**7. Antenna design and simulation**

One of the most important and commonly used parameters in antenna design is the radiation pattern in the space around antenna. By defining antenna radiation pattern1 , radiation power in each direction and the direction which maximum power is emitted will be defined.

Since selected passive antenna is spiral antenna in this work, its radiation pattern is halfspace. So if interior and exterior radiuses be selected according to the active zone and frequency range, E-plane and H-plane radiation patterns will be uniform in all frequency bandwidth and have few variations. Changing design parameters has no effect on antenna polarization and it has always circular polarization. All simulations of this chapter are done in ADS (Advanced Design System) software [19].

<sup>1</sup> Radiation Pattern

Active Integrated Antenna Design for UWB Applications 199

0 0 9 8

rout is exterior active zone radius for low frequencies and rin is interior active zone radius for high frequencies. These dimensions show that the radius of r=40 mm is a good value.

**Freq 3-10.6 GHz**

(a)

(b)

3 4 5 6 7 8 9 10 11

freq, GHz

Simulation results are calculated and depicted in figure (7) and (8).

**Figure 7.** Antenna gain with w = 4.54m, s = 4mm and r = 40mm

**Gain**

**Figure 8.** Spiral antenna parameters in the UWB Band; a) S11 and b) VSWR

2

0

4

VSWR1

6

8

high 1 1 in f c / r 11 \* 1 3 \* 1 / r r 8.7 mm = → = →= *π π* (9)

**Figure 5.** a).Trade-off between gain and bandwidth; b).high gain and wide bandwidth by distributed amplifier

**Figure 6.** Spiral antenna radiation pattern in 3.36GHz

Other parameters which are effective in defining antenna performance are S112, Z113, VSWR4 and Gain. Each of these parameters are simulated and illustrated for spiral antenna. Antenna dimensions are chosen similar to spiral antenna in reference [9], but substrate is different and a distributed power amplifier is used as the active part. To analysis of antenna dimensions and identify the active zone, relations (8) and (9) are used and radiation radius of high and low frequencies are calculated as below:

$$\mathbf{r}\_{\rm low} = \mathbf{c} / \pi \mathbf{r}\_2 \to \mathbf{3} \,\,\,\mathbf{\*}\,\,\mathbf{1}0^9 = \mathbf{3} \,\,\,\mathbf{\*}\,\,\mathbf{1}0^8 / \pi \,\,\mathbf{r}\_2 \to \mathbf{r}\_{\rm out} = \mathbf{3} \,\mathbf{1}.8 \,\,\mathbf{mm} \tag{8}$$

<sup>2</sup> return loss

<sup>3</sup> Input Impedance

<sup>4</sup> Voltage Standing Wave Ratio

Active Integrated Antenna Design for UWB Applications 199

$$\mathbf{f\_{high}} = \mathbf{c} / \pi \mathbf{r\_1} \to 11 \,\,\,\mathbf{^\ast} \,\, 10^9 = \,\,\mathbf{3} \,\,\, \mathbf{^\ast} \,\, 10^8 / \,\pi \,\, \mathbf{r\_1} \to \mathbf{r\_{in}} = 8.7 \,\, \text{mm} \tag{9}$$

rout is exterior active zone radius for low frequencies and rin is interior active zone radius for high frequencies. These dimensions show that the radius of r=40 mm is a good value. Simulation results are calculated and depicted in figure (7) and (8).

**Figure 7.** Antenna gain with w = 4.54m, s = 4mm and r = 40mm

198 Ultra Wideband – Current Status and Future Trends

**Figure 6.** Spiral antenna radiation pattern in 3.36GHz

of high and low frequencies are calculated as below:

amplifier

<sup>2</sup> return loss <sup>3</sup> Input Impedance

<sup>4</sup> Voltage Standing Wave Ratio

**Figure 5.** a).Trade-off between gain and bandwidth; b).high gain and wide bandwidth by distributed

(b)

(a)

Other parameters which are effective in defining antenna performance are S112, Z113, VSWR4 and Gain. Each of these parameters are simulated and illustrated for spiral antenna. Antenna dimensions are chosen similar to spiral antenna in reference [9], but substrate is different and a distributed power amplifier is used as the active part. To analysis of antenna dimensions and identify the active zone, relations (8) and (9) are used and radiation radius

0 0 9 8

low 2 2 out f c / r 3 \* 1 3 \* 1 / r r 31.8 mm = → = →= *π π* (8)

**Figure 8.** Spiral antenna parameters in the UWB Band; a) S11 and b) VSWR

Generally, in wireless communications, the antenna is required to provide a return loss less than -10dB over its frequency bandwidth [1]. As it is obvious, although spiral antenna parameters are good, to have desirable characteristics in the UWB band, optimization is necessary. In this work optimization is done by using a distributed amplifier and designing an active antenna [19].

