end in Ref. 1, our receiver achieved comparable conversion gain

and NF, and lower power consumption. Compared with the re-

ceiver front end in Ref. 2, our receiver achieved comparable

NF, higher conversion gain, and lower power consumption.

4. CONCLUSIONS

In this article, we report a monolithic receiver front end com-

prising an LNA, a mixer, an IF amplifier, and an IF filter imple-

mented in a standard 0.18 lm CMOS technology. The receiver

front end consumed a low power of 43.2 mW, and achieved a

high conversion gain of 20.3 dB and a low noise of 8.6 dB.

Besides, excellent LO–RF, RF–IF, and LO–IF isolation were

also achieved. These results indicate that the proposed receiver

front end architecture is very promising for high-performance

K-band (18–26 GHz) RFIC applications.

ACKNOWLEDGMENTS

This work is supported by the National Science Council of the

ROC under contracts NSC 97-2221-E-260-009-MY3 and NSC 97-

2221-E-260-010-MY3. The authors are very grateful to the support

from the National Chip Implementation Center (CIC), Taiwan, for

chip fabrication, and National Nano-Device Laboratory (NDL),

Taiwan, for measurements.

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1. X. Guan and A. Hajimiri, A 24 GHz CMOS front-end, IEEE J Sol-

id-State Circuits 38 (2004), 368–373.

2. R.M. Kodkani and L.E. Larson, A 24-GHz CMOS sub-harmonic

mixer based zero-IF receiver with an improved active balun, In:

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pp. 673–676.

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dam, Holland, October 2008, pp. 350–353.

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stability using geometrically derived parameters, IEEE Trans

Microw Theory Tech 40 (1992), 2303–2311.

7. S.G. Lee and J.K. Choi, Current-reuse bleeding mixer, IET Elec-

tron Lett 36 (2000), 696–697.

VC 2011 Wiley Periodicals, Inc.

FREQUENCY-TUNABLE TERAHERTZELECTROMAGNETIC-PULSESGENERATION BASED ON AN OPTICALFABRY–PEROT MICRORESONATOR WITHVARIABLE BIREFRINGENCE MATERIAL

Ming ChenResearch Institute of Optoelectronics and School of Informationand Communication, Guilin University of Electronic Technology,1 Jinji Way, Guilin 541004, People’s Republic of China

Received 26 February 2011

ABSTRACT: A frequency-tunable terahertz (THz)-frequency

electromagnetic-pulses generation method is proposed based on an

Figure 8 Measured (a) LO–RF and LO–IF isolation vs. LOin charac-

teristics and (b) RF–IF isolation vs. RFin characteristics of the receiver

front end

TABLE 1 Summary of the Implemented 21-GHz CMOSReceiver Front End and Recently Reported K-BandState-of-the-Art CMOS Receiver Front Ends

This

Work

[1],

2004-JSSC

[2],

2009-CICC

CMOS technology (lm) 0.18 0.18 0.13

RF (GHz) 21 21.8 24

IF (GHz) 2.4 4.9 0.03

Conversion gain (dB) 20.3 27.5 12.5

NF (dB) 8.6 7.7 < 9

RF–IF isolation (dB) 57.3 NA NA

LO–RF isolation (dB) 51.1 NA <–65.5

LO–IF isolation (dB) 30.9 NA NA

Power consumption (mW) 43.2 64.5 140.8

Chip area (mm2) 0.873 0.72 3

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 53, No. 12, December 2011 2879

optical Fabry–Perot (FP) microresonator with variable birefringencematerials. At the output FP microcavity, polarization mode beat with

high-frequency can be achieved due to the phase mismatch effect of thetwo polarization modes in the birefringence materials in the FP cavity.One can generate frequency-tunable electromagnetic pulse radiation

through changing the birefringence of the materials. When thebirefringence changed from 3.7355 � 10�4 to 7.4710 � 10�2,electromagnetic-pulses with frequencies from 0.05 to 10.0 THz can be

obtained. VC 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett

53:2879–2882, 2011; View this article online at wileyonlinelibrary.com.

DOI 10.1002/mop.26422

Key words: birefringence; Fabry–Perot; terahertz optics and devices

1. INTRODUCTION

Terahertz (THz) radiation [1], with frequencies from 0.1 to 10

THz, has attracted considerable attention over the last decade

due to its big potential for applications, such as spectroscopy

[2], imaging [3], sensing [4], communications [5], and so forth.

