If your application requires a flat frequency response extending out to 18 GHz, we suggest another device such as ADL6010, which also has wider dynamic range and better temperature compensation as added bonuses, but no output comparator, and its a little bit slower.
LTC5564 by itself can work to 18 GHz and beyond, but the connector on the factory demo board is not so good up past 15 GHz. The ground return prongs are too far apart, and the microstrip launch starts to resemble a slotline antenna. So for best results with LTC5564 up around Ku-band, we suggest reworking the factory demo board to install a connector such as the Emerson 142-0761-871. For reactive matching, start with the 15 GHz schematic shown in datasheet Figure 5, understanding that the input matching elements may need slight 'tweaking' to get up to 18 GHz. This refers primarily to the 0.5pF element, and optimal performance will likely be obtained by watching the return loss, and sliding the capacitor longitudally along the transmission line to find the location of best impedance match.