Active Integrated Antenna Design for UWB Applications 201

<sup>−</sup> <sup>=</sup> − (10)

m2


After definition of optimum load and source resistance, now optimum amplifier stages can

*opt*

*n*

attenuation constant on transistors in higher frequencies,.

higher input powers it works in the nonlinear operation mode.

RFpower=

m1

**Figure 10.** 1dB point calculation in 7GHz. RFpower is input power

PowerGain

20

12

**7.2. Simulation** 

network [11].

() () *d g*

*Ln α Ln α*

*α α*

Where *<sup>d</sup> α* and *<sup>g</sup> α* are drain and gate lines attenuation respectively. Calculation must be done in the highest frequency of bandwidth which is 11GHz because the optimum number of amplifier stages *opt n* is calculated to have less reduction in gain and lower effects of

Hear *opt n* was equal to 3. Then the 1dB point was calculated to define linear and nonlinear operation modes of the amplifier. As is shown in figure (10), m2 is 1dB point at 7GHz. In the other word, for input powers below -16 dBm, amplifier will work in the linear mode and for

Various methods can be used for linear and nonlinear analysis of such a circuit. Some of

m2

RFpower=

PowerGain=15.391

m1

Distributed amplifier shown in figure (5) is simulated in the linear region of its operation with 50Ω load and matching network. Distributed amplifier structure is shown in figure (11) [11].


RFpower

UWB distributed amplifier parameters are shown in figure (12). These results show a rather uniform gain and good return losses over this band. The results of this work and other experiences show that optimizing the integrated circuit of antenna and active circuit is more useful than optimizing each of them separately and then matching them by a matching

them are discussed in reference [19]. To more studies, see references [20 to 26].


PowerGain=16.349

*d g*

be calculated as bellow;

## **7.1. Active circuit design**

Active antennas are categorized depending on the active circuit behavior integrated with. Main functions of active antennas are generating and amplifying RF signals and frequency conversion. Here, designing a UWB distributed amplifier with uniform gain and return losses on the entire 3.1 to 10.6 GHz frequency band in the linear and nonlinear operation modes is the aim. Steps to design distributed amplifier are briefly described below;

**Step 1.** Selecting active element according to the project requirements

The first step is selecting a suitable active element which its linear and nonlinear models and parameters are accessible.

**Step 2.** Defining the optimum load resistance

After choosing suitable transistor, the optimum load resistance must be calculated to achieve maximum power in output

**Step 3.** Defining optimum number of amplifier stages

Optimum number of amplifier stages can be calculated using equation (10).

**Step 4.** Calculating 1dB point to define boundaries between linear and nonlinear regions of amplifier operation

For calculation of the optimum load resistance point, load power against load resistance curve is simulated as illustrated in figure (9). The load which gives maximum output power is the point [12]. Here Optimum Load Resistance is equal to 100 Ohms.

**Figure 9.** Load power against load resistance

After definition of optimum load and source resistance, now optimum amplifier stages can be calculated as bellow;

$$m\_{opt} = \frac{Ln(\alpha\_d) - Ln(\alpha\_g)}{\alpha\_d - \alpha\_g} \tag{10}$$

Where *<sup>d</sup> α* and *<sup>g</sup> α* are drain and gate lines attenuation respectively. Calculation must be done in the highest frequency of bandwidth which is 11GHz because the optimum number of amplifier stages *opt n* is calculated to have less reduction in gain and lower effects of attenuation constant on transistors in higher frequencies,.

Hear *opt n* was equal to 3. Then the 1dB point was calculated to define linear and nonlinear operation modes of the amplifier. As is shown in figure (10), m2 is 1dB point at 7GHz. In the other word, for input powers below -16 dBm, amplifier will work in the linear mode and for higher input powers it works in the nonlinear operation mode.

Various methods can be used for linear and nonlinear analysis of such a circuit. Some of them are discussed in reference [19]. To more studies, see references [20 to 26].

**Figure 10.** 1dB point calculation in 7GHz. RFpower is input power

#### **7.2. Simulation**

200 Ultra Wideband – Current Status and Future Trends

an active antenna [19].

