4. CONCLUSION

We have shown that the simultaneous logic gate operation

between half adder and subtractor can be formed by using the

dark-bright soliton conversion system via the add/drop optical

filter, which is formed by all-optical circuit using microring and

nanoring device structures, in which the advantage of the simul-

taneous logic gate operation between the half adder and subtrac-

tor arithmetic are seen. By using the dark-bright soliton conver-

sion system, the input data logic 0 (dark soliton) and logic 1

(bright soliton) is established, in which the logic status results

simultaneously at the drop- and through-ports, respectively. In

application, this device will be the great component to use for

digital photonic circuit design and recognized as the simple and

flexible system for logic switching system, which can be

extended and implemented for any higher number of input digits

by a proper incorporation of dark-bright soliton conversion con-

trol base optical switches.

REFERENCES

1. J. Cong, X. Zhang, and D. Huang, A propose for two-input arbi-

trary Boolean logic gates using single semiconductor optical ampli-

fier by picosecond pulse injection, Opt Exp 17 (2009), 7725–7730.

2. S.H. Kim, J.H. Kim, B.G. Yu, Y.T. Byun, Y.M. Jeon, S.Lee, and

D.H. Woo, All-optical NAND gate using cross-gain modulation in

semiconductor optical amplifiers, Electronic Lett 41 (2005),

1027–1028.

3. J. Hun, Y.M. John, Y.T. Byun, S. Lee, D.H. Woo, and S.H. Kim,

All-optical XOR gate using semiconductor optical amplifiers with-

out additional input beam, IEEE Photon Tech Lett 14 (2002),

1436–1438.

4. S. Ma, Z. Chen, H. Sun, and K. Dutta, High speed all optical logic

gates based on quantum dot semiconductor optical amplifiers, Opt

Exp 18 (2010), 6417–6422.

5. T. Kawazoe, K. Kobayashi, K. Akahane, M. Naruse, N. Yama-

moto, and M. Ohtsu, Demonstration of nanophotonic NOT gate

using near-field optically coupled quantum dot, Appl Phys B 84

(2006), 243–246.

6. J.N. Roy and D.K. Gayen, Integrated all-optical logic and arithe-

metic operation with the help of a TOAD-based interferometer de-

vice-alternative approach, Appl Opt 46 (2007), 5304–5310.

7. L. Zhang, R. Ji, L. Jia, L. Yang, P. Zhou, Y. Tiam, P. Chen, and

Y. Lu, Demonstration of directed XOR/XNOR logic gates using

two cascaded microring resonators, Opt Lett 35 (2010),

1620–1622.

8. D.K. Gayen and J.N. Roy, All-optical arithmetic unit with the help

of terahertz-optical-asymmetric-demultiplexer-based tree architec-

ture, Appl Opt 47 (2008), 933–943.

9. J.N. Roya, A.K. Maitib, D. Samantac, and S. Mukhopadhyayc,

Tree-net architecture for integrated all-optical arithmetic operations

and data comparison scheme with optical nonlinear material, Opt

Switch Netw 4 (2007), 231–237.

10. P.P. Absil, J.V. Hryniewicz, B.E. Little, F.G. Johnson, and P.-T.

Ho, Vertically coupled microring resonators using polymer wafer

bonding, IEEE Photon Technol Lett 13 (2001), 49–51.

11. R. Grover, P.P. Absil, V. Van, J.V. Hryniewicz, B.E. Little, O.S.

King, L.C. Calhoun, F.G. Johnson, and P.-T. Ho, Vertically

coupled GaInAsP-InP microring resonators, Opt Lett 26 (2001),

506–508.

12. S. Mitatha, N. Pornsuwancharoen, and P.P. Yupapin, A simultane-

ous short-wave and millimeter-wave generation using a soliton

pulse with in a nano-waveguide, IEEE Photon Technol Lett 13

(2009), 932–934.

13. V. Van, T.A. Ibrahim, P.P. Absil, F.G. Johnson, and R. Grover,

Optical signal processing using nonlinear semiconductor micro ring

resonators, IEEE J Sel Top Quantum Electron 8 (2002), 705–713.

