**1. Introduction**

152 Ultra Wideband – Current Status and Future Trends

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Ultra-wideband radio technology (UWB-RT) inherited a potential of extremely high rate of data communications, Claude Shannon discovered this in 1948 and derived the later-calledas Shannon-Hartley's channel capacity laws. This famous theoretical law however was not able to substantiate in practice until the development of the sampling oscilloscope by Hewlett-Packard in 1962, which, in accordance with the Nyquist-Shannon sampling theorem, was then capable to reconstruct at-that-time rather large UWB signals (Wilson, 2002).

UWB-RT, thus far, has been around for half a centuries but most research confined only in military applications and systems. The release of the 7.5 GHz of unlicensed spectrum by the US Federal Communications Commission (FCC, 2002) for commercial usages and applications in 2002 sparked a renewed interest in R&D of UWB-RT in industries, universities and governments. Today "ultra-wideband" usually refers UWB-RT where the electronic systems should be able to coexist with other electronic users (FCC, 2004).

UWB-RT and systems are becoming important not only to communications due to its high transmission capacity and speeds, but also gained strong foothold in many applications in the areas of industries, health monitoring, law-enforcement, defense and public security, etc.,.

Today, UWB-RT is not limited to carrier-free signaling but modulated in both analogue and digital domains typically in collision avoidance, medical imaging, security imaging

© 2012 Tran et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Tran et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

systems, through-wall, ground penetrating and LPI/LPD tactical command radar systems etc.,.

Architecture and Design Procedure of a Generic SWB Antenna with Superb Performances for Tactical Commands and Ubiquitous Communications 155

Anticipating and combining of all the advantages of its predecessors (prototypes 1, 2, 3), our new SWP-prototype 4 has been designed, fabricated and evaluated. Measurement results revealed that its SWP-performances are superior to other SWP-radiators reported in open-

First, in §2 we discussed briefly the wire-version-antennas that all planar UWB and SWB antennas were derived thereof, the concepts of quasi-electric and quasi-magnetic for planar antennas are typically discussed, also definitions pertaining to qualitatively expressing the SWB antenna's impedance bandwidth were considered. In §3, the SWBA and the FSD are proposed and discussed. In §4, we briefly examine the performance of radiator prototype 1 as a "proof of concept" and provide a methodological procedure for simplifying the multivariate optimization (MVO) process, which were intensively used in the design of other prototypes 2, 3, 4, also parametric investigations and numerical simulations of the proposed SWB radiator are shown in this section. Technical issues related to the practical consideration of the design and fabrication are discussed in §5. Measurements of impedance bandwidth, reception patterns and pulse characteristics in both frequency- and time-domain are reported in §6.

Acknowledgements are expressed in §7, and final conclusions are summarized in §8.

In designing of cm-, mw-, and mm-wave antennas and components, comparing with the traditional wire- and waveguide-technologies, the planar technology offered numerous advantages such as planar, light weight, small volume, low profile, low cost, compatible with integrated- or with active-circuits, easy integrate into passive or active phased arrays

The planar technology facilitates the designers much flexibility in creating a myriad of different UWB and SWB antennas, the architectures of these antennas may different but their topology mainly resembles the traditional wire-version of monopole- or dipoleantennas. The nomenclatural names of planar antennas are confusingly taken over from the wire-version with similar topology. Topological similarities may support such borrowed name, nevertheless it is incorrect—as discussed in the next subsections—regarding to electromagnetic-properties point of view. To avoid such inconsistent idealizations new names and definitions, which support both topological and electromagnetic point of views, will be introduced in this section. We briefly start with recalling the traditional wire-version dipole and monopole antennas in §2.1, then the correct nomenclatures—for the planarversion magnetic and electric antennas—are introduced in §2.2, and end with their

The Dipole antenna is one of the oldest radiators with theoretical expressions for the radiation fields being readily available (Balanis, 1997, p.135). The shapes of their radiation

similarities: quasi-electric and quasi-magnetic antennas in §2.3

**2.1. Dipole and monopole antennas** 

literature.