**7.1. Active circuit design** 

parameters are accessible.

achieve maximum power in output

**Figure 9.** Load power against load resistance

amplifier operation

**Step 2.** Defining the optimum load resistance

**Step 3.** Defining optimum number of amplifier stages

Generally, in wireless communications, the antenna is required to provide a return loss less than -10dB over its frequency bandwidth [1]. As it is obvious, although spiral antenna parameters are good, to have desirable characteristics in the UWB band, optimization is necessary. In this work optimization is done by using a distributed amplifier and designing

Active antennas are categorized depending on the active circuit behavior integrated with. Main functions of active antennas are generating and amplifying RF signals and frequency conversion. Here, designing a UWB distributed amplifier with uniform gain and return losses on the entire 3.1 to 10.6 GHz frequency band in the linear and nonlinear operation

The first step is selecting a suitable active element which its linear and nonlinear models and

After choosing suitable transistor, the optimum load resistance must be calculated to

**Step 4.** Calculating 1dB point to define boundaries between linear and nonlinear regions of

For calculation of the optimum load resistance point, load power against load resistance curve is simulated as illustrated in figure (9). The load which gives maximum output power

modes is the aim. Steps to design distributed amplifier are briefly described below;

**Step 1.** Selecting active element according to the project requirements

Optimum number of amplifier stages can be calculated using equation (10).

is the point [12]. Here Optimum Load Resistance is equal to 100 Ohms.

Distributed amplifier shown in figure (5) is simulated in the linear region of its operation with 50Ω load and matching network. Distributed amplifier structure is shown in figure (11) [11].

UWB distributed amplifier parameters are shown in figure (12). These results show a rather uniform gain and good return losses over this band. The results of this work and other experiences show that optimizing the integrated circuit of antenna and active circuit is more useful than optimizing each of them separately and then matching them by a matching network [11].

Active Integrated Antenna Design for UWB Applications 203

**7.3. Active antenna simulation results** 

antenna in linear mode are shown in figure (13).

1.2

1.0

**Gain**

1.4

VSWR

1.6

1.8

**Figure 13.** Linear active antenna parameters; a) S11, b) VSWR and c) Gain

After design and simulation of passive spiral antenna and UWB distributed amplifier separately, spiral antenna is added to the active circuit as a load and specifications of this combined circuit is analyzed. For more accurate results, simulation is done by electromagnetic simulator "momentum" of ADS software. Simulated parameters of active

(a)

(b)

3 4 5 6 7 8 9 10 11

freq, GHz

(c)

**Freq GHz**

**Figure 11.** Designed distributed amplifier structure.

**Figure 12.** UWB distributed amplifier parameters; a) Gain. b) S11

#### **7.3. Active antenna simulation results**

202 Ultra Wideband – Current Status and Future Trends

**Figure 11.** Designed distributed amplifier structure.

**Figure 12.** UWB distributed amplifier parameters; a) Gain. b) S11

(a)

(b)

After design and simulation of passive spiral antenna and UWB distributed amplifier separately, spiral antenna is added to the active circuit as a load and specifications of this combined circuit is analyzed. For more accurate results, simulation is done by electromagnetic simulator "momentum" of ADS software. Simulated parameters of active antenna in linear mode are shown in figure (13).

**Figure 13.** Linear active antenna parameters; a) S11, b) VSWR and c) Gain

In the figure (14), active and passive antenna simulation results are shown. Comparing these results shows that active antenna parameters are considerably optimized rather than passive one. These results were predictable when the features of active antenna were introducing and now it is approved. It is important to know that the final circuit gain is not equal to the summation of passive antenna and active circuit gains. Total gain is calculated by replacing passive antenna as a load to the active circuit and calculating circuit gain [19].

Active Integrated Antenna Design for UWB Applications 205

**Figure 15.** Passive antenna parameters and optimized parameters of active antenna [27]; a) VSWR of passive spiral antenna in w=4, 5 and 6 mm; b) VSWR of optimized active antenna in w=4, 5 and 6 mm; c) Return loss of optimized active antenna; d) Uwb distributed amplifier gain for N=3,4 and 5 ( N is the turns of spiral antenna); e) Gain of passive spiral antenna; f) Gain of optimized active antenna

(e) (f)

(a) (b)

(c) (d)

By using active circuit specifications calculated in part 7, nonlinear simulation of active antenna is done here. In this case, input power is more than the power calculated for 1dB point and antenna works in nonlinear mode. For nonlinear analysis of antenna, large signal model and parameters of cicuit elements must be used. For special applications and higher output power requirements, power amplifiers and nonlinear operation may be considered.