Many of THz technologies have been developed to achieve THz

sources [1, 6], waveguides [7, 8], and other devices. Among

them, effective, compact, and robust THz radiation sources with

high output power are very important for all of the THz applica-

tions. Many technological advances in optics and electronics

have resulted in many different types of THz sources including

continuous-wave and pulses [1, 6, 9, 10].

2. FABRY–PEROT MICRORESONATOR WITH VARIABLEBIREFRINGENCE MATERIAL

We demonstrate a novel frequency-tunable THz pulses genera-

tion method based on a Fabry–Perot (FP) microcavity with vari-

able birefringence material. Figure 1 schematically shows the

FP cavity. The variable birefringence material can be birefrin-

gence optical crystals or birefringence optical fibers or high bire-

fringence microstructure fibers, and so forth. The birefringence

can be changed using voltage, temperature, or stress over the

material. Two reflective mirrors, as the shadow part in the figure

shows, are tightly close to the two ends of the cavity. Two lin-

ear polarizers I and II are located before and after the FP cavity.

The effective axes of the birefringence material are the x-axisand y-axis. x1 and y1 are the two orthogonal principal polariza-

tion axes of the linear polarizer II. a and b denote the azimuthal

angles of the polarizer I and II with respect to the effective axes

of the birefringence material in the FP cavity, respectively.

3. THEORY FOR THz ELECTROMAGNETIC-PULSESGENERATION

The polarization effect has been subject to numerous investi-

gated [11, 12]. To simplify the calculation, we suppose that the

initial electric amplitude and intensity of the input light, which

transmitted into the FP cavity after the polarizer I, are E0 and

I0, respectively, I0 / E20. The light in the birefringence resonator

accumulates a phase-shift after one single roundtrip of

ui ¼4pniLk0

(1)

where i ¼ x, y, ui, and ni are phase-shift and effective refractive

index of polarization mode in the i direction, respectively. L ¼1 mm is the length of the birefringence material and is also the

length of the FP cavity because that the cavity mirrors is tightly

close to the two fiber ends. k0 is the wavelength of the light in

vacuum. After one roundtrip, the electric field in the cavity is

expressed as rE0i expð�juiÞ, where E0 is the initial field ampli-

tude and r denotes the amplitude attenuation due to cavity mir-

rors and absorption and scattering of the fiber medium,

j ¼ ffiffiffiffiffiffiffi�1p

. The phase difference of the two polarization modes

after one single roundtrip is

Du ¼ ux � uy

��

�� ¼ 4p

k0nx � ny��

�� ¼ 2kpþ Du0 (2)

where k is an integer number, 0 < Du0 � 2p. When a mono-

chromatic light with constant amplitude is continuously injected

into the cavity, the complex cavity field amplitude after mroundtrips will be

EðmÞi ¼ 1� rmþ1 exp½�juiðmþ 1Þ�

1� r expð�juiÞE0f ðaÞ (3)

if i ¼ x, f að Þ ¼ cosðaÞ, else f að Þ ¼ sinðaÞ. When the injecting

light is suddenly cancelled after m roundtrips time, the remain-

ing light in the cavity is still to transmit in the cavity for l addi-tional roundtrips and the electric filed can be written as

Eðm;lÞi ¼ rl expð�jluiÞEðmÞ

i (4)

After the polarizer II, the output electric field is expressed as

Ex1 ¼ E m;lð Þx cos bþ E m;lð Þ

y sin b (5a)

Ey1 ¼ E m;lð Þy cos bþ E m;lð Þ

x sin b (5b)

The normalized intensity of the output polarization mode to I0 is

INq¼ Iq

I0¼ Eq

��

��2

E0j j2 (6)

where q indicates x1 or y1, x1 and y1 denote the two output

polarization modes (x1-direction and y1-direction), respectively.von Lerber et al. [13] have shown that there include a natural

beat signal, resulting from the homodyne process of combination

of the two output polarization modes, can be expressed as

Ibeat ¼ E�ðm;lÞx Eðm;lÞ

y þ Eðm;lÞx E�ðm;lÞ

y (7)

