请教各位一个关于series-fed microstrip antenna array的问题

请问，采用series-fed 形式来作微带天线阵，其辐射主瓣是否一定会随频率的改变而改变?比方说，中心频率20GHz，此时主瓣方向为90度，符合设计需要。当频率改变为18GHz时，主瓣方向为87度；同样，主瓣在22GHz时变成了93度，不再符合设计需要。是否有办法抵消这样的偏移。仅作学术讨论，和商业项目无关，希望各位大侠不吝赐教。假设天线是采用全微带结构，单层且全地。谢谢大家。

search papers published by Sakakibara who has deigned a series-fed array with stable radiation direction.

Thanks for your reply. I did a search with author's Sakakibara in IEEE Xplore. I found several papers from him about Waveguide and Microstrip antenna. Unfortunately, I did not find any clue about design a series-fed MSA array with stable radiation direction over frequency. Could you give me some more details about papers of Prof. Sakakibara relate to such topics?