14. S. Mitatha, N. Chaiyasoonthorn, and P.P. Yupapin, Dark-bright op-

tical solitons conversion via an optical add/drop filter, Microw Opt

Technol Lett 51 (2009), 2104–2107.

15. S. Mookherjea and M.A. Schneider, The nonlinear microring add-

drop filter, Opt Exp 16 (2008), 15130–15136.

16. Q. Xu, D. Fattal, and R.G. Beausoleil, Silicon microring resonators

with 1.5-lm radius, Opt Exp 16 (2008), 4309–4315.

VC 2011 Wiley Periodicals, Inc.

A HIGH DUTY FACTOR 35-GHz PULSECOMPRESSION WEATHER RADAR ANDRAINFALL OBSERVATION

Hoon Lee and Yong-Hoon Kim

School of Information and Mechatronics, Gwangju Institute ofScience and Technology, 261 Cheomdan-gwagiro, Buk-gu,Gwangju 500�712, Republic of Korea; Corresponding author:yhkim@gist.ac.kr

Received 29 September 2010

ABSTRACT: A new millimeter wavelength vertical weather radarsystem has been developed. It uses pulse compression technique and has

the characteristics of more than half of duty factor with 5 W solid-statepower amplifier. Nonlinear FM waveforms based on Blackmanharris

function at transmitter are generated for range sidelobe suppression. Wesuccessfully obtained equivalent radar reflectivity and Doppler meanvelocity and these were compared with MRR at moderate rain events for

the system verification. VC 2011 Wiley Periodicals, Inc. Microwave Opt

Technol Lett 53:1544–1547, 2011; View this article online at

wileyonlinelibrary.com. DOI 10.1002/mop.26026

Key words: weather radar; millimeter wave radar; pulse compression;nonlinear waveform

1. INTRODUCTION

Out of many meteorological sensors, radar has a significant role

especially in a short-term prediction and for the warnings of haz-

ardous weather. Current operational weather radars are mostly S-

or C-band, bulky, high power, long range, pulse radars. These

cannot be effective for the network extension in surroundings

with much terrain blockages like the mountainous area. There are

researches to supplement or substitute such long range radar net-

works with short-wavelength distributed networks of small radar

systems via groups such as CASA [1]. Meanwhile, there are

researches to use a pulse compression technique in weather radar

to get a finer range resolution with a lower peak power. For a

given resolution, as opposed to pulse radar, it is estimated to pro-

vide increased sensitivity, possibility of lower measurement error

and higher scan speeds [2]. Although FMCW radars have been

used for certain application, linearity is critical for the range accu-

racy, but for pulse compression modulation is not limited to linear

chirp. We started to base our research on two streams above. We

developed a test-bed and performed initial experiments [3]. In

this article, detailed description of our radar structure is stated

and new experimental results are presented. For nonlinear wave-

form generation in the transmitter Blackman–Harris window

function is selected. We observed moderate rainfall and estimated

equivalent reflectivity and mean velocity. They were compared

with the data by Micro Rain Radar (MRR) which is vertically

pointing 24-GHz FMCW radar [4].

2. SYSTEM DESCRIPTION

A block diagram of the developed Ka-band radar is shown in

Figure 1. This radar system consists of a waveform generator, a

transmitter, two antennas, a receiver, two local oscillators, data

1544 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 53, No. 7, July 2011 DOI 10.1002/mop

acquisition unit, and digital signal processing part. For fully

coherent processing, direct digital synthesizer (DDS), field pro-

grammable gate array (FPGA), data acquisition of digital re-

ceiver and two-phased lock loops for local oscillators (LO) are

synchronized with a common reference clock.

2.1. Waveform GeneratorUsing DDS and fast FPGA control, 38.75–48.75 MHz of nonlinear

waveform were generated using Blackman–Harris window function

for good range sidelobe performance. For 10 MHz of FM bandwidth

and 128-ls pulsewidth, delta frequency, which means regular inter-

val change in frequency value was obtained and saved at FPGA.