Figure 1 Fabry–Perot resonator with variable birefringence materials

and two polarizes

2880 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 53, No. 12, December 2011 DOI 10.1002/mop

where quantity E* denotes the complex conjugate quantity of

the corresponding quantity E. The frequency of the homodyne

beat signal fB is

fB ¼ cDu4pnL

¼ c nx � ny��

��

nk0¼ cDn

nk0(8)

where Du is the phase-shift difference of the two light polariza-

tion modes after one roundtrip, c ¼ 299,792,458 m/s is the light

speed in vacuum. n denotes the average refraction index of the

two polarization modes, Dn indicates the difference of the two

polarization mode refractive indices and Dn � n.

4. CONCLUSION AND DISCUSSION

In our calculation, k0 ¼ 1.55 lm, n ¼ 1.45. Figure 2 shows the

relation between the frequency of the generated beat signal fBand the difference of the two polarization mode refractive indi-

ces Dn. This relation is resulted from Eq. (8). As shown in this

figure, when the difference of the two polarization mode refrac-

tive indices Dn ¼ 7.4710 � 10�3, the frequency of the gener-

ated beat signal fB ¼ 1.0 � 1012 Hz. When the difference of the

two polarization mode refractive indices Dn is changed from Dn¼ 3.7355 � 10�4 to Dn ¼ 7.4710 � 10�2, the frequencies of

the generated beat signal pulses with frequencies from 0.05 to

10.0 THz can be obtained. These frequencies (between 0.1 and

10.0 THz) of the generated beat signal pulses are within the

THz ranges. The dynamical variation of the difference of the

two polarization mode refractive indices Dn can be achieved by

tuning the high birefringence material in the FP resonator cavity.

For example, the high birefringence microstructure fibers based

on novel photonic crystal technologies can be used in our

method. The birefringence of some microstructure fibers can be

reached as high as 10�2 [14]. Those high birefringence micro-

structure fiber techniques may be used to fabricate our FP

microcavity for THz.

Now, we investigate the characteristics of this device struc-

ture with an input monochromatic light with constant amplitude

into the cavity after an on–off optical switch. By the optical

switch, we can control the light injected into the cavity or can-

celed the input light suddenly. Firstly, we suppose that the dif-

ference of the two polarization mode refractive indices Dn ¼7.4710 � 10�3. This means that the frequency of generated beat

signal pulses is 1.0 THz, as shown in Figure 2. Let r ¼ 0.99,

a ¼ b ¼ p/4 in our calculation.

Figure 3(a) shows the injected light intensity after the on–off

switch. The light with intensity I0 is injected into the cavity

firstly, and then the light is cancelled by the on–off switch sud-

denly after 1000 roundtrips time, the light is turned on again

after other 1000 roundtrips time, and recycle continuously like

that every other 1000 roundtrips time, as shown in Figure 3(a).

Figures 3(b)–3(d) shows the normalized intensity of total output

light, normalized intensity of output x1-direction polarization

mode, and normalized intensity of output y1-direction polariza-

tion mode after the polarizer II, respectively. In these three

figures, there are three phases intensity-increasing phase, inten-

sity-stability phase, and intensity-descending phase. When light

with constant intensity is injected into the microcavity, light in-

tensity is increasing with time increasing in the cavity, this is

the intensity-increasing phase. After some time, light intensity

reaches a maximum value in the cavity. When the input light is

ceased, light intensity is decreasing with time increasing in the

cavity, this is intensity-descending phase. After some time, light

intensity reaches a minimum value in the cavity. When light

intensity reaches the minimum value or the maximum value,

intensity-stability phase is reached. In Figure 3, time axes are

normalized by one roundtrip time. The generated beat signals

are depicted in Figure 3(e). We can conclude that the beat sig-

nals are generated during the intensity-increasing phase or inten-

sity-descending phase. In the intensity-stability phase, no beat

Figure 2 Frequency of the generated beat signal fB versus the differ-

ence of the two polarization mode refractive indices Dn

Figure 3 Intensity of injected light after an on–off optical switch (a)

and output characteristics after the polarizer II (b)–(e)

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 53, No. 12, December 2011 2881

signals can be generated. This is to say that beat signals are gen-

erated during the light intensity variation result from the com-

bined function of the FP microcavity and the on–off input light.