**2. Fundamentals** 

and communication systems.

This chapter is organized as follow:

The UWB-RT has established indeed as an inevitable technology in the fabric of our everyday life, however, there remains significant number of challenges for the technology to become ubiquitous, especially in the safety and security issues. Enhanced by the decision on choosing mm-wave-based airport security passenger screening sensors by the Transportation Security Administration, new research directives in public security domain are the search for sensors with higher channel capacity, and screening with higher resolution. To compromise both range and Doppler resolution (Thor, 1962), Sensors which support super-wideband (SWB) signaling could be the solution for the problem at hand. Super-wideband radio technology (SWB-RT) could possibly be a potential approach enables high-resolution sensing in free space and in matter including ground-penetrating radar and through-wall sensing. SWB-RT has unique advantages as compared to narrowband technology, and also comprised all UWB-RT's advanced features but with more channel capacity, higher precision and super resolution in communication, ranging and screening, respectively.

The system's performance and characteristics are heavily dependent on the design of the radiating element. The requirements placed on UWB antennas in terms of *impedance bandwidth*, *size*, *phase linearity* and *spectral efficiency* are more demanding than for narrowband antennas (Valderas, 2011).

One of the challenges in the realization of SWB-RT is the development of a suitable antenna that sustains SWB-signaling. To obtain wider bandwidth, several bandwidth enhancement techniques have been studied such as: using log periodic arrays in which the different elements are deduced from an homothetic ratio (Rahim & Gardner, 2004), introducing a capacitive coupling between the radiating element and the ground plane (Rmili & Floc'h, 2008), using microstrip-line feed and notching the ground plane (Tourette et al., 2006), using symmetrical notch in the CPW-feeding (Zhang et al., 2009), asymmetrical feeding by microstrip line together with reduced ground plane and appropriate gap-patch distance (Karoui et al., 2010), adding T-slots for both patch and feeding strip (Rahayu et al., 2008a), using cross-lot in the truncated circular patch with tapered micro-strip feed line (Kshetrimayum et al., 2008). All these techniques are based on the modification of the surface current distribution to broaden the antenna's impedance bandwidth.

We report here a *generic* SWB antenna architecture (SWBA), whose structure is purposely designed to support the functional section block division design approach (FSD, i.e. dividing the antenna structure into functional sections). The FSD in turn was utilized to accelerate the bandwidth optimization process; the SWBA and FSD together have conclusively enabled the designer to obtain antennas with SWB performances by optimization of just a few most-significant-parameters. It is noted here that in our SWB antenna, hereafter-named prototype 4, modifications were made not only at the feed-section but also the transition section and the radiation-section as well.

Anticipating and combining of all the advantages of its predecessors (prototypes 1, 2, 3), our new SWP-prototype 4 has been designed, fabricated and evaluated. Measurement results revealed that its SWP-performances are superior to other SWP-radiators reported in openliterature.

This chapter is organized as follow:

154 Ultra Wideband – Current Status and Future Trends

narrowband antennas (Valderas, 2011).

distribution to broaden the antenna's impedance bandwidth.

but also the transition section and the radiation-section as well.

etc.,.

respectively.

systems, through-wall, ground penetrating and LPI/LPD tactical command radar systems

The UWB-RT has established indeed as an inevitable technology in the fabric of our everyday life, however, there remains significant number of challenges for the technology to become ubiquitous, especially in the safety and security issues. Enhanced by the decision on choosing mm-wave-based airport security passenger screening sensors by the Transportation Security Administration, new research directives in public security domain are the search for sensors with higher channel capacity, and screening with higher resolution. To compromise both range and Doppler resolution (Thor, 1962), Sensors which support super-wideband (SWB) signaling could be the solution for the problem at hand. Super-wideband radio technology (SWB-RT) could possibly be a potential approach enables high-resolution sensing in free space and in matter including ground-penetrating radar and through-wall sensing. SWB-RT has unique advantages as compared to narrowband technology, and also comprised all UWB-RT's advanced features but with more channel capacity, higher precision and super resolution in communication, ranging and screening,

