Full Paper Isee2007 Micro Strip Antenna

DESIGN – SIMULATION – TESTING OF MICROSTRIP ANTENNA Huynh Ngoc Tam, Do Tan Tai, Vu Dinh Thanh Faculty of Electrical & Electronics Engineering, HCM city University of Technology, Vietnam ABSTRACT This paper introduces some studies on Microstrip Antennas (MSA) which can be used for UltraWide Band communication systems. For the short-range application, the proposed antenna is designed to operate within the band 3.1 to 10.6 GHz. The traditional Rectangular Microstrip Antenna (RMSA) and our new modified model “H” antenna are characterized and compared within the operating frequency range by simulation on microwave softwares and by testing on realized products. Some results regarding the VSWR, gain and field-pattern for these 2 kinds of MSA are presented.

1. INTRODUCTION: Nowadays, in modern communication industry, when the fast and accurate information is one of the most important requirements to the systems, Ultra-Wideband (UWB) becomes a new technology that attracts a lot of investments and research. UWB has the transmitted information spread over a large bandwidth (>500 MHz) and at very high frequency range (3.1–10.6 GHz). Due to the extremely low power emission levels currently allowed by regulatory agencies, UWB systems tend to operate in short-range and indoors. However, due to the short duration of the UWB pulses, it is feasible to design the system with extremely high data rates, which can be readily traded-off for short range conditions. The pulse energy per data bit is simply aggregated using either simple integration or by coding techniques. In UWB system, antennas are the most important components required to create a communication link. Among various kinds of UWB antennas, Microstrip Antenna (MSA) is the simplest one due to its small size, high directivity performance and integration capacity. Through the years, MSA structures are the most common option used to realize millimeter wave monolithic integrated circuits for microwave, radar and communication purposes. Due to its many advantages over the conventional antennas, the MSA has achieved importance and generated interest to antenna designers for many years. In fact, active MSA arrays and active apertures are increasingly present in phased array

radar applications. This paper focusses on the simulating and testing on MSA within the UWB frequency range (3.1 – 10.6 GHz). The implementation of MSA for UWB transmitter and receiver will be studied in another paper. 2. MICROSTRIP ANTENNAS DESIGN

2.1 Characterization of microstrip antenna It was indicated earlier that the transmissionline model is the easiest of all models for Microstrip Antenna. In this paper, all designs of MSA base on this model.

Fig 1 - E-field distribution of transmission-line model Since the substrate thickness is much smaller than the wavelength (λ), the MSA is considered to be a two-dimensional planar configuration for analysis. Here, λ is equal to

λ0 / ε e , where λ0 is the free-space wavelength and εe is the effective dielectric constant of the patch. The value of εe is slightly less than εr, because the fringing fields around the periphery of the patch are not confined in the dielectric substrate but are also spread in the air as shown in Fig 1. The expression for calculating the value of εe is given below:

Fig 2 – (a) RMSA (b) “H” Antenna printed circuit

−1 / 2

(ε + 1) (ε r − 1)  10h  (1) εe = r + 1+ 2 2  W  The radiation pattern of the Rectangular MSA (RSMA) for the TM10 mode could be calculated by combining the radiation pattern of the two slots along the width of RMSA. The normalized patterns in the E-plane (Eθ in φ= 0o plane) and the H-plane (Eφ in φ=90o plane) are given by:  k ∆L sin θ   sin  0   2   cos k0 ( L + ∆L) sin θ  Eθ =   k0∆L sin θ 2   2

 k We  sin  0 sin θ   2    cos θ Eϕ = k 0We sin θ 2

-

The width (W) of RMSA: W= 2 f0

-

-

The length (L) of RMSA:

R  L × arccos in  π  Re 

(5)

where: + Le: effective length

Le =

Before implementing MSA, the design should be simulated based on some available microwave and antenna softwares (in this paper, the IE3D software is used). The two important factors that we must notice are the resonant frequency f0 and the input impedance Rin (referred to characteristic impedance Z0) of antenna. The design and simulation are taken out for the two kinds of MSA: conventional RMSA (Rectangular MSA) and the new modified model “H” antenna, as shown in figure (2). With a certain specific resonant frequency and a characteristic impedance, we can find the size (length L and width W) and the feeding position of the conventional RMSA by referring to the following formulas (3), (4), and (5)

(4)

Feeding position:

x=

2.2 Design of MSA

(3)

L = Le − 2∆L

(2a)

(2b)

c ( ε r + 1) 2

λ0 λ c = = 2 2 ε e 2 f0 ε e

+ ∆L: extended length

W + 0.264) h ∆L = 0,412.h. W (ε e − 0.258)( + 0.8) h (ε e + 0.3)(

The new “H” antenna in our proposed model is the modified structure from the conventional RMSA, by adding a slot to the patch at the position facing to the feeding point. The prototype of RMSA and “H” antenna is shown in figure (3), with their dimensions compared to one coin.

