диафрагмированные волноводные фильтры / 5fb533d1-15ce-4866-8574-924f1b616355

A NOVEL CPW-FED ULTRA-WIDEBAND ANTENNA DESIGN

Seong H. Lee, Jong K. Park, and Jung N. Lee

Department of Radio Wave Engineering

Hanbat National University

San 16-1, Dukmyung-Dong

Yuseong-Gu, Daejeon 305-719, Korea

Received 7 August 2004

ABSTRACT: A novel ultra-wideband (UWB) antenna fed by coplanar waveguide (CPW) is designed, fabricated, and measured for UWB communications. It is designed to work on a substrate TMM4 of thickness 0.762 mm and relative permittivity 4.5, and to operate from 3.1 to 8.3 GHz. Details of the proposed antenna design and the measured results are presented and discussed. Measured insertion loss is almost constant across the frequency band and the group-delay variation is less than 1 ns, thus indicating that the proposed antenna is a good candidate for UWB applications. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 393–396, 2005; Published onlinePublished online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 20646

Key words: ultra-wideband antenna; CPW; group delay; omni-direc- tional

1. INTRODUCTION

Ultra-wideband (UWB) technology has attracted attention for use in wireless communication and sensing applications. Antennas are the particularly challenging aspect of UWB technology. Recently, various antennas have been developed for UWB communications, including a planar volcano-smoke slot antenna [1], CPW-fed bowtie/triangular patch antenna [2], and UWB antenna with partial ground plane [3]. The UWB performance of antennas result from excitation by impulse or nonsinusoidal signals, which have rapidly time-varying performances. For UWB communications applications, there is a great need for omnidirectional and wide band-

Figure 2 Measured and simulated return loss versus frequency

width, minimum size, gain flatness, phase linearity, and low cost [1–3].

Ying et al. [1] proposed an LTCC planar volcano-smoke slot antenna for UWB applications which has ultrawide bandwidth (3–12 GHz) and return loss S11 10 dB. Recently, an ultra-

Figure 4 Measured radiation patterns at 3.5 GHz: (a) E-plane (b) H- plane

wideband CPW-fed bowtie/triangular patch antenna [2] and UWB antenna with partial ground plane [3] have been designed for UWB communications. In [4], a CPW-fed planar UWB antenna with a frequency-band notch function has been studied for UWB applications.

In this paper, a novel CPW-fed UWB antenna is investigated and optimized for UWB applications. The proposed antenna can cover the UWB frequency range (3.1– 8.3 GHz) and shows stable behaviors over the band. The simulation software to design the proposed antenna is the commercially available simulation software Microwave Studio from CST. The simulated results are in reasonable agreement with the measured results and the impedance bandwidth for 10-dB return loss is approximately 5.2 GHz (3.1– 8.3 GHz). The antenna also shows a good gain flatness and

phase linearity. The antenna radiation patterns at frequencies 3.5, 5.5, and 7.5 GHz and gain versus frequency are also presented.

2. ANTENNA DESIGN AND MEASURED RESULTS

Figure 1 shows the geometry of the proposed UWB antenna. As shown, the antenna is fed by a CPW line. It is printed on the TMM4 substrate with thickness 0.762 mm and relative permittivity 4.5, respectively. The TMM4 substrate has dimensions of 30 30 mm2. The antenna has the following parameters: L1 14 mm,

W1 3 mm, L2 20 mm, W2 1 mm, Wg 10 mm, and G 2 mm. We have obtained the proposed antenna parameters using

CST Microwave Studio based on the finite-integration method. The proposed antenna was constructed and studied. The return

loss (S11) of the proposed antenna was measured using an Anritsu Vector Network Analyzer (37397C) in an anechoic chamber. Fig-

Figure 5 Measured radiation patterns at 5.5 GHz: (a) E-plane (b) H- plane

Figure 6 Measured radiation patterns at 7.5 GHz: (a) E-plane (b) H- plane

ure 2 shows the measured and simulated results for comparison and indicates a reasonable agreement between them. The impedance bandwidth of the antenna defined by S11 10 dB is approximately 5.2 GHz (3.1– 8.3 GHz). Group delay is an important parameter in UWB antenna design, which indicates the pulse distortion. In order to quantify the far-field phase linearity, we measured the group delay g, defined as

where is the far-field phase and f is the frequency. Figures 3(a) and 3(b) show the measured insertion loss (S21) and group delay ( g) in the boresight direction. From the figure, it can be seen that

Figure 7 Measured antenna gain versus frequency

insertion loss is almost constant across the frequency band and the group delay variation is less than 1 ns. For the group delay measurement, the distance between the two antennas is 15 cm.

The radiation characteristics of the proposed antenna are also studied. The measured radiation patterns at 3.5, 5.5, and 7.5 GHz are illustrated in Figures 4 – 6. The proposed antenna is characterized by a quasi-omnidirectional pattern in the azimuthal plane ( x–z plane) and the radiation is vertically polarized. Figure 7

Figure 8 (a) Pulse generator’s waveform (b) Output waveform of the proposed receiver antenna

shows the measured antenna gain versus frequency and the gain varies from 0.5 dBi to 5 dBi over the operating frequency range.

