Appendix A Abstract – The s11 parameter is defined as the reflected voltage divided by the incident voltage and is the same as the return loss which is equal to –

)log(20 11sRL −=

It is desirable to have as little reflected voltage as possible and hence a return loss of -∞. Practically this is not possible however, if the Voltage Standing Wave Ratio (VSWR) is less than 2, the antenna performs acceptably. In terms of return loss, a VSWR of less than 2 compares to a return loss less than -9.54dB (common practice is to use -10dB for simplicity). The results obtained from research papers and displayed in this report are used determine which antenna will be used for experimentation. However, there are also other factors which are taken into consideration such as ease of fabrication and also as not all data was able to be obtained for all antennas, some data may be extrapolated from certain antennas for other antennas. It is also worth noting that the group delay and phase response are related by –

( )ωωθ

∂∂−=Groupdelay

where ( )ωθ is the phase angle dependent on frequency. Hence a linear phase response gives a constant group delay.

Bicone, Monocone, LPDA, F-probe, Simulated Horn

Figure 1 – Images of simulated antenna from [1]

Figure 2 – s11 parameter results and radiation pattern of antennas in Figure 1 from [1] Discussion – Figure 2 shows the return loss of the different antennas from figure 1 between frequencies of DC and 10GHz. It can be seen from figure 2 that the best performers are the bicone (with a bandwidth of >7GHz) and the monocone (with a bandwidth of approximately 7GHz). The horn antenna performed the worst with a bandwidth of approximately 500MHz and the LPDA and f-probe antennas performed rather similarly with the LPDA having a rather poor return loss over certain frequencies and a good return loss over others due to the design of the antenna. The radiation patterns depicted in figure 2 are for the monocone antenna (top) and the f-probe antenna (bottom). Because the f-probe antenna and the horn antenna are both directional antennas, it is assumed that the horn antenna with have a similar radiation pattern to that of the f-probe antenna. The radiation pattern for the monocone shows an omnidirectional pattern which is expected due to the symmetry of the antenna’s design. It is assumed that the radiation pattern for the bicone will be similar to that of the monocone due to the similarities of design. The radiation pattern of the LPDA however is unknown from figure 2 although figure 15 does show the radiation pattern for a different LPDA and hence this can be used as a comparison. Although the cone antennas have the best performance, these are harder to fabricate than say the LPDA antenna and hence must be taken into consideration.

Section 2 - Helix Antennas

Figure 3 – Helix antenna and s11 parameter results from [2]

Figure 4 – Helix antenna with cone feed and s11 parameter results from [2] Discussion –

The helix antenna shown in figure 3 performs particularly well at certain frequencies but poorly over the range of 2 – 6GHz. The helix antenna shown in figure 4 (with a capacitive coupling) performs the best out of all the helix antennas with a bandwidth of slightly less than 4GHz. All other antennas have relatively poor bandwidth compared to the capacitive coupled helix antenna. Although the radiation pattern is not given, it can be assumed that due to the symmetrical design of the antenna that the radiation pattern will be omnidirectional. Also, due to the complex shape of the antenna, it will be harder to fabricate than an average planar antenna.

Square Planar Monopole

Figure 5 – Square Monopole antenna and s11 parameter results from [3]

Figure 6 – Radiation pattern of square monopole antenna at 5GHz from [3] Discussion – Figure 5 shows the square planar monopole antenna having a large bandwidth of approximately 10GHz. The radiation pattern is also shown at 5GHz and can be seen to be omnidirectional. Figure 1 however does show that this large bandwidth is dependent on the notches in the design however this does not make the fabrication much more difficult.

Square Monopole with various feeding strips

Figure 7 – Square monopole antenna with various feeding strips and results of s11 parameter from [3]

Figure 8 – Radiation pattern of square monopole antenna with various feeds from [3] Discussion – Figure 7 shows that a square monopole antenna with a trident shape or 2 branch feeding strip performs better than that of a simple feeding strip. The trident and double feeding strip antennas perform very similarly however the trident feeding strip does have a slightly larger bandwidth of approximately 10GHz. Once again the radiation pattern is omnidirectional and is rather simple to fabricate.

Step shaped Planar Monopole

Figure 9 – Step shaped planar monopole antenna and results of s11 parameter from [3]

Figure 10 – Radiation pattern of step shaped planar monopole antenna from [3] Discussion – The step shaped planar monopole antenna performs quite poorly over the UWB frequency range with a bandwidth of only 4.4GHz. The radiation pattern is similar to that of the previous monopole antennas and it is simple to build however the bandwidth is rather poor.

U shaped Planar Monopole

Figure 11 – U shaped planar monopole antenna and results for s11 parameter from [3] Discussion – The U shaped planar monopole antenna performed slightly better than the step planar monopole antenna with a bandwidth of approximately 5GHz however this is still rather poor over the UWB frequency range.

