spectrum shaping must comply with certain emission limit mask for coexistence with other electronic systems. Another is that the design of source pulses and transmitting/receiving antennas should be optimal for the performance of overall systems. The design of source pulses and transmitting/receiving antennas under the two considerations is discussed. First, the characteristics of transmitting/receiving antenna systems are described by a system transfer function. Then, the design of source pulses and transmitting antennas are studied based on the considerations for emission limits. Finally, the design of transmitting and receiving antennas are investigated in terms of pulse fidelity and system transmission efficiency. In the studies, thin wire dipoles with narrow bandwidths and planar dipoles with broad bandwidths are exemplified. Index Terms—Broad-band antennas, pulsed antennas, ultra- wide-band antennas (UWB). I. INTRODUCTION S INCE the 1970s, ultrawide-band (UWB) technology has widely been investigated and developed for wireless com- munication applications [1]–[5]. Recently, much effort has been devoted to commercial short-range UWB systems. Radio systems based on UWB technology offer opportunities for high resolution radar imaging, rejection of multipath cancel- lation effect, transmission of high data rate signals, coding for security and low probability of intercept, especially in multiuser network applications [6]–[9]. In general, UWB radio systems transmit and receive temporally short pulses without carriers or modulated short pulses with carriers. On the one hand, carrier-free UWB radio systems usually em- ploy very short pulses in the order of subnanosecond (ns) or oc- cupy an extremely broad bandwidth typically larger than 20% or 500 MHz. Such systems are capable of providing low system complexity and low costs because of their direct transmission and reception of pulsed signals and the least RF devices in their front-ends as against conventional narrow-band radio systems. On the other hand, the carrier-free or carrier UWB radio sys- tems may possibly interfere with existing electronic systems since short pulses or modulated pulses occupy extremely wide spectra, which cover many bands being used. Due to potential Manuscript received February 6, 2003; revised August 7, 2003. The authors are with the Institute for Infocomm Research , Agency of Science Technology And Research (ASTAR), Singapore 117674, Singapore (chenzn@i2r.a-star.edu.sg). Digital Object Identifier 10.1109/TAP.2004.831405 interference, the Federal Communication Commission (FCC) regulated the emission limits for the allocated 7.5-GHz band- width (3.1–10.6 GHz, termed the UWB band in this paper) for unlicensed use of commercial UWB communication devices (termed UWB systems in this paper). The emission limits will be crucial considerations for the design of source pulses and antennas in UWB systems. The study will show that the radi- ated power density spectrum (PDS) shaping can be controlled by selecting source pulses and tailored by designing transmit- ting antennas. Moreover, the emission limits indicate that UWB systems may operate across a 7.5 GHz or a 110% 10-dB fractional band- width with very low radiated power. Due to the extremely wide operating bandwidth, the transmission and reception of signals in UWB systems are distinct from conventional narrow-band systems. First, the design of source pulses significantly affects the performance of the UWB system. Properly selecting the source pulse can maximize the radiated power within the UWB band and meet the required emission limits without any filters before transmitting antennas. Secondly, the waveforms of the pulses arriving at a receiver usually do not resemble the wave- forms of its source pulses at a transmitter. The transmitting/re- ceiving antennas with frequency-dependant transfer response act as temporal differentiators/integrators or spectral/spatial fil- ters. As a result, the selection of a template for correlation detec- tion at a receiver strongly depends on the characteristics of both source pulses and transmitting/receiving antennas. Thirdly, the antennas should be analyzed and modeled in both time domain (TD) and frequency domain (FD) or a TD [10]–[13]. Fourthly, the assessment and the design of the antennas should be carried out from an overall system point of view not only an individual antenna element [14]–[20]. In this paper, we emphasize two essential and special de- sign considerations in UWB systems. One is that radiated PDS shaping must conform to certain emission limit masks for the reduction of possible interference with other electronic systems. Another is that the design of source pulses and transmitting/re- ceiving antennas should be optimized for the performance of overall systems, such as maximum ratio of signal to noise (S/N) or minimal bit-error-rate (BER). The following discussion is carried out under such considerations for both single-band and multiband schemes. First, a frequency-dependent transmission equation based on the Friis transmission formula is employed to describe transmitting/receiving antenna systems. Then, the design of source pulses and transmitting antennas are studied and 0018-926X/04$20.00 © 2004 IEEE