At the hearing, you must appear in person (possibly with an attorney) to cross-examine the officer and / or put on your own defense. Bring to the hearing any and all evidence / testimony that you want the judge to hear in your case.
If you need a subpoena to get your witness into court, apply to the court to have the subpoena issued and served. Remember, your case is your responsibility; take action to present a good defense. You may either appear and defend, or you may have an attorney appear for you. No other party can represent you.
Preponderance of Evidence
At the hearing, the officer’s burden is to show by a “preponderance of the evidence” that you committed the offense. Sometimes, that is described as 51% rule, that you committed the offense. For anything less than these levels, the court will enter a dismissal of the charges. If the officer does not appear, your case will also get dismissed. But if it is you that doesn’t appear, the finding usually goes to the state and against you. Be sure to attend the hearing.