**3. UWB/SWB antennas, a review**

### **3.1. Planar dipole antennas**

Common and most-used planar dipole antennas are shown in **Figure 1**. They are wellknown for their enormous impedance bandwidth (**Figure 2**), and have been used in many applications. However, their radiated/reception patterns, as shown in **Figure 1**, are not stable/usable in the whole of their claimed bandwidth, so the naming "*UWB/SWB*" may be argued, and the needs for true UWB/SWB antennas which consolidate their name in not only impedance-bandwidth, but also in other criteria as important as radiation patterns, gain, phase, group delay, etc.,. The pattern distortions have been studied and clearly pointed out by many several researchers, excellent research-works on this topic are reported, we cataloged here only some of the most pronounced works, to name a few, Marsey(2007), Biscontini(2006), Hayed(2007), Chavka(2006), Ruengwaree(2007), Garbaruk(2008), Welch (2002). Close inspection the patterns displayed in fig. 1 (and in all referenced work above) we discovered a **remarkable** general property that pattern dispersion became lesser as the antenna's sharp corners becoming more rounded. So our generic radiator


**Figure 1.** Distortion of radiation patterns of common planar UWB/SWB radiators

**Figure 2.** Typical extremely large impedance bandwidth of planar dipole antennas

#### **3.2. Planar monopole antennas**

158 Ultra Wideband – Current Status and Future Trends

SWB antennas/devices.

bandwidth of over 20%, measured at -10 dB points.

The proposed antenna possesses

**3.1. Planar dipole antennas** 

**3. UWB/SWB antennas, a review** 

20GHz). It is clearly that the nominal bandwidth *BW* of the second antenna is 10 times wider than the first one; however, formula (1) indicates that both antennas have the same percent bandwidth. Another weak point is the percent bandwidth of formula (1) is always less than or equal to 200% irrespective of how wide the antenna's nominal bandwidth was. Note also that formula (1) is often mistakenly called as *fractional bandwidth*, indeed the formula (1) consolidates its meaning "fractional bandwidth" only when the factor 100% is removed.

Alternatively, the *ratio bandwidth* (2) can also be used for expressing the bandwidth of UWB and SWB antennas and devices. The defect at zero- frequency point still lurks there but the 200%-limit is lifted. The use of the ratio bandwidth is more adequate to envision the wideband characteristics of devices under investigation. We choose for the second formula

How to choose two formulas, although no official consent however, the first formula is often used for cases that the bandwidths are less than 100%, whilst the second is for UWB and

Traditional communications systems typically used signals having a percent bandwidth of less than 1%, while standard CDMA has an approximately of 2%. Early definition in the radar and communications fields considered signals with percent bandwidth of 25% or greater (measured at the -3 dB points) to be ultra-wideband. The recent FCC regulations (FCC,2004), which will be used as a standard throughout this text, defined UWB devices/signals as having an nominal bandwidth which exceeds 500 MHz or percent

The term SWB has been often used to indicate bandwidth, which is greater than a decade bandwidth. Since the percent bandwidth confused and failed to envision the SWB property adequately as discussed in §2.4, the "ratio bandwidth" is more suitable and often be used for describing bandwidth of 10:1 or larger, we adopt this convention throughout this report.

Common and most-used planar dipole antennas are shown in **Figure 1**. They are wellknown for their enormous impedance bandwidth (**Figure 2**), and have been used in many applications. However, their radiated/reception patterns, as shown in **Figure 1**, are not stable/usable in the whole of their claimed bandwidth, so the naming "*UWB/SWB*" may be argued, and the needs for true UWB/SWB antennas which consolidate their name in not only impedance-bandwidth, but also in other criteria as important as radiation patterns, gain, phase, group delay, etc.,. The pattern distortions have been studied and clearly pointed out by many several researchers, excellent research-works on this topic are reported, we cataloged here only some of the most pronounced works, to name a few, Marsey(2007), Biscontini(2006), Hayed(2007), Chavka(2006), Ruengwaree(2007), Garbaruk(2008), Welch

(2) for describing the bandwidth for the SWB-prototype discussed in this chapter.

There are countless numbers of UWB/SWB monopole antennas have been developed in the last 20 years, the variety in shapes and architectures vary enormous. **Figure 3** represents the most important monopoles which have been already designed, patented and published in both open and close literature.

Architecture and Design Procedure of a Generic SWB Antenna with Superb Performances for Tactical Commands and Ubiquitous Communications 161

**4. Antenna topology, architecture and the FSD methodology** 

signaling such a short pulse.

our IRCTR.

Since the release of the license-free band and the regulation of the emission spectra by the FCC in 2002, a myriad of UWB antennas have been created and invented by both industry and academia, most of them are limited to the FCC-band, this 7.5GHz bandwidth corresponds to a moderate short pulse in order of nanoseconds, these short pulses are good enough for high capacity communication, accurate ranging and imaging but not enough for the more stringent needs of precise localization, high resolution screening, sensitive sensing. To satisfy such stringent requirements, challenges are placed on the design of sensors that support signaling of extreme short pulse in the order of hundreds of picoseconds or less. Sensors in the terahertz region support such short pulse and unarguably provide sharpest images, nonetheless the detection range is too short and the sensors are very costly. Note that in the terahertz region, a radiator with only 5% is capable to support , for example, a Gaussian pulse of 20 ps (assumed unity time bandwidth product), while in the RF-region one must have a SWB radiator of over 11:1 (or 167%, by a lowest frequency of 5GHz) for

There existed broadside and end-fire UWB antennas with different topologies, which comprised of many configurations are available in open literature. The pattern stability of several antenna's topologies and architectures had been thoroughly investigated and reported by (Massey, 2007, p.163-196). It seemed that there was no broadside antenna architecture could exhibit stable patterns within a bandwidth wider than 10 GHz, and most

We propose here an SWB antenna architecture which possessed not only SWB bandwidth lager than 10:1 but also exhibited a much stable patterns in its SWB bandwidth than all those which have been studied and reviewed by (Massey, op. cit.). The SWB prototype 4, and all other prototypes reported in this chapter had been designed, fabricated and evaluated at

of them are UWB-radiators with ratio bandwidth much less than 10:1.

**Figure 4.** Prototypes developed at IRCTR, resulted design dimensions are listed in table 2.

The SWB radiator reports in this chapter, was indeed a revolutionary improved version from IRCTR's previous developed prototypes. All the developed prototypes, shown together in Figure 4, shared the same topology and architecture as depicted in Figure 5a.

**Figure 3.** Monopole planar antennas(Courtesy of Dr. S.W Su, Department of EE, NSYSU)
