(b)

**Figure 14.** 3D-radiation patterns at 3, 7 and 11 GHz. (a) Simulation without cable, (b) simulation using cable A, and (c) measurement using cable A. Ground-plane size: 30 × 30 mm2.

**Figure 15.** Surface current distributions of antenna using cable A at (a) 3 GHz, and (b) 11 GHz

#### *4.3.2. Effects of feeding cable with EMI suppressant tubing (cable B)*

288 Ultra Wideband – Current Status and Future Trends

**Figure 14.** 3D-radiation patterns at 3, 7 and 11 GHz. (a) Simulation without cable, (b) simulation using

3 GHz 7 GHz 11 GHz

(c)

3 GHz 7 GHz 11 GHz

(a)

3 GHz 7 GHz 11 GHz

(b)

cable A, and (c) measurement using cable A. Ground-plane size: 30 × 30 mm2.

Figure 16 shows the simulated and measured results for using cable B. It can be seen that, with the use of the simulation model for cable B, the measured and simulated S11 and efficiencies have very good agreements for the three antennas even at lower frequencies. These results confirm the accuracy of our simulation model for the feeding cable used in the antenna measurement system. The simulated results without using the feeding cable are also shown in the same figure for comparison. It can be seen that the simulated efficiency without using the feeding cable at low frequencies is much higher than the simulated or measured efficiencies using the feeding cable. This is because at low frequencies, the current flows back to the feeding cable and causes secondary radiation which is mostly absorbed by the EMI suppressant tube enclosing the cable.

The 3D-radiation patterns of the antenna with a ground-plane size of 30 × 30 mm2 at the frequencies of 3, 7 and 11 GHz are shown in Figure 17. With the use of cable B, Figures 17(b) and (c) show no ripple on the 3D-radiation patterns. The simulated 3D-radiation patterns with and without using cable B agree quite well, indicating the effectiveness of using EMI suppressant tubing for the feeding cable. The measured 3D-radiation patterns in Figure 17(c) are similar to the corresponding simulated radiation patterns shown in Figure 17(b). Figure 18 shows the simulated current distributions on the outer surface of the feeding cable at 3 and 7 GHz. Compared with those in Figure 15, it can be seen that the surface current is very small even at 3 GHz because of the EMI suppressant material. It should be noted that, at low frequencies, since the EM fields radiated from the feeding cable are mostly absorbed by EMI suppressant tubing, the efficiency and hence the gain are much reduced.

Cable Effects on Measuring Small Planar UWB Monopole Antennas 291

**Figure 17.** 3D-radiation patterns at 3, 7 and 11 GHz. (a) Simulation without cable, (b) simulation using

3 GHz 7 GHz 11 GHz

(c)

3 GHz 7 GHz 11 GHz

(a)

3 GHz 7 GHz 11 GHz

(b)

cable B, and (c) measurement using cable B. Ground-plane size: 30 × 30 mm2.

**Figure 16.** Simulated and measured S11 and efficiencies using cable B with different ground-plane sizes

**Figure 16.** Simulated and measured S11 and efficiencies using cable B with different ground-plane sizes

(c) Ant 9: 50 × 80 mm2

(b) Ant 5: 30 × 50 mm2

(a) Ant 4: 30 × 30 mm2

**Figure 17.** 3D-radiation patterns at 3, 7 and 11 GHz. (a) Simulation without cable, (b) simulation using cable B, and (c) measurement using cable B. Ground-plane size: 30 × 30 mm2.

Cable Effects on Measuring Small Planar UWB Monopole Antennas 293

[2] Cheung SW, Liu L, Azim R, Islam MT (2011) A Compact Circular-Ring Antenna for Ultra-Wideband Applications. Microwave and Optical Technology Letters. 53: 2283–

[3] Liu L, Cheung SW, Yuk TI (2011) Bandwidth Improvements Using Ground Slots for Compact UWB Microstrip-fed Antennas. Progress In Electromagnetics Research

[4] Sun YY, Cheung SW, Yuk TI (2011) Studies of Planar Antennas with Different Radiator Shapes for Ultra-wideband Body-centric Wireless Communications. Progress In

[5] Zhang J, Sun XL, Cheung SW, Yuk TI (2012) CPW-Coupled-Fed Elliptical Monopole Antenna for UWB Applications. IEEE Radio Wireless Week 2012 (RWW2012), Santa

[6] Sun YY, Islam MT, Cheung SW, Yuk TI, Azim T, Misran N (2011) Offset-fed UWB Antenna with Multi-slotted Ground Plane. IEEE International Workshop on Antenna

[7] Sun YY, Cheung SW, Yuk TI (2012) Planar Monopole Ultra-wideband Antennas with Different Radiator Shapes for Body-centric Wireless Networks. Progress In Electromagnetics Research Symposium 2012 (PIERS2012), Kuala Lumpur, Malaysia [8] Saario SA, Lu JW, Thiel DV (2002) Full-wave analysis of choking characteristics of sleeve

[9] Chow YL, Tsang KF, Wong CN (1999) An accurate method to measure the antenna impedance of a portable radio. Microwave and Optical Technology Letters. 23: 349-352.

http://www.ece.utah.edu/~ece3300/Labs/lab3/MONOPOLE%20ANTENNAS.pdf [13] Chen ZN, Chia MYW (2006) Broadband Planar Antennas Design and Applications.

[14] Icheln C (2001) Methods for measuring RF radiation properties of small antennas. PhD

[15] DeMarinis J (1988) The antenna cable as a source of error in EMI measurements. IEEE 1988 International Symposium on Electromagnetic Compatibility Symposium Record.

[17] Awadalla K, Maclean T (1979) Monopole antenna at center of circular ground plane: Input impedance and radiation pattern. IEEE Transactions on Antennas and

[18] Weng YF, Cheung SW, Yuk TI (2010) Effects of ground-plane size on planar UWB

[19] Icheln C, Ollikainen J, Vainikainen P (1999) Reducing the influence of feed cables on

[10] The Capcon website. Available: http://www.capconemi.com/st4page1.html [11] The Satimo website. Available: http://www.satimo.com/content/products/starlab

Electromagnetics Research Symposium (PIERS) 2011. Suzhou, China.

balun on coaxial cables. Electronics Letters. 38: 304-305.

[12] Gandhi OP, Lazzi G, Furse CM. Monopole Antennas. Available:

thesis, Helsinki University of Technology, Espoo, Finland, Nov.

[16] Weiner MM, (2003) Monopole Antennas. NY: Marcel Dekker, Inc.

small antenna measurements. Electronics Letters. 35: 1212-1214.

West Sussex, England: John Wiley & Sons, Ltd.

monopole antenna. TENCON 2010. pp. 422-425.

2288.

Clara, CA, USA

pp 9-14.

Propagation. 27: 151-153.

Technology ( iWAT2011), 2011

Symposium (PIERS) 2011. Suzhou, China.

**Figure 18.** Surface current distribution of antenna using cable B at (a) 3 GHz and (b) 11 GHz
