While designing a practical antenna the following issues should be considered and should not be neglected:
Antenna Pattern: according to the needs of system design and orientation antenna gain is very important and when antenna gain is increased beam width is decreased. This antenna pattern is closely related to antenna gain.
Bandwidth: if the antenna bandwidth is narrow then the signals at the edge of the band will get truncated and also those at the center, that is why bandwidth should be large enough to accommodate all frequency in a particular system.
Gain: gain of nay antenna is inversely proportional to the power consumption of the transmitter which in turns related to the battery life of any transmitter.
Ground Plane: because of the concept of image antenna some antenna needs a reflector like vehicle based antenna.
Height: coverage of any antenna is directly proportional to the height of the antenna but higher antenna can results in interference which is a severe problem in interference limited system.
Input Impedance: for receiving low power signals it is necessary that the input impedance should be low typically 50 ohms or 72/75 ohms (depends on the particular cases)
Mechanical Rigidity: when we talk about cellular systems, the time delay greater then few milliseconds sometimes microseconds can not be tolerated, and if antenna flexes in wind then it can further adds to multipath fading and other fading and also add to Doppler spread. That is why antenna should have good mechanical rigidity.
Polarization: for cellular systems vertical polarization is standardized and some other systems have different polarization that is why polarization should be considered while designing an antenna.
These are the few issues which I came across while designing antenna (in fact mentioned in some book), Enjoy designing your own but keep them in mind 
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