the second case with a 10° down-tilt. Figure 6 shows the radiation
patterns of the four-element antenna arrays. Both antenna arrays
have an H-plane beam width of 70° and an E-plane beam width of
16°. Radiation patterns of the six-element arrays are shown in
Figure 7. Both arrays have an H-plane beam width of 69° and an
E-plane beam width of 12°. Figure 8 shows radiation patterns of
the eight-element antenna arrays. Again, both arrays have a 69°
H-plane beam width and a 9° E-plane beam width.
CONCLUSION
By means of using the L-probe coupling technique, several low-
cost wideband patch antenna arrays have been designed and pre-
sented in this paper. By optimizing element spacings and element
phases, the radiation pattern of each array is shaped to have upper
side-lobe suppression and lower side-null filling. These arrays can
be used as base station antennas for both CDMA 800 and GSM
900 cellular communication systems.
ACKNOWLEDGMENTS
This work is supported by the Research Grant Council of Hong
Kong under the project CityU 1231/00E, and the Croucher Foun-
dation under the Senior Research Fellowship award to Prof. K. M.
Luk.
REFERENCES
1. H. Wong and K.M. Luk, A dual polarized L-probe patch antenna, IEEE
Trans Antennas Propagat (2001), 930 –933.
2. C.L. Mak, K.M. Luk, K.F. Lee, and Y.L. Chow, Experimental study of
a microstrip patch antenna with an L-shaped probe, IEEE Trans An-
tennas Propagat (2000), 777–783.
3. H. Wong, H.W. Lai, and K.M. Luk, A low-cost L-probe patch antenna
array, IEEE Trans Antennas Propagat (2000), 18 –21.
4. R. Chair, K.M. Luk, and K.F. Lee, Wideband L-probe-fed 4-element
array with unequal spacing, IEEE Trans Antennas Propagat (2000),
938 –941.
© 2003 Wiley Periodicals, Inc.
RF PARAMETER EXTRACTION OF
MMIC NICHROME RESISTORS
Renu Sharma, Seema Vinayak, D. S. Rawal, Ashok Kumar,
and U. C. Ray
Solid State Physics Laboratory
Lucknow Road
Delhi–110054, India
Received 20 May 2003
ABSTRACT: The lumped-element electrical equivalent circuit of nichrome
(NiCr) resistors is important for monolithic microwave integrated circuit
(MMIC) design. This paper presents a methodology for the RF parameter
extraction of thin-film NiCr resistors fabricated on GaAs substrate. An algo-
rithm based on DUT S parameters has been developed to extract the elec-
trical parameters of the equivalent circuit up to 18 GHz for a large number
of resistors of varying geometries and geometry-scaleable curve-fitted equa-
tions for the model parameters have been obtained. The computed S pa-
rameters, based on the extracted model parameters, agree reasonably well
with the measured S parameters. © 2003 Wiley Periodicals, Inc. Microwave
Opt Technol Lett 39: 409–412, 2003; Published online in Wiley Inter-
Science (www.interscience.wiley.com). DOI 10.1002/mop.11233
Key words: nichrome resistors; MMIC; RF modelling
INTRODUCTION
MMICs consist of planar-integrated active and passive elements
that determine the circuit operation. Passive elements are com-
posed of lumped elements such as resistors, capacitors, and induc-
tors, and distributed elements such as transmission lines. In MMIC
technology, the resistors are extensively used in feedback circuits
and bias circuits, and as terminations. Two types of resistors are
commonly used in MMIC fabrication, namely, thin films of lossy
metals and lightly doped GaAs active layer (Mesa Resistors) [1].
Metal thin-film resistors are more temperature stable and are used
as precision resistors of low-to-moderate values. These are usually
fabricated from TaN and NiCr, although other metals may be used
[1, 2]. NiCr resistors have low TCR and small parasitics, and are
widely used in circuit design [3, 4].
In this paper, we present RF measurements and lumped-ele-
ment modelling of thin-film NiCr resistors for integration in GaAs
MMICs. The first wafer in the fabrication of the NiCr resistor is a
200-m-thick semi-insulating GaAs substrate on which 0.1-m
plasma-enhanced chemical vapour deposition (PECVD) silicon
nitride has been deposited. The NiCr thin films (400 Å) were
deposited on them by magnetron RF sputtering technique. The
NiCr resistor library with resistance values ranging from 5 to
2K were fabricated by a process compatible with GaAs MMIC.
The RF measurements were carried out on different resistors in the
Figure 5 Gain of the four-, six-, and eight-element arrays
Figure 4 SWR of the four-, six-, and eight-element arrays
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 39, No. 5, December 5 2003 409