Results are shown in figure (16). For more information see [19].

**Figure 14.** a) S11 and b) VSWR. The blue curve is passive antenna parameter and the red one is active antenna parameter. Active and passive antenna parameters comparison shows that linear active antenna parameters are optimized in compare with passive one.

In a similar work, M. Jalali et all. [27] optimized a spiral antenna using active integrated antenna technology for linear operation mode. Results are shown in figure (15).

circuit gain [19].

In the figure (14), active and passive antenna simulation results are shown. Comparing these results shows that active antenna parameters are considerably optimized rather than passive one. These results were predictable when the features of active antenna were introducing and now it is approved. It is important to know that the final circuit gain is not equal to the summation of passive antenna and active circuit gains. Total gain is calculated by replacing passive antenna as a load to the active circuit and calculating

**Figure 14.** a) S11 and b) VSWR. The blue curve is passive antenna parameter and the red one is active antenna parameter. Active and passive antenna parameters comparison shows that linear active

(b)

(a)

In a similar work, M. Jalali et all. [27] optimized a spiral antenna using active integrated

antenna technology for linear operation mode. Results are shown in figure (15).

antenna parameters are optimized in compare with passive one.

**Figure 15.** Passive antenna parameters and optimized parameters of active antenna [27]; a) VSWR of passive spiral antenna in w=4, 5 and 6 mm; b) VSWR of optimized active antenna in w=4, 5 and 6 mm; c) Return loss of optimized active antenna; d) Uwb distributed amplifier gain for N=3,4 and 5 ( N is the turns of spiral antenna); e) Gain of passive spiral antenna; f) Gain of optimized active antenna

By using active circuit specifications calculated in part 7, nonlinear simulation of active antenna is done here. In this case, input power is more than the power calculated for 1dB point and antenna works in nonlinear mode. For nonlinear analysis of antenna, large signal model and parameters of cicuit elements must be used. For special applications and higher output power requirements, power amplifiers and nonlinear operation may be considered. Results are shown in figure (16). For more information see [19].

Active Integrated Antenna Design for UWB Applications 207

from 4 to 3 and return losses are significantly low. Comparing figures (7 and 13), shows usefulness of adding active circuit to passive antenna to increase gain and make antenna parameters uniform and desirable. This antenna can also amplify narrow band signals which are in this frequency band in addition to amplifying UWB signals with frequency

I thank to Dr Ahmad Hakimi from Shahid Bahonar University of Kerman for his guidance and assistance and Dr Abdipour from Tehran Amirkabir University of Technology. This work was supported by South of Kerman Power Distribution Company and

[1] J. Liang. Antenna Study and Design for Ultra Wide Band Communication Applications. Department of electronic engineering Queen Mary, University of London, United

[3] J. Igor Immoreev, "Ultra-wideband Systems. Features and Ways of Development", Ultra Wideband and Ultra Short Impulse Signals, 19-22, Sevastopol, Ukraine, September,

[4] J. M Wilson, "Ultra-Wideband /a Disruptive RF Technology", Intel research &

[5] M. Tanahashi, "Design Technologies of RF devices for UWB Simulation", Ansof High Performance Applications Workshop, TRDA Inc. / Taiyo Yuden, October 27, 2005. [6] V.H. Rumsey, "Frequency Independent Antenna," IRE National Convention Record, pt.1,

[7] W.R. Deal, V. Radisic, Y. Qian and T. Itoh. "RF Technology for Low Power Wireless

[8] M. Pourjalali, "Analysis, design and simulation of active antenna in UWB band ", Tehran

[9] J. Lin, and T. Itoh, "Active Integrated Antennas", IEEE Transactions on Microwave

[10] J. R. Copeland, W. J. Robertson, and R G. Verstraete, "Antennafier arrays,'' IEEE Trans.

[11] E. Marzolf, M.H. Drissi, Global Design of an Active Integrated Antenna for Millimeter

elements in whole band.

Danial Nezhad Malayeri

**Acknowledgement** 

**9. References** 

2004.

Wave.

Kingdom, July 2006

pp. 114-118. 1957.

*South of Kerman Power Distribution Company, Kerman, Iran* 

Telecommunication Research Center of Iran.

[2] FCC, First Report and Order 02-48, February 2002.

development, Version 1.3, September 10, 2002.

Communications ", Wiley & Sons Inc. 2001

Amirkabir University of Technology, MSc. Thesis. 2006

Antennas Propagate, Vol. AP- 12, pp. 227-233, Mar. 1964.