The system's performance and characteristics are heavily dependent on the design of the radiating element. The requirements placed on UWB antennas in terms of *impedance bandwidth*, *size*, *phase linearity* and *spectral efficiency* are more demanding than for

One of the challenges in the realization of SWB-RT is the development of a suitable antenna that sustains SWB-signaling. To obtain wider bandwidth, several bandwidth enhancement techniques have been studied such as: using log periodic arrays in which the different elements are deduced from an homothetic ratio (Rahim & Gardner, 2004), introducing a capacitive coupling between the radiating element and the ground plane (Rmili & Floc'h, 2008), using microstrip-line feed and notching the ground plane (Tourette et al., 2006), using symmetrical notch in the CPW-feeding (Zhang et al., 2009), asymmetrical feeding by microstrip line together with reduced ground plane and appropriate gap-patch distance (Karoui et al., 2010), adding T-slots for both patch and feeding strip (Rahayu et al., 2008a), using cross-lot in the truncated circular patch with tapered micro-strip feed line (Kshetrimayum et al., 2008). All these techniques are based on the modification of the surface current

We report here a *generic* SWB antenna architecture (SWBA), whose structure is purposely designed to support the functional section block division design approach (FSD, i.e. dividing the antenna structure into functional sections). The FSD in turn was utilized to accelerate the bandwidth optimization process; the SWBA and FSD together have conclusively enabled the designer to obtain antennas with SWB performances by optimization of just a few most-significant-parameters. It is noted here that in our SWB antenna, hereafter-named prototype 4, modifications were made not only at the feed-section First, in §2 we discussed briefly the wire-version-antennas that all planar UWB and SWB antennas were derived thereof, the concepts of quasi-electric and quasi-magnetic for planar antennas are typically discussed, also definitions pertaining to qualitatively expressing the SWB antenna's impedance bandwidth were considered. In §3, the SWBA and the FSD are proposed and discussed. In §4, we briefly examine the performance of radiator prototype 1 as a "proof of concept" and provide a methodological procedure for simplifying the multivariate optimization (MVO) process, which were intensively used in the design of other prototypes 2, 3, 4, also parametric investigations and numerical simulations of the proposed SWB radiator are shown in this section. Technical issues related to the practical consideration of the design and fabrication are discussed in §5. Measurements of impedance bandwidth, reception patterns and pulse characteristics in both frequency- and time-domain are reported in §6. Acknowledgements are expressed in §7, and final conclusions are summarized in §8.

### **2. Fundamentals**

In designing of cm-, mw-, and mm-wave antennas and components, comparing with the traditional wire- and waveguide-technologies, the planar technology offered numerous advantages such as planar, light weight, small volume, low profile, low cost, compatible with integrated- or with active-circuits, easy integrate into passive or active phased arrays and communication systems.

The planar technology facilitates the designers much flexibility in creating a myriad of different UWB and SWB antennas, the architectures of these antennas may different but their topology mainly resembles the traditional wire-version of monopole- or dipoleantennas. The nomenclatural names of planar antennas are confusingly taken over from the wire-version with similar topology. Topological similarities may support such borrowed name, nevertheless it is incorrect—as discussed in the next subsections—regarding to electromagnetic-properties point of view. To avoid such inconsistent idealizations new names and definitions, which support both topological and electromagnetic point of views, will be introduced in this section. We briefly start with recalling the traditional wire-version dipole and monopole antennas in §2.1, then the correct nomenclatures—for the planarversion magnetic and electric antennas—are introduced in §2.2, and end with their similarities: quasi-electric and quasi-magnetic antennas in §2.3

#### **2.1. Dipole and monopole antennas**

The Dipole antenna is one of the oldest radiators with theoretical expressions for the radiation fields being readily available (Balanis, 1997, p.135). The shapes of their radiation

patterns are also well-known [ibis., p.154]. The antenna first used by Hertz in his early RF experiments in the late 19th century, as an example, was a half-wave dipole (Krauss, op. cit.) and the shapes of its 3D-radiation pattern had a similar appearance to a full-doughnut or figure-eight (Balanis op. cit. p.163).

