It also has low spurious radiation
. The coaxial probe feed on patch matching 50 [OMEGA] is given by following equation:
As a condition of the NASA CRS contract, SpaceX analyzed the orbital radiation environment on all Dragon systems, and how the spacecraft would respond to spurious radiation
But this kind of antenna structure usually suffered the spurious radiation
from the feed lines, which degraded the pattern performances, such as raising the side lobe level [11, 12], or causing distortion of the main beam shape in some shaped-beam pattern designs .
On the other hand, the lower substrate (substrate 2) is made of FR-4 board with higher permittivity [[epsilon].sub.r] = 4.7) and thickness, [h.sub.2] of 0.8 mm for tightly coupled fields that produce less spurious radiation
. FR-4 is a low cost material with good reproducibility  but high loss which may results in low gain.
The active integrated antenna, which integrates active devices directly into the antenna platform, is prospective in communication systems for its simplification of the circuitry and downsizing of the transmission system , but this configuration easily generates spurious radiation
at harmonic frequencies due to the inherent features of oscillation circuit.
Feeding by a coaxial probe has the advantages of ease in impedance matching and low spurious radiation
, and the disadvantage of having to be physically connected to the center of the patch.
Foreasy fabrication and spurious radiation
the coaxial feed technique is chosen.
The aperture-coupled structure is employed to feed the antenna due to its advantages of eliminating spurious radiation
from the feed line and reducing the backward radiation .
Possible contributing factors to the inconsistencies include alignment issues, non-symmetrical anechoic chamber, as well as spurious radiation
from the coaxial cable.
In addition, the spurious radiation
from the stub in the vertical plane can also be canceled.
The design is therefore based on the required power split for each patch, the maximum realizable impedance values for the microstrip lines to reduce spurious radiation
and coupling by the feed network, and to obtain a match a t the feed point.
present a drop-shaped dipole antenna which can be used to realize compact array antennas or to reduce the spurious radiation
level in the direction of feeding line .