Pulse repetition interval were designed as 250-ls considering drop

velocity of rain. Triggering signal which revealed the starting point

of the generated pulse is transferred to digital receiver unit.

2.2. TransmitterBaseband chirp signal was converted to 450 ~ 500 MHz interme-

diate frequency (IF) region, depending on selected channel fre-

quency by 2nd LO using a single sideband mixer. It has the more

than 40 dB of image rejection characteristic. After amplification

and filtering, signal was again converted to 35.5–36 GHz radio

frequency (RF) region, depending on selected band frequency by

1st LO using a double balanced mixer. After RF bandpass filter,

solid-sate high power amplifier (HPA) was used for amplification

up to 5 W. Around 51.2% duty factor is achieved with the use of

HPA. In practical pulse compression weather radar at Ref. 5, only

4% of duty factor is achieved with TWT power device. High duty

factor system can decrease the peak transmitter power, but range

sidelobe effects are lasted up to long ranges.

2.3. AntennasWe used separated antennas for the transmitter and receiver to

detect targets near the ground considering long pulse duration. Pre-

viously developed plano-convex type lens antenna feeing with cor-

rugated circular horn were used [6]. It showed the gain of 36 dBi, 3

dB beamwidth of 2.2� and less than�30 dB of sidelobe level.

2.4. Receiver2.8-dB low noise amplifier is used and total receiver noise figure

is maintained below 4 dB. Using 1st LO, RF signal down-con-

verted to IF but it is directly connected to digital receiver unit

with additional amplifying and filtering.

2.5. Digital Receiver and Signal ProcessingIF signal is down converted by 100-MHz analog digital convert-

ing step using under-sampling (bandpass sampling) technique.

This is for extracting adjacent radar sites’ information in future

network application. Digital processing is divided into two proc-

essing, a signal processing by extracting IQ data via pulse com-

pression and a data processing to extract meteorological parame-

ters, i.e., equivalent radar reflectivity and velocity from IQ data.

These were built-in MATLAB.

3. EXPERIMENTAL SETUP

The developed radar was installed at national institute of mete-

orological research (NIMR) Daekwanryoung site, Gangwon

province, Korea in July of 2010 as shown in Figure 2. It was

covered with thin vinyl for protecting modules during

Figure 1 Block diagram of the Ka-band fully coherent Doppler weather radar

Figure 2 Experimental Set-up at NIMR Daekwanryong site, on July

of 2010. [Color figure can be viewed in the online issue, which is avail-

able at wileyonlinelibrary.com]

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 53, No. 7, July 2011 1545

measurements. MRR was located at 10 m away, and there are

additional meteorological equipments at that site. MRR data

were acquired as an initial setup of 30 s time resolution, 200-m

range resolution and 30 range gates. Our radar captured 64 num-

bers of pulses every 2 or 5 s and stored to PC. The display reso-

lution was 12 m and effective number of range gate was 1525.

4. EXPERIMENTAL RESULT

Although there are differences between our radar and MRR in

terms of frequency, transmitting power, antenna, modulation, data

processing, etc, the overall patterns of reflectivity profiles are sim-

ilar. Figures 3 (a) and 3(b) shows time-height cross section of ra-

dar reflectivity factor by MRR and our developed radar respec-

tively. For our radar, time and spatial resolutions are better and

sensitivity is enhanced. Estimated reflectivity value is relative low

mainly due to frequency difference. Additional algorithms for

considering attenuation and Mie scattering effect will be necessary

for the next step. Although the isolation between transmitter and

receiver is more than 70 dB, considerable power is still transferred

from transmitter to receiver directly. It affects as a horizontal line

at (b) after processing. Figures 4 (a) and 4(b) shows the estimated

reflectivity and mean Doppler velocity of our radar for the strati-

form type rainfall on July 17, 2010. At 3.6 km, the bright band,

where ice particles changes into water and the reflectivity grows

up rapidly, were observed. Figures 5 (a) and 5(b) shows the verti-

cal profile of radar reflectivity and mean Doppler velocity with

bright band at 01:10 in Figure 4. For comparison with MRR data,

extracted data were again averaged for 30 s in time and 200 m in

space. Although MRR data were processed smoothly, the overall

structure shows quite similar pattern. Our radar has finer resolu-

tion and the detailed structure of rain is clearly shown.