(a) (b) Fig 3 – (a) Actual RMSA (b) “H” Antenna (a)

(b)

Some simulations and testing measurements are taken on these 2 types and their results comparisons are presented in the following section. 3. MICROSTRIP ANTENNAS SIMULATION & MEASUREMENT The MSA antennas specified above has been analyzed by the evaluation version 12.0 IE3D of Zeland. The prototypes were fabricated and measured using facilities specified up to 8 GHz (Network Analyzer: Rohde & Schwarz and Spectrum Analyzer: rfR – 393A) Fig 4 shows the comparison between the simulated and measured values of VSWR of RMSA prototype specified at designed frequency 3.3 GHz. The frequency range for measurement of VSWR < 2 are from 3.178 GHz to 3.232 GHz, thus resulting in a bandwidth of 54 MHz, although the simulation predicts a smaller bandwidth 30 MHz. The measured resonant frequency (3.209 GHz) is slightly smaller than the simulated resonant frequency (3.31 GHz). The gain performance of the simulated and measurement RMSA are shown in Fig 5 at the different distances of measurement d=10cm, d=20cm and d=100cm. The results show the max gain at the frequency 3.2 GHz approximately, which demonstrates a variation from the designed frequency (at 3.3 GHz).

(a)

(b) Fig 4 –(a) Simulated and (b) measured VSWR of RMSA at 3.3GHz

(a)

(b) Fig 5 – (a) Computed and (b) measured gain of RMSA at 3.3GHz Fig 6 and 7 present the VSWR and gain of the “H” antenna, obtained by the simulations and the measurements. In Fig 6, the simulated results of the VSWR of “H” antenna is compared to that of its prototype (measured by Network Analyser), which shows a slight variation in resonant frequency in the two models. However,

as in Fig 7, the gain of “H” antenna in the band is slightly better than that of RMSA given in Fig5 (16.21 dB of “H” antenna compared to 14.21 dB of RMSA), the BW is equally broader (58 MHz for “H” compared to 54 MHz for RMSA). This fact could be due to the better matching effect of H antenna to the feeding line, compared to that of the RMSA. Figure (8a) and (8b) show that the farfield patterns of RMSA and “H” antenna are the same. It means that the innovation in this prototype is not influential to the radiation field of our antennas. (a)

(b) (a)

(b) Fig 6 – (a) Simulated and (b) measured VSWR of “H” antenna at 3.3GHz

Fig 7 – (a) Simulated and (b) measured gain of “H” antenna RMSA at 3.3GHz

(a)

(b) Fig 8 – Simulated radiation pattern of (a)RMSA and (b) “H” antenna 4. CONCLUSION This paper has presented the studies on MSA within their nominal frequency range, applied to indoor UWB system. Some designs and simulations of the 2 types of antennas (conventional RMSA and modified model “H”), are taken, based on the IE3D software. Some prototypes RMSAs and “H” antennas with central frequency over 3.1 GHz were also implemented and measured. These prototypes show their response to the requirements of the MSA used for UWB application, where the narrow pulse of 310 ps – width is essential. Future work on this study will focus on the implementation of RMSA and “H” antenna in the UWB transmitter and receiver and the other

improvements of antenna structures to enlarge their bandwidth REFERENCES 1. Girish Kumar, K.P. Ray. (2003), Broadband Microstrip Antennas, Artech House. 2. Ramesh Garg, Prakash Bhartia, Inder Bahl, Apisak Ittipiboon. (2001), Microstrip Antenna Design Handbook, Artech House. 3. Constantine A. Balanis. (1997), Antenna Theory Analysis and Design, John Wiley & Son. 4. Ian Oppermann, Matti Hamalainen, Jari Linatti. (2004), UWB Theory and Applications, John Wiley & Son. 5. Cam Nguyen. (2001), Analysis Methods for RF, Microwave and Millimeter-Wave Planar Transmission Line Structures , John Wiley & Son. 6. Cam Nguyen. (2007), Lecture on RF, Microwave and Millimeter-wave intergrated circuit and system for wireless communications, radar and sensing, Texas A&M University 7. Aaron Michael Orndorff. (2004). Transceiver Design for Ultra- Wideband Communications . Master Thesis, Virginia Polytechnic Institute . 8. Hern Monhamed El-Halidy. (2002), Design of an UWB monostatic microwave radar . Master Thesis, Kassel University. 9. Nikolay Telzhensky, Yehuda Leviatan , (2006). Planar Differential Elliptical UWB Antenna Optimization , 54, IEEE Transaction on Antenna and Propagation. 10. K.Rambabu, H.A.Thiart. (2006), Ulrawideband Printed-Circuit Antenna , 54, IEEE Transaction on Antenna and Propagation.