HI
forgot those 21 element antenna did you seriously think that you may manage azimuth elevation whit 55" boom antenna ;-)
that wly most people use 2 or 4 smaller antenna that was more manageable ,even if my setup was 2 x 9 element that still 15 feet long by 10 feet wide to move
but then you must use more coax and connector ,and on that kind of system add 10 feet of coax was dramatic ,remember each db of loos ahead of first "gain" stage
directly add itself to noise figure ,so if you use 4 antenna whit 4 x 10" feet of coax you may easy add extra 0.5db of noise figure
here as exemple i have pre-amp and power amp mounted on the foot a less that 10 feet of antenna for minimize coax loss
that you need to manage noise pick-up and dynamic range of the first gain stage those nice preamp start to saturate whit -50dbm signal , then go out of linear zone
and start to ack like mixer ,just lime m 102,1FM radio station example ,and if put filter in front on pre-amp you again loos another 0.5 to 1db of noise figure
and above total 0.5db noise figure your out of the game ,so it quickly start to be real engineering problem
but as said on my first post whatever antenna and system you have if your in center of urban zone ,your probably screw-up even before start whit in-band noise
have fun