Architecture and Design Procedure of a Generic SWB Antenna with Superb Performances for Tactical Commands and Ubiquitous Communications 157

100% / *<sup>p</sup> <sup>c</sup> BW BW f* × (1)

25% 20%

:1 *BW BW f BW RL p* / , when 100% ≥ (4)

*H L BW f f* − (2)

(3)

**2.3. Quasi-electric and quasi-magnetic antennas** 

as quasi-electric or quasi-magnetic antennas, respectively.

**2.4. Bandwidth definitions** 

Where:

(Tran et al., 2010) belongs to the class of quasi-electric antennas.

the ratio bandwidth. They are defined respectively as follows:

*UWB*

*f*H, *f*L are the maximum and minimum frequency at -10 dB, respectively.

*BW*

*BW* is the nominal bandwidth defined by *BW* = *f*H - *f*L *fC* is the central frequency defined by *fC* = (*f*H + *f*L )/2

normalized ratio of *f*H to *f*L defined as R= *f*H/*f*L. ,( *f*<sup>L</sup> *≠ 0*)

*BP* is the percent bandwidth and,

Most of the cases, particularly in planar antenna configuration, the topology of the radiating apertures may prevent the above-indicated conditions from being rigorously satisfied. Even in such cases, either one or the other of the two situations may prevail, thus correctly determine the type of the antenna. For instant, a radiator for which the magnetic field strength H(r) or the electric field strength **E**(**r**) is parallel to **n** over most of the effective aperture will be denoted as *quasi-magnetic* antenna, or *quasi-electric* antenna, respectively.

Obviously, planar antennas fed by microstrip-line or co-planar-waveguide can be classified

As will be demonstrated hereby, our prototypes fall in the class of quasi-magnetic antennas, whilst for all patch antennas fed by micro-strip line, as an example, the RAD-NAV antenna

There are several definitions of bandwidth circulated among our antennas and propagation society; those frequently met are octave-, decade-, ratio-, fractional-, percent-, and ratiobandwidths. The two definitions, that most frequently used, are the percent bandwidth and

> , ,

*UWB DARPA p*

*BW BW*

*BW BW* <sup>≥</sup> <sup>=</sup> <sup>≥</sup>

*BWR:1* is the *Ratio bandwidth*, commonly read as *R-over-1 bandwidth*, in which *R* is the

The *percent bandwidth* (1) has originally been used to describe the narrow-bandwidth of conventional antennas and microwave-devices. Its usage is quite popular and often considered as a standard in many textbooks, nevertheless, it is mathematically not a solid definition because it possesses a defect when *f*L approaching zero. For example, suppose that the nominal bandwidth of antennas #1 is 2GHz (0-2GHz), and antenna #2 is 20GHz (0-

*UWB FCC p*

The Monopole antenna is formed by replacing one half of the dipole antenna with the ground plane, when the ground plane is large enough the monopole behaves like the dipole, except that its radiation pattern is just one half of the dipole, its gain approaches twice, while its length is one half of the dipole.

Magnetic dipole and electric dipole are standardized and well documented in [IEEE STD 145-1983, p.11-16]. The terms magnetic antenna and electric antenna were logically defined but occasionally used in literature, the first term used to describe radiators which possess radiation properties resembling those of thin wire loop (Balanis, op. cit., p.217), while the second is for those resembling of thin wire linear antennas.
