You can make a very simple and inexpensive glideslope antenna. Take two 9"-10" long pieces of 1/4" or 3/8" adhesive-back copper tape and put them in the top of the canopy positioned from side-to-side, about 1/4"-3/8' apart in the center, just slightly forward of the opening. Slip a couple of ferrite beads over the coax at the end that attaches to the antenna, strip the end of the coax, and solder the center conductor to one strip in the middle and the shield to the other. It makes no difference which goes to the right element and which to the left. Run the coax down the inside edge of the windshield to the receiver. That way you'll have a very sensitive 1/2 wave dipole for the GS and you won't lose any sensitivity in the VHF Omni-Range signal. If you don't have any of this tape, it's easily obtained. Lots of guys used the tape to make antennas for their composite airplanes; there is a little kit with the tape and the beads that ACS has for $20, but instead of the tape you can just use wire or narrow braid, and glue it in place with RTV. ACS has the beads for $0.80 each! If you used to fly a 172 you probably saw the
little GS antenna at the top of the windshield, sorta hanging loose.