5. CONCLUSIONS

In this study, we have developed the Ka-band weather radar and

observed precipitation events vertically. Using nonlinear wave-

form and pulse compression technique, the radar was imple-

mented with solid-state amplifier as a 51.2% duty factor system.

The observation shows the structure of rainfall successfully with

finer resolution in time and space. Real time signal processing is

Figure 3 Time-height cross section of radar reflectivity factor by (a)

MRR (b) our radar on July 16, 2010. [Color figure can be viewed in the

online issue, which is available at wileyonlinelibrary.com]

Figure 4 Time-height cross section of (a) radar reflectivity and (b)

mean Doppler velocity measured on July 17, 2010. [Color figure can be

viewed in the online issue, which is available at wileyonlinelibrary.com]

Figure 5 Vertical profile of averaged (a) radar reflectivity and (b)

mean Doppler velocity at 01:10 in Figure 4. [Color figure can be viewed

in the online issue, which is available at wileyonlinelibrary.com]

1546 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 53, No. 7, July 2011 DOI 10.1002/mop

being implemented in our group. Furthermore, the compensa-

tions of algorithm will be kept on.

ACKNOWLEDGMENTS

This work was supported in part by the Brain Korea program

(BK21) at Gwangju Institute of Science and Technology, Korea

and millisys, Inc. of Korea.

REFERENCES

1. D. McLaughlin, D. Pepyne, V. Chandrasekar, B. Philips, J. Kurose,

M. Zink, K. Droegemeier, S. Cruz-Pol, F. Junyent, J. Brotzge, D.

Westbrook, N. Bharadwaj, Y. Wang, E. Lyons, K. Hondl, Y. Liu,

E. Knapp, M. Xue, A. Hopf, K. Kloesel, A. Defonzo, P. Kollias,

K. Brewster, R. Contreras, B. Dolan, T. Djaferis, E. Insanic, S.

Frasier, and F. Carr, Short-wavelength technology and the potential

for distributed networks of samll radar systems, Bull Am Meteorol

Soc 90 (2009), 1797–1817.

2. T. Puhakka, V. Chandrasekar, and P. Puhakka, Evaluation of FM

pulse compression for weather radars, AMS 33rd Conference on

Radar Meteorology, 2007.

3. H. Lee and Y.H. Kim, Weather radar network with pulse compres-

sion of arbitrary nonlinear waveforms: Ka-band test-bed and initial

observations, Prog Electromagn Res B 25 (2010), 75–92.

4. Available at: http://www.metek.de/produkte.htm.

5. F.O’.Hora and J. Bech, Improving weather radar observation using

pulse-compression techniques, Meteorol Appl 14 (2007), 389–401.

6. H. Lee and Y. H. Kim, A 35 GHz narrow beam lens antenna for

aircraft mounting collision warning radar, MM-Wave Radar & Ra-

diometer Forum, Korea, 2004.

VC 2011 Wiley Periodicals, Inc.

BANDWIDTH ENHANCEMENT OFA U-SLOT PATCH ANTENNA USINGDUAL-BAND FREQUENCY-SELECTIVESURFACE WITH DOUBLE RECTANGULARRING ELEMENTS

Hsing-Yi Chen and Yu Tao

Department of Communications Engineering, Yuan Ze University,135 Yuan-Tung Road, Nei-Li, Chung-Li, Taoyuan Shian 32003,Taiwan; Corresponding author: eehychen@saturn.yzu.edu.tw

