**5. Design and fabrication**

#### **5.1. Design**

172 Ultra Wideband – Current Status and Future Trends

patterns were in fig.8.

**4.10. Comparison of the prototypes** 

coefficient [dB]; Abscissa: frequency [GHz].

in fig.9 and fig.7

LT = 1.64mm, then two SVOs were carried out first for WT and then WC. The reason that WT was chosen first is twofold, 1) WT is more sensitive on matching because the current distribution is denser at the lower part, 2) WC is the share parameter that mainly located in section IIIA where the matching effect is week, and it is purposely inserted to control the radiation patterns instead of wideband matching the radiator. The optimized parameters of prototype 4 are listed in table.2. The impedance bandwidth of the prototype 4 is plotted in fig.9, and fig.7; also, its SWB radiation

Prototypes 1, 2, 3, 4 have been design, fabricated, measured and evaluated, photographs of them are shown in fig 4. At first sign, they seemingly looked different, however they all shared the same topology and architecture as depicted in fig.5a, only one or two parameters is slightly changed to obtained difference desired performances. For comparison, their correspond impedance bandwidths are plotted together in fig.9. The impedance bandwidth enhancement is improved from 10 GHz, to 20 GHz, 40 GHz and beyond 150 GHz as shown

The design parameters of prototype 4 and all other prototypes are listed in table.2, so that,

These are results of the FSD methodology and SVO steps described in previous sub-section (§4.9). Note that the SVO should be carried out orderly by A, B and C. ( bold and capitalized in table.2), A is dedicated as the first to be optimized, keep that optimized parameter fixed, and goes on with B, then continue with C. For example, the prototype 4, (A) first fixing the taper's height LR2 to 4.335mm, then (B) optimizing the taper width WT, and then (C) adjust the WC for the radiation-characteristics. The optimized results showed an SWB impedance bandwidth of at least over 150GHz. In fact the result of prototype 4 (with parameters listed in column 4 of Table.2) shown the downtrend of reflection coefficient for increasing frequency (Fig.7), we expect that prototype 4 will well-behave beyond 150GHz as well.

**Figure 9.** Impedance bandwidth of the developed prototypes. Ordinate: magnitude of the reflection

the reader, could independently recheck, or reproduce them without much difficulty.

All prototypes depicted in Fig.4, with their design dimensions listed in table.2, have been fabricated on Duroid RT 5880 high frequency laminate with substrate height h=0.787mm, copper cladding thickness t=17μm, relative dielectric constant εr=2.2, electric and magnetic loss tangents are given by tan δE=0.0027 and tan δH=0, respectively. The foremost reason of choosing this material is that it could relatively afford SWB frequency range up to 77 GHz (Huang et al., 2008, p.64). Other reasons are assessments related to temperature, moisture, corrosion and stability, which were investigated in details by (Brown et al., 1980).

### **5.2. Feed elongation**

Since the dimension of the SMA connector's flange is considerably large in comparison with the antenna dimension (see Fig.10a), this comparable size exerts a huge impact on the antenna's electromagnetic-properties in particularly to the transmission, scattering and

radiation mechanism. In order to reduce this obstruction and to measure the antenna's scattering parameters and radiation patterns adequately, it is necessary to elongate the antenna as show in Fig. 10b. To back up the advocating of this elongation, we exploited the facts that the co planar waveguide has negligible radiation, low-loss and constant effective dielectric constant in rather wide range of application from DC to above 50GHz. we decided to elongate the CPW feed *L*F to 40mm, and carried out numerical simulations of the same SWB radiators with short and long feed. The magnitudes of the reflection coefficient are compared and plotted in Fig.10c. As expected, the numerical results exposed a negligible differences as theoretically has predicted (Simons, 2001, p.240). Note that these theoretical properties (negligible radiation and low-loss) were also experimentally consolidated by (Tanyer et al, op cit.).

Architecture and Design Procedure of a Generic SWB Antenna with Superb Performances for Tactical Commands and Ubiquitous Communications 175

GHz, this defect is inherently caused by the failure of the 3.5mm SMA-connector, whose HFrange is cataloged as 18GHz max. The result indicated that the prototype 4 is a SWB-

The far field radiation patterns are measured in the Delft University Chamber for Antenna Test (DUCAT); the anechoic chamber DUCAT (Fig.12a) is fully screened, its walls, floor and ceiling are shielded with quality copper plate of 0.4 mm thick. All these aimed to create a Faraday cage of internal dimension of 6 x 3.5 x 3.5 m3, which will prevent any external signal from entering the chamber and interfering with the measurements. The shielding of the chamber is for frequencies above 2 GHz up to 18 GHz at least 120 dB all around (Ligthart, 2006). All sides are covered with Pressey PFT-18 and PFT-6 absorbers for the small walls and long walls, respectively. It is found that one side reflects less than -36 dB. All these measures were taken together in order to provide sufficient shielding from other radiation

TX: Single polarization standard horn is used as transmitter, which can rotate in yaw-ydirection to provide V, H polarizations and all possible slant polarizations. The choice of the single polarization horn above the dual polarization one as calibrator is two-folds: 1) keeps the unwanted cross-polarization to the lowest possible level, 2) and also voids the phase

RX: Prototype 4 is put as antenna under test (AUT) on the roll-z-rotatable column (Fig.8b). For the measurements of polarimetric components (VV, HV, VH, HH, the first letter denotes

center interference and keeps the phase center deviation to the lowest level.

radiator because its measured ratio-bandwidth BR is certainly greater than 10:1.

**Figure 11.** SWB-performance: simulated and measured results.

coming from high power marine radars in the nearby areas.

**6.2. Far-field radiation patterns** 

**Figure 10.** Conceptual demonstration for advocating of CPW feed elongation, a) radiator with SMA connector, b) radiators with short and elongated feed, b) simulated reflection coefficient magnitudes of antenna with short and long feed.

### **6. Measurements**
