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

160 Ultra Wideband – Current Status and Future Trends

both open and close literature.

**3.3. Antenna miniaturization** 

most important monopoles which have been already designed, patented and published in

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

techniques, the readers please consult the references in the listed table.

**Table 1.** Most pronounced UWB/SWB monopole antennas

**Antenna Feeding Dimension~ Bandwidth Created by** Slot Coax-CPW 130x130 mm2 0.5-7 GHz Yeo, et al., 2004 Monopole CPW 70x70 mm2 1.5-3 GHz Chiou et,al, 2003

Elliptical slot Coax-CPW 55x50 mm2 3-12 GHz Ying et al., 2004 Square monopole Microstrip 50 x50 mm2 3-11 GHz Battler, M. et all,2006 Monopole Microstrip 30x40 mm2 2-12 GHz Xiao et.al., 2009 Monopole CPW 30x40 mm2 3-12 GHz Shastry et al., 2009 Elliptical slot differential 27x46 mm2 3-12 GHz Power et al., 2004 Vivaldi Microstrip 35x35 mm2 1-12 GHz Abbosh et al., 2007 Monopole Microstrip 30x35 mm2 3-12 GHz Choi et.al., 2004 Monopole Microstrip 30x33mm2 3-11 GHz Kimouche et al., 2009 Monopole Microstrip 30x32 mm2 2.9-13.2 GHz Choi et.al., 2009 Monopole Microstrip 30x30 mm2 3-11 GHz Rahayu et al., 2008b Monopole Microstrip 25x25 mm2 3.2-12 GHz Cho et al. 2006 Generic CPW 15x15 mm2 5-150 GHz This work

The bandwidth and geometrical dimensions have been remarkably reduced, best achievements are timely listed in Table 1, for the used miniaturized concepts and

Pulson 200 Microstrip 40x80 mm2 2.5-6 GHz Schantz, Time Domain. 2003

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 signaling such a short pulse.

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

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 our IRCTR.

**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.

The kernel of this topology is its simplicity, and the essence of the antenna's architecture is the logicalness of dividing the antenna into functional section blocks that enables simplifying the MVO process into a sequence of single-variable optimization (SVO) one.

Architecture and Design Procedure of a Generic SWB Antenna with Superb Performances for Tactical Commands and Ubiquitous Communications 163

antenna's topology, architecture and the FSD approach, as will be discussed in subsequence

• Choosing an antenna topology whose shape is kept simple regarding ease of fabrication, prevent diffractions, easy to scale up/down to meet designer's requirements

• Creating an architecture that providing a basis platform for implementing the "FSD approach", and deploying the conceptual "thumb-rules" for effective simplifying the

The starting point in the design of the SWB antenna reports in this section is mainly credited to the original radiator (Tran et al., op. cit.), whose topology is planar, as sketched in Fig.5a,

• An antenna patch is directly connected to the CPW-feeding, so that they together

The CPW feeding structure has been chosen because of it well-behaved properties: such as negligible radiation, low loss, the effective dielectric is constant over a sustained wide frequency range, where the later property is more suitable for super-wide-band feeding a

In antenna design if dimensions are unconstrained and by a proper design, antenna will behave as a high pass filter, and if its dimensions are physically large enough then all frequencies will pass through. Research of published papers over UWB and SWB antennas reveals that most of the UWB and SWB antennas had a considerable larger size, mostly lager than λL/2 of the lowest frequency fL, and on broadening the bandwidth, a first option, was to resort to stochastic optimization methods, nevertheless, these methods are known for

A more feasible alternative approach was provided by the critical analysis of the relationship between the geometrical parameters and the physics of the problem at hand.

The FSD approach was intentionally created in such a way that the overall dimensions are

The logical architecture together with its parameters and FSD are sketched in Figure 5a&b.

• Starting from the *feed section*—its CPW feed supports the required impedance

constrained, kept small and the process of optimization can also be simplified.

sections, were objectively aimed at two main goals:

MVO process in to SVO, a much simpler one (§4.2).

with structural topology comprised of following stack-ups:

formed a single planar pattern run on top of the structure.

• Single dielectric layer to provide structural rigidity. • CPW feeding structure on top of the structure.