The proposed antennas were used in order to demonstrate faithful UWB radiation and propagation. The time-domain behavior was measured by using time domain’s pulse generator (PulsON200TM) and Tektronix’s digital-storage oscilloscope (TDS6604). In this experiment, the separation between the antennas was 15 cm. Figure 8(a) is the pulse generator’s waveform and Figure 8(b) shows the output of the proposed receiver antenna in the boresight direction. The received signal is identical in wave shape to the 15-cm path; however, it is weaker in amplitude, thus indicating that the antenna can produce low distortion.

3. CONCLUSION

A novel CPW-fed UWB antenna has been proposed for UWB applications. The impedance bandwidth of the antenna, defined by S11 10 dB, is approximately 5.2 GHz (3.1– 8.3 GHz). The insertion loss and group delay were measured in the boresight direction. The insertion loss is almost constant across the frequency band and the group-delay variation is less than 1 ns. The antenna radiation patterns were measured at 3.5, 5.5, and 7.5 GHz in an anechoic chamber and the antenna gain in the frequency range 3–9 GHz were also presented. In addition, we performed the pulse experiment using the proposed antennas and the measured results indicate that the antenna can produce low distortion.

REFERENCES

1. C. Ying, G.Y. Li, and Y.P. Zhang, An LTCC planar ultra-wideband antenna, Microwave Opt Technol Lett 42 (2004), 220 –222.

2.N. Fortino, G. Kossiavas, J.Y. Dauvignac, and R. Staraj, Novel antennas for ultra-wideband communications, Microwave Opt Technol Lett 41 (2004), 166 –169.

3.S.H. Choi, J.K. Park, S.K. Kim, and J.Y. Park, A new ultra-wideband antenna for UWB applications, Microwave Opt Technol Lett 40 (2004), 399 – 401.

4.Y. Kim and D.H. Kwon, CPW-fed planar ultra-wideband antenna having a frequency band notch function, Electron Lett 40 (2004), 403– 405.

© 2005 Wiley Periodicals, Inc.

NEW MICROSTRIP DIPLEXERS USING OPEN-LOOP RING RESONATORS WITH TWO TRANSMISSION ZEROS

Lung-Hwa Hsieh and Kai Chang

Department of Electrical Engineering

Texas A&M University

College Station, Texas 77843-3128

Received 2 August 2004

ABSTRACT: This paper presents a diplexer with good isolation constructed by two high-selectivity bandpass filters. The high-selec- tivity filter is designed by an asymmetrically fed structure that shows two transmission zeros next to the passband of the filter. By using a simple equation, the locations of the transmission zeros are designed at the passbands of the filters in order to filter out unwanted signals and obtain good isolation for the diplexer. The insertion loss of the diplexer is less than 2.2 dB and the isolation is greater than 41 dB. This high-performance diplexer can be used in many wireless communication systems. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 396 –398, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20647

Key words: transmission zeros; open-loop ring resonator; bandpass filter; diplexer

1. INTRODUCTION

A diplexer or multiplexer is one of important microwave components that is widely used in transceiver and mixer applications to isolate two or more frequencies [1, 2]. A diplexer is a multiport device that takes two or more frequencies at one port and produces selected frequencies at other ports. Diplexers can be constructed by different filter configurations such as lowpass and highpass filters, two bandpass filters, and bandpass and bandstop filters [3]. Also, different techniques designed for diplexers have been developed [4–7]. A diplexer needs to provide good isolation and low insertion loss. For low insertion loss, diplexers using high-tempera- ture superconductor (HTS) techniques or waveguide structures have been reported [8, 9]. Also, to obtain good isolation, filters in a diplexer need a high-selectivity characteristic in order to suppress unwanted signals. To achieve this characteristic, Levy introduced filters using a cross-coupled structure [10]. The cross coupling between nonadjacent resonators creates transmission zeros that improve the skirt rejection of the microstrip filters [11]. Recently, microstrip bandpass filters were proposed that used a parallel-coupled structure with asymmetric input and output feeders tapping on the first and the last resonators to obtain two transmission zeros [12, 13]. In comparison with the cross-coupled structure in [10, 11], this configuration using only two resonators can also provide a sharp cut-off frequency response. It has lower insertion loss due to less conductor losses and more compact. The locations of the two transmission zeros of the filter using parallel-coupled structure can be calculated by simple equations obtained from a simple transmission-line model [13].

In this paper, a diplexer using open-loop ring resonators with two transmission zeros is introduced. The diplexer using filters with the high-selectivity characteristic can obtain good isolation. In addition, the diplexer has low insertion loss due to less conductor loss and the compactness of the filters.

2. DIPLEXER DESIGN USING OPEN-LOOP RING RESONATORS

Figure 1 shows a filter using two open-loop ring resonators with asymmetric feeders. The input and output feeders divide the resonators into la and lb sections. The total length of the resonator is l la lb g/ 2, where g is the guided wavelength at the center frequency. Also, the locations of the transmission zeros of the filter can be simply calculated by [13]:

where f1 and f2 are the locations of two transmission zeros, n is the mode number, c is the speed of light, and eff is the effective dielectric constant. By using Eq. (1), a diplexer can be designed to obtain good isolation. Figure 2 shows an example of a diplexer designed at 2-GHz and 2.3-GHz passbands. According to Figure 2, the location of one of the transmission zeros of the filter A is

Figure 1 High-selectivity bandpass filter