Cylindrical planar monopole

Figure 12 – Dimensions of cylindrical planar monopole antenna from [3]

Figure 13 – s11 parameter results for cylindrical planar monopole antenna from [3] Discussion – The cylindrical planar monopole antenna performs very similarly to the U shaped planar monopole antenna which has a rather poor bandwidth over the UWB frequency range.

Cross plate Monopole

Figure 14 – Cross plate monopole antenna and s11 parameter results from [3] Discussion – The cross plate monopole antenna can be seen to have a bandwidth of approximately 10GHz which is good for a UWB application. The antenna performs better with a bent cross plate rather than a planar cross plate.

LPDA

Figure 15 – Dimensions for LPDA and s11 parameter results from [4]

Figure 16 – Radiation pattern for LPDA from [4]

Figure 17 – Plot showing the group delay for LPDA from [4] Monopole Antenna

Discussion – Figure 15 shows that the LPDA has a bandwidth of approximately 10GHz which is suitable for a UWB application however the return loss does vary significantly with frequency as shown by all the downward spikes in the plot. Figure 15 also shows that the original design (shown in figure 15) performs better than the band-notched design (not shown). The radiation pattern of the LPDA can be seen to be omnidirectional, although it is not the best radiation pattern of antenna previously looked at. Figure 17 does show the LPDA to have a relatively constant group delay over the UWB frequency range which is a desirable characteristic of an antenna.

Monopole Antenna

Figure 17 – Dimensions of monopole antenna from [5]

Figure 18 – s11 parameter results for monopole antenna with various dimensions from [5] Discussion – It can be seen in figure 18 that the monopole antenna has a poor return loss between approximately 5 and 7 GHz which is rather poor compared to some of the previous antennas. It can also be assumed that the radiation pattern of this antenna will be rather similar to that of previous planar monopole antennas and hence has no stand out characteristics above other antennas.

Planar Dipole

Figure 19 – Dimensions of planar dipole antenna from [6]

Figure 20 – s11 parameter results and radiation pattern of the planar dipole antenna from [6] Discussion - Figure 20 shows a poor return loss over the UWB frequency range (particularly above 6GHz). Its radiation pattern is very similar to that of other planar monopole antennas.

Planar Monopole

Figure 21 – Dimensions of planar monopole antenna from [7]

Figure 22 – s11 parameter results of planar monopole antenna from [7] Discussion – Figure 22 shows that the monopole antenna shown in figure 21 has a bandwidth of approximately 10GHz; this is an acceptable bandwidth for an UWB application.

Vivaldi Antenna

Figure 23 – Dimensions of Vivaldi antenna from [8]

Figure 24 – VSWR plot and group delay plot of Vivaldi antenna from [8]

Figure 25 – Dimensions of a second Vivaldi antenna from [8]

Figure 26 – VSWR plot and group delay plot of second Vivaldi antenna from [8]

Discussion – Unlike previous antenna data shown, the data for the Vivaldi antenna gives a plot of the VSWR rather than the return loss. As stated in the abstract, having a return loss of less than 10dB is approximately the same as having a VSWR of less than 2. Figure 24 shows that the first type of Vivaldi antenna has a simulated bandwidth of >9GHz and a measured bandwidth of 7.5GHz and a relatively constant group delay (except at 9GHz where strange things happen for reasons unknown). Figure 26 shows that the second type of Vivaldi antenna has a simulated bandwidth of >9GHz and a measured bandwidth of approximately 8GHz and a relatively constant group delay.

Planar Dipole Antennas

Figure 27 – Circular, bow-tie and elliptical dipole antennas from [9]

Figure 28 – VSWR plot and frequency response of dipole antennas from [9]

Figure 29 – Radiation patterns of dipole antennas from [9] Discussion – Figure 28 shows that both the circular and elliptical dipole antennas have large bandwidths while that of the bow-tie dipole is slightly worse. Figure 28 also shows the phase response of the antennas and shows that the elliptical antenna has a nonlinear phase response (and hence not a constant group delay) whereas the circular

and bow-tie antenna have rather linear phase responses with that of the bow-tie being slightly better than that of the circular. The radiation patterns appear to be similar to those of previous planar antennas.

Circular Monopole Antenna

Figure 30 – Circular monopole antenna from [10]

Figure 31 – s11 parameter results of circular monopole antenna from [10] Discussion Figure 31 shows that the bandwidth of the circular monopole antenna to be less than 7.5GHz over the UWB frequency range. The impedance bandwidth is from 3.1GHz to approximately 10GHz and hence does not cover the entire UWB frequency range.