SWB-radiator than the micro-strip line (Simons, 2001).

**4.2. Antenna architecture and the FSD approach** 

The FSD approach follows the bottom-up strategy, i.e.:

carrying extremely high computational load.

bandwidth for SWB signaling.

in size and performance (§4.1).

**4.1. Antenna topology** 

**Simplicity**: the topology of the proposed antenna is simple in design with just a copper pattern on top of dielectric layer, the employment of dielectric layer is just for the purpose of structural rigidity of the prototype. In fact, without the dielectric layer, the propose antenna performs much better in terms of matching, and having more perfect symmetric and stable patterns and lower cross-polarization.

**Compactness**: Thank to the functional section block design (FSD, to be discussed in next section), we are able to miniaturize the generic antenna in an area as small as 15x15mm2, Table 2 shows comparative indication of miniaturization effectiveness of different proposed architectures.

The merits of the topology, architecture and logical functional blocks, and optimization process will be discussed in §4.1, 4.2 and 4.3, respectively.

The original antenna topology and architecture of prototype 1 leaved many flexible possibilities for adjusting parameters or scaling dimensions to meet new requirements or applications without much entangled in complicated MVO process. These possibilities have been exploited to double the antenna's bandwidth of prototype 1 (Tran et al, 2007) from 2:1 to 4:1 by (Tanyer et al., 2009a), and further broaden to 9:1 (Tanyer et al., 2009b), and scaled down to the FCC-band for IR-applications (Tanyer et al., 2010).

**Figure 5.** Proposed configuration: a) Architecture and parameters, b) logical functional sections.

The prototype 4 is a proof of concept in proving viability of the design of radiators, which are capable of supporting such extreme short-pulse in RF/mmw-region. The proposed antenna's topology, architecture and the FSD approach, as will be discussed in subsequence sections, were objectively aimed at two main goals:


#### **4.1. Antenna topology**

162 Ultra Wideband – Current Status and Future Trends

patterns and lower cross-polarization.

process will be discussed in §4.1, 4.2 and 4.3, respectively.

down to the FCC-band for IR-applications (Tanyer et al., 2010).

architectures.

The kernel of this topology is its simplicity, and the essence of the antenna's architecture is the logicalness of dividing the antenna into functional section blocks that enables simplifying the MVO process into a sequence of single-variable optimization (SVO) one.

**Simplicity**: the topology of the proposed antenna is simple in design with just a copper pattern on top of dielectric layer, the employment of dielectric layer is just for the purpose of structural rigidity of the prototype. In fact, without the dielectric layer, the propose antenna performs much better in terms of matching, and having more perfect symmetric and stable

**Compactness**: Thank to the functional section block design (FSD, to be discussed in next section), we are able to miniaturize the generic antenna in an area as small as 15x15mm2, Table 2 shows comparative indication of miniaturization effectiveness of different proposed

The merits of the topology, architecture and logical functional blocks, and optimization

The original antenna topology and architecture of prototype 1 leaved many flexible possibilities for adjusting parameters or scaling dimensions to meet new requirements or applications without much entangled in complicated MVO process. These possibilities have been exploited to double the antenna's bandwidth of prototype 1 (Tran et al, 2007) from 2:1 to 4:1 by (Tanyer et al., 2009a), and further broaden to 9:1 (Tanyer et al., 2009b), and scaled

**Figure 5.** Proposed configuration: a) Architecture and parameters, b) logical functional sections.

The prototype 4 is a proof of concept in proving viability of the design of radiators, which are capable of supporting such extreme short-pulse in RF/mmw-region. The proposed

(a) (b)

The starting point in the design of the SWB antenna reports in this section is mainly credited to the original radiator (Tran et al., op. cit.), whose topology is planar, as sketched in Fig.5a, with structural topology comprised of following stack-ups:


The CPW feeding structure has been chosen because of it well-behaved properties: such as negligible radiation, low loss, the effective dielectric is constant over a sustained wide frequency range, where the later property is more suitable for super-wide-band feeding a SWB-radiator than the micro-strip line (Simons, 2001).

