Functional Requirements

Power rating > 2.5 W, omni-directional, gain > -10 dB

Interface Requirements

A 4-way splitter is required to connect the transmitter and the patch antenna. (Mini- Circuits ZB4PD-42, 1700-4200 MHz, www.minicircuits.com). All connectors are SMA, 50ohm.

Design
The transmitting antenna on the rocket is a microstrip patch antenna, designed and built
by Ty Sullins. It is omni-directional and circularly polarized, with a central frequency of
2.2155 GHz and a bandwidth of 20 MHz. It has a theoretical gain of 0 dB.
In previous ASRP missions, the antenna on the rocket has been linearly polarized and the
ground station antenna has been circularly polarized. The circularly polarized ground station
antenna ensured that the telemetry signal was received despite the orientation of the linearly
polarized antenna on the sounding rocket. However, the polarization mismatch between the
linear and circularly polarized antennas results in a 3-dB loss. Ty Sullins designed a circularly
polarized sounding rocket antenna, which overcomes the 3 dB mismatch loss of the linear
polarized antenna.
The microstrip antenna is lightweight, thin, conformal, and inexpensive to fabricate.
Circularly polarized waves can be generated using simple geometries. The main limitation of
microstrip antennas is their narrow bandwidth.
The antenna is already fabricated. It is composed of four identical pieces with four
patches on each piece, for a total of 16 pieces. Power from the transmitter goes through a
four-way power splitter to each of the pieces. Each branch will be in turn fed into four
patches. At each port, 50-ohm SMA connectors are used.
One issue of concern is the reduced antenna gain when the rocket is at high altitudes and
the communication path has a very sharp angle to the surface of the antenna. The radiation
pattern of the patch antenna as a whole is theoretically spherical. The test result of radiation
pattern is illustrated as Figure 3.5.2.1. The largest loss will be about 3 dB, which is within the
acceptable maximum antenna gain ¡©10 dB.
Assembly Notes
Mounting holes, SMA connector holes need to be drilled on payload tube. A drilling
template will be provided to the mechanical team. To minimize coax cable losses, the coax
cable should be as short as possible. The antenna should be located so that a protective shield
is not necessary. Shield will introduce losses. The specifications of the power splitter can be
found at www.minicircuits.com (12/20/2000).