Type of Document Master's Thesis Author Zhao, Jun Author's Email Address email@example.com URN etd-08222002-152733 Title Development of Integrated "Chip-Scale" Active Antennas for Wireless Applications Degree Master of Science Department Electrical and Computer Engineering Advisory Committee
Advisor Name Title Raman, Sanjay Committee Chair Stutzman, Warren L. Committee Member Sweeney, Dennis G. Committee Member Keywords
- Microstrip antenna
- power amplifier
- integrated antenna
Date of Defense 2002-07-26 Availability unrestricted AbstractWith the rapid expansion of wireless communication services, ultra-miniature, low
cost RF microsystems operating at higher carrier frequencies (e.g. 5-6 GHz) are in
demand for various applications. Such applications include networked wireless sensor
nodes and wireless local area data networks (WLANs). Integrated microstrip antennas
coupled directly to the RF electronics, offer potential advantages of low cost,
reduced parasitics, simplified assembly and design flexibility compared to systems
based on discrete antennas. However, the size of such antennas is governed by physical
laws, and cannot be arbitrarily reduced. The critical patch antenna dimension
at resonance needs to be ~λg/2 (where λg is the guided wavelength given by λg
=λ/sqrt(er) . Several methods are available to reduce the physical size of the antenna
to enable on-chip integration. A high dielectric constant substrate reduces the guided
wavelength. Grounding one edge of the microstrip patch enables the resonant antenna
length to be further reduced to ~λg/4. However, these techniques result in degraded
antenna efficiency and bandwidth. Nonetheless, such antennas still have potential for
use in low power/short range applications.
In this work, "electrically small" (small with respect to λo) square-shaped microstrip
patch antennas, grounded on one edge by shorting posts, have been investigated. The
antenna input impedance depends on the feed position; by adjusting the feed point,
the antenna can be tuned to match a 50 Ω or other system impedance. The antennas
were designed on a GaAs substrate, with a high dielectric constant of 12.9. The size of the patch antenna is further reduced by utilizing shorted through substrate vias
along one edge. The size of the antenna is about 4.2mm × 4.2mm, which is ~1/13 of
λo at ~5.6GHz. The antennas are practical for integration on chip. Due to the size
reduction, the simulated peak gain of the antenna is only −10.2 dB ( ~3.2% radiation
efficiency). However, this may be acceptable for short-range wireless communications
and distributed sensor network applications.
Based on the above approach, integrated GaAs "chip-scale" antennas with matching power amplifiers have been designed and fabricated. Class A tuned MESFET
power amplifiers (PAs) were designed with outputs directly matched to the antenna
feed point. The antenna is fabricated on the backside of the chip through backside
patterning; the PA feeds the antenna through a backside via. The structure is then
mounted such that the antenna faces up, and is compatible with flip-chip technology.
The measurement of a 50 Ω passive (no PA) antenna indicates a gain of -12.7dB on
boresight at 5.64 GHz, consistent with the antenna size reduction. The measurement
of one active antenna (50 Ω system) shows a gain of -4.3dB on boresight at 5.80
GHz. The other version of active antenna (22.5 Ωsystem) shows a gain of -2.9 dBi
on boresight at 5.725 GHz. The active circuitry (PA) contributes an average of ~9
dB gain in the active antenna, reasonable close to the designed PA gain of 12.7dB.
The feasibility of direct integration of a PA with an on-chip antenna in a commercial
GaAs process at RF frequencies was successfully demonstrated.
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