Microstrip Antenna

Figure 32 – Microstrip antenna from [11]

Figure 33 – s11 parameter results of microstrip antenna from [11] Discussion The microstrip antenna shows a relatively poor impedance bandwidth being approximately 6GHz between 4.5GHz and 10.5GHz.

Conclusion – Firstly, because there were many antennas which had a suitable bandwidth for UWB, all of the others can be disregarded. This leaves the bicone, monocone, helix with capacitive coupling, square planar monopole, cross plate monopole, LPDA, planar monopole, Vivaldi and circular and elliptical dipole antennas. All of these antennas have very similar (omnidirectional) radiation patterns so this does not have an effect on the choice of antennas. Secondly, the bicone, monocone and helix antennas are the most difficult antennas to fabricate and do not provide much, if any, difference compared to other, easier to fabricate antenna designs. This leaves the square planar monopole, cross plate monopole, LPDA, planar monopole, Vivaldi, circular monopole, microstrip and the circular and elliptical antennas. From this point, the major determining factor has become the phase response or group delay of the antenna. Because all of the antennas have very similar radiation patterns and bandwidths, the antennas that phase responses were unable to be obtained for will be disregarded hence leaving the LPDA, Vivaldi, circular monopole, microstrip and the circular and elliptical dipole antennas. Also, because the elliptical dipole has a non-linear phase response, it can also be disregarded. This leaves a choice between five antennas, the LPDA, Vivaldi and the circular dipole. It was determined that the LPDA and circular dipole were too difficult to simulate hence the Vivaldi, circular monopole and microstrip antennas will be simulated.

Bibliography [1] – Sibbile, A 2005, ‘Modulation Scheme and Channel Dependence of Ultra-Wideband Antenna Performance’, IEEE Antennas and Wireless Propagation Letters, vol. 4 [2] – Yang, Y, et al. ‘The Design of Ultra-wideband Antennas with Performance Close to the Fundamental Limit’, Virginia Tech Antenna Group, Blacksburg, VA, USA [3] – Wong, K.L. ‘High-Performance Ultra-Wideband Planar Antenna Design’, Dept. of Electrical Engineering National sun Yat-Sen University Kaohsiung, Taiwan. [4] – Chen, S.Y., et al. 2006, ‘Unipolar Log-Periodic Slot Antenna Fed by a CPW for UWB Applications’, IEEE Antennas and Wireless Propagation, vol. 5 [5] – Xiao-Xiang, HE, 2009, ‘New band-notched UWB antenna’, College of Information Science and technology, Nanjing University of Aeronautics and Astronautics, Nanjing, P.R. China [6] – Zhao, CD, 2004, ‘Analysis on the Properties of a Coupled Planar Dipole UWB Antenna’, IEEE Antennas and Wireless Propagation Letters, vol. 3 [7] – Choi, SH, 2003, ‘A new Ultra-Wideband Antenna for UWB Applications’, Microwave and Optical Technology Letters, vol. 40, no. 5, Mar 2004 [8] – Mehdipour, A. 2007, ‘Complete Dispersion Analysis of Vivaldi Antenna for Ultra Wideband Applications’, Progress in Electromagnetics Research, pp 85-96. [9] – Hecimovic, N. ‘The Improvements of the Antenna Parameters in Ultra-Wideband Communications’, Ericsson Nikola Tesla, d.d., Croatia. [10] – Liang, J. 2005, ‘Study of Printed Circular Disc Monopole Antenna for UWB Systems’, IEEE Transactions on Antennas and Propagation, vol. 53, no. 11. [11] – Lim, K.-S. 2008, ‘Design and Construction of Microstrip UWB Antenna with Time Domain Analysis’, Progress in Electromagnetics Research, vol.3 pp 153 – 164.

Appendix B

(a) (b)

2 4 6 8 10 12-30

-25

-20

-15

-10

-5

09m Coaxial Cabling Magnitude

Frequency, GHz

Mag

nitu

de, d

B

2 4 6 8 10 12-4000

-3500

-3000

-2500

-2000

-1500

-1000

-500

09m Coaxial Cabling Phase

Frequency, GHzP

hase

, rad

Figure 1. Cable magnitude and Phase response for 9m of cables

Figure 2. Cable magnitude and Phase response for 9m of cables

Project Management Plan – Ultra Wideband Antennas

OFFCDT Andrew Spear School of Engineering and Information Technology

UNSW@ADFA Purpose The project will focus on antennas suitable for a typical Ultra Wideband (UWB) of 3.1GHz to 10.6GHz. The purpose is to research existing UWB antenna technology, identify key features of UWB antennas, analysing, characterising and constructing particular antenna designs and to give a comparison of the relative performance and trade-offs between fabrication, cost and performance. Objectives The aim of the project was to develop a diagnostic tool in order to produce an Ultra Wideband (UWB) antenna with a linear phase response in order to give a constant group delay using a passive equalisation network. Milestones The milestones for the project are – 1. To obtain one or two UWB antenna designs which can be simulated and