Theory and Techniques, Vol 12. 12th December 1994.

**Author details** 

**Figure 16.** Nonlinear active antenna parameters; a) S11. b) VSWR. c) Gain

#### **8. Conclusion**

In the designed UWB active antenna, parameters are almost uniform in the entire band. It is again emphasized that one of very important requirements of UWB systems is having uniform parameters on the all 3.1 to 10.6 GHz frequency band, because all signal frequency elements must amplify uniformly to not distort transmitted signals. Comparing with results in reference [8], gain is increased about 5dB and final amplifier stages are reduced from 4 to 3 and return losses are significantly low. Comparing figures (7 and 13), shows usefulness of adding active circuit to passive antenna to increase gain and make antenna parameters uniform and desirable. This antenna can also amplify narrow band signals which are in this frequency band in addition to amplifying UWB signals with frequency elements in whole band.

### **Author details**

206 Ultra Wideband – Current Status and Future Trends

dB(S(1,1))


0


1.5

1.0

**Gain**

2.0

VSWR

2.5

3.0

**Figure 16.** Nonlinear active antenna parameters; a) S11. b) VSWR. c) Gain

In the designed UWB active antenna, parameters are almost uniform in the entire band. It is again emphasized that one of very important requirements of UWB systems is having uniform parameters on the all 3.1 to 10.6 GHz frequency band, because all signal frequency elements must amplify uniformly to not distort transmitted signals. Comparing with results in reference [8], gain is increased about 5dB and final amplifier stages are reduced

(c)

**Freq 3-10.6 GHz**

(a)

3 4 5 6 7 8 9 10 11

RFfreq

(b)

3 4 5 6 7 8 9 10 11

RFfreq

**8. Conclusion** 

Danial Nezhad Malayeri *South of Kerman Power Distribution Company, Kerman, Iran* 

#### **Acknowledgement**

I thank to Dr Ahmad Hakimi from Shahid Bahonar University of Kerman for his guidance and assistance and Dr Abdipour from Tehran Amirkabir University of Technology. This work was supported by South of Kerman Power Distribution Company and Telecommunication Research Center of Iran.

#### **9. References**


[12] D. E.J. Humphrey, V.F. Fusco and S. Drew, "Active Antenna Array Behavior", IEEE Transactions on Microwave Theory and Techniques, Vol. 43, No. 8, August 1995.

**Chapter 10** 

© 2012 Najam 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 Najam 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.

**Multiple-Input Multiple-Output Antennas for** 

UWB is a very promising technology for short-range wireless communications providing the opportunity of high data rate communications. In 2002, the Federal Communication Commission (FCC) regulated the UWB technology utilization for commercial applications in the United States in the frequency range of 3.1–10.6 GHz [1]. Other than the United States, UWB regulations have been issued in Europe, Japan, Korea and Singapore. These regulations did not stipulate the technology type to be used. Later, two distinct techniques were envisaged: the Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) and the Impulse-UWB (I-UWB) [2]. The MB-OFDM divides the UWB spectrum in 14 subbands, the utilization of the bands is managed for a code time-frequency exploiting the spatial-temporal diversity [3], while the I-UWB transmits pulses of very short duration that occupy the entire allowable frequency band [4]. UWB has vast array of applications in wireless world. The dominant applications include WBAN, WPAN, RFIDs, sensor networks, radars, etc. The relevant IEEE standards for UWB are: 802.15.3a for high data rate and 802.15.4a for low data rate. Digital communication using Multi-Input Multi-Output (MIMO) processing has emerged as a breakthrough for wireless systems of revolutionary importance. All wireless technologies face the challenges of signal fading, multipath, increasing interference and limited spectrum. MIMO technology exploits multipath to provide higher data throughput, and simultaneous increase in range and reliability all without consuming extra radio frequency. Early studies conducted by Foschini and Gans [5] indicated that capacity increases were possible by using MIMO systems. In a rich scattering environment, Telatar showed that the capacity of system consisting of ܯ transmitter and ܰ receiver antennas is ݉݅݊ሺܯǡ ܰሻ times that of a single transmitter receiver system [6]. MIMO systems exploit the antenna diversity (spatial, polarization or pattern diversity) to increase the strength of the transmitted signals and therefore to improve the Signal Noise Ration

**Ultra Wideband Communications** 

Ali Imran Najam, Yvan Duroc and Smail Tedjini

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/50181

**1. Introduction** 