Figure 4 shows the beat signals, generated based on our pro-

posed method, with frequency of 1.0 THz in detail. The two

inset figures demonstrate a segment of beat signals generated

during the intensity-increasing phase and a segment of beat sig-

nals generated during the intensity-descending phase,

respectively.

This method may be used as an effective tool or imple-

mented. One can obtain frequency-tunable THz electromagnetic-

pulses using an optical FP microcavity with variable birefrin-

gence material because of the linear dependence between the

birefringence of the variable birefringence material and the fre-

quency of the generated beat signal. In principle, one can obtain

electromagnetic pulse radiation with frequencies from 0.05 to

10.0 THz, when the difference of the two polarization mode

refractive indices Dn is changed from Dn ¼ 3.7355 � 10�4 to

Dn ¼ 7.4710 � 10�2. This method also can be used to generate

high-frequency microwaves.

ACKNOWLEDGMENT

This work has been supported by the Foundation of Guangxi Key

Laboratory of Information and Communication

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New York, NY, 2009.

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pulsed spectroscopic, Appl Phys Lett 86 (2005), 241116–241118.

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ing, Nature 432 (2004), 376–379.

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and G.P. Williams, High-power terahertz radiation from relativistic

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Giles Davies, D.A. Ritchie, R.C. Iotti, and F. Rossi, Terahertz

semiconductor-heterostructure laser, Nature 417 (2002), 156–159.

11. N. Damask, Polarization optics in telecommunications, Springer,

New York, NY, 2004.

12. I. Kaminow and T.Y. Li, Optical telecommunications IVB, Aca-

demic Press, Orlando, FL, 2002.

13. T. von Lerber, H. Ludvigsen, and A. Romann, Resontor based

measurement technique for quantification of minute birefringence,

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VC 2011 Wiley Periodicals, Inc.

A CPW-FED SLOT ANTENNA WITHEMBEDDED RING-TYPE STRIP FORDUAL-FREQUENCY OPERATION

Meng-Ju Chiang,1 Chia-Yen Wei,2 and Sheau-Shong Bor31 Department of Antenna and Wireless System Integration, HTCCorporation, Xindian City, Taipei County 231, Taiwan;Corresponding author: mengjuchiang@gmail.com2Ph.D. Program in Electrical and Communications Engineering,Feng-Chia University, Taichung 407, Taiwan3Department of Electrical Engineering, Feng-Chia University,Taichung 407, Taiwan

Received 2 March 2011

ABSTRACT: The coplanar waveguide-fed planar slot antenna with the

embedded ring-type strip for dual-frequency operation is investigatedand experimentally explores in this letter. The prototype, which isimplemented on the 0.8-mm FR-4 substrate with er ¼ 4.4, indicates that

the embedded ring-type strip offers extended path for the electriccurrent flow, achieving 45.1% size reduction of the fundamental

resonant mode. The ratio of the center frequencies of the first tworesonant bands can be tuned within a range wider than 1.81 byincreasing the radius and line width of ring-type strip. Furthermore, the

fundamental resonant mode can be shifted to the higher frequency tocombine with the second resonant mode of the circular slot, indicating

the wideband operation with the bandwidth of 1332 MHz (40.5%).VC 2011 Wiley Periodicals, Inc. Microwave Opt Technol

Lett 53:2882–2887, 2011; View this article online at

wileyonlinelibrary.com. DOI 10.1002/mop.26370

Key words: slot antennas; multifrequency antennas; minimizationmethods

1. INTRODUCTION

A literature survey shows that there has been a growing research

activity on the printed slot antenna design, which facilitates sim-

ple prototype, compactness, and robustness for the industrial

realization. As a result, there are several simple and effective

techniques for improvement of the miniaturized planar slot

antenna with dual-frequency operation [1–8]. The dual-band slot

antenna can be realized in the following three types. First is the

slot antenna used modified slot, or multislot to obtain two or

multiple operating bands [1–3]. The second approach employs

parasitic wire or back patch designs to generate operating bands

[4–6]. Third technique is adopted the embedded strip inserted

Figure 4 Beat signals with frequency of 1.0 THz generated by the

birefringence FP microcavity structure

2882 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 53, No. 12, December 2011 DOI 10.1002/mop