## **4.2. Antenna architecture and the FSD approach**

In antenna design if dimensions are unconstrained and by a proper design, antenna will behave as a high pass filter, and if its dimensions are physically large enough then all frequencies will pass through. Research of published papers over UWB and SWB antennas reveals that most of the UWB and SWB antennas had a considerable larger size, mostly lager than λL/2 of the lowest frequency fL, and on broadening the bandwidth, a first option, was to resort to stochastic optimization methods, nevertheless, these methods are known for carrying extremely high computational load.

A more feasible alternative approach was provided by the critical analysis of the relationship between the geometrical parameters and the physics of the problem at hand.

The FSD approach was intentionally created in such a way that the overall dimensions are constrained, kept small and the process of optimization can also be simplified.

The logical architecture together with its parameters and FSD are sketched in Figure 5a&b.

The FSD approach follows the bottom-up strategy, i.e.:

• Starting from the *feed section*—its CPW feed supports the required impedance bandwidth for SWB signaling.

• Then to the *internal transition section*—this section is intentionally inserted between the feed and the patch for the purpose of impedance matching, its shape was logically chosen so that it able to serve the design-properties: resonance shifting, impedance matching, and also enable parameter to serve as independent optimized parameter.

Architecture and Design Procedure of a Generic SWB Antenna with Superb Performances for Tactical Commands and Ubiquitous Communications 165

Our generic architecture generalized, showed the connections between them, and proved

**Figure 6.** Proposed configuration: a) Architecture and parameters, b) logical functional sections.

**Prototype 1**: elaborated by (Tran et al. op. cit.), formed a basis for the designs of the later prototypes. Its 10GHz impedance bandwidth and designed parameters are plotted in fig.9 and listed in table 2, respectively. For the detailed works and the measurement results, the reader should refer to (Tran et al., op. cit). The other prototypes all took the designed parameters of prototype 1 as start-values, and used the FSD to identify the significant

**Prototype 2**: is obtained by taking the start values of the prototype 1, and using FSD to identify the LT as its significant parameter for SVO process. The resulting designed parameters and the impedance bandwidth are listed in 2nd column of table 2, and Fig.9, respectively. The SVO demonstrated the solidity of the FSD approach that the bandwidth can be doubled (from 10GH to 20 GHz) by optimization of just a single parameter LT. For

**Prototype 3**: by keeping LT fixed, the prototype 3 is obtained by optimizing the lower part of the radiation section which comprised of two parameters LR2 and WT, the first make the total length of the radiator shorter ( thus affects the higher frequency), whist the second parameter provide an better match (i.e., lower reflection coefficient). By doing two SVO sequentially (first with parameters LR2, then WT) we again doubled the nominal BW (form 20GHz to 45GHz), in term of ratio bandwidth it is of BR = 9:1 as shown in Fig. 10. The resulting parameters are listed in column 3rd table 2. Further details of measurements and

that they are just particular cases of the introduced architecture.

**4.4. Parameter identification and optimizations** 

parameter for its SVO process of bandwidth broadening.

details of the elaborated work, please refer to (Tanyer et al., 2009a, op cit.)

other properties of this prototype 3, are detailed in (Tanyer et al., 2009b, op. cit).

• In addition to the *radiating section*, we divided it in to two sub-sections, which are the *patch section* and the *external transition*. The patch section creates an extra degree of freedom to ease the optimization process, and the radiating section provides parameter for shaping radiation patterns. Two round areas had been added to the top corners of the patch for the purpose of 1) diminishing of diffraction at the antenna's top vertices (deformation of sharp corner in to circular edge) and, 2) controlling and retaining the shaped of the radiation patterns at high frequency band of the spectrum, and, 3) subduing the number of parameters to accelerate the optimization process. These four sections are orderly numerated as I, II, IIIA, and IIIB in Figure 5b.

In summary, the FSD approach assumed the following steps:


Based on the FSD approach the prototype 1 was first designed and evaluated (Tran et al. 2007). Its designed parameters are used as *start values* for the optimization process of all the later prototypes. Four prototypes (1, 2, 3, 4 shown in fig.4) were successful designed and evaluated, the prototype 4 proved to be a radiator which is superior to the others in that both of its impedance bandwidth and radiation pattern are SWB-sustainable.
