How do I render to texture only a part of the cameras view?

Hi! I want to render only a part of the cameras view.

1. I set camera's height to half so camera only captures half of screen.

   camera.rect = new Rect(0, 0, 1, 0.5f); //. set camera's height to half.

2. I set RenderTexture's size same with cameras render size in pixel. so it can contains whole contents of camera (just 1 : 1 pixel).

   _renderTexture = new RenderTexture(camera.pixelwidth, camera.pixelheight, 0, RenderTextureFormat.ARGB32);

3. I assign RenderTexture to camera.

   camera.targetTexture = _renderTexture;

4. Draws _renderTexture on screen.

   GUI.DrawTexture(rt, _renderTexuture);

I'd like to render camera's real capture view(half of screen) to texture(just half screen)

But renderTexture contains whole screen(Screen.width, Screen.height).

What's wrong with me?

How can I render only a camera's view(half of screen) to texture?

Help me.

Thank you,

Best Regards,

Adam.