Received 29 September 2010

ABSTRACT: A design strategy using a dual-band frequency-selectivesurface (FSS) consisting of double rectangular ring elements to improve

the bandwidth and gain and to optimize the onsets of two operatingfrequencies for a U-slot patch antenna is presented. After implanting the

FSS in the U-slot patch antenna, it was found that the bandwidths havebeen improved from 3.14% to 5.51% and 5.48% to 7.48% at resonantfrequencies 2.45 and 5.8 GHz, respectively. It was also found that the

antenna gain and the onset of operating frequency have been improvedfor Bluetooth and wireless local area network (WLAN) applications. TheU-slot patch antenna implanted with a FSS consisting of double

rectangular ring elements is capable of dual-band operations at 2.45and 5.8 GHz. The radiation patterns are satisfied at these dual bands.VC 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1547–

1553, 2011; View this article online at wileyonlinelibrary.com.

DOI 10.1002/mop.26066

Key words: frequency-selective surface; U-slot patch antenna;bandwidth; gain; radiation patterns

1. INTRODUCTION

A patch antenna has inherent advantages of small size, low pro-

file, lightweight, cost effect, and its ease of integration with

other circuits. It is very suitable for applications in wireless

communication systems. For today’s wireless communications,

multiband and wide-band patch antennas will become the

requirements for accurately transmitting the voice, data, video,

and multimedia information. However, the most serious problem

of a patch antenna is its narrow bandwidth because a patch

antenna on a dielectric substrate has a very narrow bandwidth due

to surface wave losses. Therefore, how to enhance the bandwidth

and frequency bands of a patch antenna has become an important

issue in the antenna design field. In recent years, to achieve multi-

band and wide-band operation in a patch antenna design, the fre-

quency-selective surface (FSS) is implemented or imbedded in a

patch antenna to carry out the goal. The FSS structure has a phe-

nomenon with high impedance surface that reflects the plane

wave in-phase and suppresses surface wave. Therefore, a patch

antenna with one FSS structure can improve its radiation effi-

ciency, bandwidth, gain, and reduce the side lobe and back lobe

level in its radiation pattern. The FSS has been widely applied in

antennas, filters, reflectors, polarizers, absorbers, propagation,

metamaterials, and artificial magnetic conductors for more than

four decades [1–36]. The FSS is usually constructed with periodic

arrays of metallic patches of arbitrary geometries or slots within

metallic screens. Typical FSS geometries are designed by dipoles,

rings, square loops, fractal shapes, etc. The transmission or reflec-

tion characteristic of a FSS depends on the shape, size, periodic-

ity, and geometrical structure of FSS elements.

In this article, a dual-band FSS consisting of double rectan-

gular ring elements was used to study its impact on the band-

widths and resonant frequencies of a U-slot patch antenna oper-

ating near 2.45 and 5.8 GHz. The frequency bands of 2.4–2.485

and 5.725–5.825 GHz are regulated by IEEE 802.11b/g and

802.11a (upper band) for Bluetooth and WLAN applications,

respectively. In simulations, the characteristics of U-slot patch

antennas were obtained by using the Ansoft high-frequency

structure simulator (HFSS, Ansoft, Pittsburgh, PA). Simulation

results of the return loss, radiation pattern, and gain of this U-

slot patch antenna were validated by measurement data.

2. THE ANTENNA AND FSS

Figure 1 shows a U-slot patch antenna and its dimensions. The

dimensions of the patch antenna are 76 � 52 mm2, and the

thickness of the substrate is 4.4 mm. The dimensions of the rec-

tangular U-slot radiator patch are 30 � 54 mm2. The length and

width of the U-slot are 28.4 and 11.2 mm, respectively. The

width of the slot is 2 mm. In our studies, a coaxial line with a

characteristic impedance of 50 X is used as the feed of the U-

slot patch antenna. The inner conductor of the coaxial line is

attached on the top patch going through the dielectric substrate,

Figure 1 A U-slot patch antenna and its dimensions. [Color figure can be

viewed in the online issue, which is available at wileyonlinelibrary.com]

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 53, No. 7, July 2011 1547