constructed for testing. 1.1. Draft a document on UWB antenna technology, highlighting the particular

requirements for UWB systems and applications. 1.2. Have construction details and published performance characteristics/

targets for antenna designs. 2. To simulate the antenna designs and obtain data which can be manipulated

using MATLAB. 2.1. Draft a document detailing the process to be used for simulation of the

antenna designs and also the desired data which is to be extracted. 2.2. Draft a report detailing the data obtained from simulation and a

comparison of this data to what theory predicts. 3. To characterise the permittivity of the antenna substrate over the frequency

range of 3.1GHz – 10.6GHz. 3.1. Have constructed test boards. 3.2. Obtain an accurate simulation model for the antenna substrate.

4. To construct the antenna design and conduct real life testing of the system. 4.1. Have constructed the antenna. 4.2. Draft a report detailing the data obtained from the real life testing and a

comparison of this to theory/data obtained from simulation. 5. To develop a diagnostic tool in order to determine whether a particular antenna

can be equalised to have a constant group delay over the UWB frequency spectrum.

5.1. Draft a document detailing the requirements for a system to give a linear phase response.

5.2. To produce the diagnostic tool to be operated in MATLAB. 5.3. To adapt the diagnostic tool in order to simulate equalisation networks of

varying complexity. 5.4. To draft a report detailing the data obtained and a comparison to what is

predicted by theory/simulation (if simulation is possible). Key Dates

• Week 25/26 – VIVA • Week 40 – 15 minute seminar • Week 44 – Thesis due

Projected Timeline Task No.

Task Start (Week No.) Finish (Week No.)

Total time spent (Weeks)

Remarks

1 Research antenna theory and UWB antenna and systems

11 13 3 Completed

2 Milestone 1.1 11 13 3 Completed 3 Milestone 1.2 11 13 3 Completed 4 Practice using simulation software 13 13 1 Completed 5 Conduct simulations 14 20 5 Completed 6 Milestone 2.1 13 13 1 Completed 7 Milestone 2.2 16 16 1 Completed 8 Milestone 3.1 20 20 1 Completed 9 Conduct testing on test boards 21 21 1 Completed 10 Milestone 3.2 22 24 3 Completed 11 Milestone 4.1 20/29 20/30 3 One antenna built 12 Conduct real life testing of antenna 23 32 6 Completed 1-port

testing for the 1 antenna

13 Milestone 4.2 33 33 1 14 Milestone 5.1 29 30 2 15 Milestone 5.2 31 32 2 16 Simulate system to give linear phase response 32 33 2 17 Milestone 5.3 34 35 2 18 Test system to give linear phase response 36 37 2 19 Milestone 5.4 37 37 1 20 Collaborate work/write thesis 40 44 4

11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

The above matrix works as follows –

• The numbers across the top represent the week number in the year • The numbers down the left represent the task number given in the projected timeline -

Anticipated Obstacles – The construction time of the antenna is unknown and hence in the event that the fabrication takes significantly longer than expected the system to give a linear phase response can begin to be designed based on the results of simulations. Obstacles Encountered – It took a lot longer than expected to get an accurate simulation result from the simulation software (CST Microwave Studio) and hence that pushed back the construction of the antennas. However, the time taken to construct the antennas was not as long as expected and hence helped me catch up some time. The construction time of the antennas was approximately 1 week hence it was not a significant issue in terms of time constraints. The biggest obstacle encountered was obtaining the 2-port measurements of the antenna network. This process took much longer than expected due to the several iterations of testing which had to be done in order to achieve accurate results. The testing was first conducted outside the anechoic chamber and it was found that there was too much backscatter in the transmission results to do any manipulation of the data in MATLAB. The test was then moved inside the anechoic chamber but in order to do this 9m of cable had to be used to connect the antennas to the network analyser. These cables introduced a significant amount of attenuation in the results which was reducing the magnitude of the transmission down to the threshold of the network analyser. The next iteration involved a setup similar to the first (outside of the anechoic chamber) but using the anechoic chamber foam tiles in an attempt to reduce the amount of backscatter. It was found that this did not work particularly well and finally the network analyser was moved closer to the anechoic chamber to reduce the amount of cable used to connect the antennas to the network analyser which gave accurate results.

Scope Changes – The scope of the project began as investigating UWB antennas and technologies and developing a system to linearise the group delay of the antennas hence giving it a constant group delay. This shifted to producing a tool to take in the 2-port parameters of an antenna and determine the effect of equalisation on the antennas using a passive network of varying complexities.