Abstract
Recently, miniaturization and high performance of a technology
of a wireless communication system are very important.
The Doppler radar produced in this paper was fabricated at
X-Band frequency with good linearity in order to detect and
locate the target through motion detection.
The radar consists of an antenna, an oscillator, a frequency
control unit, a power unit, and an IF output unit. In particular,
the high frequency circuit composed of an antenna and an
oscillator is what determines the performance of the system. The
oscillator must operate with stable oscillation and low noise. The
most important part of the design is the resonator.
Dielectric resonators are widely used for hight Q-factor, but
they are disadvantageous for integration and miniaturization due
to the three dimensional structure. Hairpin resonator are widely
used to overcome these disadvantages.
By reducing both sides of the hairpin resonator into a spiral
structure, the area and the Q-factor were increased. Two
varactor diodes were used to determine the resonance frequency
according to the value of capacitance. From 0.5pF to 2.5pF in
0.5pF increments it was confirmed that the resonance frequency
by turning on the change.
The oscillation circuit of the voltage controlled oscillator is a
series feedback structure that is simple in structure and has the
advantage of obtaining a large negative resistance, and is largely
composed of an impedance matching portion, a resonance portion,
and a negative resistance portion.
All of these design were designed using the ADS simulation
software and determined the optimal size and shape.
Unlike the Doppler radar, which uses a separate transmit and
receive antenna, the antenna meets the miniaturization
requirement. The dielectric is a FR-4 board with a dielectric
constant of 4.4. The width and length of the slot and
transmission line are CST Microwave Optimized using studio.
It is confirmed that the input reflection coefficient is minimized
to .28dB at the center frequency of 10.525GHz. The bandwidth
is about 380MHz, VSWR is 1.2 or less, and the gain is about
8dBi.
The actual radar size is 30mm wide and 24mm wide. The
output level of the oscillator is similar to that of the Doppler
radar of the same band, which was studied in the past, but the
size was reduced by about 40~71%.